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    Cause analysis of flood-drought alternation event in July 2022 in arid and semi-arid region
    of Inner Mongolia
    LIU Wei, ZHAO Yanli, GAO Jing, LI Linhui, WANG Huimin
    Journal of Arid Meteorology    2024, 42 (1): 11-18.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0011
    Abstract88)      PDF(pc) (14631KB)(122)    PDF(mobile) (14631KB)(1)    Save
    The rainfall in July of 2022 in the central and western regions of Inner Mongolia was obviously less and showed a phased
    characteristic of more in the early stage and less in the late stage. The analysis of circulation distribution and configuration in different stages is of great significance for further improving precipitation forecast ability in flood season in this region. Daily precipitation of 116 national meteorological stations in Inner Mongolia, 130 climate indexes from the National Climate Center, daily reanalysis data from National Center for Environmental Prediction/National Center for Atmospheric Science (NCEP/NCAR) and monthly sea surface temperature (SST) data from the National Oceanic and Atmospheric Administration (NOAA) were used to analyze the causes of the flooddrought transition event in the central and western regions of Inner Mongolia in July 2022. The results are as follows: (1) In July 2022, the rainfall in the central and western regions of Inner Mongolia was seriously less, which was the least in the same period since 1991 in this region, and the meteorological drought was relatively serious. (2) From July 1 to 11, the precipitation was relatively more, the cold air path was northward and the intensity was weak, the Western Pacific Subtropical high was weak and its location was northward and
    westward, and the warm and cold air intermingled in the central and western regions of Inner Mongolia. In addition, the position of upper westerly jet was northward during this period, and the central and western regions of Inner Mongolia were located in the south of the jet axis, which was conducive to upper level divergence and the development of upward movement. While from July 12 to 31, the precipitation was obviously less, the meridian of circulation increased, the cold air activity path was more southerly and the intensity increased, the Western Pacific subtropical high was obviously stronger and the location was southward, which was not conducive to water  vapor transport. In addition, the location of upper westerly jet was southward, and the central and western part of Inner Mongolia was located in the north of the jet axis, which was not conducive to upper level divergence and the development of upward movement. The stronger disturbance of the upper westerly jet in mid and late July was conducive to stimulating the meridional teleconnection wave train from East Asia to the Northwest Pacific, which led to the position of the Western Pacific subtropical high southward and less precipitation. (3) The abnormal SST from the Sea of Japan to the northwest of the North Pacific was one of the important external forcing signals that affect the amount of precipitation in central and western regions of Inner Mongolia. In July 2022, the SST in the region was abnormally high, and the cyclonic circulation triggered by the abnormal SST over the region weakened the meridional transport of warm and humid water vapor in the south, which was one of the reasons for the change of precipitation from flood to drought in central and western regions of Inner Mongolia.
     

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    Identification and characteristic analysis of compound drought and heat wave
    event in Central Asia
    YANG Yingjie, CAO Qian, SHUI Yue
    Journal of Arid Meteorology    2024, 42 (1): 19-26.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0019
    Abstract89)      PDF(pc) (12826KB)(105)    PDF(mobile) (12826KB)(15)    Save
     The compound drought and heat wave has been paid more and more attention and the combined effect is far more than ordinary drought events. The characteristic of the events was explored in Central Asia from 1981 to 2020, based on hourly temperature data and monthly potential evapotranspiration data of the Land Component of the Fifth Generation of European Reanalysis (ERA5-Land) from the European Centre for Medium-Range Weather Forecasts and daily multi-source weighted-ensemble precipitation data. Standardized Precipitation Evapotranspiration Index (SPEI) and daily maximum temperature were calculated to identify the events. The following conclusions were drawn: (1) The spatial distribution of compound drought and heat wave event in Central Asia was not concentrated. The regions with high frequency of the events in the 1980s, 1990s, 2000s and 2010s were mainly distributed in the southeast,north, northwest and west, respectively. (2) In terms of temporal distribution, the general trend of the events had changed from large fluctuation to small fluctuation, and likely to remain stable after 2020. (3) Studying the four typical years of 1984, 1993, 2010 and 2020, it is concluded that the compound drought and heat wave event in Central Asia were mainly concentrated in the southeast in 1984, sporadic occurrences in a few scattered regions in 1993, in the north in 2010 and in the west in 2020.

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    Study on monitoring method of agricultural drought in Gansu Province based on
    Temperature Vegetation Dryness Index
    SHA Sha, WANG Lijuan, WANG Xiaoping, HU Die, ZHANG Liang
    Journal of Arid Meteorology    2024, 42 (1): 27-38.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0027
    Abstract76)      PDF(pc) (10861KB)(88)    PDF(mobile) (10861KB)(6)    Save
    Improving the Temperature Vegetation Dryness Index (TVDI) and clarifying the agricultural drought grade threshold of
    TVDI is of great significance for improving the ability of TVDI to monitor agricultural drought. Based on MODIS (Moderate Resolution Imaging Spectroradiometer) remote sensing data in the past 19 years, several feature spaces are constructed by using the single-time and multi-time methods, including NDVI (Normalized Difference Vegetation Index) -LST (Land Surface Temperature), EVI (Enhanced Vegetation Index) -LST, RVI (Ratio Vegetation Index) - LST, and SAVI (Soil Adjusted Vegetation Index) -LST. The calculation methods of TVDI are discussed, the applicability of TVDI for agricultural drought monitoring in Gansu Province is analyzed, and classification standards for summer TVDI agricultural drought in Gansu Province are clarified. The research results are as follows: 1) The TVDI calculated from the SAVI-LST feature space is more suitable for agricultural drought monitoring in Gansu Province. The root mean squared error (RMSE) and mean absolute error (MAE) of its fitting relative soil moisture (RSM) decreased by 1%–5% compared with the RMSE and MAE of RSM fitted by NDVI-LST feature space TVDI for RSM, which is used more commonly. 2) TVDI is suitable for agricultural drought monitoring at shallow depths of 10 and 20 cm in non-arid areas such as semi-arid, semi-humid and humid areas in
    Gansu Province in summer. The RMSE and MAE are approximately 15.6% and 12.6%, and the fitting errors in humid areas are the least, and they are less in semi-humid areas than in semi-arid areas they are the largest. 3) Compared to TVDI drought grades divided by 0.2 intervals and TVDI with uncertain classification criteria , the TVDI agricultural drought grade determined by the linear relationship between TVDI and RSM is more conducive to improving the accuracy of TVDI monitoring agricultural drought.

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    Journal of Arid Meteorology    2024, 42 (1): 39-46.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0039
    Abstract43)      PDF(pc) (2701KB)(47)    PDF(mobile) (2701KB)(0)    Save
    Analysis of climatic resources and drought characteristics during rice growth stages with
    different sowing dates in Chengdu plain:A case study of Guanghan
    LIAO Chengrui1,3, CHEN Yongren2, XIAO Tiangui3
    (1. Guanghan Meteorological Bureau of Sichuan Province, Guanghan 618300, Sichuan, China;
    2. Meteorological Disaster Defense Technology Center of Sichuan Province, Chengdu 610072, China;
    3. Chengdu University of Information Technology, Chengdu 610225, China)
    Abstract: As a major rice-producing area in Southwest China, the Chengdu Plain has faced increasingly severe drought problems in recent years. In order to determine the most suitable sowing date for rice in this region and improve the drought resistance, this paper takes Guanghan area as an example, and adopts the climate tendency rate method to analyze the characteristics of climate resources at the rice growth stages for different sowing dates from 1991 to 2020, and evaluates the degree of drought at different growth stages of rice at growth stages by using the Crop Water Deficit Index (CWDI). The results show that the climatic characteristics of rice for different sowing dates in the study area over the past 30 years showed a trend of decreasing sunshine, increasing mean daily temperature and increasing precipitation. With the delay in sowing, the number of sunshine during the whole life cycle of rice decreased, and the average daily temperature and precipitation both increased. The CWDI values gradually decreased with rice development, and the water deficit rate was higher at the first and middle stages for each sowing date. Light and moderate drought, followed by severe drought, and exceptional drought were observed during the growing stages of rice for different sowing dates. From late March to early April was the most suitable period for rice sowing in the study area, and drought-resistant varieties should be selected for sowing in early and mid-March, while sowing in mid-to late-April people should guard against the effects of severe drought on the water demand period of the crop.

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    Variation characteristics of agricultural boundary temperature in main agricultural regions
    in basins of the Brahmaputra River and its two tributaries in Xizang from 1981 to 2022
    GUO Yinan, HUANG Zhicheng, DU Jun, XU Wei
    Journal of Arid Meteorology    2024, 42 (1): 47-53.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0047
    Abstract40)      PDF(pc) (2910KB)(62)    PDF(mobile) (2910KB)(3)    Save
    The mean daily temperature of 10 ℃ is the lower limit temperature for the suitable growth of thermophilic crop. The ≥10 ℃ active accumulated temperature (ATT10) is one of the important indexes to measure the heat resources in the main agricultural regions of the Brahmaputra River and its two tributaries over Xizang (BRTX). Based on the daily average temperature data of 9 meteorological stations in BRTX from 1981 to 2022, the linear trend estimation, Pearson coefficient, Mann-Kendall test and R/S analysis method were used to analyze climate change characteristics of ≥10 ℃ boundary temperature (BT10). The results are as follows: (1) With the increase of altitude, the BT10 showed obvious vertical zonal characteristics in the main agricultural regions of BRTX, including the delay of initial date, the advance of the last day, the decrease of duration days and the ATT10. (2) From 1981 to 2022, the initial date of BT10 was advanced by -2.53 d·(10 a)-1, and the final date delayed with a rate of 3.33 d·(10 a)-1, the duration days and ATT10 significantly increased with a rate of 5.87 d·(10 a)-1 and 106.19 °C·d·(10 a)-1, respectively. Compared with the Qinghai-Xizang Plateau, the magnitude of BT10 change was significantly larger. (3) The 1980s was the decade with the latest initial date, the earliest final date, the shortest duration days and the lowest ATT10 in the past 40 years, while the 21st century was the opposite. (4) The H indexes of the BT10 were all greater than 0.65, indicating that in the future the BT10 will maintain a strong persistence of earlier initial day, later final day, prolonged duration days and increased ATT10. The mutation change of the initial date of BT10 occurred in the early 1990s, while the abrupt change of the final date, duration days and ATT10 occurred in the first decade of the 21st century.

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    Characteristics of 10–20 days low-frequency oscillation of autumn precipitation over the
    Beijing-Tianjin-Hebei region in 2021
    HAN Shiru, CHE Shaojing, YU Changwen, MA Guidong
    Journal of Arid Meteorology    2024, 42 (1): 54-63.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0054
    Abstract62)      PDF(pc) (20762KB)(69)    PDF(mobile) (20762KB)(7)    Save
     It is important to study the characteristics of precipitation anomaly in the Beijing-Tianjin-Hebei region to improve the understanding and prediction ability of precipitation in the autumn extended period. In recent years, the phenomenon of“ summer rain in autumn” has occurred frequently in the Beijing-Tianjin-Hebei region, showing the characteristics of precipitation intensity increase and more extreme precipitation in autumn. The autumn precipitation in the Beijing-Tianjin-Hebei region in 2021 was the most since 1981, and the precipitation at many stations in October of 2021 broke the historical extreme values. Based on daily precipitation data in autumn and NCEP/NCAR reanalysis data in Beijing-Tianjin-Hebei region, the Morlet wavelet analysis and Lanczos filtering methods were used to analyze the low-frequency oscillation period of autumn precipitation and the evolution of atmospheric low-frequency circulation characteristics in the Beijing-Tianjin-Hebei region in 2021 in order to explore its abnormal characteristics. The results show that the main low-frequency oscillation period of autumn precipitation in the Beijing-Tianjin-Hebei region in 2021 is 10-20 days, and the variance of low-frequency oscillation is 44%. The low frequency circulation at 500 hPa during the low frequency precipitation activity period shows that there is convergence movement before the low-pressure anomaly, which is conducive to the strengthening of the low-level anomaly cyclone and upward movement. During the low frequency precipitation activity period, an abnormal cyclone moves northward from the South China Sea to the Beijing-Tianjin-Hebei region, which was conducive to the transport of warm and humid air from the south to the Beijing-Tianjin-Hebei region. The intensity of water vapor transport will affect the intensity of precipitation process. The stronger the intensity of water vapor transport is, the greater the intensity of precipitation is.

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    Prediction of the future temperature in Qinghai Lake
    DONG Jingwei, WEN Lijuan, YU Tao, YANG Yongshun, LUO Ying, WANG Mengxiao, NIU Ruijia
    Journal of Arid Meteorology    2024, 42 (1): 64-74.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0064
    Abstract55)      PDF(pc) (15063KB)(59)    PDF(mobile) (15063KB)(6)    Save
     Qinghai Lake plays an important role in the ecological security of the Qinghai-Tibet Plateau, and it is very important to
    deeply understand the characteristics of future lake surface temperature changes of Qinghai Lake. We evaluated the conventional meteorological data of three global climate models in the Coupled Model Intercomparison Project 6 (CMIP6) through site observations and reanalysis data. Freshwater Lake Model (FLake) was evaluated by using the observed data and MODIS (Moderate-resolution Imaging Spectroradiometer) surface temperature data to predict the evolution trend of lake temperature under four different discharge scenarios (SSP126、SSP245、SSP370、SSP585)in the future, and to elucidate the driving mechanism of lake surface temperature change and its potential impact on the living environment of Gymnocyprisprzewalskii. The results are as follows:(1) The historical meteorological data of the reanalysis data and the CMIP6 multi-model collection are superior to the single model. From 2015 to 2100, the average annual lake
    surface temperature of Qinghai Lake continued to rise under four scenarios. Under SSP126 scenarios, the warming rate after 2050 is lower than that in the historical period, while under SSP245, SSP370 and SSP585 scenarios, the warming rate before and after 2050 is higher than that in the historical period, in which air temperature is the main driving factor of lake surface temperature. (2)In the future different periods, the monthly and daily maximum lake surface temperature in different stages will appear in August, and in the recent period (2020-2041), there is little difference among different scenarios. In the middle period (2041-2080), the differences between the scenarios gradually increased. In the long run (2081-2100), the average daily lake surface temperature in August basically exceeded 20.00 ℃, and the maximum daily temperature even reached 23.31 ℃, Gymnocyprisprzewalskii would be at a high risk.

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    Simulation of a multi-phase precipitation process over Yungui-Huanan quasi-stationary
    front in winter
    YANG Qi, ZHANG Haipeng, WU Jianrong, LI Hao, ZENG Huarong, LU Zhengqi
    Journal of Arid Meteorology    2024, 42 (1): 75-83.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0075
    Abstract45)      PDF(pc) (16023KB)(54)    PDF(mobile) (16023KB)(1)    Save
    The presence of the Yungui-Huanan quasi-stationary front make its north region an ideal platform for studying different pre⁃
    cipitation phase across the rain-snow transition zone. The impact of the temperature the subfreezing layer and the activation temperature of the ice core on the formation of different precipitation phases were qualitatively explored based on the analyses of the meteorological and cloud microphysical parameters over a southern freezing weather event from January 25 to 27, 2018. The precipitation phase, the freezingrain zone, and the total amount of freezing rain in this case were simulated as well by the use of the WRF model coupling the BTC precipitation phase diagnosis parameterization scheme. The results show that a “cold-warm-cold” vertical temperature structure formed by the quasi-stationary fronts across the Yunnan-Guizhou Plateau and the Southern Ridge region is favorable for the occurrence of multi-phase precipitation. The spatial distribution of different precipitation phase drop zones can be well simulated by the WRF model coupled with the BTC parameterization scheme, showing good agreement with observations, but the false rate for ice particles is relatively high. The vertical distribution characteristics of temperature, relative humidity and hydrometeors during the multi-phase precipitation simulated by WRF model are analyzed. The initial phase of hydrometeors in the cloud is liquid. Under the premise of the existence of highaltitude inversion layer, the ice core activation temperature in the subfreezing layer is the critical index to distinguish freezing rain and ice particles and has a clear physical mechanism. The accuracy of freezing rain prediction is improved by 13% after by substituting the ice core activation temperature of the subfreezing layer for the discrimination of freezing rain and ice particles in the BTC scheme, which indicates the feasibility of the use of the ice core activation temperature in the subfreezing layer to determine freezing rain.


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    Analysis about the rear inflow of a warm zone squall line causing strong winds
    SANG Minghui, ZHU Li, SHEN Xiaoling, ZHANG Chunyan, ZUO Jun
    Journal of Arid Meteorology    2024, 42 (1): 84-94.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0084
    Abstract53)      PDF(pc) (32177KB)(391)    PDF(mobile) (32177KB)(2)    Save
    A squall line with a long life is very likely to cause a wide range of catastrophic gale weather. The study of its structure and
    maintenance mechanism is of great reference significance to the forecast of catastrophic gale weather. The rear inflow of a warm zone squall line that caused strong gale in Jiangnan area on March 4, 2018 was analyzed by using the ground observations, radar data, NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) FNL (Final Operational Global Analysis) reanalysis and high-resolution model simulation results, and the maintenance mechanism of the squall line was discussed. The results show that the squall line occurred in a warm environment in front of the south branch trough with the same southwesterly airflow in upper and lower layers. The environment was characterized by moderate to strong vertical shear of 0–6 km, high convective effective potential energy, and obvious dry areas in the middle layer and near the surface. The 3 h negative barotropic anomaly index has
    a good indication in this process. The squall line showed a “TS” structure, but the stratus area was relatively narrow. The reflectivity factor kernel was located in the downdraft below the mid-level radial convergence. The results of the model simulation show that the rear inflow and downdraft forced counterclockwise and clockwise vertical circulation in the interior and rear of the system, respectively, which constituted the most important structural characteristics of the squall line. The rear inflow was close to the rear edge of the system and located in the middle troposphere, which caused the updraft to change from inclined to vertical direction. After that, the rear inflow moved away from the system and merged with the lower outflow to continuously lift the warm and moist air. The synergistic effect of the rear inflow and the front inflow made the squall line maintain for a longer time.

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    Characteristic analysis of early spring hail in Chengdu based on S-band polarization radar
    ZHOU Cong, ZHANG Tao, XIA Xin, ZHANG Kui
    Journal of Arid Meteorology    2024, 42 (1): 95-106.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0095
    Abstract58)      PDF(pc) (35923KB)(107)    PDF(mobile) (35923KB)(4)    Save
     In order to better carry out the monitoring, forecasting and early warning of hail weather in Chengdu, the characteristics of
    dual-polarization parameters of hail in early spring in Chengdu were studied by using the S-band dual-polarization radar detection of Chengdu, combined with the regional automatic weather station and conventional observation data. The fine structure of hail cloud was analyzed and compared with the short-term heavy precipitation in early spring of the same year. The results show that under the dynamic condition of strong ascending motion formed by the coupling of the high and lower-level jets, the high-level cold advection combined with the surface cold air jointly triggered the hail weather of Chengdu “3·16”. At the maturity stage, the central reflectivity factor (ZH) of hail cloud was more than 70 dBZ and there were obvious overhanging strong echo. Besides, the differential reflectivity (ZDR) and correlation coefficient (CC) of hail cloud were concentrated in –2–1 dB and 0.8–0.95, respectively, accompanied by specific differential phase shift rate (KDP) hole and CC valley structure in front of the cloud, and there was a typical ZDR column near strong updraft. With the
    weakening of the ascending motion, the ZDR large value area decreases with distance appeares in front of hail cloud, while CC shows increasing trend. Compared to hail cloud, the ZH of heavy precipitation convective cloud was smaller, while the ZDR and CC were significantly larger, and there was no overhanging strong echo and obvious ZDR column in front of the convective cloud.

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    Comparative analysis of two rainstorm cases in Longnan of Gansu Province
    SHI Yanzhao, LIU Weicheng, FU Zhao, FU Zhengxu, XU Lili, ZHENG Xin
    Journal of Arid Meteorology    2024, 42 (1): 107-116.   DOI: 10. 11755/j. issn. 1006-7639(2024)-01-0107
    Abstract56)      PDF(pc) (29000KB)(92)    PDF(mobile) (29000KB)(7)    Save
    In August 2017, there were torrential rains in Longnan, Gansu Province. The 24-hour precipitation at the Li County and
    Wudu weather stations broke through the historical extreme values, with obvious extremes and localities. Based on ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts, radar data and ground observation data, a comparative analysis of two heavy rain cases that occurred in Longnan, Gansu Province from 6 to 7 and from 19 to 20 August 2017 are carried out. The circulation background and the radar reflectivity factor, radial velocity and physical quantity characteristics of the heavy rainfall processes of the two cases are discussed emphatically. The results show that the two rainstorms all occurred at the intersection between the northerly airflow in the westerly trough and the southerly warm and humid airflow in the middle-lower layer, but the main impact systems and triggering conditions are different. The radar echo shows from August 6 to 7, the convective system caused by the cold shear line is stronger, with higher reflectivity factor, lower central height, higher precipitation rate and shorter duration. The reflectivity factor of precipitation in warm region from August 19 to 20 is lower, and its central height is higher, and the precipitation rate is smaller, and the precipitation process maintained for longer time.

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    Suitability study of ERA5-Land precipitation product for drought monitoring in the Yellow River Basin
    ZHU Li, LYU Xiaoyu, GUO Hao, MENG Xiangchen, TIAN Yunfei
    Journal of Arid Meteorology    2023, 41 (5): 677-687.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0677
    Abstract319)   HTML22)    PDF(pc) (16670KB)(1285)       Save

    The ERA5-Land reanalysis product is an important global data for surface variables, and its error assessment in drought monitoring is of great significance for further improving drought early warning ability and reducing disaster risk. Based on daily precipitation grid data from the National Meteorological Information Center during 1981-2020, combined with the standardized precipitation index (SPI), the error characteristics of the Land component of the Fifth Generation of European Reanalysis (ERA5-Land) precipitation data from the European Centre for Medium-Range Weather Forecasts (ECMWF) in monitoring drought in the Yellow River Basin and its sub-basins were evaluated quantitatively, and overestimate or underestimate of precipitation and the ability of describing drought characteristics of ERA5-Land precipitation products in different regions on different time scales were explored. The results show that the ERA5-Land precipitation products are obviously overestimated in the Yellow River Basin, especially in the upper reaches, followed by the middle reaches, and in the lower reaches errors are relatively small. At different time scales, the ability of ERA5-Land precipitation products to reflect dry and wet conditions is obviously different, and the difference increases with the increase of time scale. For drought events in the Yellow River Basin, the ERA5-Land precipitation products have obvious overestimation of drought frequency and underestimation of drought duration. In the upper reaches, drought intensity and severity are mainly overestimated, while in the middle and lower reaches, drought intensity and severity are obviously underestimated. Although the ERA5-Land precipitation products can effectively capture the spatial distribution of typical drought events, the description of drought areas of different grades is not accurate. Therefore, when using ERA5-Land precipitation products for drought monitoring, it is necessary to pay special attention to its overestimation or underestimation.

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    Meteorological drought variation characteristics in the Gannan Plateau based on standardized precipitation evapotranspiration index
    ZHAO Huizhen, HE Tao, GUO Ruixia, WANG Chengfu, ZHANG Yanrong, LI Qi
    Journal of Arid Meteorology    2023, 41 (5): 688-696.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0688
    Abstract288)   HTML25)    PDF(pc) (18542KB)(489)       Save

    Drought disaster is one of the most frequent meteorological disasters in the Gannan Plateau, which seriously affects agricultural and animal husbandry production and ecological environment security in this region. Monthly precipitation and air temperature data from 31 meteorological stations in the Gannan Plateau and its surrounding areas from 1973 to 2022 are used to characterize meteorological drought employing the Standardized Precipitation Evapotranspiration Index (SPEI), and the temporal and spatial distribution of drought and its variations on annual and seasonal scales in the Gannan Plateau are analyzed by using Mann-Kendall test and Sen’s slope estimation methods. Results show that the annual SPEI in the Gannan Plateau presented significant downward trend with an obvious turning point in 1986, and the whole Gannan Plateau tended to be dry in the past 50 years. There were seasonal differences in the variation trend of drought, and the trend of drought intensified in summer and autumn, but in spring and winter it mitigated. In addition, there were spatial differences in the trend of annual and seasonal SPEI. In summer, it presented drought intensification trend in the middle and eastern regions of the Gannan Plateau, and in spring it showed similar to that in summer, but the area and degree of drought intensification were obviously smaller than that in summer. While in winter, it showed drought decreasing trend in the whole region. There were obvious spatial differences in the frequency of drought with different levels in the Gannan Plateau at the annual and seasonal scales. Light drought occurred frequently in the central and eastern parts of the Gannan Plateau, while medium and severe drought occurred frequently in the southern part of the Gannan Plateau, and the frequency of serious drought was less across the whole regions. Overall, the frequency of drought in the western was less than that in the central and eastern parts of the Gannan Plateau.

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    Characteristics of dry-wet climate change and its influence on NDVI in Shiyang River Basin
    ZHANG Jindan, LIU Mingchun, LI Xingyu, DING Wenkui, YANG Hua, JIANG Jufang
    Journal of Arid Meteorology    2023, 41 (5): 697-704.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0697
    Abstract204)   HTML8)    PDF(pc) (2740KB)(450)       Save

    Under the background of global warming, studying the characteristics of dry-wet climate changes in the Shiyang Rive Basin and their influence on vegetation coverage has significant importance for the ecological environment construction of the basin. Based on the precipitation temperature homogenization index (S) in the Shiyang River Basin from 1971 to 2020, the spatial-temporal changes of the dry-wet climate in the basin were analyzed from the aspects of drought station frequency ratio, drought frequency, and more. Combined with the Normalized Differential Vegetation Index (NDVI) remote sensing data, the influence of dry-wet change on NDVI was analyzed. The results showed that the inter-annual and seasonal S indices showed an increasing trend in the Shiyang River Basin over the past 50 years, with the most pronounced increase in summer. The drought degree and drought occurrence area have shown a decreasing trend in the basin. The intensity of drought in the midstream and downstream were more severe compared to the upstream, with higher drought frequencies in the downstream. The annual NDVI increased with the alleviation of drought, the increase of precipitation and decrease of temperature. The precipitation in the early and middle period of growth, as well as the temperature in the middle period had a great influence on the annual NDVI. In February, May and July, the NDVI had a lag effect in response to drought.

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    Characteristics of LAI variation in East China and its relationship with climate factors from 1982 to 2016
    ZENG Yingting, LI Cheng, LIN Yan, CHEN Li, LIN Binbin
    Journal of Arid Meteorology    2023, 41 (5): 705-713.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0705
    Abstract224)   HTML5)    PDF(pc) (15560KB)(367)       Save

    In order to understand the characteristics of vegetation change in East China, based on the Global Land Surface Satellite Leaf Area Index (GLASS LAI) remote sensing data from 1982 to 2016, the spatial and temporal variation characteristics of vegetation leaf area index (LAI) in East China over the past 35 years were studied using trend analysis method, the correlation between vegetation LAI and climatic factors (temperature, precipitation and solar radiation) was analyzed using the partial correlation method, and the dominant climatic factors of LAI changes in different regions were explored. Results are as follows: (1) The annual average LAI in East China ranged from 0.05 to 7.20, and the multi-year average annual maximum LAI ranged from 0.04 to 8.60, both showing a decreasing trend from south to north. (2) The overall annual average LAI and annual maximum LAI in East China in the last 35 years showed a fluctuating increase trend, with growth rates of 0.007 9 (p<0.05) and 0.022 6 (p<0.05) per year, respectively. Although the LAI in the northern part of East China was lower than that in the southern part, the increasing trend was obvious in the last 35 years; the LAI in the southern part of East China was higher, but there was a decreasing trend in some regions. (3) The pixels with significant increasing trend of annual mean LAI and annual maximum LAI accounted for 60.9% and 60.5% of the whole region, respectively, and were mainly located in the north of Jianghuai regions. In contrast, the pixels with significant decreasing trend of annual mean LAI and annual maximum LAI accounted for 8.9% and 6.4%, respectively, which were concentrated in northern Zhejiang and southern Jiangsu. (4) There were differences in the major climate factors affecting annual mean LAI and annual maximum LAI changes in different regions. As for annual mean LAI, the regions mainly affected by temperature and precipitation accounted for 13.9%, and the regions mainly affected by solar radiation accounted for 10.0%. As to annual maximum LAI, there was 26.5% region dominated by temperature, and they were mainly distributed in the south-central part of the study area.

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    Temporal and spatial variation characteristics of extreme precipitation in central and eastern Tibetan Plateau
    YAO Yanling, WANG Yue, CHEN Quanliang, LIAO Yujing
    Journal of Arid Meteorology    2023, 41 (5): 714-722.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0714
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    With global warming, the extreme precipitation events increase significantly, leading to serious natural disasters. The Qinghai-Tibet Plateau is a sensitive region to global climate change, and the analysis of extreme precipitation events in this region is conducive to providing theoretical reference for plateau climate prediction and disaster prevention and reduction. Based on the daily precipitation data from 68 meteorological stations of central and eastern Tibetan Plateau during 1961-2017, the percentile threshold method, linear tendency estimation method and extreme precipitation index were used to comprehensively analyze the temporal and spatial distribution characteristics of extreme precipitation in this region, and to explore the contribution of precipitation with different intensities to the total precipitation. The results show that the extreme precipitation indexes decreased from southeast to northwest in the central and eastern part of the Qinghai-Tibet Plateau as a whole, and the total precipitation and extreme precipitation in the southeastern part of the plateau were high, but the influence of precipitation change in this area on the increase of total precipitation was small. In the past 57 years, the extreme precipitation indexes showed an overall increasing trend. Among them, total precipitation and its intensity, heavy precipitation, 1-day maximum precipitation and continuous five-day maximum precipitation showed a significant increasing trend. The climatic tendency rate of heavy precipitation was greater than that of extremely heavy precipitation, and the proportion of heavy precipitation to total precipitation obviously increased, while the proportion of extremely heavy precipitation decreased slightly, which indicated that the contribution of heavy precipitation to total precipitation increase is greater than that of extremely heavy precipitation. The trend spatial distributions of heavy precipitation, heavy rainfall days and moderate rain days were basically agree with total precipitation and its intensity, and the significant increase area distributed in the northeast part of the region, which led to the increase of total precipitation and extreme precipitation in the central and eastern parts of the plateau.

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    Characteristics of heavy snowfall in the Qinghai-Tibetan Plateau in early and late winter during 1961-2021
    GUO Yingxiang, FENG Xiaoli, LIU Chang, SHEN Hongyan, CHEN Haicun, LI Moyu
    Journal of Arid Meteorology    2023, 41 (5): 723-733.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0723
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    It is of great significance to study the climatic characteristics of heavy snowfall in winter over the Qinghai-Tibet Plateau for winter precipitation prediction and snow disaster prevention in the Qinghai-Tibetan Plateau. Based on the daily precipitation data from 99 meteorological observation stations in the Qinghai-Tibetan Plateau in winter (from November to February of the following year) during 1961-2021, the spatial distribution and temporal variation characteristics of heavy snowfall and heavy snowfall days in early and late winter over the Qinghai-Tibetan Plateau and their relationship with sea surface temperature (SST) in different basins and Arctic oscillation (AO) were analyzed by using linear tendency estimation, correlation analysis and ensemble empirical mode decomposition methods. The results show that there were more snowfall processes with larger magnitude in early winter, while snowfall in late winter were more frequent and lasted longer duration in the Qinghai-Tibetan Plateau during 1961-2021. Both heavy snowfall and heavy snowfall days in early winter showed a "less-more-less-more" variation, while heavy snowfall and heavy snowfall days showed a significant increasing trend in late winter. The contribution rate of heavy snowfall and heavy snowfall days in early winter was significantly greater than that in late winter. The central and eastern parts of the plateau are areas with high value of heavy snowfall in early and late winter, and heavy snowfall in the northeast side was also large in early winter. The sea surface temperature anomalies in the tropical Indian Ocean, the north Atlantic Ocean and the Pacific Ocean were important factors affecting heavy snowfall in winter in the Qinghai-Tibetan Plateau. There was a significant positive correlation between heavy snowfall in early winter and SST in tropical middle-east Pacific Ocean and the western tropical Indian Ocean, while the positive correlation between heavy snowfall in late winter and SST in the tropical Indian Ocean, the northwestern Pacific Ocean and the north Atlantic Ocean was the most significant. Since the mid-1990s, the Indian Ocean dipole has changed from a weak positive correlation to a significant positive correlation with heavy snowfall in early winter, and the Arctic oscillation anomaly has an important impact on heavy snowfall in late winter, and both have always shown a stable positive correlation.

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    Characteristics and causes of fog along the Yangtze River from 2016 to 2020
    WANG Xiaoci, WANG Jizhu, MENG Yingjie, LI Shuangjun
    Journal of Arid Meteorology    2023, 41 (5): 734-743.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0734
    Abstract137)   HTML14)    PDF(pc) (15211KB)(400)       Save

    In order to strengthen the understanding of the low visibility impact events on the navigation meteorological conditions of the Yangtze River trunk line and improve the level of weather forecast for channel impact, using observational data from the National Meteorological Station and ERA5 reanalysis data (the fifth ECMWF reanalysis), we conducted an analysis of the spatiotemporal distribution characteristics of fog days at 51 stations along the Yangtze River, as well as the weather conditions and meteorological element changes during fog occurrences. The main findings are as follows: (1) Most stations along the river experienced a high incidence of fog from November to next January. The Sichuan and Chongqing area exhibited a consistently high fog occurrence throughout the year, while in the Hubei-Anhui Plain region fog incidents are frequent in spring. Thick fog and heavy fog predominantly occurred during the late-night and early morning hours, with strong fog typically occurring about 2 hours later. (2) In winter, fog along the Yangtze River primarily occurred in the Sichuan section (Yibin-Chongqing), the southwest and central sections of Chongqing (Chongqing-Wanzhou), followed by the Anhui section (Anqing-Hexian) and the Jiangsu section (Dantu-Taicang). (3)When fog was present along the river, the average 10-minute wind speed ranged from 0 to 3 m·s-1, occasionally exceeding 4 m·s-1. Northerly wind is the main wind, followed by easterly wind and westerly wind.(4) Mountainous areas along the Yangtze River exhibited a high proportion of rain and fog, with a notable frequency of thick fog, which was strongly correlated with precipitation. In contrast, in plain areas, radiation fog in early morning was more prevalent, and the occurrence of thick fog was often not directly linked to precipitation. The proportion of rain and fog in the eastern plain area was similar to that in mountainous areas, with relatively minor station-to-station fluctuations. (5) Strong fog weather events were associated with four primary near-surface weather situations: the low-pressure rear type, low-pressure trough type, weak high-pressure type, and high-pressure bottom type. Among them, the weak high-pressure type had the highest incidence, followed by the low-pressure trough type, while low-pressure rear type and high-pressure bottom type were less common.

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    Analysis on the causes of freezing stage characteristics in Guizhou in winter of 2021/2022
    REN Manlin, LI Zhongyan, WANG Boqing, TAN Yaheng, WANG Shuo
    Journal of Arid Meteorology    2023, 41 (5): 744-752.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0744
    Abstract144)   HTML6)    PDF(pc) (10893KB)(317)       Save

    During the winter of 2021/2022, the low SST (Sea Surface Temperature) in the equatorial Middle Eastern Pacific Ocean led to low temperature and increased precipitation in Guizhou Province. But the number of freezing days was generally lower, showing a phased distribution characteristic of weak in the early stage and strong in the later stage. Based on the daily observation data of 84 national meteorological stations in Guizhou Province, the reanalysis data of NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) and the SST data of NOAA (National Oceanic and Atmospheric Administration), the causes of freezing stages characteristics were analyzed from the aspects of SST field, height field, wind field, temperature field and water vapor condition. The results show that the southern branch frontal zone of the upper level was generally weak in the early stage and strong in the later stage, which provided a favorable large-scale circulation background for the freezing stage characteristics of Guizhou Province. After January 26, 2022, the stable maintenance of shear line in lower troposphere, and the abnormal strong of northerly airflow, which made the 0 ℃ isotherm moved southward obviously. At the same time, with the continuous enhancement of the southerly airflow, the water vapor convergence in the lower troposphere is also rapidly enhanced, and the unstable stratification and ascending motion of the low-level convergence and mid-level divergence were maintained, which provided favorable water vapor conditions for the stage characteristics of freezing in Guizhou Province. In the temperature field, the warm layer was relatively deep in the early stage, and the cold air was weak in the early stage and strong in the later stage, which provided favorable temperature conditions for the characteristics of freezing in Guizhou Province. However, due to the absence of the inversion layer in the whole winter, the intensity of the 3 regional freezing processes was relatively weak.

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    Analysis on mesoscale feature of a extremely rainstorm process caused by the convergence line frontogenesis in Guizhou Province
    WU Guhui, PENG Fang, QI Dapeng, DU Xiaoling, YANG Xiuzhuang
    Journal of Arid Meteorology    2023, 41 (5): 753-763.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0753
    Abstract129)   HTML17)    PDF(pc) (39243KB)(396)       Save

    Based on ground conventional observation data and intensive observation data from automatic weather stations, cloud images of FY-2G satellite, Doppler radar data and ERA5 reanalysis data, the mesoscale synoptic characteristics of a extremely rainstorm process caused by convergence line frontogenesis in eastern and northern Guizhou on 10 May 2021 were analyzed, and the formation mechanism was preliminary discussed. The results show that the extremely rainstorm process occurred under the background of low vortex shear, and the strong southerly wind at low level transported abundant water vapor and unstable energy for the occurrence and development of the mesoscale convective system, the surface convergence line and its frontogenesis provided triggerring condition for the rainstorm. The rainstorm areas mainly occurred in the large gradient areas of temperature black body (TBB), in which were located on the west or south side of the low value center of cloud cluster TBB, and they appeared a strip-shaped distribution in east-west direction along the surface convergence line. The strongest precipitation occurred at the merging stage of convective cloud cluster. The frontogenesis caused by the convergence line frequently triggered convective cells on the west side of the convergence line, and the new convective cells moved and developed eastward along the surface convergence line, which continuously affected the eastern and northern regions of Guizhou Province. At two stages of the strongest precipitation, the warm cloud and overhang structure characteristics of radar echo were obvious. The surface convergence line and its frontogenesis, the cooling and increasing pressure generated by the upstream precipitation and continuously strengthening southerly wind were conducive to the enhancement of water vapor convergence in rainstorm areas. In the vertical direction, the ascending branches of meridional and zonal mesoscale secondary circulation were located near the extremely rainstorm center, which was conducive to the maintenance and enhancement of mesoscale convective system.

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    Analysis on development mechanism of two consecutive warm zone squall lines in Zhejiang Province
    QIAN Zhuolei, ZHAO Chiyu, ZHU Zhejun, SHENG Zhewen
    Journal of Arid Meteorology    2023, 41 (5): 764-773.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0764
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    Two consecutive squall lines affected Zhejiang Province on 25 April 2022, causing a large-range wind disaster. The study of the occurrence and development of continuous squall lines is of important reference value for the forecast of such catastrophic weather. The development process and mechanism of two consecutive squall lines are analyzed by using ERA5 reanalysis data, observations of surface automatic meteorological stations, blackbody brightness temperature (TBB) and doppler radar data. The results show that the two consecutive squall lines (named “squall line 1” and “squall line 2”, according to the sequence of squall lines) developed in the upper jet stream divergence area, in front of the middle-level trough and in the warm zone in the south side of the low vortex at the lower level and at the top of the southwest jet stream axis. The squall line 1 was a medium β scale squall line triggered by the upper dry intrusion and the weak cold front near the surface in the early stage. The meso-scale convergence line caused by the bottom outflow and the strong inflow of southeast wind over the Hangzhou Bay and the vertical wind shear at the lower level promoted the squall line to strengthen gradually during its movement. The squall line 2 rose from the middle β scale to the middle α scale during the primary to mature stage. It was related to the migration of the upstream convective system in the early stage. Its formation was related to the migration of the upstream convective system in the early stage, affected by the upper dry intrusion, the vertical wind shear at the lower level, the convergence line of the weak cold front behind the squall line 1 and the merging of the upstream echoes, the upscaling phenomenon occurred in the mature stage. When the vertical wind shear decreased and the northern segment of the squall line 2 moved into the sea faster, the squall line 2 broke.

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    Distribution characteristics of atmospheric vapor and liquid water in central Guanzhong Plain based on observation data of ground-based microwave radiometer
    WANG Wenyan, WANG Ruiying, LEI Lianfa, FAN Chao, LI Guoping
    Journal of Arid Meteorology    2023, 41 (5): 774-782.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0774
    Abstract128)   HTML5)    PDF(pc) (1817KB)(483)       Save

    The research on the distribution of cloud water content and its evolution rules has important significance for the exploitation and utilization of regional cloud water resources. The paper analyzed the temporal variation characteristics of liquid water path (LWP) and integrated water vapor (IWV) in central Guanzhong Plain by using observation data of MWP967KV ground-based microwave radiometer at Jinghe station of Shaanxi Province from October 2017 to December 2020. Combined with ground precipitation and Doppler weather radar observation data, the development and evolution characteristics of water vapor and liquid water before precipitation in various cloud systems were compared by some cases study. The results indicate that the IWV exhibits obviously seasonal variations in central Guanzhong Plain, with the highest in summer, followed by autumn and spring, and the lowest in winter. Specifically, the peak appears in July, and the valley appears in December. The LWP is higher in autumn and summer, in winter it is the lowest. Notably, the peak is in September, and the valley is in December. The distribution of the IWV and LWP exhibits a single peak and single valley pattern over the course of a day, but the occurring time of their peak and valley is different. The diurnal maximum of the IWV occurs from 07:00 to 08:00 in summer and autumn, 23:00 in spring and 13:00 in winter, while the diurnal minimum of the IWV occurs at about 12:00 in spring, summer and autumn, 22:00 in winter. The diurnal maximum of the LWP occurs from 07:00 to 09:00 in spring, summer and autumn, while in winter it is slightly late (10:00). The diurnal minimum of the LWP appears at the nighttime in all seasons. The growth time of cloud water content before precipitation is different for different types of cloud systems. On average, the development time of stratiform cloud systems is 15.6 hours, and for other cumulus cloud systems it is 9.0 hours. In the initial stage, the IWV in both cloud systems varies prior to the LWP, and the fluctuation amplitude is increasingly violent as precipitation approaches. Additionally, the LWP in both cloud systems firstly exhibits a sudden violent increase before the rainfall being triggered, and the IWV and LWP in stratiform cloud system vary greatly in different seasons as precipitation is triggered. In the afternoon, the duration of strong convection developing is short, with an average time of 30 minutes. In the initial stage of development and before precipitation, the LWP varies and jumps sharply at the first.

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    Study of soil moisture prediction method based on soil temperature and moisture persistence
    WEI Sentao, WANG Chenghai, ZHANG Feimin, YANG Kai
    Journal of Arid Meteorology    2023, 41 (5): 783-791.   DOI: 10.11755/j.issn.1006-7639(2023)-05-0783
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    Soil temperature and moisture are the important parameters in land surface process, and they are also important physical parameters in boundary conditions of atmospheric numerical model. This paper tried to obtain spatial-temporal evolution of soil moisture of the model through the machine learning method according to the memory characteristics of soil moisture. Considering the influence of soil temperature on soil moisture, the soil temperature and moisture of ERA5 reanalysis at depths of 0-7, 7-28, 28-100, 100-289 cm are used as predictors to predict changes of soil moisture on a monthly and seasonal scale based on convolutional neural networks (CNN). The results show that the method proposed in this paper is reliable and can effectively predict soil moisture 6 months in advance. The mean bias of predicted soil moisture in the shallow layer (0-28 cm) and deep layer (28-289 cm) is less than 0.05 and 0.02 m3·m-3, respectively. In the humid area, the mean bias is basically within 0.03 m3·m-3, showing a good effect.The prediction method and results presented in this paper can be used for both soil drought prediction and the initial and boundary conditions for numerical models.

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    Meteorological drought and atmospheric circulation anomalies characteristics in Heilongjiang Province from May to September in recent 50 years
    WANG Ying, ZHANG Shu, XU Yongqing, QUE Linjing, LI Xinhua, HUANG Yingwei, CHEN Xue, WANG Lei
    Journal of Arid Meteorology    2023, 41 (4): 540-549.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0540
    Abstract282)   HTML44)    PDF(pc) (10420KB)(691)       Save

    Heilongjiang Province is the major grain production base in China, the study of drought climate characteristics in Heilongjiang Province is of great importance for scientific prevention and management of drought disasters. Based on daily temperature and precipitation data from 80 national meteorological stations in Heilongjiang Province from May to September during 1971-2020, the daily meteorological drought composite index (MCI) of Heilongjiang Province was calculated, and the spatial and temporal distribution characteristics of drought, severe drought and extreme drought days in Heilongjiang Province were analyzed. At the same time, the circulation characteristics of typical dry and wet years were further analyzed. The results show that from May to September during 1971-2020, the southern part of the Greater Hinggan Mountains and the western part of Songnen Plain in Heilongjiang Province are drought-prone areas. The number of dry days is more in the west and some areas of the central hinterland and less in the east. The inter-decadal characteristics of medium drought, severe drought and extreme drought are obvious and show a decreasing trend. The decreasing trend of medium drought was the most obvious with a rate of -1.7 d·(10 a)-1. There are significant differences in circulation patterns between typical dry years and wet years. In typical dry years, the area west of Lake Baikal is controlled by anticyclones, while Heilongjiang is controlled by the westerly jet stream, resulting in prevailing descending airflow, which is not conducive to the intersection of cold and warm air, and the water vapor transport channel is not obvious, so water vapor is difficult to reach the Heilongjiang region. Conversely, in typical wet years, the situation is the opposite.

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    Spatio-temporal evolution characteristics of drought in the “Heng-Shao-Lou drought corridor”
    YANG Yang, ZHAO Weiming, HU Yingbing, SHENG Dong, WEI Yongqiang, SHEN Zhigao, TAN Jun
    Journal of Arid Meteorology    2023, 41 (4): 550-559.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0550
    Abstract208)   HTML11)    PDF(pc) (12268KB)(494)       Save

    Recently, the droughts attack frequently in the Yangtze River basin, resulting in more and more loss. To further improve regional drought risk management and drought resistance capabilities, it is of great significance to conduct research on the spatio-temporal evolution characteristics of drought in typical drought-prone areas. “Heng-Shao-Lou drought corridor” in Hunan Province is a region with most severe droughts, the standardized precipitation index (SPI) dataset based on monthly precipitation data from 33 meteorological stations in this area from 1971 to 2022 is constructed. Citing the case of Shaoyang County, run theory is applied to integrate drought events, and Gumbel-Copula is adopted to construct the joint distribution function of drought duration and severity, then the joint return periods of drought are calculated and the method is extended to the whole study area. On the basis of it, the classification standard of drought grades is established, and the spatial distribution characteristics of drought probability for each level in the whole study area are analyzed. The results show that the peaks of theoretical joint return period of drought duration and severity for the type Ⅰ and type Ⅱ in Shaoyang County are around 97 a and 27 a, respectively, which indicates that the probability of drought events with long duration and high severity is very small and far lower than that of drought events with long duration or high severity, it is a common feature of drought events in research area. Furthermore, the combination of drought duration and severity joint distribution can effectively avoid segmentation of the whole drought event when drought grades are identified by a single variable, and can evaluate the complexity and large-scale impact of drought more accurately. In the past 52 years, the slight drought occurs most frequently in western region of the “Heng-Shao-Lou drought corridor”, while the frequency of severe or extreme drought is low. Extreme drought mainly distributes in Shaoyang County, Shaodong County and Shuangfeng County.

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    Desertification monitoring in the Qaidam Basin based on NDVI-Albedo feature space
    SUN Shujiao, CAO Xiaoyun, XIAO Jianshe, SUN Weijie, ZHU Cunxiong
    Journal of Arid Meteorology    2023, 41 (4): 560-569.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0560
    Abstract161)   HTML5)    PDF(pc) (17279KB)(461)       Save

    Desertification has become a major threat to the global ecological environment, and the desertification monitoring is crucial for desertification prevention and control. Based on the Suomi/NPP (National Polar-orbiting Partnership) remote sensing data and the observation data of 8 meteorological stations during the vegetation growing season (from May to September) from 2014 to 2021 in the Qaidam Basin, the desertification difference index (DDI) was calculated by using NDVI-Albedo (Normalized Difference Vegetation Index-Albedo) feature space. Moreover, the natural discontinuity method, Sen+M-K trend analysis method, correlation analysis method, accuracy error matrix and transfer matrix analysis were also used to explore the spatial and temporal dynamic evolution of land desertification and the influence of meteorological factors to desertification in the Qaidam Basin from 2014 to 2020 during the vegetation growing season. The results are as follows: (1) The NDVI-Albedo feature space performs a high applicability in the Qaidam Basin (R2 greater than or equal to 0.65), with an overall classification accuracy of 79.38% and a Kappa coefficient of 0.62. (2) From 2014 to 2021, the degree of land desertification in the eastern and southern Qaidam Basin is lower than that in the western and central Qaidam Basin. Furthermore, DDI shows a significantly increase in some areas, especially in southern and eastern region with the increase rate of DDI over 0.01a-1. The total area of desertification land in the Qaidam Basin shows a decreasing trend with a rate of -1 173 km2·a-1. Additionally, a transforming characteristic occurs between different degrees desertification land that severe desertification lands transferred to mild desertification land. (3) Correlation analysis shows that precipitation and average relative humidity are significantly positively correlated with DDI (P<0.01), and correlation coefficients are 0.91 and 0.86, respectively, indicating that the water is the dominant factor affecting desertification in the Qaidam Basin.

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    Aerosol types discrimination in semi-arid region of Northwest China using ground-based lidar data
    LIAO Jiayan, ZHOU Tian, HAN Biseng, HUANG Zhongwei, BI Jianrong
    Journal of Arid Meteorology    2023, 41 (4): 570-578.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0570
    Abstract117)   HTML4)    PDF(pc) (2866KB)(514)       Save

    The accurate identification of aerosol types is an important prerequisite for further research on its climatic and environmental effects. In this study, based on the observation data of ground-based dual-wavelength polarization lidar from the Semi-arid Climate and Environment Observation Station of Lanzhou University from October 2009 to November 2012, several cases were selected under four typical scenarios: clean day, anthropogenic pollutants, dust events and strong sandstorm events. The aerosol extinction coefficient, volume linear depolarization ratio and aerosol depolarization ratio were analyzed statistically, and the determination thresholds of different aerosol types were defined. The results show that the extinction coefficient of aerosol in this region is less than 0.085 km-1 on clean day. When the extinction coefficient is greater than 0.085 km-1, the volume linear depolarization ratio of anthropogenic pollutants is less than 0.07, and the corresponding aerosol depolarization ratio is less than 0.09. The volume linear depolarization ratio of polluted dust is between 0.07 and 0.22, and the aerosol depolarization ratio is between 0.09 and 0.31. The volume linear depolarization ratio of pure dust is greater than 0.22, and the aerosol depolarization ratio is greater than 0.31. In particular, when severe sandstorms occur, the volume linear depolarization ratio is greater than 0.35, and the aerosol depolarization ratio is greater than 0.49.

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    Study on the suitability of surface meteorological stations in Sichuan Province based on relief degree of land surface
    HUANG Xiaolong, WU Wei, XU Xiaoli, WANG Liwei, SONG Yunfan, LI Xue
    Journal of Arid Meteorology    2023, 41 (4): 579-588.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0579
    Abstract161)   HTML8)    PDF(pc) (17339KB)(890)       Save

    In order to scientifically determine the topographic relief characteristics of meteorological stations, based on the 30 m data of Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM), the optimal analysis window of relief degree of land surface (RDLS) model in Sichuan Province was determined by using the mean change point analysis method. On this basis, the relief amplitude characteristics of surface meteorological observation stations in Sichuan Province were analyzed to explore the spatial pattern of the layout of meteorological stations. The results are as follows: (1) The best window for RDLS in Sichuan Province is 39 × 39 rectangular neighborhood pixels, with a corresponding area of about 1.369 km2. The established RDLS model is consistent with the trend of mountains and can capture the topographic relief of various scales, which accords with the topographic characteristics of Sichuan Province. (2) The terrain of national stations and regional stations is dominated by platforms, hills, and small undulating mountains. The proportion of national stations with small topographic undulations stations is significantly higher than that of regional stations, indicating that national stations are more representative of the region. (3) Suitable meteorological observation stations in Sichuan Province are mainly distributed the basin, in the north and west regions of the west Sichuan Plateau, as well as the eastern and southern parts of Panxi, accounting for 69.74% of the province’s total area. The analysis window area determined by the mean change point analysis method can take into consideration various geomorphic types, and the extracted RDLS can better reflect the topographic characteristics of meteorological stations, which can provide an important reference for the adaptive layout of meteorological stations and the optimization of station network.

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    Spatio-temporal distribution characteristics of summer hourly heavy rainfall in the Three Gorges Reservoir area from 1992 to 2021
    TANG Yonglan, XU Guirong, WANG Xiaofang, XIAO Yanjiao, QI Haixia, LENG Liang
    Journal of Arid Meteorology    2023, 41 (4): 589-598.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0589
    Abstract170)   HTML10)    PDF(pc) (23455KB)(538)       Save

    The Three Gorges Reservoir area (TGRA), which is located in the hinterland of the Yangtze River Basin, is a typical area with frequent meteorological disasters and fragile ecological environment, especially the hourly heavy rainfall (HHR) in summer is prone to disasters due to suddenness and difficulty in prediction. Based on the hourly precipitation data in summer during 1992-2021 from the National Meteorological Information Center of China Meteorological Administration, the fine spatio-temporal distribution characteristics of HHR and heavy rainfall event (HRE) in the TGRA are investigated. The results show that the summer HHR in the TGRA has strong local features, its intensity is strong, and makes main contribution to total summer precipitation due to its high frequency. The southeastern TGRA is the center of summer HHR precipitation, frequency and intensity. In the past 30 years, the summer HHR precipitation in the TGRA has been non-significant increase. Both the diurnal variations of summer HHR precipitation and frequency in the TGRA show a bimodal pattern, with peaks appearing in the morning and afternoon, respectively, and the peak time phase is related to the terrain. Besides, the summer HREs in the TGRA are mainly short duration (1-6 hours), with precipitation mostly ranging from 20 to 60 mm, while the long duration (>12 hours) HREs seldom occur, with precipitation mostly ranging from 60 to 100 mm. Moreover, the short duration HREs mostly start in the afternoon, and most of their maximum hourly precipitation also occur in the afternoon, while the HREs with medium (7-12 hours) and long durations mostly start at night, and most of their maximum hourly precipitation occur in the morning.

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    Distribution characteristics of typical stratiform clouds water vapor and liquid water in Tianjin area based on airborne microwave radiometer
    NIE Haohao, WANG Wan, GUO Xiaojun, LIN Xiaomeng
    Journal of Arid Meteorology    2023, 41 (4): 599-606.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0599
    Abstract143)   HTML5)    PDF(pc) (12854KB)(386)       Save

    Based on the detection data of airborne microwave radiometer GVR (G-band water Vapor Radiometer) and Hotwire Liquid Water Content Sensor, cloud top brightness temperature of FY-2E satellite, radar reflectivity at Tanggu station of Tianjin and FNL reanalysis data from NCEP (National Centers for Environment Prediction) and NCAR (National Center for Atmospheric Research) on 20 November 2016, the distribution characteristics of water vapor and liquid water for typical stratiform clouds in Tianjin area are analyzed. The results show that the liquid water path of stratiform clouds in Tianjin area decreases with the increase of height from the bottom of clouds, and it drops to 0 mm at the height of ice cloud and above. The integrated water vapor content gradually decreases from the ground with the increase of height, and its value holds at 0.3-0.5 cm during the level flight at 3 500 m above clouds. The density of liquid water increases firstly and then decreases with the increase of height. The liquid water detected by GVR above the cloud base (900 m) is supercooled water. During the ascent of aircraft, the supercooled water is mainly distributed at the height of 900-2 400 m, and the maximum density is 0.63 g·m-3. During the descent of aircraft, the supercooled water is mainly distributed at the height of 900-1 600 m, and the maximum density is 0.78 g·m-3. Compared with the Hotwire Liquid Water Content Sensor, GVR can better reflect the supercooled water content of clouds, the height and thickness of the supercooled layers. The water vapor in Tianjing area mainly comes from the advection transport. The water vapor density increases continuously at the height of 400 m, and accumulates obviously near the cloud base, and then decreases rapidly. Within the height of 1 400-3 000 m, the water vapor density fluctuates little. With the approaching of precipitation, the maximum value of water vapor density and its corresponding height increases during the descent of aircraft, and the thickness of the high water vapor density layer increases, which can provide some references for precipitation prediction and weather modification.

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    Pollution characteristics of two strong dust processes in northern China in March 2021
    TU Aiqin, WANG Zhenzhu, ZHU Genghua, WANG Zhifei, ZHANG Hai, ZHANG Shuai, LIU Dong, WENG Ningquan
    Journal of Arid Meteorology    2023, 41 (4): 607-619.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0607
    Abstract155)   HTML3)    PDF(pc) (52478KB)(501)       Save

    In order to study the development law and pollution characteristics of dust weathers, two strong sandstorm processes occurring in northern China in March 2021 (the processes on March 15 and 27, referred to as “3·15” process and “3·27” process, respectively) are analyzed based on polarized mie-scattering lidar observation data and hourly urban particulate mass concentration data in Shijiazhuang and Jinan. The results are as follows: (1) When the dust arrived, the mass concentration of PM10 in the two cities increased rapidly, and the mass concentration ratio of PM2.5 and PM10 decreased rapidly. (2) The PM10 mass concentration of the two cities conformed to the normal distribution during the two processes, and the determination coefficients of the Gaussian fitting of the PM10 mass concentration in Shijiazhuang and Jinan during the “3·15” process and the “3·27” process were 0.92 and 0.76, 0.83 and 0.89, respectively. (3) During the dust outbreak period, the extinction coefficient and depolarization ratio near the ground increased significantly. (4) Due to dust sedimentation and different sources of dust, a multi-layer structure appeared during dust transport, which can be divided into near-surface dust layer, low-altitude dust layer and high-altitude dust layer. The appearance time of near-surface dust layer was basically consistent with the sharp rise time of ground particle mass concentration. (5) At the height of 195 m (close to the ground and with reliable radar data quality), the maximum depolarization ratio in Shijiazhuang and Jinan during the “3·15” process (the“3·27” process) was 0.29, 0.28 (0.23, 0.20), and the maximum extinction coefficient was 3.94, 3.84 km-1 (3.10, 1.83 km-1), respectively, which showed that the strength of dust became weaker and the large particles decreased continuously during the transport process. The time when the depolarization ratio at this height began to rise rapidly was about 1 h earlier than the time when the mass concentration of ground particles began to rise rapidly. (6) According to the pollution characteristics of dust weather, its development can be divided into four stages: the early stage, the outbreak stage, the maintenance stage and the late stage. The different stages of dust can be well identified by comprehensive use of PM10 mass concentration, PM2.5 and PM10 mass concentration ratio, extinction coefficient and depolarization ratio.

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    Analysis on scavenging effect of precipitation processes on PM2.5 in different cities of Sichuan Basin
    LIN Dan, GUO Xiaomei, WANG Weijia
    Journal of Arid Meteorology    2023, 41 (4): 620-628.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0620
    Abstract124)   HTML6)    PDF(pc) (1800KB)(501)       Save

    Studying the impact of precipitation on PM2.5 mass concentration in different regions can provide an important scientific support for the air quality assessment and forecast as well as pollution prevention in this region. Based on the hourly precipitation observation data and PM2.5 mass concentration monitoring data in five typical cities (Chengdu, Leshan, Yibin, Mianyang and Dazhou) of Sichuan Basin from 2016 to 2021, the scavenging effect of precipitation processes on PM2.5 was analyzed in different cities from some aspects including the occurrence time, duration, intensity of precipitation and the initial mass concentration of PM2.5. The results show that the proportion of positive scavenging processes of precipitation on PM2.5 increases with the increase of precipitation intensity or initial mass concentration of PM2.5 in Sichuan Basin, and the scavenging rate rises. Under the condition of air pollution, the scavenging effect of precipitation with intensity exceeding 1 mm·h-1 on PM2.5 improves obviously in Sichuan Basin, and the scavenging rate reaches 35.0%. The scavenging effect is positively correlated with the duration of precipitation processes, and the scavenging rate of precipitation processes with the duration more than 3 hours is 9.0%-18.0% higher than that of precipitation processes with the duration less than or equal to 3 hours. The probability of positive scavenging processes is higher in the early morning and afternoon in Sichuan Basin, and the precipitation processes in the early morning have better scavenging effect on PM2.5. In comparison, the proportion of positive scavenging processes is higher in Leshan and Yibin after the precipitation, and under different initial mass concentrations of PM2.5, the scavenging rate is significantly higher than that in other cities with the increase of precipitation duration.

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    Analysis on synoptic causes of a severe convective rainstorm in Yunnan
    MA Zhimin, WANG Jiang, LIAN Yu, ZHANG Wancheng, NIU Fabao, YANG Suyu
    Journal of Arid Meteorology    2023, 41 (4): 629-638.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0629
    Abstract206)   HTML20)    PDF(pc) (29336KB)(634)       Save

    In order to improve the accuracy of rainstorm forecast and reduce the disaster losses caused by rainstorm, based on the ground conventional meteorological observation data, TBB (Black Body Temperature) data from satellite images and reanalysis data from National Centers for Environmental Prediction (NCEP), the synoptic causes of a strong convective rainstorm in Yunnan in August 2017 were analyzed. The results show that the eastward movement of 500 hPa trough, the southward movement of 700 hPa shear line and the westward movement of surface cold front are the synoptic background of this precipitation process. The mesoscale convective systems (MCS) on the Meso-α and Meso-β scales directly trigger the convective rainstorm. The heavy rainfall generally happens in the region with a high gradient of TBB. The MCS is closely related to 700 hPa wind shear line where is located to the east of Mid-Yunnan. The MCS is elliptically-shaped, developing along the neighboring and backside of the wind shear line. After the wind shear line getting close and cross over the Ailao Mountain, the MCSs distribute in a belt from northwest to southeast, and develop in front of the wind shear line. The wind shear line moves fast during the daytime before crossing over the Ailao Mountain, mainly producing thunderstorm weather while it moves slowly at nighttime, and the rainfall is strong. The forecast of strong convective rainstorm should focus on the large value area of water vapor flux convergence and the area where the temperature difference between 800 hPa and 500 hPa is greater than 20 ℃. During the heavy rainfall, the whole layer atmosphere is ascending, and the heavy rainfall area maintains the dynamic pumping mechanism of convergence at lower level and divergence at middle and upper levels.

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    Spatial and temporal variations of heat resources utilization efficiency of summer maize in growth season under climate change in Hebei Province
    HAN Yaojie, PENG Jiyong, ZHANG Xihe, LI Shuyan
    Journal of Arid Meteorology    2023, 41 (4): 639-647.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0639
    Abstract139)   HTML4)    PDF(pc) (8295KB)(467)       Save

    Exploring the spatial and temporal distribution characteristics of heat resources utilization efficiency of summer maize in growth season could provide theoretical basis for the adjustment of summer maize variety layout and guarantee of a high and stable maize yield. Based on the daily meteorological data of 15 agricultural meteorological observation stations from 1981 to 2019, and the observation data of the growing period of summer maize and wheat in the later crop rotation in Hebei Province, the regression analysis and spatial interpolation methods are used to analyze the spatial and temporal variations of heat resources utilization efficiency of summer maize in growth season under climate change. The results show that the potential growing days of summer maize in Hebei Province had no significant change from 1981 to 2019, while the potential accumulated temperature increased significantly (P<0.05). The utilization efficiency of heat resources during growth season increased significantly (P<0.05), the utilization efficiency of growing days increased from 80.4% in 1981 to 94.5% in 2019, and the utilization efficiency of accumulated temperature increased from 84.5% in 1981 to 94.9% in 2019. The potential growing days and accumulated temperature of summer maize were more in the south and less in the north, and the utilization efficiency of growing days and accumulated temperature were lower in the south and higher in the north. There was higher utilization efficiency (more than 95%) of growing days and accumulated temperature in Langfang, while in Handan the utilization efficiency of growing days was lower (less than 85%). The accumulated temperature of summer maize increased at a rate of 19.6 ℃·d·(10 a)-1 before anthesis and 58.7 ℃·d·(10 a)-1 after anthesis. The increase rate of accumulated temperature after anthesis was obviously higher than that before anthesis, and the ratio of accumulated temperature showed an obvious downward trend, it fell 28.5% from 1.6 in 1981 to 1.1 in 2019. The results demonstrate that the utilization efficiency of climate resources of summer maize in the southern Hebei had some space for improvement. The medium and late maturing varieties with a longer growing season could be selected, and the varieties with a longer filling stage could be selected for breeding or cultivation, so as to make full use of the heat conditions in the growing season and improve maize yield.

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    Study on soil thermal characteristics in wine grape planting area in the eastern foot of Helan Mountain in Ningxia in winter
    ZHAO Tuxiang, LI Fusheng, GUO Xiaolei, HU Yue, WEI Jianning, LI Xiaoyu
    Journal of Arid Meteorology    2023, 41 (4): 648-656.   DOI: 10.11755/j.issn.1006-7639(2023)-04-0648
    Abstract168)   HTML1)    PDF(pc) (7035KB)(483)       Save

    In order to scientifically manage grape being covered with soil to over winter, based on the ground temperature observation data of 10 vineyards at the eastern foot of the Helan Mountain in Ningxia in the winter of 2021/2022, the variation characteristics of daily mean ground temperature and the thermal diffusivity of 10-20 cm soil in different vineyards at the eastern foot of the Helan Mountain were analyzed. The results are show that in winter, the soil temperature decreased firstly and then increased, and soil temperature increased with the increase of depth. The temperature fluctuation of deep soil was smaller than that of surface soil, and the changing trend also lagged behind that of surface soil. The heat conduction method can well simulate the soil temperature of 10 cm and 20 cm in the eastern foot of the Helan Mountain in winter, and the effect of 20 cm soil temperature is the best, with the regression correction coefficient reaching 0.947 5. The soil thermal diffusivity (k) of vineyards in the eastern foot of the Helan Mountain in winter was generally higher. There were some differences of k value in each vineyard, the soil thermal diffusivities of Hedong Manor in Dawukou district at the north end of the producing region and St. Louis winery in Yongning county to the east were small, and the average k value was 6.11×10-6 and 4.53×10-6 m2·s-1, respectively. However, the thermal diffusivities in Guanlan Winery, Xige Winery, Legacy Peak Estate, Hennessy Winery near the Helan Mountain, D.F.Yuxing Winery and Pink Carrin Winery at the southern end of the producing region were larger, with average k values of 11.08×10-6 to 14.94×10-6 m2·s-1. The average k values of Emperial Horse and Meiyu Wineries were 9.63×10-6 and 8.52×10-6 m2·s-1, respectively.

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    Effects of different irtigation sources on growth characteristics and yields of celery in semi-arid region
    LI Yongjun, ZHAO Xiaole
    Journal of Arid Meteorology    2023, 41 (3): 359-367.   DOI: 10.11755/j.issn.1006-7639(2023)-03-0359
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    In order to seek a suitable irrigation water source in the Tao river irrigation area of Dingxi of Gansu Province, this study adopts a completely randomized treatment design and sets three irrigation water sources including local shallow underground water and the Tao river irrigation and their alternative irrigation, among the underground water irrigation as a control treatment, and the effects of different irrigation water sources on celery growth characteristics, water consumption, yield, water use efficiency and economic benefits are explored in semi-arid region. The results show that compared with underground water irrigation, the plant height of celery under the Tao river irrigation and alternative irrigation both underground water and the Tao river decreases by 6.07 cm and 3.33 cm, the stem thicknesses decrease by 1.22 mm and 0.78 mm, the soil water storage decrease by 1.27% and 1.98%, the yields of celery decrease by 15.08% and 1.57%, the water use efficiency decrease by 15.53% and 2.46%, and the irrigation water use efficiency decrease by 15.46% and 2.01%, respectively, while the total water consumption increase by 0.09% and 0.47%, and the net income of celery increase by 3.1% and 18.0%, respectively. The increase of celery yields is the most obvious under the underground water irrigation, but its water cost is the most expensive, so its economic benefit is lower. Although the celery yields and water use efficiency under the alternative irrigation are slightly lower than that under the underground water irrigation, the water cost reduced greatly, so the economic benefit is the highest. The water cost under the Tao river irrigation is low, but its economic benefit increase slightly due to all indexes of celery decreasing significantly (P<0.05). In summary, the alternative irrigation both underground water and the Tao river can be used as a feasible and effective irrigation mode to increase production and income of farmers in the Tao river irrigation area of Dingxi.

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    Evaluation of CLM 5.0 on simulating soil temperature in alpine mountainous area in arid environment
    ZENG Xuan, ZHANG Lanhui, BAI Xuliang, LIU Yu, AN Qi
    Journal of Arid Meteorology    2023, 41 (3): 368-379.   DOI: 10.11755/j.issn.1006-7639(2023)-03-0368
    Abstract159)   HTML9)    PDF(pc) (6886KB)(447)       Save

    Soil temperature reflects the thermal state of soil and plays a crucial role in the exchange of surface energy, and it directly influences the water and heat redistribution of soil. In alpine mountainous area, the hydrological and energy transfers are more special and complex. Therefore, it is essential to simulate accurately soil temperature in investigating hydrological cycles in alpine mountainous areas. CLM 5.0 (Community Land Model 5.0) is the latest version of the CLM model, which is one of the most advanced land surface process models in the world. In this paper, the soil temperature simulation performance of CLM 5.0 is evaluated based on the measured data of 9 typical observation stations in the upper reaches of the Heihe River Basin. The results are as follows: (1) CLM 5.0 can well simulate the annual and inter-annual changes of soil temperature in alpine mountainous areas, but the simulated values are generally underestimated. (2) The simulation performance of CLM 5.0 on soil temperature in alpine meadow is slightly higher than that in grassland, and it in shallow soil layers is better than in deep soil layers. (3) CLM 5.0 exhibits greater underestimation to soil temperature in the non-growth period than in the growth period, and greater underestimation under frozen state than under unfrozen state. (4) The underestimation of CLM 5.0 simulated soil temperature in the non-growth period is mainly due to the underestimation of soil temperature under frozen state, which results from errors in estimating soil ice. These results provide insights for future applications and improvements of CLM 5.0 in alpine mountainous areas.

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    Changes of summer water vapor in Bengal region and its linkage with the interdecadal Pacific oscillation
    GUO Jingyan, XIAO Dong
    Journal of Arid Meteorology    2023, 41 (3): 380-389.   DOI: 10.11755/j.issn.1006-7639(2023)-03-0380
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    Located in the middle zone between the Tibetan Plateau and the Bay of Bengal, the Indian Peninsula and the Indo-China Peninsula, the Bengal region is the first region affected by the outbreak of the Asian monsoon. The change of water vapor in the Bengal region is of great significance to the climate of South Asia and East Asia. The causes and possible physical processes of the atmospheric precipitable water (APW) change in summer (June-September) in the Bengal region are analyzed using the ERA5 reanalysis data from the European Center for Medium-Range Weather Forecasts (ECMWF) and sea surface temperature data from the National Oceanic and Atmosphere Administration (NOAA) from 1979 to 2020. The results show that APW in the Bengal region is the largest at the same latitude in southern Asia. The summer APW accounts for more than 50% of the whole year, and the average summer APW presents a significant increase trend. According to the whole layer water vapor budgets and water vapor budget vertical profiles of the four boundaries of the Bengal region, the trends of the whole layer water vapor budgets of the eastern and southern boundaries are favorable to the increase of APW there, while the trends of the whole layer water vapor budgets of the western and northern boundaries are unfavorable to the increase of APW there. The summer APW in the Bengal region is negatively correlated with the interdecadal Pacific oscillation (IPO) on both inter-annual and inter-decadal scales. When the IPO is in its positive phase, in the lower troposphere, the westerly (easterly) wind anomaly prevails in the equatorial Pacific (equatorial Indian Ocean), while it is the opposite in the upper troposphere, indicating a weakening of the Walker circulation over the Indian and Pacific Oceans. The Gill-type anticyclonic circulation anomaly is observed in the lower troposphere in the north and south sides of the equatorial Indian Ocean. The Indian monsoon is weak, and a northwest wind anomaly prevails from the Arabian Peninsula to the Bengal region. The westerly airflow is not conducive to the transport of water vapor to the Bengal region, while the sinking airflow accompanying the anticyclonic circulation is not conducive to the convergence of water vapor in this region, resulting in the reduction of APW in the Bengal region. On the contrary, when the IPO is in a negative phase, it is favorable for the increase of APW in the Bengal region in summer.

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    Analysis on spatio-temporal variation of evapotranspiration in the Yellow River Basin based on ERA5-Land products
    YANG Yang, WANG Lijuan, HUANG Xiaoyan, QI Yue, XIE Rui
    Journal of Arid Meteorology    2023, 41 (3): 390-402.   DOI: 10.11755/j.issn.1006-7639(2023)-03-0390
    Abstract277)   HTML15)    PDF(pc) (17539KB)(545)       Save

    The climate in the Yellow River Basin has undergone significant changes in recent years, which has a significant impact on surface hydrological and ecological processes in the basin. Studying the spatial and temporal variation of evapotranspiration in the Yellow River Basin is indicative for understanding deeply land-atmosphere interactions and regional water resources management. In this paper, the appliability of ERA5-Land evapotranspiration in the Yellow River Basin was evaluated using in-situ observations of Haibei, SACOL (Semi-Arid Climate and Environment Observatory) and Yucheng stations which are selected as representative stations from the source region, Hetao region and the lower reach of the Yellow River Basin, respectively. Then based on monthly latent heat flux from ERA5-Land data, the spatial and temporal variation of evapotranspiration in the Yellow River Basin in the past 42 years (1980-2021) are analyzed using EOF (Emipirical Orthogonal Function), power spectrum and regression analysis methods. The results show that ERA5-Land data can reflect the variation characteristics of evapotranspiration at Haibei, SACOL and Yucheng stations with good correlation and small error and root mean square deviation, which is applicable for the analysis on spatial and temporal variation of evapotranspiration in the Yellow River Basin. There are multi-timescale variations of evapotranspiration in different regions of the Yellow River Basin, with significant oscillation periods of main 5 a and 15 a, and obvious inter-annual and inter-decadal variations. The first mode in different regions of the Yellow River Basin characterizes the consistency in spatial distribution, which decreases around 2004. The second mode is dipole distribution, indicating the reverse change in space. The deceleration of evapotranspiration in the Yellow River Basin in the past 42 years is not same in different regions, with the fastest rate of -3.74 mm·a-1 in the lower reaches and -2.82 mm·a-1 in the Hetao area, while the deceleration in the source area is relatively gentle. The summer evapotranspiration variability is the largest, and the deceleration is faster in the Hetao area and the lower reaches. The winter evapotranspiration variability is smaller, but the source area has the largest winter evapotranspiration deceleration of -0.48 mm·a-1.

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    Analysis of spatial-temporal variation of urban heat island and driving mechanism in Zhengzhou in recent 17 years
    ZHANG Yuchen, TIAN Hongwei
    Journal of Arid Meteorology    2023, 41 (3): 403-412.   DOI: 10.11755/j.issn.1006-7639(2023)-03-0403
    Abstract191)   HTML7)    PDF(pc) (11478KB)(521)       Save

    In order to make an in-depth study of urban thermal environment of Zhengzhou, the temporal evolution and spatial distribution characteristics of urban heat island effect are analyzed based on the MODIS land surface temperature product (MYD21A1), and the causes and driving mechanism of urban heat island effect are discussed from both natural and anthropogenic factors in combination with the data of land use/land cover types and Zhengzhou statistical yearbooks. The results show that there is no significant difference in the spatial distribution of annual mean heat island intensity between day and night in Zhengzhou, and the areas with stronger heat island intensity or above are mainly in the main urban area. The temporal variation of heat island effect in Zhengzhou has diurnal and seasonal differences. During the daytime, the proportion of heat island area increased insignificantly in spring and significantly in summer, and decreased insignificantly in autumn and winter. In spring, summer and autumn, the proportion of heat island area at night increased insignificantly, while in winter, the heat island effect was weak and there was no obvious change characteristics. The inter-annual variation of urban heat island proportion index of Zhengzhou was consistent with heat island intensity. The urban heat island proportion index during daytime and nighttime was higher in summer, then in spring, autumn and winter in turn. The heat island effect of different land use/land cover types was obviously different, with the highest in urban and rural building land, followed by cultivated land, and the lowest in woodland and water area. There is a negative correlation between vegetation coverage and land surface temperature. Solar radiation intensity has a positive driving effect on urban heat island effect, and population density, GDP and built-up area are all positively correlated with urban land surface temperature.

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