To overcome the limitation of traditional meteorological drought indices, which rely on historical climatic probability data of the same period for calculation, this paper establishes a meteorological drought index that can reflect the degree of soil drought but only requires current precipitation and evaporation data. Based on the soil water balance equation and in conjunction with the standard classification of soil drought levels, this study utilizes the relationship between the evaporation intensity of the dry soil surface layer and the water surface, along with soil evaporation calculation methods, to derive the expressions of the critical lines representing various drought levels within the cumulative precipitation-cumulative evaporation coordinate system. The four derived expressions of critical lines correspond to four drought grades, namely, mild drought, moderate drought, severe drought, and extreme drought, respectively. Through a forward daily rolling calculation, the point where the cumulative precipitation and cumulative evaporation coordinates are farthest from their respective critical line is identified as the maximum distance point for that critical line. The drought level is determined by the coordinate point that is located in the highest drought level region and has the maximum distance from the nearest lower critical line. The drought index is then constructed based on the distances from this coordinate point to each critical line. The drought index established in this study reflects the level of soil drought. The drought index calculated using the soil drought level distance index model presented in this paper is compared with soil moisture measurement data and drought disaster records. The results indicate that the variations in the drought index presented in this paper exhibit a high negative correlation with changes in soil moisture and a strong consistency with actual drought impacts. The drought index proposed in this study possesses advantages such as clear physical meaning, convenient calculation, and short response time scale, making it of great significance for practical drought monitoring operations.
Based on meteorological and hydrological observation and NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research) reanalysis data, the variation characteristics of compound dry and hot events, and their causes and impact on runoff in the main confluence area of the upper Yellow River in summer were analyzed. The results show that, from the average spatial distribution, the number of high temperature days in summer increases gradually from southwest to northeast in the main confluence area of the upper Yellow River, and the opposite is true for summer precipitation. From temporal and spatial distribution, the number of summer high temperature days in the main confluence area of the upper Yellow River has been increasing consistently since 1961. The precipitation shows fluctuating consistently changes from a long-term trend perspective, but increased consistently after 2000. The compound dry-hot events have increased significantly since this century. From the perspective of multi-time scale changes, the summer compound dry-hot events in the main confluence area of the upper Yellow River exist mainly inter-annual changes and trend changes, and the significant increase of summer compound dry-hot events since 2000 is mainly caused by trend changes. From the perspective of influencing factors, the changes of summer compound dry-hot events in the main confluence areas of the upper Yellow River are mainly influenced by multiple circulation factors, but the influencing factors differ greatly on different time scales. On the inter-annual scale, the influence of westerly circulation, East Asian summer monsoon, South Asian summer monsoon, plateau summer monsoon, and north wind circulation is relatively weak, on the inter-decadal scale, compound dry-hot evencs are mainly influenced by the Tibetan Plateau summer monsoon and they are also influenced by the westerly circulation, the East Asian summer monsoon, the South Asian summer monsoon, the Tibetan Plateau summer monsoon and the north wind circulation on the multi-decadal scale. From the background field of large-scale circulation, the West Pacific subtropical high is stronger and westward, the lack of abnormal water vapor transport in the southwest and the abnormal downward motion in the vertical field are the main reasons for the increase of summer compound dry-hot events in the main confluence area of the upper Yellow River since this century. The increase of compound dry-hot events in the main confluence area of the upper Yellow River will reduce the runoff of Lanzhou station in the basin, the main reason for the increase in runoff of the Yellow River Lanzhou section since 1998 is the increase in precipitation.
The study of the evolution characteristics of agricultural drought disasters and their relationship with climatic factors can identify the critical periods of the impact of climatic factors on drought disasters, reduce the losses caused by drought disasters effectively, and improve the technology and management level of drought disaster risk assessment. By using agricultural drought disaster data, precipitation, average temperature, and effective irrigation area data, this paper analyzed spatiotemporal distribution characteristics of agricultural drought disasters, studied the relationship between agricultural drought disasters and climatic factors, and constructed a drought disaster assessment model based on multiple climatic factors during the critical periods. The results show that from 1978 to 2022, the agricultural drought disaster-affected rate and disaster-damaged rate in Yunnan both showed a decreasing trend. The decreasing rate was 0.49% and 0.09% per 10 years for the agricultural drought disaster-affected rate and disaster-damaged rate, respectively. The agricultural drought disaster-affected rate and disaster-damaged rate experienced two abrupt changes from 1978 to 2022: an increase from less to more in 2004 and a decrease from more to less in 2013. The drought disaster was relatively severe from 2005 to 2013. The comprehensive drought loss rate in 14 prefectures (cities) was 2%-6% higher than the average from 1996 to 2022. From 2014 to 2022, the severity of agricultural drought disaster was lower than the average level from 1996 to 2022 in most areas in Yunnan. Precipitation in May, average temperature in May, and meteorological drought from January to March and from May to September are crucial climate factors to agricultural drought disaster losses in Yunnan, which impact more significantly than those of similar climatic elements at the annual scale. After 2014, precipitation in May generally decreased, average temperature in May and meteorological drought from January to March and from May to September were intensified. However, the agricultural drought disaster in Yunnan was relatively less severe than the average from 1996 to 2022. The one of important reason was that the number of water conservancy facilities increased, the effective irrigation area increased, and the ability of drought disaster prevention and mitigation was enhanced. Based on multiple climatic factors during the critical period, the fitted model has been built, which has a better estimation of agricultural drought disasters in Yunnan and has a better fitting relationship than that with similar climatic elements at the annual scale.
In order to explore whether the deep plateau vortex and southwest vortex system can trigger the material exchange between the atmospheric stratosphere-troposphere, based on the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data, the dynamic structure, the cross-tropopause mass flux and the trajectory of the gas block during the deep southwest vortex on June 30, 2013 and the plateau vortex on July 23, 2010 were analyzed in detail. The results show that: The deep southwest vortex and plateau vortex develop significantly in the vertical direction, and their internal updrafts develop exceptionally strongly, reaching up to 100 hPa and crossing the troposphere into the stratosphere. There is a strong mass exchange between the stratosphere and troposphere during the formation and mature stages of the vortexes, and the vertical transport term contributes the most to the total flux. The unusually strong upward motion of the low vortex causes part of the tropospheric air mass to be transported to the stratosphere. These results reveal some new important facts: The deep southwest vortex and plateau vortex can cause the mass exchange of the stratosphere-troposphere, and may be a new transport window for the troposphere-stratosphere atmospheric exchange.
The changes of low-level wind field play an important role in the formation of sudden precipitation, which can change the flow field structure in the lower atmosphere, thereby affect the stability and vertical movement of the lower atmosphere and promote the development of convective clouds. Based on wind profile radar data at Chang’an Station, observation data, the fifth generation atmospheric reanalysis data released by the European Center for Medium Range Weather Forecasting, and Doppler radar data, this study analyzed the evolution characteristics of the low-level wind field during three typical sudden precipitation events under the control of the subtropical high at the northern foothills of the Qinling Mountains in midsummer. These events occurred on August 6, 2023, from 11:00 to 12:00 (referred to as “Process I”), July 13, 2023, from 00:00 to 01:00 (referred to as “Process II”), and August 3, 2022, from 18:00 to 19:00 (referred to as “Process III”). The results show that all three events occurred under the circulation background of the subtropical high combined with the intrusion of cold air at low level, exhibiting strong suddenness. For Process I and Process II, the intrusion of cold air at low level was characterized by westerly winds, while for Process III, it was characterized by easterly winds. Before the precipitation, the atmosphere over the Chang’an region was in a significantly unstable state, with weak vertical wind shear in the middle troposphere, which was the main reason for the highly localized nature of these three precipitation events. In midsummer, the multi-year average low-level wind speed at Chang’an Station generally exhibited a single-peak pattern, the wind speed initially increased with height and then decreased. The average wind speed below an altitude of 1 000 meters did not exceed 3.14 m·s?1, and the hourly wind speed shows distinct diurnal variation characteristics. The low-level wind direction displayed a counterclockwise rotation with increasing height, shifting gradually from southwesterly to southeasterly winds.The 4-6 h before the occurrence of three sudden precipitation processes, there was a cold air intrusion process in the low-level over Chang’an, and the wind speed was significantly bigger than the multi-year average. With the continuous invasion of low-level cold air, the 2 m temperature decreased rapidly, the air pressure rose, convection was triggered, and heavy precipitation occurred. The continuous intrusion of low-level cold air could generate strong mesoscale frontogenesis in the lower atmosphere, providing energy and triggering conditions for sudden precipitation. On the other hand, due to the obstruction of the local terrain at the northern foot of the Qinling Mountains and the Guanzhong Basin, the low-level cold air was forced to rise, promoting an increase in precipitation.
Understanding the variation characteristics and possible causes of lake-land breeze speed in Dongting Lake under large-scale climate background is of reference significance for the development and utilization of wind energy resources，water transportation and disaster prevention and reduction. The hourly wind direction and wind speed data at Yueyang Station from 1954 to 2021 are used to analyze the wind speed characteristics and long-term trends of the shoreline and lake-land wind by using the linear tendency estimation，Mann-Kendall mutation detection and sliding t-test methods. The results show that about the wind direction and wind speed characteristics of the four times，02：00，08：00 and 20：00 （Beijing time，the same as below） were almost the same，and the easterly wind and land breeze were dominant，while the westerly wind and lake breeze prevailed at 14：00，and the wind speed at 14：00 was significantly higher than other times. At the inter-annual scale，the variation trend of lakeshore and lake-land wind speed was consistent at four times，both the wind speeds at four times and the land breezes at 02：00，08：00 and 20：00 all showed an obvious decreasing trend，while the change of the lake breeze at 14：00 was not significant. For monthly scale，the wind speed peaks at 02：00，08：00 and 14：00 were all in July，and at 14：00 in winter months land breezes were dominated，and in other months it was dominated by lake breezes. It was dominated by land breezes at 02：00，08：00 and 20：00 in each month，and lake breeze speed was the highest in flood season throughout the year. On the hourly scale，the variation trend of hourly wind speed from 2004 to 2021 was basically the same as that of the lake-land breezes. The frequency of the land breezes was higher than that of the lake breezes，and the wind speed was larger and lake breeze was dominated from 10：00 to 17：00，and the lake breezes with a duration of 3 to 10 hours occurred from 09：00 to 18：00 in each month. The mutation tests find that the wind speed at four times decreased significantly from the 1970s，but only at 14：00 it changed abruptly around 1970，and the abrupt changes of the lake-land breeze speeds at four times occurred in 2002 or 2003. The increase of lake breeze speed and short-term wind speed caused by the change of detection environment can not change the long-term decrease trend of wind speed，and the change of instruments has little effect on wind speed and lake-land wind speed.
High temperature weather occurs frequently in Shandong Province. Studying the variation law of different high temperature indexes and their circulation background is conducive to better defense against the adverse effects of high temperature weather. Based on the daily meteorological observation data of daily maximum temperature, daily minimum temperature and relative humidity of 122 national meteorological stations in Shandong Province from 1981 to 2022, the variation characteristics of high temperature weather in Shandong Province were studied by analyzing the annual maximum temperature, high temperature days, warm night days, and high temperature heat wave days, and the circulation situations of typical high temperature heat wave processes were analyzed. The results show that high temperature weather mainly occurs in the central and western regions of Shandong, and less in the peninsula area. The annual maximum temperature is higher in the west and lower in the east, and high temperature days, warm night days and high temperature heat wave days are characterize by the distribution of more in the west and less in the east. The annual maximum temperature, high temperature days, warm night days and high temperature heat wave days with different grades in Shandong Province show an increasing trend, and the increase range is larger in the west and smaller in the east. The increase range of annual high temperature heat wave days with different grades is mild, moderate and severe in descending order. The wet type high temperature heat wave weather is dominant and shows a significant increasing trend. When there is an obvious circulation situation of “two ridges and two troughs” or “two ridges and one trough” in the middle and high latitudes, it is prone to high temperature and heat wave weathers in Shandong Province, and the subtropical high pressure over the northwest Pacific Ocean is abnormally strong and northerly, and the downdraft under continuous fine weathers causes the temperature to rise and high temperature persist.
The study on the causes of extreme hot weather in Zhejiang Province can provide scientific basis for the prediction and prevention of extreme hot weather. Based on conventional meteorological observations, the ERA5 reanalysis data from European Centre for Medium-Range Weather Forecasts, the outgoing long-wave radiation (OLR) data from National Oceanic and Atmospheric Administration, and daily climate system monitoring indices from the National Climate Center, this study compares and analyzes the spatial and temporal distribution and characteristics of two extreme high temperature events in Zhejiang Province in the summers of 2013 and 2022, and constructs a conceptual model of extreme hot weather. The results indicate that both hot events were characterized by wide coverage, long duration, strong extremity, and severe impacts. The high temperature event in 2022 had a longer duration and wider coverage area, while the single station extreme high temperature value in 2013 was higher. The western Pacific subtropical high (WPSH) in 2022 had a larger extent with a more westward ridge point, whereas in 2013, the duration of the 850 hPa warm ridge temperature exceeding 24 ℃ was longer. The center of extreme high temperature in 2022 was located farther south, with temperatures above 42 ℃ mainly occurring in central and southern Zhejiang, whereas in 2013, extreme high temperatures were concentrated in central and northern Zhejiang. The intensification and westward shift of the WPSH were the direct causes of both extreme high temperature events, corresponding well to a stronger and eastward-displaced South Asian high. When the 1 252 dagpm contour at 200 hPa extends eastward beyond 122°E, the 588 dagpm contour at 500 hPa extends westward beyond 115°E, the 850 hPa warm ridge temperature exceeds 22 ℃, and weak southerly winds prevail in the lower troposphere, it is more likely to experience extreme high temperature exceeding 40 ℃ in Zhejiang. Additionally, negative OLR anomalies over the Maritime Continent (MC) enhance the WPSH by modulating meridional vertical circulation and low-frequency wave propagation. Meanwhile, anomalous zonal vertical circulation between the Pacific at the same latitude as Zhejiang and eastern China further strengthens the WPSH. These findings provide scientific insights for predicting and mitigating extreme heat events in Zhejiang Province.
The National Stadium (Bird’s Nest), Beijing Olympic Park (Osen) and the National Olympic Sports Center (Oti) within a 3 km radius represent three distinct near-ground meteorological detection environments: the dense building sports venue area, the natural underlying surface, and the vicinity of large sports venues, respectively. Using hourly observation data of temperature, rainfall, wind speed and wind direction from meteorological stations in the Bird’s Nest, Osen, and Oti areas from 2020 to 2021, this study conducted a detailed analysis of temperature characteristics in these different environments. Results show that the annual average temperature at the Oti and the Bird’s Nest seat areas was 1.3 and 2.1 ℃ higher than that at the Osen. The temperature differences were more pronounced during the winter half-year than in the summer half-year. Within the Bird’s Nest, the monthly average temperature of the seat area was generally higher than that of the canopy, with the east seats being 0.2 ℃ warmer than the west seats. This difference was closely related to the shading effects of the semi-closed canopy structure, which showed a strong correspondence with changes in the solar elevation angle. The hourly average temperature trends at Oti and Osen were largely consistent, but the temperature changes more rapidly at Osen. The study revealed that temperature differences between stations were associated with variations in wind speed and precipitation conditions.
With the acceleration of climate warming and urbanization, the heat island effect is intensifying. How to take effective measures to mitigate the heat island effect on the basis of quantitative evaluation had become an urgent problem to be solved. Based on annual average temperature of national meteorological stations in Yinchuan and its surroundings from 1961 to 2022 and the data of Landsat8 in summer from 2017 to 2021, the relationship between heat island intensity and urbanization process in Yinchuan urban area was analyzed. The typical high temperature processes were selected, and the cooling effect of different buffer distances of lake wetland was evaluated quantitatively aiming at the lake wetland which could effectively alleviate the urban thermal environment. The results show that the effect of urban heat island was not obvious during 1961-2000 in Yinchuan, but after 2000, the average temperature and warming rate were significantly higher than those of reference stations, indicating that the effect of urban heat island was obvious. The correlation coefficient between heat island intensity and urbanization level reached 0.78, which passed the 0.01 significance test and showed a positive correlation. The typical lake wetland in Yinchuan urban area had obvious cooling effect during the summer high temperature processes, especially the surface temperature cooling effect within 500 m, in which the surface temperature dropped the most (up to 2.5 ℃) within 100 m, and the cooling range gradually decreased with the increase of distance from the water body. The average land surface temperature drops by 0.5 ℃ in the distance of 400-500 m.
An in-depth understanding of the daily variation characteristics of precipitation at classified stations is essential for optimizing and improving accurate forecasting methods. Based on the hourly precipitation observation data from 105 national meteorological stations in Xinjiang during the warm season (May to September) from 2010 to 2019, the stations were classified using the K-means clustering method, and the precipitation characteristics of each category of stations were analyzed according to hourly average precipitation amount, precipitation frequency, and precipitation intensity. The results show that the stations in Xinjiang can be classified into four categories: southern Xinjiang and desert areas (Class I), Tianshan Mountains (Class II), northern Xinjiang and the southern slope of the West Tianshan Mountains (Class III), and valley areas (Class IV). The clustering result is similar to that of classifications based on geographic location and topographic height but it is more detailed and scientific. The distribution of cumulative precipitation and precipitation hours of four types of stations is relatively concentrated, with annual average cumulative precipitation of 54, 354, 110, and 217 mm, corresponding to 67, 311, 118, and 213 hours, respectively. The diurnal variation of precipitation frequency in the warm season at most stations in Xinjiang follows a ‘single-peak’ pattern, but the times of the peaks and valleys vary depending on altitude differences. Precipitation and precipitation intensity generally follow a ‘multi-peak’ structure, and hourly precipitation intensity greater than 1 mm mainly concentrated at Class II stations, with the peaks occurring at 16:00—17:00. Precipitation and precipitation frequency are highest in June and lowest in September. The monthly distribution and the month-to-month diurnal variation characteristics of precipitation intensity differ significantly, but the peak intensity does not show a notable difference. In 2016, all three precipitation indicators characteristics during the warm season were significantly higher than those of other years. In 2010, Class I stations had the highest precipitation intensity, and the precipitation amount and frequency reached a secondary peak, while the changes at the other categories of stations were relatively small.
Studying the evolution characteristics of a gust front and the physical mechanisms of extreme winds behind it using multiple types of radar products is of great reference significance for improving the forecasting and early warning capabilities of catastrophic gale weather. Using conventional upper-air and surface observational data, ERA5 reanalysis data of the European Center for Medium-Range Weather Forecasts, S-band dual-polarization radar data and X-band phased-array radar data, the characteristics of radar products of a gust front and the extreme wind process behind the gust front in Shaoxing of Zhejiang Province on July 10, 2023 were analyzed. The results show that this process occurred under the background of southwest airflow at both high and low altitudes. The upper air was at the edge of the subtropical high, and at 925 hPa, it was in the convergence area of southwest wind speeds. The atmospheric thermal instability and uplift conditions were better. After multiple convective cells merged into a multi-cell storm, the gust front was formed at the outflow boundary of it. The gust front underwent three stages: development, rupture, and weakening. At the weakening stage, a new mesoscale convective zone was triggered behind it, and the backward propagation characteristics were obvious. The maximum wind speed induced by the gust front occurred during its weakening stage, while the extreme wind of the process occurred during the eastward movement and northward lifting of the mesoscale convective band triggered by the gust front. The internal vortex structure of the convective cells which generated the extreme winds only existed at an altitude of 800 m, and the convergence of wind direction and speed was mainly at the middle and upper levels. The gusts of 6-7 levels were generated when the vortex circulation weakened and disappeared, and the core of the reflectivity factor decreased, and the lower levels of the storm turned into downdraft. The extreme wind was generated later when the inflow behind the storm turned back into updraft and converged with the downdraft at middle levels. It was also accompanied by radial convergence in the middle layer horizontally, which indicated an increase in sinking airflow. Due to the relatively small contribution of downward momentum transfer, the extreme wind was mainly caused by strong sinking airflow.
Real-time identification of cloud microphysical characteristics and seeding ability of stratiform cloud precipitation system is beneficial for improving the understanding of the catalytic potential of stratiform cloud precipitation system, and providing technical support for real-time identification of artificial rainfall enhancement. The microphysical characteristics and the seeding ability of stratiform cloud in the middle of Inner Mongolia were analyzed by using airborne detection data of 8 stratiform cloud aircraft operations from 2018 to 2019. The results show that the occurring frequencies of cloud water, liquid water, and supercooled water in stratiform clouds are 59.97%, 82.99% and 70.84%, respectively. The liquid water content is mainly concentrated between 0.001 and 0.100 g·m-3, while the supercooled water content is mainly distributed between 0.010 and 0.100 g·m-3, which indicates good potential for crystal seeding catalysis. The average number concentration of large cloud particles is 8 cm-3, and the number concentration more than 20 cm-3 accounted for 14.10%. The small cloud particle number concentration is 20 cm-3 on average, and the number concentration greater than 20 cm-3 accounted for 28.54%. More than 70% cloud particles are located in the negative temperature region, and the particle number concentration is generally small. When the number concentration of small cloud particle reaches 15 cm-3, the cloud region has certain seeding ability, while when the number concentration of large cloud particle is less than 10 cm-3, the cloud region has highly seeding ability.
In the context of climate change, it is of great significance to explore how winter wheat responds to temperature increase in terms of main agronomic traits and dry matter distribution during its growth stage in the tablelands of Guanzhong, Shaanxi, which can provide references for assessing its sensitivity and adaptability under climate change. In this paper, Zhengmai No. 1860 was selected as the research object to analyze the influence of the warming effect simulated by Open Top Chamber (OTC) on the growth and development of winter wheat. The results show that there were significant differences in temperature inside and outside OTC during growth stage (p<0.05) of winter wheat. The average temperature in OTC was 0.8 ℃ higher than that of the outside. In OTC, all the phenological stages of winter wheat came in advance of those in the control group, with an average of 6 days earlier. The plant height inside OTC was higher than that of the outside. OTC promoted leaf area of wheat at the stage of greening and heading, while inhibited leaf area at the stage of flowering and milk ripening.The warming effect promoted root growth, increasing root length by 37.48% and surface area of fine roots by 35.28%, but inhibited root biomass, decreasing it by 7.60%. The warming effect of OTC can promote the dry matter weight of stem, leaf and ear, except the dry matter weight of leaf at milk-ripening stage. In conclusion, OTC can significantly promote the functional traits of winter wheat at the vegetative growth stage, but at the reproductive growth stage, it can not promote the functional traits and even show a certain inhibitory effect.
In order to assess the potential impact of climate change on agriculture and develop scientific adaptation strategies, the variability characteristics and risk on agriculture of regional high temperature, drought and their compound events in Hubei Province were identified and analyzed based on daily temperature, precipitation and other observations from 76 national meteorological stations during 1994-2023. The analysis employed classification standards for regional high temperature process and monitoring and assessment methods for drought process. The results show that regional high temperature events occurred an average of 4.3 times per year, with an overall increasing trend and 61.2% of severe and strong events occurred in July and August. Regional drought events occurred an average of 1.5 times per year, showing a deceasing trend before 2010 and increasing trend thereafter, with slightly higher frequencies in winter and spring than in summer and autumn. Regional compound high temperature and drought events mainly occurred from June to August, with an significant increase in frequency after 2010. The spatial distribution of intensity and agricultural risk for regional high temperature and drought events was generally similar. High intensity and high risk areas for high temperature events were mainly located in eastern Hubei, while low intensity areas were in the southwest. For drought events, high intensity and high risk areas were mainly located in central-eastern Hubei, decreasing towards surroundings regions. The agricultural risk of compound high temperature and drought events showed a decreasing trend from east to west. The most widely distributed risk levels for regional high temperature, drought and their compound events were classified as high-risk, moderate-risk and extreme high-risk areas, accounting for 37.6%, 53.8% and 46.6% of Hubei Province’s total area, respectively. In the background of global warming and increasing frequency of extreme weather events, the probability and risk of regional extreme high temperature, drought and their compound events are expected to rise in eastern Hubei Province.
Compound high-temperature and drought events is one of the complex extreme climate events with high incidence in the Shiyang River Basin, which has more serious impact on industrial and agricultural production and ecological environment than a single extreme climate event. Based on the average temperature, maximum temperature and precipitation data of five meteorological stations in the Shiyang River Basin from 1961 to 2023, the compound high-temperature and drought events were identified and determined using percentile threshold method and Ped meteorological drought index, and spatial and temporal evolution characteristics of compound high-temperature and drought events were analyzed with linear trend method. The results show that the spatial difference of annual average frequency of compound high-temperature and drought events was small in the Shiyang River Basin, however, the spatial difference of compound high-temperature and drought events frequency was obvious in each decade and increased decade by decade. Annual frequency of compound high-temperature and drought events decreased first and then increased in the Shiyang River Basin, it decreased before 1996 and then increased in the whole basin. Compound high-temperature and drought events mainly occurred from June to August, and the most occurred in July. The frequency of compound high-temperature and drought events with different grades changed greatly, with the increase of drought grade, the frequency of drought increased first and then decreased, the frequency of medium drought was the highest, and the frequency of extreme drought was the least.
Studying the spatial and temporal distribution characteristics of drought at different scales in Chengdu is of great significance to agriculture, economic development and drought disaster prevention and mitigation in this region. Using the monthly precipitation data of 14 national meteorological stations in Chengdu from 1960 to 2022, combining the standardized precipitation index (SPI), the optimal probability distributions of the series of annual and seasonal precipitation data of 14 national meteorological stations in Chengdu were determined based on the optimization of probability distributions belonging to SciPy package firstly. Secondly, based on the optimal probability distribution function, the annual scale SPI (SPI12) and the seasonal scale SPI (SPI3) were calculated, respectively. Finally, based on SPI12 and SPI3, the spatio-temporal distribution characteristics of drought at the annual and seasonal scales in Chengdu were analyzed. The results show that the optimal probability distributions of precipitation series at different scales past the K-S test at significant level of α=0.05, representing the distribution characteristics of precipitation series at different scales in Chengdu. The annual and seasonal drought station ratio, as well as the drought intensity in Chengdu, show a slight increasing trend. The drought frequency at annual and seasonal scales in Chengdu range from 25.40% to 36.51%. There are significant differences in the spatial distribution of drought frequencies at different scales, with spring and summer droughts occurring slightly more frequently compared to autumn and winter droughts. The spatial distribution of different grades of annual drought, spring drought, summer drought, autumn drought, and winter drought in 14 districts and counties of Chengdu show considerable variability, but light and moderate droughts occur with the higher frequency in all cases.
Typhoon “Rumbia” was the most disastrous tropical cyclone, triggering rare floods in Shandong. Based on the conventional meteorological observation data, the reanalysis data from the National Centers for Environmental Prediction, and the precipitation data from automatic weather stations, the frontogenesis mechanism of an extreme rainstorm in Shandong Province caused by Typhoon“Rumbia” from 17 to 20 August 2018 was studied in this paper. The results indicate that the precipitation affected by Typhoon “Rumbia”can be divided into three stages: the precipitation of the typhoon outer cloud system, the precipitation of the interaction of the middle and low latitude weather systems and the precipitation triggered by the typhoon trough. The frontogenesis area of the typhoon rainstorm is mainly in the lower level, and the location of the frontogenesis area is closely related to the location of the cold air. The locations of the heavy precipitation are consistent with the frontogenesis area. The large-value center of frontogenesis intensity corresponds well to the center of the heavy rainstorm, and the intensity of frontogenesis can well indicate the rainfall in the next 6 hours. Favorable convergence flow field on the south side of the dense area of pseudo-equivalent potential temperature (θse) lines was the key to cause frontogenesis. The location of the elongation deformation frontogenesis is consistent with the convergence center of the divergence, the large value center of θse and the total frontogenesis area in this rainstorm process is consistent. The elongation deformation term, shear deformation term and divergence term all contribute positively to the total frontogenesis. The typhoon rainstorm is caused by frontogenerative dynamics, and the area with the strongest ascending motion of the frontal secondary circulation corresponds to the area of the strongest rainstorm. Under the conditions of strong water vapor transport, convergence and strong convective instability, the convergence of typhoon trough and strong frontogenic secondary circulation together produce strong upward movement, and the dynamic uplift effect is rapidly enhanced, resulting in strong convergence of water vapor and transport to the upper level and causing extremely heavy rain in Shandong Province. The rainstorm area is located at the 700 hPa positive helicity center and its right side, and the period of rapid enhancement of positive helicity corresponds to the period of heavy precipitation, and the maximum value center of positive helicity moves down to the vicinity of 900 hPa, which indicates the weakening of typhoon heavy precipitation.
Studying the distribution of convection during the warm season over Fujian Province has important significance for forecasting and warning of convective weather. Based on four weather radars data of Jianyan, Longyan, Changle and Xiamen in Fujian from 2008 to 2017, convection in warm season (from April to August) was identified, and the spatial-temporal and vertical structure of convection, as well as spatial and diurnal variation characteristics of convective systems with different areas and extension heights were analyzed. The results show that the peak period of convective activity is from May to June and August during the warm season in Fujian. The convection in warm season has obvious regional distribution characteristics, the high incidence area is located in the inland from April to June, and from July to August it is in the coastal mountains. From June to August, it is dominated by medium-deep convection, and it is dominated by large area convection in April, and from May to June and from July to August it is dominated by medium and large area convection, medium and small area convection, respectively. The monthly distribution of vertical structure of convection is different. The echo intensity of moderate convection is the maximum from July to August. The echo extension height in northwest Fujian is the highest. There is obvious diurnal variation of convective frequency. Convection often occurs from 15:00 to16:00 (BST), and it is the mainly single peak in the afternoon from July to August, while from April to May there are bimodal or multi-peak. The frequency peaks of convective systems with larger area appear later, and the mid-deep and deep convective peaks are obvious in the afternoon. From May to June, the high incidence of inland convection from night to morning was caused by the diurnal variation of the wind field formed by the inertia oscillation of the boundary layer and the interaction between the disturbing wind and terrain. In August, the high incidence of convection in coastal mountains was caused by the fact that the coastal mountains are located in the near ground heating center, the convergence of wind field and the high energy value area in the afternoon.
As one of the main driving factors of evapotranspiration, the VPD (Vapor Pressure Deficit) reflects the atmospheric capacity to extract water from the surface. Understanding the spatio-temporal variation of VPD is crucial for exploring the response of regional atmospheric dryness and wetness to climate change. Based on data from 11 meteorological stations in the Mt. Qomolangma region of China during 1981-2023, including monthly sunshine duration, average air temperature, maximum and minimum air temperature, precipitation, relative humidity, vapor pressure, and wind speed, this study analyzed the spatio-temporal characteristics and influencing factors of VPD using climate tendency rate, stepwise regression, and the Mann-Kendall test. Results show that the annual and seasonal averages of VPD in the Mt. Qomolangma region generally exhibited lower values in the southwest and higher values in the northeast. Monthly VPD showed a bimodal pattern, with peaks in June and September and a minimum in January. Seasonally, VPD was characterized by higher values in summer, followed by spring, autumn, and the lowest in winter. Over the past 43 years, annual VPD increased at a rate of 0.029 kPa·(10 a)-1, with the most significant growth observed in summer. On a decadal scale, VPD values were relatively low in the 1980s and 1990s, particularly during the 1990s. In the 2000s, VPD was lower in spring and autumn and higher in summer and winter. The 2010s saw elevated VPD values across all seasons, especially in summer and autumn. Spring and flood season VPD mutations occurred in the late 2000s, while mutations in the other three seasons and annual averages appeared in the early 2010s. Changes in VPD were primarily driven by saturated water vapor pressure, particularly in spring and autumn. The significant increase in VPD was dominated by rising air temperatures across all seasons and annually. Additionally, the decrease in water vapor pressure during the flood season contributed to the VPD increase.
The use of different climatological normal periods means the change of the evaluation results of meteorological elements, the abnormal state of climate events and their change characteristics, which have a substantial impact on the climate monitoring and prediction operations. Using temperature and precipitation observation data from national meteorological stations in Ningxia from 1981 to 2021, this study conducted a comparative analysis of the temperature and precipitation characteristics between the old climatological normal period (1981-2010) and the new climatological normal period (1991-2020). Additionally, it explored the changes in extreme characteristics of these factors. The results are as follows: Compared to the old climatological normal period, the annual and seasonal average temperatures in Ningxia are generally higher in the new climatological normal period, which is particularly evident in spring, summer and winter, and the frequency of abnormally high (low) temperatures increases (decreases) accordingly. Yinchuan, the western part of Wuzhong, and the northern part of Zhongwei are areas experiencing significant temperature increase. The overall intensity of extreme high (low) temperature has intensified (weakened), and their frequency has increased (decreased). In summer, the threshold and intensity of extreme high-temperature rise across various regions, especially in the central and northern areas, while in winter, the intensity of extreme low-temperature weakens in most regions, the amplitude of extreme low-temperature varies significantly. The average annual precipitation, as well as the summer, autumn and winter average precipitation, are greater in the new climatological normal period compared to the old. There’s an increased frequency of abnormally more precipitation in summer and autumn, whereas the opposite trend is observed in spring and winter. Meanwhile, the frequency of abnormally less precipitation in all seasons has decreased to some extents. There are significant spatial differences in seasonal precipitation, with a general increase in precipitation in summer and autumn, and a pattern of “decreasing in the north and increasing in the south” in spring and winter. The overall trend of extreme precipitation in spring and autumn (summer and winter) is intensifying (weakening), albeit with fewer (more) extreme precipitation events. In summer, the threshold and intensity variations of extreme precipitation are greater in the north and south, and smaller in the central region, with a notable increase in extreme precipitation in Shizuishan.
In order to deepen the understanding of extreme snowfall and reveal the possibility of anomalous influencing factors leading to extreme snowfall events, the extremes of two major snowfall weather processes in Shanxi Province on February 24, 2021 and from February 27 to March 1 (referred to as “Process I” and “Process II”, respectively) were analyzed by using the meteorological observations and reanalysis data. The results show that Process Ⅰ was a convective snowfall process, caused by the combined influence of a plateau trough, a surface trough and a return flow. The rapid climb of the strong southwest warm and wet jet on the “cold pad” and the symmetric instability together led to the rapid release of potential unstable energy, resulting in a concentrated precipitation range, a large snowfall intensity and a short duration. During this process, cold air quickly invaded and the precipitation phase changed from rain to snow quickly. Process Ⅱ, on the other hand, was characterized primarily by stability, which was influenced by an upper-level trough, a surface cyclone and an inverted trough. During the systematic invasion of cold air, an extreme snowfall event was formed, with a large area of precipitation and a prolonged duration, and the phase changes during this snowfall process were complex. Significant differences were found in the circulation patterns, moisture transport mechanisms, instability mechanisms, and vertical motion characteristics before the precipitation of two snowfall processes. However, compared to the climatological averages, both processes exhibited anomalously high local relative humidity, 700 hPa energy, and vertical upward motion, which was identified as one of the key reasons for the occurrence of extreme weather. The precipitation centers of both events were located in the downstream of the anomalous physical quantity centers 6 to 12 hours before precipitation, and the moisture transport and the thickening of the moist layer were also provided some indication for the precipitation starting time. Additionally, the transition of precipitation phase was closely related to the vertical distribution of temperature and frontal structure.
Moving out of the Qinghai-Xizang Plateau vortex (QXPV) often causes a wide range of disastrous weather such as heavy rain in the lower reaches of the Qinghai-Xizang Plateau. Aiming at the question of why the moving-out QXPV (MQXPV) develops or weakens after moving out of the Qinghai-Xizang Plateau, based on the QXPV database in warm seasons (from May to September) during 1990-2019, the ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the 3B42 precipitation data retrieved from the Tropical Rainfall Measuring Mission (TRMM) satellite, this paper discusses the occurrence rules, circulation characteristics, the differences and similarities of the development mechanisms of the two typical cases of the moving out type and the weakening type by using meteorological statistical analysis, synoptic analysis and diagnostic analysis methods. The results show that in the past 30 years, the frequency of the MQXPV showed a weak increasing trend, with an average of 6.5 times per year, and in May it was the largest. It can be divided into the western vortex, the central vortex and the eastern vortex according to the birth location, the western vortex was mainly concentrated in Shiquan River and the north of Gerze, the central vortex was mainly concentrated in the north of Shenzha and the Tuotuo River, and the eastern vortex was mainly located in Zadoi and Qumalai, among them the eastern vortex occurred most and the moving path was mainly eastward. The 200 hPa south Asian high had a large range and strong intensity, which strengthened the horizontal divergence in the upper layer and vertical ascending motion. The 500 hPa western Pacific subtropical high was weaker, and its blocking effect on the movement of the QXPV was weakened, which resulted in the eastward movement of the QXPV. The MQXPV includes two types: developing and weakening. The comparative analysis shows that during the eastward movement of the QXPV, for the developing vortex, the convergence of cold and warm advection was clear and the frontogenesis enhanced gradually, and the potential vorticity presented a zonal distribution from southwest to northeast in the horizontal direction, with an eastward transmission phenomenon, and in the vertical direction, the upper positive potential vorticity passed down obviously. For the weakening vortex, it maintained a warm heart structure, after moving out of the Qinghai-Xizang Plateau, the weakening vortex gradually separated from the large value region of the potential vorticity, and the upper positive potential vorticity passing downward tended to be less obvious. The precipitation caused by the developing vortex appeared in the center and south side of the vortex, the precipitation intensity was stronger and the range was larger, while the intensity was weaker and the range was smaller of the precipitation caused by the weakening vortex.
It is of great significance to study the near-cloud turbulence for improving the prediction ability of aircraft turbulence and ensuring the safety of air transportation. The WRF (Weather Research and Forecasting) model v4.3.1 is used to conduct a high-resolution numerical simulation of a moderate intensity near-cloud turbulence event over Fujian Province, China. The synoptic-scale background and turbulence indices are examined, and the causes of the turbulence event are analyzed. A sensitivity experiment excluding the moist process is conducted to investigate the impact of cloud system evolution on the turbulence generation. The results indicate that the turbulence event was mainly influenced by the low-level clouds area on the periphery of the cold high-pressure system over the southeast coastal region of China. The upper level southern jet stream gradually moved eastward above the turbulence region, and vertical wind shear enhanced and tropopause folding phenomenon was observed. The high-resolution simulation reasonably reproduced the large-scale circulation during the turbulence event. The turbulence indices, including Ri (Richardson number) and NCSU1 index (Version 1 of North Carolina State University Index), effectively indicated the intensity and location of this turbulence event. Inertial instability and high turbulence kinetic energy (TKE) values were distributed around the cloud region near the turbulence area. Specifically, influenced by stratiform clouds, the increment of zonal wind in the turbulence area gradually increased from south to north and the increment of the meridional wind gradually decreased from west to east, both contributing to negative absolute vorticity. Updrafts near the cloud top affected the local wind field in the turbulence region. Downdrafts mixed with saturated moist air through the cloud top, leading to inertial instability and ultimately causing the turbulence event. In contrast, the TKE in the turbulence region disappeared in the absence of clouds, and the vertical wind shear weakened, both two turbulence indices failed to diagnose the turbulence event.
The study of the impacts of climate change and human activities on the vegetation of the Gansu section of the Yellow River main stream is of significance for the construction of ecological security in the Yellow River Basin. Based on the NDVI (Normalized Difference Vegetation Index) of MODIS (Moderate-resolution Imaging Spectroradiometer) and the precipitation and air temperature data of 18 ground meteorological observation stations in the Gansu section of the Yellow River main stream, the spatial and temporal characteristics of NDVI and the contribution of climate change and human activities to the changes of NDVI in the Gansu section of the Yellow River main stream from 2001 to 2020 were quantitatively analyzed by using the methods of linear trend analysis, bias correlation analysis and residual analysis. The results show that the growth rate of NDVI in the Gansu section of the Yellow River main stream was 0.05·(10 a)-1 from 2001 to 2020, of which the 2001-2010 period was a slow increase stage with a growth rate of 0.04·(10 a)-1, and the 2011-2020 period was a rapid increase stage with a growth rate of 0.08·(10 a)-1. The vegetation ecology of the Gansu section of the Yellow River main stream showed a benign development in the past 20 years, and the vegetation improvement area was located in the north-central part of Linxia Hui Autonomous Prefecture, Lanzhou City and the southeastern part of Baiyin City. The climatic factors that dominate the changes of NDVI in the study area are different, the positive correlation between NDVI and air temperature is higher in most parts of Gannan Prefecture, while the correlation between NDVI and precipitation is more significant in the northern part of Linxia Prefecture, Lanzhou City and Baiyin City. The vegetation change in the Gansu section of the Yellow River Basin is the result of the joint action of climate factors and human activities, and the contribution of climate factors to the NDVI change from 2001 to 2020 is 75.27%, while the contribution of human activities is 24.73%. Climate factors are still the dominant factors for the vegetation change in the Gansu section of the Yellow River Basin, but the influence of human activities on the vegetation change is gradually deepening.
It is of great significance to study the change of vegetation cover and the influence of climate factors in Ganzi Prefecture for ecological protection and development. Based on MODIS (Moderate-resolution Imaging Spectroradiometer) -NDVI (Normalized Difference Vegetation Index) data during 2003-2022, trend analysis, Hurst index were used to analyze the changes in vegetation cover in Ganzi Prefecture over the past twenty years. Temperature and precipitation data which are significantly correlated with vegetation index were used to analyze the relationship between vegetation cover change and climate factors. The results indicated that NDVI in Ganzi Prefecture showed an overall upward trend during the study period, and the distribution of vegetation cover was correlated with altitude and watershed. In the past twenty years, the area of vegetation cover increasing accounted for 67.83% of the total area of Ganzi Prefecture, and 25.37% of the area may maintain the same evolution trend as the present in the future. There are regional differences in the spatial distribution of precipitation and temperature, and the precipitation fluctuates significantly in summer, which is related to the influence of Qinghai-Tibet High Pressure in summer. Compared with precipitation, the correlation between temperature and NDVI is more significant. The influence of precipitation and temperature can explain 70% of the regional vegetation cover change during the study period, and the contribution of temperature to vegetation cover change is higher than that of precipitation.
Soil moisture is an important indicator for monitoring soil drought, and studying its relationship with climate change helps to reveal the mechanisms of soil drought under the context of global change. Based on the Web of Science Core Dataset, this study analyzes the literature on the topic of the relationship between climate change and soil moisture. The results show that the number of related publications from 1988 to 2023 follows a trend of “stability, growth, sharp increase”. Chinese scholars and research institutions contributed the most publications, but their overall international influence remains lower compared to developed countries such as the United States. In terms of subject areas, research is primarily concentrated in environmental science and ecology, earth sciences, as well as agricultural and forestry sciences. Key research focuses include soil-climate interactions, soil ecosystem management, hydrometeorology and soil drought monitoring, as well as climate data analysis and ecological modeling. In recent years, research hotspots have gradually shifted to the application of cutting-edge technologies, such as multi-source sensing and artificial intelligence, in soil drought monitoring. Furthermore, the impact of extreme climate events on various ecosystems and their corresponding response strategies have become important research directions.
The impact of climate change on agricultural climate resources will directly affect agricultural production. It is of great significance to accurately analyze the change of agricultural climate resources to guide agricultural production. Based on historical meteorological data from 1971 to 2005 of 113 ground meteorological observation stations in Henan Province, simultaneous simulation data of Representative Concentration Pathways (RCP) scenario model output, and simulation data of regional climate model under RCP4.5 and RCP8.5 emission scenarios, the spatial distribution and change trend of high-quality wheat agro-climatic resources in Henan Province from 2021 to 2050 under RCP4.5 and RCP8.5 scenarios were analyzed by using eight climate factors, such as precipitation and accumulated temperature ≥0 ℃ during the whole growth period of winter wheat, total radiation and rain days from March to April, precipitation, diurnal temperature range, daily maximum temperature ≥32 ℃ days and total radiation in May. The results indicate that the accumulated temperature of ≥0 ℃ during the whole growth period of winter wheat showed a significant increasing trend (α=0.05), and the average climate tendency rates under RCP4.5 and RCP8.5 scenarios are 46.8-61.0 and 49.5-65.5 ℃·d·(10 a)-1, respectively, and the temperature rise is more obvious under RCP8.5 scenario. The number of days with maximum temperature ≥32 ℃ in May at 83.2% of sites under RCP4.5 scenario and all sites under RCP8.5 scenario show a significant increasing trend (α=0.05), and the climate tendency rates are 0.2-0.8 and 0.3-1.0 d·(10 a)-1, respectively. The precipitation at the sites in the southwest during the whole growth period of wheat shows a decreasing trend, and at the other sites it shows an increasing trend, but none of them are significant. At most sites, rain days from March to April and radiation in May show an insignificant increasing trend. The radiation amount in March and April and the precipitation in May show an insignificant decreasing trend. The diurnal range of average temperature in May in the northern and western regions shows a decreasing trend, while in other regions it shows an increasing trend, but none of them are significant. In general, the future agro-climatic resources will have a certain adverse effect on the planting of strong gluten wheat in Henan Province.
Net Primary Productivity (NPP) is not only the main parameter for estimating carbon sequestration and oxygen release in ecosystems and measuring terrestrial carbon cycle, but also the main index for evaluating ecosystem health. In view of the limited application of domestic satellites in remote sensing monitoring of grassland NPP, a set of NPP inversion model of grassland NPP in Inner Mongolia was constructed based on FY-3D/MERSI2 data. The NPP of grassland under clear sky condition in Inner Mongolia was obtained by using a strict cloud detection algorithm, which was driven by remote sensing data products and CLDAS meteorological assimilation data, combined with light energy utilization model and ecological process model. In this study, lattice meteorological data with high resolution are introduced, which greatly improves the precision of inversion results. At the same time, based on the observation data and MODIS products, multiple relationship models of above-ground biomass, the Fraction Photosynthetic Active Radiation Absorption Ratio (FPAR) and Normalized Difference Vegetation Index (NDVI) in different months (from May to August) of grassland growth period in Inner Mongolia were constructed, and process parameters such as Leaf Area Index (LAI) and FPAR could be directly estimated based on FY-3D data. By comparing several key ecological process parameters with MODIS products, it is found that they have good correlation and spatial consistency. Finally, the grass observation data of 18 ecological meteorological observation stations in June 2021 were compared with the estimated results, showing that there was a good consistency between them, with a correlation coefficient of 0.86. The NPP inversion using FY-3D/MERSI2 can fully present the general state of vegetation productivity in Inner Mongolia.
Amidst the ongoing global warming and the rapid urbanization process in recent years, examining the relationship between extreme temperature events and urbanization in Sichuan Province is crucial for mitigating the risks associated with these events and for informing future urban planning. Using daily temperature records from 36 meteorological stations in Sichuan Province during 1980-2020, along with data on nighttime lights, land use, and spatial grids of economic and population distribution, we calculated 16 extreme temperature indices recommended by the World Meteorological Organization. By applying a combination of K-means clustering and hierarchical clustering, meteorological stations were classified into urban, suburban, and rural categories. The study analyzed the temporal trends of extreme temperature events in relation to urbanization and explored the regional trends across three time periods of 1980-2010, 1980-2015, and 1980-2020, along with the differences across station types. The results showed a rising trend in extreme high-temperature events and a decline in extreme low-temperature events from 1980 to 2020. Urban stations exhibited the most pronounced increases in maximum temperatures, warm days, and diurnal temperature ranges, while rural stations experienced the sharpest decreases in frost days, cold nights, and cold days. Suburban stations saw the greatest increases in summer days and warm nights. The warming trends of extreme temperature events were evident across all three time periods, with rural stations showing a stronger warming tendency compared to urban and suburban stations. Throughout the periods studied, urban and suburban stations recorded more summer days than rural stations, while rural stations observed more frost days. Additionally, the reduction in cold events was less pronounced at urban and suburban stations than at rural stations. These findings underscore both the shared patterns and regional variations in how urbanization influences extreme temperature events, warranting further research into the underlying mechanisms.
In order to improve the forecasting capability of rainstorm in Jiangxi Province, based on the fifth generation European Center for Medium Weather Forecasting (ECMWF) atmospheric Re-Analysis (ERA5) data of the global climate, the daily precipitation data of the national meteorological observation stations in Jiangxi Province from 1990 to 2022 and the hourly precipitation data in 2023, the average and rainstorm day mean of total column water vapour（TCWV）in Jiangxi Province were analyzed, and threshold criteria are given for determining the TCWV that is favorable to the occurrence of regional rainstorms in Jiangxi. The results show that the TCWV on rainstorm day in Jiangxi Province show obvious spatial and temporal differences. The monthly mean TCWV is 20.0 to 36.0 mm in December and January, the lowest in the year; it can reach 64.0 mm in July and August, the highest in the whole year, and is mainly concentrated in the plains and hilly areas in northern and central Jiangxi. The median monthly mean TCWV at rainstorm sites in July and August exceeds 65.0 mm; the maximum value of TCWV in August could reach 77.5 mm. During rainstorm, the TCWV at the relevant stations usually reached or approached the monthly mean before heavy precipitation, and decreased to below the monthly mean after heavy precipitation. The monthly mean TCWV value on the day of rainstorm can be used as a threshold for predicting regional rainstorm in Jiangxi during that month: if the value of TCWV is close to or exceeds the upper limit of the monthly mean, the probability of the occurrence of extreme precipitation in Jiangxi Province increases. The central area of the maximum TCWV does not exactly coincide with the location of the rain band at the central area of the rainstorm, but it is usually located within the high value zone near it, so the central area of the maximum TCWV can be used as an important reference for predicting the location of the rain band of the rainstorm during heavy precipitation weather.
To identify the weather patterns and threshold values of meteorological factors associated with ozone (O3) pollution in the central and western Inner Mongolia, the obliquely rotated Principal Components in T-mode (PCT), was used to analyze the surface and upper air circulation O3 pollution process in six cities in the region from 2015 to 2021, the relationship between the weather situation, meteorological elements and O3 pollution is discussed. The results show that the O3 pollution process in central and western Inner Mongolia can be divided into three types in the 500 hPa circulation: the high pressure ridge, the westerly flow pattern in flat direction, and the northeast flow pattern in the bottom of high pressure. There are four types of sea level pressure field: pressure equalization,low pressure control, high pressure south, low pressure front. The circulation configuration can be divided into five types: high pressure ridge-pressure equalization field type, the northwest flow at the front of the ridge-low pressure control field,,the westerly flow pattern in flat direction- high pressure south field, the northwest flow at the front of the ridge-low pressure south field, and the northwest flow at the front of the ridge-pressure equalization field. In Alxa and Wuhai, the O3 overrun is mainly found in the flat westerly-southern type of high pressure, while in other cities it is mostly found in the NW flow-high pressure-controlled type in front of the ridge. These two general circulation configurations are the main meteorological conditions for the occurrence of O3 pollution. The typical regional O3 pollution usually occurs in a specific atmospheric general circulation situation. When there is an inversion layer in the boundary layer, the stronger the inversion intensity is, the worse the vertical diffusion condition is, which is unfavorable to the near-surface pollutant diffusion. Meteorological factors such as surface maximum temperature, sunshine duration and average relative humidity have influence on O3 pollution. In dry areas such as Alxa, Wuhai and Bayannur, O3 mass concentrations are higher than normal, with maximum temperatures of at least 30℃ and hours of sunshine of at least 10 hours, while in relatively wet areas such as Ordos, Baotou and Hohhot, the maximum temperature is usually not less than 27 ℃ and the sunshine duration is not less than 8 hours when O3 exceeds the standard. In addition, when the wind direction is southwest, south and southeast, and the wind speed is 2.0-5.0 m·s -1, O3 pollution is easy to occur.
Spring snowmelt flood simulation and forecasting in the mountainous region has been a difficulty of cold region hydrological study. Current forecasting studies mainly use complex snow melt energy balance models, and take into account underlying surfaces such as frozen soil, vegetation, and runoff processes, resulting in complex model structures. This method needs a lot of data support and has a great uncertainty in prediction, which leads to difficulties in application in operational forecasting. In this paper, a simple and effective spring snowmelt flood forecasting method is established by using statistical methods and the snow depth observation data in winter of meteorological stations as well as a variety of snow remote sensing data in the Xiying River Basin, combined with the flood observation data of Jiutiaoling Hydrology Station on its control section. The study shows that the snow water equivalent information of the basin from MODIS snow cover products in March and April and the integration of microwave remote sensing snow depth products can well reflect the magnitude of spring snowmelt flood at Jiutiaoling Hydrological Station in the Xiying River Basin. This method provides a useful reference for snowmelt flood forecasting in other stable snow cover areas.
Light and temperature are important factors affecting greenhouse tomato growth. In order to find the relationship between light and temperature with growth and development of tomato，a Logistic growth model was constructed for the number of flowers and fruit set, fruit stalk growth, dry matter partition and cumulative Photo-thermal Product (PTP). The model was validated using different crops, locations, and tomato varieties. The results show that the cumulative PTP required for the number of flowers set, fruit set and fruit growth were 146.59, 146.90 and 252.00 mol·m-2, respectively. The model demonstrated high accuracy in simulating the number of flowers and fruit set, fruit stalk growth and dry matter of tomato, with root mean square errors ranging from 0.208 to 14.229, normalized root mean square errors from 0.027 to 0.246, and correlation coefficients from 0.905 to 0.999, respectively. Varieties differences affected the accuracy of tomato growth model, and variations in fruit stalk growth among different crops increased after the fruit setting period, but the overall applicability of the model remained strong. This PTP growth model can accurately predict the timing of flowering and fruit set as well as the growth process of the fruit, providing a scientific basis for forecasting the yield and market timing of greenhouse tomatoes.
In order to find out the change rules of extreme climatic events in China and its different regions, the extreme weather and climate events ( short for “extreme events”) such as extreme high temperature, extreme low temperature, extreme precipitation, extreme drought and extreme typhoon were analyzed by using the daily observation data of 2 254 meteorological observation stations in China (except Hong Kong, Macao and Taiwan) over the past 60 years and in 2023. The results show that since 1961, the overall trend of extreme events in China has been decreasing, and the trend of decreasing from 1970 to the early 1990s was obvious, and the trend of increasing since the late 1990s was obvious. The extreme high temperature events showed a significant increasing trend, which was more obvious after entering the 21st century. Extreme low temperature events showed a decreasing trend. Extreme precipitation events showed an increasing trend in general. The extreme drought events showed a decreasing trend with obvious stage characteristics. In recent 60 years, the extreme wind speed and precipitation events affected by typhoons showed a decreasing trend, which was mainly caused by the decrease of extreme typhoon wind speed events, while the extreme typhoon precipitation events showed a slow increasing trend. The extreme events occurred frequently in 2023, with an average occurrence of 139 times per station, which was 28.3% more than the annual average from 1991 to 2020. Extreme high temperature events were 79 times per station, which was the most since 1961 and 76.8% more than normal average. Extreme low temperature events were 20 times per station, which was 23.8% less than normal average. Extreme precipitation events were 14 times per station, and extreme drought events were 26 times per station, both were close to the annual average values. Extreme typhoon events occurred 0.41 times on average in China, which was slightly more than normal average, and it was mainly dominated by extreme typhoon precipitation events. In 2023, extreme events mainly occurred in Southwest China, western areas of the south of the Yangtze River, western South China, central and northern Northwest China, western Inner Mongolia, and Beijing-Tianjin-Hebei and other places. Especially in eastern Sichuan, southern Guizhou, western Gansu, western Inner Mongolia, the extreme events were more than 200 times per station. Through the analysis of different types of extreme events in 2023, it was found that the increase of extreme events was mainly caused by more extreme high temperature and extreme drought events. According to the analysis of multiple extreme events composite risk index (MXCI), high risk areas were mainly located in the southern region of the mainland of China, especially in the southeast coastal region. In the past 60 years, the increase of MXCI was mainly located in the transition zone from Southwest China to south Northeast China. High risk areas in 2023 mainly appeared in the Southwest China and the central and northern parts of Northwest China. Through the study of the change rules of extreme events in different regions of China, it was helpful to improve the ability of disaster prevention and reduction and effectively cope with the risk of climate change.
The continuous high temperature is affecting China’s environment, economy and social production in varying degrees. Based on the daily precipitation and maximum temperature data of 234 meteorological stations in the middle reaches of the Yangtze River from 1971 to 2022, the reanalysis data from National Centers for Environmental Prediction/National Center for Atmospheric Research and sea surface temperature (SST) data from National Oceanic andAtmospheric Administration, the characteristics of atmospheric circulation in summer high temperature anomaly years and its relationship with SST are analyzed. The results are as follows: The summer high temperature days in the middle reaches of the Yangtze River presented a significantly increasing trend in the past 52 years, especially since the beginning of the 21st century. The annual average number of high temperature days in summer in the middle reaches of the Yangtze River was 19 days. In 2022, the number of high temperature days in summer was the most (74 days), compared with the average climate state in the past 30 years, the anomaly percentage is 163 % higher, and in 1987 it was only 5 days. Under the influence of the teleconnection wave train of the subpolar waveguide, the East Asian continental high pressure is enhanced, and the anticyclonic circulation controls the middle reaches of the Yangtze River. At the same time, the position of the East Asian summer westerly jet is northward, which promotes the west Pacific subtropical high to extend westward and northward. The strong sinking motion suppresses the development of low-level convection, and the radiation warming effect is obvious. As a result, the high temperature days in summer in the middle reaches of the Yangtze River are abnormally more. The high temperature days in summer in the middle reaches of the Yangtze River are positively correlated with SST (especially in summer) of the equatorial northern Indian Ocean, the North Atlantic and the mid-low latitude western Pacific. Beside, the summer high temperature days are negatively correlated with SST of the equatorial central and eastern Pacific. From the beginning of the previous winter, the SST of the equatorial northern Indian Ocean and the North Atlantic continues to be high, and the SST of the western Pacific in the middle and low latitudes gradually begins to increase. At the same time, the equatorial central and eastern Pacific is in an abnormal La Nina state in summer, which is conducive to abnormally more high temperature days in the middle reaches of the Yangtze River.
Hanjiang River Basin is an important water source area in China, and studying its precipitation characteristics is of great significance for flood prevention and drought resistance. Based on the daily precipitation data of 62 stations in the Hanjiang River and NCEP/NCAR reanalysis data, the intraseasonal variation characteristics of the precipitation over the Hanjiang River from August to October in 2021 and its relationship with atmospheric circulation and sea surface temperature were studied by using percentile, correlation methods and T-N wave activity flux. The results show that the record-breaking precipitation in the Hanjiang River during this period occurred in the upper reaches of the basin, characterized by extreme intensity and large total precipitation. Precipitation was above normal in both the summer and autumn periods, but the rainy regions in autumn were positioned further to the north. In summer, the energy of Rossby waves dispersing eastward from the North Atlantic through Siberia maintained a “two-troughs-two-ridges” pattern over Eurasia, bringing strong cold air. Affected by the strengthening and westward extension of the subtropical high in the western Pacific, moist water vapors were transported to the north through the southwest and eastward water vapor channels. The old and warm air confronted and converged on the south side of the upper-level jet stream, resulting in abnormally high precipitation. In autumn, the energy from Rossby waves dispersing from the North Pacific maintained a “two-troughs-one-ridge” circulation pattern over Eurasia, with relatively weaker cold air. The breaking of the subtropical high in the western Pacific led to southern water vapor channel. The northward movement of the high-altitude jet stream caused the convergence of cold and warm air to rise northward, resulting in the northward movement of above-average precipitation. The abnormal precipitation during summer in 2021 in the Hanjiang River Basin was influenced by the positive anomalies in sea surface temperatures in the tropical eastern Atlantic, while the autumn was influenced by the cold sea surface temperatures in the central equatorial Pacific.
The analysis of the difference of forming environment of thunderstorm gales in different regions of Shaanxi Province is helpful to better understand thermal, dynamic and circulation characteristics of this kind of processes, and provide reference for the forecast and early warning of this kind of weather. Based on the surface observation data, lightning data and ERA5 reanalysis data of European Centre for Medium-Range Weather Forecasts from 2017 to 2022, the temporal and spatial distribution characteristics of thunderstorm gales in Shaanxi are analyzed, and the environmental parameters and circulation characteristics of warm type thunderstorm gales are compared and analyzed in different regions. The results show that northern Shaanxi and eastern Guanzhong are high-occurrence areas of thunderstorm gales, and warm type process is significantly more than cold type one. In summer this kind of weather process is much more than that in other seasons, and from June to August, the frequency of warm type processes in northern Shaanxi is significantly higher than that in Guanzhong and southern Shaanxi. The high occurrence period of thunderstorm gales is from 15:00 BT to 21:00 BT, and from 14:00 BT to 18:00 BT, the frequency of warm type processes in northern Shaanxi is significantly higher than that in Guanzhong and southern Shaanxi. There are some differences in thermal and dynamic conditions before the occurrence of warm type thunderstorm gales in different regions. Before the occurrence of warm type processes in northern Shaanxi, the energy and water vapor conditions are relatively weak, while the dynamic condition is relatively strong. But in southern Shaanxi, the energy and water vapor conditions are relatively strong, and the dynamic condition is relatively weak. The circulation types with frequency higher than 15% are northern Shaanxi west wind type and anticyclone with west wind type, Guanzhong west wind type and anticyclone with west wind type, southern Shaanxi cyclone with west wind type and anticyclone with west wind type. For the northern Shaanxi west wind type and anticyclone with west wind type, northern Shaanxi is located at the bottom of cold vortex or low trough, or between the bottom of low trough and the subtropical high, and the temperature difference between 850 and 500 hPa is larger, which provides certain unstable conditions for the occurrence of convective weathers. There is shear near the average occurrence position of warm type thunderstorm gales, which is conducive to the triggering of convective weather. For the west wind type in Guanzhong, the southerly airflow in the lower layer is stronger, and the dew point depression is smaller. For the cyclone with west wind type in southern Shaanxi, the T-ln P diagram shows a near-V shape and the energy condition is better. For the anticyclone with west wind type in Guanzhong and southern Shaanxi, the T-ln P diagram shows a near-V shape and the water vapor conditions are better.
Typhoon “Ambi” was the first tropical cyclone to enter Inner Mongolia, causing rare catastrophic heavy rainstorm in the central and eastern parts of the region. This paper analyzes the transformation mechanism of “Ambi” during its northward movement and its impact on the heavy rainfall weather in Inner Mongolia using simulation results from the mesoscale numerical forecasting model (Weather Research Forecast, WRF), reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), typhoon path data, and routine observational data. The results indicate that the large-scale atmospheric circulation background of the heavy rainstorm was the interaction between the typhoon and the mid-to-high latitude westerly trough, where the cold air provided by the westerly trough met with the warm and moist airflow of the typhoon, triggering this heavy rainfall event. During the process of the westerly trough merging with the typhoon, cold air intruded from west to east and moved downward, generating a strong cold advection that lifted the warm and moist air, disrupted the barotropic warm core structure of the typhoon, and formed an asymmetric temperature structure of “warm in the east and cold in the west”, transforming the typhoon into an extratropical cyclone. The main precipitation area was located in the overlapping zone of positive MPV1 and negative MPV2 values, where the accumulation of convective instability and baroclinic instability energy promoted the development of intense precipitation. In the region where cold and warm air intersected, strong frontogenesis occurred, forming a distinct frontal zone, which provided the dynamical conditions for heavy rainstorm. Near the frontal band, a noticeable secondary circulation developed, with ascending airflow at the front and descending airflow at the rear, with the area of strongest precipitation corresponding to the region of strongest ascending airflow.
In order to understand the thermodynamic evolution characteristics of the convective system before and after the occurrence of hailstorm, and strengthen the application of new detection data in hailstorm monitoring and early warning, a strong hailstorm weather process occurring in the western of Chongqing in the early morning of April 18, 2014 was analyzed by using the observation data of microwave radiometer, wind profiler radar and Doppler radar. The results show that the hailstorm process was a typical strong convective weather forced by low-level warm advection, and the radar echo overhanging characteristics and radial velocity convergence were obvious. Before the occurrence of the hailstorm, the temperature and humidity retrieved by microwave radiometer data increased significantly. From 1.0 to 3.0 hours before the occurrence of hailstorm, K index, 850 hPa and 500 hPa pseudo-equivalent potential temperature differenc (θse850-500), CAPE (Convective Available Potential Energy), vertical wind shear from 0 to 3 km (SHR0-3) etc. increased significantly with time. The atmospheric refractive index structure constant (Cn2) increased to its peak within 0.2 to 0.5 hours before the occurrence of hailstorm, and the vertical velocity observed by wind profile radar in middle and lower layers, fluctuated significantly with height. The commonness of the parameters of multiple hail processes show that the brightness temperature of 25.00 GHz, Cn2 and the area of atmospheric refractive index structure constant (SCn2) of microwave radiometer had a significant increase trend within half hour before the occurrence of hail, and SCn2 was greater than the threshold of -500 dB·km within 10 minitutes before the occurrence of hailstorm. The vertical integral liquid water and the vertical velocity difference from the ground to the high altitude reached the maximum when the hail fell on the ground, and the Cn2 jumped to the threshold value of -120 dB in the middle and low layers. All the characteristics mentioned above have a good indication for identifying the occurrence of hail.
