Based on the monthly precipitation grid data from GPCC, reanalysis data from NCEP/NCAR and sea surface temperature (SST) from NOAA, etc, the evolution characteristics of drought and its possible causes in China and the United States in 2012 were analyzed. The results are as follows: (1) In 2012, the drought was light in China, and it was discontinuous in time and disperse in space, while the drought in the United States reached a record high level, and the spatio-temporal distribution of drought was continuous, and the intensity of drought was significantly stronger than that in China. (2) In 2012, the average temperature was close to normal in China, while in the United States, a record high temperature occurred, which aggravated the air drying, and further the drought was more serious. (3) There were connections between drought in China and the United States in 2012 and La Niña event. La Niña events with a short interval of four months occurred twice from July 2010 to February 2012. The high-pressure ridge controlled the United States for a long time due to the persistent low temperature in the equatorial central and eastern Pacific, and the downdraft prevailed over the United States, especially the North American-North Atlantic subtropical high strengthened significantly in summer of 2012, which caused the record high temperature and more serious drought in the United States in summer. Meanwhile, the high pressure ridge controlled China in winter of 2011/2012, spring and autumn of 2012, and the downdraft prevailed over China, so the intensity of drought was relatively strong. In summer of 2012, the intensity of the western Pacific subtropical high was weak, and its location was more southward and eastward than normal, which had few influence on Chinese mainland. Therefore, the summer drought in China wasn’t serious.
Based on MCI (meteorological drought composite index) at 103 stations of Sichuan Basin from 1961 to 2018, the temporal and spatial variation characteristics of extreme summer drought days (ESDD) in quasi-biennial period and its possible causes in Sichuan Basin were analyzed by using MTM-SVD (multi taper method and singular value decomposition) and EOF (empirical orthography function), etc. The results show that the main mode of ESDD in Sichuan Basin appeared the same variation in the whole region, the interannual and interdecadal variation characteristics were obvious, and the interannual oscillation periods with 2.3-2.5 a were the most significant in recent 58 years. The typical cycle with quasi-biennial period showed the more or less ESDD oscillated alternatively in Sichuan Basin, and the large value center appeared in the middle of the basin, which was basically consistent with the main mode of EOF. However, the quasi-biennial period signal of ESDD in Sichuan Basin did not always exist from 1961 to 2018, and the signal was the strongest from the late 1960s to the early 1980s. In the first year of typical cycle with quasi-biennial period, the locations of the western Pacific subtropical high ridge line and the subtropical westerly jet axis were to the north, Sichuan Basin located in the west of vapor abnormal transport belt from the south of Japan to the west of South China, and there was abnormal divergence, which wasn’t conducive to the formation of precipitation, further led to more ESDD. The anomaly distribution of atmospheric circulation in the second year was opposite to that in the first year, and ESDD was less.
The experiment was conducted during the growth season of summer maize in 2018 in moisture control field of automatic control rain shelter in agriculture meteorological test station of Linyi. With ‘Zhengdan 958’ (ZD958) as test material, five-gradient water control tests were designed during the critical period of water (jointing to blooming stage). The effects of continuous drought stress on photosynthetic physiology and yield formation of summer maize in the critical period of water were simulated and studied. The results show that the leave chlorophyll a content, net photosynthetic rate, stomatal conductance, transpiration rate and plant height, leaf area, total dry weight above ground parts of summer maize at the flowering stage decreased under continuous drought stress during the water critical period, and the heavier drought stress was, the greater reduction was. The above elements under T5 treatment were 42.6%, 75.5%, 83.2%, 65.1%, 27.5%, 18.2% and 44.9% lower than those under T1 treatment in turn. The water use efficiency of summer maize leaves increased firstly and then decreased with the intensification of drought stress, and it reached the highest under light drought stress. Under continuous drought stress, the nutrient allocation of maize leaves and sheaths increased, while the nutrient supply of stems, fruits and roots decreased, which wasn’t conducive to healthy growth of summer maize, the risk of lodging increased, and the yield formation was difficult. In addition, the continuous drought stress also caused increase of bald tip ratio and double spike rate of summer maize and significant decrease of 100-kernel weight and theoretical yield.
Based on the meteorological observation data at seven national stations in Chuzhou of Anhui Province from 1961 to 2019 and the observation data in growth periods and yield per unit area of wheat from 1980 to 2019, the characteristics of meteorological drought and flood in Chuzhou and its impact on wheat yield were discussed and analyzed by using the multi-time-scale SPEI. The results show that the monthly and seasonal variation characteristics of SPEI were obvious in Chuzhou, and the astringency of SPEI in each month of winter was the strongest, while the dispersion of SPEI in each month of summer was the biggest. The climate characteristic of drought in spring and flood in summer was obvious in Chuzhou. The continuous drought from spring to summer was the most serious seasonal continuous drought in Chuzhou, and the continuous flood from spring to summer was the most serious seasonal continuous flood in the whole year. There was a trend of drought in spring since 2000 in Chuzhou, and the climate in summer and winter became wet after the 1990s, especially in winter, while the trend of dry and wet in autumn wasn’t significant, but there was a slight humidifying trend after 2009. The correlation between SPEI3 in March and wheat climate yield was the most significant, and there was parabola relationship with negative quadratic coefficient between them. When the value of SPEI3 in March was greater than 0.81 or less than -1.93, the yield of wheat was likely to reduce highly.
Based on the hourly precipitation data at 81 national meteorological observation stations of Gansu Province from 1981 to 2018 and NCEP reanalysis data, the climate and circulation characteristics of extreme rainstorms were emphatically analyzed in different falling areas of Gansu Province. The results are as follows: (1) The extreme rainstorm weathers occurred mainly in Longnan, Tianshui, Pingliang and Qingyang of eastern Gansu, and the heavy rainfall centers concentrated in Kangxian and Huixian of Longnan. The extreme rainstorms were classified into four types including eastern Gansu, southern Gansu, southeastern Gansu and dispersion patterns, according to the falling areas of rainstorms. (2) The extreme rainstorms were easily to occur in July and August in Gansu, especially in mid-August. The extreme rainstorms in southern Gansu were earlier than in eastern Gansu. The precipitation of extreme rainstorms at night was more than in the daytime as a whole, the night rain characteristic was remarkable in Gansu, especially in southern Gansu and southeastern Gansu. In additional, the convective characteristic was significant in Gansu. (3) There were 2.5, 5 and 10 years period of extreme rainstorms in Gansu during 1981-2018, and the 2.5-year periodic oscillation was obvious. (4) The extreme rainstorms in Gansu were correlated with the subtropical high, and the falling area of rainstorm was significantly related to the location of subtropical high. Moreover, the extreme rainstorms in eastern Gansu were also related to the easterly airflow at the bottom of northern high ridge, the extreme rainstorms with dispersion pattern were related to the tropical low pressure in South China Sea, while the extreme rainstorms in southern and southeastern Gansu depended on the intensity and location of short-wave trough in Tibet Plateau.
Based on daily precipitation data at eighteen meteorological stations of Hainan Island, and 6-hour NCEP reanalysis data in winter from 1951 to 2016, the temporal and spatial distribution characteristics of winter rainstorms in Hainan Island were analyzed statistically. And the main influencing synoptic systems and anomalous circulation characteristics of winter rainstorms were contrastively analyzed, taking two persistent rainstorm processes from 27 to 28 December 2008 and 14 to 15 December 2013 in Hainan Island as examples. The results are as follows: (1) The winter rainstorms were easily to occur in the early winter (December) in Hainan Island, and its inter-annual and inter-decadal variation characteristics were obvious during 1951-2016, the winter rainstorms were frequent since 2000. (2) The days and precipitation of winter rainstorms increased gradually from west to east in Hainan Island, and the center of winter rainstorms located in Wanning of southeastern Hainan Island. (3) During the rainstorm processes in winter, Hainan was in front of southern branch trough and the back of the bottom of cold high. The easterly jet maintained in low layer, the southern branch trough was stronger and southward than the normal, and the cold air was weaker. The intensive disturbance in front of southern branch trough was beneficial to the enhancement of southwesterly wind anomaly and the occurrence of negative anomaly of low-level water vapor flux divergence over Hainan Island (especially the big negative anomaly of water vapor flux divergence in the east), which provided water vapor and disturbance transport for winter rainstorms in Hainan.
Based on conventional observation data from weather stations of Zhejiang Province and its surrounding and ERA-Interim reanalysis data from March to May during 2007-2016, the circulation characteristics and meso-scale conceptual model of warm sector rainfall processes in spring in Zhejiang Province were analyzed and summarized. The results show that the cloud was more, the precipitation was small, the temperature was high and the daily temperature difference was small during warm sector weathers in spring in Zhejiang Province. The warm sector rainfall processes were divided into four types according to 850 hPa wind field, and they were the southwestern airflow pattern, warm shear northward extending pattern, cold shear approaching pattern and southeastern airflow pattern, respectively. The warm sector rainfall for cold shear approaching pattern was the strongest, and then followed by warm shear northward extending pattern, their precipitation was large in the southwest and was small in the northeast, while that for southeastern airflow pattern was the smallest. Meso-scale analysis found that the warm sector rainfall often appeared in the dense isoline area of θse on 850 hPa and the convergence upward area of intersection of southeasterly airflow near surface and low-level southwesterly airflow over the coastal of Zhejiang, and rain belt paralleled to θse isolines. The baroclinic instability which caused by residual cold air near surface and temperature difference between land and sea could significantly increase the precipitation of warm sector.
Based on 31 aviation records of low-level wind shear, surface observational data at Shijiazhuang Zhengding international airport of Hebei Province and NCEP/NCAR reanalysis data from 2014 to 2017, the characteristics of low-level wind shear and corresponding weather situations were analyzed. The results show that the low-level wind shear mainly occurred in the afternoon and nightfall, with the peak at 14:00 BST. The majority of low-level wind shear events occurred in spring, and the low-level wind shear events occurred most in April. The number of low-level wind shear events at Zhengding international airport was the highest in 2015. The mainly weather situations which were conducive to occurrence of low-level wind shear events were northwest airflow type, vortex type, west wind trough type and horizontal trough type. Furthermore, low-level wind shear occurred most under the weather situation of northwest airflow type, especially in spring and winter. The convective weather under the vortex weather situation was prone to occurrence of low-level wind shear. In addition, more attention should be paid on 3 hours and 1 hour anallobaric and negative temperature variation under the northwest airflow weather situation, as well as allobaric and variable temperature in a short time under the vortex weather situation for forecasting low-level wind shear.
Based on hourly ground conventional observation data, L-band sounding data, wind profile radar data, Himawari satellite data from Japan and ERA-Interim reanalysis data, the characteristics of a persistent sea fog process from 15 to 25 February 2018 over the Qiongzhou Strait were analyzed. The results show that the persistent sea fog process was divided into four stages and three types, including radiation fog from 15 to 17 February, advection fog from 18 to 20 and 24 to 25 February and frontal fog on 22 February, respectively. During the radiation fog, the circulation situation of pressure field over the Qiongzhou Strait was uniform, the air temperature dropped and the water vapor was saturated at night, and the double-layer inversion appeared below 1000 m, the fog top appeared at the bottom of the first inversion layer. During two advection fogs, the stronger east-southeast airflow at the back of denatured high pressure ridge entering sea controlled the Qiongzhou Strait, and the temperature (relative humidity) kept constant (saturated) for a long time. Compared with the advection fog from 24 to 25 February, the low-level wet advection of advection fog from 18 to 20 February was stronger, the water vapor convergence layer was thicker, and the specific humidity increased persistently, which were conducive to its persistence for the long time. The larger vertical wind shear below 600 m mixed the air evenly, and the fog top reached 1000 m and above. During the frontal fog, the wind speed of northerly wind exceeded 4 m·s-1 at Xuwen station, and accompanied by weak precipitation. The center of wet advection (water vapor convergence) and the frontal area of intersection between cold and warm advection located at lower layer near the Qiongzhou Strait. In each stage of sea fog, the air-sea temperature differences were -2 to 3 ℃. When the temperature difference increased, the sea fog dissipated.
Based on multi-source meteorological observation data, the two consecutive squall line processes in the northern Jiangsu Province on May 16, 2018 were studied by using comprehensive observational comparative analysis and numerical simulation. The results are as follows: (1) The two squall line processes were generated in different environmental fields, but under the influence of the same weather system. The leeward wave disturbance on the leeward side of the Dabie mountains was the common trigger mechanism of the two squall lines. (2) The two processes had the same characteristics of the rear inflow jet and mid-altitude radial convergence on the radar echo images. For the first process, the rear inflow jet was stronger and higher, and the mid-altitude radial convergence was stronger and thicker. The difference in the vertical shear of the ambient wind was the main impact factor which led to the difference of the structural characteristics of the two squall lines. (3) Under the condition of similar convective available potential energy, the richer water vapor condition, the stronger vertical wind shear and the higher vertical shear extension height in the first process were beneficial to development of squall line system. (4) The main physical mechanisms for the formation of the two squall line gales were different. The inflow jet at the rear of the first squall line guided the mid-and high-level (5-8 km) dry and warm air to sink and intrude into the storm body, prompting its precipitation particles to evaporate strongly, and the cold pool was formed. At the same time, the high-level momentum was guided downward to produce a strong outflow airflow, which eventually led to the formation of ground gale. The inflow jet at the rear of the second squall line guided the low-and middle-level (3-5 km) dry and cold air to invade the convective system, forming cold pool and strong wind on the ground. (5) The structural characteristics of the squall line formed under the vertical wind shear condition of the environmental field in the first process were more conducive to the strong evaporation of precipitation particles to form a stronger cold pool and downdraft, which made the first squall line stronger than the second squall line.
Based on hourly temperature and precipitation grid data of CMA land data assimilation system (CLDAS), ground meteorological observation data at 119 weather stations of Inner Mongolia and the spatial distribution of irrigated crop fields, the key meteorological factors and climatic division indexes were determined by considering fully planting technology and agricultural climatic characteristics of sunflower following spring wheat harvest in agro-climatic ecological regions of Inner Mongolia. And taking suitable growth days and climate suitability in the whole growth period as zoning indicators, the refined climatic suitability division of sunflower following spring wheat harvest in Inner Mongolia was studied under the operation of ArcGIS. The results show that the heat shortage and drought in growing season mainly restricted the regular growth and yield formation of sunflower following spring wheat harvest in Inner Mongolia, and the whole region was divided into unsuitable zone, more suitable zone, suitable zone and the most suitable zone. The irrigation conditions in Hetao irrigation district, Tumochuan plain and West Liaohe plain were better, which were particularly suitable to the growth of sunflower following spring wheat harvest, so these regions were the most suitable districts of sunflower growing. Due to serious shortage of heat resource in most areas of middle and eastern Inner Mongolia and the deficit of precipitation in the north of mid-western Inner Mongolia after the transplanting, the sunflower following spring wheat harvest was quite immature, so these regions were unsuitable areas of sunflower growing. The climatic suitability division of sunflower following spring wheat harvest based on grid data of CLDAS was consistent with the division distribution based on meteorological data of weather stations in Inner Mongolia, but the details of CLDAS data division were more refined than that of stations data. Hetao irrigation district was the most suitable area of sunflower following spring wheat harvest in Inner Mongolia, which was accord with the current layout of sunflower following spring wheat harvest. Therefore, this division result could provide some references for the rational layout of sunflower following spring wheat harvest in Inner Mongolia under the background of climate change.
Based on the conventional meteorological observation data at 119 weather stations of Inner Mongolia from 1961 to 2018 and the observation data during the growth period at 11 agro-meteorological stations from 1981 to 2018, the temporal and spatial variation characteristics of potato climatic production potential were simulated and analyzed by using step-by-step correction method, and the response of potato climatic production potential to radiation, temperature and precipitation changes were discussed. The results are as follows: (1) The average climatic production potential of potato during the growing period was 18 889 kg·hm-2 in Inner Mongolia, and it was significantly lower than photosynthetic production potential (32 095 kg·hm-2) and light-temperature production potential (30 829 kg·hm-2). (2) The production potential of potato with each level during the growing period decreased non-significantly in Inner Mongolia in the past 58 years, and their inter-annual fluctuations were large, while that of climatic production potential was the largest, it was significantly and positively correlated with precipitation change. (3) The photosynthetic production potential of potato decreased from west to east in Inner Mongolia, the light-temperature production potential of potato was low in eastern and western Inner Mongolia and high in the central, while the high value of climatic production potential of potato mainly appeared in the south-central area. (4) The climatic production potential of potato in most areas of Inner Mongolia decreased non-significantly from 1961 to 2018, while that in central and northern Hulunbuir, northwestern Xing’an League, northeastern Xilin Gol League and western Chifeng increased. (5) The effect of radiation change on climatic production potential of potato wasn’t obvious in most areas of Inner Mongolia. The impact of temperature change on climatic production potential of potato was negative in most areas, and the negative effect was the most obvious in most regions of the central and the west and southeastern Inner Mongolia, while the positive effect concentrated in north-central part of Hulunbuir and northwestern part of Xing’an League. The influence of precipitation change on climatic production potential of potato was positive in most areas of western Inner Mongolia, Hohhot, western part of Chifeng and eastern part of Xing’an League, while that in southern Ulanqab, eastern Chifeng and western and eastern Hulunbuir was negative.
Dew is an important part of vineyard water cycle, which plays a vital role in the regulation of vineyard microclimate, and it is also a necessary condition for the germination of microbial spores. Based on the hourly meteorological observation data during the growing period of wine grape from April to October at Yinchuan agro-meteorological station from 2003 to 2020 and microclimate station of Meiyu Chateau from 2019 to 2020 and the 10-minute leaf surface temperature data from a typical winery in the same area in June 2019, the leaf temperature and air temperature were compared, firstly. When the dewing temperature was less than leaf surface temperature, the dew occurred. Taking the vineyard of Meiyu Chateau as an example, the temporal variation characteristics of dewing temperature, dewing days, dewing duration and dewing time during the growing period of grape and its influencing factors in vineyards of eastern Helan Mountain area were analyzed. The results show that the monthly dewing temperature from April to October appeared single-peak pattern in vineyards of eastern Helan Mountain area, and it reached the peak in July and the minimum in October. In the past 18 years, the monthly dewing days and duration increased gradually during the growing period, and it was the most (longest) in September, while it was the least (shortest) in April, and their inter-annual changes were obvious. Dewing could occur in the whole day, but it mainly occurred from 17:00 to next 01:00, and the range of dewing time gradually increased from April to October, it was the widest in September and the narrowest in April. The dew point temperature was significantly positive correlated with the minimum temperature and precipitation, the dewing usually occurred before and after rainfall processes and under the low minimum temperature weathers. The pests and diseases had a closely relation with dewing, so when temperature was higher in the evening in September and October, the drying and ventilating was very important for preventing pests and diseases in the vineyard.
Grassland is the main ecosystem of the Korqin area, and the quantitative study of its surface evapotranspiration is of great significance to master the ecological effect of the Korqin grassland. Based on surface evapotranspiration dataset of MOD16 and meteorological observation data from 2000 to 2019, the temporal and spatial variation characteristics of surface evapotranspiration and its meteorological influencing factors in the Korqin grassland were analyzed. The results are as follows: (1) MOD16 products have good applicability in the Korqin grassland, and the determination coefficient between surface potential evapotranspiration of MOD16 products (MOD16-PET) and evaporation of evaporating pan was above 0.9. (2) The monthly distribution of MOD16-ET and MOD16-PET presented a typical single-peak pattern in the Korqin grassland, and their evapotranspiration increased at first and then decreased. The inter-annual change of MOD16-ET was obvious than MOD16-PET in the Korqin grassland from 2000 to 2019. MOD16-ET increased significantly with 28.86 mm·(10 a)-1 rate, and the increasing area was more than 75%, while MOD16-PET decreased significantly with a rate of 13.35 mm·(10 a)-1 as a whole, and the increasing area was greater than the reducing area. (3) The high values of ET distributed in the northwest of the Korqin grassland, while that of PET distributed in the central region, and they had a reverse spatial differentiation characteristics to some extent. The surface evapotranspiration was different under different types of land use, and ET reduced from woodland, grassland and farmland in turn, while PET was opposite. (4) The mutation of ET from weak to strong occurred in 2003 and 2011, respectively, while that of PET from strong to weak occurred in 2015 in the Korqin grassland from 2000 to 2019, and ET in about 20% region would be likely to continue the current trend in the future. (5) The correlations of ET and PET with meteorological factors were consistent, and they were significantly and positively correlated with precipitation and sunshine hours, while their correlations weren’t obvious with temperature, relative humidity and wind speed.
Based on daily conventional observation data at 19 meteorological stations of Hainan Island from 1980 to 2018, the climatic season in Hainan Island was divided according to China’s meteorological industry standard (QX/T152-2012). Then, the comfortable degree of human body was calculated by using sensible temperature of human body based on ‘golden ratio’ method. And on this basis the comprehensive division of human body comfortable degree was done in each season in Hainan Island by using rotated empirical orthogonal function (REOF), further the optimum comfortable zones of climatotherapy rehabilitation were obtained in Hainan Island. The results are as follows: (1) The climate was mild and moist in Hainan Island, and the annual average temperature was 22.9 to 25.3 ℃, the average annual precipitation was 1157 to 2615 mm, the annual average relative humidity was 74% to 86%, and the annual average specific humidity was 14.8 to 16.4 g·kg-1, which was suitable to rehabilitation. (2) Compared with the conventional climate statistical method, the meteorological industry standard was more in accordance with season division in Hainan Island. According to the climate division, the summer was from mid-March to mid-November in Hainan Island, the autumn and spring were from mid-November to next mid-March, which indicated that there wasn’t winter in Hainan Island, and the optimum period of climatotherapy rehabilitation appeared in spring and autumn. (3) The comfortable region of human body in spring and autumn located in northern Hainan, central Hainan and southern Hainan. Overall, the climate in central Hainan was the most optimal, and the climate in three regions was stable from 1980 to 2018.
