Drought is one of the natural disasters with the widest global impact. The anomalous drought and heatwave event that occurred in the Yangtze River Basin in summer of 2022 is not only of high intensity but also of long duration, it is a rare and significant drought event leading to very serious socioeconomic impacts in China. In view of the extreme nature of this event, this paper reveals the possible influence of atmospheric circulation and external forcing anomalies on this drought event based on an objective analysis of the evolutionary characteristics of this event. It is found that the meteorological drought index and soil moisture monitoring results consistently indicate that this drought event started to appear in June, developed rapidly in July, and further expanded and intensified in both extent and intensity in August. At the same time, the overall temperature in the basin was high, with the number of high temperature days exceeding 40 days in some areas. In addition, anomaly of evapotranspiration over the basin in summer was the second highest on record since 1960, second only to the high temperature drought event in 2013, which further exacerbated the degree of water deficit in the Yangtze River Basin. From the perspective of circulation characteristics, the abnormal intensifying and westward extension of the western Pacific subtropical high pressure, the small area and weak strength of the polar vortex and the intensifying and eastward shift of the South Asian high pressure in summer jointly led to weak water vapor transport conditions and prevailing sinking air currents in the Yangtze River Basin, making the overall conditions unfavorable for the occurrence of precipitation. The persistence of the La Niña event, the appearance of negative Indian Ocean Dipole (IOD) and the persistence of the negative snow cover anomaly in the northwestern Tibet Plateau in spring may be the main external forcing factors leading to the circulation anomaly in this summer.

Based on European Centre for Medium-Range Weather Forecasts （ECMWF） fifth-generation global atmospheric reanalysis （ERA5） every day from May to August during 1979-2020, three land-atmosphere indexes to investigate land-atmosphere coupling processes were calculated,characteristics of land-atmosphere coupling in climatology and their difference under different dry and wetsoil conditions were analyzed over eastern and southern Asia. The results show that Northeast and North China,the Tibetan plateau, India, Yunnan Province of China and Southeast Asia,the middle latitude arid zone were strong land-atmosphere coupling zones in climatology. In the middle latitude arid zone, land-atmosphere coupling had no significant difference under different soil conditions due to the low soil moisture and its little variability. In the other strong coupling zones, the coupling strength decreased with increasing soil moisture condition because of the bigger variability of soil moisture in these regions, and this law is applicable to the coupling processes between soil moisture（SM） and evapotranspiration （ET）, between ET and water vapor condition of boundary layer, between ET and instability condition of boundary layer. The land-atmosphere couplings over South China were weak in climatology, coupling between SM and ET was significant only under dry soil conditions, while the coupling between ET and atmospheric boundary layer were not significant under all soil moisture conditions.

Based on the monthly precipitation data from 57 weather stations in the Loess Plateau from 1961 to 2015, the standardized precipitation index (SPI) was calculated as the index of drought and flood to study the circulation characteristics in abnormal drought and flood years in April in the Loess Plateau and their earlier forcing signals. The results are as follows: (1) The ridge from Ural Mountains to Xinjiang in China was stronger, and East Asian trough was deeper on 500 hPa, and the south wind was weaker on 700 hPa over the Loess Plateau and its east, and the temperature was  lower on 700 hPa from east China to Japan, and the westerly jet from east China to the ocean on the east of Japan moved southerly  and  became stronger. For these reasons, it became drought in April in the Loess Plateau, vice versa. (2) The frequency of the blocking in April in the range of 180°E-150°W in mid-high latitude of the Northern Hemisphere was more in the abnormal flood years than in the abnormal drought years. (3) The south Indian ocean dipole (SIOD) or the southwest Indian ocean SST could be used as a previous forcing signal for drought and flood in April. There was a significant negative correlation between SPI in April and SIOD of December in the previous years. (4) The responses of the circulation field to the positive and negative phase anomalies of SIOD were mainly reflected in the differences of the Ural high pressure ridge, the East Asian trough on 500 hPa and the circulations over the area from Lake Baikal to northeast China and Ural Mountains on 700 hPa.

It has been well known that the triple － pattern interannual SST anomalies in the North Atlantic are principally forced by the dominant modes of Atmosphere variability，the North Atlantic Oscillation(NAO)or Arctic Oscillation(AO) ，but to what extent the North Atlantic SST anomalies can affect the Storm Track in the midlatitudes remains to be an issue． Here we estimate the response of North Atlantic Storm Track to SST anomalies by a GCM named CAM3． 0． The atmospheric CAM3． 0 was forced by the triple SST anomalies firstly，then the simulation results in winter (December to January)were compared with the NCEP/NCAR reanalysis data． We found the simulation results could reproduce the anomalies of Atlantic Storm Track and Jet accompanying the AO anomalies． Conclusions can be summarized as follows:when the SSTA was positive(negative) ，the storm track enhanced (weakened) ， and the jet exit region had a meridional displacement to polar (equator) ． The SSTA may influence the storm track through two ways，one is to change the lower atmospheric baroclinicity to affect the intensity of storm track directly，the other is to influence the meridional displacement of jet firstly，and then the jet influence the storm track． The positive feedback effection between eddies and mean flow becomes severe ( weakening)when SSTA is positive (negative) ．