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

Based on meteorological observation data, Doppler radar (CINRAD/CA) observation data, global topography data (1°×1°) and NCEP FNL 6-hour reanalysis data (1°×1°), the blizzard weather in spring in southeastern Inner Mongolia on 20 March 2019 was analyzed. The results show that the process was a typical backflow heavy snowstorm weather, the southwesterly warm and humid air at 700 hPa climbed along the low-level cold pad to produce frontogenesis, which was the main cause of this backflow blizzard. Obvious vertical wind shear and temperature differences generated because of the northeasterly jet at 925 hPa and southwesterly jet at 700 hPa, resulting in strong dynamic frontogenesis, and the dynamic frontogenesis mechanism played a significant role. The convergence of divergence at low-level was conducive to development of vertical upward movement. The southerly and easterly at 850 hPa transported water vapor to the southeast of Inner Mongolia. There was a strong inversion stratification between 850 hPa and 700 hPa, where the cold and warm air met violently. The north-south topography of the Greater Khingan Mountains had a blocking effect on the northeasterly ultra-low-level jet stream on the windward slope of the eastern foothills, which was conducive to accumulation of dry and cold air for a long time and increasing thickness of the cold pad in lower layer. Then the warm and humid air flow was forced to lift to higher layer, which was conducive to condensation of water vapor and increase of snowfall. At the strongest period of snowfall, there was a northerly in lower layer, and an obvious “S” shape in middle layer for warm advection on the radial velocity chart of radar. At the upper level, there was a southwesterly jet maintaining for a long time, and the shear lines of northwest-southwesterly wind and southwest-southeasterly wind maintained at the same time. There was a good correspondence between the strong snowfall and the warm and humid jet from southwest climbing on the cold pad on the radar radial velocity chart, which was instructive for short-term forecast and early warning.