In order to deeply understand the difference of the occurrence conditions of different types of severe convective weather under the influence of cold vortex, different types of severe convective processes in Shandong Province on 13 June 2016 (process I) and 13 June 2018 (process II) which were dominated by short-term heavy rainfall and hail and extreme gale respectively were compared and analyzed based on the aerological and surface meteorological observation data, Doppler radar data, wind profiler radar data and the fifth generation atmospheric reanalysis ERA5 from European Centre for Medium-Range Weather Forecasts (ECMWF). The results are as follows: (1) In process I, which was dominated by short-term heavy rainfall, the precipitation efficiency was high. The echo centroid height was comparatively low in its developing stage, and a high precipitation supercell formed in its mature stage, the strongest precipitation occurred near the mesocyclone. In process II, which was dominated by hail and extreme gale, the intensity of thunderstorm gale was extreme, the convection storm developed deep, and the strong echo above 60 dBZ developed above the -20 ℃ layer and continued, playing an important role in the occurrence of large hail. The strong gales during the two processes appeared in the front of the bow echo reflectivity factor core and the rear flank downdraft (RFD) of the supercells. (2) In process I, the instability condition is moderate. The southwest airflow cooperated with the wet area to humidify the lower layers, and the near saturated layer was formed from 950 hPa to 850 hPa and thickened, the dry layer was above 500 hPa, forming the stratification of dry in the upper level and wet in the lower level, which was conducive to short-term heavy rainfall, and the convections were triggered at the superposition of the surface convergence line and the tip of the surface moisture tongue. In process II, the thermal and dynamic instabilities are strong, and the mid-tropospheric jet and the prominent dry layer from 800 hPa to 600 hPa provided favorable conditions for the formation of thunderstorm gales and the growth of hails. The triggering mechanism of process II was a warm front, which was deeper than the system of process I. Different environmental conditions of the two processes lead to the different types of convective weathers.

Based on the Ji'nan S-band dual-polarization Doppler weather radar (CINRAD/SA-D) data, combined with automatic weather station data and conventional observation data, comparative analysis of the environmental conditions are made, and emphasis is laid on the analysis of dual-polarization signatures for the Wangzhuangji storm and Da'an storm, which are short for the two extreme rainfall storms separately occurring at Wangzhuangji county of Shenxian and Da'an county of Yanzhou, Shandong on 5 and 6 August 2020. The results show that: the two extreme heavy rain occurred in the conditions of high K index, large convective available potential energy (CAPE), deep wet layer, and moderately weak vertical wind shear. In contrast, the storm relative helicity (SRH) is evidently larger for the extreme rainfall event on 6 in August. The flow structures of the storms are significantly different: the Wangzhuangji storm tilts upward and intensively diverges at high-level inducing higher storm top and specific differential phase K_DP column, while Da'an storm performs as cyclonic rotation with weaker high-level divergence. The microphysical structure varies at different levels: for the both two storms, there are high concentration of solid (liquid) particles separately above (below) -10 ℃ layer. But Wangzhuangji storm has more abundant graupels above -10 ℃ layer, a few element of liquid particles from -20 ℃ to -10 ℃ layer, and a certain amount of ice particles below -10 ℃ layer. The two storms exhibit comparable dual-polarization characteristics with moderate differential reflectivity Z_DR, bigger K_DP and correlation coefficient (CC) at low-level, which indicate that the rainfall storms constructed with abundant moderate particle size liquid raindrops are rich of water favorable for extreme rainfall.

Based on daily precipitation observation data at 120 national meteorological stations in Shandong Province, monthly reanalysis data of ERA-Interim from ECMWF (European Centre for Medium-Range Weather Forecasts) and 6-hour reanalysis data from NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) from 1979 to 2018, the influence of spring atmospheric heat source intensity over the Tibetan Plateau on summer rainstorm in Shandong Province was analyzed. The results show that rainstorm days presented an increasing trend in most areas of Shandong Province from 1979 to 2018, and the increasing trend of rainstorm days was significant in southwestern Shandong and the mid-east part of northwestern Shandong. The atmospheric heat source over the Tibetan Plateau was stronger than that in other areas of East Asia in spring and summer. The intensity of spring atmospheric heat source in strong central region over the Tibetan Plateau was significantly and positively correlated with summer rainstorm index in Shandong. When the atmospheric heat source over the Tibetan Plateau strengthened in spring, the South Asia high enhanced and extended to eastward in summer, and it was easily to appear “the central pattern” at 200 hPa. At the same time, the cold vortex at 500 hPa over northeastern China was easily to generate and moved southward, and the west Pacific subtropical high over eastern Japan strengthened and moved northward, the cold and warm airflow intersected over Shandong. In additional, there was significant water vapor transporting to Shandong from south to north. The circulation configuration with low-level convergence and upper-level divergence prompted updraft enhancement over Shandong, which was beneficial to rainfall. The intensity of atmospheric heat source over the Tibetan Plateau in spring had significantly positive and negative correlation with the South Asia high intensity and the Silk Road teleconnection correlation in summer, respectively, and the circulation situation under atmospheric heat source enhancement was conducive to occurrence of heavy rainfall in Shandong.