From the afternoon to night on 5 July 2021, severe convective weather including short-time heavy precipitation, thunderstorm wind and small hail occurred in the central region of Beijing-Tianjin-Hebei. The atmospheric environmental conditions and mesoscale characteristics of the formation of this weather process were analyzed by using the data of egional automatic meteorological station, Doppler radar, FY-2G meteorological satellite and microwave radiometer, and the fifth generation atmospheric reanalysis ERA5 from European Centre for Medium-Range Weather Forecasts. The results show that favourable water vapor conditions appeared before the occurrence of the severe convective weather including heavy precipitation, thunderstorm winds and local hail. Strong convergence of water vapor fluxes in lower and middle layers occurred 1 to 2 hours earlier than precipitation. The whole layer atmospheric precipitable water had accumulated continuously under strong uplift. The heat and power unstable environment of severe convection breaking out was created by formation of vertical θ_se energy frontal zone, maintenance of "upper dry and lower wet" unstable stratification, establishment of strong vertical wind shear from 0 to 6 km and enhancement of CAPE, K and SI indexes. Unstable stratification formed by eastward movement of the upper though carrying dry and cold air southward and low warm tongue, which had provided synoptic-scale upward movement for the occurrence of severe convection. The strong convective happening released more energy in the afternoon than in the evening. Heavy rainfall caused the local temperature to drop significantly and cold pool effect was more significant, which corresponded to the heavy precipitation area during the southward movement process. The surface convergence line at the cold pool boundary was the mesoscale trigger system. The cloud base height dropped and infrared brightness temperature increased rapidly, which indicated the formation of strong convective cloud cluster. The clear shadow at the southeast boundary of cloud body indicated the strong development of cumulonimbus cloud. Under the background of large-scale weather system, the important characteristic indexes obtained from in-depth analysis of mesoscale system can be used for the short term forecast and warning of severe convective weather.

Based on the observation data of national weather station, Doppler radar data, National Centers for Environmental Prediction (NCEP) reanalysis data and European Centre for Medium-Range Weather Forecasts (ECMWF) fifth-generation global atmospheric reanalysis (ERA5) from 2010 to 2019, the echo pattern,climatic characteristics as well as the change of physical quantity of heavy precipitation with quasi-linear MCSs were analyzed qualitatively and quantitatively. The results are as follows: (1) There were three types of echo patterns, namely trailing stratiform (TS) type, leading stratiform (LS) type, and parallel stratiform (PS) type.TS type had the highest frequency, while LS and PS types were relatively rare. Heavy precipitation with quasi-linear MCSs had obvious characteristics of monthly and diurnal variation, and it occurred frequently in July and first half of the night. (2) The heavy precipitation with quasi-linear MCSs formed under four synoptic-scale circulation patterns, namely low trough, transverse trough, low vortex and westerly circulation types, and the low trough type was most. (3) The relatively dry and cold air coming from the west direction at 700 hPa and the low level southwest airflow acted together, and it intensified the stratification instability of the atmosphere and improved the precipitation efficiency. The larger southerly wind component of water vapor at 850 hPa was more conducive to the formation of rainfall weather with relatively small rain area but large rain intensity. The coordination of the southeasterly wind at 925 hPa significantly enlarged the heavy rainfall area. (4) The heavy precipitation with quasi-linear MCSs generated under strong thermal environment. The convective available potential energy (CAPE) varied from 316.7 to 1545.7 J·kg^-1, vertical energy helicity (VEH) was positive and it was obviously greater than 2×10^-4 J·m·kg^-1·s^-2, which were the favorable energy conditions for the formation of the heavy precipitation with quasi-linear MCSs. In the process of heavy precipitation of PS type MCSs, the upper level horizontal divergence strengthened the pumping effect, and it allowed the large ascent rate to be maintained. The superior dynamic condition was one of the important reasons for the longer duration heavy precipitation.

Based on precipitation data of 642 stations in China and NCEP/NCAR reanalysis data during 1961-2016, the interdecadal variation characteristics of summer precipitation over the Huaihe River Basin and corresponding atmospheric circulation anomalies since 2000  were  analyzed, and the change of possible predictive signals around  the year 2000 was discussed. The results show that summer precipitation over the Huaihe River Basin had obvious interdecadal change, which was from the period of more precipitation during 2000-2008 to the period of less precipitation during 2009-2016, and the precipitation differences were significant between two periods. The atmospheric circulations during the two different precipitation periods were obviously different. During the period of more (less) precipitation, the high ridge (low trough) over the Lake Baykal was obvious, the low trough (high ridge) over the Ural mountains and the Sea of Okhotsk was obvious. And the South Asia high became weaker (stronger) and shifted westward (eastward-shifted), the East Asian Subtropical Westerly Jet Stream was weaker(stronger), the tropical easterlies jet was stronger (weaker). Meanwhile, during the periods of more (less) precipitation ,there  was  strong (weak) Somali cross-equatorial flow, Mascarene high and Australian high of southern hemisphere. The pre-winter North Pacific Oscillations (NPO) could still be a precursory signal of summer precipitation over the Huaihe River Basin. However, the interdecadal variation  of  relationship between the NPO and summer precipitation over the Huaihe River Basin had arisen around the year 2000. There was a significant negative correlation before 2000 and positive correlation after 2000. For both strong (weak) pre-winter NPO years before 2000 and weak (strong) pre-winter NPO years after 2000, the summer high ridge (low trough) over the Ural mountains and the Sea of Okhotsk was obvious, the summer low trough (high ridge) over the Lake Baykal was  obvious and the summertime western Pacific Subtropical High was located from South China sea to north Philippine(sea area near Taiwan), which influenced summer precipitation less (more) over the Huaihe River Basin.