Comparative Analysis of Two Heavy Rainfall Events in Northern Sichuan Basin
Based on the conventional meteorological observation data,the merged grid precipitation data and the ERA5 reanalysis data,two heavy rainfall weather processes in northern Sichuan Basin-southern Gansu and Shaanxi from June 15 to 17,2020(20·616)and from June 15 to 17,2021(21·617)were compared and analyzed.The results show that:(1)The two heavy rainfall processes have the same characteristics of two-day duration,large cumulative rainfall,large precipitation intensity,and strong precipitation concentration period from night to morning.Among them,the"20·616"rain belt is mobile,while the"21·617"rain belt is more stable.(2)The two processes occurred under the favorable large-scale circulation background,and the low-level shear line and low-level jet were the main influencing systems.The former occurred during the eastward retreat of the subtropical high,which was a low-trough eastward-moving rainfall.The heavy rainfall belt was located between the left front of the southwesterly low-level jet at 700 hPa and the two-layer shear at the head of the southeasterly low-level jet at 850 hPa.The latter occurred during the westward extension of the subtropical high,belonging to the east-high and west-low rainstorm.The heavy precipitation zone was located on the warm side of the 700 hPa shear line,in front of the 700 hPa southerly jet and in the 850 hPa northerly jet.(3)The positive vorticity and negative divergence in the lower layer of the rainstorm center in the"20·616"process showed strong vertical ascending motion,which was consistent with the period of heavy rainfall in the rainstorm center,which might be related to the increase of vertical ascending motion caused by the terrain uplift in the northwest of Sichuan Basin.Although the negative divergence of positive vorticity in the lower layer of the"21·617"process was stronger than that of the"20·616"process,the vertical upward motion condition was weaker,and there was a position deviation from the rainstorm center.(4)The key to the persistence of precipitation in the two rainstorm weather processes was that the two low-level jets in the lower layer continuously transpor-ted the warm and humid air from the sea to the northern part of the Basin and the southern part of Gansu and Shaanxi.The strong conver-gence of water vapor coincided with the occurrence time and falling area of heavy precipitation.(5)Before the rainstorm occurred,the at-mosphere was in a state of strong instability.The"20·616"rainfall occurred on the side of warm and humid air flow in front of the en-ergy front and the position of θse850 energy tongue,and the"21·617"rainfall occurred on the side of the cold air in the energy front.
Northern part of Sichuan BasinHeavy downpourLow-level jetLow vortex shearBaroclinic
NETL
NSTL
万方数据
