Diagnosis of Different Definitions Potential Vorticity in an Extreme Rainstorm in the Western Sichuan Basin

Abstract

The data of NCEP reanalysis （1°×1°）， national ground automatic stations， radiosonde and Sichuan encrypted automatic stations were used to diagnose the three definitions potential temperature and potential vorticity in an extreme rainstorm which occurred in the western Sichuan Basin during August 15 -18， 2020.The results indicate that： Rainfall occurs in the ‘high east and low west’ circulation in the 500 hPa， the low-level shear line and vortex are the favorable dynamic conditions.There is an obvious pseudo-equivalent potential temperature and generalized potential temperature （θ* ） gradient in the heavy rain area， but potential temperature is not.Potential vorticity （PV） anomaly area corresponds well to the precipitation area near 500 hPa and 800 hPa.In the mid-low troposphere， the overlapping area of the negative vertical component （MPV1） and horizontal component （MPV2） of moist potential vorticity， and negative MPV1 in lower level， positive in higher level are warning areas of the storm.Meanwhile， the rainfall center is close to the negative and positive junction area of MPV1， and the rainstorm was mainly affected by convective instability in the low troposphere.The generalized moist potential vorticity （GMPV） abnormal disturbance area in 800~600 hPa can be used as the rainstorm warning area， and its positively correlated with the change of low-level water vapor.The space-time distribution of three definitions potential vorticity and precipitation have a good correspondence in a single station， and the precipitation intensity is positively correlated with the disturbance intensity.The indicated height of PV， MPV and GMPV is 650~550 hPa， 600~500 hPa and 800 hPa.Three definitions potential temperature has obvious difference， which the θ* can best reflect the high-water vapor of rainstorm.

Keywords

• potential temperature
• potential vorticity
• relative humidity
• extreme rainstorm