ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 41 Issue 12 > 2015,41(12):1477-1487. DOI:10.7519/j.issn.1000-0526.2015.12.005 Prev Next
Comparative Analysis of Easterly Air Stream Triggering Two Convection Rainstorms in the Eastern Side of Sichuan Plateau
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Abstract:
Using intensive surface observation, NCEP/CFSR 0.5°×0.5° reanalysis data and 0.01°×0.01° global terrain data etc., the contrast role and characteristics of the easterly air stream in two convection rainstorms in the terrain transition zone of Western Sichuan Plateau in the summer of 2013 was analyzed in this paper. The activity characteristics, vertical structure and temperature and humidity characteristics, and the role in the two convective rainstorms were focused on. The results showed that: (1) The easterly activity on 3 July 2013 is below 850 hPa, lasting for about 20 h with wind speed averaged 2 m·s-1 in Sichuan Basin, while easterly activity on 6 August is below 700 hPa, also with duration 20 h but wind speed is about 4 m·s-1. Both of the two processes are composed of westerly trough moving eastward and the effect of terrain, which induce the easterly air stream. The easterly airflow forms about 12 h earlier than convective precipitation appears. (2) The easterly flows of the two processes have high equivalent potential temperature property with the dry cold air activities in the midupper troposphere, thus, forming the favorable convective unstable stratification. In contrast, after the height and wind speed of the easterly flow in the later process is obviously enhanced, much stronger lowlevel vertical wind shear is formed together with the west wind, and the local concentration characteristics of the warmwet energy is more significant, more beneficial for the sustained delivery of water vapor and energy. So the induced convective precipitation is more intensive. (3) The undulated easterly air stream, convergence center and cyclonic vorticity center are poorly related in the previous process, except when the easterly wind forces the uplift and inspires convection making the rainfall near the terrain. However, the straight easterly air stream has good relations with the convergent center and vorticity center during the second process, with almost equivalent scales. Therefore, severe convection intensifies to larger ranges and the extremely heavy rains develop to the west of the basin along the terrain.
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