Climatological characteristics of Sichuan Basin vortex during 1979-2016

doi:10.12006/j.issn.1673-1719.2019.051

Abstract

Abstract:

Using the 6 h, 0.25°×0.25° ERA-Interim reanalysis data during 1979-2016, the vortexes generated from Sichuan Basin are detected and analyzed. The results show that the generation of Sichuan Basin vortex is mainly concentrated in Sichuan Basin. It is the most frequent in June and strongest in July. Sichuan Basin vortexes can be divided into 5 categories according to its migration, including eastward-migrating type, northeastward-migrating type, southeastward-migrating type, westward-migrating type and stationary type. The generation of eastward-migrating, southeastward-migrating, and stationary types of Sichuan Basin vortexes peaks in June, while that of other types peaks in July. Structure and precipitation of long-lived Sichuan Basin vortexes in summer are discussed through a composite analysis. The northeast-migrating type is the strongest and the stationary type is the weakest. Concerning the structure in the maturation stage, except the westward-migrating type, vortexes of other categories are cold at lower layers and warm at middle layers, with a northwest or west tilt. Eastward-migrating, northeastward-migrating and westward-migrating types can reach higher levels than others. The strongest ascent motion of southeastward-migrating and westward-migrating types coincides with the vorticity center, while it is located at the east side of the vortex center for others. For precipitation, except for the westward-migrating type, the maximum 6 h-precipitation appears at the east or northeast side of the vortex center. And 6 h-precipitation of northeastward-migrating type is the strongest among all types. For the Sichuan Basin vortex, there is a good correspondence among the strong ascent motion, the high relative humidity, the convergence and divergence centers at the middle and lower troposphere, and the location of precipitation. The interaction of various physical quantity fields jointly promotes the development of the vortex.

Key words: Sichuan Basin vortex, Climatological characteristics, Composite analysis, Vertical structure, Precipitation

LIU Chong,ZHAO Ping. Climatological characteristics of Sichuan Basin vortex during 1979-2016[J]. Climate Change Research, 2020, 16(2): 203-214.

Figures/Tables 9

Fig. 1 Regional distribution of the generation number of Sichuan Basin vortexes during 1979-2016

Fig. 2 Distribution of the generation number of Sichuan Basin vortexes as a function of size (a) and duration (b)

Fig. 3 Monthly variation of Sichuan Basin vortexes in the generation number (a), averaged size (b), averaged duration (c),and migration rate (d)

Fig. 4 The moving tracks of Sichuan Basin vortexes that move out of the target area (a) eastward-migrating type, (b) northeastward-migrating type, (c) southeastward-migrating type, (d) westward-migrating type (blue dot indicates the generation of a vortex, green dot indicates the degeneration of the vortex, while red line connecting the two dots shows the moving track of the vortex)

Tab.1 Monthly variation of the generation number of different types of Sichuan Basin vortex

Fig. 5 South-north cross sections of composite fields for different types of long-lived Sichuan Basin vortexes in summer (vertical velocity has been increased a hundredfold, unit for wind vectors: m/s; blue lines indicate relative humidity, unit: %)

Fig. 6 Same as Fig. 5, but for west-east cross sections of composite fields for different types of long-lived Sichuan Basin vortexes in summer

Fig. 7 Composite temperature and divergence fields for long-lived Sichuan Basin vortexes in summer (black lines indicate divergence)

Fig. 8 Composite moving tracks and precipitation in 6 hours for long-lived Sichuan Basin vortexes in summer (the black dot indicates the averaged initial location of the vortex in different developing periods, and the red dot indicates the location of the vortex after 6 h)

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