An Analysis of Trigger and Enhance Mechanisms of Two Typical MeiyuFront Heavy Rains in Midwest Zhejiang Province
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Abstract:
Based on the conventional observed data, NCEP/NCAR 1°×1° reanalysis data and the intensive observed data of automatic weather stations, two typical torrential rain processes during the Meiyu period of 21 to 22 and 24 to 25 June 2017 are compared. The differences are as follows: (1) The former at lower levels was a warm shear line, and the latter was a stationary front shear line. The slope of the former was about 45°, and that of the latter was nearly 90°. On the other hand, the low level jet of the latter was stronger than that of the former. (2) The water vapor of the former came from the East China Sea and then the South China Sea; that of the latter came from both South China Sea and East China Sea, which had stronger vertically integrated moisture transport. (3) The former was located near the zero isoline of moist potential vorticity in Midwest Zhejiang Province, which means that the former was triggered by the cold air activities at lower levels. The latter was caused by the middlelevel cold air overlying warmwet air transported by the southwest lower jet stream, which had a positive (negative) value at upper (lower) levels. (4) The latter had a high E index center and negative Δθ58 in Midwest Zhejiang Province, where summermonsoon highhumidity and highenergy masses accumulated in this area, and smallscale convective systems frequently developed. However, the former had positive values of Δθ58 in most parts of Zhejiang Province, over which the potential stratification was relatively stable.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.