The weather situation and mesoscale systems characteristics of the extreme torrential rain occurred in Beijing on 21 July 2012 was analyzed. With the mesoscale numerical mode WRFV3.2 the extreme heavy precipitation is simulated. And based on the dry intrusion theory, the process of dry cold air activities during the heavy rain and its impact of the torrential rain are analyzed. The results show that: The torrential rain occurred in weather situation of the violent intersection of the southward cold air guided by upper trough and strong southwest warm wet air in North China area. WPSA prevented the upper-level trough from moving eastward and thus the precipitation process in Beijing kept a long time. The convective development process is along with the obvious mesoscale convective complex (MCC) activities, and MCC's ongoing activities and the rainfall centers are temporal and spatial consistent. The WRF model could accurately simulate this torrential rain process. Within 24 h before the precipitation occurs there is constant high potential vorticity and low humidity dry cold air from 35°N near the tropopause being transported along northward and downward path to 39°N near 700 hPa at the lower-level atmosphere in Beijing area. Dry intrusion changed little from 24 h to 10 h before the start of the precipitation, soon afterwards had a slight weakening and weakened rapidly after the precipitation started. The dry intrusion changed atmospheric thermal and dynamic environment of the Beijing area to impact the torrential rain before the precipitation started. Dry intrusion could increase the atmospheric potential instability in rainfall area and reserve CAPE abundant for the development of convection, providing the environment conducive for the occurrence and development of MCC. At the meantime, it increased the low-level cyclonic vorticity which is conducive to low-level air convergence and upward motion and this may be the trigger mechanism of severe convective weather, such as the MCC and its accompanying torrential rain in Beijing area.
TANG Pengyu
,
HE Hongrang
,
YANG Xiangrong
,
YAN Yuxiang
,
WANG Yahua
,
MIAO Ziqing
. Research and Analysis of Dry Intrusion during Beijing ‘7·21' Extreme Torrential Rain[J]. Plateau Meteorology, 2015
, 34(1)
: 210
-219
.
DOI: 10.7522/j.issn.1000-0534.2013.00128
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