Study+on+Formation+and+Development+of+a+Mesoscale+Convergence+Line+in+Typhoon+Rananim.pdf

LI Ying, CHEN Lianshou, QIAN Chuanhai, et al. 413
Study on Formation and Development of a Mesoscale Convergence
Line in Typhoon Rananim∗
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LI Ying ( ), CHEN Lianshou ( £¥¤§¦ ), QIAN Chuanhai ( ), and YANG Jiakang ( )
1 State Key Laboratory of Severe Weather (LaSW ), Chinese Academy of Meteorological Sciences, Beijing 100081
2 National Meteorological Center, Beijing 100081
3 Yunnan Institute of Meteorology, Kunming 650034
(Received April 29, 2010)
ABSTRACT
This study investigated the formation and development of a mesoscale convergence line (MCL) within
the circulation of Typhoon Rananim (0414), which eventually led to torrential rainfall over inland China.
The study is based on satellite, surface and sounding data, and 20 km×20 km regional spectral model data
released by the Japan Meteorological Agency. It is found that midlatitude cold air intruded into the typhoon
circulation, which resulted in the formation of the MCL in the northwestern quadrant of the typhoon. The
MCL occurred in the lower troposphere below 700 hPa, with an ascending airflow inclined to cold air, and a
secondary vertical circulation across the MCL. Meso-β scale convective cloud clusters emerged and developed
near the MCL before their merging into the typhoon remnant clouds. Convective instability and conditional
symmetric instability appeared simultaneously near the MCL, favorable for the development of convection.
Diagnosis of the interaction between the MCL and the typhoon remnant implies that the MCL obtained
ic energy and positive vorticity for its further development from the typhoon remnant in the lower
troposphere. In turn, the development of the MCL provided ic energy and positive vorticity at upper
levels for the typhoon remnant, which may have slowed down the decaying of the typhoon.
Key words: typhoon circulation, mesoscale convergence line, convective and symmetric instability, inter-
action
Citation: Li Y