NUMERICAL DIAGNOSIS OF THE ABRUPT CHANGE OF TROPICAL CYCLONE 0411
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Chen Guixing Lin Liangxun Feng Yerong Lin Gang Yuan Zhuojian
1 Guangzhou Central Meteorological Observatory, Guangzhou 510080
2 Department of Atmospheric Science/Research Center for Monsoon andEnvironment,
Sun YatSen University, Guangzhou 510275
Abstract
The killer tropical cyclone 0411 struck the eastern coast of Guangdong abruptly from
00:00 UTC to 06:00 UTC 27 July 2004 due to its significant intensification and
sudden ‘northward jump' from around 19°N to 22.7°N . Characterized by the
ascending of moist southerly (i.e. the ingredients of CISK mechanisms), a linearized
model of 106°-126°E averaged meridional circulation is applied to a quantitative
diagnosis for revealing the abrupt change. The linearized model includes boundary
effect, effects of hydrodynamic stabilities and 17 internal dynamic and
thermodynamic processes. This study reveals that a strong southerly jet with weak
zonally averaged inertial stability in the Northeastern region of the South China
Sea provided abundant moisture and lifting (driving) conditions favorable for the
geneses and development (northward jump) of TC. The geostrophic component of the
southerly was driven by the pressure gradient force associated with the monsoon
trough, the western Pacific subtropical high, and the upper level easterly
disturbance. Across the southern boundary (5°N) of the study area, the convergence
of the southwesterly from the Southern Hemisphere and the southeasterly from the
Western Pacific equatorial region also made partly contribution to the moist air
lifting around 22.7°N. The ageostrophic component of the southerly was driven by
the zonally averaged meridional temperature advection due to the baroclinic
instability, the meridional transport of eddy zonal momentum resulted from the wind
shear of the southwesterly jet, the zonally
averaged zonal transport of zonal
momentum associated with the interaction between the summer monsoon circulation and
the upper level easterly disturbance, and the eddy modes of horizontal temperature
advections related with the inhomogeneous wind and temperature distributions, and
moreover, the first (last) two factors also initiated (suppressed) the new TD growth
around 22.7°N ( the old TD around 19°N) through driving the rising motion (sinking
motion) there. The intensification of new tropical cyclone around 22.7°N was
tightly associated with the latent heating and zonally averaged meridional
temperature advection. Based on the above diagnostic results, this study suggests
that forecasters should pay more attentions to the interaction between the
deep/strong southwesterly jet and temperature advections in order to predict the
similar cases of TC sudden change effectively in the future.
Key words: Tropical cyclone, Abrupt change, Meridional circulation, Diagnostic
analysis.