学术活动

LASG学术报告

学术报告】Changes in Track and Structure Associated With Tropical Cyclone Landfall

【报告人】     Prof. Johnny Chan
【报告人单位】School of Energy and Environment, City University of Hong Kong
【报告时间】   2011年3月10日(星期四)10:00
【报告地点】   科研楼303会议室
【报告简介】
Abstract

As a tropical cyclone (TC) makes landfall, the underlying surface and
the atmospheric conditions associated with the TC circulation changes.
These include changes in friction (both due to changes in roughness
and topography), heat and moisture fluxes as well as moisture
availability. All such changes will therefore modify the dynamic and
thermodynamic properties of the TC, and subsequently track and
structure of the TC. In this talk, we will present results from
observational studies and numerical simulations to understand such
changes. Numerical simulations of idealized vortices encountering
changes in surface properties suggest that a TC tends to be
"attracted" towards an area of enhanced roughness, with or without the
beta effect. This result implies another "inherent" effect associated
with TC motion in the presence of a roughness discontinuity (in
addition to the beta effect). In other words, as a TC makes landfall,
changes in the roughness will cause its track to deviate from that
given by the steering flow and the beta effect, although such a
deviation may not be significant or easily observable if the steering
flow is relatively strong. In terms of structure, these numerical
simulations further suggest that convection over the ocean tends to be
enhanced on the offshore side of the TC.  Analyses of radar and
satellite observations seem to confirm such simulation results
although the effect of vertical wind shear might override the effect
of roughness. Very recent analyses of rain gauge data, on the other
hand, show that rainfall is generally higher over land on the onshore
side. This might imply that in the control of convection associated
with TC landfall, the effect of topography is more dominant over land
while discontinuities in surface properties contribute more over the
ocean.

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