Mon. Wea. Rev.
A potential vorticity tendency diagnostic approach for tropical cyclone motion
Department of Meteorology, School of Ocean and Earth Science and Technology, University of Hawaii
In order to understand the roles of various physical processes in baroclinic
tropical cyclone (TC) motion and the vertical coupling between
the upper- and lower-level circulations, a new dynamical framework is
advanced. A TC is treated as a positive potential vorticity (PV) anomaly from
environmental flows, and its motion is linked to the positive PV tendency.
We show that a baroclinic TC
moves to the region with maximum tendency of the azimuthal wave-number-one PV component,
but not necessarily follows the ventilation flow (the asymmetric flow over the TC
center). The contributions of individual
physical processes to TC motion are equivalent to their
contributions to the tendency of the wave-number-one PV component.
A PV tendency diagnostic approach is described based on this framework.
This new approach is evaluated with idealized
numerical experiments using a realistic hurricane model.
The approach is capable of estimating TC propagation with a suitable accuracy
and determining fractional contributions of individual
physical processes (horizontal and vertical advection, diabatic heating and friction)
Since the impact of the ventilation flow is also included as a part of the influence
of horizontal PV advection, this dynamical framework is more general and particularly
useful in understanding of
physical mechanisms of baroclinic and diabatic TC motion.
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