Downstream Development Associated with the Extratropical Transition of Tropical Cyclones over the Western North Pacific
Abstract
The movement of a tropical cyclone
into the midlatitudes involves interactions
among many complex physical processes
over a variety of space and time scales.
Furthermore, the extratropical transition (ET)
of a tropical cyclone may also result in a
high-amplitude Rossby-wave response that
can extend to near hemispheric scales. After
an ET event over the western portion of a
Northern Hemisphere ocean basin, the highamplitude
downstream response often
forces anomalous midlatitude circulations for
periods of days to a week. These
circulations may then be related to highimpact
weather events far downstream of
the forcing by the ET event.
In this study, downstream
development following ET events over the
western North Pacific is examined. Local
eddy kinetic energy analyses are conducted
on four cases of North Pacific tropical
cyclones of varying characteristics during ET
into varying midlatitude flow characteristics
during 15 July – 30 September 2005. The
goal is to examine the impact of each case
on downstream development across the
North Pacific during a period in which these
events might increase midlatitude
cyclogenesis across the North Pacific during
a season in which cyclogenesis is typically
weak. Cases are chosen to represent the
wide spectrum of variability in ET. This
includes a case that directly resulted in an
intense midlatitude cyclone, a case in which
a weak midlatitude cyclone resulted, a case
in which the decaying tropical cyclone was
absorbed into the midlatitude flow, and a
case in which the tropical cyclone decayed
under the influence of strong vertical wind shear. The variability in downstream
response to each ET case is related to
specific physical characteristics associated
with the evolution of the ET process and the
phasing between the poleward-moving
tropical cyclone and the midlatitude
circulation into which it is moving.
Description
Extended Abstract
Rights
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