The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment - Part 3: Dynamics of low-level spin-up during the genesis
Abstract
Aircraft reconnaissance data collected during the
Tropical Cyclone Structure 2008 field campaign are used to
examine further kinematical, dynamical, and thermodynamical
aspects of the genesis of Typhoon Nuri. Data from the
first two missions into the pre-Nuri disturbance document
the transition from a tropical wave to a tropical depression.
Dropwindsonde-derived tangential wind profiles at several
radii from the low-level circulation center indicate that the
magnitude of low-level circulation increases and that the corresponding
tangential velocity maximum moves inward from
the first to second reconnaissance mission. To compliment
these findings, a three-dimensional variational analysis incorporating
both dropwindsonde and aircraft Doppler radar
data is conducted. These data are used to perform circulation
tendency calculations at multiple distances from the lowlevel
circulation center. The results demonstrate a net spinup
of the system-scale circulation in the low levels near the
center and in the outer regions of the recirculating Kelvin
cat’s eye circulation. In these regions, the spin-up tendency
due to the influx of cyclonic absolute vorticity exceeds the
frictional spin-down tendency for both Nuri missions. The
system-scale spin-up is found to be accompanied by areas of
low-level vorticity concentration through vortex-tube stretching
associated with cumulus convection. The areal coverage
and intensity of these high-vorticity regions increase between
the first and second Nuri missions. The findings of this study are consistent in some respects
to the Nuri observational analysis carried out by Raymond
and López-Carrillo (2011), but differ in their suggested
key results and related scientific implications that the pre-Nuri disturbance was spinning down in the planetary boundary
layer on the first day of observations. The findings herein
strongly support a recent tropical cyclogenesis model positing
that the Kelvin cat’s eye circulation of the parent wavelike
disturbance provides a favorable environment for convective
vorticity organization and low-level spin-up on the
mesoscale.
Description
The article of record as published may be located at http://dx.doi.org/10.5194/acp-14-8795-2014
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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