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The
Structure and Evolution of a Hurricane in Vertical Wind Shear:
Hurricane
Elena (1985)
Kristen Corbosiero
NCAR ASP Postdoctoral Fellow
One of the most
complete datasets of a tropical cyclone was recorded in Hurricane Elena (1985),
as the storm made a three-day loop in
the
On the first
day of study, Elena was under the influence of strong vertical wind shear from
an upper tropospheric trough. The storm had no discernable eyewall and nearly steady values of tangential wind and
relative vorticity.
Early on the second day, a near superposition and constructive
interference occurred between the trough and Elena, initiating a period of rapid
intensification. Tangential wind spin-up
and diabatic heating within the eyewall
produced an annular vorticity profile, like those
that have been shown to support barotropic
instability. In the three to four hour
window before intensification ceased, the amplitude in
wavenumbers one and two increased significantly as
the unstable vorticity profile broke down. This was accompanied by the appearance of an
elliptical eyewall, asymmetric mixing between the eye
and eyewall, and propagating inner spiral rainbands with properties consistent with vortex Rossby wave theory.
The asymmetric mixing between the eye and eyewall
appeared to act as a brake on intensification from which Elena was unable to
recover due the storm’s proximity to land and the ingestion of low equivalent
potential temperature air.
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