O. Bousquet et M. Chong, The oceanic mesoscale convective system and associated mesovortex observed12 December 1992 during TOGA-COARE, Q J R METEO, 126(562), 2000, pp. 189-211
Citations number
32
Categorie Soggetti
Earth Sciences
Journal title
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY
This study documents the precipitation and kinematic structure of a mature/
mature-to-decaying, westward propagating, near-equatorial oceanic mesoscale
convective system (MCS) observed by airborne Doppler radars during TOGA-CO
ARE, the Tropical Ocean/Global Atmosphere Coupled Ocean-Atmosphere Response
Experiment. This system occurred on 12 December 1992 during the convective
ly active phase of an intraseasonal oscillation, and was followed, at its d
issipating stage, by a redevelopment of convection that led to the MCS obse
rved on 13 December 1992. These two successive MCSs were associated with a
two-day atmospheric disturbance. Radar-deduced airflows at two time periods
reveal many similarities with other tropical oceanic cloud clusters. In pa
rticular, a marked rear inflow jet associated with a midlevel cyclonic meso
vortex was observed within the rear of the stratiform region.
The mesovortex was better defined both in size and depth during the mature-
to-decaying stage and was located more inside the system within a region of
convergence, due to the westward propagation of the rear inflow. Countergr
adient transports of momentum normal to the mean orientation of the system
at midlevels, and downgradient transports at lower and higher levels helped
to intensify this rear inflow. These transports were mostly accomplished b
y eddy structures. Cyclonic vorticity was concentrated at the rear of the M
CS and peaked at the centre of the observed closed wind circulation. As pre
viously observed, stretching of the pre-existing vertical vorticity was the
dominant dynamical mechanism which helped to amplify the mesovortex at mid
-to-upper levels, while tilting of the horizontal vorticity into the vertic
al was a lesser mechanism and had an opposite effect. In most respects, adv
ective processes were negatively correlated with the stretching and tilting
mechanisms, but not sufficiently to be balanced. The resulting tendency wa
s an increase of cyclonic vorticity at low-to-mid levels and a net decrease
above.