Critical levels and mixing layers
induced by convectively generated gravity waves during CEPEX
H TEITELBAUM ; M
MOUSTAOUI ; R SADOURNY ; F LOTT
Quarterly
Journal of the Royal Meteorological Society
Volume:
125
Number:
557 Page: 1715 -- 1734, 1999,
DOI: 10.1256/smsqj.55711.
Abstract
We
study data from the Central Equatorial Pacific Experiment, in
particular the soundings providing temperature, pressure, wind and
ozone profiles, and we link them to the large-scale conditions deduced
from the analyses of the European Centre for Medium-Range Weather
Forecasts. To the west of the date line, the mean wind shows a strong
shear at the tropopause between the easterlies of the upper troposphere
and the westerlies of the lower stratosphere. These are conditions
propitious to the formation of critical levels for quasi-stationary
gravity waves generated by deep convection. The measured wind profiles
show the main characteristics of the encounter of a wave with its
critical level and, in the ozone and potential-temperature profiles,
the existance of a conspicuous mixing layer in the vicinity of this
critical level. Our interpretation that the mixing layer is a
consequence of the critical level is supported by numerical simulations
with a nonlinear time-dependent two- dimensional model. The occurrence
of a mixing layer in the tropopause structure seems to be
characteristic of large-scale equatorial convective areas during
westerly phases of the quasi-biennial oscillation.
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