East Asia and Western Pacific METEOROLOGY AND CLIMATE

150
STRUCTURAL FEATURES OF A SQUALL LINE OVER THE TAIWAN
STRAITS REVEALED BY DUAL-DOPPLER RADAR
Y. J. Lin, R. W. Pasken and H. Shen
Saint Louis University
St. Louis, MO 63103
U. S. A.
ABSTRACT
In this study, structural features of a subtropical
squall line, which occurred on 17 May 1987 over the
Taiwan straits, were investigated using the dual-Doppler
data collected during the Taiwan Area Mesoscale Experiment
(TAMEX). Fields of the storm-relative wind and reflectivity
were derived in the horizontal domain of 45 km by
25 km using an objective analysis scheme with 1 km grid
spacing in all three directions. Vertical velocities were
computed from the anelastic continuity equation by
integrating downward with variational adjustment. Fields
of pressure and temperature were then retrieved from the
Doppler derived winds using the three momentum equations.
Results show that many structural features of a
subtropical squall line are similar to those for a fastmoving
tropical squall line. A low-level jet (LLJ) associated
with the frontal system provides the necessary
strong shear at lower levels. On the front side of a
squall line, the front-to-rear environmental flow prevails
at all levels and is accompanied by the shallow rear-tofront
flow on the back of the line. There are many individual
cells embedded within the squall line. Relatively
weak convective downdrafts occur between the cells and
behind the main cells. The retrieved pressure and temperature
deviations are in good agreement with the
updraft-downdraft structure. In general, high pressure
forms on the upshear side of the updraft with low pressure
on the downshear. The temperature excess (deficit)
corresponds well to the updraft (dowiidraft). The interaction
between the convective updraft and downdraft plays an
important role in maintaining the three-dimensional circulation
within a squall line.