East Asia and Western Pacific METEOROLOGY AND CLIMATE

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expense of smaller droplets and to increase the median
diameter by a factor of 2-3 from the bottom of the melting
layer downward to the ground level. Still the competition
between the coalescence and the breakup processes through
binary interactions eventually leads to an equilibrium
state. The analyses of the raindrops spectra reveal the
existence of three peaks below 1.5km as proposed by other
theoretical and observational studies for equilibrium
raindrop spectra.
1. INTRODUCTION
Using the data collected by the PMS (Particle
Measuring Systems, Inc.) 2D-C imaging cloud probe and the
2D-P precipitation probe onboard the NOAA WP-3 aircraft,
we have analyzed the microphysical processes in the
melting layer and the warm-rain region in the stratiform
precipitation area of an open-ocean mesoscale convective
system (MCS) which occurred on June 16-17 1987 just off
the southeast coast of Taiwan during the Taiwan Area
Mesoscale Experiment (TAMEX).
The observed MCS consists of a multi-cell convective
line system oriented approximately north-south and a
widespread stratiform precipitation area. Two box flight
tracks (marked by 1 and 2, respectively, in Fig. 1) are in
the stratiform area. In both tracks the aircraft descends
spirally from 5.5km toward. 0.35km in 19min (descending
speed about 4.5m-s~ 1 ). Studies of the aircraft data
collected along tracks 1 and 2 provide us with an
opportunity to identify the general features in the
melting layer and the warm-rain region.
The 0°C isothermal layer is approximately below the
5km level and is about a few hundred meters deep (Willis
and Heymsfield, 1989). The melting layer extends from the
0°C level toward the 2-3°C level (about 4.5km altitude)
(Stewart et al., 1984, Willis and Heymsfield, 1989). The
warm-rain region below 4.5km interfaces both the melting
layer and the precipitation at the surface.
The analyses schemes for the 2D-C and 2D-P imaging
probe data are those described by Heymsfield and Parrish
(1978), Heymsfield and Baumgardner (1985) and Parrish and
Heymsfield (1987).
2. THE MELTING LAYER
Analyses of the in-situ measurement data show that
from the top to the bottom of the melting layer, there are
(1) a sharp decrease of the LWC (liquid water content,
measured by the Johnson-Williams device) from 0.6 to