East Asia and Western Pacific METEOROLOGY AND CLIMATE

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1. Introduction
Observational results obtained from airborne observations on
June 16-17, 1987 (Liu and Lo, 1989} show, among other things, the
following results:
(1) Within the melting layer, the total number of particles
in a unit volume decreases significantly from the top to the
bottom of the melting layer. If the particle spectra are assumed
to satisfy the analytic function of Notexp{-AD)), where No is the
intercept and ,X the slope, No decreases significantly from top to
bottom. The slope first increases and then decreases. If we
consider only the values of the slope above and below the melting
layer, the change is slight compared with the enormous change of
the intercept. The median diameter increases slightly from the
top to the bottom of the melting layer.
(2) In the warm rain region, the total number of raindrops
in a unit volume decreases with the decrease of height. The
particle median diameter increases quite significantly with the
decrease of height.
This paper attempts to explain theoretically the observed
results.
2. Melting Layer
Within the melting layer, since both the total number of
raindrops in a unit volume and the intercept decrease
significantly from the top to the bottom, while the slope changes
only slightly, it is postulated that the decrease of the first
two parameters is mainly due to the increase in terminal
fallspeed uhen snow crystals melt to become raindrops. Other
processes, such as condensation and binary interactions are
comparatively not that important. The results will show that the
postulates are correct.
It is obvious that the precipitation rate should be the same
above and below the melting layer, otherwise there would be
convergence or divergence of precipitation particles somewhere.
Then, using the conservation of precipitation rate, we can
formulate