WMOD00590

• Title: Analysis and Classification of Mesoscale Cloud and Precipitation Systems
• Date: 8/1/1983
• Weather Modification - Doc Type: Report

limiting convective development to isolated cells and clusters. Str~ng
upper-level divergence of 10 to 40 x 10-5/s produces deep regions of
lifting from 900 to 400 mb in quadrants 2 and 4 which triggered the ~ore
intensive line and mesosynoptic events. Nearly all of the larger
convective clouds were located in regions of lifting and moderate
vertical moisture flux of 4 to 8 (g/m2)/h.

Composite analyses of each type indicate physically distinct and
statistically significant variations. Average rainfall of each type
increased logarithmically from isolated to mesosynoptic events, indi-
cating more homogeneous samples with this classification scheme. Radar
echoes with durations >1 h accounted for 95% of the total rain volume of
which 25% of these echoes had minimum echo-top temperatures in the
supercooled temperature region. Between 96 and 98% of the tctal rain
volume estimated by radar in each type of event occurred with maximum
rain rates >30 mm/h. From 82 to 97% of this total rain volu~e was
observed in echoes having rain rates >40 mm/h; while 94% of the total
rain volume from all echoes in this sample occurred with maximum rain
rates >50 mm/h. These relatively high peak values of rain rates suggest
that most significant rainfall occurs from convective cells which are
triggered by transient mesoscale features, rather than from purely
stratiform echoes of synoptic origin with peak rain rates <30 mm/h.

Analyses of total volume of rain from all echoes within 150 km of
Big Spring, Texas, and contributions by individual echoes indicate that
between 21 and 40% of the total volume in any type of event was contri-
buted by one echo system from a sample of 69 to 313 echoes within each
type. Thus, between 0.3 and 1.4% of the echoes account for 21 to 40% of

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