WMOD00590

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

1.2 Hypothesis

A hierarchy of hypotheses has been proposed for evaluation in this
research to understand the natural variability of convective precipita-
tion in west Texas. The fundamental assumption is that mesoscale rawin-
sonde observations separated by 80 to 100 km may be used to detect the
kinematic and thermodynamic mechanisms which control the natural vari-
ability of convective precipitation. Different physical mechanisms are
hypothesized for the four types of mesoscale organization which produce
convective rainfall as follows:

1. Isolated convective clouds occur in an environment with little
or no low-level mesoscale convergence and lifting; cloud development
is driven primarily by solar heating with local variations in sta-
bility, moisture and albedo primarily controlling the location and
intensity of cloud growth and precipitation.

2. Clusters of convective clouds form in a weakly forced environment
with little initial organization and are initiated by processes out-
lined in hypothesis 1. However, the stability and moisture charac-
teristics of the cluster environment permit the evolution of meso-
scale systems through downdraft-outflow triggering of new convective
clouds, resulting in clusters or complexes of meso-~ cumulonimbus and
cumulus congestus systems.

3. Lines of convective clouds form in a mesoscale-forced environment
where low-level convergence and upper-level divergence couple to pro-
duce strong meso-~ regions of upward vertical motion and moisture
flux. This environment must have sufficient moisture and have stable

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