A diagnostic modeling study of the cloud and precipitation
processes, and also frontogenesis have been analyzed in a severe
narrow cold-frontal rainband with the aid of a three-dimensional,
diagnostic cloud model.
The results of the model simulations indicate that the heavy
precipitation just behind the surface cold front was associated
with a low-level warm rain process driven by the severe prefrontal
updraft. The precipitation well behind the leading edge of cold
front resulted from the melting of graupel. The sensitivity
studies for the rain water distribution indicated that the
Analytical Gamma distribution may be a more suitable functional fit
for the raindrop distribution as compared with the Marshall-Palmer
distribution.
The differential heating due to microphysical processes
(condensation and evaporation) at the leading edge of the surface
cold frontal region facilitated the required density contrast
across the front and thus maintained the propagation of the density
current. The leading edge of the cold front was also characterized
by frontogenesis for levels above 0.9 kin and frontolysis just ahead
and immediately behind the cold front. The low level frontolysis
indicated that buoyancy effects were almost negligible at the
leading edge of the cold front. Instead the upward motion was
created by mechanical lifting (pressure effects). The frontogenetical
effects due to diabatic heating were quite important at
the 1.2 - 2 km levels where the peak updraft occurred. / Graduation date: 1987
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29292 |
| Date | 04 August 1986 |
| Creators | Wijesekera, Hemantha |
| Contributors | Rutledge, Steven A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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