On the Parameterization of Shallow Convective Precipitation Induced by Heterogeneous Landscapes for GCMs

R Avissar and Y Liu
Department of Environmental Sciences
14 College Farm Road
Cook College - Rutgers University
New Brunswick, NJ 08901-8551
Tel: 732-932-9520; Fax: 732-932-1038; E-mail: avissar@gaia.rutgers.eduTo develop a parameterization of shallow convective clouds and precipitation
induced by land-surface processes in GCMs, a set of simulations was
performed with a high-resolution 3D atmospheric model. Results indicate that
landscape discontinuities could significantly affect the timing of onset of
clouds, and the intensity and distribution of precipitation. In most cases,
landscape discontinuities enhance precipitation. Current parameterizations
of clouds and precipitation in GCMs do not account for such effects.
Similarity theory was used to develop such a parameterization. For this
purpose, Buckingham Pi Theory, a systematic method for performing
dimensional analysis, was used to derive a set of dimensionless groups,
which describes the large-scale atmospheric background conditions, the
spatial variability of surface sensible heat flux, and the characteristic
structure of the landscape. These dimensionless groups were used to
calculate the coefficients of a Chebyshev polynomial, which represents the
self similar vertical profiles of dimensionless mesoscale heat fluxes
obtained for a broad range of large-scale atmospheric conditions and
different landscapes. The numerous 3D numerical experiments performed to
evaluate this similarity relationship suggest that the parameterization
provides reasonable results.
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Deadline for camera-ready abstract is January 15, 2001.