WMOD00541

• Title: Adaptation of the Rhea Winter Orographic Precipitation Model to Morocco
• Date: 4/1/1989
• Weather Modification - Doc Type: Report

The Moroccan weather modification program (Al Ghait) has been
designed to increase the winter snowpack over the Atlas Mountains by
cloud seeding. To improve the program's efficiency, the Rhea winter
orographic precipitation model, which is a 2-D (in the x-z plane)
steady-state multilayer model, is being adapted to the Atlas Mountains
to meet the following objectives: a) forecast orographic precipitation,
b) estimate streamflow (for eventual use in the statistical evaluation),
c) evaluate cloud seeding effects on the precipitation (after calibra-
tion of the efficiency factor), and d) determine the ability of the
model to diagnose the magnitude of the orographic effects on winter
precipitation. Also, preliminary sensitivity tests on some of the model
parameters have been accomplished (Sec. 2.7).
Indeed, since the project started in 1984, several Moroccan~) have
come to the United States to learn more about cloud physics and dynamics
and therefore contribute more effectively to the success of Al Ghait.
The subject of this thesis is part of this training.
1.2 8ackqround
In this study, we will try to meet the above mentioned objectives
using routinely available upper air soundings from 8eni Mellal (Fig.
1-1) and a fine mesh topographic grid (Fig. 1-2) as computational
input.
The total orographic precipitation (RT) can be considered as a sum
of three components, namely:
a. the orographic (or forced lifting) precipitation component
(Ro),
b. the convective precipitation component (Rc), and

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