WMOD00399

• Title: WMO Training Workshop on Weather Modification for Meteorologists - Lecture Notes
• Date: 12/1/1979
• Weather Modification - Doc Type: Report

'11
- "'~ -

(b) To demonstrate, at a satisfactory statistical significance level over a
relatively short experimental period (five years), that any increase observed
is not a chance event but is associated with the seeding. The principal
evaluation of this experiment \lrill be in terms of precipitation at the ground;

(c) To obtain sufficient understanding of the meteorology and cloud physics in
the area of the experiment to ensure that the statistical association of
seeding, and any increase in precipitation, will be generally acceptable as a
cause-and-effect relationship;

(d) To make an examination outside the target area in order to determine whether
any benefits of seeding extend over areas greater than the target area, or
whether there has merely been a comparatively local redistribution of pre-
cipitation;

(e) To make systematic measurements, varying from mesoscale to cloud micro-
structure, in order to develop additional co-variates to strengthen the
power of the statistical analysis;

(f) To obtain well-documented scientific evidence that may lead to the optimiza-
tion of the effects of seeding. For this purpose, a series of systematic
cloud physics measurements should be taken on a routine basis. This would
allow the application of statistical stratification techniques to relevant
physical parameters, and could shed more light on the quantitative aspects
of seeding techniques;

(g) To be able to make some :recomm€ndations about the applicability of the PEP
procedures to other areas of the world;

(h) To assess the environmental impact of precipitation-enhancement activities,
both within and outside the experiment target area.

3. PEP PLAN AND DESIGN

3.1 The PEP Phases

The first general description of PEP was given in PEP Report No. 3 "Plan for the
Precipitation Enhancement Project". Thereby, PEP was split into three phases:
The selection and preparatory phase;
The precipitation enhancem'~nt experiment;
The evaluation period.

The type of enhancement experiment \lras specified as the seeding with AgI (silver
iodide) of clouds and cloud systems in which the ice phase - if it is not already there or
expected to arise due to an ice-multiplicatioft mechanism - can be enhanced and thus, the
precipitation mechanism be started or re-inforced. Further, PEP was conceived as a random-
ized experiment with the primary evaluation based on observations with a rain gauge network,
with physical observations backing up the statistical results and allowing a possible trans-
fer to other areas of the world.

3.2 The Site Selection Phases (SSPs)

The site selection was split into three phases:

SSP-I: Initial identification of the most promising sites from the answers by
WMO Members to a first questionnaire;

SSP-2: Site visit by experts, numerical simulation of past rainfall data, and
studies of climatic and synoptic nature;