WMOD00488

• Title: The Use of Microwave Radiometry to Determine a Cloud Seeding Opportunity
• Date: 9/9/1982
• Weather Modification - Doc Type: Report

1288

JOURNAL OF APPLIED METEOROLOGY

VOLUME 21

10 12 14
TIME (GMT)

FIG. I. Total path liquid measured by the radiometric system on 3 March 1980. Rainfall data were
measured at the radiometer site using a weighing bucket raingage.

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4. Location of ground-based instruments

In the 1979-80 SCPP field season, the satellite re-
ceiver-radiometer was located near Sheridan, Califor-
nia. From this location the elevation angle of the prop-
agation path to the satellite is 32.60. The half-power
beamwidth of the system antenna is 0.60; thus, the
width of the beam is - 100 m at a range of 10 km
from the receiver-radiometer. The instrument was
located upwind from the SCPP test area(Fig. 2). Dur-
ing the three month field season, the system operated
continuously and unattended, measuring the amount
of liquid water contained in clouds as they drifted
through the fixed antenna beam and into the SCPP
test region.
Additional instrumentation at the Sheridan site in-
cluded a 5 em wavelength radar operated by the Bu-
reau of Reclamation, a rawinsonde facility and in-
struments for standard meteorological surface data.
The total liquid observed by the radiometric system
was displayed in the radar van.
A second 5 em wavelength Doppler radar, operated
by the National Center for Atmospheric Research,
was located 10 km south of the Sheridan site.

5. Cloud seeding in the SCPP
The primary objective of the SCPP is to develop

DAY NO. 63
3 MAR 1980

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a technology for augmenting winter precipitation and
snow pack in the Sierra Nevada in California by, cloud
seeding. Until now, experiments have been conducted
to study the microphysical response of clouds to seed-
ing rather than to increase precipitation. Accordingly,
the areas treated and the amounts of seeding materials
used have been relatively small. Typical seeding rates
of materials dispensed from aircraft are 0.5 kg min-I
for dry ice and 2-20 AgI flares min-I (Carleyet al.,
1980). .

Initiation of cloud seeding experiments is con-
trolled by the Bureau of Reclamation site director lo-
cated at the Sheridan site. The site director utilizes
available data from radars, soundings, forecasts and
in situ observations by the aircraft to determine if a
seeding experiment should be performed. It is gen-
erally accepted that successful seeding of cold clouds
for the enhancement of precipitation requires as a
critical but not necessarily sufficient conditio~, the
presence of supercooled liquid and a relative absence
of ice. However, these conditions are not always
readily recognized; therefore one objective of the
SCPP is to develop improved techniques for identi-
fication of regions in clouds that have seeding poten-
tial. We now show that the microwave radiometer
may provide part of the means to achieve this im-
provement.