WMOD00548

• Contract/Permit #: 6-07-DR-20020
• Project Name: Sierra Cooperative Pilot Project
• Title: Satelite Studies During the 1976-77, 1977-78 Sierra Cooperative Pilot Project
• Date: 2/1/1979
• Weather Modification - Doc Type: Report

ABSTRACT

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SATELLITE STUDIES DURING THE 1976~77 AND
1977-78 SIERRA COOPERATIVE PILOT PROGRAM

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Digital imagery from the SMS~2 geostationary satellite was recorded

for analysis in support of the Sierra Cooperative Pilot Project.

Imagery of five storms during the 1976-77 and 1977-78 seasons of the

project have been analyzed in detail using the CSU ADVISAR. Temporal

variations ~n cloud top temperature were charted and synoptic and meso-

scale cloud features have been studied.

Results show the highest precipitation and lowest cloud top tempera-

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tures, below -35 C, occur about one or two hours ahead of the surface

cold front within the frontal band. Following the frontal passage, an

unstable convective orographic cloud remains over the Sierra for up to

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8 hours, with cloud top temperatures around -lSoC, well within the

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seeding window range.

Mesoscale features including banded and cellular convection and

cloud streets have been observed by the satellite, with their effects

often showing up in the precipitation gage records. Large convective

lines and cells were tracked onshore and were found to move with the

winds somewhat below the 50 kPa level. Cells intensify in the Central

Valley of California, usually dissipating as they climb the Sierra.

Trajectories of large cells curve to the left upon encountering the

foothills, becoming nearly parallel to the mountains under certain

conditions.

Precipitation is greatest on the west slopes of the Sierra due to

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the orographic effect. Lee-side precipitation appears to be dependent

on the presence of high, cold cloud tops which lead to precipitation

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particles being carried over the crest.

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