WMOD00402

• Project Name: Sierra Cooperative Pilot Project
• Title: Sierra Cooperative Pilot Project - Final Report for Period November 1984 - September 1986
• Date: 6/1/1987
• Weather Modification - Doc Type: Report

1.12

The engines were started at 13:15, PST and this is apparent in the
SF6 noise level increase. Takeoff occurred at 13:32 and the aircraft
climbed to about 2400 m ASL. The SF6 instrument was readjusted at 13:44.
The climb is annotated A, Band C at 13:36, 13:42 and 13:46. The chart is
also labeled along the track at A, Band C so there is a direct reference
between strip chart times and aircraft positions.

Figure 1.3 shows encounters with the SF6 at 13:49, 13:53, 14:05, 14:10,
etc. The chart scale was changed at about 14:36 to expand the scale by a
factor of five so it would be easier to follow. The map, Figure 1.7, shows
the ground release point for the SF6 on the experiment of 22 April 1985 as
a broad arrow. The thin arrows show the hill around which the aircraft
concentrated its sampling path. The SF6 drifted roughly in the direction
of the broad arrow. The day was clear and sunny, with continuous convec-
tion and a moderate wind until later in the day.

In Figure 1.4, the chart shows race track patterns which correspond with
turns near the narrow arrows in Figure 1.7. In Figure 1.4 there are strong
SF6 traces recorded at 15:24, 29, 33-1/2, 38, 41-1/2, 46 and 50 (last are
,in Figure 5). These are near positions (A-B), C, 0, E, F, G and B which
locate at 1, 2, 3, 4, 5 and 6 as marked over the chart of Figure 1.4.

The observed positions for the SF6 are clustered on the northwestern
flanks of the mountain, near the 5513 ft peak, on the upwind side but on
the downwind side they are further to the south. one chart division in
latitude is 24/5 nautical miles, or about 5 NM.

The points on Figure 1.4 with the crosses are copied from Figure 1.5,
where the major SF6 detection points are marked.

The comparison of the points on Figure 1.4 with the release point
marked on the map, where distances are about the same scale, suggests an
apparent change in the drift direction from about 1100T to l600T after
crossing the peak.

There is a strong correlation between altitude changes and SF6 signal
which is evident from the plot. There is little doubt, however, that no
SF6 was detected upstream from points 4 and 5 in Figure 1.5 on the higher
run, at a location just before point K. on the following reverse leg there
does seem to be some SF6 after point L. The aircraft altitude was reduced
by about 500 ft to about 110 or 200 ft above terrain for the detection at
points 4 and 5. Since SF6 was not found at one of the higher runs upstream
this seems to indicate that the SF6 may tend to remain close to the ground
even when there is appreciable convection.

Flights were conducted on the following dates: 26 March, and 7, 9,
10, 11 and 22 April 1985. The flight yielding most information was the
22 April mission.

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