WMOD00509

• Title: Physics of Winter Orographic Precipitation and it's Modification - Summary of Presentations
• Date: 10/1/1985
• Weather Modification - Doc Type: Report

In-cloud observations were made by f"lying a pre-selected flight track
on radials extending eastwards over the mountain ranges from Cranbrook, British
Columbia. Flight levels generally ranged from 11,000 to 13,000 ft MSL,
approximately 2000 to 4,000 ft above the maximum barrier height. Minimum
aircraft flight levels were frequently within 500 feet of cloud tops. Most
clouds were broken stratiform layers with occasional embedded convective
elements.

1.2 RESEARCH AIRCRAFT

Measurements were obta i ned us i ng The INTERA/Al berta Research Counc il
instrumented research aircraft. This Cessna 441 Conquest turboprop aircraft is
equipped to perform a variety of atmospheric studies including cloud physics
and air qual ity resE~arch. The results presented here were obtained on the last
three field seasons and were obtained with essentially the same research
aircraft instrumentation system configuration..

Aircraft instrumentation encompasses a variety of sensors including the
following used in this study: an E. G. and G. dew point sensor, a Rosemount
total temperature sensor, a Johnson-Williams hot wire liquid water content
probe and a platinum wire reverse flow temperature sensor (NCAR design). Four
probes from Particle Measuring Systems are located at the belly location: ASASP
(aerosols o.i to 3 um), FSSP (cloud droplets 0.5 to 47 um), 2-D C Probe (ice
crystals, 25 to 800 urn), and a 2-D P Probe (precipitation particles 0.2 to 6.4
mm). Position keeping is accomplished using a Litton inertial navigation
system. Instrument data are sampled through a CAMAC modular interface, managed
by a computer based system and are stored on a streaming tape drive. Data
analysis is performed on the ground using a VAX 11/780 computer. A more
complete description of the aircraft system is listed in Cheng et al, 1985.

1.3 CLOUD MICROPHYSICAL CLIMATOLOGIES

r

The generalized results of the microphysical measurements made on these
seven days are given in Tables 1 and 2 for all "in-cloud" data. "In-cloud"
data points were identified as those one-second values where either a droplet
concentration greatE!r than 10 cm-3 was indicated by the FSSP or an observation
of ICC greater than 1 L-1 was indicated by the 2D-C. Liquid water measurements
were derived from FSSP probe data for all Cillses except for the February 1984
1'1 ights. Thi s was due to problems initially encountered with the operation of
the J-W probe. LWC values for February used the J-W measurements after
instrument problems with the FSSP precluded quantitative LWC measurements.

The values in Tables 1 and 2 represent the arithmet i c average of all
in-cloud one-second data averages. Included are the 1'1 ight date, number of
one-second in-cloud samples, environmental temperature at measurement level,
liquid water contents, ice crystal concentration, ratio of liquid water to ice
crystals and mean ice crystal diameter. The LWC/IC ratio expresses the amount
of water available per ice crystal and has been suggested as an index of
"seedability" (Heggli, et al, 1983).

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