WMOD00483

• Title: Microphysical Observations of Winter Clouds Over the Southern Canadian Rockies
• Weather Modification - Doc Type: Report

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MICROPHYSICAl CHARACTERISTICS OF WIITER ClOUDS
OYER THE SOUTHERN CAMDIM ROCKIES

F.O. Barlow, R.H. Myrick, F.E. Robitaille, J.H. Renick

Atmospheric Sciences Department
Alberta Research Council
Edmonton, Alberta, Canada

1.

INTRODUCTION

The principle water source for the
agricultural, doAestic and industrial
requirements of southern Alberta is the
accumulated winter snowpack on the eastern slopes
of the Rocky Mountains. The Alberta Research
Council has conducted preliminary research into
the feasibility of applying cloud seeding
techniques to augment this snowpack in the
southern Canadian Rockies (Figure 1). This
1 imited initial effort has focused on providing
background information on the snow climate and
winter cloud characteristics within the area.
The results of the climatological study of the
snow regime have been reported elsewhere
(Barlow, et al., 1983). In addition, an
instrumented researc,h aircraft was used to
document the characteristics of winter clouds and
to assess the efficiency of the winter cloud
systems to determine if a potential "seeding
window" exists (Renick et al., 1979). This
sur.wnary wi 11 note some orthe key findin gs of
these aircraft measurements.

2. FInD RESEARCH P~OGRAM

The major emphasis of the snow research
effort to date has been the in-situ measurement
of cloud characteristics. To this end an
instrumented research aircraft was used in March
1982 and three subsequent periods to measure t~e
mi crophysi ca 1 properties of clouds over the
southern rockies. This research has concentrated
only on documenting the characteristics of
natural clouds and no cloud seeding has been
conducted. Research flights were made on 29 days
with a combined fligtlt time of over 100 hours.
Si gnificant cloud cover was unfortunately rare
during these field periods, but measurements
within orographic cloud systems were made on 11
flight days.

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"In-cloud" observations were made by
flying a pre-selected flight track on radials
extending eastwards over the muntain ranges from
Cranbrook, British Columbia (Figure 1). Flight
levels generally ranged from 11,000 to
13,000 feet HSL, approximately 2000 to 4,000 feet
above the maximum barrier hei ght. Minilllum
aircraft flight levels were frequently within
500 feet of cloud tops. Most clouds were broken
stratiform layers with occasional embedded
convective elements.

2.1

Research Aircraft

Cloud microphysical measurements were
obtained us in 9 the INTERA/A 1 berta Research
Council instrumented research aircraft. This
Cessna 441 Conquest turboprop aircraft is
equipped to perform a variety of atllOspheric
studies including cloud physics and air quality
research. Aircraft instrumentation encompasses a
variety of sensors including the following used
in this study: an E. G. and G. dew point sensor,
a RosellOunt total temperature sensor, a
Johnson-Williams hot wire liquid water content
probe and a platinum wire reverse flow
temperature sensor (NCAR design).

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Ftpn-e 1. Alberta ~esearch Council Snowpack
Project area. The line labelled leg C is the
primary aircraft f11 ght leg radial.