WMOD00466

• Title: Dynamical and Microphysical Characteristics of Winter Storms over the Sierra Nevada
• Weather Modification - Doc Type: Report

i 'i

DYNAMICAL AND MICROPHYSICAL CHARACTERISTICS

OF WINTER STORMS OVER THE SIERRA NEVADAS

John D. Marwitz and Ronald E. Stewart

University of Wyoming
La!amie, Wyoming

James A. ~10ore

U. S. Bureau of Reclamation

1.

INTRODUCTION

The Department of Atmospheric Science
at the University of Wyoming participated in the
1977-78 Sierra Cooperative Pilot Project (SCPP).
The Wyoming participation was with their newly
instrumented Beechcraft King Air cloud physics
aircraft. Two objectives were pursued by the
Wyoming group. They were to study the natural
dynamical and microphysical characteristics of
Sierra Nevada storms and to conduct transport and
diffusion (T&D) experiments which closely simula-
ted T&D during actual storm situations. In this
paper we will only discuss some preliminary re-
sults from the first objective.

The SCPP had a number of components
among which were the cloud physics aircraft oper-
ated by Wyoming, a.S-cm radar and rawinsonde
operated by North American Weather Consultants,
two 3-cm Doppler radars operated by NOAA/WPL, a
S-cm Doppler radar operated by NCAR, a tracer/
seeder aircraft operated by Aero Systems, Inc.
and surface microphysics, precipitation and over-
all project direction by the Bureau of Reclama-
tion. Even though the tri-Doppler system and
tracer/seeder aircraft were not present in Dec:-
ember, it was considered worthwhile to describe
some preliminary results in this and other papers.
We mutually considered the storm of 14-15 Decem-
ber 1977 to be reasonably typical and the best
documented of those studied in December 1977.

2.

THE KING AIR DATA SYSTEM

The newly instrumented cloud physics
research aircraft is a Beechcraft Super 200 King
Air. This was the first field project in which
it was used. As such there were a number of
early failures of aircraft and data system com-
ponets plus a continual process of training new
crew members as well as developing procedures and
flight plans which would maximize the research
efforts.

To study the orographic storms it
was desirable to fly as close to the mountain
parrier as legal, and safety requirements would

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allow. Since the aircraft was equipped with a
flight director system i.n which up to ten way-
points could be inserted, and flown in any de-
sired sequence, a letter of agreement Wa$ devQl-
oped among Oakland ARTCC, The Bureau of Reclama-
tion and the Department of Atmospheric Science.
The letter of agreement allowed Wyoming to fly
minimum obstruction clearance altitudes (MOCA) if
they accepted responsibility for mainta:1.ning their
own clearance of 2000 ft above and 5 NMi fro~ all
obstructions along their proposed flight path.
With this agreement and the assistance of the var-
ious FAA controllers, we were never restricted in
flying the research missions as desired.

The position keeping of t.he aircraft
was maintained by recording DME/vOR as well a.
heading, static pressure, indicated airspeed and
rate of climb. The horizontal winds were obtain-
ed with a Doppler navigation system Bind a deiced
yaw angle sensor located on a nose boom. The
vertical velocities were obtained witl. a vertical
accelerometer, pitch and roll gyros plus a deiced
angle of attack sensor also located on the nOS8
boom. Two temperature probes were rE~corded: a
reverse flow and a Rosemount probe. The moisture
sensor was a dewpoint hygrometer. The cloud phy-
sics instruments consisted of four Particle Mea-
surement Systems probes which covered the range
of particles from I to 4500 pm. Two of the ima-
ging probes were 2-D probes. In addition, a J-W
liquid water content sensor, an MRI turbulence
sensor, an NCAR ice nucleus detector, a rotating
filter sampler for ice nuclei and a decelerator
for collecting ice crystals were also included.

To optimize the research missions the
scientist-copilot and scientist-data system oper-
ator could independently select any Ii of approxi-
mately 200 voltages, counts or derived parameters
for real time digital display. In addition the
scientists could view on a storage scope histo-
grams from the l-D PMS probes or images from the
2-D PMS probes. To further.optimize research
missions, to maintain data quality control and to
justify placing a number of scientists in the

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