WMOD00275

• Contract/Permit #: 85-5071
• Title: Cooperative Weather Modification Research Program - 1985 Analysis Plan
• Date: 1/1/1985
• State: UT
• Weather Modification - Doc Type: Report

.

.

.

.

.

,.--..'"

.

.

.

.

.

Experiment 5: Hydrometeclr trajectories

Lead Scientist: Alexis B. Long, DRI

Participating Scientists: IRobert A. Kropfli, William R. Moninger,
Taneil Uttal, WPL
lLewis O. Grant, Robert M. Rauber, CSU
INorihiko Fukuta, Kenneth Sassen, UU

The objective is to describe the trajectories taken by hydrometeors

as they grow from cloud to precipitation sizes. Trajectories of hydro-

meteors which do not grow will also be described. The primary analysis

technique will involve the La~~rangian tracking of identifiable moving

features in the C-band radar pattern of reflectivity factor (Z) and in

the Ka-band radar patterns 01' equivalent reflectivity factor (Ze) and

circular depolarization ratio (CDR). If particles within a feature grow

these variables should 'change in specified ways. Tracking of features

will be based largely on thie Doppler particle motion data. The

dual-Doppler data will be more useful in this respect whether collected

in the elevation scan mode along the connecting baseline with the wind

in that direction (see Fig. 2) or in the volume scan mode (see Fig. 3).

Since dual-Doppler data will bE! of limited coverage and frequency some

of the trajectory analysis will utilize particle velocities estimated

with the V AD technique or from data collected with elevation scans in

the plane of the average wind.

Some hydrometeor trajectories will be estimated from the chaff-

tracking data.

So long as th,e chaff has a vertical velocity similar to

that of hydrometeors, the chaff should go where the surrounding hydrome-

teors go. When the hydrometeors are small cloud particles, however, the

chaff will fall more rapidly, and when the hydrometeors are large preci-

pitation particles the chaff w ill fall more slowly.

Chaff trajectories

31