WMOD00293 ‎(2)‎

• Contract/Permit #: 14-06-D-6467
• Project Name: Project No. 15-1371-1113
• Title: A Case Study of the Water Budget of an Orographic Cloud
• Prepared By: L. K. Balick, J. L. Rasmussen
• Date: 5/1/1972
• State: CO
• Country: United States
• Weather Modification - Doc Type: Report

6

Where 8 is potential temperature, L is the latent heat of condensation,

~

w is the mixing ratio, Cp is the specific heat at constant pressure and

Ts is the temperature at which the parcel would be saturated if lifted

adiabatically. The trajectories are based upon the determination of

travel times of parcels between stations, the wind analysis, and the

restriction to conserve the equivalent potential temperature.

The location of the condensation for individual trajectories then

is determined from the initial humidity and temperature of the air

parcel lifted along the trajectory to the lifting condensation level

(LCL). The locus of points indicating condensation for each trajectory

then defines the upwind border of the cloud. The top and bottom of the

cloud are limited by trajectories along which condensation is not reached.

The downwind edge of the cloud must be subjectively placed.

"',

Integer values of 8e trajectories are used to define the edges of

0;;

volumes of air channels through which the air flows without mixing across

the isentropes (lines of constant 8e). The exchange of mass then must

take place at the ends. The water balance is computed for each of these

channels by evaluating an equation similar to that of Elliot and Hovind

(1964) or Rasmussen (1970). Assuming no evaporation from the ground

and that the mixing ratios of liquid water and ice are small enough to

be negligible for our purpose, the equation may be written

c

1
g

J f cnwdldp
dp dl

(2)

..

..

C is the rate of net condensation, g is the acceleration due to gravity,

cn is the component of the wind normal to the volume and defined posi-

tive outward, w is the mixing ratio of the water vapor, dl is the line