WMOD00439 - Laserfiche WebLink

Home Browse Search

APRIL 1984 SMITH ET AL. 511 pass through the cloud about 2 min after treatment. (The depolarization signal is believed to indicate only about 25% of the actual ice-crystal concentration.) The average was computed over a I km distance contained within the 4 km flight segment centered on the closest approach to Pointer I. That I km distance was required to have an average cloud liquid water concentration > 0.1 g m -3 and the suitable I km path with the highest average ice-crystal concentration was used to define CIC2. That 1 km path was expected to be the center of the seeding plume, if any. In cases where the mea- sured cloud liquid water concentration was less than 0.1 g m-3, the median observed value for the cloud class involved was used as a default value. CIC5: The computation was similar to CIC2, but was based on an average over a 2 km distance contained within the 4 km flight segment centered on the closest approach to Pointer I during the second post-treatment pass, about 5 min after treatment time. The 2 km leg with the highest average ice-crystal concentration was used, and the constraint on L WC was removed. CCR5: The concentration of rimed ice crystals as determined by analysis of a decelerator slide exposed (for approximately 5 s, or 0.5 km of flight) within a 2 km flight segment centered on the closest approach to Pointer 2 during the pass 5 min after treatment time. PIC8: The average number concentration of pre- cipitation-sized ice particles, taken over a 4 km distance centered on the closest approach to (the vertical pro- jection of) Pointer I during the pass about 8 min after treatment. Only particles observed to be 0.6 mm in size (three "pixels") or larger by the PMS 2D-P probe were included in the calculation. MVD8: The mean volume: diameter of the precip- itating ice particles included in PIC8; defined by (MVD8)3 = L: mm n(D)D3dD / L: mm n(D)dD where D = particle size. If n(D) = 0 for D ~ 0.6 mm, 0.6 mm was taken as a default value (see Section 5 for a discussion of the reasons for this). A WC8: The average cloud liquid water concentra- tion measured overthe same path used in determining PIC8, by the Johnson-Williams cloud liquid water concentration sensor. TFPI: The time (since treatment time) at which the first concentration of precipitating ice particles (~0.6 mm in size) exceeding 0.1 L-' was observed. The av- erage concentration over a distance of I km contained entirely within a maximum distance of 6 km from (the vertical projection of) Pointer I was used, The value of TFPI was not available in real time during the experiment. The cloud physics aircraft therefore remained at the -50C level until 17 min after treatment time, unless the aircraft radar indicated an echo within 5 km of Pointer I. In that case, it made one pass through the center of the echo. In either case, it then descended to the + 100C level for observations of the precipitation shaft below the cloud base. If the con- ditions for TFPI were not met at the -50C level, a default value of 1020 s (17 min) was used. TFE: The time (since treatment time) of the first appearance of a 15 dBz echo measured by the SWR- 75 radar. This echo had to appear within the box de- fined by the analyst on the basis of the reported location and time of the treatment, the estimate of the diffusion of the ice crystals, and estimates of wind drift of the cloud. If no 15 dBz echo appeared during the test case duration, a default value of 2400 s (40 min) was taken. TIPA: The time (since treatment time) at which a rainfall rate in excess of I mm h - I averaged over a I km distance was first observed at the + WOC level. The I km distance had to lie entirely within 8 km of the (vertical projection of the) location of Pointer 1. The rainfall rates were computed according to the procedure described by Cooper (1980). If the criteria for TIPA were never met during the test case, a default value of 2400 s (40 min) was taken. TIPR: The time (since treatment time) of the first appearance of a 15 dBz echo at the + 100C level, as observed by the SWR-75 radar. This 15 dBz threshold is lower than that which would correspond to the I mm h -I rainfall rate threshold used for TIP A, according to most Z-R relationships. However, the I km path used in computing TIP A was smaller than the reso- lution capability of the radar over most of the area, so the measured reflectivity from the radar resolution cells might well be smaller than the I mm h-I rate would suggest. If the criteria for TIPR were never met during the test case, a default value of 2400 s (40 min) was taken. AER: An estimate of the rain volume from the cloud, based on data from the PMS 2D-P probe on the cloud physics aircraft. The rather involved procedure for cal- culating AER is spelled out in Cooper (1980). RERC: An estimate of the rain volume from the cloud computed from the SWR-75 radar data from the + 100C level, using the relationship Z = 520RI.35 which is based on the exploratory studies in Montana with conventional space and time integration proce- dures. REFERENCES Arnesen, K. R., 1982: Analysis of HIPLEX-I raindrop data from 1979 and 1980. M.S. thesis, Dept. Meteor., South Dakota School of Mines and Technology, Rapid City, SD, 36 pp. Bethwaite, F. D., E. J. Smith, J. A. Warburton and K. J. Heffernan, 1966: Effects of seeding isolated cumulus clouds with silver iodide. J. Appl. Meteor.. 5, 513--520. Braham, R. R., Jr., L. J. Battan and H. R. Byers, 1957: Artificial nucleation of cumulus clouds. l\.leteor. Monogr., No. II, Amer. Meteor. Soc., 47-85. Bureau of Reclamation, 1977: Summary report: HIPLEX design workshop, 5-9 December 1977, Dillon, CO. Bureau of Rec- lamation, U.S. Department of the Interior, Denver, CO 79 pp.