WMOD00289 ‎(3)‎

• Title: Augmentation of Rainfall from Summer Cumulus Clouds
• Date: 2/5/1983
• Weather Modification - Doc Type: Report

6

TABLE I

HIPLEX-l primary response variables

1. C1C 2, Cloud ice concentration, 2 min after treatment
2. CIC 5, Cloud ice concentration, 5 min after treatment
3. CCR 5, Concentration of crystals rimed, 5 min after treatment
4. PIC 8, Precipitating ice number concentration, 8 min after treatment
5. MVD 8, Mean volume diameter of precipitating ice particles, 8 min after treatment
6. AWC 8, Average liquid water concentration, 8 min after treatment
7. TFPI, Time to first precipitating ice (particles with diameters> 0.6 mm in concentra-
tions > 0.1 I.')
8. TFE, Time to first radar echo (15 dBZ)
9. (a) TIPA, Time to initial precipitation at +10oC level, aircraft measurement
(b) TIPR, Time to initial precipitation at +lO'C level, SWR-75 radar (15 dBZ)
10. (a) RERA, Radar-estimated rainfall at +10oC level, Z-R relationship adjusted by
hydrometeor measurements
(b) RERC, Radar-estimated rainfall at +10oC level, using a constant Z-R relationship
(c) AER, Aircraft-estimated rainfall at + 1 00 C level

CURRENT VIEWS ON POTENTIAL FOR RAINFALL AUGMENTATION

Canvective pracesses, including rainfall, are daminated by synaptic and
mesa scale systems which cantral claud size and arganizatian. Observatians
to. suppart this statement have been reparted fram Flarida (Ulanski and
Garstang, 1978), Texas (Tex. Dep. Water Resaur., 1982) and Mantana
(Miller et al., 1981). In general, canvergence values af 5 X 10-4 S-l ar mare
(in absalute terms) aver several hundred square kilameters are required to.
produce a majar canvective starm. The mesa scale canvergence is assaciated
with air rising at rates appraaching 0.5 m S-l in the lawer trapasphere.
Matthews and Silverman (1980) have used a numerical madel simulatian to.
demanstrate haw mesascale lifting increases the ability af the atmasphere
to suppart deep, maist canvectian.
Mast canvective rainfall is praduced by clusters ar lines af canvective cells
which require mesoscale suppart, rather than by isalated cells. Table II,
based an Jurica et al. (1981), illustrates the paint far west Texas. The small
amaunts af rainfall cantributed by is alated canvective clauds is attributable
to. the relatively small amounts af water vapor candensed in such clauds and
their law precipitatian efficiencies.
It has been suspected far a lang time that is alated cumulus clouds are in-
efficient precipitation praducers because they are dissipated by mixing with
ambient dry air befare the claud draplets have sufficient time to. caalesce
into. raindrops ar be collected by salid hydrometears (Braham, 1981). Evi-
dence an this point campiled by Canadian researchers (Schemenauer et aI.,
198!.) during experiments in Ontario. and the Narthwest Territories and
during the HIPLEX experiments at Miles City is shawn in Table III. The set
of 'Miles City' clauds referred to in Table III is nat the same as the set af