PRECIPITATION AS REVEALED BY RADAR 
83 
MOIS FIRST 
aoe ECHOES 
N=77 
20- T=-9.1 
r ‘cal JUL 20 
o 32 24 -16 -8 fo} +8 -16 
40 40 
N=31 firma N= 31 
elk T=-15.4 Viola 420 
beats filorscl 
= = =a = 15 
=32i a 2d mcsiGry Tee Oo. 6+8 =\6anmes Ons +85 416 
= N=26 N= 26 5 
cs = ee 
toned T=-15.1 T=42°5) 420 7) 
12) 
« t JUL 27 5 a 
esl [ II i r= al a gha: 
-32 -24 -16 -8 fo) +8 “16 -8 oO +8 +16 
; 2a 60 | 
ot | > 
mao N= 30 N=30 ile 
2 e 
wie ft 7-913 T=+8.0 lees 
@ 20r a 420 9 
WwW 
[ (ce a ey es ss ae ll eee 
a 
i io. fo J! L 3} 4 fo) - 
EFA 24 16 -8 {e) +8 16 =6 fo +8 +16 
w WwW 
> N= 26 — es 
= 20 T==9'5 | a {commer 
aoe 
Z ol lal Wj, e 
Ww 
a 0° an ZaREEEIG -8 lo} +8 ers 
40 — 40 
N=67 
=a al 
ae TW =2.1 ile 
4 
eee ine 
32 -24 -16 -8 ie) +8 
40 40 
L N= 32 4 
20h M1316) 420 
L el eel 4 
Al aoe : 
40 = -32 -24 -16 -8 {e} +8 
TEMPERATURE-DEG C 
-16 +8 +16 
-8 fe} +24 
TEMPERATURE-DEG C 
Fra. 5—Frequency distributions of the temperatures at the tops and 
bases of first echoes for each of the seven days studied; a few cases for which 
top height measurements were questionable were not included, causing the 
small discrepancies noted in sample sizes (N) 
tiation of precipitation by the ice and water 
mechanisms. The differences in the thermal and 
humidity structure of the atmosphere from day 
to day were relatively small, and no correlation 
could be found between the heights of echo for- 
mation and the small fluctuations in the heights 
of the condensation and freezing levels. 
Since the sizes and kinds of condensation nu- 
clei certainly must be a factor in determining 
the time required for the condensation-coales- 
cence mechanism to produce precipitation-size 
drops, it is suggested that a possible explanation 
of the day-to-day differences mentioned above 
may lie in the variations in the sizes and kinds 
of nucleating agents in the atmosphere. A pro- 
gram for the sampling of condensation nuclei 
may well prove enlightening. 
The data reveal that a condensation-coales- 
cence process is effective in initiating precipita- 
tion, even in an arid mountainous region. More- 
over they indicate that precipitation may be 
initiated either by an all-water process in the 
lower reaches of a cloud or by the ice-crystal 
mechanism in the upper reaches or both, either 
simultaneously or one lagging the other. A criti- 
cal parameter is the time required for these 
mechanisms to develop large drops. The factors 
deciding the time constants remain to be deter- 
mined. Unexplored also is the problem of the 
relative efficiency as far as surface rainfall is 
