Physics of Precipitation in Winter Storms at 
Santa Barbara, California 
Ciement J. Topp 
Meteorology Research, Inc., Altadena, California 
Abstract—The immediate purpose of the physical analysis of storms at Santa 
Barbara, is to increase the sensitivity of the statistical analysis, (a) by finding physical 
explanations of as much of the variability between target and control as possible, and 
(b) by finding physical methods of classifying which precipitation mechanisms are 
operating in order that the storm periods may be stratified according to a reasonable 
hypothesis of seedability for a statistical test. 
Introduction—Meteorology Research, Inc., is 
engaged in a study using radar and other tools 
of physical analysis to see what light can be shed 
on the physics of natural and seeded precipita- 
tion in Southern California winter storms. The 
study is in conjunction with the Santa Barbara 
Cooperative Seeding Project. The Cooperative 
Seeding Project was designed as a statistical 
study to evaluate a commercial seeding opera- 
tion. In the design of the statistical experiment 
the primary concern is on safe guards against 
all sources of bias. 
The seeding operation is as follows: if the 
commercial operator forecasts the ensuing twelve 
hour period to be seedable he is instructed to 
seed or not to seed according to a random pro- 
cedure controlled by the statistician. The physi- 
cal observations are all passive. 
Physics of rain distribution—Probably for a 
long time to come the best estimate of what 
would have been the unaffected precipitation 
over a target will come from the comparison of 
the actual precipitation in an unaffected control. 
There have been many attempts to make this 
comparison more sensitive by stratifying the 
storms according to synoptic scale types. Our 
approach is to go to the mesoscale and vertical 
structure and classify the storms ito short pe- 
riods that have physical similarity. 
Operating a 3-cm radar at La Cumbre Look- 
out on a 4000-ft ridge six miles north of Santa 
Barbara for the last three years has convinced 
us that there are several different types of storm 
periods. The types are apt to persist for several 
hours at a time and they reoccur in different 
storms and in different years. The consistency 
of types is no doubt due to dominance of terrain 
effects. Only the surface has been scratched in 
understanding the significant physical causes of 
the different types, but we have a faith that 
understanding will come from inquiry. 
Just scratching the surface has shown that a 
most pronounced rain anomaly is associated with 
the height of the stability layer. If it is low 
with respect to the ridge of the Santa Ynez 
Mountains, the surface air does not flow easily 
over the range. It piles up and is forced out to 
the west, as indicated by strong east surface 
winds at Santa Barbara. Figure 1 shows a cross 
section of the February 25, 1958 storm, an un- 
oap 16P. o4P 16P 
ao FEB 24-25 ] 
—TEMP~0.P*C) 1958 
—- AIR TEMP: 
ast 4 
L 250MB 
| 
| 
so+ 
2et 20°C 
20°C 
20+ sal 
——— 500 
STABLE 
| HEIGHT (THSDS. FT.) 
A 
| Sra BED 
TIME - HEIGHT STORM STRUCTURE 
Fic. 1—Time-height cross section over Santa 
Barbara for February 24-25, 1958, a typical low- 
level stable layer storm; broken lines represent air 
temperatures in °C; solid lines, the difference be- 
tween air temperature and dew point 
402 
