Z 
Z 
pu 
+4 
| 
| 
| 3 3 4 5 6 AD 
Fic. 7—Raindrop size distribution expected 
from ice origin rain is shown by straight line; 
dashed line shows goodness of fit of Sample 10 and 
11 
origin and that ice precipitation started just 
before 20h 00m and is represented in Sample 10 
and 11. 
Figure 4 is a time-height cross section of this 
storm. The warm cloud precipitation occurs 
when the top of the moisture layer is lower than 
—5°C. Ice precipitation starts when it goes above 
—5°C. Incidentally, this storm was seeded. Ice 
precipitation becomes general when the top of 
the moisture layer is above —15 or —20°C. 
Sometimes the drop size distribution indicates 
that the two precipitation processes occur to- 
gether. 
We have not yet been able to go far enough 
to separate the artificially induced and natural 
ice precipitation on anything approaching the 
DISCUSSION 
general case. We will have to intensify our phys- 
ical measurements. Equipment is now on hand, 
such as vertical radar, electronic raindrop size 
counters, along with more potential gradient 
devices and nuclei counters. These did not re- 
ceive full field application this year due to the 
history making dry period the latter half of the 
seeding season. In addition to the above it would 
be very helpful to make coordinated aireraft ob- 
servations on top of the storm. 
Comments—Mesoscale analysis combined with 
appropriate physical observations will certainly 
be the backbone of seeding analysis. In order not 
to use up all available degrees of freedom it is 
of utmost importance to make intensive use of 
mesoscale analysis of historical storms. This is 
especially true here in Southern California where 
a relatively good network of upper-air soundings 
provides an extraordinarily good chance of re- 
lating mesoscale structure and seeding effects, 
where seeding has gone on for ten years now and 
where two steel foundries are highly suspected 
of producing seeding anomalies [MacCready, 
1957]. 
Conclusions—As we become skillful at using 
our physical tools, we have the possibility of de- 
veloping greatly increased sensitivity of test, 
to a degree where we will be able to check hy- 
pothesis of when, where, how much, and under 
what conditions seeding is effective. 
Acknowledgement—This research was sup- 
ported by the National Science Foundation and 
the Department of Water Resources, State of 
California. 
REFERENCES 
Bercreron, T., The problem of artificial control of 
rainfall on the globe, Tellus, 1, no. 3, 1949. 
Fusiwara, M., Formation of stationary rainbands, 
Proc., Seventh Wea. Radar Conf. I-33, 1958. 
MacCreapy, P. B., Jr., T. B. Smrru, C. J. Topp, ann 
K. M. Bresmer, Nuclei, cumulus, and seedability 
studies, Final Report of the Advisory Committee 
on Weather Control, pp., 137-200, 1957. 
MacCreapy, P. B., Jr., T. B. Surry, anv C. J. Topp, 
Discrimination between condensation-coalescence 
and ice-crystal-produced precipitation, Proc., Sev- 
enth Wea. Radar Conf. A-17, 1958. 
Discussion 
Dr. Tor Bergeron—I like this paper very 
much. Especially, I appreciate the fact that we 
see here the influence of the orography. That is 
very much to be appreciated, and of course, you 
have also used every other means at your disposal 
for the physical analysis of these precipitation 
patterns. 
I would like to repeat what I said in my open- 
