DISCUSSION 279 
Discussion 
Mr. C. J. Todd—t like Dr. Essenwanger’s idea 
of looking for discontinuities in the probability 
distribution and using them as a lead in the 
search for a physical cause. Some years ago I 
was interested in Los Angeles hourly precipita- 
tion and probability functions, and I found out 
it rained nine per cent of the hours. I plotted the 
cumulative frequency of this nine-per-cent tail 
starting at 91% on linear probability paper, and 
got a very nice straight line. 
Dr. O. Essenwanger—There are several ways 
to approach accumulated frequency amounts. As 
shown in hydrology hourly precipitation may fol- 
low a straight line in the log probability paper 
quite well, if they are from a homogeneous popu- 
lation. If we have different types of physical 
processes, depending on the regional climate, 
then it might be that this is practically a formal 
approach. The result is caused by the fact that 
one is missing the small precipitation amounts. 
The frequency distribution is practically trun- 
cated. 
Dr. Tor Bergeron—I was very impressed to 
see what you could achieve just only by statistics 
of precipitation frequencies. From my experience 
with precipitation maps of all sorts, of all scales, 
and in many countries, I have always been look- 
ing for maps containing what I call a one-factor 
rain, and it has always been very difficult to find 
typical one-factor rains from daily precipitation 
measurements. We would like to have precipita- 
tion observations twice a day, as in the tele- 
graphic reports. There is not a sufficiently large 
number of stations, but we would be so much 
better off. The 12-hour period often manages to 
take a one-factor rain. The 24-hour period does 
not. I have no figures, just general experience, 
and I would like to invite Dr. Essenwanger or 
somebody else to look into this matter. If the 
figures could be produced, then this could per- 
haps be recommended and carried through in 
the WMO. Although, as you know, it is generally 
easier for the observers to measure once a day in 
the morning upon arising. 
Dr. Essenwanger. 
I can support Professor 
Bergeron’s remark absolutely, because this is 
just what I wanted to say. Our daily amount is 
probably not sufficient for a subdivision into 
physical collectives. I rather would like to see 
very short periods like hourly amounts and then 
everybody who works in this field can analyze 
the period he likes. But this is probably not pos- 
sible, at least on a world-wide basis. 
Dr. Bergeron—Hourly amounts one can get 
in the United States, but you can not get them 
anywhere else. That 1s why I propose twelve 
hours. 
