PRODUCTIVENESS OF FOG PRECIPITATION 
at 8 to 9 ». The efficiency of fog precipitation is 
scanty. Types e¢ and d are maritime warm air 
masses from moderate (Type ¢) or subtropical 
(Type d) zones. The droplet spectrum then indi- 
cates a broader range of 4 to 25 » and a most fre- 
quent diameter of 8 to 14 1. Fog precipitation be- 
comes more and more productive. The deposits 
are heaviest with amounts of 2 to 8 mm/h in case 
of non-raining cloud decks formed on the wind- 
ward side of the Alps. The air masses are often 
degenerated by continental influences and the 
droplet spectrum indicates a wide range from 5 
to 60 » with a maximum number at 12 to 18 
p. This result conforms with investigations of 
Mahrous [1954], who established the increase of 
droplet sizes as typical evidence of degeneration 
in the dense coastal fog in England. In the case 
of a narrow spectrum with smaller diameters of 
droplets a meridional circulation exists whereas 
the broad spectrum predominantly shows up with 
zonal circulation. Selected cases of these two 
types are demonstrated, with the microphoto- 
graphic records of droplets in Figures 5 and 6. 
Water content of samples—The different pro- 
ductiveness of these types of fog precipitation 
classified according to the droplet spectrum is 
easy to understand if the water content of each 
sample is caleulated from the product n-7/6-D*. 
With increasing droplet diameter D the water 
115 
content grows rapidly even if the concentration 
n of these droplets is small. Integrated over the 
whole spectrum, the results for the samples are: 
Type a, bie, di se 
Total water content* 3 23 76 105 473 
* Unit is 10° mm’. 
Even this rough estimate indicates that the pro- 
ductiveness of fog deposit in case of a broad spec- 
trum is a direct consequence of the microphysi- 
cal structure of the clouds. 
REFERENCES 
Dirm, M., Messungen der Grésse von Wolkenele- 
menten, Met. Rdsch., 1, 261-273, 1947. 
Grunow, J., Nebelniederschlag: Bedeutung und 
Erfassung einer Zusatzkomponente des Nieder- 
schlags, Ber. Deut. Wetterd. US-Zone, 7, no. 42, 
30-34, 1952. 
Grunow, J., Vergleichende Messungen des Nebel- 
niederschlags, Assn. Int. Hydrol. Sci.. IUGG, 
Publ. 44 Gen. Assembly, Toronto, II, 485-501, 
1958. 
Manrovs, M. A., Drop sizes in sea mists, Q. J. R. 
Met. Soc., 80, 99-101, 1954. 
Nace, J. F., Fog precipitation on Table Mountain, 
Q. J. R. Met. Soc., 82, 452-460, 1956. 
Tapata, T., T. Huztoxa, anp N. Matsumura, On a 
recording fog meter, Studies on fogs in relation 
to fog-preventing forest (T. Hori, ed.), Tanne 
Trading Co., Sapporo, pp. 169-173, 1953. 
Discussion 
(Relating to the two immediately 
preceding papers) 
Dr. C. E. Junge—Figure 3 of the paper just 
presented showed the increase of precipitation. 
This was the total increase plotted against area 
where there is no fog precipitation, is that right? 
You had figures of 200 to 300%. 
Dr. J. Grunow—The figures represent only the 
additional fog precipitation amount deposited 
on the wire net of the gage at different mountain 
stations, without any consideration of rain or 
snow. 
Dr. Junge—#. Eriksson, for instance, found 
that in Scandinavia the total amount of sea 
salt which is deposited from the atmosphere is 
approximately three times higher than can be 
accounted for by precipitation. The mountains 
in this area are often within clouds and the in- 
crease of precipitation by fog drip may be con- 
siderable and may explain the increase in sea 
salt deposit. 
Dr. Grunow—At some places in higher alti- 
tudes, for instance, on the mountain station 
Wasserkuppe we have found the same result. 
The most interesting point where measurements 
were made with this type of gage, is Table Moun- 
tain in South Africa. In January 1955 the ad- 
ditional fog precipitation was tenfold the rain 
precipitation. In the annual average the unit 
with fog gage received four to fivefold the catch 
of the rain gage. According to the very critical 
evaluations of Nagel there was an assured excess 
of 1.7 fold of rain, derived only from days with 
fog without drizzle or rain. The best conditions 
for deposit are given if fresh maritime air masses 
are in action. 
Dr. Junge—One more question: These 200 
to 300% resulted from measurements with the 
