PRECIPITATION ON MOUNTAIN SLOPES POCKELS <)\ 



the specific humidity is at this cloud level, F {y)' = 9.0, and the 

 temperature is n° C. We will further assume that the upper limit 

 of the clouds is at an altitude of about 5000 meters, or y' — 4530 

 meters, where the temperature has sunk to — 13. 6° and the specific 

 humidity to &{y) =2.5. At the altitude of 3000 meters the tem- 

 perature o° C. is attained. The application of the Hertzian tables 

 assumes that for temperatures below o° C. the product of condensa- 

 tion is ice; whether this is really true is at least questionable for 

 moderately low temperatures, but the assumption that water below 

 the freezing point is precipitated will not change the results very 

 much. Since corresponding to the assumed stationary condition, 

 we have to assume that all condensed water immediately falls from 

 the clouds; therefore, in our computation we have to omit the hail 

 stage of Hertz, in which the water that is carried along with the 

 cloud is frozen. 5 



For the computation of the integral according to equation (15) 

 the cloud is divided into four layers whose mutual boundaries or 

 limits occur at y l = 1530, again y 2 = 2440, and y 3 = 3460 meters; 

 for these altitudes we have s = 1.00 and 0.912 and 0.816, and cor- 

 responding to these F(y) =6.9 and 5.35 and 3.8. 



We thus find the following values for W/a: 



XXX 



x = ± — ± - ± - 



12 8 6 



W 



— = 0.475 0.241 0.0985 0.0081 grams per second per 



square meter. 

 From this table we obtain the depth of the precipitation in milli- 

 meters per hour by multiplying by 3.6; the result is shown in the 

 lower curve of fig. 1. The values of the precipitation for a mean 

 horizontal velocity of the current of 1 meter per second are as fol- 

 lows: 



X X X XX 



x = ± — ± ± — ±— ±- 



24 12 8 6 4 



W = 1.71 1.47 0.867 0.355 0.029 



Hence, the precipitation is heaviest above the middle of this slope 

 of the mountain, where for the very moderate wind velocity of 7 

 meters per second, it attains the very considerable rate of 12 milli- 



5 The influence upon the adiabatics of condensation, whether we assume, 

 as in the Hertzian table, all condensed water to be carried with it or to imme- 

 diately fall away, is of no importance in the present problem. 



