HUMIDITY 51 
from the minimum value mentioned. 
Variation of Relative Humidity 
with Latitude 
The mean values of relative humidity for the vari- 
ous ranges of latitude are presented in figure 32. It may 
be observed that the values are lowest in the subtropical 
regions between mean latitudes +10° and +30°, and high- 
est at the equator and in higher latitudes. These results 
are in accord with the conclusians which have been 
reached through similar treatment of air-temperature 
and vapor-pressure data, that is, the differences be- 
tween air temperature and vapor pressure (specific hu- 
midity) are greatest within subtropical regions. 
Hourly values of the various meterological elements 
for certain groups of consecutive days have been plotted 
and two representative diagrams are reproduced as fig- 
ures 35 and 36. The first is for seven days during Feb- 
ruary 1929, while the Carnegie was in tropical waters of 
the South Pacific between longitudes 112° and 126° west. 
The prevailing weather was cloudy to partly cloudy with 
easterly winds and moderate sea. The plot of figure 36 
is for seven days during July 1929, in the North Pacific 
between latitudes 38° and 46° north, longitudes 123° and 
143° west. The prevailing weather during this period 
Was mostly overcast with frequent rainstorms and much 
drizzle, fog, and mist. Winds were variable. 
The general features of the curves can be readfrom 
the figures. Air and sea temperatures show a strong 
tendency to follow one another. The curve of differ- 
ences between sea and air temperature correspond 
closely to the curve of air temperature. There also ap- 
pears to be a positive correlation between short-period 
changes (1 to 3 hours) in relative humidity, but an in- 
verse relation for the long-period (seven-day) variation. 
The closest correlation between differences of sega and 
air temperatures seems to be with relative humidity or 
Saturation deficit. This was verified by determining the 

Table 62. Variation of relative humidity 
with differences between sea and air 
temperature, Carnesie, 1928-29 

At Relative No. 
(sea - air) humidity | days 
"e€ o/o 
>+1.0 84.71 16 
+0.6 to +1.0 77.81 31 
<+0.6 78.31 39 
< -0.6 80.99 50 
-0.6 to -1.0 86.84 18 
>-1.0 91.06 i4 
Mean and total 83.29 166 
Weighted mean 

saturation deficit (E - e) for several series of days. In- 
variably the two curves of sea temperature minus air 
temperature and saturation deficit followed each other 
very closely in both short- and long-period variations. 
CONC LUSION 
The Carnegie data indicate that variations of vapor 
pressure and relative humidity over the oceans are al- 
Ways small and, in individual instances, highly irregular. 
Only by examining large quantities of humidity data can 
Significant conclusions be drawn concerning the relations 
between sea-surface temperature, air temperature, and 
vapor pressure. Many of the results presented in this 
chapter, therefore, are to be considered qualitative only, 
since a sufficient quantity of data is not available to 
establish the various relations quantitatively. It is quite 
possible that additional humidity observations over the 
sea will serve to change some of the views which have 
been presented here. 
