HUMIDITY 43 
Table 49. Frequencies of hours of occurrence of minimum vapor pressure, Carnegie, 1928-29 
Local mean hours 
G 
ae EEE EEE 8 
I 1 1 
I BAB 1 fs wee 2 2 ye 
IV tas 3 2 1 1 1 1 
v aoe Bee o55 1 2 ae 
VI 1 1 me 2 
Vil 
( 1 1 3 2 1 1 
(b 1 1 1 1 =e re 
VI Ses 1 2 vee 1 2 
Ix 555 555 200 1 2 1 
x ahs 1 1 1 uf 1 
XI 1 2 3 2 1 1 2 
XII 2 3 2 1 3 3 1 
xl 
{3} 5 1 2 3 2 3 ane 
b 1 mae 508 300 1 
XIV 2 nee 2 2 1 2 
XV 1 noG 1 ane 1 1 
XVI Sec 1 eee ace 
XVII 
a 1 eae 1 
b ae 1 was 2 
c 1 3 1 1 1 1 
XVII 3 1 2 3 
mS Coe ee 
el nd a Oc 
1 2 2 3 
sor 208 1 i 1 "2 ane aoe 
il 2 2 2 4 2 sce 
4 4 1 sac 2 Sec 1 
1 1 506 1 Sc6 1 
1 1 2 1 1 ad0 
3 1 4 1 6 1 4 3 
2 1 1 noe 1 2 1 
208 1 505 1 1 1 oe 1 
2 3 1 1 1 1 sab 5c6 
2 2 1 260 2 ac0 CoE soe 
2 2 2 1 1 1 1 1 
1 a08 3 1 3 5 3 1 
1 1 502 1 1 oar 
3 1 1 3 1 1 2 
oa 2 oes 
1 1 1 1 1 1 ane s08 
2 1 2 2 1 S62 1 
3 1 2 nos 266 2 
1 3 1 4 2 

Table 50. Frequency distribution of the 
unperiodic diurnal amplitude of vapor 
pressure, Carnegie, 1928-29 
Range No. P ca Cumulative . 
(mm) days et percentage 
<1 (see 32 10.4 10.4 100.0 
1-2 144 47.1 57.5 89.6 
2-3 92 30.1 87.6 42.5 
>3.0 38 12.4 100.0 12.4 
Total 306 UO osanadon  eocése0 
est in the SouthGreenland Group. It might be mentioned 
that the prevailing winds during most of the period that 
the Carnegie spent in the South Greenland Group were 
from some northerly direction, and thus it may be as- 
sumed that much of the air imported to this region dur- 
ing the period was Polar Continental. 
The frequencies of hours of occurrence of maximum 
and minimum vapor pressure are illustrated in tables 
48 and 49. It can be seen that the data are quite scat- 
tered, although there is positive indication that the max- 
imum vapor pressure tends to occur around 14h with the 
greatest frequency. This result appears reasonable in 
that the period falls between the most frequent hours for 
maximum sea-surface- and air-temperature occurrence 
(15h and 13h respectively). There is also a slight indi- 
cation of a tendency toward a secondary maximum fre- 
quency at 06h. We should expect this hour also to pre- 
sent the maximum stability in the air immediately above 
the sea surface. Under such conditions it is conceivable 
that this hour might frequently be one of maximum vapor 
‘pressure in that convection would not be mixing the 
Table 51. Mean unperiodic diurnal amplitude of vapor 
pressure for ranges in latitude, Carnegie, 1928-29 
Range in | Ampli-| No. | Range in | Ampli- 
latitude tude jdays latitude tude |days 
° ° ° mm 
>45.N 0.8 27 5N- 5S 1.8 34 
45 N-35 N 2.2 26 5 S-15S 1.8 37 
35 N-25 N 2.3 40 15 S-25S 2.0 31 
25 N-15 N 1.9 32 25 S-35 S 2.1 24 
15 N- 5N 2.2 46 35 S-45 S 1.4 9 
Mean and 
GAEL 7 aatonassogne 1.8 306 

moist surface layers of air with drier air aloft.2 We 
should expect this effect to be most pronounced during 
clear, calm weather and especially when the sea-surface 
temperature is very near the surface air temperature. 
The minimum vapor pressure seems to occur 
around 05h with the greatest frequency, simultaneously 
with the most frequent hour for minimum air-tempera- 
ture occurrence. This is exactly the result which would 
be expected under average conditions. 
Diurnal Variation of Vapor Pressure 
General Remarks 
Table 44 contains the mean hourly values of vapor 
pressure for the various Groups of Carnegie data. It 
will be noted that there is considerable variation in the 
4 There is also a strong possibility that a tendency 
to wash-down the decks of the Carnegie at about this 
hour would frequently account for such maxima. 
