36 
METEOROLOGICAL RESULTS OF LAST CRUISE OF CARNEGIE 
Table 42. Diurnal variation of weighted means and differences between temperatures of sea and air 
(uncorrected) in groups I to VII (a), Carnegie, 1928-29 
Local mean hours 
G 
rou days Rit rar ae ey es Sao 


2¢ =C ae os 2¢ °C cc °C °c we xe AG 
I 9 +0.66 +0.75 +0.87 +0.91 +0.85 +0.80 +0.88 +0.69 +0.59 +0.40 +0.06 +0.02 
84 4 +1.88 +2.06 +1.98 +1.84 +1.65 +1.39 +1.53 +1.68 +1.55 +0.83 +0.49 +0.54 
UI 13 +0.49 +0.47 +0.45 +0.46 +0.38 +0.38 +0.45 +0.45 +0.18 +0.10 -0.29 -0.54 
IV 21 +0.86 +0.93 +0.95 +0.96 +0.92 +0.86 +0.74 +0.54 +0.11 -0.30 -0.68 -0.91 
V 9 +0.43 +0.47 +0.54 +0.69 +0.68 +0.68 +0.43 +0.18 -0.02 -0.18 +0.03 -0.07 
vt 12 41.35 +1.47 +1.51 +1.39 41.42 +1.44 +1.57 +1.50 +1.35 +1.35 +1.24 +1.24 
6 
(a)35 +0.77 +0.83 +0.81 +0.81 +0.89 +0.88 +0.73 +0.48 +0.25 +0.01 +0.15 -0.17 
ROtal: WOSe aie esccsmn!eansiesy cieaciessag Kaose anche mate censpemne cease tocaaaccta naccec cen cence oon eee eee nee nee mais 
Weighted 
means +0.82 +0.89 +0.90 +0.90 +0.90 +0.87 +0.81 +0.65 +0.40 +0.16 -0.05 -0.15 
bs a ae ae Local mean hours 
ore 200) [ai | aa ea eee 
“¢ aC aC: aC xC ac aC 26 2¢ cc 2¢ <C 
I -0.05 +0.00 -0.19 -0.24 -0.29 -0.13 +0.05 +0.40 +0.59 +0.54 +0.56 +0.76 +0.40 
T -0.11 +0.46 +0.65 +1.14 +1.20 +0.84 +1.09 +1.81 42.12 +2.35 +2.29 +1.88 +1.38 
I -0.80 -0.87 -0.80 -0.74 -0.71 -0.50 -0.27 +0.09 +0.21 +0.40 +0.33 +0.48 +0.01 
Iv -0.73 -0.71 -6.51 -0.29 +0.08 +0.29 +0.51 +0.61 +0.71 +0.72 +0.73 +0.79 +0.30 
Vi -0.29 -0.32 -0.38 -0.20 +0.04 +0.48 +0.60 +0.54 +0.64 +0.60 +0.60 +0.42 +0.27 
VI +0.94 +0.80 +0.85 +0.88 +0.85 +1.06 +1.29 +1.41 +1.41 41.33 +1.41 +1.36 +1.27 
Vil 
(a) _-0.18 -0.i8 -0.13 +0.14 +0.24 +0.36 +0.54 +0.62 +0.59 +0.66 +0.61 +0.64 +0.42 
Weighted 
means 
-0.24 -0.23  -0.17 -0.09 +0.13 +0.30 +0.50 +0.66 +0.73 +0.77 +0.75 +0.77 +0.47 
variation in differences between sea-surface and air 
temperatures would be small -- about 1° --and that in 
general, air temperatures would be lower than sea tem- 
peratures during the night, and would approach and 
probably exceed sea temperatures during the day. An 
examination of table 42 indicates that such a condition 
definitely obtains where air-temperature data have not 
been corrected for radiational effects. As shown in fig- 
ure 27, however, no such simple relationship appears to 
exist in the case of air-temperature data which have 
been corrected for excessive heating during daylight 
hours. These data show that the sea-surface tempera- 
ture (under average summer conditions) tends to be high- 
er than the air temperature throughout the entire 24- 
hour period, but that this difference is at a maximum 
from Oth to 06h, and at a minimum at 09h. On first con- 
sideration it might be assumed that the minimum differ- 
ence should occur between 12h and 13h, when the air 
temperature is at a maximum. It may be explained, 
however, that air temperatures on board the Carnegie 
were obtained at a height of 3.7 meters above the sea 
surface, whereas sea-surface temperatures were meas- 
ured at a depth of 2 meters. The surface air undoubted- 
ly heats more rapidly after sunrise than does the sur- 
face sea water at a depth of 2 meters. We may specu- 
late on the possibility that such an effect might produce 
the minimum difference at 09h indicated by the data 
plotted in figure 27. 
The maximum difference noted during the early 
morning hours probably would be less pronounced if the 
air-temperature data could be corrected for errors 
arising through excessive cooling of deck, shelter, and 
thermal elements by radiation at night. 
Data concerning the diurnal variation of sea- and 
air-temperature differences for Groups J to XI are pre- 
sented in table 43, which indicates that mean sea-sur- 
face temperatures exceed mean air temperatures in all 
Groups except in the Southwest Juan Fernandez Island 
Group. As stated by Miss Clarke [23, p. 184]. 
“For the groups which include that part of the cruise 
from Iceland to the Central North Atlantic (17° north, 
38° west) and from Barbados to Callao, none of the 24 
mean hourly air temperatures exceeded the mean hourly 
sea temperatures. For all other groups the mean hour- 
ly air temperature at some time during the day rose 
higher than the mean sea temperatures. However, when 
air temperatures not corrected for radiation were used 
in this comparison, for every Group except that of the 
Gulf Stream and of the Gulf of Panama, air temperatures 
exceeded sea temperatures sometime during the day. 
This seems to indicate that if the effect of radiation 
could be climinated, the mean daily air temperature 
would seldom exceed mean daily sea temperature. 
After the mean curves of sea and air temperature 
had been plotted for all groups, two distinct types of di- 
urnal curves were recognized. In one type the air tem- 
perature exceeds the’sea temperature only during the 
forenoon from 08h to noon. In others, the air tempera- 
ture rises above the sea temperature about 08h or 09h 
and remains above it until late afternoon. Two repre- 
sentative curves of these types are shown in figure 17. 
A study of the cause of this variation revealed that in 
