SEA-SURFACE TEMPERATURE 
distribution of hours of minimum-temperature occur- 
rence. but it was found that the data produced 2n almost 
complete scatter, with no concrete evidence that the 
minimum temperature tended to occur at any given hour 
between 17h and 09h. The explanation for this interest- 
ing result is obvious. As the surface layers of the sea 
cool by radiation to the sky, the surface particles be- 
come heavier than those particles immediately beneath 
the surface, and, as a result, a state of instability is 
produced. It may safely be assumed that as rapidly as 
the surface layers are cooled, they sink and are re- 
placed by layers from below. The net result of such 2 
mechanism would be to preserve 2 more or less uni- 
form and stable sea-surface temperature for 2 consid- 
erable period. There is a slight indication that the max- 
imum frequency occurs at 09h, but when it is considered 
that the frequencies at 03h, 04h, 05h, 06h, O7h, and 08h 
are respectively 52, 52, 51, 55, 50, 56, and 57 cases, it 
can readily be seen that such evidence is hardly conclu- 
sive. The most that can be said is that the minimum 
sea-surface temperature occurs most frequently be- 
tween midnight and 09h. 
The Snellius data [24], however, indicate that the 
minimum sea-surface temperature in — re- 
gions tends to occur at 06h. 
Diurnal Variation 
of Sea-Surface Temperature 
General Remarks 
Table 36 shows the small diurnal variation of sea- 
31 
surface temperature over the ocean. From the fre- 
quencies of amplitude as computed from the Carnesie 
data, it can be stated that the apparent diurnal variation 
of sea-surface temperature is 1~ or less, approxim2te- 
ly 60 per cent of the time; between 1° and 2°, 28 per 
cent of the time; and over 2°, only 12 per cent of the 
time. Meinardus [33] found the corresponding v2lmes 
from the Gauss def2 to be 63, 23, and 14 per cent re- 
spectively. One may conclude from these dat (666 dys 
of observations) that on approximately 60 per cent af 
the deys the diurnal variation of sea-surfizce tempera- 
ture will be less than 1°, and that on about 85 per cent 
of the days it will not exceed 2°. 
It is the belief of the writers, however, that these 
data are not conclusive, and that the actual diurnal veri- 
ations of sea-surface temperature are somewhat less 
| than the above values. An examination of the hourly se2- 
surface temperature data indicates that lerge diurnal 
variations in such temperatures are, in every case, the 
result of 2 change of water mass, for example, of the 
vessel's moving from warmer to colder water, or the 
contrary. Owing to such influences, it thus appears im- 
possible to establish the amplitude of the diurnal veria- 
tion of sea-surface temperature from the Carnesie d:i2 
with any degree of certainty. 
Variation of Sea-Surface Temperature for all Days 
The mean hourly sea-surface temperatures, cor- 
rected for noncyclic change, are plotted in figure 24. 
These data appear to present 2 well-defined maximum 
at 15h, with a less well-defined minimum at 05h. It is 

Table 35. Frequencies of hours of occurrence of maximum sea-surface temperature, 
Carnesie, 1928-29 

I — = ee : = 2 
IV a = > a 1 2 
Vv see = 1 1 1 2 
VI 2 2 - 6 6 ~ 4 
vu 
a 1 3 1 1 2 6 
Vit = se a 1 1 1 
x 2 1 2 2 1 1 2 
XI 1 1 a 1 
xi 1 2 2 1 2 1 3 
xi 
(a) 1 1 me i 
(b) ae = =<: x 
XIV 2 2 : 1 : 
XVI aa 
XVII 
(a £ ~Aa 1 - me aos 
(b < pee 2 2 1 2 2 
(c) 1 1 1 1 1 1 1 
XVII 1 1 1 2 2 3 3 
2 2 1 2 3 1 2 1 
<2 = — a 2 1 1 a 1 
2 3 3 4 4 3 1 = 
1 3 8 ll ) 2 1 == 
2 4 4 2 1 1 = 1 
2 1 1 2 3 = — 
7 9 8 T 6 3 < 6 2 
1 2 2 2 3 3 3 3 1 
— <— 2 1 2 1 1 1 1 
2 2 4 4 2 3 3 3 1 
2 1 1 2 4 4 2 1 2 
=< 3 4 6 3 3 2 3 1 
2 2 ll 10 9 5 3 < 3 
— 1 1 = < ¥ 3 2 
1 1 3 1 1 3 1 1 2 
= oe — 1 1 2 2 2 2 
1 1 aoe —_ = 1 1 
— 1 3 4 2 3 1 <— 
2 2 1 1 = — a3 = 
1 2 4 3 3 — 1 1 
5 7 ll 9 9 7 3 4 < 
& 
