658 
demonstrated numerically by superimposing the pres- 
sure fields of land and sea breezes and gradient wind 
[54]. 
Development of Land and Sea Breezes as a Function 
of Geographical Location, Season, and Time of Day. 
On tropical coasts, the land and sea breezes appear with 
great regularity [9, i1, 53, 70], because the clear sky 
there causes large variations in temperature over the 
land in the course of the day. Also the usually weak 
general air motion does not interfere with the develop- 
ment of local winds. It is only in India that the land 
breeze is completely obscured from May to September 
by the strong monsoon, which acts as a steady sea 
breeze during that season. Partial superimposition of 
mountain and valley winds on land and sea breezes may 
also cause peculiar wind conditions, as for mstance on 
the coast of Samoa. In higher latitudes these local winds 
appear almost exclusively, or at least preferably, during 
the warmer seasons, since only then can sufficiently 
large temperature or pressure differences develop. In 
the cooler climates of higher latitudes, as for instance 
at the shores of the Baltic Sea [46], we can expect 
land and sea breezes, even in summer, on not more 
than about 20 per cent of the days. The role of solar 
radiation becomes apparent in a brief summary (Table 
I) of the probability of a sea-breeze day for different 
Taste I. RELATIONSHIP BETWEEN CLOUDINESS AND SEA- 
BREEZE PROBABILITY 
Cloudiness (per cent)............- 0-50 60-80 | 90-100 
Probability of a sea-breeze day (per 
(GTi ia he eee Rares cesta NS cha Siero emer 90 39 27 
amounts of cloudiness at the Black Sea. Little cloudiness 
and strong sunshine are decisive in promoting the 
occurrence of land and sea breezes. In polar regions 
the phenomenon disappears almost completely and oc- 
curs only once in a while on particularly clear summer 
days. 
In the tropics (Batavia) [70] we find about 40-50 
per cent of land-breeze occurrences and 70-80 per cent 
of sea-breeze occurrences to be fairly reliable values 
for the dry season. During the rainy season both fre- 
quencies increase; the land-breeze probability rises to 
between 60 and 80 per cent, that of the sea breeze to 
more than 80 per cent. Ramdas [63] gives frequencies 
for extratropical land and sea breezes in Karachi, India, 
(25°N) for every month of the year (Table II). We can 
Taste II. ANNUAL VARIATION OF LAND- AND SEA-BREEZE 
FREQUENCY aT Karacati, INDIA 
(After Ramdas [63]) 
S) 
100 
O 
26 
N/D 
42 
Month... J | F|M| A 
27 
M 
100 
A 
100 
J 
100 
J 
100 
| 
Per cent. . 29 | 39 | 31 30 
see from this table a 100 per cent occurrence during 
the summer months in contrast with the low percentage 
in the winter. Similarly, in etesian climates (as for in- 
LOCAL CIRCULATIONS 
stance the Mediterranean climate) spring has land and 
sea breezes on 31 per cent of the total number of days, 
the first half of June on 82 per cent, July on 91 per cent, 
and autumn on only 35 per cent of the days. 
Finally, the phenomenon is in almost all regions a 
function of the time of day, since its periodic course is 
a consequence of the diurnal temperature variation. 
Usually, the sea breeze starts between 1000 and 1100, 
reaches its maximum velocity around 1300 to 1400, and 
subsides toward 1400 to 2000, whence it is replaced by 
the nocturnal land breeze. These approximate times 
naturally vary with the season and with climatic and 
local differences. 
Intensity, Vertical Extent, and Range of Land and 
Sea Breezes. The height of the sea-breeze layer varies 
with climatic and local conditions. Its altitude ranges 
from 150 m at medium-sized lakes to 200-500 m at 
large lakes and the seacoast. Extending to 1000 m in 
moderately warm climates, the sea breeze reaches al- 
titudes of 1300-1400 m in tropical coastal regions, as 
can be clearly seen in Fig. 3. In India, maximum alti- 
tudes of 2 km have been observed. In these areas, the 
nocturnal land-breeze layer is rather shallow by com- 
parison. In Batavia, for instance, it reaches only to 
about 200-300 m. The difference in height between 
land and sea breezes is smaller in the temperate zones. 
The intensities of the sea breeze cover the entire 
Beaufort scale. This breeze is of small force at lake and 
sea shores in the temperate zone (0 to 3 Beaufort); 
only at the seacoast do some peak values reach 4 to 
5 Beaufort at noon. In the tropics, however, the wind 
may rise to storm intensity with the onset of the sea 
breeze. A particularly strong increase occurs on coasts 
with cold ocean currents offshore. While the horizontal 
speeds are of the order of meters per second, the vertical 
components are only of the order of centimeters per 
second. 
The landward range of the sea breeze is estimated by 
many observers at 15-50 km in the temperate zones. 
Some values, for instance, are 16-32 km in New Eng- 
land, 20-30 km at the Baltic Sea, 30-40 km in Holland, 
up to 50 km in Jutland, 15 km on the Flemish coast, 
40 km in Albania, more than 50 km on the northern 
coast of Java, and 40-50 km in Sweden. However, 
land and sea breezes are often augmented by mountain- 
and valley-wind effects which are difficult to separate 
from them. In tropical countries the sea breeze reaches 
50-65 km, sometimes even 124-145 km into the in- 
terior. The seaward range of the much weaker land 
breeze appears to be everywhere much smaller. At the 
Baltic Sea, for instance, it extends only to 9 km. 
Regarding the vertical temperature distribution in 
the temperate zone where condensation is relatively 
rare, nearly adiabatic or slightly superadiabatic gradi- 
ents are to be expected. In the tropics, however, super- 
adiabatic gradients are the rule, but probably reach 
only to the upper boundary of the sea breeze and 
decrease rapidly above it. 
Conrad’s Minor Sea Breeze, or Sea Breeze of the 
First Kind. The wind designated by Conrad [13] as 
“minor sea breeze” does not progress from the sea 
