LOCAL WINDS* 
By FRIEDRICH DEFANT 
University of Innsbruck 
INTRODUCTION AND DEFINITION 
The terms of the complete equation of atmospheric 
motion are determined by a number of forces which, 
through their interplay, cause the movements of the 
atmosphere. These effective forces are gravity, hydro- 
statie pressure, friction, and the Coriolis force. 
If the Coriolis and friction terms are negligibly small, 
we deal with Hulerian wind equations in which the 
acceleration can be measured by the pressure gradient. 
However, if the Coriolis term is large as compared to 
the acceleration and friction terms, so that the pres- 
sure gradient is balanced only by the deflective force 
of the earth’s rotation, we speak of geostrophic winds. 
As a third possibility, the friction terms may be so 
large that they are of the same order of magnitude as 
the pressure gradient term, and the Coriolis and ac- 
celeration terms may be neglected. In that case the 
wind blows approximately in the direction of the pres- 
sure gradient and it is called an antitriptic wind [42]. 
The antitriptic wind introduces the field of winds 
restricted to relatively small areas. Their range is of 
the order of 100 km or less. In this category belong the 
land and sea breezes, the mountain and valley winds, 
the jet-effect (Diiseneffekt) winds, and, at least in so far 
' as their characteristics are determined by the orog- 
raphy of the ground, the foehn and bora winds. These 
winds of locally restricted influence are classed under 
the general name local winds. They are an elementary 
yet meteorologically very interesting part of the move- 
ment of the atmosphere and a phenomenon which 
always attracts the attention of the layman. 
In the following sections the basic principles of these 
local winds will be discussed. These winds very closely 
fulfill almost all conditions of the antitriptic wind since 
they blow roughly at right angles to the isotherms and 
isobars and are limited in the vertical to a relatively 
low altitude. 
LAND AND SEA BREEZES 
Description of the Phenomenon. In coastal areas, 
especially on tropical coasts and on the shores of rela- 
tively large lakes, we can observe in the course of a day 
the reversal of onshore and offshore winds, called land 
and sea breezes. The phenomenon takes the following 
course: 
A few hours after sunrise, depending on location and 
season, a sea breeze develops, particularly on calm 
summer days. This sea breeze usually has a noticeable 
cooling effect, particularly in the tropics; it continues 
throughout the daylight hours and dies down around 
sunset. After that the seaward-blowing land breeze 
appears. This phenomenon, which is restricted to the 
* Translated from the original German. 
coastal area proper and which extends only in tropical 
regions over a 100-km range, must be attributed to the 
difference in heat response between land and water. On 
warm, clear, summer days, the horizontal tempera~ 
ture difference between land and water provides the 
energy that leads to the development of vertical and 
horizontal air currents of strictly circulatory charac- 
ter. To the ground observer, only the horizontal parts of 
the circulation are noticeable; the vertical branches can 
be observed only indirectly, for example, through the for- 
mation of clouds over the land. The daytime sea breeze 
considerably surpasses in intensity the nocturnal land 
breeze. This is understandable because of the greater 
daytime arc of the sun during summer and the increased 
instability and consequently increased vertical austausch 
in daytime. The nocturnal cooling, on the other hand, 
produces an immediate stabilization of the air layers 
near the ground. 
It is noteworthy that the direction of the sea breeze 
does not remain constant in the course of the day, and 
that this breeze often sets in with considerable gustiness, 
sometimes in the form of a protrusion similar to a cold 
front. 
It is logical that the gradient wind, as determined 
by the over-all weather situation, should be superim- 
posed on this local wind system and should at times 
obscure or even conceal it completely. 
As an example of a typical day. with land and sea 
breezes, the wind, temperature, and humidity record- 
ings of the Danzig airfield, 3.35 km inland from the 
Baltic Sea coast, from June 3 to June 5, 1932, are re- 
produced in Fig. 1. This diagram clearly shows the 
onset of the sea breeze from the northeast and north- 
northeast, respectively, at 1420 on June 3, and at 1430 on 
June 5, while on June 4 a gradient wind from west- 
southwest—west-northwest completely conceals the sea 
breeze. After a calm from 1930 to 2245 on June 3, and 
from 2100 to 2220 on June 5, the land breeze sets in 
from southwest and west, respectively, and continues as 
a mild breeze until 0600 the following day. During the 
night of June 4-5, a calm from 0030 to 0130 and a 
shift in wind direction to the southeast are the only 
indications of the onset of the land breeze, but here 
also a gradient wind that subsequently appears hinders 
its development until 0600 in the morning. The tem- 
perature and humidity curves of Fig. 1 show char- 
acteristic irregularities in their normal trend at the 
onset and cessation of the sea breeze. 
Figure 2 gives an example of the above-mentioned 
change in velocity of land and sea breezes in the course 
of the day, as observed at Hoek van Holland on July 
31, 1938. We can see from this figure the increase in 
the speed of the sea breeze up to the daily maximum 
between 1300 and 1400 and a concurrent steady shift 
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