LOCAL WINDS 
toward the coast, but is formed on the boundary line 
between sea and land and progresses seaward. It is 
caused by the different heating processes on the flat, 
sandy beach. This minor sea breeze precedes the major 
sea breeze, the beginning of which is somewhat re- 
tarded by it until the air over the land has become 
considerably warmer than that over the water. The 
border line between warm land air and cool sea air, 
which has been displaced seaward by the minor sea 
breeze, is eventually overrun, and the cool sea air 
reaches the coast with an impact. This minor sea 
breeze, designated as a sea breeze of the first kind, 
will occur wherever strong pressure gradients connected 
with the large-scale weather situation do not hinder 
its development. 
The Cold Front-Like Sea Breeze, or Sea Breeze of 
the Second Kind. The character of the sea breeze 
having a normal, front-free, and steady development is 
modified if a wind determined by the general weather 
situation hinders its regular course. This sea breeze, 
which develops in opposition to the gradient wind, is 
characterized by its retarded beginning (usually as late 
as 1500 to 1600), by its formation at sea and its slow 
progress toward the coast, and finally by a pronounced 
break-through of a cold front-like character (distinct 
gust with wind shift of 180 degrees). The development 
of this cold-air invasion can be considered to take place 
in the following way: 
In the morning, the offshore gradient wind carries 
warmed air from the land out to sea and thus displaces 
seaward and weakens the pressure gradient between 
land and sea. An air-mass boundary is thus formed at 
sea against the cool sea air. The warmed land air, 
which accumulates in a nearly adiabatic layer, is highly 
turbulent and is able to carry along some of the stably 
stratified, cold sea air and is forced to rise with it. 
For a while, a stationary equilibrium between the two 
air masses may be maintained by an increasingly steep- 
ening frontal surface as is depicted in Fig. 5. However, 
WARM AIR 
LAND SEA 
Fic. 5.—Stationary condition before outbreak of the sea 
breeze. The dash-dotted line is the boundary layer between 
currents of opposite direction in the cool air mass. (After 
Koschmieder [54).) 
with further heating this equilibrium breaks down, the 
system becomes unstable, and the sea air now breaks 
through toward the land in the form of a front. This 
sufficiently explains the gusty onset and the cold-air 
character. If we consider that the largest vertical tem- 
perature gradients are not reached until 1200 to 1400, 
the retarded onset of the sea breeze is also under- 
standable. 
659 
Theory of Land and Sea Breezes. A complete theory 
of the land and sea breezes must necessarily consider 
(in addition to the gradient force caused by land-water 
temperature difference) (1) the influence of the vertical 
turbulent heat exchange, (2) the turbulent friction of 
the air motion, and (3) the influence of the earth’s 
rotation. In all existing theories these contributory 
factors receive only partially satisfactory consideration. 
Usually, the land and sea breezes are treated as simple, 
antitriptic currents caused by the unequal heating of 
land and water. 
An older treatment of a stationary circulation is that 
by Jeffreys [42], who applied it primarily to the sea 
breeze and to monsoon winds. He considers friction, 
pressure, and Coriolis force and reaches a solution in 
which the daily wind change is in phase with the daily 
temperature oscillation. This result does not conform to 
reality. The application of this theory to the extended 
monsoon currents allows the calculation of the height of 
the monsoon reversal as well as of the amplitude of the 
surface pressure variations connected with the circu- 
lation. The agreement of these calculations with ob- 
servation proves to be satisfactory. 
VY. Bjerknes and his collaborators [8] consider the 
land- and sea-breeze circulation a periodic current 
around isobaric-isosteric solenoids in which the wind is 
ninety degrees out of phase with the change in density. 
Accordingly, the sea breeze would start at the time of 
the greatest heating and would reach its greatest in- 
tensity at the time of the smallest temperature dif- 
ference between land and sea in the evening. This is 
not in accordance with observation. 
Kobayasi and Sasaki [52] as well as Arakawa and 
Utsugi [2] base their theories on Lord Rayleigh’s con- 
vection theory [64]. They consider vertical and horizon- 
tal heat transfer in addition to turbulent friction of 
the air motion, whereby their basis for calculation 
becomes more complete than that of Jeffreys. Their 
solutions of the problem allow a comparison between 
theory and observation, although in order to reach 
complete agreement a heat conductivity one hundred 
times greater than that derived by Taylor from ob- 
servations must be assumed. A further shortcoming of 
the theory is that the height to which the circulation 
(including the countercurrent) extends must be known, 
whereas it actually should result from the boundary 
conditions of the theory. This theory still neglects fric- 
tion, which, as had already been pointed out by Godske 
[30], is responsible for the phase shift between density 
and wind-velocity variations. 
A simple elementary theory of land and sea breezes 
is due to F. H. Schmidt [67]. In this theory he is less 
concerned with giving a complete explanation of the 
circulatory movement than with clarifying character- 
istic phenomena of the land and sea breezes, such as 
the phase shift between wind and temperature or the 
influence of the earth’s rotation. A definite temperature 
distribution in accordance with observations is assumed, 
and the entire system of currents is calculated, taking 
the compressibility of the air into account. The Coriolis 
force is also introduced into the calculations, and thus 
