Sea and Land Breezes

AVIATION WEATHER

CHAPTER TWO

Sea and Land Breezes

The differences in the specific heat of land and water cause land surfaces to warm and cool more

rapidly than water surfaces through insolation and terrestrial radiation. Therefore, land is

normally warmer than the ocean during the day and colder at night. This difference in

temperature is more noticeable during the summer and when there is little horizontal transport of

air in the lower levels of the atmosphere. In coastal areas, this difference of temperature creates

a tendency for the warmer, less dense air to rise, and the cooler, denser air to sink, which

produces a pressure gradient. During the day, the pressure over the warm land becomes lower

than over the colder water. The cool air over the water moves toward the lower pressure,

replacing the warm air over the land that moved upward. The resulting onshore wind, blowing

from the sea, is called a sea breeze, with speeds sometimes reaching 15 to 20 knots (Figure 2-

10).

Figure 2-10 Sea Breeze

At night, the circulation is reversed so that the air movement is from land to sea, producing an

offshore wind called the land breeze (Figure 2-10). The sea breezes are usually stronger than the

land breezes, but they seldom penetrate far inland. Land and sea breezes are shallow in depth,

and should be considered during takeoff and landing near large lakes and oceans.

Atmospheric Mechanics of Winds, Clouds and Moisture, and Atmospheric Stability

2-11