Nature and Causes
Sea breezes occur during hot, summer days and are caused by unequal heating of adjacent land and water. During the day, solar radiation causes the land surface to heat up more quickly than the water surface. Therefore, the air above the land is warmer than the air above the ocean. Because of the fact that warmer air is lighter than cooler air the warm air above the land surface is rising. At the same time the cool air above the ocean is flowing over the land as to replace the rising warm air. This is the sea breeze. As the sea breeze moves inland, the cool sea air advances like a cold front characterized by a wind change, a temperature drop and a rise in humidity. A drop in temperature of 2 to 10 C degrees within 15-30 minutes is usual as the sea breeze advances.
FLSWizards
Development of Sea Breezes
With weak general wind circulations, a sea breeze will occur over the coastline soon after the temperature of the land surface begins to become higher than the water temperature (late morning to early afternoon). The more the difference increases, the stronger the sea breeze will become and the farther will extend inland. It will also increase in depth from about 100m to 450m or even 800m if the breeze is well developed. The highest wind speed will occur during the several hours after the temperature of the land has reached its maximum. This happens during the mid to late afternoon. A weak sea breeze will die away soon after sunset, but a stronger sea breeze will remain at the coast until 8 to 10 p.m.
With stronger general wind circulations, together with the required temperature gradient, the sea breeze development can be a bit complicated. A moderate or strong, predominant off-shore surface wind will delay the occurrence of the sea breeze and if strong enough will not allow its development at all. On-shore surface winds are generally enhanced by the sea breeze component. On the other hand, if there is a light or moderate predominant 900m off-shore wind, then there will probably be a re-enforced sea breeze at the surface.
The rule is that 900m off-shore wind help the sea breeze to develop, while those on-shore either complicate the sea breeze or don’t allow its occurrence at all.
Sea Breeze Direction and Speed
A sea breeze generally starts as a light on-shore surface wind blowing perpendicular to the coast. As the breeze becomes stronger it moves in a counter-clockwise direction. During the day friction and Coriolis effects act to change the wind direction until it parallels the coastline.
The start-up and final direction of the sea breeze will depend on the orientation of the coastline and its complexity (steepness, headlands, bays, estuaries, etc.).
From the time of the sea breeze front passage until late afternoon the wind will blow inland at speeds of 13 to 19 km/h, sometimes even 40 km/h.The landward penetration of the sea breeze reaches 15 to 50 km in the temperate zones and 50 to 65 km in the tropics. The further inland the breeze extends the weaker and less detectable it becomes, and the shorter it continues. By late afternoon, the sea breeze strength slowly decreases because the influx of solar energy diminishes. The dacay of the circulation pattern happens first at the shoreline and goes on farther inland.
Climatology of the Sea Breeze
The sea breeze occurs most frequently in the tropical zones, continuing for about 3 out of 4 days. The increased solar radiation, higher temperatures and weaker predominant winds in these regions help the sea breeze to develop. In the temperate zones breezes are phenomenon occurring in late spring and summer when the climatic conditions are most favorable to their formation.
Land Breeze
Nature and Causes
Land breezes occur at night. The land surface cools down more quickly than the water surface. Therefore, the warmer air above the ocean is lighter and is rising. The heavier cool air over the land is flowing towards the water in order to replace the rising warm air. This flow is called land breeze. As like as the sea breeze, the land breeze is also influenced by the strength of the largescale winds and the coastline configuration. The land breeze is weaker in speed and less frequent than the sea breeze. The land breeze usually prolongates for only a few hours and changes its direction. Nevertheless, it can expand for about 10 km seaward.
FLSWizards
Climatology of the Sea Breeze
The land breeze occurs less commonly. Along coasts with steep shorelines or volcanic island coasts, however, it is a frequent phenomenon sometimes reaching speeds up to 32 km/h. in the temperate zones the land breeze occurs in the cold seasons, especially when there is a warm sea current flowing along the coast.
Lake-Land and Mountain Breeze
Lake-Land Breeze
Lakes may also develop a similar local wind circulation pattern. In this case the wind that moves inland is called lake breeze. Lake breezes occur most commonly in late spring and summer
Mountain Breeze
There is still another type of breeze known as mountain breeze which is influenced by the presence of mountain features. It is caused by the different heating or cooling along the slopes. During the day, the air above the heated sunlit slopes moves upslope. At night, the slopes cool down and cool down slope motion of air occurs. Such winds can be either very light or extremely strong, depending on the topographic configuration.
