Sea Breezes
A sea-breeze is a surface wind from the sea that develops over land near coasts.
Because it is a transparent liquid the sea is warmed by the sun to a greater depth than the land. The sea therefore has a greater capacity for absorbing heat than does the land and so the surface of the sea warms up more slowly than the land's surface. As the temperature of the surface of the land rises, the land heats the air above it. The warm air is less dense and so it rises. This rising air over the land lowers the barometric pressure by about 0.2%. The cooler air above the sea then flows towards the land into the lower pressure, creating a cool breeze.
Strong sea-breezes occur most often in mid-summer when there is a large difference between the temperature of the air over the land and the temperature of the air over the still cold sea.
Land Breezes
Since the pressure at any location is determined by the weight of the air above it, the accumulation of air at higher levels causes the pressure at levels below to increase. In the case of a developing land-breeze circulation, an area of high pressure develops over land at the surface in response to the accumulation of air at higher levels by onshore flow. Conversely, an area of surface low pressure develops over water in response to the removal of air from higher levels.
These areas of high and low pressure establish a surface pressure gradient which generates an offshore flow of air at the surface, or land breeze.
Vertical motions are induced in response to the horizontally moving air. Over water, for example, offshore flow causes air to pile up at lower levels while onshore flow removes air from higher levels. As a result, air rises up from lower levels to replace the air that is being removed aloft.
On the other hand, over land, air is accumulated at higher levels while being removed from lower levels. In response, air descends from higher levels to replace the air that is being removed from lower levels. These rising and sinking motions complete the loop that makes up the land-breeze circulation.