sea breezes often blow frm the sea to the land during the day.at night they blow from the land to sea.why?

Answer 1

Wind always goes from high pressure to low pressure.

Low pressure originates when warm air drifts upwards.

During the day, sun radiation can heat up dry land rather quickly because it has a comparably low heat capacity - it doesn't take much heat to change the temperature. Water has a higher heat capacity and will take longer to warm up.

In the night, the process is reversed. Dry land cools down quickly, the sea cools down only slowly.

During the day, the land is likely to be warmer than the sea, creating a lower pressure - hence the breezes will go from sea to land. During the night, the sea is likely to be warmer than the land, reversing that direction.

Answer 2

I wrote this piece about seabreezes for a local radio station.

The land and the sea are both heated by the sun. The sun's radiation, however, penetrates only a few millimetres into the ground but metres into the sea. The land does not move but the sea surface is constantly in motion with waves and ripples. Consequently, the surface of the land heats up much faster than the surface of the sea and gets a lot hotter too. Anyone who has walked along a beach knows that the dry sand can be unbearably hot while the wet sand is cool.

The air in contact with the ground is heated by the ground. This in turn heats the air above it and so on through the troposphere. Rather than thinking that air cools with height, it is better to think of it as warming as you get lower because it is heated from below. When air is heated it expands. There is really only one direction in which it can expand and that is upwards.

Let us now consider a device called a column of air, in fact two columns, one over the land and one over the sea. The air over the land is heated by the hot land while that over the sea is heated by the cooler sea. The air over the land is going to get hotter and will expand more than the air over the sea.

These two columns are not far apart, perhaps two or three kilometres. The air pressure is the same at the base of each column. Before the sun rose and started heating the land, the columns were identical. Now the land column has expanded upwards more than the sea column. While the pressures at the surface remain the same, the pressures higher up the column have changed at the same level.

Let us look at what is happening 1000m up. The air over the land has expanded upwards more than the air over the sea so there is now more air in the land column above 1000m than there is in the sea column. While the air pressure at the surface remains the same because the mass of air has not changed, the pressure at 1000m is higher over the land than it is over the sea. This pressure difference is rectified by air moving from the land column to the sea column at 1000m.

What happens at the surface? Air has been taken from the column over the land so the pressure falls. The amount of air has increased in the column over the sea so the pressure rises. There is now a higher pressure over the sea and a lower pressure over the land so the air moves from the sea column to the land column at sea level This we feel as the sea-breeze. The greater the temperature difference between the land and the sea, the stronger the sea-breeze when it arrives.

If school teachers want to demonstrate the Coriolis effect for their students, they can use the sea-breeze. It is a much better indicator than water going down a plughole. The sea-breeze always begins normal to the coastline, that is at right-angles to the coastline. If the coastline is north/south, the sea-breeze will start as an easterly. The Earth rotates once a day thus Coriolis produces a rotation of 360° every 24 hours. In the southern hemisphere, Coriolis makes anything moving across the surface turn to the left. Thus a sea-breeze that starts as an easterly will change direction during the course of the day.

The sea-breeze usually begins at about 9am. By 3pm, the wind will have been blowing for six hours. This is a quarter of a day. Applying Coriolis, we should expect the sea-breeze to have changed direction through a quarter of 360° or 90°. The sea-breeze that starts as an easterly at 9am should be a northerly at 3pm and that is exactly what we find. Schools near the beach can check it for themselves. In the northern hemisphere, the seabreeze will veer rather than back.

At night, the land cools down faster than the sea and the reverse process occurs. Instead of air flowing from the sea to the land, it flows from the land to the sea. This is called the Land Breeze.

In many parts of the world, the cool, refreshing sea breeze is called the Doctor while the warm land breeze is called the Undertaker.

Answer 3

I am not sure your statement is all its cracked up to be. I think that the wind blows to the sea at high tide and there are several high tides in 24 hrs. I could be wrong its just my theory but I think the air flows to the middle of the see because the water is leaving the center at high tide..