The surface of the Earth warms up more quickly in the morning than the surface of the water. This is the reason the air above the beach becomes warmer and thinner creating low-air pressure. While the air above the sea is cooler and denser, creating high pressure. This difference in the air pressures creates the movement of the wind from high-pressure areas to low-pressure areas. Hence, cool air moves from the sea towards the land. This is called sea breeze, which blows during the day.
♦ Warm air expands because the molecules present in warm air move apart on heating. This makes the air lighter and a low pressure zone is created.
♦ Cool air is heavy and compressed because the molecules present in the cool air are close to one another. And due to this, a high-pressure zone is created in cool air regions.