Onshore and offshore Breeze. (Convection current: gases)

During the day:

The land heats up quicker and is warmer than the sea. The warm air which passes over the land rises and the cool air over the sea sinks to replace it. This creates an onshore breeze

image for onshore breeze

During the night:

The land cools off faster than the sea, the air above the sea is warmer and rises whilst the air above the land sinks to replace it. This creates and offshore breeze.

image for offshore breeze