The summer phase of the annual cycle of winds driven by the land–sea thermal contrast. The heating of the landmasses during summer leads to a deficit of atmospheric pressure over the continents, resulting in an onshore flow. Other factors such as the topography of the land have a considerable effect. The summer monsoon is strongest on the southern and eastern sides of Asia, but it can also occur over northern Australia, parts of Africa, the southwestern United States, and the Mediterranean. See monsoon; Compare winter monsoon.