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One of the most important and predictable seasonal atmospheric cycles is associated with monsoons, particularly those of southeast Asia, where the surface winds change with the seasons over a vast area. Less‐pronounced monsoons are found over eastern Africa, North America, northern Australia, China, and Japan.

The primary cause of the Asian summer monsoon is convection, when warm, rising air over the extremely hot Indian subcontinent creates an area of low atmospheric pressure. The rising air is replaced by extremely moist air flowing from the Indian Ocean, where pressure is relatively high. The result is a season of torrential downpours and floods, often made worse by tropical cyclones. Rainfall is particularly high over the southern slopes of the Himalayan mountains – the wettest place on Earth – where moist air is cooled as it is forced upward. The arrival of the summer monsoon usually occurs around the same date each year.

In winter, the air flow is reversed. The interior of the Asian land mass becomes very cold, creating an area of intense high pressure. The dense, sinking air flows away from the land and out to sea, resulting in dry conditions over most of continental Asia.