Monsoons are created by the Earth's tilt in relation to the sun. They are a reoccurring phenomenon, yet it is very difficult to predict the exact timing, duration, and amount of rain each season. Monsoons are determined by the land and sea temperature differences. The land reflects the sun's rays, which heat air over land significantly faster. The water is able to absorb much of the heat without changing its temperature considerably, so air over water stays relatively cool.
Monsoons occur in Asia because the northern hemisphere has much more land than the southern hemisphere. During the summer, the earth is tilted so that the sun's rays are focused on the northern hemisphere. The heat is absorbed by the land masses, warming the air above it. The hot air rises and the ocean air rushes inland from the southern hemisphere to replace it. During this shift, the moisture travels with it and is released over land. This is known as the summer monsoon. This cycle continues as the cooling air creates precipitation and releases more energy. This energy heats the air, which rises and flows back to the sea where it cools, descends, and comes back to land to replace the rising air. This creates the Southeast Asian summer monsoon.
There is also a winter monsoon, which occurs during the winter months when much of the sun's rays shine on the southern hemisphere. During this time, the water is warmer than the continents. This reverses the air circulation, with the warm air rising over the oceans and the cooler air from the land, also known as cold surges, moving in to replace it. The surges retain the warm moisture as it travels over the tropical waters in order to release it over Indonesia and other countries in that area.