In the warm pool region of the western Pacific, the warm surface waters and the strong tradewinds (trade winds) cause large amounts of water to evaporate from the surface of the ocean. The evaporation of the warm, moist air causes the air to rise and creates an atmospheric low pressure system at the surface. This low pressure system is known as the Indonesian Low. The rising air encounters lower temperature and pressure at higher altitudes leading to the formation of intense cumulonimbus, or rain producing cumulus clouds. Further cooling of the rising clouds produces heavy rainfall over the western Pacific convergence zone. After the water condenses and rains out, the dry air continues to travel aloft. Some of the air mass travels back towards the east and accumulates over the eastern Pacific. The accumulation of air sinks creating an atmospheric high pressure system over the eastern tropical Pacific.