Under normal circumstances water in the western part of the Pacific Ocean exceeds 28 degrees Celsius. In that case belt of a low pressure system ITCZ (Inter Tropical Convergence Zone) occurs in that region of the world (south east Asia), which draws in heavy and moist air. Such conditions are responsible for heavy rain over that region. On the other side of the Pacific Ocean weather conditions drastically change. Eastern part of the ocean is cooler, which is the outcome of two main factors. First one is the upwelling of cold, fish rich water and the second one is the rapid movement of dry winds from the land. Such a global atmospehric oscillation is called SO and it is closely related to El Nino.