In normal years, the upwelling of cold water off the coast of Peru creates a region of high pressure in the area. The barometric pressure in the ocean off of Indonesia is lower, and the resulting pressure gradient draws air towards Indonesia from the high-pressure zone.
秘魯外海的湧升流形成後，就在當地造成高壓，牽動遙遠太平洋彼岸的印尼外海形成低壓，高壓氣流再順勢流向印尼。