ERS Radar Altimeter sea level map

ERS-2's Radar Altimeter generated this annual mean sea level height map for 1996. The 'normal' state of the ocean is such that the sea level on the western side of the Pacific Ocean is higher than on the eastern side. This difference is due to the Trade Winds blowing constantly from east to west, causing the waters to pile up at the western side. Also due to the Trade Winds, the surface water on the eastern side is constantly transported westward, and replaced by cold, nutritious water that comes from deeper layers. So generally along the South American coast, cold and nutritious waters prevail, while on the western side this is warm surface water. During an El Nino event the Trade Winds relax, and become very weak (and may even reverse). This causes the warm surface waters to flow back eastward, and stops the upwelling on the eastern side. No more upwelling means that the sea surface temperatures rise - implying a sea level rise. Effects can be monitored using altimetry data. [Image Date: 1996] [97.11.014-001]