Sea Surface Temperature Anomaly
Sea Surface Temperature Anomaly & Total Rainfall
The atmosphere and the ocean are intimately connected. Ocean temperatures influence rainfall patterns throughout the world, so when ocean temperatures change, rainfall patterns tend to change as well. Scientists monitor changes in ocean temperatures, looking for warmer or cooler than average waters, to predict floods or droughts. For example, El Niño warms the equatorial Pacific Ocean off South America. The atmosphere becomes warmer and more humid over the eastern Pacific in response. Cascading atmospheric changes can shift the position of the jet stream, which then steers stronger winter storms to the southwestern United States. At the same time, El Niño cools the western Pacific, which usually results in less rain over Australia and Indonesia.
Sea surface temperature refers to the temperature of the top millimeter of the ocean. An anomaly is a departure from average conditions. These maps compare temperatures in a given month to the long-term average temperature of that month from 1985 through 1997. Blue shows temperatures that were cooler than average, white shows near-average temperatures, and red shows where temperatures were warmer than average. Regions for which no data were available are gray. The maps are made from data collected by the Advanced Microwave Scanning Radiometer-EOS (AMSR-E) compared to historical data collected by a series of National Oceanic and Atmospheric Administration (NOAA) satellites.
The rainfall maps show total monthly rainfall in millimeters as recorded by NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite. High rain totals are represented in dark blue, while small rainfall totals are shown in white. TRMM measures rainfall in the tropics. High-latitude regions, where TRMM does not record rainfall, are gray.
The relationship between sea surface temperature anomaly and total rainfall is impossible to see in these maps because it is difficult to pick out small changes in total rainfall on a regional scale. A rainfall anomaly image, one that depicts a change in rainfall instead of total rainfall, would best illustrate the relationship. The most obvious pattern in the total rainfall map is seasonal change. A band of heavy rain moves north and south of the Equator seasonally. The Asian monsoon brings rain to China, Southeast Asia, and India between April and September. From October through May, South America goes through a rainy season.
Seasons are more difficult to see in the sea surface temperature anomaly map because it does not depict absolute temperature, but rather how much cooler or warmer the water was compared to normal conditions. The sea surface temperature anomaly map does show the El Niño/La Niña cycle. From July 2006 through January 2007, ocean temperatures off northwest South America were warmer than average while El Niño reigned. Later in the year, from August through December, La Niña took over and the eastern Pacific was cooler than normal.