NASA'S live tropical sea surface temperature Web site gives climate, hurricane clues

There are two primary types of sea surface temperature data that scientists use. The first is the actual temperature readings from the ocean water surface. The second is called a sea surface temperature anomaly that compares present temperatures to the long-term average.

Visualizers at NASA's Scientific Visualization Studio at NASA's Goddard Space Flight Center, Greenbelt, Md. have created two products. The first is a daily update of actual sea surface temperatures. Whenever clouds in the satellite data block the sea surface, the product interpolates the data. Interpolation is a calculation method for estimating data in regions that fall between points of actual measurement.

The second product is a 10-day average of sea surface temperatures over specific areas. This 10-day average helps to show or calculate the temperature anomaly.

“Climate and weather are great dances between the oceans and the global atmosphere,” says Bill Patzert, climatologist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. “Sea surface temperature changes control whether these dances are slow and graceful, as with climate, or stormy and violent, as with wild hurricanes and winter storms. Floods, droughts, hurricanes or balmy weather can often be foretold by shifting sea surface temperatures. Sea surface temperatures are a crystal ball that helps us see and plan for the future.”

The web page graphics are the result of data from the Advanced Microwave Scanning Radiometer (AMSR-E) instrument that flies aboard NASA's Aqua satellite.

Big climate events like El Nino and La Nina in the eastern Pacific Ocean are directly related to ocean temperatures and can be seen in the sea surface temperature anomaly product. If the Eastern Pacific ocean temperatures deviate from average, this product will show that. El Nino and La Nina are also connected to changes in air pressure systems.

In a normal year, steady winds blow westward and push warm surface water toward the western Pacific Ocean. In contrast, during an El Niño year, weakened winds allow warm water to occupy the entire tropical Pacific, so scientists look at sea surface temperatures for a signal of El Nino's return. Usually sea surface temperature readings off South America's west coast range from 60 to 70 degrees Fahrenheit (15-21 degrees Celsius), while they exceed 80 degrees Fahrenheit (27 degrees Celsius) in the “warm pool” located in the central and western Pacific. Rainfall tends to follow the warm water eastward, causing drought in Indonesia and Australia and also altering the path of the jet stream – a region of strong winds high in the atmosphere – that helps control weather patterns and storm paths.

La Niña is characterized by unusually cold ocean temperatures in the central Equatorial Pacific. Sea-surface temperatures along the equator can fall as much as 7 degrees Fahrenheit (4 degrees Celsius) below normal. During La Niña, the easterly trade winds strengthen and cold upwelling – the transport of colder, deeper waters to the ocean's surface – intensifies along the equator and the West coast of South America. Like her counterpart El Nino, La Nina also changes weather patterns around the world.

La Niña tends to bring nearly opposite effects of El Niño to the United States — wetter than normal conditions across the Pacific Northwest and drier and warmer than normal conditions across much of the southern tier. Both La Niña and El Niño tend to have the most profound influence in the winter. During El Niño years, temperatures in the winter are typically warmer than normal in the North-Central States, and cooler than normal in the Southeast and the Southwest. During a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest.

Hurricane forecasters rely on daily sea surface temperatures to determine the behavior of tropical cyclones, the general name for tropical depressions, tropical storms, typhoons and hurricanes. Sea surface temperatures must be at least 82 degrees Fahrenheit (28 degrees Celsius) for a tropical cyclone to develop and maintain itself. If there are no winds to tear a storm apart, warm ocean waters often allow a tropical cyclone to strengthen, since it is the primary “fuel” for development.

Maps of sea surface temperatures and anomalies are highly valuable to ocean and atmospheric scientists. They are one the primary tools climatologists use to monitor and forecast El Nino and La Nina events, and to forecast the frequency and intensity of hurricanes in all oceans.