NASA Spacecraft Data Improves Tropical Forecasts

The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) represents the first microwave spacecraft sensor capable of accurately measuring sea-surface temperatures through clouds. These findings were reported today in the Journal Science, by Frank Wentz and colleagues at Remote Sensing Systems, Santa Rosa, CA, who also are TRMM Science Team members.

Science team members have found that data from the TRMM Microwave Imaging (TMI) sensor onboard the spacecraft has great potential to increase the accuracy of tropical storm and climate forecasts.

Microwave radiation penetrates clouds with little loss of signal thereby providing an uninterrupted view of the ocean surface whereas much of the infrared radiation, typically used for measuring sea-surface temperatures from satellites, are blocked by cloud cover.

"The microwave imager can give consistent readings of sea-surface temperatures even through clouds," said Wentz, director of Remote Sensing Systems. "To date we’ve been limited by infrared sensors. Having the complete picture of ocean surface temperatures should greatly improve numerical models being run by the National Weather Service.

"After a long wait the satellite technology for measuring the ocean's temperature through clouds is now operational," said Wentz. "We expect that this new satellite capability will have a major impact on ocean sciences and storm forecasting."

The first microwave radiometers operating at low frequencies were flown on the SeaSat and Nimbus-7 missions launched in 1978. Those instruments demonstrated the feasibility of measuring sea-surface temperatures with microwaves. The usefulness of these early radiometers were constrained by a limited calibration system. Though subsequent microwave radiometers, such as the Special Sensor Microwave Imager (SSM/I) have improved calibration systems, they still lacked the low frequency channels needed to accurately retrieve sea-surface temperatures.

Sea-surface temperature play a fundamental role in the exchange of energy, momentum, and moisture between the ocean and the atmosphere and is a central factor of air-sea interactions and climate variability. A better understanding of air-sea dynamics will translate into better weather forecasting.

"Better sea-surface temperature readings will help the models determine if the storms will gain strength," said Max Mayfield, acting director, National Hurricane Center, Miami, FL. "Warm tropical waters are a fuel for hurricanes and other storms -- helping them grow in intensity."

This is particularly important when it comes to the forecasting of El Niño and La Niña, which have a profound effect on the world’s climate, and are a dramatic manifestation of the coupling of sea-surface temperature and atmospheric circulation.

TRMM has produced continuous data since December 1997. Tropical rainfall, which typically falls between 35 degrees north latitude and 35 degrees south latitude, comprises more than two-thirds of the rainfall on Earth. TRMM is NASA’s first mission dedicated to observing and understanding tropical rainfall and how it affects the global climate.

In the future, this all weather capability to observe sea-surface temperature will continue from the NASA Earth Observing satellite called "Aqua," which is scheduled for launch late this year.

TRMM is a joint U.S.-Japanese mission and part of NASA’s Earth Science Enterprise, a long-term research program designed to study the Earth's land, oceans, air, ice and life as a total system. Information and images are available at URLs:

http://trmm.gsfc.nasa.gov/

http://www.gsfc.nasa.gov

http://www.remss.com