Joanne Simpson

The NASA Years

“I had never in my life been at a place before where anyone else other than the secretaries and me used the ladies room,” says Simpson. She recounts that the second day she arrived at Goddard Space Flight Center, she went to the ladies room to freshen up and found to her surprise two other women scientists washing their hands and discussing meteorology. Never before had she encountered a working environment so friendly to women.

Early on at NASA, a brilliant young researcher named Wei-Kuo Tao joined her group. With his arrival, cloud modeling made its most important leap forward. He had begun a model of cloud ensembles that built on Simpson’s one-dimensional approach. Simpson’s observations had long showed the importance of cloud interactions and mergers. The experiments she had conducted in Florida when she was leading the Experimental Meteorology Laboratory plainly illustrated how the huge clouds formed from the mergers of smaller ones. “The modeled cloud mergers occurred exactly the way we observed them to occur. So when you can get a model and observations to agree, you feel much more confident that your ideas are correct,” says Simpson.

Diagram of Cloud Bridging and Cumulus Merger

Early in her career at NASA, Simpson described how two cumulonimbus clouds merge. These merged clouds produce the majority of rainfall in the tropics. (Diagram by Simpson, Westcott, Clerman, and Pielke)

In 1986, NASA asked Simpson to lead the “study” science team for the proposed Tropical Rainfall Measuring Mission (TRMM), a satellite to carry the first space-based rain radar, which would measure rainfall across the tropics and subtropics. Between 1986 and launch in November 1997, Simpson worked in close partnership with the project engineers, and recruited brilliant scientists to develop the data system.

Simpson believes that her involvement with TRMM is the single biggest accomplishment of her long career. Many in the meteorological community agree. The satellite has led to some remarkable discoveries in meteorology. TRMM has been instrumental in helping scientists learn how hurricanes start in the Atlantic Basin and in demonstrating how dust and smoke can drastically influence rainfall. But of all the results that came about from TRMM, Simpson says the discovery she is most excited about occurred in 2002, on the fifth anniversary of the satellite’s launch.

By that time, TRMM had met or exceeded nearly all of its important goals. One of its goals, however, still remained, which was to measure from orbit the profile of latent heating released by tropical cloud systems. The ability to measure latent heat profiles over wide areas has long been on the wish list of the meteorological community. The difficulty has always been that latent heat cannot be measured directly. Today, scientists can accurately estimate latent heat in the tropics using a model based on TRMM rain profiles. Professor Robert Houze and Courtney Shumaker showed that for several different areas, the TRMM profiles and those profiles directly observed were in good agreement. Simpson’s early groundbreaking work on latent heating of the atmosphere had come full circle with TRMM’s many successes.

map of latent heating in the tropics derived from TRMM data

The Precipitation Radar aboard the TRMM satellite provided data used to calculate latent heat (in degrees Celsius per day) across the tropics. These measurements confirmed Simpson’s early observation on a grand scale. (Map courtesy Courtney Schumacher and Robert A. Houze Jr.; Department of Atmospheric Sciences, University of Washington)

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