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Joanne Simpson, 1923-2010

Dr. Joanne Simpson, the first woman to earn a Ph.D. in meteorology, died March 4, 2010, at the age of 86. Her groundbreaking, influential career spanned more than half a century, beginning with her teaching meteorology to World War II Aviation Cadets and ending with her retirement as the head of the Severe Storms Branch in the Laboratory for Atmospheres at NASA’s Goddard Space Flight Center.

In the photo above, taken in the 1950s, Simpson is bent over reams of images of clouds that she filmed during long flights between islands in the tropical Pacific. From the photos, she is drawing detailed maps of cloud formations. These observations underpinned her first major contribution to atmospheric science: the boat-rocking hypothesis that tropical clouds weren’t just the passive result of atmospheric circulation, as meteorologists of the day believed, but were in fact the cause of it.

The large-scale patterns of air circulation in the tropics were already well-established: fueled by solar heating, air rose over the tropics, spread poleward at high altitudes, sank back to the surface at subtropical latitudes, and flowed back toward the equator at the surface. The pattern, the Hadley Circulation, is the foundation of the global atmospheric circulation.

But while the Hadley Circulation had been documented and described, meteorologists didn’t really understand how it physically worked. Through her observations and models, Simpson and her advisor, Herbert Riehl, demonstrated that some tropical clouds reach towering heights—as high as 15,000 meters (9 miles). These cumulonimbus clouds, which Simpson called “hot towers,” act like chimneys for the warm, moist air rising from the tropical oceans. The hot towers allow water vapor to reach unusually high altitudes. The heat released when the vapor in these very tall clouds condenses into water droplets and ice crystals is the main driver of the rising-air part of the Hadley Circulation.

Many scientists go their entire careers without the satisfaction of making such a significant contribution to their field. For Simpson, though, seeing her hot tower hypothesis verified over the next two decades was surely a kind of poetic justice as well. Her interest in tropical clouds was considered acceptable by the all-male faculty at the University of Chicago, where she earned her doctorate, because, as the department head told her, no one was very interested in them, so it was a good subject “for a little girl to study.”

After establishing their importance to the global atmospheric circulation, Simpson went on to demonstrate the influence of hot towers on hurricane intensification. In the late 1960s and early 1970s, she led research into the potential of cloud-seeding to reduce the intensity of hurricanes. In the 1980s, she became the driving force behind the first satellite mission to study tropical rainfall from space. Simpson said that she considered her involvement with the Tropical Rainfall Measuring Mission, launched in 1997 and still operating today, to be the most important accomplishment of her career.

To read more about Simpson’s influential and award-winning career, the childhood experiences that fueled her ambitions, and what it was like to be pioneer for women in science, please read her biography, written in 2004 for our series “On the Shoulders of Giants.”

Photograph courtesy Joanne Simpson and the Schlesinger Library.