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The Woman Who Unlocked the Hurricane’s Power

Joanne Simpson became an expert on clouds because she was a pilot, but also because, as her mentor said, scientists’ lack of interest in them made the subject good “for a little girl to study.”

Joanne Simpson studies images of clouds taken on her tropical flyovers.   Photo: NASA Earth Observatory

Joanne Simpson’s path to becoming the first woman to get a PhD in meteorology—on which she would figure out the heat engine that drives hurricanes and pilot some of the first flights through the storms to get first-hand data—began in a dentist’s office with an article she read about the University of Chicago.

She was intrigued by the school’s philosophy, then led by university president Robert Maynard Hutchins, who “believed in having his most distinguished professors teaching the undergraduates. I was impressed that they made their courses so interesting that there was no compulsory attendance,” she later said.

The child of journalists, she came from an accomplished family, and her mother, grandmother, and aunts had all attended Radcliffe; her means of rebellion was to pass up what she called the “Eastern Seaboard Syndrome” and head to the Midwest. Simpson was a headstrong young woman who learned to fly from her father, childhood flights in which the germ of her career was sown by a fascination with clouds. (Later, she would develop the first computer model of their formation.)

As a college student, Simpson was more interested in the social sciences, but she arrived at the University of Chicago during World War II, when its meteorology department, arguably the greatest in the world at the time under the direction of Carl-Gustaf Rossby, was being mined for the war effort. Simpson was dissuaded from enlisting by her parents, but as in so many other fields, the shortage of manpower caused by the war opened up a window for women to serve on the homefront. For Simpson, that meant going into the meteorology training program and teaching aviation cadets after she finished her bachelor’s degree.

She was still leaning towards medical school, but her sex locked her out of scholarships, so she pursued a master’s and PhD in meteorology while working her way through school, first at the University of Chicago as a research assistant and lab tech. Fired from that under a “nepotism rule” after marrying her first husband, a university employee, she found work at the Illinois Institute of Technology, which was flooded by new students on the GI Bill. The school’s desperate need for teachers was a boon to Simpson, and the money she earned as a teacher allowed her to finish her degree in the absence of scholarship money.

“This was the greatest thing that ever happened to me,” she told the meteorologist Margaret LeMone in an oral history, “to be forced a) to take these courses and b) to be forced to teach them. Before I left Illinois Tech, I was teaching all the undergraduate courses, including advanced mechanics and electrodynamics. This was an education that was absolutely priceless.”

Simpson studied clouds under Rossby, but he was a poor mentor: He declared her topic a good choice “for a little girl to study” because no one else was interested; she said that he was “very unencouraging because of the woman situation and he didn’t think there was any future at all for women in meteorology.” (In retrospect, however, she also called him “my early hero” and credited his insistence on field observation, including his near-insistence that all meteorologists train as pilots or sailors, for influencing her methods. Late in life she would win a medal named after Rossby, one of the field’s highest honors.)

Rossby’s attitude, combined with his return to his native Sweden, moved her to ask his colleague, Herbert Riehl, to be her thesis advisor on the subject of tropical convection. She’d studied it under him in a graduate-level tropical meteorology course that, because so little was known about the topic—Riehl said that it “invented itself as it went along"—became a turning point in the profession. Among his protégés was Robert Simpson, Joanne Simpson’s future husband and co-creator of the Saffir-Simpson Hurricane Scale, from which we get the five categories of hurricane severity. (Riehl himself is fascinating: A German Jew who fled soon after the rise of the Nazi party, washed out of his uncle’s Wall Street firm, he rose from tour guide to screenwriter at MGM, and finally, like Simpson, became a meteorologist because of the armed services’ need for them.)

“[Riehl] said, ‘Well, I really don’t know any more about that topic than I talked about in those two weeks in my tropical course, but it’s interesting stuff and I’ll give it a try,” according to Simpson.

She finished her PhD in 1949 and began working at the Woods Hole Oceanographic Institution, which gave her the opportunity to do aircraft-based field experiments while continuing her collaboration with Riehl on tropical meteorology. She outfitted a Navy plane with instruments, but Woods Hole refused to let a woman fly in the plane; the Office of Naval Research made Simpson’s presence a condition for using it. So she completed the circle, and flying through the clouds she loved became her career.

Riehl’s knowledge of tropical meteorology combined with Simpson’s study of cloud formation to reveal the inner workings of the hurricane’s heat engine:

Scientists knew that the eye, or center, of a hurricane was made of a ring of towering clouds around a core of warm air and water, but they couldn’t explain how a core 10-18 degrees Celsius warmer than the surrounding area was created and sustained. Simpson solved an important part of the “warm core” mystery when she applied her “hot-tower hypothesis” to hurricanes. Hurricane winds spray warm water off the tops of ocean waves, and it easily evaporates into water vapor. The heat of the warm ocean water is latent—hidden—in the water vapor. Simpson proposed that a few of the huge cloud towers in the eyewall are active at any one time and that inside these “hot towers” the warm air rises, and water vapor condenses. During condensation, the heat that was latent in the water vapor is released into the upper part of the hurricane eyewall, shedding some of the high energy air into the eye on the way. This process maintains the essential warm core.

The release of the latent heat strengthens the low-pressure center in the eye of the hurricane, and winds rush in to fill that low-pressure “void.” The intensified winds suck up more heat and moisture from the ocean. The evaporated ocean water condenses once again into water droplets, replenishing the moisture in the storm clouds, and releasing even more latent heat. Simpson’s “hot-tower hypothesis” explained how this self-sustaining engine can drive the hurricane until it hits land or runs into colder water, or encounters one of the other “hurricane enemies” such as wind shear that can tear the warm core apart.

Simpson and Riehl, despite the technological innovations she made in the first-person observation of storms, were working with primitive tools and data; she made her first model of cloud formation using a slide rule. Further confirmation of their thesis would wait until decades later, when Simpson’s career cycled around again. In 1986, NASA named her the scientific lead on the Tropical Rainfall Measuring Mission, a rain-measuring satellite, the creation of which she considered the peak of her career. Development of the satellite took 11 years, launching in 1997. Almost seven years after that, and about forty years since Simpson and Riehl proposed the hot-tower theory, two NASA scientists, Owen Kelley and John Stout, used TRMM data to connect hot-tower clouds to the intensification of hurricanes.

“To me she’s the hero of this story. She came up with the idea of hot towers, she hypothesized they were important to the circulation of the atmosphere in general,” Kelley said. “And then, years later, she chaperoned the construction of the TRMM satellite, which ended up confirming that her hypotheses were correct.”

But Simpson’s triumph at NASA was also clouded by the misogyny she’d faced since her entry into the field. She ended up at NASA a few years before the TRMM project as the chief scientist for meteorology at the Goddard Space Flight Center—a prestigious job, but one she took in order to end a deeply unhappy five years at the University of Virginia.

“And when we talk about prejudice against women, I think I found that probably was more intense there than any place I had been. There were, in fact, a few remarks made, well, if you weren’t a woman you wouldn’t have been hired for this Chair,” Simpson said. “I was on the Dean’s Advisory Council and we were talking about hiring Joan Feynman, who is an excellent geophysicist. [Feynman herself was discouraged from science by her parents, but her brother, the legendary physicist Richard Feynman, fed her interest.] Well, the dean said, the government has forced us to take X percent of women in our science department, and you are it.”

Simpson worked for 30 years at NASA until her death at age 86, which was just what she wanted, as she told LeMone 21 years before her death:

Simpson: “By the time you get to be 65 years old you realize you can be an eccentric old lady as Bertrand Russell said, you can be a licensed lunatic. In many ways I’m the same. I am an eccentric old lady and I enjoy it…. However, there is another problem, but this may be due more to me than being a woman, and that is I have a big hang-up about what to do if I ever retired. Because I have worked so hard and with such enthusiasm all my life…. My greatest wish would to be like Grady Norton, who died of a heart attack while forecasting a hurricane; or like my early hero, Rossby, who keeled over and died in the middle of giving a seminar. I don’t like the idea of when I won’t be a meteorologist anymore. It’s just inconceivable to me.”

LeMone: "I hope you get your wish, I’m sure you will.”

Simpson: "I hope it’s not a morbid wish.”

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