Joanne Simpson  
  Portrait of Joanne Simpson

An animated speaker with sharp eyes and a crackling voice, Joanne Simpson strikes one as the type of person who has simply been too busy to worry about growing old. Becoming an octogenarian has not dimmed her enthusiasm so far. Behind her in her office sit over a dozen pictures of her children and grandchildren. To her left, a mosaic of accolades from her 54 years in meteorology tiles the wall.

Looking back at Simpson’s achievements, it is easy to see why she does not want to retire. In addition to being the first female meteorologist with a Ph.D., she’s been granted membership to the National Academy of Engineering, awarded the Carl-Gustaf Rossby Award (the highest honor bestowed by the American Meteorological Society), presented with a Guggenheim Fellowship, and served as President of the American Meteorological Society.

Photos of Joanne Simpson, Past and Present

Joanne Simpson’s career spans six decades, from field research aboard an aircraft in the Tropical Pacific (left) to her work with satellite data at NASA Goddard Space Flight Center (right). Not only the first woman to receive a Ph.D. in meteorology, she made many significant discoveries, led research projects, and influenced generations of scientists. [Photographs courtesy Joanne Simpson (left, right) and the Schlesinger Library (left)]

Although Simpson’s praises have been sung publicly as an example of a woman who has defied the odds and the male chauvinism of her profession, surprisingly few people outside of meteorology know precisely what she did for the science. Simpson’s scientific endeavors, aside from being exciting, have had a tremendous impact on meteorology over the years.

Enhanced Satellite Image of Hurricane Linda

One of Joanne Simpson’s greatest discoveries was the hurricane “heat engine.” This process brings energy from the ocean surface to the clouds high above, driving the storm’s awesome power. (Image courtesy Marit Jentoft-Nilsen, NASA GSFC)

Early in her career, Simpson developed the first cloud model, discovered what makes hurricanes run, and revealed what drives the atmospheric currents in the tropics. During her 40s and 50s, Simpson conducted some unique “weather modification” experiments that continue to have an impact on meteorology today. For the past 24 years, she has been with NASA, leading efforts in cloud modeling and space-based meteorological experiments. With both her mind and her desire to work as sharp as ever, Simpson will undoubtedly continue to make important contributions to the study of the atmosphere.

next: Discovering the Thrill of Science


Simpson's scientific endeavors have had a tremendous impact on meteorology over the years.

Portrait by Martin Mueller, NRC/NASA GSFC

  Joanne Simpson

Discovering the Thrill of Science

Born in Boston, Massachusetts, on March 23, 1923, Joanne Gerould did not have an ideal childhood. Watching her mother struggle through a bad marriage and subsequent divorce gave Simpson a strong drive to be self-sufficient. “There were many times my mother stated, ’If it weren’t for you children, I would go back and earn my living,’” she recounts. “I made up my mind, I think by the time I was ten years old, that there was absolutely no way I was going to get myself into that sort of situation. No matter what happened, I was going to be able to make my own living and to provide for whatever children I might have without depending on anybody else.”

Photograph of Joanne Simpson at age 5, with a Velveteen Rabbit

Joanne Simpson was born in Boston, Massachusetts, in 1923, and posed for this photo at age 5. She became interested in weather and clouds while sailing off Cape Cod. (Photograph courtesy Joanne Simpson and the Schlesinger Library)

Simpson recalls that she was fascinated by clouds as she sailed her small catboat off Cape Cod. But she didn’t get excited about science until she entered the University of Chicago, where she took a course in astrophysics. “Had it not been for World War II, I probably would have tried to go into astrophysics,” she says. But as a student pilot, she had to take course in meteorology. She was fascinated and asked the instructor if the university had any more courses in meteorology. He told her that Carl-Gustaf Rossby, who many still consider to be the greatest meteorologist ever, had just arrived at the University of Chicago to set up an institute of meteorology. “I made an appointment with him, went into his office, and ten minutes later, I was in the World War II meteorology program as a teacher-in-training,” says Simpson. Until the war ended, she had great fun teaching meteorology to Aviation Cadets, many older than herself.

After the war, women were supposed to go home and get behind a mop, but Simpson was more interested in weather than housework. She completed her Masters Degree and wanted to go into the Ph.D. program. The Faculty Advisor told her and two other women that no woman ever got a Ph.D. in Meteorology, none ever would, and if any of them did, she would never be given a job. Simpson struggled on with student loans. After completing a course with Herbert Riehl on tropical meteorology, she decided to concentrate on tropical cumulous clouds and asked Riehl if he would be her Ph.D. advisor. To her and everyone’s surprise he agreed.

Photograph of Joanne Simpson at woods Hole Map of Clouds in the Tropical Pacific

Simpson’s early research at Woods Hole involved filming clouds on long flights between islands in the tropical Pacific. She then drew intricate maps of cloud formations, revealing for the first time patterns that are now routinely shown by satellites. Her work helped show the critical role tropical clouds play in global atmospheric circulation. (Photograph courtesy Joanne Simpson and the Schlesinger Library; Map from Malkus and Riehl, 1964)

At the time, nobody thought clouds were a big part of what drives the weather; they were more the result of weather, not the cause. “So I was interested in clouds for just themselves because they were fascinating,” explains Simpson. Rossby said that no one was very interested in them, so it was a good subject “for a little girl to study.” Despite the hostility and guffaws she received from some of the all-male faculty at the University of Chicago along the way, Simpson went on to become the first woman to hold a Ph.D. in meteorology.

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Simpson went on to become the first woman to hold a Ph.D. in meteorology.

  Joanne Simpson

“Hot Tower” Hypothesis

Upon earning her Ph.D., Simpson had a husband, one child, and no job. Frustrated after being repeatedly turned down because of her gender, she eventually landed a position at the Illinois Institute of Technology, where she eventually became an Assistant Professor of Physics. During the summers, Simpson (now Joanne Malkus) traveled to Woods Hole Oceanographic Institute with her family (now two boys) to work on an exciting project involving tropical clouds. Simpson moved to the Woods Hole Oceanographic Institution after deciding to leave Chicago for a better place to raise her young children. There she began to develop a model of cumulus clouds and to take the first steps in demonstrating how important these clouds were in driving tropical circulations.

Photograph of Convective Tower

Simpson, in collaboration with Herbert Riehl, proposed the “Hot Tower” hypothesis of tropical convection in 1958. Predictions of the hypothesis were verified by field experiments 20 years later. Hot towers are clouds that carry undiluted warm, moist air from the ocean surface 15,000 meters (50,000 feet) into the air. This tower was photographed from a NOAA aircraft in 1970. (Photograph courtesy NOAA Photo Library)

No one at that time really understood the workings of the Hadley circulation (the atmospheric movements that transport heat and moisture from the tropics toward higher latitudes). Simpson felt the answers lay in the very tall clouds in equatorial regions. But to get answers, she needed many more observations. At Simpson’s request, the Office of Naval Research provided the Woods Hole team with an old PBY-6A airplane, which they outfitted with instruments that measured wind motions, humidity, liquid water, air pressure, temperature, and more. “Getting the first instrumented airplane,” she says, “and arguing that trade cumulus clouds were important and that we ought to go make measurements of them was the biggest contribution I made at Woods Hole.” Initially, Woods Hole said that women were not allowed on their field trips. The Navy Officer who had arranged the aircraft to go to Woods Hole told the Director, “No Joanne, no airplane.”

Joanne Simpson and the Crew of the Woods Hole PBY

The Navy provided a PBY flying boat to the Woods Hole Oceanographic Institute so Joanne Simpson could study tropical clouds. In this photograph she stands with her crew in front of the aircraft. (Photograph courtesy Joanne Simpson and the Schlesinger Library)

The results of that first field trip established her reputation as a good scientist. In the late 1950s, Simpson and her former Ph.D. advisor, Riehl, turned meteorology on its ear when they showed that heat generated by the condensation of water within tall, anvil-shaped, cumulonimbus clouds called “hot towers” provides the energy needed to keep the Hadley circulation and the trade winds running. Some people doubted this “hot tower hypothesis.” They claimed that the energy released by the clouds would be diluted by outside air before it ever reached the cloud tops. Simpson and Riehl demonstrated that these “protected cores” of energy transport are not only possible, but that they occur all the time in equatorial regions.

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In the late 1950s, Simpson turned meteorology on its ear when she showed that heat generated by the condensation of water within clouds called 'hot towers' provides the energy needed to keep the trade winds

  Joanne Simpson

Warm Core Mystery

At about this time, Dr. Robert Simpson of the U.S. Weather Bureau, who had also been a Ph.D. student of Riehl’s, founded the multi-aircraft Hurricane Research Project, based at Palm Beach Florida. Simpson, who had gone on to work at the University of California Los Angeles, was invited to come down and study the new data. With this amazing opportunity, Simpson made new discoveries on how the “eye” of the hurricane works. Before Simpson’s work with Riehl and (Bob) Simpson, meteorologists did not have an understanding of how the “heat engine” inside a hurricane worked. How did hurricanes sustain their tremendous power as they moved over great distances?

Photograph of Joanne Simpson and Herbert Riehl

Joanne Simpson (second from right) collaborated with Herbert Riehl (right) and Bob Simpson (second from left) to extend her theories of “hot towers” to hurricanes. Standing in front of Simpson is her daughter, Karen Elizabeth Malkus. (Photograph courtesy Joanne Simpson and the Schlesinger Library)

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.

TRMM Image of Hot Tower in Hurricane bonnie

The Tropical Rainfall Measuring Mission (TRMM) provided dramatic confirmation of hot towers in hurricanes when it collected data of Hurricane Bonnie on August 22, 1998. A column of intense rainfall rose to the astonishing altitude of 18,000 meters (59,000 feet)—twice the height of Mt. Everest. (Image courtesy NASA GSFC Scientific Visualization Studio, based on data provided by the TRMM science team.)

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 solved an important part of the of the 'warm core' mystery when she applied her 'hot-tower hypothesis' to hurricanes.

Diagram of Hurricane Shear

Simpson’s landmark paper, “On the structure and maintenance of the mature hurricane eye,” described the heat transport in hurricanes. (Diagram from Malkus, 1958)

As if unraveling the mysteries behind tropical circulation and hurricanes weren’t enough, Simpson also created the first cloud model. “From the beginning my greatest dream was to be able to make a model of a cloud that was either an analytic equation or a computer model,” says Simpson. She says that her first model was a one-dimensional depiction of a buoyant cloud plume growing vertically. At first, she used a slide rule to do the calculations because computers had not been invented. Despite the model’s limitations, Simpson’s work sparked an entire field of study within meteorology. Around the time when she began working on cloud models, there were two or three other people in the field. After only a year or two, there were up to about 350 meteorologists working on cloud models and related observations. The popularity was largely driven by scientific and practical interest in cloud seeding and weather modification.

next: The Weather Modification Roller Coaster
back: “Hot Tower” Hypothesis

  Joanne Simpson

The Weather Modification Roller Coaster

In 1960, Simpson was a full Professor at the University of California Los Angeles, where she designed and taught graduate classes, and wrote two books. She also “computerized” her cloud model and began looking for ways to test it. Simpson realized that cloud seeding experiments would be a good way to test how well the model she had developed described how clouds really behaved. Since the late 1940s, scientists had known that silver iodide introduced into a cloud with super-cooled water droplets led to the formation of ice crystals. But by the 1960s, no one had figured out exactly how clouds behaved after being seeded. Simpson’s model predicted that the large amount of latent heat released as the cloud’s water droplets changed to ice would, under certain conditions, cause a cloud to grow much taller and to more than double in size compared to an unseeded cloud.

Photograph of Joanne Simpson at UCLA

Joanne Simpson became a full professor at UCLA in 1961. While there she developed the first computer cloud model. (Photograph courtesy Joanne Simpson and the Schlesinger Library)

Simpson got her chance to test this hypothesis in 1963 by “bootlegging” aircraft time during Project Stormfury, a weather modification experiment started in 1961 by Simpson’s future husband, Bob Simpson. She flew up above clouds and ejected flares from a chute under the airplane. The flares ignited and created silver iodide smoke, which dispersed silver iodide fairly evenly over clouds. The clouds behaved just as her cloud model predicted. “We wrote an article and a furor broke loose,” said Simpson. “I was totally unaware of the level of emotion and hostility that was directed against anything that had to do with cloud seeding.” Many in and outside of the scientific community were skeptical of weather modification. The main fear was that meteorology would get a bad name by the promises of charlatans.

In 1964, Simpson left UCLA to take a position with the National Weather Bureau (which later became the National Oceanic and Atmospheric Administration). In 1965 she married Bob Simpson, who headed the Weather Bureau’s Severe Storms Program. The Simpsons moved to Miami, where Bob became the Director of the National Hurricane Center and Simpson headed the Experimental Meteorology Laboratory. She somewhat reluctantly agreed to take charge of Project Stormfury. Stormfury’s primary objective was to test a hypothesis that a hurricane’s maximum winds could be weakened by about 10 percent if the most active area of the eyewall could be massively seeded.

The project was based on a reasonable hypothesis that required careful testing, but it became bitterly controversial, with insults in speech and print that were often assaults on the personal integrity of the scientists involved in Stormfury. Permission for seeding was restricted to a very small area in the western Atlantic. Between 1964-68, Stormfury deployed its aircraft, only to find that the sole suitable hurricane moved out of the permitted seeding area. Simpson decided she had ridden long enough on the weather modification roller coaster, and she passed the Stormfury Directorship on to a another good hurricane expert. Stormfury eventually fizzled in the 1970s after the low-flying aircraft in use at that time failed to find the kind of super-cooled clouds in which seeding was known to be effective.

Photograph of Joanne Simpson at NOAA

From 1964 to 1974 Simpson worked for the National Weather Bureau (later NOAA). While there she was the head of the Experimental Meteorology Laboratory. In 1972 she was awarded the Department of Commerce Gold Medal. (Photograph courtesy Joanne Simpson and the Schlesinger Library)

Simpson decided to concentrate on cloud seeding experiments with an emphasis on the scientific processes involved, rather than on how they might be applied to weather modification. Simpson developed a double-blind experiment that convinced the science community that her cloud seeding hypothesis was correct. Simpson had tried to leave weather modification behind, but a young co-worker, Bill Woodley, found that the seeded clouds in Simpson’s experiment rained about twice as much as the controls. NOAA management got on the weather modification wagon again. They wanted the Experimental Meteorology Laboratory to show that the rainfall over a large area in south Florida could be increased by seeding. This was the beginning of a project called FACE (the Florida Area Cumulus Experiment).

Photograph of Joanne During FACE

In 1973 Joanne Simpson lead the Florida Area Cumulus Experiment (FACE)—a NOAA program to enhance rainfall with cloud seeding. She is shown here aboard a NOAA Research Flight Facility C-130. (Photograph courtesy Fritz Hoelzl, NOAA)

Early results looked favorable for area-wide rainfall increase. But scientists involved estimated that to detect just a 10-15 per cent rainfall increase they would need at least 600 cloud seeding test cases. NOAA management agreed to fund no more than 100. With so few cases, sharp scientists would mistrust the results, even if FACE seemed successful. Confronted with the agency’s militaristic, “no-argument” management style of the time, Simpson realized that she had to leave. Ultimately, FACE failed to demonstrate that cloud seeding could increase rainfall, effectively killing weather modification research in the United States.

In 1974, Simpson left NOAA and became an Endowed Chair Professor in the Environmental Science Department at the University of Virginia, but even after her already substantial accomplishments, the mostly-male faculty did not regard her as a real professor simply because she was a woman. In fact, it became clear over the years that women faculty were held in such low regard there that it was nearly impossible to get a secretary!

Photograph of Joanne Simpson Working With Claude Ronne, UVA

After leaving NOAA Simpson moved to the University of Virginia. Despite her record of ground-breaking science and leadership, she was often treated poorly by the male-dominated institution. In this photograph she studies data from the Global Atmospheric Research Program Atlantic Tropical Experiment with Claude Ronne. (Photograph courtesy Joanne Simpson and the Schlesinger Library)

Luckily Simpson had been in touch with Dave Atlas, who at the time was putting together a new Laboratory for Atmospheres at NASA’s Goddard Space Flight Center. “He’d been going at it for about a year or so, and I asked him if he had any jobs left. He said, ’The Severe Storms Branch needs leadership, please come tomorrow morning.’” A one-year leave from the University extended into two, and in the end Simpson decided that Goddard was a far more favorable environment in which to work. Simpson counts the choice as the best career decision she ever made.

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  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)

next: Retiring as a Role Model
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  Joanne Simpson

Retiring as a Role Model

From her early work at Woods Hole to TRMM, Simpson says she really doesn’t have any regrets. She does, however, admit that she would like to have given her three kids more mothering in their early childhoods, but she says that meteorologists are typically in their prime productivity in their 30s or 40s. In the 1950s and 1960s, day care centers did not exist, so Simpson had frequently to hire new baby sitters and sometimes bring her kids with her to work. Now Simpson says she has a wonderful relationship with her grown children and that they have all become involved in science in some capacity. “They all tell me that they are glad I continued on my career path. They seem to have pretty happy memories of their childhoods,” she says.

Photograph of Joanne Simpson receiving the WMO award

In the 21st century, Simpson continues to receive accolades and break new ground. Here she gives the acceptance speech for the International Meteorological Organization Prize in 2002. She was the first woman to win the award. (Photograph courtesy NASA)

Regardless of the obstacles faced by women in her time, Simpson says she was lucky to get into meteorology when she did. She was in the profession during a time when some of the biggest discoveries were made. However, being the first woman in meteorology really pushed her. Not only were her personal goals and profession on the line, but also she felt responsible for the fate of other, younger women who wanted to be meteorologists. “I have always felt that I’ve been carrying a big burden for other women, because if I mess up then the chances for other women to get the same kind of job are going to be diminished,” says Simpson. But here is one arena from which Simpson is willing to retire. “I think I can now retire as a role model, since there are so many really great younger women meteorologists—many of whom have children, too—who are serving that function extremely well.”

  • Acknowledgements:
  • Jacalyn R. Blume & Kathy Jacob, Schlesinger Library, Radcliffe Institute for Advanced Study, Harvard University
  • References:
  • Malkus and Riehl, Cloud Structure and Distributions over the Tropical Pacific Ocean, 1964
  • Tao, Wei-Kuo, and Adler, Robert Cloud Systems, Hurricanes, and the Tropical Rainfall Measuring Mission (TRMM)—A Tribute to Joanne Simpson, 2003

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