Joanne Simpson (1923–2010) Meteorologist Who Brought the Study of Clouds to the Forefront of Earth Science

NEWS & VIEWS NATURE|Vol 464|1 April 2010 obituaRy Joanne Simpson (1923–2010) Meteorologist who brought the study of clouds to the forefront of Earth science. s E

Before Joanne Simpson got into meteorology, used to mitigate the strength of hurricanes. h neither women nor clouds were taken The technology did not prove effective, but, NT A very seriously in the emerging field of like the Florida cumulus work, these field atmospheric science. She liked to tell the experiments led to new understanding — in ARD

story of a pre-eminent professor advising particular, that it is difficult to reduce the Rich sy

her that clouds would be “a good subject for strength of hurricanes by artificially seeding RTE ou a little girl” because they were just passive hurricane clouds because they are naturally c phenomena determined by the larger filled with ice particles. dynamics of the atmosphere. That little girl Mesoscale cloud systems remained a went on to show that clouds are essential focus for Simpson during and after the interactive elements of the atmosphere — Florida years; to study them, she helped lead critical not only to the physics of major expeditions to the equatorial Atlantic, the storms, but also to the general circulation Asian monsoon and the South Pacific. By the and climate of the whole atmosphere. 1990s, though, Simpson had arrived at NASA Simpson, who died on 4 March, was and was moving away from the piecemeal an explorer. She undertook treks in the study of clouds, through observations Himalayas, undersea diving and long sailing from aircraft, to the comprehensive study expeditions. But most of all, she explored of tropical clouds by satellite. She became clouds — first by aircraft and later by satellite. project scientist for the Tropical Rainfall She focused her life’s work on cumulus and Measuring Mission (TRMM) satellite, which cumulonimbus clouds because she wanted put the first meteorological radar into space most to understand the clouds that carry in 1997. energy from the warm tropical oceans to the This satellite still orbits the tropical upper atmosphere. latitudes today. It observes critical details of Simpson’s early work at the Woods Hole the entire population of clouds that release Oceanographic Institution in Massachusetts happens are still debated, the basic hot-tower energy into the tropical atmosphere and drive and at the University of California, Los energy-transport idea has become key to the global climate. The satellite has been Angeles, in the 1950s and 1960s took her understanding the global climate. revolutionary — spawning global studies of over the ocean in crude airplanes to observe Less widely recognized, but just as rainfall and a host of other factors crucial how the smallest tropical cumulus clouds important, is Simpson’s recognition that the for understanding the global climate, such carried energy up from the sea. Further astute hot towers reaching the upper atmosphere as how the hot towers and other clouds of observations of tropical cloud forms led her needed the ‘protection’ of larger, ‘mesoscale’ the tropics distribute energy, how monsoon to postulate how these clouds become diluted cloud systems. When weather satellites rains occur, how the Himalayas and Andes by drawing air into themselves from the started to be used, researchers realized that affect the distribution of tropical clouds, and uncloudy environment. Her work inspired these mesoscale systems were the extensive how anthropogenic effects are influencing some of the first numerical cloud modelling, bright areas that dominated the satellite weather. Simpson considered the TRMM her which she later promoted in her laboratories pictures taken over tropical oceans. Much greatest achievement. at the National Oceanic and Atmospheric later in her career, in 1992, Simpson led She received numerous formal accolades Administration (NOAA), the University a flight into a mesoscale system that was and awards throughout her working life, of Virginia in Charlottesville and, finally, evolving into a tropical storm, and so began including the Los Angeles Times Woman of NASA’s Goddard Space Flight Center in to reveal how the larger mesoscale systems the Year and the American Meteorological Greenbelt, Maryland. Indeed, at NASA, she are involved in the early stages of a hurricane. Society’s 1983 Carl-Gustaf Rossby Research and her colleagues developed one of the most In the mid-1960s to 1970s, while head of a Medal — the highest award in atmospheric respected cloud-modelling research centres NOAA laboratory in Coral Gables, Florida, sciences, named for the very professor who in the world today. Simpson focused on whether clouds could told her clouds were not all that important. Simpson’s most famous work is her be artificially modified by seeding them with But she is also remembered for pushing ‘hot tower’ hypothesis, posited with her silver iodide. This stimulates water drops atmospheric sciences forward by the great colleague Herbert Riehl in 1958. Around this to freeze and thus release energy. Although force of her personality and her charisma. time, meteorologists were mystified by the cloud seeding has never proved feasible, Whether in a broad-brimmed hat or flight observation that warmer, high-energy air in Simpson’s studies led to improved cloud suit and sunglasses, Joanne Simpson at the the upper atmosphere of the tropics seemed modelling and to an understanding of how height of her career, walking into a crowd and to be separated from the warm ocean by a smaller clouds merge with each other to form aligning the group towards the mission of the region of low energy in the middle levels of mesoscale systems. day — that will not be forgotten. Her powerful the atmosphere. From their knowledge of the During this time, she collaborated with combination of intellect, determination, buoyant nature of the air inside cumulus and Robert Simpson, then the director of the leadership and drive will be missed. cumulonimbus clouds, Simpson and Riehl National Hurricane Center in Miami, Robert a. houze Jr suggested that it was the cumulonimbus Florida, who would become her husband Robert A. Houze Jr is in the Department of clouds that penetrated the low-energy region of 45 years. Together, they designed an Atmospheric Sciences, University of Washington, and carried energy to upper levels. Although experiment called Project Stormfury, to Seattle, Washington 98195, USA. the details of the mechanism by which this explore whether cloud seeding could be e-mail: [email protected]