The dynamics and energetics of tropical cyclones--a brief history (Invited Presentation)
Tropical cyclones have always been a subject of fascination, not only because of their terrible effects on people, but also from a scientific point of view because of their relative isolation from other atmospheric systems and their dynamic and thermodynamic characteristics that made them different from any other atmospheric system on Earth. It was recognized very early on that their existence depended upon heat and water vapor transfer from the warm ocean and the release of latent heat in convective clouds. In this talk I briefly review the history of tropical cyclone research and forecasting, including tropical cyclone modeling.
I begin the history of tropical cyclone forecasting and research with one of the first known forecasts of an Atlantic hurricane, an 1847 forecast of a Barbados hurricane by William Reed. I review the remarkable career of Father Benito Viñes, a Jesuit priest in Cuba who studied tropical storms from the observations he had at the time, pressure, wind, and cirrus cloud motions, and made many successful forecasts based on these limited observations. I then trace the important foundations for modern-day tropical cyclone prediction: numerical weather prediction, upper-air soundings from pilot balloons and radiosondes, aircraft reconnaissance, radars and satellites.
The first numerical models of hurricanes began in 1950 with a barotropic model developed by the Princeton group. A decade later, Akira Kasahara experimented with a primitive equation, axially symmetric hurricane model and observed the rapid growth of small-scale convective elements instead of a cyclone-scale vortex. The 1960s and 1970s was a vibrant decade of hurricane research, much of it involving the concept of “hot towers, “conditional instability of the second kind (CISK)” and a number of detailed observational studies carried out by the National Hurricane Research Project led by Bob Simpson (and later the National Hurricane Research Laboratory led by Cecil Gentry). This period was marked by unforgettable discussions and friendly arguments involving Bob and Joanne Simpson, Bill Gray, Banner Miller, Vic Ooyama, Akio Arwakawa, Stan Rosenthal, Jule Charney and many others.
As a young student of Don Johnson at the University of Wisconsin-Madison, I was motivated to study the energetics and dynamics of tropical cyclones from the view point of available potential energy. I even accepted Don's challenge to develop a model of the tropical cyclone in isentropic coordinates, in spite of the irony that tropical cyclones were dominated by non-isentropic (diabatic heating and cooling) processes! For my Master's thesis I studied the generation of available potential energy from various diabatic sources in Hurricane Hilda (1964) and Don and I published the results in the Monthly Weather Review in 1968. A portion of the abstract of that paper is reprinted below:
The generation of available potential energy is shown to be closely dependent on differential heating within the baroclinic structure of the hurricane, occurring primarily in the middle and upper troposphere of the core of the storm. The diabatic heating components (condensation, emission of long wave radiation, direct absorption of solar radiation, and sensible heating) are modeled and the contribution to the total generation from each component computed. The results from the latent heating model based on Kuo's work portray the dependence of the deep cumulus convection on the sea surface temperature. The best estimate of the total generation of available potential energy within the hurricane scale is 10.3 × 1012 watts, of which 77 percent is generated by latent heating, 17 percent by infrared cooling, and 6 percent by direct solar absorption. The total generation compares favorably with estimates of kinetic energy production in mature hurricanes.”
As I was finishing my PhD thesis under Don (a two-dimensional model of the tropical cyclone in isentropic coordinates), I turned my attention to the development of a three-layer, three-dimensional hurricane model, but now I used sigma coordinates because of the difficulties in modeling the lowest few km of the troposphere in isentropic coordinates and the importance of diabatic heating, which countered one of the main advantages of isentropic coordinates. The hurricane model went on to become the Penn State-NCAR Mesoscale Model (MM), which became best known and most widely used 1n the 1980s and 90s as MM5 (the fifth generation version of MM). If Don was ever disappointed in this switch of coordinates, he never let on, supporting me through my whole career and he and his wife Dorthea remaining close friends today.