UCLA hurricane tracker to present seminar Thursday Robert Fovell, a professor at the University of California, Los Angeles' Department of Atmospheric and Oceanic Sciences, will present a seminar on "Why and How Cloud Microphysics Influences Hurricane Tracks" at 3 p.m. Thursday, Aug. 28, in 106 Streibel Hall. Recently, Fovell showed that the choice of microphysics scheme could significantly influence the track of hurricanes simulated with the Weather Research and Forecasting (WRF) model, even over relatively short (54 hours) integration periods. Simulations of Hurricane Rita, for example, revealed a spread of predicted landfalls comparable to those forecasted by the National Hurricane Center's multi- model consensus, just by varying how condensed water is handled. The reasons why microphysical assumptions can have a first- order influence on hurricane motion are demonstrated and explained using an idealized version of the same model. In a nutshell, hurricane motion is sensitive to the winds at relatively large radius (300- 700 km) from the core. Those winds depend on pressure gradients that can be easily and directly altered by manipulating the radial variation of temperature. Through evaporation rates, fallout speeds, and radiative effects, microphysics determines how condensation is formed and where it spreads, and thus influences radial temperature gradients, which determines radial pressure gradients, which produces the winds that determine the tracks. As a result, high quality observations from a wide region surrounding the storm are of great value, and the development and tuning of new and better microphysical schemes is strongly motivated. This seminar is free and open to the public. Faculty, staff and students are encouraged to attend.