Tuesday, 11 February 2003
LASE characterization of the hurricane environment and the influence of moisture on hurricane forecasting
The Lidar Atmospheric Sensing Experiment (LASE) system was developed at the NASA Langley Research Center for airborne remote profile measurements of atmospheric water vapor, aerosols, and clouds. The LASE system was operated onboard the NASA DC-8 aircraft during the Convection and Moisture Experiments (CAMEX-3 and CAMEX-4) that were conducted during August-September 1998 and August-September 2001, respectively, over the Atlantic Ocean. The main objective of these field experiments was the collection of new data for research in hurricane development, tracking, intensification, and landfall impact using NASA-funded aircraft and surface remote sensing instrumentation. The DC-8 conducted a number of long duration flights around and through hurricanes or tropical storms Bonnie, Danielle, Earl, Georges, Erin, Humberto, Chantel, and Gabrielle during these field experiments. LASE measured high-resolution moisture, aerosol, and cloud distributions in and around several hurricanes; across the eye of several hurricanes; across rain bands; under cirrus outflow; and in synoptic regions not available from conventional observations. LASE water vapor measurements of water vapor were compared with other remote and in situ measurements. Comparison of LASE water vapor measurements with dropsonde moisture data from the Airborne Atmospheric Profiling System showed, in general, a good agreement between the two measurements. However, the dropsonde moisture profiles were 10-20% dryer compared to LASE during CAMEX-3. The degassing of the desiccants in the Vaisala humidity sensors that were used at that time probably caused this dry bias. At Florida State University, these new data sets were analysed and medium range forecasts were carried out by integrating the NWP model out to 5 days. The impact studies using CAMEX-3 data show the improvement of forecast tracks and some improvement in hurricane intensity forecast. Use of LASE data sets impacts the moisture analysis and prediction at almost all atmospheric levels. In case of Hurricane Bonnie the 3-5 day track forecast improved by about 100km by the utilization of LASE data. Furthermore, a large impact of LASE data set can be seen in the convergence of mass and moisture fluxes during the intensification of Hurricane Erin. Water vapor in the low-, mid-, and upper-troposphere varied by more than an order of magnitude indicating dynamical and thermodynmical processes associated with hurricanes. A dry descending air in the vicinity of Tropical Storm Gabrielle probably inhibited its expected rapid re-intensification off the coast of Florida. LASE measurements of hurricane characteristics and their role in hurricane forecasting will be presented in this paper.