Monday, 12 January 2004: 11:30 AM
Impact of high resolution water vapor measurements from airborne lidar on hurricane characterization and forecasting
Airborne investigations of hurricane and tropical storm characteristics were conducted over the Atlantic Ocean during August-September of 1998 and 2001 as part of the ongoing series of NASA Convective and Moisture Experiments (CAMEX-3 and 4, respectively). 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 NASA DC-8 aircraft was one of the aircraft used in these experiments, and it had onboard a lidar system called LASE (Lidar Atmospheric Sensing Experiment), which is capable of measuring water vapor profiles with high vertical (330 m) and horizontal (42 km) resolution from the surface to near the tropopause along the aircraft flight track. LASE also simultaneously measures aerosol and cloud distributions with even higher resolution (60 m vertical and 2 km horizontal) to correlate with the water vapor measurements. Dropsondes were also used from the DC-8 to provide occasional wind, water vapor, and temperature profiles to the surface. 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. During these flights, LASE measured high-resolution moisture, aerosol, and cloud distributions in and around several hurricanes and tropical storms; across the eye of several hurricanes; across rain bands; under cirrus outflow; and in synoptic regions not available from conventional observations.
The impact on hurricane data assimilation and forecasting from the use of LASE and dropsonde data was evaluated using hurricane modeling capability at Florida State University. The results of this investigation show that the use of these additional data sets, above those of the conventional world weather watch, have a positive impact on hurricane predictions. The forecast tracks and intensity from these experiments show a marked improvement compared to the control experiment where such data sets were excluded. A study of the moisture budget in these hurricanes showed enhanced evaporation and precipitation over the storm area and this resulted in these data sets making a large impact on the estimate of mass convergence and moisture fluxes, which were much smaller in the control runs. Overall this study points to the importance of high vertical resolution humidity data sets for improved model results. In addition, it was found that the added humidity data have a strong impact on hurricane track forecasts with an improvement of the order of 100 km on day 3 of the forecast for the CAMEX storms. There was also a slight improvement in the intensity forecasts. More robust humidity budgets were found from the inclusion of these additional humidity data sets, i.e. an enhancement of evaporation, precipitation and divergence and fluxes of moisture in the inner rain area of these hurricanes. LASE measurements of hurricane characteristics and their impact on hurricane forecasting will be presented in this paper.