Hurricane water vapor, aerosol, and cloud distributions determined from airborne lidar measurements

During the CAMEX-3 (Convection And Moisture EXperiment) conducted in August-September 1998 over the Atlantic Ocean and Gulf of Mexico, the LASE (Lidar Atmospheric Sensing Experiment) instrument was flown on the NASA DC-8 aircraft to investigate the distribution of water vapor, aerosols, and clouds around hurricanes with the objective of improving the capability for predicting hurricane behavior. The LASE instrument was developed at the NASA Langley Research Center as the first autonomously operating DIAL (DIfferential Absorption Lidar) system, and it was initially designed to be flown on a high-altitude ER-2 aircraft for profiling water vapor, aerosols, and clouds across the troposphere. The LASE water vapor measurements acquired during CAMEX-3 have a vertical resolution of 330 m in the lower troposphere and 510 m in the middle to upper troposphere, and the horizontal resolution is less than about 14 km. The capabilities of this system were first demonstrated in 1994 during the most extensive lidar validation experiment ever conducted. In comparison to calibrated in situ and remote water vapor measurements, the LASE water vapor profile measurements were found to be accurate to better than 6 percent or 0.01 g/kg, whichever is larger, over the range of water vapor mixing ratios from over 10 g/kg near the surface to less than 0.02 g/kg near the tropopause.

For the CAMEX-3 field experiment, LASE was configured for the first time to operate on the NASA DC-8 aircraft and to make simultaneous measurements of water vapor, aerosols, and clouds below and above the aircraft. Patrick Air Force Base in Florida was chosen as the base for conducting the CAMEX-3 field experiment, and from August 21 to September 23, 1998, nine flights were conducted to investigate four hurricanes (Bonnie, Danielle, Earl, and Georges). LASE flights were made to characterize conditions in various regions around each hurricane including: synoptic conditions ahead of the hurricane; inflow conditions feeding the hurricane; hurricane eye characteristics; vortex motions and development; and landfall characteristics. LASE measurements were made in conjunction with other remote and in situ measurements made from the DC-8 and ER-2 aircraft during these missions. These flights, conducted in conjunction with NOAA and Air Force Reserve aircraft, provided the most comprehensive set of measurements ever obtained around a hurricane. The LASE measurements showed the extent of the dry subsiding air ahead of the hurricane, the inflow of very moist air in the lower troposphere into the hurricane, the distribution of clouds, rain, and water vapor associated with the hurricane rain bands, and the first detailed moisture distribution across the eye of a hurricane. These data provide a detailed characterization of hurricane properties that are being used for forecast model evaluation and improvement and for assessing the impact of high-resolution water vapor, aerosol, and cloud data on predictions of hurricane evolution and motion.

This paper discusses LASE measurements of water vapor, aerosol, and cloud distributions made during CAMEX-3 in conjunction with flights around Hurricanes Bonnie, Danielle, Earl, and Georges. These results are also related to other atmospheric measurements made during CAMEX-3 from satellite, aircraft, balloon, and ground-based sensors.