88th Annual Meeting (20-24 January 2008)

Wednesday, 23 January 2008
LASE Measurements of Water Vapor, Aerosol, and Cloud Distributions in Regions of African Easterly Waves and Saharan Dust Layers
Exhibit Hall B (Ernest N. Morial Convention Center)
Syed Ismail, NASA, Hampton, VA; and E. Browell, R. Ferrare, A. Notari, S. Kooi, C. Butler, T. N. Krishnamurti, J. P. Dunion, and G. Heymsfield
LASE (Lidar Atmospheric Sensing Experiment) on-board the NASA DC-8 was used to measure high resolution profiles of water vapor and aerosols, and cloud distributions during 14 flights over the eastern North Atlantic region during the NAMMA (NASA African Monsoon Multidisciplinary Analyses) field experiment which was conducted from August 15 to September 12, 2006. These measurements were made in conjunction with African Easterly Waves (AEWs), tropical disturbances, and Saharan Air Layers (SALs); and in clear air and convective regions. Interactions of SALs with tropical disturbances that were in the early stages of development were observed. LASE measurements were used to profile the SAL and guide in situ aircraft sampling of its suspended mineral dust.

LASE measurements have been used to derive water vapor mixing ratio and aerosol scattering ratio profiles. Relative humidity profiles have been derived for selected data sets, using temperature profiles from GPS dropwindsondes, to study the humidification of dust aerosols, cloud formation, and air mass transport. The dust layers over the ocean and the continent were found to range in altitude from near surface to 6 km. Aerosol scattering ratios at 817 nm ranged from 0 to >20, and their layer optical thickness ranged from 0 to >0.4. Dust layers were generally anti-correlated with the water vapor distributions, however, highly attenuating (cloud) regions with high RH (~100%) were occasionally observed within the dust layers. Moistening of the SAL in regions of convection was observed, and in general, greater moistening in the lower altitude regions was observed. Convection was also generally suppressed in the vicinity of the dust layers. Dust layers were situated generally north of the tropical disturbances that were observed, however, dust layers were also observed in and around several of the tropical disturbances. NAMMA provided an opportunity to compare LASE water vapor, aerosol, and cloud measurements with in situ aircraft, GPS dropwindsonde, and satellite observations. Examples of LASE measurements along with their relationship with several AEWs, at various stages of their developments, will be presented in this paper.

Mesoscale model simulations for hurricane Debby were conducted at Florida State University (FSU) using data collected during the NAMMA field experiment. These are based on forecast experiments carried out jointly with the FSU group. This covers the area of genesis of Debby through the dust covered eastern Atlantic. Results from these studies will also be presented in this paper.

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