PACDEX From a Satellite Perspective

Satellite observations from the TOMS, OMI, and MODIS experiments are used to place the April-May 2007 PACDEX mission in both a historical and geographical perspective. TOMS monthly averaged aerosol optical depths for 1979-2000 indicate the well known fact that dust storms are most prevalent in April and May, and are used to quantify the time-averaged trans-Pacific gradient in aerosol optical depth. Aerosol optical depths are largest over the Taklimakan desert source region, with smaller contributions from the Gobi desert, in both the TOMS historical record and in April-May 2007 OMI observations. MODIS aerosol fine mode data indicate that larger particles are observed over land and smaller particles over the ocean. Finally, MODIS radiances are analyzed to relate 3.75 micron cloud reflectance to aerosol amount. The Twomey effect, in which increases in aerosol amount are associated with increases in cloud reflectance, is readily apparent over the Taklimakan desert, but less so over the Pacific.