Shortwave direct radiative forcing of Saharan dust aerosols over the Atlantic Ocean

Abstract

Using collocated Visible and Infrared Scanner (VIRS) and Clouds and the Earth's Radiant Energy Budget Scanner (CERES) data on board the Tropical Rainfall Measuring Mission (TRMM) satellite, the instantaneous Shortwave Aerosol Radiative Forcing (SWARF) and daytime diurnally averaged SWARF at the top-of-atmosphere (TOA) are estimated for Saharan dust over the Atlantic Ocean (10° N–25°N, 30° W–15° W) for July 1998. A combination of reflectance thresholds, along with infrared spatial coherence techniques, are used to separate dust aerosols from clouds. Using Mie and Discrete Ordinate Radiative Transfer (DISORT) calculations and the VIRS channel 1 reflectance, dust optical thickness (τ) is retrieved. The average instantaneous direct SWARF of dust aerosols per unit τ is −50 W m−2. The daytime diurnally averaged SWARF of dust aerosols is −15.2±10.9 W m−2 for a mean z of 0.79±0.39. This study demonstrates that the synergistic use of instruments from different parts of the electromagnetic spectrum can be used to study the radiative effects of dust aerosols. This study is also among the first to estimate the diurnal SWARF of dust aerosols using satellite sensor data.