Potential Impacts of Sahara Dust Aerosol on Rainfall Vertical Structure Over the Atlantic Ocean as Identified From EOF Analysis

Abstract

The current study investigates the potential impacts of Sahara dust on rainfall vertical structure over the Atlantic Ocean by employing multisensor satellite observations. The variabilities in rainfall vertical structure are decomposed by empirical orthogonal function (EOF) analysis. For a given near surface rain rate, the mean storm height of stratiform rain under dust-laden condition is significantly higher than that under the dust-free condition. The stratiform rain rate at the layers well above the freezing level is substantially enhanced under dust-laden condition. Those changes may result from dynamic and thermodynamic effect of Sahara Air Layer effect and/or the effect that dust aerosol acting as additional ice nuclei. For convective rain, there is no significant difference in the leading three normalized EOF modes between the dust-laden and dust-free sectors, implying that dust effect, if exists, is not strong enough to cause evident changes in convective rainfall profiles. For stratiform rain, the EOF1 shows no signals of dust effect either. However, significant difference is found in the EOF2 and EOF3 modes between dust-laden and dust-free conditions. The normalized EOF2 and EOF3 under dust-laden condition both represent enhanced rain rate at the upper layer well above the freezing level, where heterogeneous ice nucleation prevails. The statistical study shows consistent results with the case study, except that the aerosol-related changes in stratiform rainfall vertical structure is isolated in the EOF3 only. This study suggests that EOF analysis is a promising way for isolating the potential and relatively weak aerosol effects on precipitation from the strong dynamic effects.