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Using MODIS and GRAPE data to investigate the correlations between aerosol and cloud properties in a synoptic context

Benjamin Grandey(1), Philip Stier(1) and R. G. Grainger(1)

(1) University of Oxford, AOPP, Clarendon Laboratory, University of Oxford, OX1 3PU, United Kingdom

Abstract

Microphysical and dynamical interactions between clouds and aerosols are associated with some of the largest uncertainties in projections of future climate. Several correlations between cloud and aerosol properties have been published in recent years. However, much uncertainty remains and further work needs to be done in order to identify and quantify the physical reasons for these observations. We use data from both the MODIS instrument and the GRAPE project to investigate some of these cloud-aerosol correlations. We find a surprisingly strong and globally persistent negative correlation between aerosol optical depth (AOD) and cloud top pressure, showing that higher clouds are associated with higher AODs, and a positive correlation between AOD and cloud fraction. We propose possible microphysical, dynamical, synoptic and retrieval-related explanations for these observations, and proceed to probe these hypotheses. By analysing the data in a synoptic context, we aim to quantify the contribution of synoptic effects to the observed correlations.