Articles | Volume 17, issue 6
Research article
24 Mar 2017
Research article |  | 24 Mar 2017

Satellite retrievals of dust aerosol over the Red Sea and the Persian Gulf (2005–2015)

Jamie R. Banks, Helen E. Brindley, Georgiy Stenchikov, and Kerstin Schepanski

Abstract. The inter-annual variability of the dust aerosol presence over the Red Sea and the Persian Gulf is analysed over the period 2005–2015. Particular attention is paid to the variation in loading across the Red Sea, which has previously been shown to have a strong, seasonally dependent latitudinal gradient. Over the 11 years considered, the July mean 630 nm aerosol optical depth (AOD) derived from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) varies between 0.48 and 1.45 in the southern half of the Red Sea. In the north, the equivalent variation is between 0.22 and 0.66. The temporal and spatial pattern of variability captured by SEVIRI is also seen in AOD retrievals from the MODerate Imaging Spectroradiometer (MODIS), but there is a systematic offset between the two records. Comparisons of both sets of retrievals with ship- and land-based AERONET measurements show a high degree of correlation with biases of  <  0.08. However, these comparisons typically only sample relatively low aerosol loadings. When both records are stratified by AOD retrievals from the Multi-angle Imaging SpectroRadiometer (MISR), opposing behaviour is revealed at high MISR AODs ( >  1), with offsets of +0.19 for MODIS and −0.06 for SEVIRI. Similar behaviour is also seen over the Persian Gulf. Analysis of the scattering angles at which retrievals from the SEVIRI and MODIS measurements are typically performed in these regions suggests that assumptions concerning particle sphericity may be responsible for the differences seen.

Short summary
From an 11-year analysis of satellite measurements of atmospheric dust presence over the Red Sea, it is clear that there is a strong north–south gradient in dust activity and a pronounced interannual variability in this activity. Analysing two commonly used satellite retrieval methods to quantify dust presence, we find that under the most extreme dust storm conditions the measured dust optical thicknesses can diverge strongly between the two methods.
Final-revised paper