Quantifying the response of the ORAC aerosol optical depth retrieval for MSG SEVIRI to aerosol model assumptions
Bulgin, C. E., Palmer, P. I., Merchant, C. J., Siddans, R., Gonzi, S., Poulsen, C. A., Thomas, G. E., Sayer, A. M., Carboni, E., Granger, R. G., Highwood, E. and Ryder, C. L. (2011) Quantifying the response of the ORAC aerosol optical depth retrieval for MSG SEVIRI to aerosol model assumptions. Journal of Geophsyical Research-Atmospheres, 116. D05208. ISSN 0148-0227
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To link to this article DOI: 10.1029/2010JD014483
We test the response of the Oxford-RAL Aerosol and Cloud (ORAC) retrieval algorithm for MSG SEVIRI to changes in the aerosol properties used in the dust aerosol model, using data from the Dust Outﬂow and Deposition to the Ocean (DODO) ﬂight campaign in August 2006. We ﬁnd that using the observed DODO free tropospheric aerosol size distribution and refractive index increases simulated top of the atmosphere radiance at 0.55 µm assuming a ﬁxed erosol optical depth of 0.5 by 10–15 %, reaching a maximum diﬀerence at low solar zenith angles. We test the sensitivity of the retrieval to the vertical distribution f the aerosol and ﬁnd that this is unimportant in determining simulated radiance at 0.55 µm. We also test the ability of the ORAC retrieval when used to produce the GlobAerosol dataset to correctly identify continental aerosol outﬂow from the African continent and we ﬁnd that it poorly constrains aerosol speciation. We develop spatially and temporally resolved prior distributions of aerosols to inform the retrieval which incorporates ﬁve aerosol models: desert dust, maritime, biomass burning, urban and continental. We use a Saharan Dust Index and the GEOS-Chem chemistry transport model to describe dust and biomass burning aerosol outﬂow, and compare AOD using our speciation against the GlobAerosol retrieval during January and July 2006. We ﬁnd AOD discrepancies of 0.2–1 over regions of intense biomass burning outﬂow, where AOD from our aerosol speciation and GlobAerosol speciation can diﬀer by as much as 50 - 70 %.
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