Simulation of the Ozone Monitoring Instrument aerosol index using the NASA Goddard Earth Observing System aerosol reanalysis products

摘要

We provide an analysis of the commonly used Ozone MonitoringInstrument (OMI) aerosol index (AI) product for qualitativedetection of the presence and loading of absorbing aerosols. In ouranalysis, simulated top-of-atmosphere (TOA) radiances are producedat the OMI footprints from a model atmosphere and aerosol profileprovided by the NASA Goddard Earth Observing System (GEOS-5)Modern-Era Retrospective Analysis for Research and Applicationsaerosol reanalysis (MERRAero). Having established the credibility ofthe MERRAero simulation of the OMI AI in a previous paper wedescribe updates in the approach and aerosol optical propertyassumptions. The OMI TOA radiances are computed in cloud-freeconditions from the MERRAero atmospheric state, and the AI iscalculated. The simulated TOA radiances are fed to the OMI near-UV aerosol retrieval algorithms (known as OMAERUV) is comparedto the MERRAero calculated AI. Two main sources of discrepancy arediscussed: one pertaining to the OMI algorithm assumptions of thesurface pressure, which are generally different from what the actualsurface pressure of an observation is, and the other related tosimplifying assumptions in the molecular atmosphere radiativetransfer used in the OMI algorithms. Surface pressure assumptionslead to systematic biases in the OMAERUV AI, particularly over theoceans. Simplifications in the molecular radiative transfer lead tobiases particularly in regions of topography intermediate to surfacepressures of 600 and 1013.25 hPa. Generally, the errors inthe OMI AI due to these considerations are less than 0.2 inmagnitude, though larger errors are possible, particularly overland. We recommend that future versions of the OMI algorithms usesurface pressures from readily available atmospheric analysescombined with high-spatial-resolution topographic maps and includemore surface pressure nodal points in their radiative transferlookup tables.