DUE GlobAEROSOL: Feedback from ECMWF

1. DUE GlobAEROSOL: Feedback from ECMWF R. Siddans summarising feedback from J-J. Morcrette on behalf of GEMS

2. Backgound: ECMWF interest in GlobAerosol • At ECMWF, as part of GEMS (Global Environmental Monitoring of the atmosphere using Satellite data, a FP6 project) ECMWF building an analysis system including aerosols, based on the existing 4D-Var assimilation system. • Already have a forward model including sea-salt, desert dust, organic and black carbon, and sulphate • Can run forecasts with prognostic aerosols, starting with zero aerosols, then letting the aerosol processes build up atmospheric amounts of aerosols (~2 weeks) • Observational data are important for two purposes, • first as validation of the modelling effort, and • second and more important for the future as (real-time) data to be possibly included in the analysis.

3. Backgound: ECMWF interest in GlobAerosol • Currently, using MODIS and MISR optical thicknesses to check the behaviour of the forecast model on the past periods (2003-2004), which are the "officially designed study periods" in the GEMS project. • Forecasts over the years 2003-2004 started with zero aerosols on 1 December 2002. • Comparisons with AERONET data are also carried out over the same period. • Have also started using MODIS retrieved optical thicknesses in the analysis over a number of 2-3 week periods within 2003 and 2004. • Since the 1 June 2007, we have a near-real time forecast going on for 72-hours with archiving every 3 hours • Current and the past 30 forecasts can be seen on: • http://www.ecmwf.int/products/forecasts/d/inspect/catalog/research/gems/aer/optical_depth/

4. Backgound: ECMWF interest in GlobAerosol

5. Comments on Preliminary Results • ECMWF are likely to be (at least at first) more interested in SEVIRI retrievals than in the retrievals from other sensors, mainly because of their time resolution. So comments focus on SEVIRI • Agreement over most of the African land mass is quite worrying when looking at Dhadnah, Cinzana, Mongu, Ouagadougou, Sir Bu Nuair (also sometimes have good agreement at one wavelength and not the other) • Response from RAL was that • these problems identified in PVAR, caused by uncertainty in aerosol type and land-surface BRDF • In many cases discrepancies are bias (time-series still captured) • Discrepancies reduced in many cases if correct type assumed • potential strengths of GlobAerosol are that (a) cost-function often indicates when assumed type is not appropriate (b) if user has prior knowledge of type then discrepancies may be reduced by choosing specific retrieval

6. Comments on Preliminary Results • Puzzled by choice of stations: • RAL double checked & confirmed that all stations which provided coincident data passing quality control of Aeronet and satellite data were used. • Question on apparent differences between nearby stations (Venise, ISDGM-CNR and Nicelli Airport) • RAL response that apparent differences caused by different sampling of the time-series reported by the stations introduced by cloud / quality control.

7. What ECMWF want from GlobAerosol in Future • For validation purposes/further model development: • For the 2003-2004 period and/or near-real time: • GLOBAER data (daily averages: SEVIRI , MERIS, AATSR dual-view, Merged dual-view) to be compared along side MISR and MODIS data with what we are producing with the forward model. • Both optical thickness at 550 and 870 nm would be very useful. • Other wavelengths (when/if available) would be helpful. • Speciation/Angstrom coefficient would also be desirable. • For analysis purposes: • GLOBAER data within the 2003-2004 period and/or near-real time data as alternate data for the analysis. • Particularly SEVIRI data, specially if they can be made available, say, for more time-slots per day • e.g.10h12, 12h12, 14h12, 16h12 GMT. • However data will be used only if we are confident they are not likely to throw the analysis out of track.