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Monthly averages: discussion item

A detailed discussion on monthly mean products for clear and all-sky conditions, comparing solutions by Imperial College and CM-SAF, highlighting advantages and disadvantages.

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Monthly averages: discussion item

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  1. Monthly averages: discussion item J E Russell Imperial College, London j.e.russell@imperial.ac.uk

  2. Monthly averages: original proposal • Monthly mean products would include: • time-step mean: 15 minute monthly average diurnal product for clear and all-sky • Overall monthly mean for clear and all-sky (sum of 15 minute averages) • Produced at RAL from the BARG Edition product (already an average over an exact 15 minute period) • Requires night-time cloud flag • Would benefit from additional clear sky information added to the BARG determined from the HR data – these could be adjusted by clear sky specific correction factors. • All sky = summation of all data where none missing • Clear sky missing points filled by interpolation based on diurnal models (albedo interpolated in SW according to ADM) • Anticipated that missing all sky data would be treated in the same way where appropriate and consistent with GERB processing

  3. Monthly averages: CM-SAF products • Monthly mean products would include: • time-step mean: hourly average diurnal product for all-sky • Overall monthly mean for all-sky (sum of hourly averages) • Produced at RMIB from the GERB ARCH (high resolution snapshot data) • ARCH fluxes (at SEVIRI acquisition times) interpolated in time and integrated by trapezium rule • Missing all-sky points filled with GERB-like (where present) corrected with gross factor to adjust between GERB and GERB-like fluxes. This includes SZA > 80 and sunglint, both of which have GERB radiance observations. • Currently no separate clear sky average • Requires night-time cloud flag • Would benefit from additional clear sky information added to the BARG determined from the HR data – these could be adjusted by clear sky specific correction factors.

  4. Monthly averages • CM-SAF advantages and disadvantages • CM-SAF represents a cheap solution in that already produced by RMIB, thus the availability of the average product should be more rapid • Will free up man-power at RAL to allow addressing of more fundamental issues of product improvement • In common with the RAL based solution still requires additional clear sky for which night-time cloud flags are needed. Unlike the RAL solution the production of the clear sky average may have to re-specified for consistency with the all sky product • Not the ideal or most obvious GERB monthly average product and will be harder to validate, so may in fact not be available validated any sooner than the RAL solution. • Not consistent with the GERB BARG data, uses more GERB-like data to fill than required, based on ARCH data which is not a standard GERB product, not planned to be part of the edition archive and the furthest from validation • Co-ordination of reprocessing or updates with the GERB products may be problematic as produced as part of an external project

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