Rutherford Appleton Laboratory Cloud Model for operational Retrievals from MSG SEVIRI PM2, RAL, 17 Feb 2009 Overview of Phase II & Cloud Model Code.

Overview Phase I: Initial Review Phase –Radiative effects of the inhomogeneous and non plane- parallel clouds with particular reference to SEVIRI –Radiative transfer modelling of inhomogeneous clouds. –Retrieval strategies –Define scope of phase II Phase II: Development Phase Phase III: Demonstration with real data

55 o N40 o S 0o0o

Focus of Phase II Retrieval of multi-layer cloud, in particular assess capability to extend OCA to retrieve ice over liquid cloud layer. –define approach to constrain retrieval using information on the height of the two layers from neighbouring scenes –extending the current look-up-table (LUT) based forward model (FM) to handle two cloud layers. Quantitative assessment of impact of 3D RT effects: Use 3D cloud model data + SHDOM RTM to simulate realistic radiances in all channels. Use these to –characterise the magnitude of 1D/3D errors on retrievals –investigate approximate 3D RT methods –investigate possibility of defining FM errors using spatial context to improve behaviour of 1D scheme –test the original and new two-layer retrieval scheme. Use of HRV channel to define sub-pixel cloud fraction.

Prototype Cloud Model code ECP / OCA / Grape code at RAL & Oxford –Diverse versions –Fortran code not suitable for experimentation Extensive IDL tools at RAL existed for simulations purposes (e.g. Eumetsat A-band study) –Makes use of call external for computational efficiency Initial work in phase II was consolidation of the IDL tools into a convenient, better documented set of code for experimentation with OCA-type retrievals Code allows switch between “reference” and LUT RT This code then extended to two-layer case by Oxford & used throughout phase II (& phase III) Code on RAL ftp site with user-guide

Test harness; generates standard plots Prototype Cloud Model code Test LUT vs Ref. RTM & analytic derivatives LUT FM intended for use in retrieval Reference FM (similar call syntax as LUT) Optional RT solvers for reference model Simple call with switch to run LUT or reference FM Read / create LUTs from basic optical properties and reference RTM On-line RTTOV calls from IDL for clear-sky transmission (both LUT & reference FM) Read basic optical properties RUN_TESTS –TEST5,TEST_LUT_KNS CALL_CLDMODEL –MK_OCA_LUT »FM_CLDMODEL_REF –CALL_RTTOV –FM_CLDMODEL »FM_CLDMODEL_SOLAR »FM_CLDMODEL_IR –FM_CLDMODEL_REF »FMI_SUM_SCATTER_OCA »GT_FM2D »DISORT »SHDOM

0.8 μm channel Liquid cloud 500 hPa, Re 15 μm SZA 45 o Zero surface albedo

0.8 μm channel Liquid cloud 500 hPa, Re 15 μm SZA 45 o Lambertian albedo 0.4

0.8 μm channel Liquid cloud 500 hPa, Re 15 μm SZA 45 o “Rainforest” BRDF

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Original study schedule