- Slides: 18
Land Surface Analysis SAF: Contributions to NWP Isabel F. Trigo
Scope of Presentation I – LSA SAF - Products relevant for NWP - Schedule - Beta – Users II – LSA SAF / ECMWF joint Collaboration - Assimilation of LST ? - ECMWF Land Surface Scheme - Future Work
I – Land Surface Analysis SAF Satellite Application Facilities Development & Processing Centres within the EUMETSAT Applications Ground Segment: Meteorological products Software Packages Using MSG and EPS data. LSA SAF Consortium of 13 organisations / 8 member states Host Institute: IM
LSA SAF PRODUCTS Priority 1 & 2 Benefits for NWP Snow Cover Validation; Albedo of Snow Areas; Initialisation of snow mass in DA Albedo Broadband/Spectral albedo updates Land Surface Temperature Validation; DA Sfc Short-wave Fluxes Sfc Long-wave Fluxes Validation; forcing for global soil moisture AN.
LSA SAF PRODUCTS Priority 3 & 4 Benefits for NWP Soil Moisture Validation Evapotranspiration Vegetation Cover Possible use for monthly/seasonal updates LAI Development 2003 Pre-operational 2004 2005 2006 2007 Operational 2008
Snow Coverage – Europe; (Global) Resolution – 5 x 5 km; (1 x 1 km) 15 min for MSG; daily maps Delivery Time - Near Real Time white - class “snow”; light grey -class “partially snow covered”; green class – class “clear land”; Beta-Users Operational Development 2003 2004 2005 2006 2007 2008
Albedo Broadband Albedo Coverage – MSG disk; (Global) Resolution – 3 x 3 km; 10 days 0. 30 Delivery Time - Near Real Time Content – Spectral & Broadband: 0. 15 VIS 0. 6; VIS 0. 8; IR 1. 6 0 300 -4000 nm; 400 -700 nm; 700 -4000 nm Accuracy - ~1% Beta-Users Operational Development 2003 2004 2005 2006 2007 2008
Land Surface Temperature Coverage – MSG disk; (Global) Resolution – 3 x 3 km; 15 min Delivery Time - Near Real Time Accuracy – ~1 – 2 K Beta-Users Operational Development 2003 2004 2005 2006 2007 2008
II – LSA SAF / ECMWF Collaboration (Pedro Viterbo and Anton Beljaars) Assimilation of LST ? Window Channel Brightness Temperatures (10. 50 – 12. 50 m) METEOSAT – 7 clear sky . . Tb_OBS ECMWF model equivalent . . Tb_ECMWF To assess the quality of modelled land surface temperature. To monitor the quality of the observations by identifying gross errors / systematic problems in the data.
Underestimation of Tb daily cycle over arid/semi-arid regions Overestimation Tb diurnal cycle, mostly along the ITCZ Tb_obs Tb_ECMWF averaged for 1 -15 Feb 2001
Sources of Window channel Tb Systematic Errors: (i) cloud screening of the observations. . . (ii) - threshold for the %Clear Sky pixels; - MSG will allow more accurate cloud masks. (ii) underestimation of modelled diurnal amplitudes of Tb_ECMWF in clear sky conditions underestimation of LST diurnal cycle (particularly over arid and semi-arid regions) Further Details: Trigo and Viterbo (2003), J. Appl. Met. , 42, 1463 -1479.
A pre-requisite to contemplate assimilation: The model has to look like the observations Window Channel Tb bias (and thus LST bias) ~ 10 K in semi-arid regions strongly limits the assimilation of: Window channel TOA Radiances / LST product; TOVS channels sensitive to the lower troposphere, over land. A set of sensitivity experiments of Tb amplitude to surface parameters / variables pointed Model deficiencies in the LAND – ATMOSPHERE Aerodynamic Coupling
ECMWF Land Surface Model - TESSEL Dry Vegetated Surfaces Ra, nv Ra Tc Tskin Bare Ground Tile: Ra does not take into account the wind shielding effect of surrounding vegetation. Hbare_g is overestimated, particularly over sparsely vegetated areas.
Revised TESSEL Ra, nv Tc Ra Rs Tskin Rs – Resistance to turbulent heat transfer within the under canopy layer. - sparseness of the vegetation; - canopy height; -. . .
ECMWF 1 -Column Model Western Sahara – Validation Period Parameters in Rs 1) Estimated by fitting daily Tb_ECMWF amplitudes to Tb_OBS; 1 -15 Feb 2001; 2) Fixed for each grid point 1 -15 Feb 2002. Tb Daily Amplitude
Summary I – LSA SAF • Priority 1 Products: Snow Cover, Albedo, and Land Surface Temperature • Priority 2 Products: Downwelling Surface Short & Long wave Fluxes • Priority 3 - Vegetation Parameters: FVC, LAI - Soil Moisture / Evapotranspiration • Beta-Users - Please contact LSA SAF NOW ! - Pre-Operational in 2005 • Operational Phase - 2007
II – LSA SAF / ECMWF Collaboration • The comparison of Meteosat-7 window channel Tb (clear sky) with Tb_ECMWF shows that the modelled Tskin diurnal cycle is underestimated over arid / semi-arid regions. Limits assimilation of LST & Channels that peak in the lower troposphere. • Sensitivity experiments pointed to deficiencies in the Land Surface – Atmospheric aerodynamic coupling. TESSEL Bare Ground Tiles ignore wind shielding effect of the surrounding vegetation. • Introducing an extra resistance Rs to turbulent heat transfer within the canopy layer substantially reduces the ECMWF cold bias of Tb daily amplitudes.
Next • Estimate Rs parameters for Meteosat (MSG) disk (by fitting daily amplitudes of Tb_ECMWF to the observations). • Study the impact of the improved land Tskin in the assimilation of TOVS channels sensitive to the lower troposphere. • Test 1 D-var assimilation of window channels TOA radiances/ retrieved LST to further improve the model Tskin over land.