Down-welling Long-wave Fluxes at the Surface

Apresentação em tema: "Down-welling Long-wave Fluxes at the Surface"— Transcrição da apresentação:

1 Down-welling Long-wave Fluxes at the Surface
Thermal Radiation Down-welling Long-wave Fluxes at the Surface Isabel F. Trigo

2 MSG-based Radiation Products
Down-welling Long-wave Flux (DSLF) Definition Algorithm Basis The LSA SAF DSLF product from MSG Validation

3 ? ? Radiation Budget Earth Surface 30% 23% 47% Thermal Radiation
90% 4% 47% Thermal Radiation Solar Radiation Earth Surface Short-Wave Net Radiation Loss Gain ? Long-Wave Net Radiation Loss Gain ? Adapted from K. Trenberth, J. Fasullo, and J. Kiehl.

4 Radiation Budget Earth Surface X X Thermal Radiation Solar Radiation
30% 23% 7% Thermal Radiation Solar Radiation 90% 4% Earth Surface Short-Wave Net Radiation Loss Gain X Long-Wave Net Radiation Loss Gain X Adapted from K. Trenberth, J. Fasullo, and J. Kiehl.

5 Surface Down-welling Long-Wave Radiation
Down-welling Long-wave Fluxes at the Surface Long-wave Radiation reaching the Surface: Essentially emitted by the lowest 100 m of the atmosphere Emitted by the atmosphere, Ra It is controlled by concentration of abosrbing gases CO2, CH4, H2O, ... presence of clouds, clouds phase temperature profile & temperature of cloud base .... Reflected by the surface, Rrefl Emitted by the surface, Rsup

6 FLW = Surface Down-welling Long-Wave Radiation
Total irradiance at the surface within the [4 – 100 m] interval: Spectral irradiance emitted downwards by the atmosphere FLW = Observed Downward Spectra Radiance – a clear sky day Wavelength (m) (adapated from Turner et al., 2004 in J. Atmos. Sci.

7 Surface Down-welling Long-Wave Radiation
Remote Sensing Satellite observations provide information on variables that control Down-welling Longwave Fluxes at the surface: Clouds Temperature Profiles Humidity profiles 7

8 Surface Down-welling Long-Wave Radiation
FLW as estimated in the LSA SAF from MSG/SEVIRI Down-welling Longwave Flux at the Surface (DSLF) SEVIRI/MSG SEVIRI/MSG Data: Channel 1 VIS 0.6 m Channel 2 VIS 0.8 Channel 3 NIR 1.6 Channel 4 MIR 3.9 Channel 5 WV 6.2 Channel 6 WV 7.3 Channel 7 IR 8.7 Channel 8 IR/O3 9.7 Channel 9 TIR 10.8 Channel 10 TIR 12.0 Channel 11 IR/CO2 13.4 Channel 12 HRV Cloud identification: channels 1-4, 7, 9 & 10 Other Information: atmosphere screen temperature (ECMWF forecast) total column water vapour (ECMWF forecast)

9 Surface Down-welling Long-Wave Radiation
FLW as estimated in the LSA SAF from MSG/SEVIRI Down-welling Longwave Flux at the Surface (DSLF) Parameterization based on Stefan-Boltzman Law: Tcloudy-sky , cloudy-sky Tclear-sky , clear-sky Cloud cover fraction

10 Surface Down-welling Long-Wave Radiation
FLW as estimated in the LSA SAF from MSG/SEVIRI Down-welling Longwave Flux at the Surface (DSLF) Fraction of Cloud Parameterization based on Stefan-Boltzman Law: Total column water vapour 2m air temperature 2m dew point depression Forecasts: (ECMWF)

11 Surface Down-welling Long-Wave Radiation
15 November 2011 00 UTC UTC Cloud’s signature?

12 Surface Down-welling Long-Wave Radiation
15 November 2011 00 UTC UTC Clear Sky - Cloudy/Partially Cloudy -

13 Surface Down-welling Long-Wave Radiation
Generation Frequency - 30 min MSG projection & resolution Over land ... Available since Europe – Feb 2005 Full disk – Jul 2005 But ... Algorithm changed in 2008! Also distributed with quality flag (pixel by pixel basis)

14 Surface Down-welling Long-Wave Radiation
Daily Accumulated Long-wave Flux MSG projection & resolution Over land ... Available since Full disk 2010 Also distributed number of time-slots used for each (pixel) estimation.

15 Comparison with in situ measurements
DSLF - Validation Comparison with in situ measurements Comparison with other satellite products (CERES onboard Aqua and Terra) Location of Ground Observations

16  clear sky  cloudy DSLF - Validation Northern Europe Stations
LSA SAF DSLF colocated in space and time with Ground Stations & CERES ( Northern Europe Stations Jan Apr 2007  clear sky  cloudy CERES SEVIRI DSLF Bias RMSE Clear Sky -0.0 12.7 -2.2 22.3 All Sky -2.1 23.5 3.1 25.3 Problems: Cloud identification at the edge of Meteosat disk DSLF model for ice clouds Temperature inversions

17 Central Europe Stations
DSLF - Validation LSA SAF DSLF colocated in space and time with Ground Stations & CERES ( Central Europe Stations Jan Apr 2007 CERES SEVIRI DSLF Bias RMSE Clear Sky -0.9 13.4 0.8 14.5 All Sky -1.4 22.7 1.6 22.5 Problems: Temperature inversions

18 Semi-arid & Desert Stations
DSLF - Validation LSA SAF DSLF colocated in space and time with Ground Stations & CERES ( Semi-arid & Desert Stations Jan Apr 2007 CERES SEVIRI DSLF Bias RMSE Clear Sky 13.0 26.8 -4.4 14.1 All Sky 17.5 29.6 -5.4 16.9 Problems: Impact of high aerosol loads

19 DSLF LSA SAF estimates DSLF at the original satellite resolution (3 km at the sub-satellite point), every 30 –minutes, covering Meteosat disk Satellite data provide Cloud information Comparison with in situ data -10 Wm-2 < Bias < 10 Wm-2 Root Mean Square Differences (RMS) ranges from considerably (from ~15 to 25 Wm-2)

20 DSLF Applications – Please see presentation in Session 8
As one of the components of the Surface Radiation Budget, DSLF applications include: Forcing of Land Surface (and Hydrology) models Model Assessment (surface and atmospherirc) Case Studies