Ministério da Educação e Ciência Instituto de Meteorologia, I. P. Rua C – Aeroporto de Lisboa 1749-077 Lisboa – Portugal Tel.: (351) 21 844 7000 Fax: (351)

Ministério da Educação e Ciência Instituto de Meteorologia, I. P. Rua C – Aeroporto de Lisboa 1749-077 Lisboa – Portugal Tel.: (351) 21 844 7000 Fax: (351) 21 840 2370 e-mail: [email protected] URL: http://www.meteo.pt

Thermal Radiation

Down-welling Long-wave Fluxes at the Surface

Isabel F. Trigo


MSG-based Radiation Products

Down-welling Long-wave Flux (DSLF)

Definition

Algorithm Basis

The LSA SAF DSLF product from MSG

Validation


Adapted from K. Trenberth, J. Fasullo, and J. Kiehl.

30%

23%

90%4%

47%

Thermal RadiationSolar Radiation

Radiation Budget

Earth Surface

Short-Wave Net Radiation

• Loss

• Gain

Long-Wave Net Radiation

• Loss

• Gain

?

?


Adapted from K. Trenberth, J. Fasullo, and J. Kiehl.

30%

23%

7%

23%

Thermal RadiationSolar Radiation

90% 4%

Radiation Budget

Earth Surface

Short-Wave Net Radiation

• Loss

Gain

Long-Wave Net Radiation

Loss

• Gain

X

X


Emitted by the atmosphere, Ra

Emitted by the surface, Rsup

Reflected by the surface, Rrefl

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

It is controlled by

concentration of abosrbing gases

CO2, CH4, H2O, ...

presence of clouds, clouds phase

temperature profile & temperature of cloud base

....


FLW =

dE

100

4

2

1

Total irradiance at the surface within the [4 – 100 m] interval:


Spectral irradiance emitted downwards by the

atmosphere

Wavelength (m)

20 15 12.5 10.5 9 8 7

Observed Downward Spectra Radiance – a clear sky day

(adapated from Turner et al., 2004 in J. Atmos. Sci.


7

Satellite observations provide information on variables that control Down-welling Longwave Fluxes at the surface:

Clouds

Temperature Profiles

Humidity profiles

Remote Sensing



FLW as estimated in the LSA SAF from MSG/SEVIRI

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

SEVIRI/MSG SEVIRI/MSG Data:

Other Information: atmosphere screen temperature (ECMWF forecast) total column water vapour (ECMWF forecast)

Cloud identification:

channels 1-4, 7, 9 & 10

Down-welling Longwave Flux at the Surface (DSLF)



Parameterization based on Stefan-Boltzman Law:

44 )1( skycloudyskycloudyskyclearskyclear TnTnDSLF



Tclear-sky , clear-sky

Tcloudy-sky , cloudy-sky Cloud cover fraction



clearcloudyskysky DSLFnnDSLFTDSLF )1(4

m

sky

ww

10exp

1011 22 TdTTsky

Fraction of Cloud

Fraction of Cloud

Total column water vapour

2m air temperature

2m dew point depression

Parameterization based on Stefan-Boltzman Law:



Forecasts:(ECMWF)




15 November 2011

00 UTC 12 UTC

Cloud’s signature?



15 November 2011

00 UTC 12 UTC

Clear Sky - Cloudy/Partially Cloudy -



Generation Frequency - 30 min

MSG projection & resolution

Over land ...

Available since

Europe – Feb 2005

Full disk – Jul 2005

Also distributed with quality flag (pixel by pixel basis)

But ... Algorithm changed in 2008!



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.


DSLF - Validation

Comparison with in situ measurements

Comparison with other satellite products (CERES onboard Aqua and Terra)

Location of Ground Observations


DSLF - Validation

LSA SAF DSLF colocated in space and time with

Ground Stations & CERES (http://aqua.nasa.gov/about/instrument_ceres.php)

Northern Europe Stations

clear sky cloudy

Jan 2006 - Apr 2007

CERES SEVIRI DSLF

Bias RMSE 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


DSLF - Validation



Central Europe StationsJan 2006 - Apr 2007

CERES SEVIRI DSLF

Bias RMSE 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


DSLF - Validation



Semi-arid & Desert StationsJan 2006 - Apr 2007

CERES SEVIRI DSLF

Bias RMSE 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


DSLF

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)

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


DSLF Applications – Please see presentation in Session 8

DSLF

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

Documents

Ministério da Educação e Ciência Instituto de Meteorologia, I. P. Rua C – Aeroporto de Lisboa 1749-077 Lisboa – Portugal Tel.: (351) 21 844 7000 Fax: (351)