the concordiasi workshop, toulouse, 29-31 march 2010 impact study of amsu-a/b data over land and...
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The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Impact study of AMSU-A/B data over Impact study of AMSU-A/B data over land and sea-ice in the Météo-France land and sea-ice in the Météo-France
global assimilation systemglobal assimilation system
Fatima Karbou and Florence Rabier Fatima Karbou and Florence Rabier
CNRM-GAME, Météo-France & CNRSCNRM-GAME, Météo-France & CNRS
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Assimilation of AMSU-A & AMSU-B over Assimilation of AMSU-A & AMSU-B over landland
Since July 2008, a “dynamical retrieval method” is used in ARPEGE to estimate the land surface emissivity at microwave frequencies (Karbou et al. 2006):• Instantaneous emissivity retrieval at one surface surface channel (89 GHz for AMSU-B and 50 GHz for AMSU-A)• The emissivity is then given to sounding channels (with no frequency dependency)
Top of Atmosphere
Energy source
Surface (emissivity, temperature)
(1) Upwelling radiation(2) Dow
nwelling radiation
(3)
Surf
ace
em
issi
on
Signal attenuated by the atmosphere
),(),(.)).,(1(.).,(),( TTpTsppT
Plane parallel non scattering atmosphere, specular Plane parallel non scattering atmosphere, specular surfacesurface
)),((
),(),(),(),(
TTs
TTpTp
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Indirect measurements of temperature and humidity
AMSU-A & AMSU-B observationsAMSU-A & AMSU-B observations
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
More humidity in EXP
TCWV (EXP-REF)
Correlations with GPS
Evaluation wrt GPS data from AMMA
Assimilation of AMSU-B (low peaking humidity channels) over Assimilation of AMSU-B (low peaking humidity channels) over land land
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
More humidity in EXP
TCWV (EXP-REF)
Diurnal cycle of TCWV, Timbuktu (MALI)
Assimilation of AMSU-B over land operational in April 2010
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Current usage of AMSU-B channel 5 (183.31 7.0 GHz) in ARPEGE, dec 2008
One of the limitations: large uncertainties about the surface description (emissivity and surface temperature) over snow and sea-ice
AMSU-A & AMSU-B observationsAMSU-A & AMSU-B observations over sea-ice
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Assimilation of observations over sea-ice Assimilation of observations over sea-ice
July 2009January 2009
Difficult modelling of sea-ice emissivity
OPER Emis=0.99
Emissivity at 89 GHz
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
(a) For AMSU-B in particular, can we still use the 89 GHz emissivities for sounding channels without any frequency dependence parameterization ?
(b) Can we safely use the specular assumption over sea ice ?January 2009
July 2009
Assimilation of AMSU-A & AMSU-B over Assimilation of AMSU-A & AMSU-B over sea-icesea-ice
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
(a) For AMSU-B in particular, can we still use the 89 GHz emissivities for sounding channels without any frequency dependence parameterization ?
(b) Can we safely use the specular assumption over sea ice ?
Introduction of frequency parameterization for sea ice: to describe the emissivity change from 89 GHz to 183.31 GHz
(AMSU-B)(AMSU-B) Emissivity (~183 GHz) = Emissivity at 89 GHz + f (Tb 89, Tb150, Emissivity (~183 GHz) = Emissivity at 89 GHz + f (Tb 89, Tb150, Ts)Ts)
(AMSU-A)(AMSU-A) Emissivity (~52-60 GHz) = Emissivity at 50 GHz Emissivity (~52-60 GHz) = Emissivity at 50 GHz
Data impact studies for evaluation:
• Period: 15/12/2009 to 04/02/2010• CTL: the operational system• EXP: CTL + emissivity model over sea ice + assimilation of
AMSU-A/-B over sea ice
Assimilation of AMSU-A & AMSU-B over Assimilation of AMSU-A & AMSU-B over sea-icesea-ice
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Data impact resultsData impact results
Usage of AMSU-B channel 5 (183.31 7.0 GHz) in ARPEGE
CTL EXP
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Usage of AMSU-B channel 5 (183.31 7.0 GHz) in ARPEGE
CTL EXP
Snow (effect of specular approximation ?, Harlow, 2009, Guedj et al. 2010)
Data impact resultsData impact results
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Assimilation of observations over sea-iceAssimilation of observations over sea-ice Operational in Nov Operational in Nov 20102010
Wind scores wrt radiosondes (January 2009)Wind scores wrt radiosondes (January 2009)
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
Assimilation of observations over sea-ice Assimilation of observations over sea-ice
ScoresScores: Plutôt positifs en particulier sur l’Hémisphère : Plutôt positifs en particulier sur l’Hémisphère NordNord
The CONCORDIASI Workshop, Toulouse, 29-31 March 2010
SummarySummary
Objective: extend the use of AMSU observations over sea ice
Method to calculate the sea ice emissivity to be used to assimilate humidity and temperature observations
Beneficial for ARPEGE: data usage, RTTOV performances, Fit to all available observations, quality of analyses/forecasts
Issues: the use of AMSU data over snow surfaces