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ECMWF/EUMETSAT NWP-SAF Satellite data assimilation Training Course 1 to 4 July 2013.

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Presentation on theme: "ECMWF/EUMETSAT NWP-SAF Satellite data assimilation Training Course 1 to 4 July 2013."— Presentation transcript:

1 ECMWF/EUMETSAT NWP-SAF Satellite data assimilation Training Course 1 to 4 July 2013

2 ECMWF/EUMETSAT NWP-SAF Satellite data assimilation Training Course The infrared spectrum, measurement, modelling and information content

3 Sensors

4 High Spectral Resolution IR sounders on Polar Spacecraft ( GEO covered in winds lecture )

5 What do we mean by high spectral resolution ?

6 IASI HIRS Why is high spectral resolution important ? HIRS 19 channels IASI 8461

7 AIRS IASI CrIS 15 um4 um6 um

8 IASI v CrIS

9 Infrared Atmospheric Sounding Interferometer (IASI) Cross-track Infrared Sounder (CrIS)

10 IASI has higher spectral resolution compared to CrIS

11 IASI has higher instrument noise compared to CrIS

12 IASICrIS Inter-channel correlation Observation error (K) CrIS has stronger inter-channel correlations than IASI

13 Case study: The assimilation of IASI

14 NH SH EU US The assimilation of IASI results in a significant reduction of forecast error

15 What does IASI measure (and what do we assimilate)

16 15 um4.2um6.4 um 9.6 um3.7 um The infrared spectrum of atmospheric radiation

17 15 um 4.2um6.4 um 9.6 um3.7 um The infrared spectrum of atmospheric radiation The long-wave temperature sounding band ~ 200 channels assimilated

18 Zoom of long-wave temperature sounding channel usage for IASI

19 15 um 4.2um6.4 um 9.6 um 3.7 um The infrared spectrum of atmospheric radiation The long-wave ozone sounding band ~ 20 channels assimilated

20 15 um 4.2um6.4 um 9.6 um 3.7 um The infrared spectrum of atmospheric radiation The long-wave water vapour sounding band ~ 10 channels assimilated

21 15 um 4.2um6.4 um 9.6 um 3.7 um The infrared spectrum of atmospheric radiation The short-wave temperature sounding band ~ 0 channels assimilated – IASI noise high

22 15 um 4.2um6.4 um 9.6 um 3.7 um The infrared spectrum of atmospheric radiation The surface sensing channels (window channels) channels mostly used for cloud detection

23 -Issues specific to IR Ambiguity Nonlinearity Clouds Channel selection (PC)

24 Ambiguity in infrared radiance observations

25 When the absorbing gas is itself a variable

26 AMBIGUITY BETWEEN GEOPHYSICAL VARIABLES When the primary absorber in a sounding channel is a well mixed gas (e.g. oxygen) the radiance essentially gives information about variations in the atmospheric temperature profile only. When the primary absorber is not well mixed (e.g. water vapour, ozone or CO 2 ) the radiance gives ambiguous information about the temperature profile and the absorber distribution. This ambiguity must be resolved by : differential channel sensitivity synergistic use of well mixed channels (constraining the temperature) the background error covariance (+ physical constraints)

27 When sounding channels are sensitive to the surface

28 + Surface emission + Surface reflection/ scattering + Cloud/rain contribution +... Atmospheric sounding channels …selecting channels where there is no contribution from the surface….

29 + Surface emission + Surface reflection/ scattering + Cloud/rain contribution +... Surface sensing Channels (passive) …selecting channels where there is no contribution from the atmosphere…. Screen data to remove clouds / rain

30 AMBIGUITY WITH SURFACE AND CLOUDS By placing sounding channels in parts of the spectrum where the absorption is weak we obtain temperature (and humidity) information from the lower troposphere (low peaking weighting functions). BUT … These channels (obviously) become more sensitive to surface emission and the effects of cloud and precipitation. In most cases surface or cloud contributions will dominate the atmospheric signal in these channels and it is difficult to use the radiance data safely (i.e. we may alias a cloud signal as a temperature adjustment) K(z )

31 Practical session

32 Metview web pages: https://software.ecmwf.int/metview Download (Open Source) Documentation and tutorials available Metview articles in recent ECMWF newsletters

33 RTTOV Radiative Transfer Model Y radiances X (z) RTTOV

34 Task 1: Overlay Tropical and Polar IASI spectra View the map of TCWV (visualise PLOT_TCWV) Select a Tropical profile ( edit / save profile extractor) Select a Polar profile ( edit / save profile extractor) Edit / visualise IASI SPECTRUM (with tropical.nc) Edit / drop IASI SPECTRUM (with polar.nc)

35 Task 1: Overlay Tropical and Polar IASI spectra

36 Task 2: Overlay Tropical and Polar IASI channel 272 weighting function Edit / visualise IASI JACOBIAN (with tropical.nc) Edit / drop IASI JACOBIAN (with polar.nc) Change channels and do similar ?

37 Task 3: Tropical and Polar IASI weighting functions

38 Task 3: Overlay Tropical and Polar IASI matrix of jacobians Edit / visualise IASI MATRIX JAC (with tropical.nc) Edit / drop IASI MATRIX JAC (with polar.nc)

39 Task 3: Overlay Tropical and Polar IASI matrix of jacobians

40 End… Questions ?


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