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Introduction into the Absorption Channels

Learn about WV channels in meteorology, WV absorption bands, radiation sources, and its applications and characteristics in WV images.

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Introduction into the Absorption Channels

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  1. Introduction into the Absorption Channels Description of characteristics and content of the WV channels:Ch05: 6.2  Ch06: 7.3  Contact person: Veronika Zwatz-Meise zwatz-meise@zamg.ac.at Version 1.0. 13 July 2004

  2. All MSG channels • Channel 01: VIS 0.6  • Channel 02: VIS 0.8  • Channel 03: NIR 1.6  • Channel 04: MIR 3.9  • Channel 05 WV 6.2  • Channel 06: WV 7.3  • Channel 07: IR 8.7  • Channel 08: IR 9.7  („Ozon“) • Channel 09: IR 10.8  • Channel 10: IR 12.0  • Channel 11: IR 13.4  „CO2“) • Channel 12: HRV (High Resolution Visible)

  3. Sun radiation Earth radiation Watt/ m2 and micron Ozone Carbon dioxid Water vapour Wavelength (micron)

  4. Comparison of radiation sources sun - earth • For wave length < 5 m solar radiation is dominant • For wave length > 5 m radiation of earth is dominant • Ch01, 02, 03, 12: only sun radiation • Ch04: both: radiation from sun and earth • Ch 05, 06, 07, 08, 09, 10, 11: only thermal earth radiation Sun radiation Earth radiation Watt/ m2 and micron only VIS VIS + IR only IR

  5. Watervapour channels Ch05, Ch06 • WV has an absorption band around 6 m • absorbs radiation from below • emits radiation according to the 2nd Kirchhoff law • Greyshades in the WV are indicative of the WV content in the upper part of the troposphere

  6. Ch05 and Ch06 within WV absorption band around 6

  7. Ch05 is more in the centre of the absorption band with strong absorption; consequently radiation only from higher levels comes to the satellite; Ch06 is more to the wings of the absorption band with less strong absorption; consequently radiation also from lower layers comes to the satellite Energy spectrum Source:EUMETSAT Ch05 Ch06

  8. Max. signal in Ch05 from approx. 350 hPa Max signal in Ch 06 from approx. 500 hPa But: If there is no WV radiation from far below reaches the satellite Weighting functions Source:EUMETSAT

  9. Max. signal in Ch05 from approx. 320 hPa Max signal in Ch 06 from approx. 450 hPa But: If there is no WV radiation from far below reaches the satellite Weighting functions Source:EUMETSAT

  10. Application areas for the WV channels • Identification of areas with high upper level WV • Identification of jet axes • Cloud intensification areas within jet streaks (left exit region) • Wave developments within jet streaks (right entrance region) • Identification of dry areas in WV • special interest are areas of stratospheric air protruding downward • tropopause folding • PV anomalies • release of secondary cyclogenesis

  11. Some characteristica: WV 6.2 und 7.3 WV • WV content in two different layers • Differentiation between WV content in the lower and higher middle troposphere • AMV computation • Height determination of semi-transparent clouds 6.2 Clouds 7.3

  12. Ch05

  13. Ch06

  14. WV images in connection with upper level humidity and the vertical humidity gradient

  15. Ch05:6.2 Black (dry) in upper levels 1 st example

  16. W06:7.3

  17. Orange: dry: < 30 % cyan: wet: >60 %

  18. PV anomaly

  19. W05:6.2

  20. W06:7.3

  21. Orange: dry: < 30 % cyan: wet: >60 %

  22. No remarkable PV anomaly

  23. W05:6.2

  24. W05:7.3

  25. Orange: dry: < 30 % cyan: wet: >60 %

  26. Presentation in form of WV differences • Difference image indicates the amount of high level moisture • Connection to downgliding dry air

  27. Ch05

  28. Ch06

  29. Ch05 Distinct black stripe only in upper layers grey area in both levels; darker in the lower layer No big difference between the two channels: cloud edge

  30. Difference Ch05 - Ch06

  31. Difference Ch05 - Ch06

  32. Example for dry air in lower levels below frontal surface and jet axis wet dry wet dry

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