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 Version 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 05WV 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  „CO 2 “) Channel 12:HRV (High Resolution Visible)

3 Sun radiation Earth radiation Wavelength (micron) Watt/ m 2 and micron Ozone Carbon dioxid Water vapour

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 only VIS VIS + IR only IR 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/ m 2 and micron

5 Watervapour channels Ch05, Ch06 WV has an absorption band around 6  m –absorbs radiation from below –emits radiation according to the 2 nd 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 Ch05Ch06 Energy spectrum Source: EUMETSAT

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 content in two different layers –Differentiation between WV content in the lower and higher middle troposphere AMV computation Height determination of semi-transparent clouds WV Clouds

12 Ch05

13 Ch06

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

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

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 drywet dry

33