1 introduction into the absorption channels description of characteristics and content of the wv...
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Introduction into the Absorption Channels
Description of characteristics and content of the WV channels:
Ch05: 6.2
Ch06: 7.3
Contact person:Veronika Zwatz-MeiseVersion 1.0
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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)
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Sun radiation Earth radiation
Wavelength (micron)
Watt/m2 andmicron
Ozone
Carbondioxid
Watervapour
Sun radiation Earth radiation
W/m2/m
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Comparison of radiation sources sun - earth
• For wavelength < 5 m solar radiation is dominant
• For wavelength > 5 m terrestrial radiation 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
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Water vapour 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
Sun radiation Earth radiation
Ozone
CO2
H2O
Wavelength (m)
W/m2/m
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Ch05 and Ch06 within WV absorption band around 6 m
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• 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
Ch05 Ch06
EnergyspectrumSource:EUMETSAT
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Max. signal in Ch05 from approx. 350 hPaMax signal in Ch 06 from approx. 500 hPaBut: If there is no WV radiation from far below reaches the satellite
WeightingfunctionsSource:EUMETSAT
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Max. signal in Ch05 from approx. 320 hPaMax signal in Ch 06 from approx. 450 hPaBut: If there is no WV radiation from far below reaches the satellite
WeightingfunctionsSource:EUMETSAT
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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
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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
• Height determination of semi-transparent clouds
WV
Clouds
6.2
7.3
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Ch05
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Ch06
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WV images in connection with upper level humidity and the vertical humidity gradient
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Ch05:6.2
1 st example
Black (dry) in upper levels
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W06:7.3
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Orange:dry:< 30 %cyan:wet:>60 %
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PV anomaly
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W05:6.2
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W06:7.3
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Orange:dry:< 30 %cyan:wet:>60 %
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No remarkable PV anomaly
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W05:6.2
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W05:7.3
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Orange:dry:< 30 %cyan:wet:>60 %
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Presentation in form of WV differences
• Difference image indicates the amount of high level moisture
• Connection to downgliding dry air
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Ch05
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Ch06
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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
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Difference Ch05 - Ch06
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Difference Ch05 - Ch06
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Example for dry air in lower levels below frontal surface and jet axis
drywet
wetdry
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