Introduction into the Absorption Channels

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Introduction into the Absorption Channels

• Description of characteristics and content of the
  WV channelsCh05 6.2 ?
• Ch06 7.3 ?

Contact person Veronika Zwatz-Meise zwatz-meise_at_z
amg.ac.at
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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
Watt/ m2 and micron
Ozone
Carbon dioxid
Water vapour
Wavelength (micron)
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Comparison of radiation sources sun - earth

• For wave length lt 5 ?m solar radiation is
  dominant
• For wave length gt 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
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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

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Ch05 and Ch06 within WV absorption band around 6
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Energy spectrum SourceEUMETSAT
Ch05
Ch06

• 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

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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 SourceEUMETSAT
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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 SourceEUMETSAT
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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
• AMV computation
• Height determination of semi-transparent clouds

WV
6.2
Clouds
7.3
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Ch05
13
Ch06
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WV images in connection with upper level humidity
and the vertical humidity gradient
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Ch056.2
Black (dry) in upper levels
1 st example
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W067.3
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Orange dry lt 30 cyan wet gt60
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PV anomaly
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W056.2
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W067.3
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Orange dry lt 30 cyan wet gt60
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No remarkable PV anomaly
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W056.2
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W057.3
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Orange dry lt 30 cyan wet gt60
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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
wet
dry
dry
wet
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