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Water vapour (H2O)
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Tropospheric
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monitoring |
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monitoring |
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monitoring |
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Aviation control |
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overview |
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23 January 2004
Product services of TEMIS: Contents of this page:
- NOTE:
-
the data product Water vapour has been removed
from the TEMIS project.
Water vapour
Water vapour is one of the most important, most abundant and highly variable greenhouse gases in the Earth's atmosphere.Water vapour affects the energy budget of the atmosphere, which drives and maintains the atmospheric motions through energy input into the atmosphere directly by:
- absorption of solar radiation,
- non-radiative (convection and condensation) transport from the Earth's surface,
- absorption of thermal radiation from the Earth's surface.
Specific humidity decreases rapidly with decreasing pressure, almost
following an exponential function, and with latitude. In general, more than
50% of the water vapour is concentrated below the 850 hPa level, while more
than 90% is confined to the layers below 500 hPa. The stratospheric water
vapour concentration is very small, with a typical value of about 3-4 ppmv
in the lower stratosphere. More than 99% of the water vapour is located in
the troposphere, where it plays a key role in the atmospheric chemistry,
weather prediction and climate.
Retrieval of water vapour amounts
Many experiments have been done in order to obtain the atmospheric water vapour amount. Apart from in-situ measurements there are several space borne instruments, such as, for example, TIROS-N Operational Vertical Sounders (TOVS) and the Spectral Sensor Microwave Imager (SSM/I), that are the most important sources of water vapor data.Algorithms under development for SCIAMACHY will analyze atmospheric water content on a global scale, in the spectral region corresponding to the rho-sigma-tau water vapour absorption band, which will be a new source of water vapour information. At present, a scale-down algorithm has been applied to GOME data, in the spectral region around 720 nm.