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| Titel |
An interpretation of the Free Tropospheric Humidity interannual variability observed from METEOSAT using a transport model |
| VerfasserIn |
H. Brogniez, R. Roca, L. Picon |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028551
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| Zusammenfassung |
| Satellite remote sensing of water vapor in the 6.3µm strong water vapor absorption band, offers a unique observational estimate of the free tropospheric relative humidity (FTH). A database of clear sky radiances from the METEOSAT First Generation series, spanning July 1983 – June 2005 with a 3 hourly time step and a spatial resolution of 0.625°, has been developed and is exploited to document the variability of the water vapor content of the free troposphere. A particular effort has been done on the dry subtropical highs that play a key role in the water vapor feedback through a significant impact on the longwave cooling to space.
The region of the Eastern Mediterranean reveals strong inter-annual features such as an extreme dryness during the summer (6%) and a higher relative variability (50%) than the convectively active regions of the African monsoon (20%) that underlines it’s importance in the Earth’s radiative balance. The link between such inter-annual variations and large-scale dynamic is performed with a lagrangian transport model. This technique, applied onto the whole set of summers, reveals a complex scheme of mixing between air masses of tropical (<25ºN) and/or extra-tropical (>25ºN) origins that explains for a large part the variability of FTH at the inter-annual scale. Hence, the tropical air ending its trajectory over the Eastern Mediterranean high has mainly a drying influence while extra-tropical parcels generally moisten the free troposphere. |
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