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| Titel |
Observations of water vapour in the lower tropical troposphere and their implication for a preferred mode of cloudiness near the triple point |
| VerfasserIn |
Bjorn Stevens, Helene Brogniez, Christoph Kiemle, Johannes Killiani |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250146567
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| Publikation (Nr.) |
 EGU/EGU2017-10596.pdf |
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| Zusammenfassung |
| Airborne measurements from NARVAL-2 are used to characterize the structure of water
vapor in the lower tropical troposphere, below the height, z∗, of the triple-point isotherm, T∗.
Elevated moist layers, perhaps associated with a a preferred level of convective detrainment
are found to be common and are shown to be associated with radiative cooling profiles that
would effectively drive circulations that reinforce such features. These findings are consistent
with a well documented preferred mode of cloudiness near z∗ being associated with a
preferred deposition of moisture at temperatures near T∗. A theory for this preferred
level of cumulus termination is advanced, whereby differences in the temperatures
at which primary ice forms, and T∗ gives a ’first-mover advantage’ to glaciating
cumulus convection, thereby concentrating the regions of the deepest convection
and leading to more convection in other regions terminating below the level of
primary ice formation, causing increased cloudiness and moisture near the triple point.
The airborne measurements, including water vapor profiling by lidar, are used to
evaluate microwave humidity retrievals from space to assess the ability of such
measurements to identify how wide-spread such features are. The retrievals capture the
general features, but the water vapor in the retrievals is more bottom heavy than is
observed. If systematic, these biases would imply an underestimate of the amount of
mid-level water vapor and its effect on circulations within the lower troposphere. |
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