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| Titel |
Characteristics of a persistent "pool of inhibited cloudiness" and its genesis over the Bay of Bengal associated with the Asian summer monsoon |
| VerfasserIn |
Anish Kumar M. Nair, K. Rajeev, S. Sijikumar, S. Meenu |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 29, no. 7 ; Nr. 29, no. 7 (2011-07-13), S.1247-1252 |
| Datensatznummer |
250017058
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| Publikation (Nr.) |
 copernicus.org/angeo-29-1247-2011.pdf |
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| Zusammenfassung |
| Using spatial and vertical distributions of clouds derived from multi-year
spaceborne observations, this paper presents the characteristics of a
significant "pool of inhibited cloudiness" covering an area of >106 km2
between 3–13° N and 77–90° E over the Bay of Bengal (BoB),
persisting throughout the Asian summer monsoon season (ASM). Seasonal mean
precipitation rate over the "pool" is <3 mm day−1 while that over the
surrounding regions is mostly in the range of 6–14 mm day−1. Frequency of
occurrence of clouds in this "pool" is ~20–40 % less than that over
the surrounding deep convective regions. Zonal and meridional cross sections
of the altitude distribution of clouds derived from CloudSat data reveal a
vault-like structure at the "pool" with little cloudiness below ~7 km,
indicating that this "pool" is almost fully contributed by the substantially
reduced or near-absence of low- and middle-level clouds. This suggest the
absence of convection in the "pool" region. Spaceborne scatterometer
observations show divergence of surface wind at the "pool" and convergence
at its surroundings, suggesting the existence of a mini-circulation embedded
in the large-scale monsoon circulation. Reanalysis data shows a
mini-circulation extending between the surface and ~3 km altitude, but
its spatial structure does not match well with that inferred from the above
observations. Sea surface at the south BoB during ASM is sufficiently warm
to trigger convection, but is inhibited by the subsidence associated with
the mini-circulation, resulting in the "pool". This mini-circulation might be
a dynamical response of the atmosphere to the substantial spatial gradient
of latent heating by large-scale cloudiness and precipitation at the vast
and geographically fixed convective zones surrounding the "pool". Subsidence
at the "pool" might contribute to the maintenance of convection at the above
zones and be an important component of ASM that is overlooked hitherto. |
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