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| Titel |
Sensitivity of the simulated precipitation to changes in convective relaxation time scale |
| VerfasserIn |
S. K. Mishra, J. Srinivasan |
| 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 ; 28, no. 10 ; Nr. 28, no. 10 (2010-10-06), S.1827-1846 |
| Datensatznummer |
250016893
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1827-2010.pdf |
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| Zusammenfassung |
The paper describes the sensitivity of the simulated precipitation to
changes in convective relaxation time scale (TAU) of Zhang and McFarlane
(ZM) cumulus parameterization, in NCAR-Community Atmosphere Model version 3
(CAM3). In the default configuration of the model, the prescribed value of
TAU, a characteristic time scale with which convective available potential
energy (CAPE) is removed at an exponential rate by convection, is assumed to
be 1 h. However, some recent observational findings suggest that, it is
larger by around one order of magnitude. In order to explore the sensitivity
of the model simulation to TAU, two model frameworks have been used, namely,
aqua-planet and actual-planet configurations. Numerical integrations have
been carried out by using different values of TAU, and its effect on
simulated precipitation has been analyzed.
The aqua-planet simulations reveal that when TAU increases, rate of deep
convective precipitation (DCP) decreases and this leads to an accumulation
of convective instability in the atmosphere. Consequently, the moisture
content in the lower- and mid- troposphere increases. On the other hand, the
shallow convective precipitation (SCP) and large-scale precipitation (LSP)
intensify, predominantly the SCP, and thus capping the accumulation of
convective instability in the atmosphere. The total precipitation (TP)
remains approximately constant, but the proportion of the three components
changes significantly, which in turn alters the vertical distribution of
total precipitation production. The vertical structure of moist heating
changes from a vertically extended profile to a bottom heavy profile, with
the increase of TAU. Altitude of the maximum vertical velocity shifts from
upper troposphere to lower troposphere. Similar response was seen in the
actual-planet simulations. With an increase in TAU from 1 h to 8 h,
there was a significant improvement in the simulation of the seasonal mean
precipitation. The fraction of deep convective precipitation was in much
better agreement with satellite observations. |
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