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| Titel |
Using a WRF simulation to examine regions where convection impacts the Asian summer monsoon anticyclone |
| VerfasserIn |
N. K. Heath, H. E. Fuelberg |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 4 ; Nr. 14, no. 4 (2014-02-21), S.2055-2070 |
| Datensatznummer |
250118422
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| Publikation (Nr.) |
 copernicus.org/acp-14-2055-2014.pdf |
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| Zusammenfassung |
The Asian summer monsoon is a prominent feature of the global circulation
that is associated with an upper-level anticyclone (ULAC) that stands out
vividly in satellite observations of trace gases. The ULAC also is an
important region of troposphere-to-stratosphere transport. We ran the
Weather Research and Forecasting (WRF) model at convective-permitting scales
(4 km grid spacing) between 10 and 20 August 2012 to understand the role of
convection in rapidly transporting boundary layer air into the ULAC. Such
high-resolution modeling of the Asian ULAC previously has not been
documented in the literature. Comparison of our WRF simulation with
reanalysis and satellite observations showed that WRF simulated the
atmosphere sufficiently well to be used to study convective transport into
the ULAC. A back-trajectory analysis based on hourly WRF output showed that
> 90% of convectively influenced parcels reaching the ULAC
came from the Tibetan Plateau (TP) and the southern slope (SS) of the
Himalayas. A distinct diurnal cycle is seen in the convective trajectories,
with a majority of them crossing the boundary layer between 1600 and 2300 local
solar time. This finding highlights the role of "everyday" diurnal
convection in transporting boundary layer air into the ULAC.
WRF output at 15 min intervals was produced for 16 August to examine the
convection in greater detail. This high-temporal output revealed that the
weakest convection in the study area occurred over the TP. However, because
the TP is at 3000–5000 m a.m.s.l., its convection does not have to be as strong
to reach the ULAC as in lower altitude regions. In addition, because the
TP's elevated heat source is a major cause of the ULAC, we propose that
convection over the TP and the neighboring SS is ideally situated
geographically to impact the ULAC.
The vertical mass flux of water vapor into the ULAC also was calculated.
Results show that the TP and SS regions dominate other Asian regions in
transporting moisture vertically into the ULAC. Because convection reaching
the ULAC is more widespread over the TP than nearby, we propose that the
abundant convection partially explains the TP's dominant water vapor fluxes.
In addition, greater outgoing longwave radiation reaches the upper levels of
the TP due to its elevated terrain. This creates a warmer ambient upper-level
environment, allowing parcels with greater saturation mixing ratios to
enter the ULAC. Lakes in the Tibetan Plateau are shown to provide favorable
conditions for deep convection during the night. |
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