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| Titel |
Meteorological observations on the northern Chilean coast during VOCALS-REx |
| VerfasserIn |
J. A. Rutllant, R. C. Muñoz, R. D. Garreaud |
| 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 ; 13, no. 6 ; Nr. 13, no. 6 (2013-03-25), S.3409-3422 |
| Datensatznummer |
250018540
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| Publikation (Nr.) |
 copernicus.org/acp-13-3409-2013.pdf |
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| Zusammenfassung |
Surface coastal observations from two automatic weather stations at Paposo
(~25° S) and radiosonde observations at Paposo and
Iquique (~20° S) were carried out during VOCALS-REx (VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment).
Within the coastal marine boundary layer (MBL), sea–land breezes are
superimposed on the prevailing southerlies, resulting in light northeasterly
winds from midnight to early morning and strong southwesterlies in the
afternoon. The prevailing northerlies above the MBL and below the top of the Andes
are modulated by the onshore-offshore (zonal) flow forced by the diurnal
cycle of surface heating/cooling along the western slope of the Andes. The
daytime phase of this diurnal cycle is consistent with an enhanced afternoon
coastal subsidence manifested in afternoon warming near the top of the
subsidence inversion (~1.8 K at 800 hPa), lowering
(~130 m) of its base (top of the MBL), and clearing of
coastal Sc (stratocumulus) clouds. Results from a numerical simulation of the atmospheric
circulation in a mean zonal cross section over the study area capture the
afternoon zonal wind divergence and resulting subsidence of about 2 cm s−1 along a narrow (~10 km) coastal strip maximizing at
around 800 hPa. Day-to-day variability in the MBL depth during VOCALS-REx
shows sub-synoptic oscillations, aside from two major disruptions in
connection with a deep trough and a cutoff low, as described elsewhere.
These oscillations are phase-locked to those in sea-level pressure and
afternoon alongshore southerlies, as found in connection with coastal lows
farther south.
From 24-h forward trajectories issued from significant points at the
coast and inland at the extremes of the diurnal cycle, it can be concluded
that the strong mean daytime Andean pumping prevents any possibility of
continental sulfur sources from reaching the free troposphere above the Sc cloud
deck in at least a one-day timescale, under mean conditions. Conversely,
coastal sources could contribute with sulfur aerosols preferentially in the
morning, provided that the weak daytime inland flow becomes partially
blocked by the coastal terrain. |
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