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| Titel |
A quantitative evaluation of the role of the Argentinean Col and the Low Pressure Tongue East of the Andes for frontogenesis in the South American subtropics |
| VerfasserIn |
H. M. J. Barbosa, J. M. Arraut |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7340
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| Digitales Dokument |
URL |
| Erschienen |
In: 4th EGU Alexander von Humboldt Conference "The Andes: Challenge for Geosciences" ; Nr. 22 (2009-10-13), S.67-72 |
| Datensatznummer |
250014730
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| Publikation (Nr.) |
 copernicus.org/adgeo-22-67-2009.pdf |
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| Zusammenfassung |
| Previous studies have found the South American subtropics to exhibit
high climatological frontogenesis in equivalent potential temperature
during the austral summer. An important contribution to this pattern
is given by frontogenesis over the Argentinean Col (AC), which
separates the Northwestern Argentinean Low (NAL) from transient
troughs to the south of it. The NAL and the Low Pressure Tongue east
of the Andes (LPT) promote efficient transport of Amazonian humidity
to the subtropics during the incursion of transient disturbances over
the continent. The convergence of this strong warm and humid flow with
mid-latitude air brought into the subtropics by the disturbance occurs
preferentially in the neighborhood of the AC. The main difficulty in
quantifying the contribution of the NAL, AC and LPT structure to
frontogenesis in the South American subtropics is the automatic
detection of the AC and LPT. In this paper an algorithm developed to
this end is briefly presented and applied to obtain statistics on the
role of these structures in frontogenesis. Six-hourly data from ECMWF
ERA-40 Reanalysis over 21 austral summer periods (December–March) is
used. Occurrences of the AC are highly concentrated between 34–39° S and
66–69° W, being present in this region in 42% of the time instants
analyzed. The spatial average of the positive values of the
frontogenesis over this region was calculated for each time step as a
measure of intensity and histograms were built for the cases when the
AC was and was not found inside this region. Mean, median and mode are
larger for the distribution of cases with the presence of the AC. In
addition, we present the frequency of occurrence of the AC as a
function of the frontogenesis, showing that it grows with the
intensity of the frontogenesis, rising above the 0.955 quantile. We
have not found any correlation between the AC frequency and the
frontolysis intensity. |
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