CICYTTP   12500
CENTRO DE INVESTIGACION CIENTIFICA Y DE TRANSFERENCIA TECNOLOGICA A LA PRODUCCION
Unidad Ejecutora - UE
artículos
Título:
The Role of the Observed Tropical Convection in the Generation of Frost Events in the Southern cone of South America
Autor/es:
MULLER, GABRIELA VIVIANA; AMBRIZZI, TÉRCIO; FERRAZ, SIMONE E.
Revista:
Annales Geophysicae
Editorial:
Copernicus Publications
Referencias:
Año: 2008 vol. 26 p. 1379 - 1390
ISSN:
0992-7689
Resumen:
Based on previous results obtained from observations
and linear wave theory analysis, the hypothesis
that large-scale patterns can generate extreme cold events
in southeast South America through the propagation of remotely
excited Rossby waves was already suggested. This
work will confirm these findings and extend their analysis
through a series of numerical experiments using a primitive
equation model where waves are excited by a thermal forcing
situated in positions chosen according to observed convection
anomalies over the equatorial region. The basic state
used for these experiments is a composite of austral winters
with maximum and minimum frequency of occurrence
of generalized frosts that can affect a large area known as
the Wet Pampas located in the central and eastern part of Argentina.
The results suggest that stationary Rossby waves may be
one important mechanism linking anomalous tropical convection
with the extreme cold events in the Wet Pampas.
The combination of tropical convection and a specific basic
state can generate the right environment to guide the Rossby
waves trigged by the tropical forcing towards South America.
Depending on the phase of the waves entering the South
American continent, they can favour the advection of anomalous
wind at low levels from the south carrying cold and dry
air over the whole southern extreme of the continent, producing
a generalized frost in the Wet Pampa region. On the
other hand, when a basic state based on the composites of
minimum frosts is used, an anomalous anticyclone over the
southern part of the continent generates a circulation with a
south-southeast wind which brings maritime air and therefore
humidity over the Wet Pampas region, creating negative
temperature anomalies only over the northeastern part
of the region. Under these conditions even if frosts occur
they would not be generalized, as observed for the other basic
state with maximum frequency of occurrence of generalized
frosts.