CIMA   09099
CENTRO DE INVESTIGACIONES DEL MAR Y LA ATMOSFERA
Unidad Ejecutora - UE
artículos
Título:
La Plata basin precipitation variability in spring: role of remote SST forcing as simulated by GCM experiments
Autor/es:
ANNALISA CHERCHI; ANDREA F. CARRIL; CLAUDIO G. MENÉNDEZ; LAURA ZAMBONI
Revista:
CLIMATE DYNAMICS
Editorial:
SPRINGER
Referencias:
Lugar: Berlin; Año: 2014 vol. 42 p. 219 - 236
ISSN:
0930-7575
Resumen:
Abstract An ensemble of nine experiments with the
same interannually varying sea surface temperature (SST),
as boundary forcing, and different initial conditions is used
to investigate the role of tropical oceans in modulating
precipitation variability in the region of La Plata Basin
(LPB). The results from the ensemble are compared with a
twentieth-century experiment performed with a coupled
ocean-atmosphere model, sharing the same atmospheric
component. A rotated empirical orthogonal functions
analysis of South America precipitation shows that the
dominant mode of variability in spring is realistically
captured in both experiments. Its principal component
(RPC1) correlated with global SST and atmospheric fields
identifies the pattern related to El Nin?o Southern Oscillation
and its large-scale teleconnections. Overall the pattern
is well simulated in the tropical southern Pacific Ocean,
mainly in the ensemble, but it is absent or too weak in other
oceanic areas. The coupled model experiment shows a
more realistic correlation in the subtropical South Atlantic
where air-sea interactions contribute to the relationship
between LPB precipitation and SST. The correspondence
between model and data is much improved when the
composite analysis of SST and atmospheric fields is done
over the ensemble members having an RPC1 in agreement
with the observations: the improvement relies on avoiding
climate noise by averaging only over members that are
statistically similar. Furthermore, the result suggests the
presence of a high level of uncertainty due to internal
atmospheric variability. The analysis of some individual
years selected from the model and data RPC1 comparison
reveals interesting differences among rainy springs in
LPB. For example, 1982, which corresponds to a strong
El Nin?o year, represents a clean case with a distinct wave
train propagating from the central Pacific and merging
with another one from the eastern tropical south Indian
Ocean. The year 2003 is an example of a rainy spring in
LPB not directly driven by remote SST forcing. In this case
the internal variability has a dominant role, as the model
is not able to reproduce the correct local precipitation
pattern.