INVESTIGADORES
VERA Carolina Susana
artículos
Título:
Subseasonal Variations of Rainfall in South America in the Vicinity of the Low-Level Jet East of the Andes and Comparison to Those in the South Atlantic Convergence Zone
Autor/es:
LIEBMANN, BRANT; KILADIS, GEORGE; VERA, CAROLINA; SAULO, CELESTE; CARVALHO, LEILA
Revista:
JOURNAL OF CLIMATE
Editorial:
American Meteorological Society
Referencias:
Lugar: Boston, Estados Unidos; Año: 2004 vol. 17 p. 3829 - 3842
ISSN:
0894-8755
Resumen:
Regional and large-scale circulation anomalies associated with variations in rainfall downstream of the South
American low-level jet are identified and compared to those in the South Atlantic convergence zone (SACZ).
Composites of precipitation associated with strong jets reveal an approximate doubling of the quantities one
would expect from climatology, with an evolution of the rainfall pattern from south to north. The occurrence
of extreme precipitation events follows a similar pattern. Meridional cross sections of composite wind reveal a
distinct low-level jet near 208S and a baroclinic development farther south that appears to force the jet. Geopotential
height, temperature, and large-scale wind composites suggest that this developing disturbance is tied
to a wave train that originates in the midlatitude Pacific and turns equatorward as it crosses the Andes Mountains.
Similar composites based on SACZ rainfall reveal similar features, but of opposite sign, suggesting that the
phase of the wave as it crosses the Andes Mountains determines whether rainfall will be enhanced downstream
of the jet or in the SACZ. The alternate suppression or enhancement of rainfall in these adjacent regions results
in a precipitation dipole. Many previous studies have found a similar out-of-phase relationship over many
time scales. The phase of the MaddenJulian oscillation (MJO) is composited relative to anomalous precipitation
events, revealing statistically relevant amplitudes associated with rainfall both downstream of the jet and in the
SACZ. The MJO is a particularly interesting intraseasonal oscillation because it has some predictability. It is
speculated that the slowly varying dipole that has been observed is a consequence of the preferred phasing of
synoptic waves due to variations of the planetary-scale basic-state flow, which is at times associated with the
MJO.8S and a baroclinic development farther south that appears to force the jet. Geopotential
height, temperature, and large-scale wind composites suggest that this developing disturbance is tied
to a wave train that originates in the midlatitude Pacific and turns equatorward as it crosses the Andes Mountains.
Similar composites based on SACZ rainfall reveal similar features, but of opposite sign, suggesting that the
phase of the wave as it crosses the Andes Mountains determines whether rainfall will be enhanced downstream
of the jet or in the SACZ. The alternate suppression or enhancement of rainfall in these adjacent regions results
in a precipitation dipole. Many previous studies have found a similar out-of-phase relationship over many
time scales. The phase of the MaddenJulian oscillation (MJO) is composited relative to anomalous precipitation
events, revealing statistically relevant amplitudes associated with rainfall both downstream of the jet and in the
SACZ. The MJO is a particularly interesting intraseasonal oscillation because it has some predictability. It is
speculated that the slowly varying dipole that has been observed is a consequence of the preferred phasing of
synoptic waves due to variations of the planetary-scale basic-state flow, which is at times associated with the
MJO.