Abstract
The goal of this paper is to study month-to-month impacts of Southern Hemisphere Annular Mode (SAM) phases over South America (SA). Composite analyses were performed excluding ENSO years. Southeastern SA (SESA), part of Southeastern and Central-West of Brazil seem to be more affected by SAM. However, SAM influences are different for each month, and there are also differences of the influences between SAM phases (not always opposite). For air temperature, March, May, July, August, September, and November show positive (negative) anomalies affecting regions cited above during the negative (positive) SAM phase. Although, the coverage of these anomalies is different among these months. February and December present a temperature anomaly dipole, with positive (negative) anomaly at SESA and negative (positive) northward, in the negative (positive) SAM phase. January has a different behavior compared with other months but also presents a nearly opposite signal between SAM phases. Precipitation anomalies composites indicate a weakening (strengthening) of South Atlantic Convergence Zone configuration at negative (positive) SAM phase (November-January and March). SESA region shows positive (negative) precipitation anomalies at negative (positive) SAM phases, during March-June and December. Nevertheless, in October, SAM oppositely influences this region. A case study (January 2017 - negative SAM - neutral ENSO) shows great similarity with the precipitation composites, ratifying the results. However, for temperature, the coastal region is the only which presents similarity with the composites.
Highlights
The leading modes of the extratropical circulation variability in both hemispheres are characterized by deep, zonally symmetric or annular structures, with geopotential height perturbations of opposing signs in the polar cap region and in surrounding the zonal ring, centered near 45° latitude
This paper aimed to study month-to-month impacts of Southern Hemisphere Annular Mode (SAM) phases over South America (SA)
Southeastern SA (SESA) and parts of Southeastern and Central-West Regions of Brazil seem to be more affected by SAM pattern
Summary
The leading modes of the extratropical circulation variability in both hemispheres are characterized by deep, zonally symmetric or annular structures, with geopotential height perturbations of opposing signs in the polar cap region and in surrounding the zonal ring, centered near 45° latitude. The positive (negative) phase for these oscillations indicates less (higher) than normal geopotential heights at high latitudes and an opposite signal at middle latitudes (Thompson & Wallace, 2000). The impacts of Northern Hemisphere Annular Mode (NAM, known as Arctic Oscillation) have been extensively documented, whereas for Southern Hemisphere (SH) the Annular Mode (SAM, known as Antarctic Oscillation) has received less attention
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