The 1976/77 Austral Summer Climate Transition Effects on the Atmospheric Circulation and Climate in Southern South America

Abstract

Previous works suggest that more El Niño-like conditions can be expected over the South American (SA) climate and atmospheric circulation because of the similarity of the predominately warm conditions in the sea surface temperature (SST) over the central-equatorial Pacific after the 1976/77 summer with those of the SSTs during El Niño events. Here, the summer (October to March) low-level atmospheric circulation over southern SA is studied in order to determine the specific changes that can be related with the global climate transition 1976/77. The rotated principal component analysis is applied to the daily 850-hPa geopotential height fields from the NCEP-NCAR reanalysis I for the periods before and after 1976/77. The second and third principal patterns reveal changes both in the order of explained variances and in some of their spatial features. They can be associated with an expansion of the subtropical South Atlantic anticyclone over SA and lower midlatitude cyclone activity after the 1976/77 summer. The latter is partly associated with the actual tendency toward the positive phase of the southern annular mode. The main patterns can even explain some changes in the observed precipitation over subtropical central-west Argentina as well as for other subtropical regions. Different inhomogeneity tests applied to the atmospheric circulation climatology support the changes. Results suggest that the atmospheric circulation change could be somewhat unique (not observed in the twentieth century) and, thus, it could not be thoroughly ascribed to the El Niño-like variability.

Tree-ring based reconstruction of Río Bermejo streamflow in subtropical South America

“…This periodicity has been detected in various instrumental records in tropical/subtropical South America and is consistent with variations in the Pacific Decadal Oscillation [PDO, a low-frequency (20-30 yr) oceanic oscillation of the North Pacific SSTs;Mantua et al, 1997]. A well-known transition in thePDO, occurred in 1975PDO, occurred in -1977 and is associated with the onset of a positive precipitation trend in southern Amazonia since early 1970s(Agosta and Compagnucci, 2008). It is embedded in a 26 year cycle, suggesting a decadal-scale variability in precipitation for southern Amazonia and the adjacent subtropics in South America(Marengo, 2004).…”

Ozone and upper troposphere/lower stratosphere variability and change at southern midlatitudes 1980–2000: Decadal variations

“…The longitude height plots highlight the temporal weakening of the transient wave activity west of 180°W, observed through the decades. Some authors found a weakening of the cyclonic activity in the SH since early 1980s [ Haylock et al , 2006; Agosta and Compagnucci , 2008].…”

Ideas and perspectives: Southwestern tropical Atlantic coral growth response to atmospheric circulation changes induced by ozone depletion in Antarctica

“…Several studies postulate a great contribution of the PDO to this climate shift, particularly in the Northern Hemisphere (e.g., Mantua et al, 1997). Nevertheless, according to Agosta and Compagnucci (2008), in the regional context of southern South America and the adjacent South Atlantic, changes in the basic atmospheric circulation of the late 1970s climate transition cannot be solely attributed to the PDO or associated El Niño-like variability. In Fig.…”