Affiliation:
1. Department of Atmospheric Sciences, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, São Paulo, Brazil
2. Institute for Computational Earth System Science, University of California, Santa Barbara, Santa Barbara, California
Abstract
Abstract
The Antarctic Oscillation (AAO) has been observed as a deep oscillation in the mid- and high southern latitudes. In the present study, the AAO pattern is defined as the leading mode of the empirical orthogonal function (EOF-1) obtained from daily 700-hPa geopotential height anomalies from 1979 to 2000. Here the objective is to identify daily positive and negative AAO phases and relationships with intraseasonal activity in the Tropics and phases of the El Niño–Southern Oscillation (ENSO) during the austral summer [December–January–February (DJF)]. Positive and negative AAO phases are defined when the daily EOF-1 time coefficient is above (or below) one standard deviation of the DJF mean. Composites of low-frequency sea surface temperature variation, 200-hPa zonal wind, and outgoing longwave radiation (OLR) indicate that negative (positive) phases of the AAO are dominant when patterns of SST, convection, and circulation anomalies resemble El Niño (La Niña) phases of ENSO. Enhanced intraseasonal activity from the Tropics to the extratropics of the Southern (Northern) Hemisphere is associated with negative (positive) phases of the AAO. In addition, there is indication that the onset of negative phases of the AAO is related to the propagation of the Madden–Julian oscillation (MJO). Suppression of intraseasonal convective activity over Indonesia is observed in positive AAO phases. It is hypothesized that deep convection in the central tropical Pacific, which is related to either El Niño or eastward-propagating MJO, or a combination of both phenomena, modulates the Southern Hemisphere circulation and favors negative AAO phases during DJF. The alternation of AAO phases seems to be linked to the latitudinal migration of the subtropical upper-level jet and variations in the intensity of the polar jet. This, in turn, affects extratropical cyclone properties, such as origin, minimum/maximum central pressure, and their equatorward propagation.
Publisher
American Meteorological Society
Reference41 articles.
1. Ambrizzi, T., and E. B.Souza, 2003: Hadley and Walker circulations associated with the ENSO episodes during the 1970s, 1980s and 1990s: Impacts on the South American seasonal rainfall. Proc. Seventh Int. Conf. on Southern Hemisphere Meteorology and Oceanography, Wellington, New Zealand, Amer. Meteor. Soc., 14–15.
2. The South Atlantic convergence zone: Persistence, intensity, form, extreme precipitation, and relationships with intraseasonal to interannual activity and extreme rainfall.;Carvalho;J. Climate,2004
3. Changes of subseasonal variability associated with El Niño.;Compo;J. Climate,2001
4. Evolution of the tropospheric split jet over the South Pacific Ocean during the 1986–89 ENSO cycle.;Chen;Mon. Wea. Rev.,1996
5. Lanczos filter in one and two dimensions.;Duchon;J. Appl. Meteor.,1979
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