Southern Annular Mode: different definitions of the index and their climate impacts

0508532 - ÚFA 2020 DE eng A - Abstract
Beranová, Romana - Huth, Radan
Southern Annular Mode: different definitions of the index and their climate impacts.
EMS Annual Meeting Abstracts, Vol. 16. Berlin: European Meteorological Society, 2019.
[EMS Annual Meeting 2019. 09.09.2019-13.09.2019, Copenhagen]
Institutional support: RVO:68378289
Keywords : climate * circulation * southern annular mode (SAM) * antarctic oscillation
OECD category: Climatic research
https://meetingorganizer.copernicus.org/EMS2019/EMS2019-76.pdf

The teleconnection patterns such as the North Atlantic Oscillation (NAO) and Pacific / North American pattern
(PNA) strongly affect surface climate conditions, including temperature, precipitation, sunshine duration, and
other variables in the northern hemisphere. Southern Annular Mode (SAM), also known as the Antarctic
Oscillation, is the leading mode of circulation variability in the southern hemisphere. SAM is characterised by
synchronous anomalies of opposite geopotential height in the mid and high latitudes. SAM variability has large
impacts on surface temperatures and precipitation mainly in Antarctica, Southern America and Australia. Several
definitions of the SAM have been employed in climatological studies. Perhaps the most widely used measure is
the difference between normalized monthly zonal mean of sea level pressure at 40◦S and 65◦S. Some indices are
based on station data and some on principal component analyses (PCA) applied to different geopotential height
levels.
In this contribution, we compare several different definitions of SAM, which have often been employed in recent
studies, for their effects (quantified in terms of correlations) on surface temperature and precipitation in different
places in the southern hemisphere. The analysis is based on monthly mean data. The preliminary results show
that there are no large differences in the similarity of time series of indices between winter and summer. Low
correlations are found between PCA-based indices and the others. The sensitivity of SAM effects on both surface
temperature and precipitation to the choice of the circulation index is considerably higher in summer. Correlations
differ among the indices not only in their magnitude but in some regions in summer also in their sign.
Permanent Link: http://hdl.handle.net/11104/0299405