Welhouse, L.J. 1 *, Lazzara, M.A. 2, Tripoli, G.J. 1, Keller, L.M. 1 1 Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison 2 Antarctic Meteorological Research Center, Space Science and Engineering, University of Wisconsin-Madison

 Background on ENSO interactions in the Antarctic  Data  European center for midrange weather forecasting(ECMWF) reanalysis(ERA)-40  Automatic Weather Stations(AWS)  Verification  Composites  Discussion/Conclusions  Future work

 ENSO positive events induce a Pacific South American (PSA) pattern.  Negative events have a similar, though opposite, impact for much of the year. Karoly 1989

Mo and Higgins 1998

 ERA-40  Use of 500 hPa geopotential heights  Surface Temperatures  Surface Pressures  AWS data  Used for verification, checked surface temperature

 Time period of study:  This period is of higher accuracy than prior periods(Bromwich 2004)  Upper Level data used: 500 hPA heights contoured in 10gpm  Compared with prior work (Turner 2004)  Surface data: Pressure and Temperature  Used to both check for physical consistency with upper level and to determine surface effects  Used in both composite analysis and point comparisons with AWS stations to ensure the model reproduces ground stations accurately.

 Many sites were analyzed, all being in relative agreement  Focus of Dome C, Dome C 2, Byrd, and Elaine gives us stations in three major regions where we see effects  Data primarily used in verification process

BYRD STATION YEARS  A comparison between station data and ERA-40 grid points interpolated to the station location  The first three data harmonics of each data set are removed to remove the annual cycle  Stations shown are Byrd, Elaine, Dome C, and Dome C II  All correlations between station and reanalysis are.8-.87

ELAINE YEARS DOME C YEARS

DOME C II YEARS

 Doing composites slightly differently from prior work  El Nino – neutral  La Nina – neutral  This can increase signal visibility in the composites  Definition of ENSO events is 5 month running mean sea surface temperature deviation of.4 degrees Celsius for at least 6 month (Trenberth 1997)

 Trenberth definition was compared with a basis of events being a Multivariate ENSO index of more than one standard deviation from the mean.(Wolter 1993)  Focused on peak ENSO months, September- November(SON) and December-February(DJF)  Circled regions indicate statistical significance at either 95% or 90% as indicated.

 Composites seem to indicate El Nino and La Nina have different regional signals within Antarctica and especially in the case of La Nina these signals vary heavily within the season  Surface effects seem to be largely dependent on the location of the upper level signal.  Reasons for the difference in location of signal warrants further investigation  Potentially associated with changes in the Walker Circulation.

 Utilize ERA interim to expand the analysis into more recent ENSO events  Expand composites to other surface variables  Verify more stations to increase confidence in the model.  Investigate variations between El Nino and La Nina that could account for East Antarctic signal

 This material is based upon work supported by the National Science Foundation under Grant Nos. ANT  ECMWF ERA-40 data used in this study/project have been provided by ECMWF/have been obtained from the ECMWF data server.

 Automatic Weather Stations from the University of Wisconsin-Madison (  Bromwich, D. H. and R. L. Fogt, 2004: Strong trends in the skill of the ERA-40 and NCEP–NCAR reanalyses in the high and middle latitudes of the Southern Hemisphere, 1958–2001. J. Climate, 17:4603–4619  Fogt, R. L., and D. H. Bromwich, 2006: Decadal variability of the ENSO teleconnection to the high latitude South Pacific governed by coupling with the Southern Annular Mode. J. Climate, 19,  Karoly, D. J., 1989: Southern Hemisphere circulation features associated with El Niño–Southern Oscillation events. J. Climate, 2:1239– 1  Kållberg, P., A. Simmons, S. Uppala and M. Fuentes: The ERA-40 archive. [Revised October 2007] September 2004  Mo, K. C. and R. W. Higgins, 1998: The Pacific–South American modes and tropical convection during the Southern Hemisphere winter. Mon. Wea. Rev., 126:1581–15  Renwick, J. A., 1998: ENSO-related variability in the frequency of South Pacific blocking. Mon. Wea. Rev, 126:3117–3123  Trenberth, K. E., 1997: The definition of El Niño. Bull. Amer. Meteor. Soc, 78:2771–2777  Turner, J., 2004: Review: The El Niño-Southern Oscillation and Antarctica. Int. J. Climatol, 24:1–31.  Wolter, K., and M.S. Timlin, 1993: Monitoring ENSO in COADS with a seasonally adjusted principal component index. Proc. of the 17th Climate Diagnostics Workshop, Norman, OK, NOAA/NMC/CAC, NSSL, Oklahoma Clim. Survey, CIMMS and the School of Meteor., Univ. of Oklahoma,