Welhouse, L.J.1*, Lazzara, M.A.2, Tripoli, G.J.1, Keller, L.M.1

1Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison

2Antarctic 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: 1979-2002 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 1984-2002

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 1993-2002 DOME C YEARS 1980-1995

DOME C II YEARS 1996-2002

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-0636873

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 (http://amrc.ssec.wisc.edu) 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, 979-997. 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, 52-57.