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COMPOSITE ANALYSIS OF THE SURFACE EFFECTS OF EL NINO SOUTHERN OSCILLATION TELECONNECTIONS ON ANTARCTICA.

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  1. COMPOSITE ANALYSIS OF THE SURFACE EFFECTS OF EL NINO SOUTHERN OSCILLATION TELECONNECTIONS ON ANTARCTICA Welhouse, L.J.1*, Lazzara, M.A.2, Tripoli, G.J.1, Keller, L.M.11Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison2Antarctic Meteorological Research Center, Space Science and Engineering, University of Wisconsin-Madison

  2. Outline • 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

  3. ENSO Interactions • 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

  4. ENSO Interactions Mo and Higgins 1998

  5. Data • ERA-40 • Use of 500 hPa geopotential heights • Surface Temperatures • Surface Pressures • AWS data • Used for verification, checked surface temperature

  6. ERA-40 • 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.

  7. 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

  8. Verification 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

  9. Verification ELAINE YEARS 1993-2002 DOME C YEARS 1980-1995

  10. Verification DOME C II YEARS 1996-2002

  11. Composite Analysis • 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)

  12. Composite Analysis • 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.

  13. El Nino Composite 500 hPa heights

  14. El Nino Composite Surface Pressure

  15. El Nino Composite Surface Temperature

  16. La Nina Composite 500 hPa heights

  17. La Nina Composite Surface Pressure

  18. La NinaComposite Surface Temperature

  19. Discussion/Conclusions • 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.

  20. Future Work • 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

  21. Acknowledgements • 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.

  22. Citations • 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.

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