1 / 16

Understanding the SAM influence on the South Pacific ENSO Teleconnection

Understanding the SAM influence on the South Pacific ENSO Teleconnection. Ryan L. Fogt Department of Geography Ohio University, Athens, OH David H. Bromwich & Keith M. Hines Polar Meteorology Group, Byrd Polar Research Center The Ohio State University, Columbus, OH. H.

kyros
Download Presentation

Understanding the SAM influence on the South Pacific ENSO Teleconnection

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Understanding the SAM influence on the South Pacific ENSO Teleconnection Ryan L. Fogt Department of Geography Ohio University, Athens, OH David H. Bromwich & Keith M. Hines Polar Meteorology Group, Byrd Polar Research Center The Ohio State University, Columbus, OH

  2. H Increased meridional pressure gradient H L H Stronger circumpolar westerly winds SAM positive phase The Southern Annular Mode (SAM)

  3. Compositing ENSO / SAM Events • Marshall (2003) SAM index and inverted Niño 3.4 SST Anomalies • Data from 1957-February 2009 • Detrended data • Standardized by month, 1971-2000 base period • Used a 0.5 standard deviation threshold to define ENSO and SAM events

  4. Compositing ENSO / SAM Events Individual Months # 1. SAM + 88 2. SAM - 69 3. La Niña 59 4. El Niño 75 In-Phase Events 5. La Niña / SAM + 65 6. El Niño / SAM - 67 Out-of-Phase Events 7. La Niña / SAM - 53 8. El Niño / SAM + 47 Climatology 103

  5. NCEP MSLP Composites SAM + SAM - La Niña El Niño

  6. Combined NCEP MSLP Composites La Niña & SAM + El Niño & SAM - La Niña & SAM - El Niño & SAM +

  7. Rossby Wavetrains: 500 hPa Streamfunction zonal anomalies SAM + SAM - Shading denotes zonal anomalies outside 2 stdev of zonal mean La Niña El Niño

  8. Rossby Wavetrains: 500 hPa Streamfunction zonal anomalies La Niña & SAM + El Niño & SAM - La Niña & SAM - El Niño & SAM +

  9. Detailing the SAM Impact

  10. 500 hPa Height Anomalies La Niña El Niño

  11. Determining the Causality for the Differences • We examined the transient eddy - mean flow interactions for each case • Only show the La Nina composites, since the interaction is more clearly observed • Based on data from NCEP-NCAR reanalysis 1979-2009

  12. Zonal Mean Zonal Wind Composites: La Niña Case Shading: zonal mean zonal wind anomalies Thin contours: meridional transient eddy momentum flux Thick contours: meridional transient eddy momentum flux convergence

  13. Zonal Mean Zonal Wind Composites: La Niña Case

  14. Spatial Perspective of Forcing • The ENSO forcing is most marked in the Pacific Sector • Use the Euvectors to see local forcing • Similar to E-P fluxes, but for transient wave propagation • Divergence of Eustrengthens local zonal wind, and vice-versa

  15. Eu Vectors: La Niña Case

  16. Conclusions • ENSO response in South Pacific dependent on SAM phase / strength • Transient eddy interactions in the Pacific play a key mechanistic role in modifying the circulation during each case • In Phase cases: reinforce each other, maintaining or amplifying the teleconnection • Out of Phase cases: oppose each other, drastically reducing the teleconnection magnitude • Supported by NSF ATM-0751291

More Related