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

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, base period
Used a 0.5 standard deviation threshold to define ENSO and SAM events

4. Compositing ENSO / SAM Events
Individual Months #
1. SAM
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

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

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 Eu vectors to see local forcing
Similar to E-P fluxes, but for transient wave propagation
Divergence of Eu strengthens 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