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
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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. - PowerPoint PPT Presentation
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Understanding the SAM influence on the South
Pacific ENSO Teleconnection
Understanding the SAM influence on the South
Pacific ENSO Teleconnection
Ryan L. FogtDepartment of Geography
Ohio University, Athens, OH
David H. Bromwich & Keith M. HinesPolar Meteorology Group, Byrd Polar Research Center
The Ohio State University, Columbus, OH
Ryan L. FogtDepartment of Geography
Ohio University, Athens, OH
David H. Bromwich & Keith M. HinesPolar Meteorology Group, Byrd Polar Research Center
The Ohio State University, Columbus, OH
The Southern Annular Mode (SAM)
The Southern Annular Mode (SAM)
L
H
H
H
SAM positive phase
Increased meridional pressure gradient
Stronger circumpolar westerly winds
Compositing ENSO / SAM Events
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
• 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
Zonal Mean Zonal Wind Composites: La Niña CaseZonal Mean Zonal Wind
Composites: La Niña Case
Spatial Perspective of Forcing
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
• 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
Eu Vectors: La Niña CaseEu Vectors: La Niña Case
ConclusionsConclusions• 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
• 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