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Title: Role of Tropical Variability in Driving Decadal Shifts in the Southern Hemisphere Summertime Eddy-Driven Jet

Journal Article · · Journal of Climate
 [1];  [2];  [3];  [4];  [5];  [3];  [3]
  1. Monash Univ., Melbourne, VIC (Australia). ARC Centre of Excellence for Climate Extremes
  2. Monash Univ., Melbourne, VIC (Australia). ARC Centre of Excellence for Climate Extremes ; National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States)
  3. National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States)
  4. Univ. of New South Wales, Sydney, NSW (Australia). ARC Centre of Excellence for Climate Extremes, Climate Change Research Centre
  5. Bureau of Meteorology, Melbourne, VIC (Australia)

The Southern Hemisphere summertime eddy-driven jet and storm tracks have shifted poleward over the recent few decades. In previous studies, explanations have mainly stressed the influence of external forcing in driving this trend. Here we examine the role of internal tropical SST variability in controlling the austral summer jet’s poleward migration, with a focus on interdecadal time scales. The role of external forcing and internal variability are isolated by using a hierarchy of Community Earth System Model version 1 (CESM1) simulations, including the pre-industrial control, large ensemble, and pacemaker runs. Model simulations suggest that in the early twenty-first century, both external forcing and internal tropical Pacific SST variability are important in driving a positive southern annular mode (SAM) phase and a poleward migration of the eddy-driven jet. Tropical Pacific SST variability, associated with the negative phase of the interdecadal Pacific oscillation (IPO), acts to shift the jet poleward over the southern Indian and southwestern Pacific Oceans and intensify the jet in the southeastern Pacific basin, while external forcing drives a significant poleward jet shift in the South Atlantic basin. In response to both external forcing and decadal Pacific SST variability, the transient eddy momentum flux convergence belt in the middle latitudes experiences a poleward migration due to the enhanced meridional temperature gradient, leading to a zonally symmetric southward migration of the eddy-driven jet. This mechanism distinguishes the influence of the IPO on the midlatitude circulation from the dynamical impact of ENSO, with the latter mainly promoting the subtropical wave-breaking critical latitude poleward and pushing the midlatitude jet to higher latitudes.

Research Organization:
University Corporation for Atmospheric Research, Boulder, CO (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
FC02-97ER62402
OSTI ID:
1799699
Journal Information:
Journal of Climate, Vol. 33, Issue 13; ISSN 0894-8755
Publisher:
American Meteorological SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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