Preferred zonal-mean flow structures responding to climate warming

Open Access
Author:
Park, Mee Rea
Graduate Program:
Meteorology
Degree:
Master of Engineering
Document Type:
Master Thesis
Date of Defense:
November 30, 2011
Committee Members:
  • Dr Sukyung Lee, Thesis Advisor
  • Sukyung Lee, Thesis Advisor
Keywords:
  • climate warming
  • baroclinic life cycle
  • poleward jet shift
Abstract:
This study is motivated by the observation of Moon and Feldstein (2009), which identified two life cycles in the Southern Hemisphere summer: a weak barotropic (WB) life cycle and a strong barotropic (SB) life cycle. In that study, they found that the eddy amplitude of the WB life cycle is larger than that of the SB life cycle even though the WB zonal mean state has a weaker baroclinicity. In the present study, initial-value calculations are performed with the dynamical core of the National Oceanographic and Atmospheric Administration/Geophysical Fluid Dynamics Laboratory climate model to examine whether the difference in the eddy energy between the WB and SB life cycles can be explained in terms of the stabilizing effect of the horizontal zonal wind shear in the background state. Consistent with observations, the idealized life cycle calculations show that a greater maximum eddy energy is attained for the WB basic state than for the SB basic state, suggesting that the horizontal zonal wind shear indeed plays the dominant role in determining the eddy amplitude. In addition, the WB life cycle produces a more pronounced poleward jet shift. Because warmer climates simulated by climate models tend to show both a poleward jet shift and more intense zonally localized tropical convection that , according to Moon and Feldstein (2009), prefers the WB state, our result suggests that the poleward jet shift in the warm climates ultimately may arise from the strengthening of tropical convection.