Inhomogeneous potential vorticity homogenization and equilibrium in simple models of baroclinic instability with implications for the extratropical circulation by Pablo Zurita-Gotor.

Baroclinic eddies are an important component of the General Circulation which regulate the extratropical climate by transporting heat and momentum. An idealization of this feedback is provided by baroclinic adjustment theories (Stone, 1978), which envision a linearly neutralized mean state. Based on the Charney-Stern condition, most baroclinic adjustment formulations propose basic states with homogenized potential vorticity. In this thesis we investigate the degree of potential vorticity homogenization in the extratropical troposphere. We show that homogenization is only observed across a shallow region around 700 mb, and propose an adjusted state with homogenized PV at the steering level alone. We demonstrate that this state can be neutral under certain conditions, and investigate its relevance for the equilibration of an idealized model. Because of the role of the PV flux as an eddy forcing of momentum, it is illuminating to describe the equilibration in terms of the redistribution of momentum. This affects both the PV gradient and the steering level of the waves, but the condition of homogenization at the steering level is very robust. In the 2D problem, a local balance can be written between the dynamical and frictional forcing of momentum. However, in the 3D problem there is an additional redistribution by a remotely forced meridional circulation. To circumvent this difficulty, we have developed a momentum-based formulation that exploits the interchangeability of momentum and temperature for quasi-balanced stratified rotating flow. By rewritting the thermodynamic equation as a momentum equation, we eliminate the forcing by the mean meridional circulation and formulate a local balance between the eddy PV flux and the non-conservative forcing of momentum.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Zurita-Gotor, Pablo, 1970-

Advisor dc:contributor.advisor

• Richard S. Lindzen and Edmund K.M. Chang.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/58520

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/58520