A theory for polar cyclones on giant planets

features, with a deep, hot and rapid cyclone situated directly over each pole, and a rapid jet marking the cyclone boundary at 3° from the pole. Extant theories for the zonal jets preclude the possibility of a jet at such high latitudes. This thesis proposes and tests a moist convective hypothesis for polar cyclone formation. Using purely baroclinic forcing, with statistical characteristics motivated by moist convection observed on Jupiter and Saturn, a robust tendency to form a barotropic polar cyclone is identified. A 2 1/2 layer shallow water model is built to test our hypothesis. An 11-dimensional parameter space is explored to determine the most importance controls on cyclone formation. Two sets of experiments are performed: 1) Barotropic and baroclinic 'storms' are briefly forced and then allowed to freely evolve on the polar beta plane, and 2) Forced-dissipative simulations are run, with periodic and randomly placed storms, until statistical equilibrium is reached. Results confirm the well known tendency of positive vorticity anomalies to self-advect poleward if they are intense enough for nonlinear advection to be significant. Likewise, strong negative vorticity anomalies move equatorward. Simulations span several orders of magnitude of energy density, ranging from weak wave-dominated flows to strong cyclones that experience instabilities. We find that a range of behavior, including what is observed on all four giant planets as well as previous simulation studies, can be expressed by varying only 2 nondimensional control parameters: a second baroclinic deformation radius scaled by the planetary radius, LD2=a; and a total energy parameter Êp that scales with the kinetic+potential energy density of the system at statistical equilibrium. In the context of an idealized model, the difference between Jupiter's and Saturn's polar flow regimes may be explained by their different planetary and deformation radii.

Department dc:contributor.department

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

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2015

Author dc:creator

• O'Neill, Morgan E

Advisor dc:contributor.advisor

• Kerry A. Emanuel.

• 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/1721.1/97335

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/97335