Effect of density stratification on dynamos in gas planets and low-mass stars

by Rakesh Kumar Yadav
Doctoral thesis
Date of Examination:2015-01-23
Date of issue:2015-05-29
Advisor:Prof. Dr. Ulrich Christensen
Referee:Prof. Dr. Ansgar Reiners
Referee:Prof. Dr. Ulrich Christensen
Referee:Dr. Julien Aubert
Persistent Address: http://dx.doi.org/10.53846/goediss-5093

 

 

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Abstract

English

Numerical simulations of the Geodynamo have reproduced many of the features of the Earth's magnetic field. An ensemble of these simulations has been used to formulate a predictive scaling law which agrees with the Earth's mean magnetic field strength. Surprisingly, this scaling law also predicts the field strength in Jupiter and some rapidly rotating stars whose convection-zones are drastically different from the one in Earth. The main aim of this thesis is to explore scaling laws in  dynamos which incorporate ingredients suitable for convection-zones of gas-planets and low-mass stars, i.e. stress-free flow boundary conditions and compressible fluids. The resulting simulations indicate that despite drastic changes in the flow structure the scaling law relating the field strength to the flow-driving power is mostly unaffected, indicating that dynamos in rapidly-rotating planets and stars might behave similarly. We also use numerical simulations to investigate latitudinal differential rotation in planets and stars to provide a common framework, and the effect of various control parameters, initial condition, and magnetic field on its nature and vigour is also explored. Inspired by the idea that some planetary and stellar dynamos might belong to the same category I run dedicated high-resolution dynamo simulations of stellar dynamos. The control parameters for these simulations were such that an Earth like dipole-dominated magnetic field was produced. The resulting simulations spontaneously generate dark spot at high latitudes, providing a self-consistent mechanism for high-latitude starspot formation in rapidly rotating stars.
Keywords: Magnetic fields; Planetary and stellar dynamos; Scaling laws; Differential rotation; Starspots
 
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