5/10/2013 - Periodicities in Saturn’s magnetosphere driven by vortical flows in the upper atmosphere/ionosphere

Information:

3:30 PM - 5:00 PM
6704 Geology

Presented By:
Xianzhe Jia -

Abstract

Despite the high degree of axial symmetry in its intrinsic magnetic field, Saturn’s electromagnetic radiation (SKR), its magnetic perturbations and its particle populations all exhibit rotation-associated modulations at periods close to the planet’s rotation period. Furthermore, recent Cassini observations reveal that the electromagnetic period not only drifts slightly over a time scale of years but also differs for sources at high latitudes in the north and south. Identifying the cause of the periodicities has proved challenging because different parts of the system are tightly coupled. The upper atmosphere/ionosphere, with low enough inertia to allow drift and high enough inertia to maintain phase coherence, has been considered to be a plausible source region of the periodicities. This presentation will describe results from an atmospheric vortex model put forward to account for the various observed periodicities. Using the global magnetohydrodynamic (MHD) model, BATSRUS, we have quantitatively characterized how Saturn’s magnetosphere would respond to vortical flows in the ionosphere. Our initial modeling focused on the magnetospheric modulations at the dominant southern period by including a localized vortical flow structure in the southern high-latitude ionosphere that rotates at roughly the rate of planetary rotation. The model is found to reproduce a variety of observed magnetospheric periodicities associated with the period of the dominant southern SKR. Emboldened by the initial success, we have extended our atmosphere vortex model to investigate the contributions of northern hemisphere perturbations at a different period by including an additional vortical structure in the northern ionosphere. The dual-source model is shown to reproduce many well-documented results of Cassini data analysis including the features that appear distinctly at each of the two periods and those that appear as a carrier signal with amplitude modulation and phase shifts.

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