The Cushion Region and Dayside Magnetodisc Structure at Saturn

N R Staniland,N Achilleos,M K Dougherty,A Masters

doi:10.1029/2020gl091796

N R Staniland, N Achilleos + Show 2 more

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https://doi.org/10.1029/2020gl091796

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Abstract

AbstractA sustained quasi‐dipolar magnetic field between the current sheet outer edge and the magnetopause, known as a cushion region, has previously been observed at Jupiter, but not yet at Saturn. Using the complete Cassini magnetometer data, the first evidence of a cushion region forming at Saturn is shown. Only five examples of a sustained cushion are found, revealing this phenomenon to be rare. Four of the cushion regions are identified at dusk and one pre‐noon. It is suggested that greater heating of plasma post‐noon coupled with the expansion of the field through the afternoon sector makes the disc more unstable in this region. These results highlight a key difference between the Saturn and Jupiter systems.

Highlights

At the gas giants, the presence of an internal plasma source coupled with their rapid rotation (∼10 h) significantly perturbs their magnetic field configuration
We suggest that greater heating of the magnetodisc plasma at dusk compared to dawn (Kaminker et al, 2017) and the expansion of the magnetic field as it rotates through the afternoon sector produces these disc instabilities
Using the complete Cassini orbital magnetometer data set, we have identified five examples of a cushion region at Saturn, of which four were observed at dusk

Summary

Introduction

The presence of an internal plasma source coupled with their rapid rotation (∼10 h) significantly perturbs their magnetic field configuration. At Jupiter, a region adjacent to the magnetopause where the magnetodisc structure breaks down and the field is quasi-dipolar, referred to as the “cushion region," has been identified (Went, Kivelson, et al, 2011) and is argued to be populated by mass-depleted flux tubes following tail reconnection (Kivelson & Southwood, 2005). This region has yet to be identified at Saturn (Went, Kivelson, et al, 2011), despite the similarities between these two systems

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Conclusion