Internally driven large‐scale changes in the size of Saturn's magnetosphere

Abstract

Saturn's magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the system's dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10–15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively “plasma‐loaded” or “plasma‐depleted” states, defined in terms of the internal suprathermal plasma pressure.

Spinning, breathing, and flapping: Periodicities in Saturn's middle magnetosphere

“…Periodicities at the SKR frequency have also been observed in auroral hiss [ Gurnett et al ., ], ultraviolet (UV) auroral emissions [ Nichols et al ., , ; Provan et al ., ; Carbary , ], north‐south displacement of the equatorial current sheet [ Khurana et al ., ; Arridge et al ., ] (commonly referred to as flapping ), energetic electron and neutral atom fluxes [ Carbary et al ., , ; Paranicas et al ., ], the location of the magnetopause [ Clarke et al ., , , ; Pilkington et al , ], and the plasma electron density [ Gurnett et al ., ]. The changing location of the magnetopause is associated with periodic global‐scale compression and expansion, a feature that is well represented in the magnetohydrodynamic simulations of Jia et al .…”

A Self‐Regulating Equilibrium Magnetopause Model With Applications to Saturn

“…Inflation of Saturn's magnetopause due to hot plasma pressure as a function of plasma -see equation (18). The green dotted lines correspond to the means 20.7R s and 27.1R s for the bimodal distribution found by Pilkington et al (2015) after fitting their model to magnetopause crossing data. The green dotted lines correspond to the means 20.7R s and 27.1R s for the bimodal distribution found by Pilkington et al (2015) after fitting their model to magnetopause crossing data.…”

“…The magnetopause crossings of the Cassini spacecraft mentioned in this study were identified by Pilkington et al (2015) using the Cassini MAG, CAPS-ELS, and MIMI data available from the Planetary Data System (http://pds.nasa.gov/). F. H. was supported by a studentship jointly funded by UCL's Perren and Impact schemes.…”

Energetic Electron Patterns in the New SLS5 Longitude System

“…The charged particle data were restricted to locations within the magnetopause , which is the range to the magnetopause based on the model of Pilkington et al (). A solar wind ram pressure of 0.010 nPa was assumed to compute r MP , which insures that the observations lie within the magnetosphere and that subsequent binning excludes magnetosheath and solar wind data.…”

“…Sample maps in SLS5 north longitude at (top) z A = +2 R S , (middle) z A = 0 R S , and (bottom) z A = − 2 R S . Each dot represents a 15‐min average, and data outside of a model magnetopause (Pilkington et al, ) have been removed. The top panel also indicates a sample longitude grid between 23 and 25 R S .…”