Coupled rotational dynamics of Jupiter's thermosphere and magnetosphere

Abstract

Abstract.We describe an axisymmetric model of the coupled rotational dynamics of the thermosphere and magnetosphere of Jupiter that incorporates self-consistent physical descriptions of angular momentum transfer in both systems. The thermospheric component of the model is a numerical general circulation model. The middle magnetosphere is described by a simple physical model of angular momentum transfer that incorporates self-consistently the effects of variations in the ionospheric conductivity. The outer magnetosphere is described by a model that assumes the existence of a Dungey cycle type interaction with the solar wind, producing at the planet a largely stagnant plasma flow poleward of the main auroral oval. We neglect any decoupling between the plasma flows in the magnetosphere and ionosphere due to the formation of parallel electric fields in the magnetosphere. The model shows that the principle mechanism by which angular momentum is supplied to the polar thermosphere is meridional advection and that mean-field Joule heating and ion drag at high latitudes are not responsible for the high thermospheric temperatures at low latitudes on Jupiter. The rotational dynamics of the magnetosphere at radial distances beyond ∼30 R J in the equatorial plane are qualitatively unaffected by including the detailed dynamics of the thermosphere, but within this radial distance the rotation of the magnetosphere is very sensitive to the rotation velocity of the thermosphere and the value of the Pedersen conductivity. In particular, the thermosphere connected to the inner magnetosphere is found to super-corotate, such that true Pedersen conductivities smaller than previously predicted are required to enforce the observed rotation of the magnetosphere within ∼30 R J . We find that increasing the Joule heating at high latitudes by adding a component due to rapidly fluctuating electric fields is unable to explain the Correspondence to: C. G. A. Smith (cgasmith@gmail.com) high equatorial temperatures. Adding a component of Joule heating due to fluctuations at low latitudes is able to explain the high equatorial temperatures, but the thermospheric wind systems generated by this heating cause super-corotation of the inner magnetosphere in contradiction to the observations. We conclude that the coupled model is a particularly useful tool for study of the thermosphere as it allows us to constrain the plausibility of predicted thermospheric structures using existing observations of the magnetosphere.

Auroral Processes at the Giant Planets: Energy Deposition, Emission Mechanisms, Morphology and Spectra

“…Typical values for the auroral electron characteristics are highlighted in bold in Table 2 and yield Pedersen conductance values in the 1.5-2 mho range at Jupiter and in the 10-15 mho range at Saturn (see Table 2). These jovian values are supported by estimations from field-aligned potential models -using parameterized Pedersen conductance relations: they spread from 0.7 to 1.5 mho (Smith and Aylward 2009;Tao et al 2009;Ray et al 2010). Therefore, difference in auroral forcing reduces the difference in conductances between Jupiter and Saturn down to one order of magnitude.…”

“…Finally, Smith and Aylward (2009) found negative values of k in the ionospheric regions mapping to magnetospheric radii inside of 20 R J as a result of super-rotation of the neutrals.…”

“…Other limiting factors of the electron density assessment include: (1) the exact amount of water influx, which has significant effect at Saturn at low latitudes Moore et al 2010), but whose contribution is not well known at Jupiter; and (2) the effect of dynamics, which could be large in the auroral regions (e.g. Smith and Aylward 2009;Tao et al 2009;Galand et al 2011;). In addition, it seems highly relevant to try to characterize the properties and identify the origin of the sharp, narrow electron density peaks seen in Cassini/RSS profiles and most likely responsible for the diurnal distribution derived from SED analysis.…”

“…They have been calculated using ionospheric models applied to Jupiter (e.g. Millward et al 2002;Hiraki and Tao 2008;Smith and Aylward 2009;Tao et al 2010) and to Saturn (e.g. Moore et al 2010;Galand et al 2011;Ray et al 2012a; or derived using Cassini/RSS electron density (Moore et al 2010).…”

Transport of Mass, Momentum and Energy in Planetary Magnetodisc Regions

“…Other theoretical studies of the magnetosphere-ionosphere coupling have included more realistic, global-circulation models for the thermosphere-ionosphere (e.g. Achilleos et al 2001;Smith and Aylward 2009;Yates et al 2012). The most recent study of this kind (Yates et al 2012) found that the total energy transferred from the planet's rotation to the atmosphere and magnetosphere varies with magnetodisc size.…”