Neutral wind control of the Jovian magnetosphere‐ionosphere current system

Abstract

[1] In order to clarify the role of neutral dynamics in the Jovian magnetosphere-ionosphere-thermosphere coupling system, we have developed a new numerical model that includes the effect of neutral dynamics on the coupling current. The model calculates axisymmetric thermospheric dynamics and ion composition by considering fundamental physical and chemical processes. The ionospheric Pedersen current is obtained from the thermospheric and ionospheric parameters. The model simultaneously solves the torque equations of the magnetospheric plasma due to radial currents flowing at the magnetospheric equator, which enables us to update the electric field projected onto the ionosphere and the field-aligned currents (FACs) depending upon the thermospheric dynamics. The self-consistently calculated temperature and ion velocity are consistent with observations. The estimated neutral wind field captures the zonally averaged characteristics in previous three-dimensional models. The energy extracted from the planetary rotation is mainly used for magnetospheric plasma acceleration below 73.5°latitude while consumed in the upper atmosphere, mainly by Joule heating at above 73.5°latitude. The neutral wind dynamics contributes to a reduction in the electric field of 22% compared with the case of neutral rigid corotation. About 90% of this reduction is attributable to neutral winds below the 550-km altitude in the auroral region. The calculated radial current in the equatorial magnetosphere is smaller than observations. This indicates that the enhancement of the background conductance and/or the additional radial current at the outer boundary would be expected to reproduce the observed current.Citation: Tao, C., H. Fujiwara, and Y. Kasaba (2009), Neutral wind control of the Jovian magnetosphere-ionosphere current system,

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.…”

“…showed that the parameter k increases when the incident electron energy increases, while it decreases when the equatorward auroral voltage is enhanced. Tao et al (2009) found regions where the slippage can yield a height-dependent kz parameter larger than 1: this corresponds to a region where the neutral wind velocity is larger than the ion drift velocity in the planetary rotation frame caused by Coriolis forces and viscosity. For regions where kz < 1, they derived values for k between 0.25 and 0.35 over the 63-73…”

“…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.…”

On the feasibility of characterizing jovian auroral electrons viaH3+infrared line-emission analysis

“…IR light is emitted from thermally excited ions and molecules when they transition between vibrational and rotational states, thus the emitted IR intensity reflects the atmospheric temperature. The enhancement of H þ 3 in the high-latitude atmosphere (e.g., Miller et al, 1997;Satoh and Connerney, 1999) is mainly produced by incident auroral electrons through ion chemistry (e.g., Tao et al, 2009). Because of this close relationship of H þ 3 production with the auroral electrons of our interest, we focus on H þ 3 IR lines in this study.…”

Magnetosphere‐Ionosphere‐Thermosphere Coupling at Jupiter Using a Three‐Dimensional Atmospheric General Circulation Model

“…This coupled system is investigated using numerical models, where the neutral atmosphere is represented by a general circulation model (GCM), which is coupled to either a simplified model representing the currents Journal of Geophysical Research: Space Physics 10.1029 in the magnetosphere-ionosphere (MI) system (Ray et al, 2015;Smith & Aylward, 2009;Tao et al, 2009Tao et al, , 2010Tao et al, , 2014Yates et al, 2012Yates et al, , 2014Yates et al, , 2018 or by imposing electric fields directly into the thermospheric GCM (Achilleos et al, 1998(Achilleos et al, , 2001Bougher et al, 2005;Majeed et al, 2005Majeed et al, , 2009Majeed et al, , 2016Millward et al, 2002Millward et al, , 2005. This coupled system is investigated using numerical models, where the neutral atmosphere is represented by a general circulation model (GCM), which is coupled to either a simplified model representing the currents Journal of Geophysical Research: Space Physics 10.1029 in the magnetosphere-ionosphere (MI) system (Ray et al, 2015;Smith & Aylward, 2009;Tao et al, 2009Tao et al, , 2010Tao et al, , 2014Yates et al, 2012Yates et al, , 2014Yates et al, , 2018 or by imposing electric fields directly into the thermospheric GCM (Achilleos et al, 1998(Achilleos et al, , 2001Bougher et al, 2005;Majeed et al, 2005Majeed et al, , 2009Majeed et al, , 2016Millward et al, 2002Millward et al, , 2005.…”