Response of the Jovian thermosphere to variations in solar EUV flux

Abstract

Examining the response to solar extreme ultraviolet (EUV) radiation is an established diagnostic method used to understand the physics of planetary environments. In this study, we focus on the response of the Jovian thermosphere to variations in the solar EUV flux and discuss the consequences for the coupled thermosphere-ionosphere-magnetosphere system. We use a model that simulates both the thermospheric dynamics and the magnetospheric plasma velocity distribution under conditions of angular momentum transport between these regions. The simulations show that when the EUV flux increases by~100% and 200%, the thermospheric neutral wind velocity at~45°latitude increases by 16% and 22%, respectively. The short-term variation over a few Earth days causes an increased velocity at middle latitudes which are magnetically conjugate to the Jovian radiation belt. Increased heating due to solar EUV contributes to this velocity change. The other contribution arises~30 planetary rotations after the initial solar EUV flux increase. This second ("delayed") effect is due to propagation of momentum from high latitudes (the auroral region), where Joule heating is dominant, and is related to the behavior of the ionospheric conductance and magnetosphere-ionosphere coupling currents. The modeled velocity enhancement is smaller than that required to explain the observed enhancement of the synchrotron emission by radial diffusion of the trapped energetic electrons. In this context, we discuss the sensitivity of the underlying thermosphere-ionosphere response to short-wavelength solar radiation and the ensuing three-dimensional wind fields.

Mapping H3+ Temperatures in Jupiter's Northern Auroral Ionosphere Using VLT‐CRIRES

“…Through IR observations using the Fourier transform spectrometer (FTS/BEAR) instrument at the Canada‐France Hawaii Telescope (CFHT), Chaufray et al () derived an upper limit on the LOS velocity of <1.0 km/s for the H 2 , at altitude ~560–690 km above the 1‐bar level (Uno et al, ). Models such as Achilleos et al (), Bougher et al (), and Tao et al () show that the neutral wind velocity remains less than ~1 km/s. In this paper we study H 3 + fundamental emission that occurs at an altitude of ~550 km above the 1‐bar level (Melin et al, ), where Chaufray et al () defined the upper limit of the neutrals to be ~1 km/s.…”

Saturn’s Variable Thermosphere

“…We thereby rely on the use of numerical models to examine the general circulation of Saturn's mesosphere and thermosphere, for which only the STIM model has published results (Müller-Wodarg et al, 2006;2012). But for Jupiter, however, several such models have been published (Achilleos et al, 1998;Bougher et al, 2005;Tao et al, 2014). These build on a heritage of thermosphereionosphere models for Earth which have been adapted to simulate the giant planet environment.…”

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.…”

“…Self-consistently coupling the magnetosphere and ionosphere-thermosphere allows the field-aligned currents (FACs) to affect the magnetospheric convection electric field and magnetospheric plasma. The works of Yates et al (2014), Tao et al (2014), andYates et al (2018) were the first to include time dependence outside of the thermospheric GCM by either having a time-dependent magnetospheric size (Yates et al, , 2018 or solar EUV flux (Tao et al, 2014). Due to the complexity of such coupling the models were designed to initially be axisymmetric.…”

“…The interaction between a planet's upper atmosphere, consisting of an ionosphere embedded in a neutral thermosphere, and magnetosphere is known as magnetosphere-ionosphere-thermosphere (MIT) coupling. 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. The Jovian Ionosphere Model (JIM; Achilleos and Millward) and the Jupiter Thermospheric GCM (JTGCM; Bougher and Majeed) are models that investigated the 3-D dynamics and chemistry of Jupiter's upper atmosphere and its MIT coupling.…”