Multifluid Block‐Adaptive‐Tree Solar wind Roe‐type Upwind Scheme: Magnetospheric composition and dynamics during geomagnetic storms—Initial results

Abstract

[1] The magnetosphere contains a significant amount of ionospheric O + , particularly during geomagnetically active times. The presence of ionospheric plasma in the magnetosphere has a notable impact on magnetospheric composition and processes. We present a new multifluid MHD version of the Block-Adaptive-Tree Solar wind Roe-type Upwind Scheme model of the magnetosphere to track the fate and consequences of ionospheric outflow. The multifluid MHD equations are presented as are the novel techniques for overcoming the formidable challenges associated with solving them. Our new model is then applied to the May 4, 1998 and March 31, 2001 geomagnetic storms. The results are juxtaposed with traditional single-fluid MHD and multispecies MHD simulations from a previous study, thereby allowing us to assess the benefits of using a more complex model with additional physics. We find that our multifluid MHD model (with outflow) gives comparable results to the multispecies MHD model (with outflow), including a more strongly negative Dst, reduced CPCP, and a drastically improved magnetic field at geosynchronous orbit, as compared to single-fluid MHD with no outflow. Significant differences in composition and magnetic field are found between the multispecies and multifluid approach further away from the Earth. We further demonstrate the ability to explore pressure and bulk velocity differences between H + and O + , which is not possible when utilizing the other techniques considered.

Constraining the pickup ion abundance and temperature through the multifluid reconstruction of the Voyager 2 termination shock crossing

“…These models do not yield a self-consistent description of the pickup ions; therefore, additional assumptions are needed to link the upstream pickup ion pressure with the downstream pickup ion pressure across the termination shock [Zank et al, 1996[Zank et al, , 2010Fahr and Chalov, 2008]. The truly self-consistent treatment of the thermodynamics of each ion species and electrons is implemented in multi-ion multifluid MHD models [Harnett and Winglee, 2006;Glocer et al, 2009;Najib et al, 2011;Tóth et al, 2012]. These models solve separate continuity, momentum, and energy equations for each ion species.…”

“…We use the following set of multi-ion multifluid MHD equations [Glocer et al, 2009] to describe the three-fluid solar wind model with thermal ions (SW), pickup ions (PUI), and electrons:…”

Modeling of Venus, Mars, and Titan

“…However, due to this concern, Najib et al (2011) (V S (2.27) where V + is the average velocity of all ion fluids. Although, this method is not strictly conservative, Glocer et al (2009) claims it gives "roughly correct jump conditions across shocks when the magnetic energy density is small relative to the kinetic and thermal energy densities". Glocer et al (2009) also couples the ion fluids in their multi-fluid model by approximating the two-stream instability along field lines by adding an additional friction term to the momentum equation.…”

What Controls the Structure and Dynamics of Earth’s Magnetosphere?

“…This, as well as other applications, required the extension of the capabilities of the BATS-R-US code towards XMHD. Currently it can solve for Hall MHD (Toth et al 2008) with separate electron pressure, multiple ion and neutral fluids (Glocer et al 2009c), and anisotropic ion pressure (Meng et al 2012a(Meng et al , 2012b. BATS-R-US can also solve for a non-ideal equation of state, heat conduction (isotropic or field aligned), resistivity (constant or anomalous) and viscosity.…”

“…The reason for this unphysical behaviour is that XMHD does not contain the kinetic instabilities that limit the relative speed or the anisotropy. To solve these issues, one can use source terms based on the theory of kinetic instabilities that mimic such kinetic effects on the XMHD scales (Glocer et al 2009c;Meng et al 2012a).…”