Stationary incompressible MHD perturbationsgenerated by a current source in a moving plasma

On the possible formation of Alfvén wings at Mercury during encounters with coronal mass ejections

“…The inductive interaction of magnetized plasmas with conducting bodies has been studied both in the MHD approximation and at higher frequencies [see Woodward and McKenzie , 1999, and references therein]. Analytically tractable solutions of the linear MHD disturbance induced by a current source were obtained by Woodward and McKenzie [1999] (hereinafter referred to as WM99) as a function of M A under the following simplifications: (1) the plasma is incompressible, supporting only shear Alfvén waves; (2) the flow is perpendicular to the uniform background magnetic field; and (3) a point source current, driven through the obstacle, is specified a priori pointing to the direction of the motional electric field. Although the flow is generally only 20°–30° off the ambient field direction at Mercury, assumption (2) is justified at times of ICMEs when large non‐radial IMF components are typical (Figure 2).…”

“…We use the WM99 model to determine the conditions under which the Alfvén wing magnetic field perturbation becomes comparable to the lobe and magnetosheath magnetic fields. These analytic modelling results are meant to anticipate future numerical simulations and allow us to estimate the dependence of the solar wind interaction with Mercury on M A .…”

“…If x and y are the directions of the background magnetic field, B 0 , and of the current driven through the conductor, J 0 , respectively, the perturbation magnetic field is (WM99, equation (23)): where M A the Alfvén Mach number, k = , [x y z] the Cartesian coordinates, and The far‐field perturbation in the direction of the flow, V SW , is (WM99, equations (24)–(26) of that paper, excluding the dipole term): where I Bz 1 = δ ( y )[ δ ( ζ + ) + δ ( ζ − )], and in which ζ ± = x ± z / M A , and γ = .…”

Partially Ionized Plasmas in Astrophysics

“…when the ram pressure of the stellar wind dominates the magnetic pressure, an Earth/Jupiter-type magnetosphere with a bow shock, magnetopause, and magnetotail, is formed. At the same time, in the case of an extremely close-orbit location of an exoplanet (e.g., d < 0.03 AU for the Sun analogue star), where the stellar wind is still under acceleration and remains sub-magnetosonic and sub-Alfvénic (Ip et al 2004;Preusse et al 2005;Strugarek et al 2015), an Alfvénic wing-type magnetosphere without a shock in the upstream region is formed (Woodward and McKenzie 1999;Strugarek et al 2015). The character of the stellar wind impact on the planetary nearby plasma environment and inner atmosphere is different for the super-and sub-Alfvénic types of the magnetosphere and in each particular planet case it has to be properly taken into account.…”