The impact of the plane front of an interplanetary rotational discontinuity, which has a circular polarization and propagates in the solar wind along the Sun-Earth radius, on the Earth`s bow shock and the magnetosheath is investigated in the three-dimensional formulation. The most characteristic values of the solar wind parameters and the interplanetary magnetic field strength in the Earth`s orbit are considered. The global three-dimensional pattern of the flow is constructed as a mosaic of exact solutions of the Riemann problem of breakdown of the MHD discontinuity behind the interacting waves. The exact solutions are found numerically in computer using an original Riemann solver for the non-plane-polarized three-dimensional magnetohydrodynamic Riemann problem. The pattern developed is a function of the latitude and longitude of points on the surface of the bow shock. It is found that all the waves and discontinuities appearing in the interaction significantly depend on the angle of rotation of the magnetic field and their type can transform in the process of propagation. The waves are found using relations on strong MHD discontinuities for fast and slow shocks and rotational discontinuities and systems of ordinary differential equations for rarefaction waves.
It is found that the plane-polarized formulation of the problem can adequately describe the flow only in the plane of the ecliptic whereas outside it the interaction between a rotational discontinuity and the bow shock has principally different nature and obeys other mechanisms.
An original software, which makes it possible to construct the density, pressure, velocity, and magnetic field strength distributions in the neighborhood of the Earth`s bow shock and in the magnetosheath using the exact solutions obtained and variations of the physical parameters in all the waves appearing in the interaction, is developed.
The electric currents flowing in the rotational discontinuity and the associated sudden changes in the interplanetary magnetic field lead to significant changes in the density, pressure, and velocity distributions after interaction with the bow shock. Being initially asymmetric with a maximum density in the plane of the ecliptic on the dawn flank, the density variation pattern in the bow shock rotates together with rotation of the magnetic field so that in the transformed bow shock the maximum density is reached on a curve inclined to the plane of the ecliptic on the angle of rotation of the magnetic field (in the north part of the bow shock). In the fast shock waves penetrating in the magnetosheath the maximum change in the density is related with rotation of the magnetic field, but is not proportional to its angle of rotation, and is reached on the dawn flank in the south flank. At the same time, the density decreases in these zones in the highest degree in slow rarefaction waves propagating in the wake of fast shock waves.
The maximum changes in the magnetic field take place in rotational discontinuities, both in the refracted ones (propagating into the magnetosheath) and in the reflected ones (propagating behind the transformed bow shock). A complex pattern of redistribution of the electric currents leads to the formation of narrow zones in which the magnetic field change sharply so that its components can change sign to opposite and their maxima and minima are reached in neighboring points. For the refracted and reflected rotational discontinuities these zones have close longitudes and latitudes. Variation of the velocity are tightly related with variations of the magnetic field, namely, the electric currents flowing in the shocks and rotational discontinuity provoke acceleration or deceleration of the gas.
The solutions obtained are clear illustration of asymmetry of the impact of the interplanetary magnetic field on the processes during impingement of sudden solar wind perturbations of the magnetic field (directional discontinuities of the interplanetary magnetic field) on the Earth`s bow shock and penetration of them into the magnetosheath and the necessity of taking the three-dimensionality and the non-plane-polarized nature of the interaction into account. They are necessary to interpret measurements of the solar wind parameters and the interplanetary magnetic field carried out on spacecraftlocated in the neighborhood of the Lagrange point L1, where the Sun`s and Earth`s gravitational attraction are equal, in the magnetosheath, and in the neighborhood of the magnetopause for the purpose of prediction of the cosmic weather which manifests itself in the Earth`s magnetosphere as sudden storm commencements, magnetic substorms, and sudden impulses.
The work was carried out with support from RFBR (project No. 14-01-00335a) and a Program for the Support of Leading Science Schools (project No. NSh-3530.2014.1).
