The heliospheric plasma sheet: analytical modeling and observations

Abstract:

Analytical modeling of the heliospheric plasma sheet (HPS) – a structure that surrounds the heliospheric current sheet (HCS) in the solar wind, is an important task, since the HPS origin and its evolution with heliocentric distance is poorly understood both theoretically and observationally. We develop a single-fluid 2-D analytical model of axially-symmetric thin heliospheric current sheet embedded into the HPS and compare the obtained results with observations. We suggest the HCS-HPS system to be a relatively thin plasma disk that is separated from the Parker solar wind by separatrices at both edges of the HPS. We have found that separatrices represent current sheets as well, which is in agreement with Ulysses observations in the apogee, when it crossed the HCS perpendicular to its plane. Our model employs the differential rotation between the solar photosphere and the corona, which leads to unipolar induction in the corona. Three components of the interplanetary magnetic field (IMF), the solar wind speed, and the thermal pressure are taken into account. The model allows finding spatial distributions of the magnetic field, the speed within the HPS, and electric currents within the HCS. We found that the HPS thickness L decreases with distance r, becoming a constant far from the Sun. L ~2.5 solar radii at 1 AU. The important result is that the IMF spiral may be non-Parker inside the HPS, and even may experience a sharp change of direction under some boundary conditions (Kislov et al., 2015). Additionally, we explore three cases: (i) a purely dipole solar magnetic field of the Sun, (ii) a purely quadrupole magnetic field, and (iii) a mixed case. We show that both the quadrupole and the mixed cases produce additional stable current sheets in the solar wind at higher heliolatitudes, and the last case easily explains the South-North IMF asymmetry.

Kislov R. A., O. V. Khabarova, H. V. Malova (2015), A new stationary analytical model of the heliospheric current sheet and the plasma sheet, J. Geophys. Res. Space Physics, 120, doi:10.1002/2015JA021294