Structure of the Front of a Collisionless Oblique Interplanetary Shock Wave from High Time Resolution Measurements of Solar-Wind Plasma Parameters

Abstract

Data from the Fast Solar Wind Monitor (BMSW) of the science payload onboard the SPEKTR-R satellite and data from instruments on board the WIND spacecraft are used to study statistically the structure of the front of oblique interplanetary shock waves with respect to the θ_Bn angle and the fulfillment of the Rankine–Hugoniot conditions at the fronts of collisionless shock waves. The experimental wavelength of oscillations upstream of the ramp is compared with the estimated theoretical wavelength to determine that the dispersion of oblique magnetosonic waves plays the decisive role in the formation of the fronts of quasiperpendicular (45° ≤ θ_Bn < 90°) collisionless interplanetary shock waves with small Mach numbers М_A < 3 and a parameter of β₁ < 1. Comparison of the Rankine–Hugoniot relations M_A(ρ₂/ρ₁), which were measured at the fronts of 47 interplanetary shock waves with β₁ < 5 and Alfven Mach numbers of 1 < М_А < 10 by calculations performed within the ideal magnetic hydrodynamics (MHD), has revealed that the effective adiabatic index γ, which characterizes the processes inside the shock front, lies mainly within the range from 2 to 5/3.