Substorm Activity and Orientation of the Front of a Shock Wave of an Interplanetary Magnetic Cloud

Abstract

The paper draws attention to the complex structure of the fast magnetic clouds of the solar wind, which, in addition to the actual cloud body, contain a turbulent transition layer (cloud sheath) with a large and irregular magnetic field following the shock wave. The orientation of the plane of the magnetic-cloud shock wave with respect to the interplanetary magnetic field modified by the shock wave propagating in the solar wind for 33 cases of the registration of fast magnetic clouds has been calculated. The dependence of the substorm activity in the auroral zone on the level of turbulent processes occurring in the sheath of magnetic clouds has been studied. It was taken into account that the turbulent phenomena in the sheath are largely determined by the orientation of the shock-wave plane with respect to the interplanetary magnetic field. It is shown that the level of magnetic activity in the auroral zone, which is characterized by the integral AL index, increases with a decrease in the angle between the direction normal to the shock-wave front and the vector of the interplanetary magnetic field. Thus, the most geoeffective are magnetic clouds with a quasi-parallel shock wave, and the least geoeffective are those with a quasi-perpendicular shock wave. It was concluded that the intensity of turbulent processes in the cloud sheath increases with a decrease in the magnetic field penetrating the sheath, which plays a stabilizing role for turbulent magnetohydrodynamic perturbations.