Magnetospheric Convection Induced by Interplanetary Magnetic-Field Variations

Abstract

The dependence of the polar-cap magnetic disturbance on the polarity and magnitude of the Z-component of the interplanetary magnetic field is investigated by regression analysis using hourly values. The Svalgaard-Mansurov effect has been eliminated assuming a linear dependence on the Y-component of the interplanetary field. It is shown that as the northward component of the interplanetary magnetic field increases, a characteristic current system appears in the polar cap. This current system is composed of two current vortices in the dayside polar cap, one in the pre-noon sector and the other in the afternoon sector. The current direction is antisunward in the central polar cap, suggesting that the sunward plasma convection is induced in the polar cap. Current intensity is strongest at ø M ~ 84° around the noon meridian.We propose that the tail field lines are reconnected with the northward interplanetary field on the polar side of the dayside polar cusp, and as a result plasma convection is induced which is closed within the high-latitude magnetosphere. On the other hand, when the interplanetary magnetic field is directed southward, a transpolar current sheet appears covering the whole polar cap (ø M ⩾ 77.5°). The characteristics of this transpolar current sheet are as follows: (i) On the dayside, especially around noon, the direction of the current is roughly consistent with the Hall current direction expected from the dawn-to-dusk electric field, while at night it is considerably skewed from the noon-midnight meridian. Skewing of the current direction can be explained by the effect of the currents external to the ionosphere. (ii) Strength of the current is almost linearly dependent on B z when the interplanetary magnetic field is directed southward (θ < −45°). However, the current intensity is also a function of the magnitude of B y , this being apparent when B z ~ 0. This indicates that the dayside reconnection rate is a function of |B y | as well as of B z , and information is derived about the applicability of the three-dimensional reconnection model in the presence of finite |B y |.KeywordsSolar WindInterplanetary Magnetic FieldMagnetic Local TimeMagnetospheric ConvectionTail LobeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.