Comparison of magnetic field perturbations and solar electron profiles in the polar cap

Abstract

Northern hemisphere geomagnetic field perturbations and solar electron profiles measured during the magnetic storm of August 4–5, 1972, are compared. Pitch angle distributions of the solar electrons are used to infer the locations of closed geomagnetic field lines that are compared with the locations of certain features of the magnetic perturbations. An example is given, when the interplanetary magnetic field (IMF) is southward, that shows a peak in the postnoon cleft region perturbation occurring near the location where the solar electron pitch angle distribution changes from anisotropic to isotropic, consistent with the suggestion that the peak in the cleft region perturbation occurs at or close to the dayside limit of closed field lines. The same pass shows isotropic pitch angle distributions throughout the polar cap where the magnetic perturbation is sunward (antisunward convection), consistent with open geomagnetic field lines in this region. Examples are also given for times when the IMF is northward, and one type of perturbation pattern that is observed shows antisunward perturbations (sunward convection) in the central polar cap, sunward perturbations (antisunward convection) in adjacent regions changing again to antisunward perturbations (sunward convection) at lower latitudes. In one of these examples, pitch angle distributions throughout the polar cap are isotropic, and it is probable that in most cases when this type of perturbation pattern is observed, the whole polar cap is open. However, two examples are given where antisunward perturbations (sunward convection) in the polar cap are associated with a closed field region surrounded by open field lines. This field configuration may be rather rare and is probably associated with unusual IMF conditions that were present at the time. The measurements are discussed in terms of a magnetic merging model, and in a qualitative way the model appears to account for the observations.