Magnetic perturbations due to current structural variations
Cloutier, Paul A.
Master of Science
Study of the magnetic perturbations caused by auroral currents has been conducted by rocket-borne magnetometer measurements for years. Since the horizontal auroral currents were usually found to be confined near the visible auroral arcs, as determined by Heppner , Davis , and Davis and Kimball , a number of current models have been established in order to explain observed data by rockets or satellite measurements. In those models, the requirement that the current be continuous across the highly conducting arc results in either polarization electric fields to reduce the current in the highly conducting region or Birkeland currents to provide return current to the outer part of the magnetosphere. Bostrom found two basic solutions, one in which a horizontal electrojet connects two filamentary Birkeland currents, and the other in which broad Birkeland sheet currents (Fig. 2) flow to the edges of the arc, with a transverse closing current and a Hall electrojet. In this thesis, we adopted a model similar to the second solution and assumed that the arc was bombarded by energetic precipitating electrons. In this thesis, the effect of a spatial fold on the magnetic vector field in the vicinity of the arc is examined. Fig. 1 shows the current model used in the initial calculations. It has a displacement of thickness of 3 km from its center and is composed of two current parts. One part is the two oppositely directed Birkeland sheet currents having an equal current density of .5 amp/m and an equal thickness of 3 km for each sheet, in which the downward current sheet is on the south side of the arc and the upward on the north. And the 3 other part is an electrojet having a magnitude of 5 x 1 amp flowing eastward at an altitude of 1 km. Model computations were performed with the Rice IBM 37/155 computer. The variations of the vector components as well as the directions of the magnetic fields due to the following three cases, such as the electrojet, the sheet currents and the combination of the two along a path of rocket flight were individually included in details. For the electrojet current which was a kinked line current at the center, we get more details from a comparison with a straight line current in Chapter 2.