A test of the Dessler‐Parker‐Sckopke relation during magnetic storms

Abstract

The Dessler‐Parker‐Sckopke relation (DPS) predicts a linear dependence of the perturbation magnetic field at the surface of the Earth on the total ring current kinetic energy. In this paper, we test DPS by using measurements of the major ring current ion species made by the charge‐energy‐mass spectrometer on the Active Magnetospheric Particle Tracer Explorers CCE spacecraft. We use spectra from passes through the equatorial storm time ring current near the maximum phase of 80 magnetic storms between 1984 and 1989 to estimate the global ring current energy content ERC and compare it with the average value for Dst during each pass. Our work shows that DPS holds well on average. In particular, there is a strong linear correlation between ring current energy estimated from nightside ion measurements and the Dst index, and the slope of the least squares fit line giving Dst as a function of nightside ERC is in good agreement with the prediction of DPS. In contrast, day side measurements of ERC do not yield a robust correlation with Dst. Although we cannot rule out the possibility that currents other than the ring current (for example, tail currents and the magnetopause current) may cause large magnetic perturbations, we conclude that these perturbations, if they exist, must be largely compensating. By examining how the ratio of Dst to ERC varies with the local time sector of the in situ ion measurements, we obtain statistical information on the anisotropy of the storm time ring current. We find that the largest values of ERC/Dst result from nightside measurements and the smallest values result from measurements in the 0600 to 1200 LT region, as would be expected for an ion population injected on the nightside that must drift westward around the Earth, undergoing losses, to reach the dayside morning sector.