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

The Dessler-Parker-Sckopke relation (DPS) predicts a linear dependence of t he perturbation magnetic field at the surface of the Earth on the total rin g 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 spectr ometer on the Active Magnetospheric Particle Tracer Explorers CCE spacecraf t. We use spectra from passes through the equatorial storm time ring curren t near the maximum phase of 80 magnetic storms between 1984 and 1989 to est imate the global ring current energy content E-RC and compare it with the a verage value for Dst during each pass. Our work shows that DPS holds well o n 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 n ightside E-RC is in good agreement with the prediction of DPS. In contrast, dayside measurements of E-RC do not yield a robust correlation with Dst. A lthough we cannot rule out the possibility that currents other than the rin g current (for example, tail currents and the magnetopause current) may cau se large magnetic perturbations, we conclude that these perturbations, if t hey exist, must be largely compensating. By examining how the ratio of Dst to E-RC 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 E-RC/Dst result from nightside measurements and the smallest values result from measurements in the 0600 t o 1200 LT region, as would be expected for an ion population injected on th e nightside that must drift westward around the Earth, undergoing losses, t o reach the dayside morning sector.