Abstract
S. A. Fuselier, S. M. Petrinec, and K. J. TrattnerLockheed Martin Advanced Technology Center, Palo Alto, CA, USAReceived: 30 August 2008 – Revised: 30 November 2008 – Accepted: 10 December 2008 – Published: 26 January 20091 IntroductionIn a recent paper, Whitaker et al. (2007) (hereafter referredto as paper 1) described energetic particle observations in themagnetospheric cusp from the International Sun Earth Ex-plorer (ISEE)-1 spacecraft. This event, on 30 October 1978,has been studied by the authors in a previous publication(Whitaker et al., 2006) and some ISEE-2 observations fromthis event were presented by Phillips et al. (1993). In paper 1,the authors argue that energetic particle pitch angle distribu-tions observed in and “above” the cusp demonstrate that 24–44.5keV ions observed in the region cannot be from the bowshock. In particular, they present energetic ion fluxes at sev-eral pitch angles that appear to indicate that the 24–44.5keVions propagate to the spacecraft from “below” (presumablyfrom the cusp). From these observations, they conclude that:“if the bow shock was the source, a large population of par-ticles would be observed from above”, “The deficit in par-ticles with pitch angles less than about 60
Highlights
In a recent paper, Whitaker et al (2007) described energetic particle observations in the magnetospheric cusp from the International Sun Earth Explorer (ISEE)-1 spacecraft
This event, on 30 October 1978, has been studied by the authors in a previous publication (Whitaker et al, 2006) and some ISEE-2 observations from this event were presented by Phillips et al (1993)
In paper 1, the authors argue that energetic particle pitch angle distributions observed in and “above” the cusp demonstrate that 24– 44.5 keV ions observed in the region cannot be from the bow shock
Summary
In a recent paper, Whitaker et al (2007) (hereafter referred to as paper 1) described energetic particle observations in the magnetospheric cusp from the International Sun Earth Explorer (ISEE)-1 spacecraft. In paper 1, the authors argue that energetic particle pitch angle distributions observed in and “above” the cusp demonstrate that 24– 44.5 keV ions observed in the region cannot be from the bow shock They present energetic ion fluxes at several pitch angles that appear to indicate that the 24–44.5 keV ions propagate to the spacecraft from “below” (presumably from the cusp). “The [energetic] particles streaming from below are lost on these [cusp] open field lines and must be generated locally to have flux enhancements that persist for more than two hours”, and “The observation of energetic particles after the spacecraft had exited the [Cusp Diamagnetic Cavity] and was above the cavity supports the theory of local energization.” These results were obtained by studying pitch angle distributions of ions that represent a small fraction of the total ion density or energy. This tracing demonstrates that they originated in the quasi-parallel region of the Earth’s bow shock (prior to reconnection) and, contrary to the conclusion in paper 1, the bow shock is a strong candidate for the 24– 44.5 keV ions observed continuously in this event
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