The free escape continuum of diffuse ions upstream of the Earth's quasi-parallel bow shock

Trattner, K. J.; Allegrini, F.; Dayeh, M. A.; Funsten, H. O.; Fuselier, S. A.; Heirtzler, D.; Janzen, P.; Kucharek, H.; McComas, D. J.; Möbius, E.; Moore, T. E.; Petrinec, S. M.; Reisenfeld, D. B.; Schwadron, N. A.; Wurz, Peter (2013). The free escape continuum of diffuse ions upstream of the Earth's quasi-parallel bow shock. Journal of Geophysical Research: Space Physics, 118(7), pp. 4425-4434. AGU Publications 10.1002/jgra.50447

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The Earth's bow shock is very efficient in accelerating ions out of the incident solar wind distribution to high energies (≈ 200 keV/e). Fluxes of energetic ions accelerated at the quasi-parallel bow shock, also known as diffuse ions, are best represented by exponential spectra in energy/charge, which require additional assumptions to be incorporated into these model spectra. One of these assumptions is a so-called "free escape boundary" along the interplanetary magnetic field into the upstream direction. Locations along the IBEX orbit are ideally suited for in situ measurements to investigate the existence of an upstream free escape boundary for bow shock accelerated ions. In this study we use 2 years of ion measurements from the background monitor on the IBEX spacecraft, supported by ACE solar wind observations. The IBEX Background Monitor is sensitive to protons > 14 keV, which includes the energy of the maximum flux for diffuse ions. With increasing distance from the bow shock along the interplanetary magnetic field, the count rates for diffuse ions stay constant for ions streaming away from the bow shock, while count rates for diffuse ions streaming toward the shock gradually decrease from a maximum value to ~1/e at distances of about 10 RE to 14 RE. These observations of a gradual decrease support the transition to a free escape continuum for ions of energy >14 keV at distances from 10 RE to 14 RE from the bow shock.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Wurz, Peter

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics

ISSN:

2169-9380

Publisher:

AGU Publications

Language:

English

Submitter:

Cléa Serpollier

Date Deposited:

11 Jul 2014 11:59

Last Modified:

20 Apr 2015 12:13

Publisher DOI:

10.1002/jgra.50447

BORIS DOI:

10.7892/boris.44358

URI:

https://boris.unibe.ch/id/eprint/44358

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