ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-27-4305-2009 The Earth's magnetopause as a source and sink for equatorial nightside energetic charged particles Klida M. M. 1 Fritz T. A. 1 Center for Space Physics, Boston University, Boston, MA 02215, USA 26 11 2009 27 11 4305 4316 Copyright: © 2009 M. M. Klida 2009 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/27/4305/2009/angeo-27-4305-2009.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/27/4305/2009/angeo-27-4305-2009.pdf

The Imaging Proton Spectrometer (IPS) and the Imaging Electron Spectrometer (IES) on the Polar satellite have measured temporary deviations in the isotropy of the pitch angle distributions (PADs) of charged particles in the inner magnetosphere. As Polar passes through the nightside equatorial region, the IPS and IES observe dropouts of charged particles with pitch angles near 90°, known as butterfly distributions caused by the shadowing of the magnetopause. Additionally, Polar observes a lower energy (<60 keV) intensification of locally mirroring ions while simultaneously detecting butterfly PADs in both higher energy ions and electrons. While it is accepted that charged particles can be lost to the magnetopause due to shadowing effects, the modeling here can suggest that the magnetopause can also be a direct source for particles observed in magnetosphere, with a strong dependence upon both pitch angle and particle energy.

 References Ashour-Abdalla, M., Bosqued, J M., El-Alaoui, M., Peroomian, V., Zelenyi, L M., Walker, R J., and Wright, J.: A stochastic sea: The source of plasma sheet boundary layer ion structures observed by Cluster, J. Geophys. Res. (Space Physics), 110, 12221–12238, \doi10.1029/2005JA011183, 2005. Blake, J B., Fennell, J F., Friesen, L M., Johnson, B M., Kolasinski, W A., Mabry, D J., Osborn, J V., Penzin, S H., Schnauss, E R., Spence, H E., Baker, D N., Belian, R., Fritz, T A., Ford, W., Laubscher, B., Stiglich, R., Baraze, R A., Hilsenrath, M F., Imhof, W L., Kilner, J R., Mobilia, J., Voss, D H., Korth, A., Gull, M., Fisher, K., Grande, M., and Hall, D.: Ceppad, Space Sci. Rev., 71, 531–562, 1995. Bogott, F H. and Mozer, F S.: Equitorial electron angular distributions in the loss cone and at large angles, J. Geophys. Res., 76, 6790–6805, 1971. Fritz, T A., Alothman, M., Bhattacharjya, J., Matthews, D L., and Chen, J.: Butterfly pitch-angle distributions observed by ISEE-1, Planet. Space Sci., 51, 205–219, 2003. Kaye, S M., Lin, C S., Parks, G K., and Winckler, J R.: Adiabatic modulation of equatorial pitch angle anisotropy, J. Geophys. Res., 83, 2675–2682, 1978. Pfitzer, K A., Lezniak, T W., and Winckler, J R.: Experimental verification of drift shell splitting in the distorted magnetosphere, J. Geophys. Res., 74, 4687–4693, 1969. Richard, R L., El-Alaoui, M., Ashour-Abdalla, M., and Walker, R J.: Modeling the entry and trapping of solar energetic particles in the magnetosphere during the November 24–25, 2001 storm, J. Geophys. Res. (Space Physics), 114, 4210–4225, \doi10.1029/2007JA012823, 2009. Roederer, J G.: On the adiabatic motion of energetic particles in a model magnetosphere, J. Geophys. Res., 72, 981–992, 1967. Roederer, J G.: Dynamics of Geomagnetically Trapped Radiation, no 2 in Physics and Chemistry in Space, Springer-Verlag, Berlin, 1970. Russell, C T., Snare, R C., Means, J D., Pierce, D., Dearborn, D., Larson, M., Barr, G., and Le, G.: The GGS/Polar Magnetic Fields Investigation, Space Sci. Rev., 71, 563–582, 1995. Serlemitsos, P.: Low-energy electrons in the dark magnetosphere, J. Geophys. Res., 71, 61–77, 1966. Stern, D P.: Charged particle motions in a magnetic field that reduce to motions in a potential, Am. J. Phys., 43, 689–694, \doi10.1119/1.9714, 1975. Tsyganenko, N A.: Modeling the Earth's magnetospheric magnetic field confined within a realistic magnetopause, J. Geophys. Res., 100, 5599–5612, 1995. Tsyganenko, N A. and Sitnov, M I.: Modeling the dynamics of the inner magnetosphere during strong geomagnetic storms, J. Geophys. Res., 110, 3208–3223, \doi10.1029/2004JA010798, 2005. Volland, H.: A model of the magnetospheric electric convection field, J. Geophys. Res., 83, 2695–2699, 1978. Walker, R J., Ashour-Abdalla, M., Ogino, T., Peroomian, V., and Richard, R L.: Modeling Magnetospheric Plasma Sources and Losses, AGU Spring Meeting Abstracts, 2001. West Jr., H I.: Some observations of the trapped electrons produced by the Russian high-altitude nuclear detonation of October 28, 1962, in: ASSL Vol. 5: Radiation Trapped in the Earth's Magnetic Field, edited by: McCormac, B M., pp. 634–662, 1966. West Jr., H I. and Buck, R M.: Pitch angle distributions of energetic electrons in the equatorial regions of the outer magnetosphere – OGO-5 observations, in: Magnetospheric physics: proceedings of the Advanced Summer Institute held at Sheffield, UK, August 1973, edited by: McCormac, B M., pp. 93–104, D. Reidel Publishing Co., Dordrecht, 1974. West Jr., H I., Buck, R M., and Walton, J R.: Electron pitch angle distributions of energetic electrons throughout the magnetosphere as observed on OGO 5, J. Geophys. Res., 78, 1064–1081, 1973.