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GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 5, 1058, doi:10.1029/2001GL013988, 2002

Solar cycle and geomagnetic N⁺¹/O⁺¹ variation in outer dayside magnetosphere: Possible relation to topside ionosphere

S. P. Christon

Focused Analysis and Research, Columbia, Maryland, USA

U. Mall

Max Planck-Institute fur Aeronomie, Katlenburg-Lindau, Germany

T. E. Eastman

Plasmas International, Silver Spring, Maryland, USA

G. Gloeckler

Department of Physics, University of Maryland, College Park, USA

A. T. Y. Lui

JHU/APL, Laurel, Maryland, USA

R. W. McEntire

JHU/APL, Laurel, Maryland, USA

E. C. Roelof

JHU/APL, Laurel, Maryland, USA

Abstract

O⁺¹ and N⁺¹ are important ring current ions in great magnetic storms. We study ∼10–210 keV/e O⁺¹ and N⁺¹ in dayside outer ring current (ORC) at ∼9–15 R_E using Geotail's EPIC/STICS ion spectrometer. We find: average N⁺¹/O⁺¹ (Γ_N/O) varies by ∼2 over a solar cycle, ∼40% (∼20%) at solar minimum (maximum); individual Γ_N/O values range from ∼0.15 (moderate solar maximum storm) to ∼1 (18-hr solar minimum superquiet interval); and N⁺¹ is third in importance after H⁺ and O⁺¹ during two moderate storms (Dst_min ∼ −80 nT, ∼25% great storm intensity), one at minimum, one maximum. High-latitude topside ionospheric AE-D/MIMS ion composition data form a baseline reference used to argue that ORC Γ_N/O variations generally reflect and may be partially explained by topside ionospheric density Γ_N/O spatial variations.

Published 8 March 2002.

Index Terms: 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; 2730 Magnetospheric Physics: Magnetosphere—inner; 2778 Magnetospheric Physics: Ring current; 2788 Magnetospheric Physics: Storms and substorms.

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Citation: Christon, S. P., U. Mall, T. E. Eastman, G. Gloeckler, A. T. Y. Lui, R. W. McEntire, and E. C. Roelof (2002), Solar cycle and geomagnetic N⁺¹/O⁺¹ variation in outer dayside magnetosphere: Possible relation to topside ionosphere, Geophys. Res. Lett., 29(5), 1058, doi:10.1029/2001GL013988.

Copyright 2002 by the American Geophysical Union.