References

ANGEO

Annales Geophysicae

ANGEO

Ann. Geophys.

1432-0576

Copernicus Publications

Göttingen, Germany

10.5194/angeo-27-1573-2009

Magnetic field and electric currents in the vicinity of polar cusps as inferred from Polar and Cluster data

Tsyganenko

N. A.

Institute of Physics, Saint-Petersburg State University, Saint-Petersburg 198504, Russia

02 04 2009

27 4 1573 1582

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/27/1573/2009/angeo-27-1573-2009.html

The full text article is available as a PDF file from https://angeo.copernicus.org/articles/27/1573/2009/angeo-27-1573-2009.pdf

A detailed statistical study of the magnetic structure of the dayside polar cusps is presented, based on multi-year sets of magnetometer data of Polar and Cluster spacecraft, taken in 1996–2006 and 2001–2007, respectively. Thanks to the dense data coverage in both Northern and Southern Hemispheres, the analysis spanned nearly the entire length of the cusps, from low altitudes to the cusp "throat" and the magnetosheath. Subsets of data falling inside the polar cusp "funnels" were selected with the help of TS05 and IGRF magnetic field models, taking into account the dipole tilt and the solar wind/IMF conditions. The selection funnels were shifted within ±10° of SM latitude around the model cusp location, and linear regression parameters were calculated for each sliding subset, further divided into 10 bins of distance in the range 2≤R≤12 RE, with the following results. (1) Diamagnetic depression, caused by the penetrated magnetosheath plasma, becomes first visible at R~4–5 RE, rapidly deepens with growing R, peaks at R~6–9 RE, and then partially subsides and widens in latitude at the cusp's outer end. (2) The depression peak is systematically shifted poleward (by ~2° of the footpoint latitude) with respect to the model cusp field line, passing through the min{|B|} point at the magnetopause. (3) At all radial distances, clear and distinct peaks of the correlation between the local By and By(IMF) and of the corresponding proportionality coefficient are observed. A remarkably regular variation of that coefficient with R quantitatively confirms the field-aligned geometry of the cusp currents associated with the IMF By, found in earlier observations.

References 1

Balogh, A., Dunlop, M. W., Cowley, S. W. H., Southwood, D. J., Thomlinson, J. G., Glassmeier, K. H., Musmann, G., Lühr, H., Buchert, S., Acuna, M. H., Fairfield D. H., Slavin, J. A., Riedler, W., Schwingenschuh, K., and Kivelson, M. G.: The Cluster magnetic field investigation, Space Sci. Rev., 79, 65–92, 1997.

Boardsen, S. A., Eastman, T. E., Sotirelis, T., and Green, J. L.: An empirical model of the high-latitude magnetopause, J. Geophys. Res., 105, 23193–23219, 2000.

Chapman, S. and Ferraro, V. C. A.: A new theory of magnetic storms, J. Geophys. Res., 36, 171–186, 1931.

Erlandson, R. E., Zanetti, L. J., Potemra, T. A., Bythrow, P. F., and Lundin, R.: IMF By dependence of Region~1 Birkeland currents near noon, J. Geophys. Res., 93, 9804–9814, 1988.

Fairfield, D. H.: Magnetic Fields of the Magnetosheath, Rev. Geophys. Space Phys., 14, 117–134, 1976.

Hill, P., Paschmann, G., Treumann, R. A., Baumjohann, W., Sckopke, N., and Lühr, H.: Plasma and magnetic field behavior across the magnetosheath near local noon, J. Geophys. Res., 100, 9575–9583, 1995.

King, J. H. and Papitashvili, N. E.: Solar wind spatial scales in and comparisons of hourly Wind and ACE plasma and magnetic field data, J. Geophys. Res., 110, A02104, https://doi.org/10.1029/2004JA010649, 2005.

McDiarmid, I. B., Burrows, J. R., and Wilson, M. D.: Magnetic Field Perturbations in the Dayside Cleft and Their Relationship to the IMF, J. Geophys. Res., 83, 5753–5756, 1978.

McDiarmid, I. B., Burrows, J. R., J. R., and Wilson, M. D.: Large-Scale Magnetic Field Perturbations and particle measurements at 1400 km on the dayside, J. Geophys. Res., 84, 1431–1441, 1979.

Ohtani, S., Potemra, T. A., Newell, P. T., Zanetti, L. J., Iijima, T., Watanabe, M., Yamauchi, M., Elphinstone, R. D., de la Beaujardiere, O., and Blomberg, L. G.: Simultaneous prenoon and postnoon observations of three field-aligned current systems from Viking and DMSP-F7, J. Geophys. Res., 100, 119–136, 1995.

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.

Shue, J.-H., Song, P., Russell, C. T., Steinberg, J. T., Chao, J. K., Zastenker, G., Vaisberg, O. L., Kokubun, S., Singer, H. J., Detman, T. R., and Kawano, H.: Magnetopause location under extreme solar wind conditions, J. Geophys. Res., 103, 17691–17710, 1998.

Sotirelis, T. and Meng, C.-I.: Magnetopause from pressure balance, J. Geophys. Res., 104, 6889–6898, 1999.

Tsyganenko, N. A. and Russell, C. T.: Magnetic signatures of the distant polar cusps: Observations by Polar and quantitative modeling, J. Geophys. Res., 104, 24939–24955, 1999.

Tsyganenko, N. A.: A model of the near magnetosphere with a dawn-dusk asymmetry: 1 Mathematical structure, J. Geophys. Res., 107(A8), 1179, https://doi.org/10.1029/2001JA000219, 2002.

Tsyganenko, N. A. and Sitnov, M. I.: Modeling the dynamics of the inner magnetosphere during strong geomagnetic storms, J. Geophys. Res., 110, A03208, https://doi.org/10.1029/2004JA010798, 2005.

Zhang, H., Dunlop, M. W., Zong, Q.-G., Fritz, T. A., Balogh, A., and Wang, Y.: Geometry of the high-latitude magnetopause as observed by Cluster, J. Geophys. Res., 112, A02204, https://doi.org/10.1029/2006JA011774, 2007.

Zhou, X.-W. and Russell, C. T.: The location of the high-latitude polar cusp and the shape of the surrounding magnetopause, J. Geophys. Res., 102, 105–110, 1997.

Zhou, X.-W., Russell, C. T., Le, G., Fuselier, S. A., and Scudder, J. D.: The polar cusp location and its dependence on dipole tilt, Geophys. Res. Lett., 26, 429–432, 1999.

Zhou, X.-W., Russell, C. T., and Le, G.: Local time and interplanetary magnetic field By dependence of field-aligned currents at high altitudes, J. Geophys. Res., 105, 2533–2539, 2000.

Zhuang, H. C. and Russell, C. T.: An analytic treatment of the structure of the bow shock and magnetosheath, J. Geophys. Res., 86, 2191–2205, 1981.