ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-27-1267-2009 The structure of low-latitude Pc3 pulsations observed by CHAMP and on the ground Ndiitwani D. C. 1 2 Sutcliffe P. R. 1 2 Hermanus Magnetic Observatory, P.O. Box 32, Hermanus, 7200, South Africa University of Kwazulu-Natal, Private Bag X54001, Durban, 4000, South Africa 12 03 2009 27 3 1267 1277 Copyright: © 2009 D. C. Ndiitwani 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/27/1267/2009/angeo-27-1267-2009.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/27/1267/2009/angeo-27-1267-2009.pdf

The structure of low-latitude continuous pulsations termed Pc3, which are naturally occurring MHD waves in the Earth's magnetosphere, were studied by comparing ground and satellite magnetic field measurements. Data from two induction magnetometers, located at Hermanus and Sutherland in South Africa were used in conjunction with Challenging Minisatellite Payload (CHAMP) satellite observations to study a Pc3 event observed on 15 February 2003, at a time when CHAMP was passing over the ground stations. We observed a number of discrete frequency oscillations for the fast mode wave, one of which drives a field line resonance (FLR) at characteristic latitude as detected by both ground and satellite measurements. Consequently, our observations confirmed the compressional wave as being the driver of the field line resonance. The toroidal mode frequency observed on CHAMP experienced a Doppler frequency shift due to the rapid motion across the resonance region. Polarization hodograms in the resonance region clearly showed the expected 90° rotation of the field line resonant magnetic field components.

 References Baransky, L. N., Borovkov, J. E., Gokhberg, M. B., Krylov, S. M., and Troitskaya, V. A.: High resolution method of direct measurement of the magnetic field line's eigenfrequencies, Planet. Space Sci., 33, 1369–1374, 1985. Burg, J. P.: Maximum entropy spectral analysis, Paper presented at 37th meeting, Soc. Geophys., Oklahoma City, Okla., October 1967. Burg, J. P.: A new analysis technique for time series data, Paper presented at NATO Advanced Study Institute on Signal processing, Enschede, Netherlands, August 1968. Chen, W. Y. and Stegen, G. R.: Experiment with maximum entropy power spectra of sinusoids, J. Geophys. Res., 79, 3019–3022, 1974. Dent, Z. C., Mann, I. R., Goldstein, J., Menk, F. W., and Ozeke, L. G.: Plasmaspheric depletion, refilling, and plasmapause dynamics: A coordinated ground-based and IMAGE satellite study, J. Geophys. Res., 111, A03205, https://doi.org/10.1029/2005JA011046, 2006. Hattingh, S. K. F. and Sutcliffe, P. R.: Pc3 pulsation eigenperiod determination at low latitudes, J. Geophys. Res., 92, 12433–12436, 1987. Haykin, S. and Kesler, S.: Prediction-error filtering and maximum-entropy spectral estimation, in: Nonlinear Methods of Spectral Analysis, edited by: Haykin, S., Springer-Verlag, Berlin, 9–72, 1979. Heilig, B., Lühr, H., and Rother, M.: Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground, Ann. Geophys., 25, 737–754, 2007. Hughes, W. J. and Southwood, D. J.: An illustration of modification of geomagnetic pulsation structure by the ionosphere, J. Geophys. Res., 81, 3241–3247, 1976. Jacobs, J. A., Kato, Y., Matsushita, S., and Troitskaya, V. A.: Classification of geomagnetic micropulsations, J. Geophys. Res., 69(1), 180–181, 1964. Kim, K. H. and Takahashi, K.: Statistical analysis of compressional Pc3-4 pulsations observed by AMPTE CCE at $L$=2–3 in the dayside magnetosphere, J. Geophys. Res., 104, 4539–4558, 1999. Kivelson, M. G. and Southwood, D. J.: Hydromagnetic waves and the ionosphere, Geophys. Res. Lett., 15, 1271–1274, 1988. Le, G. and Russell, C. T.: The Morphology of ULF Waves in the Earth's Foreshock, in: Solar wind sources of magnetospheric Ultra-Low-Frequency waves, pp. 87–98, Geophysical Monogr., 81, AGU, Washington, D.C., 1994. Menk, F. W., Waters, C. L., and Fraser, B. J.: Field line resonances and waveguide modes at low latitudes: 1. Observations, J. Geophys. Res., 105, 7747–7761, 2000. Menk, F. W., Mann, I. R., Smith, A. J., Waters, C. L., Clilverd, M. A., and Milling, D. K.: Monitoring the plasmapause using geomagnetic field line resonances, J. Geophys. Res., 109, A04216, https://doi.org/10.1029/2003JA010097, 2004. Odera, T. J., Van Swol, D., Russell, C. T., and Green, C. A.: Pc 3,4 magnetic pulsations observed simultaneously in the magnetosphere and at a multiple ground stations, Geophys. Res. Lett., 18, 1671–1674, 1991. Reigber, C, Lühr, H., and Schwintzer, P.: CHAMP mission status, Adv, Space Res., 30, 129–134, 2002. Russell, C. T., Luhmann, J. G., Odera, T. J., and Stuart, W. F.: The rate of occurrence of day side Pc3, 4 pulsations; the L-value dependence of the IMF cone angle effect, Geophys. Res. Lett., 10, 663–666, 1983. Sutcliffe, P. R. and Lühr, H.: A comparison of Pi2 pulsations observed by CHAMP in low Earth orbit and on the ground at low latitudes, Geophys. Res. Lett., 30(21), 2105, https://doi.org/10.1029/2003GL018270, 2003. Swingler, D. N.: A comparison between Burg's maximum entropy method and a nonrecursive technique for the spectral analysis of deterministic signals, J. Geophys. Res., 84, 676–685, 1979. Ulrych, T. J. and Clayton, R. W.: Time series modelling and maximum entropy, Phys. Earth Planet. Inter., 12, 188–200, 1976. Vellante, M., Lühr, H., Zhang, T. L., Wesztergom, V., Villante, U., De Lauretis, M., Piancatelli, A., Rother, M., Schwingenschuh, K., Koren, W., and Magnes, W.: Ground/satellite signatures of field line resonance: A test of theoretical predictions, J. Geophys. Res., 109, A06210, https://doi.org/10.1029/2004JA010392, 2004. Verõ, J., Lühr, H., Vellante, M., Best, I., St\vreštik, J., Cz Miletits, J., Holló, L., Szendrõi, J., and Zieger, B.: Upstream waves and field line resonances: simultaneous presence and alternation in Pc3 pulsation events, Ann. Geophys., 16, 34–48, 1998. Waters, C. L., Menk, F. W., and Fraser, B. J.: The resonance structure of low latitude field line resonances, Geophys. Res. Lett., 18, 2293–2296, 1991. Waters, C. L., Menk, F. W., and Fraser, B. J.: Low-latitude geomagnetic field line resonance: experiment and modeling, J. Geophys. Res., 99, 17547–17558, 1994.