The Earth's passage of the April 11, 1997 coronal ejecta: geomagnetic field fluctuations at high and low latitude during northward interplanetary magnetic field conditions

An analysis of the low frequency geomagnetic
field fluctuations at an Antarctic (Terra Nova Bay) and a low latitude (L'Aquila, Italy) station during the Earth's passage of a coronal ejecta on April 11, 1997 shows that major solar wind pressure variations were
followed at both stations by a high fluctuation level. During northward interplanetary magnetic field conditions and when Terra Nova Bay is close to the local
geomagnetic noon, coherent fluctuations, at the same frequency (3.6 mHz) and with polarization characteristics indicating an antisunward propagation, were observed simultaneously at the two stations. An analysis of simultaneous measurements from geosynchronous satellites shows evidence for pulsations at approximately the same frequencies also in the magnetospheric field.
The observed waves might then be interpreted as oscillation modes, triggered by an external stimulation, extending to a major portion of the Earth's magnetosphere.

Berdichevsky, D., J.-L. Bougeret, J.-P. DelaboudinieÁ re, N. Fox, M.
Kaiser, R. Lepping, D. Michels, S. Plunkett, D. Reames, M.
Reiner, I. Richardson, G. Rostoker, J. Steinberg, B. Thompson,
and T. von Rosenvinge, Evidence for multiple ejecta; April 7±11,
1997 ISTP Sun-Earth connection event, Geophys. Res. Lett., 25,
2473, 1998.
Burlaga, L. F., Magnetic clouds, in Physics of the Inner Helio-
sphere, Eds. R. Schwenn and E. Marsch, vol 2, p. 1, Springer-
Verlag, Berlin Heidelberg New York 1991.
Carbary, J. F., and C. I. Meng, Correlation of cusp latitude with Bz
and AE (12) using nearly one year's data, J. Geophys. Res., 91,
10 047, 1986.
Farrugia, C. J., M. P. Freeman, L. F. Burlaga, R. P. Lepping, and
K. Takahashi, The Earth's response under continued forcing;
substorm activity during the passage of an interplanetary
magnetic cloud, J. Geophys. Res., 98, 7657, 1993.
Farrugia, C. J., R. P. Lepping, L. F. Burlaga, A. Szabo, D.
Vassiliadis, P. Stauning, and M. P. Freeman, The WIND
magnetic cloud of October 18±20, 1995: implications for the
magnetosphere, EOS, Trans. Am. Geophys. Un., 77 (17), S241,
1996.
Francia, P., and U. Villante, Some evidence of ground power
enhancements at frequencies of global magnetospheric modes at
low latitude, Ann. Geophysicae, 15, 17, 1997.
Francia, P., S. Lepidi, U. Villante, and A. J. Lazarus, Geomagnetic
response at low latitude to multiple solar wind pressure
variations, in press. J. Geophys. Res., 1999.
Gosling, J. T., Coronal mass ejections and magnetic ¯ux ropes in
interplanetary space, in Physics of Magnetic Flux Ropes,
Geophys. Monogr. Ser., vol 58, Eds. C.T. Russell et al., 343,
AGU, Washington, D.C., 1990.
Lepidi, S., P. Francia, U. Villante, L. J. Lanzerotti, and A. Meloni,
Polarization pattern of low frequency geomagnetic ®eld ¯uctu-
ations (0.8±3.6 mHz) at high and low latitude, J. Geophys. Res.,
104, 305, 1999.
Lepping, R. P., L. F. Burlaga, B. T. Tsurutani, K. W. Ogilvie,
A. J. Lazarus, D. S. Evans, and L. W. Klein, The interaction
of a very large interplanetary magnetic cloud with the
magnetosphere and with cosmic rays, J. Geophys. Res., 96,
9425, 1991.
Meloni, A., and F. Molina, Study of the S variation at L'Aquila
Geomagnetic observatory, Ann. Geophysicae, 7, 387, 1989.
Russell, C. T., and M. Ginskey, Sudden impulses at subauroral
latitudes: response for northward interplanetary magnetic ®eld,
J. Geophys. Res., 100, 23 695, 1995.
Russell, C. T., M. Ginskey, and S. M. Petrinec, Sudden impulses at
low latitude stations: steady state response for northward
interplanetary magnetic ®eld, J. Geophys. Res., 99, 253, 1994.
Samson, J. C., Three-dimensional polarization characteristics of
high-latitude Pc5 geomagnetic micropulsations, J. Geophys.
Res., 77, 6145, 1972.
Sibeck, D. G., W. Baumjohann, R. C. Elphic, D. H. Fair®eld, J. F.
Fennell, W. B. Gail, L. J. Lanzerotti, R. E. Lopez, H. Luehr, A.
T. Y. Lui, C. G. Maclennan, R. W. McEntire, T. A. Potemra, T.
J. Rosenberg, and K. Takahashi, The magnetospheric response
to 8-minute period strong amplitude upstream pressure varia-
tions, J. Geophys. Res., 94, 2505, 1989.
Southwood, D. J., Some features of ®eld line resonances in the
magnetosphere, Planet. Space Sci., 22, 483, 1974.
Villante, U., S. Lepidi, P. Francia, P. Palangio, and A. Meloni,
Long period geomagnetic ®eld ¯uctuations at Terra Nova Bay
(Antarctica), Geophys. Res. Lett., 24, 1443, 1997.
Villante, U., P. Francia, S. Lepidi, M. De Lauretis, E. Pietropaolo,
L. Cafarella, A. Meloni, A. J. Lazarus, R. P. Lepping, and F.
Mariani, Geomagnetic ®eld variations at low and high latitude
during the January 10±11, 1997 magnetic cloud, Geophys. Res.
Lett., 25, 2593, 1998.
Walker A. D. M., J. M. Ruohoniemi, K. B. Baker, R. A. Greenwald
and J. C. Samson, Spatial and temporal behavior of ULF
pulsations observed by the Goose Bay HF radar, J. Geophys.
Res., 97, 12 187, 1992.