Mid-to-low-latitude ground magnetometers located on the dayside observe an unusual negative bay in the $H$-component as a direct response to the solar wind dynamic pressure (SWPd) pulse occurring during period of steadily intense southward IMF in the course of the magnetic storm main phase. Occurrence of geomagnetic depression maximizes in the postnoon sector. Geosynchronous satellite also observes a decrease of the dayside magnetic field. Simultaneous high-latitude magnetic disturbances are likely indicative of large strengthening of Region~1 field-aligned current (FAC). Observations seem to confirm the theoretical prediction that Chapman-Ferraro dynamics is replaced by Region~1 FAC dynamics when the IMF is strongly southward and SWPd is high.
Solar wind, magnetic cloud, magnetic storm, mid-to-low latitude geomagnetic disturbances
1. Hargreaves, J. K. The Solar-Terrestrial Environment - Cambridge: Cambridge University Press., 1992. - 420 pp.
2. Lukianova, R. Magnetospheric response to sudden changes in solar wind dynamic pressure inferred from polar cap index, // J. Geophys. Res., 2003. - v. 108 - no. A12 - p. .
3. Lukianova, R. Comment on ``Unified PCN and PCS indices: Method of calculation, physical sense, and dependence on the IMF azimuthal and northward components'' by O. Troshichev, A. Janzhura, and P. Stauning, // J. Geophys. Res., 2007. - v. 112 - no. A7 - p. .
4. Nishida, A. Geomagnetic Diagnosis of the Magnetosphere - New York: Springer-Verlag., 1978. - 256 pp.
5. Riazantseva, M. O., Dalin, P. A., Zastenker, G. N., Richardson, J. Orientation of sharp fronts of the solar wind plasma, // Cosmic Res., 2003. - v. 41 - no. 4 - p. .
6. Russell, C. T., Ginskey, M., Petrinec, S. M. Sudden impulses at low latitude stations: Steady state response for southward interplanetary magnetic field, // J. Geophys. Res., 1994. - v. 99 - p. .
7. Siscoe, G. L., Crooker, N. U., Siebert, K. D. Transpolar potential saturation: Role of region 1 current system and solar wind ram pressure, // J. Geophys. Res., 2002. - v. 107 - no. A10 - p. .
8. Zesta, E., Singer, H., Lummerzheim, D., Russel, C., Lyons, L. R., Brittnacher, M. The effect of the January 10, 1997 pressure pulse on the magnetosphere-oinosphere current system // Magnetospheric Current Systems, ed. by S. Ohtani and R. Lysak - Washington: AGU., 2000. - p. .
