Substorm growth phase

The growth phase starts the substorm process. The main magnetospheric processes are directly driven by changes in the solar wind.

• Lasts about one hour
• The phase starts with southward turning of the IMF, which enhances the convection electric field as the solar wind energy is transferred to the magnetosphere via reconnection between interplanetary and magnetospheric field lines
• The tail lobe field strength increases (e.g. Fairfield and Ness, 1970; McPherron, 1972). This compresses the near-Earth plasma sheet (e.g., Fairfield et al., 1981; Nagai et al., 1997).
• The cross-tail current increases, leading to a tailward stretching of field lines in the near-Earth tail (Kaufmann, 1987).
• Furthermore, a thin current sheet (TCS, down to 0.1 Re) forms just tailward of the dipole-like field lines (6-15 Re). This can be important for the triggering of the substorm (onset of the expansion phase). See, e.g., Sergeev et al. (1990).
• Pseudobreakups can occur during the growth phase
• Enhanced convection leads to earthward displacement of trapped energetic particles drifting along constant B. This results, together with strong radial flux gradient, into decrease of the flux of energetic particles at a given location (Sauvaud, 1992)
• Also complete dropouts of energetic particle can be observed by non-equatorial satellites, if they enter the lobe because of the magnetic field changes (Lopez et al., 1989)
• Concentration of O+ increases in the magnetosphere, most likely due to nightside auroral activity related to the upcoming substorm (Daglis et al., 1994; Gazey et al., 1996)
• Quiet auroral arcs drift equatorwards, following the energetic electron arc (EEA) on the equatorward side of the visible arcs (Sergeev et al., 1983; see also Kirkwood and Eliasson, 1990)
• The visible arcs often fade away 1-2 min before the auroral breakup (e.g., Pellinen and Heikkila, 1984; Kauristie et al., 1997)
• The onset arc is typically located just equatorward of the Harang discontinuity
• Also dayside activations are often seen prior the nightside onset. (Elphinstone et al., 1991)

References

• Daglis, I. A., S. Livi, E. T. Sarris, and B. Wilken, Energy density of ionospheric and solar-wind-origin ions in the near-earth magnetotail during substorms, J. Geophys. Res., 99, 5691-5703, 1994.
• Elphinstone, R. D., J. S. Murphree, L. L. Cogger, D. Hearn, and R. Lundin, Observations of changes to the auroral distribution prior to substorm onset, in Magnetospheric Substorms, Geophys. Monogr. Ser., vol. 64, edited by J. R. Kan, T. A. Potemra, S. Kokubun, and T. Iijima, pp. 257-275, AGU, Washington, D. C., 1991.
• Fairfield, D. H., and N. F. Ness, Configuration of the geomagnetic tail during substorms, J. Geophys. Res., 75, 7032-, 1970.
• Fairfield, D. H., R. P. Lepping, E. W. Hones, Jr., S. J. Blame, and J. R. Asbridge, Simultaneous measurements of magnetotail dynamics by IMP spacecraft, J. Geophys. Res., 86, 1396-1414, 1981.
• Gazey, N. G. J., M. Lockwood, M. Grande, C. H. Perry, P. N. Smith, S. Coles, A. D. Aylward, R. J. Bunting, H. Opgenoorth, and B. Wilken, EISCAT/CRRES observations: nightside ionospheric ion outflow and oxygen-rich substorm injection, Ann. Geophysicae, 14, 1032-1043, 1996.
• Kaufmann, R. L., Substorm currents: growth phase and onset, J. Geophys. Res., 92, 7472-7489, 1987.
• Kauristie, K., T. I. Pulkkinen, A. Huuskonen, R. J. Pellinen, H. J. Opgenoorth, D. N. Baker, A. Korth, and M. Syrjäsuo, Auroral precipitation fading before and at substorm onset: ionospheric and geostationary signatures, Ann. Geophysicae, 15, 967-983, 1997.
• Kirkwood, S., and L. Eliasson, Energetic particle precipitation in the substorm growth phase measured by EISCAT and Viking, J. Geophys. Res., 95, 6025-6037, 1990.
• Lopez, R. E., A. T. Y. Lui, D. G. Sibeck, K. Takahashi, R. W. McEntire, L. J. Zanetti, and S. M. Krimigis, On the relationship between the energetic particle flux morphology and the change in the magnetic field magnitude during substorms, J. Geophys. Res., 94, 17105-17119, 1989.
• McPherron, R. L., Substorm related changes in the geomagnetic tail: The growth phase, Planet. Space Sci., 20, 1521-1539, 1972.
• Nagai, T., T. Mukai, T. Yamamoto, A. Nishida, S. Kokubun, and R. P. Lepping, Plasma sheet pressure changes during the substorm growth phase, Geophys. Res. Lett., 24, 963-966, 1997.
• Pellinen, R. J. and W. Heikkila, Inductive electric fields in the magnetotail and their relation to auroral and substorm phenomena, Space Sci. Rev., 37, 1-, 1984.
• Sauvaud, J.-A., Characteristics of the cross-tail current disruption at substorm onset and associated particle acceleration, Proceedings of the International Conference on Substorms, ESA SP-335, 243-253, 1992.
• Sergeev, V. A., A. G. Yahnin, and R. J. Pellinen, Relative arrangement and magnetospheric sources of zones of energetic electron precipitation, diffuse and discrete auroras during the growth phase of a substorm, Geomagn. Aeron. Engl. Transl., 23, 792, 1983.
• Sergeev, V. A., P. Tanskanen, K. Mursula, A. Korth, and R. C. Elphic, Current sheet thickness in the near-Earth plasma sheet during substorm growth phase, J. Geophys. Res., 95, 3819, 1990.

See also:

• Space Physics Text Book of Oulu