Storm-substorm both driven by solar wind-magnetopause dynamo powered up or down by dayside or tail reconnection
J. R. Kan, et al
Geophysical Institute, University of Alaska Fairbanks
Extended Abstract:
Storm and substorm are both driven by solar wind-magnetopause (SW-MP) dynamo during southward IMF (interplanetary magnetic field). Dayside reconnection (Sonnerup, 1971; Paschmann et al., 1979; Russell and Elphic, 1979) generates reconnection E-field on open field lines. Solar wind flowing across open field lines along the tail magnetopause drives the SW-MP dynamo, converting solar wind kinetic energy to electromagnetic energy in the magneto-tail. The dynamo current in the magnetopause closes by the cross-tail current in the plasma sheet to form tail lobe current loops. Lorentz force of the cross-tail current distributed along the plasma sheet overcomes the pressure gradient force to drive global earthward convection ~10 to ~30 km/s. The convection generates the E-field in the plasma sheet (PS). Thus dayside reconnection E-field on open field lines penetrates onto closed field lines in the PS via the SW-MP dynamo, without depending on tail reconnection. Flow bursts with speed upward of several 100 km/s are first observed and produced by tail reconnection as proposed by Baumjohann et al. (1990). Chen and Wolf (1993) proposed that flow busrts were bubbles produced by tail reconnection of field lines of reduced entropy content.
Global earthward convection enhances plasma pressure in the plasma sheet to intensify the storm-time ring current during prolonged southward IMF. On the other hand, precipitations of plasma sheet particles (Newell et al., 2009), energized by the global earthward convection powered by the SW-MP dynamo, generate the non-uniform anisotropic oval conductance in the ionosphere (Hardy et al., 1987; Robinson et al., 1987). Auroral electrojet (westward Pedersen current) intensifies into Cowling electrojet (westward Pedersen + Hall current) by the induced southward E-field first observed by Mozer, 1971) due to the blockage of northward Hall current from closure in the plasma sheet due to lack of radial currents (Iijima et al., 1990) in the midnight sector. Intense field-aligned currents, produced by the divergence and convergence on the pre-midnight and post-midnight sides of the Cowling electrojet, respectively. These field-aligned currents close in the Alfvén wavefront to form the Cowling electrojet current loop (CECL). The closure current in the Alfvén wavefront is in the direction opposit to the cross-tail current in the plasma sheet. The Alfvén wavefront, leading the CECL, propagates from the ionosphere to the plasma sheet. Incidence of the Alfvén wavefront on the near-Earth plasma sheet triggers the dipolarization onset in the plasma sheet. Brightening of onset arc is observed to precedes the dipolarization onset by ~80 sec, which is estimated to be the Alfvén travel time from the ionosphere to the dipolarization onset region. Kan et al. (2011) published a new substorm model based on the observations described above that the substorm dipolarization onset is triggered by the Alfvén wavefront incident on the near-Earth plasma sheet. However, the driver for the global earthward convection has yet to be identified.
Kan et al. (2013) propose a new model for storm and substorm that both are driven by the global earthward convection in the plasma sheet enhanced by the solar wind-magnetopause (SW-MP) dynamo, powered up or down by dayside or tail reconnec-tion. This new model is consistent with existing observations described above, and will undergo additional observational verifications for years to come.