Plasma transport during substorm growth phase and relation to breakup

For omega < omega (bi),omega (be), the electron and ion bounce frequencies, the response of a plasma to an externally applied electromagnetic perturba tion is nonlocal. This implies, via the quasi-neutrality equation, the deve lopment of an electrostatic potential which is constant for a given magneti c field line. In the near equatorial region the corresponding potential ele ctric field is shown to oppose the effect of the induced electric field ass ociated with the externally applied perturbation. Thus the effect of the in duced electric field is partially shielded; the total azimuthal electric fi eld (i.e. induced plus potential) tends to be small, which explains why the radial flow velocity is slow during quasi-steady conditions prevailing dur ing the growth phase and after the active phase. The nonlocal response of t he plasma also leads to the development of a parallel current that may gene rate current driven Alfven (CDA) waves, which mode convert into shear Alfve n (SA) waves. CDA/SA waves are systematically observed at early breakup; th ey grow very fast and produce a parallel diffusion of electrons. As soon as the diffusion time is shorter than the bounce time (tau (d)< tau (b)), the nonlocal response vanishes. Thus the shielding disappears, and an enhanced transport is restored at the rate fixed by the induced electric field alon e. We show that fast flows effectively occur when CDA waves have enough pow er to diffuse electrons (over tau (d)< tau (b)). Electron parallel diffusio n also leads to an interruption of the parallel current and therefore to a disruption of the perpendicular current.