Effect of the day night ionospheric conductivity gradient on polar cap convective flow

Abstract

The electric field data in the polar cap do not display the expected mirror symmetry for positive and negative values of the solar magnetospheric y component of the interplanetary magnetic field, suggesting that an additional effect is squeezing the antisunward flow toward the dawnside of the polar cap. It is shown that a conductivity decrease toward the nightside will produce such an effect. Results are both for a model with a discontinuous decrease in density and for models with a smooth exponential decrease in conductivity with distance across the polar cap. Steeper conductivity gradients cause stronger squeezing of the flow toward the dawnside of the polar cap. Outside the polar cap the return flow towards the dayside spreads over a wider latitude range on the dawnside than on the duskside. Comments on a paper by J. P. Heppner, 'Polar cap electric field distributions related to interplanetary magnetic field direction,' J. Geophys .. Res., 78, 4001, 1973. Atkinson and Hutchison' Brief Report 729 Wolf, R. A., Effects of ionospheric conductivity on convective flow of plasma in the magnetosphere,

Magnetosphere–Ionosphere Convection as a Compound System

“…The cell structures show that the ionospheric convection potential correlating with IMF B y and B z components is not a mere projection of magnetospheric convection structure controlled by the IMF, but a result of two-way interaction between the magnetospheric and ionospheric convections (Atkinson and Hutchison 1978;Tanaka 2001). The IMF B y effects show the active role of the ionosphere in the convection system (limitation and redistribution of convection) and reveal the nature of convection structure normally hidden under the symmetry of the system to show the two-way interaction nature of M-I convection.…”

“…The rotation of cell centers to earlier MLTs, however, cannot directly be derived from the squeezing mechanism by Atkinson and Hutchison (1978). It is a result of more synthesized effect.…”

“…When is non-uniform (bottom row), the relationship between convection shear and FAC is slightly modified, because charge accumulation and the resulting change in electrostatic field occur in the ionosphere in order to maintain current continuity (Atkinson and Hutchison 1978;Tanaka 2001). Compared with the case of uniform conductivity, modifications seen in the bottom row of Fig.…”

“…It is only Atkinson and Hutchison (1978) that proposed the mechanism for non-uniform conductivity effects on the convection. They proposed a mechanism for the effect of day night conductivity gradient on the breakdown of the mirror symmetry in convection.…”

Solar-terrestrial coupling poleward of the auroral zone.

“…ATKINSON and HUTCHINSON (1978) and NOPPER and CAROVILLANO (1979) showed that this distorts the flow (for the northern hemisphere) so that equipotentials are closer together on the dawnside than on the duskside as sketched in Fig. 5(b).…”