Effect of electrojet irregularities on DC current flow

摘要

A study is presented of the effect of plasma density irregularities in the auroral and equatorial electrojets on the DC currents giving rise to these irregularities. It is shown that the theory predicts extra dissipation and deviation in the direction of the mean current flow from that of E 0 × B 0 /B 2, in general agreement with observations. The average power input to the turbulent plasma, equal to the product of the externally applied electric field and the mean current, can be equated to the power input with that resulting in a plasma devoid of irregularities but with an increased collision frequency. Similarly one can compute the deviation in direction of the current flow due to the irregularities and compare this with the deviation caused in a plasma without irregularities, but with an increased collision frequency, and from this comparison assign an anomalous dissipation in the plasma caused by the irregularities. Our study applies elementary principles and deals with the mean current driven by an external field, including effects of the mean values of second order terms in the perturbed quantities. We do not discuss the elementary processes giving rise to the irregularities in the plasma; only their effect on the mean current flow. The anomalous dissipation or the increased apparent collision frequency, is related directly to the angular power spectrum of plasma density fluctuations. It is shown that the power dissipated by the DC current in these anomalous collisions is exactly the same as the power dissipated through normal collisions by the wave modes making up the power spectrum leading to the anomalous DC current dissipation. The study also suggests that the saturation of the instabilities, giving rise to the electrojet turbulence, is likely to be caused by the control of the current by the anomalous resistivity rather than by local nonlinear effects.