Hall-induced inductive shielding effect on geomagnetic pulsations

A new formula describing the inductive response of the magnetosphere-ionosphere-atmosphere-Earth electromagnetic coupled system to the time development of the field-aligned current (FAC) source-field is developed. Using this new formula, the Hall-induced inductive shielding effect (ISE) on geomagnetic pulsation is investigated. The ISE is caused by the reduction of the amplitude of total rotational current because of the generation of "inductive" rotational current by the inductive part of ionospheric divergent electric field, which originates the existence of divergent Hall current. It will be shown that the ISE is more efficient for high-frequency pulsations, large horizontal scale phenomena and high-conducting ionospheric conditions. Quantitative analysis strongly suggests that the ionospheric conductivity in the dayside hemisphere can easily reach and sometimes exceed the turning point of geomagnetic pulsations of which frequencies are in the Pc 3 ∼ 4 pulsations range.