Electromagnetic Fields of Magnetospheric ULF Disturbances in the Ionosphere: Current/Voltage Dichotomy

Abstract

A circuit analogy for magnetosphere‐ionosphere current systems has two extremes for drivers of ionospheric currents: the “voltage generator” (ionospheric electric fields/voltages are constant, while current varies) and the “current generator” (current is constant, while the electric field varies). Here we indicate another aspect of the magnetosphere‐ionosphere interaction, which should be taken into account when considering the current/voltage dichotomy. We show that nonsteady field‐aligned currents interact with the ionosphere in a different way depending on a forced driving or resonant excitation. A quasi‐DC driving of field‐aligned current corresponds to a voltage generator, when the ground magnetic response is proportional to the ionospheric Hall conductance. The excitation of resonant field line oscillations corresponds to the current generator, when the ground magnetic response only weakly depends on the ionospheric conductance. According to the suggested conception, quasi‐DC nonresonant disturbances correspond to a voltage generator. Such ultralow frequency (ULF) phenomena as traveling convection vortices and Pc5 waves should be considered as the resonant response of magnetospheric field lines, and they correspond to a current generator. However, there are quite a few factors that may obscure the determination of the current/voltage dichotomy.

Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation Events Relevant to GICs

“…Quantitative relationships between conjugate Δ B amplitudes and height‐integrated ionospheric conductances for these two generators were examined by Pilipenko et al (2019) using a simple “plasma box” model of the magnetosphere with asymmetric conjugate ionospheres driven by an external current located at the magnetospheric equatorial plane. The ranges of validity of current and voltage generators are determined by the ratio between an internal generator resistance and a load resistance.…”

Incidence of Alfvenic SC Pulse Onto the Conjugate Ionospheres

“…The conclusions made here are valid for a short pulse when a conjugate ionosphere does not influence the pulse interaction with the ionosphere of interest. The presented study completes together with Pilipenko et al (2019) the consideration of ULF wave and transient interactions with the ionosphere and its dependence on the ionospheric conductance from the view of the current-voltage dichotomy. At low latitudes, the SC can be considered as driven by a quasi-DC source, and its properties must correspond to the voltage generator regime.…”

“…Judging from the seasonal and interhemispheric variations of SCs at low‐latitudes, it may be concluded that the SC in this region is caused by a voltage generator rather than a current generator. Thus, the observed strong dependence on conductance corresponds to the regime of a voltage generator, natural for a nonresonant quasi‐DC disturbance (Pilipenko et al, ).…”

“…Oscillatory FACs interact with the ionosphere in a different way depending on the relationship between the driver periodicity and the Alfven field line eigenperiod . Two possible situations were examined in Pilipenko et al (): a forced quasi‐direct current (quasi‐DC) driving of FAC ( ), and resonant excitation of field line oscillations ( ). They considered a simple “plasma box” model of the magnetosphere with asymmetric conjugate ionospheres driven by an external current located at the magnetospheric equatorial plane and compared the ground magnetic response in both hemispheres.…”

Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation Events Relevant to GICs

“…Quantitative relationships between conjugate ΔB amplitudes and height-integrated ionospheric conductances for these two generators were examined by Pilipenko et al (2019) using a simple "plasma box" model of the magnetosphere with asymmetric conjugate ionospheres driven by an external current located at the magnetospheric equatorial plane.…”