Interhemispheric field‐aligned currents: Simulation results

Abstract

We present simulation results of the 3-D magnetosphere-ionosphere current system including the Region 1 and Region 2 field-aligned currents, ionospheric currents, and interhemispheric field-aligned currents flowing between the northern and southern conjugate ionospheres in the case of asymmetry in ionospheric conductivities in two hemispheres. The model shows that the interhemispheric currents can be an important part of the global 3-D current system in high-latitude ionosphere, especially during summer-winter months, when in winter ionosphere they can be comparable and even exceed both Region 1 and Region 2 currents. An important feature of these interhemispheric currents is that they link together processes in two hemispheres, so that the currents observed in one hemisphere can provide us with information about the currents in the opposite hemisphere. Although the interhemispheric currents might play a notable role in the total 3-D current system, they have not been sufficiently studied yet. The study of the contribution from the interhemispheric currents into the total 3-D current system allows us to improve understanding and forecasting of geomagnetic, auroral, and ionospheric disturbances in two hemispheres.

Effect of interhemispheric currents on equivalent ionospheric currents in two hemispheres: Simulation results

“…In previous papers [ Lyatskaya et al ., , ], we showed that during summer/winter conditions, in addition to R1 and R2 currents, also significant IHCs could appear. These IHCs emerge at the gradients of ionospheric conductivity in any hemisphere; it is going along the magnetic field lines between conjugate regions in two hemispheres.…”

“…Although inside the summer polar cap, the EICs are usually directed to noon; in winter polar cap they decrease in magnitude and turn toward dawn. The reversal in the direction of the EICs at the nightside, which is well seen in both ionospheres, is observed not just at the polar cap boundary (where the R1 currents are located) but equatorward of it in the region of IHCs location; this shows the important role played by the IHCs in nightside winter ionosphere, where the IHCs are, in fact, the main source of ionospheric currents [see also Lyatskaya et al, 2014aLyatskaya et al, , 2014b. A similar equatorward displacement of the convection reversal relatively to the polar cap boundary was earlier reported by Sotirelis et al [2005].…”

“…So in the case of asymmetry between ionospheric conductivities in two hemispheres (e.g., during summer/winter months), the initial electric field and currents may be redistributed between two ionospheres by interhemispheric currents (IHCs). These IHCs were discussed by Rishbeth [1997], Lyatskaya et al [2008Lyatskaya et al [ , 2009, Yamashita and Iyemori [2002], Østgaard et al [2005], and other authors, and were computed numerically by , , and Lyatskaya et al [2014aLyatskaya et al [ , 2014b. Figure 1 shows a sketch of the FACs, including the R1, R2, and interhemispheric currents (IHCs), in the meridional cross section of Earth's magnetosphere as seen from the magnetotail during northern summer.…”

“…As mentioned above, since the boundaries of the auroral zones during substorms experience fast and significant changes (they may expand and move equatorward or poleward [e.g., Akasofu , ]), it may be difficult to separate IHCs from other FACs using statistical data, and the IHCs may even disappear from a statistical picture of the FACs or be mistaken as a part of the R1 or R2 currents. Nevertheless, the total IHCs (integrated across the auroral zone) may be significant (up to 20% of R1 current in summer hemisphere [e.g., Benkevich et al ., ]) and even exceed the R1 currents in winter hemisphere [e.g., Lyatskaya et al ., ]. Statistically averaged maps of FACs presented in many papers [e.g., Papitashvili et al ., , and others] may significantly differ from both instantaneous maps of the FACs and the maps obtained from numerical simulations.…”

“…The main goal of this study is to compute the EICs in two ionospheres during the summer/winter conditions (when the IHCs are especially significant) with accounting the IHCs flowing between two conjugate ionospheres (i.e., located at the same field lines in ionospheres of two hemispheres) and compare the computed maps of the EICs with the available observation data. This study is an extension of our previous studies [ Lyatskaya et al ., , ]; it examines the effect of IHCs on EICs in two hemispheres, which was never investigated before.…”