Relationship between substorm activity and magnetic disturbances in two polar caps

Abstract

We examined the effect of magnetic disturbances in two polar caps on the generation of magnetospheric substorms. For this purpose we investigated the correlation between the AL index (showing substorm activity in the Northern hemisphere) and two geomagnetic activity indices, the Polar Cap (PC) index and Polar Magnetic (PM) index showing the magnetic disturbances in the Northern and Southern polar caps. For the analysis we used the data for four years when geomagnetic activity indices were available in both hemispheres. We obtained an unexpected yet important result: while in northern winter the correlation between AL index and northern PC/PM indices is very good, in northern summer the AL index correlates much better with southern PC/PM indices. Thus, substorm activity in summer months correlates much better with geomagnetic activity not in the nearby polar cap but in the opposite polar cap. This effect may be caused by the interhemispheric field‐aligned currents flowing from the summer high‐latitude ionosphere and closing through the ionosphere in the opposite auroral zone. An interesting feature of these interhemispheric currents is that they are directed opposite to the substorm field‐aligned currents in the summer hemisphere but along the substorm field‐aligned currents in the winter hemisphere. This leads to decreasing the total field‐aligned currents and their contribution to magnetic disturbances in the summer hemisphere but increasing these currents and related magnetic disturbances in winter hemisphere, which explains the experimental results obtained in our study.

New Results on Ionospheric Irregularity Drift Velocity Estimation Using Multi‐GNSS Spaced‐Receiver Array During High‐Latitude Phase Scintillation

“…In the middle subplot, the SYM ‐ H index was on a decreasing trend from the SSC, until reaching maximum intensity at ~2300 UT on 20 December 2015. The SYM ‐ H upturns in this period indicated substorms (Lyatskaya et al, ). The interplanetary magnetic field B Z component turned northward at the SSC, followed by some oscillations, until it suddenly turned to the opposite direction at ~0300 UT on 20 December 2015.…”

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

“…Similar equatorward displacement of the convection reversal relatively to the polar cap boundary was earlier reported by Sotirelis et al . []. Despite the low ionospheric conductivity in the area between the R1 FACs and the region of enhanced ionospheric conductivity, the magnitude of the ionospheric and equivalent currents in the nightside auroral electrojet (measured with the auroral electrojet AL index) is approximately the same in two hemispheres [e.g., Lyatskaya et al ., , ], which also is a result of the IHCs, branching from the sunlit summer hemisphere and closing the Westward Auroral Electrojet in winter hemisphere. In this case, the IHCs are a substitute for the R1 currents in the winter hemisphere.…”

“…These IHCs were discussed by Rishbeth [], Lyatskaya et al . [, ], Yamashita and Iyemori [], Østgaard et al . [], and other authors, and were computed numerically by Benkevich et al .…”

Effect of Interhemispheric Field-Aligned Currents on Region-1 Currents

“…More recent studies [ Benkevich et al, ; Benkevich and Lyatsky , ; Ohtani et al, ; Ohtani et al, ; Østgaard et al , ; Lyatskaya et al, , ; etc.] showed that an important role in the global 3‐D current system can be played by the interhemispheric currents (IHCs).…”

“…showed that an important role in the global 3‐D current system can be played by the interhemispheric currents (IHCs). The IHCs redistribute ionospheric currents between two polar ionospheres in the regions of closed magnetic field lines in case of asymmetry of ionospheric conductivity between two polar ionospheres, which may happen during unequal illumination of polar ionospheres and other effects [e.g., Richmond and Roble , ; Kozlovsky et al, ; Atkinson and Hatchinson , ; Rishbeth , ; Benkevich et al , ; Benkevich and Lyatsky , ; Yamashita and Iyemori , ; Lyatskaya et al, , ; Ohtani et al , , ; Østgaard et al , , and references therein]. However, since it is difficult to separate the IHCs from other FACs (especially when they flow in the same region), despite the important role of the IHCs in dynamics of the global 3‐D current system, they have not been sufficiently investigated.…”