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Abstract We examined rapid variations in the electron zebra stripe patterns, specifically atL = 1.5, over a three‐month duration, using twin Van Allen Probes within Earth's inner magnetosphere. During geomagnetically quiet intervals, these stripes exhibit a peak‐to‐valley ratio (Δj) ∼1.25 in detrended electron fluxes. However, during geomagnetic storms, they became highly prominent, with Δj > 2.5. The correlation between Δjand net field‐aligned currents (FACs) is observed to be high (0.70). Global magnetohydrodynamic (MHD) simulation results indicate that the westward electric field at midnight at low latitudes in the deep inner magnetosphere correlates well with net FACs. An increase in net FACs could amplify the dawn‐to‐dusk electric field in the deep inner magnetosphere, thereby causing the inward transport of electrons. Given that FACs are linked to the interaction between solar wind and the magnetosphere, our findings emphasize the importance of solar wind‐magnetosphere coupling in the deeper regions of the inner magnetosphere. 

Abstract We review observations of solar activity, geomagnetic variation, and auroral visibility for the extreme geomagnetic storm on 1872 February 4. The extreme storm (referred to here as the Chapman–Silverman storm) apparently originated from a complex active region of moderate area (≈ 500μsh) that was favorably situated near disk center (S19° E05°). There is circumstantial evidence for an eruption from this region at 9–10 UT on 1872 February 3, based on the location, complexity, and evolution of the region, and on reports of prominence activations, which yields a plausible transit time of ≈29 hr to Earth. Magnetograms show that the storm began with a sudden commencement at ≈14:27 UT and allow a minimum Dst estimate of ≤ −834 nT. Overhead aurorae were credibly reported at Jacobabad (British India) and Shanghai (China), both at 19.°9 in magnetic latitude (MLAT) and 24.°2 in invariant latitude (ILAT). Auroral visibility was reported from 13 locations with MLAT below ∣20∣° for the 1872 storm (ranging from ∣10.°0∣–∣19.°9∣ MLAT) versus one each for the 1859 storm (∣17.°3∣ MLAT) and the 1921 storm (∣16.°2∣ MLAT). The auroral extension and conservative storm intensity indicate a magnetic storm of comparable strength to the extreme storms of 1859 September (25.°1 ± 0.°5 ILAT and −949 ± 31 nT) and 1921 May (27.°1 ILAT and −907 ± 132 nT), which places the 1872 storm among the three largest magnetic storms yet observed. 

Abstract Recent studies of Pc5‐band (150–600 s) ultralow frequency waves found that foreshock disturbances can be a driver of dayside compressional waves and field line resonance, which are two typical Pc5 wave modes in the dayside magnetosphere. However, it is difficult to find spatial structure of dayside Pc5 waves using a small number of satellites or ground magnetometers. This study determines 2‐D structure of dayside Pc5 waves and their driver by utilizing coordinated observations by the THEMIS satellites and the all‐sky imager at South Pole during two series of Pc5 waves on 29 June 2008. These Pc5 waves were found to be field line resonances (FLRs) and driven by foreshock disturbances. The ground‐based all‐sky imager at South Pole shows that periodic poleward moving arcs occurred simultaneously with the FLRs near the satellite footprints over ~3°latitude and had the same frequencies as FLRs. This indicates that they are the auroral signature of the FLRs. The azimuthal distribution of the FLRs in the magnetosphere and their north‐south width in the ionosphere were further determined in the 2‐D images. In the first case, the FLRs distribute symmetrically in the prenoon and postnoon regions with out‐of‐phase oscillation as the odd toroidal mode in the equatorial plane. In the second case, the azimuthal wavelengths of the 350–500 s and 300–450 s period waves were ~8.0 and ~5.2 Re in the equatorial plane. It also shows a fine azimuthal structure embedded in the large‐scale arcs, indicating that a high azimuthal wave number (m~ 140) mode wave coupled with the low‐wave number FLRs.