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We studied the spatiotemporal structure of ground magnetic pulsations on the dayside by displaying magnetic field perturbations detected by the European quasi‐Meridional Magnetometer Array (EMMA) as 2‐D images in the magneticLvalue versus time space, called EMMAgrams. We generated EMMAgrams from observations made on 15 August 2015, including a previously studied pulsation event associated with an interplanetary shock. In addition to signatures of field line resonance driven by a cavity mode oscillation, we found poleward propagating structures withL‐independent periods in the Pc2 band. The Pc2 structures are attributed to periodic magnetohydrodynamic pulses (upstream waves) originating from the ion foreshock and propagating in the magnetosphere along the path proposed by Tamao. Ringing of local field lines atL‐dependent periods (transient pulsations) is also clearly detected as dispersive poleward propagating structures not only immediately after the shock impact but also during time periods of less obvious external disturbances. A transient pulsation decays after a few wave periods, and cross‐spectral analysis of transient pulsations detected at two stations with a small latitudinal separation indicates elevation of the cross phase in a band delimited by the field line resonance frequencies at the stations. Successive excitation of transient pulsations by variations of the solar wind dynamic pressure appears to contribute significantly to formation of similar cross‐phase peaks that are widely used in magnetoseismic studies.

 

Pc3 range frequency (22–100 mHz) auroral pulsations often occur at daytime high latitudes, equatorward of the cusp/cleft and typically map to the dayside outer magnetosphere. In this paper we present simultaneous observations of compressional Pc3 magnetic pulsations in the dayside outer magnetosphere that occurred in direct association with daytime Pc3 auroral pulsations at South Pole Station (−74.4° magnetic latitude). The pulsations were almost identical at the two locations, and their correlation was clearest when the magnetospheric pulsations were highly monochromatic. Lower‐band chorus waves and keV electron fluxes were also modulated in the Pc3 range, likely by the compressional magnetic pulsations. The common Pc3 frequency in the magnetosphere and aurora matched well with the predicted frequency of upstream ultralow frequency waves. These results provide the first compelling evidence for the direct dayside outer magnetosphere‐ionosphere linkage between upstream‐generated compressional Pc3 waves, Pc3 range modulations of chorus waves and keV electrons, and Pc3 auroral pulsations.

 

Abstract The Earth’s magnetosphere and its bow shock, which is formed by the interaction of the supersonic solar wind with the terrestrial magnetic field, constitute a rich natural laboratory enabling in situ investigations of universal plasma processes. Under suitable interplanetary magnetic field conditions, a foreshock with intense wave activity forms upstream of the bow shock. So-called 30 s waves, named after their typical period at Earth, are the dominant wave mode in the foreshock and play an important role in modulating the shape of the shock front and affect particle reflection at the shock. These waves are also observed inside the magnetosphere and down to the Earth’s surface, but how they are transmitted through the bow shock remains unknown. By combining state-of-the-art global numerical simulations and spacecraft observations, we demonstrate that the interaction of foreshock waves with the shock generates earthward-propagating, fast-mode waves, which reach the magnetosphere. These findings give crucial insight into the interaction of waves with collisionless shocks in general and their impact on the downstream medium.