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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 degrees 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.

Plain Language Summary South Pole Station, Antarctica (SPA), is a unique polar observatory, which can monitor dayside aurora from the ground throughout austral winter. High time resolution optical instruments at SPA frequently capture auroral pulsations with Pc3 frequencies (22-100 mHz) around the midday hours. Here we use unique conjunctions of similar to 2-Hz SPA all-sky camera and Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft to identify the origin of the periodicity of daytime Pc3 auroral pulsations observed at SPA and their driver in the magnetosphere. Simultaneous in situ measurements in the dayside outer magnetosphere observed identical Pc3 magnetic pulsations in the compressional component. Lower-band chorus waves and keV electron fluxes were observed to be modulated also with the Pc3 range. The common Pc3 frequency in the magnetosphere and ionosphere matched well with the expected frequency of upstream ultralow frequency (ULF) waves generated in the foreshock region. The simultaneous SPA-THEMIS spacecraft conjunctions provide, for the first time, direct evidence that upstream-origin compressional Pc3 magnetic pulsations drive daytime auroral pulsations through wave-particle interactions. One important implication of this study is that the high temporal cadence 2-D observations of daytime auroral pulsations can be a useful tool for remote sensing the dynamics of outer magnetospheric Pc3 ULF waves.