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  1. Abstract

    South Pole Station, Antarctica (SPA, magnetic latitude = −74.5°, magnetic local time (MLT) = UT–3.5 h), is a unique observatory which can capture daytime auroral forms throughout austral winter season. We have studied the properties and origin of ultralow‐frequency (ULF) range modulation of daytime diffuse aurora, using data acquired on June 23, 2017 by multi‐instrument measurements at SPA and in situ measurements in the dayside outer magnetosphere. At 1500–1600 UT, monochromatic Pc5‐range pulsations (period ∼10 min) emerged in the midday diffuse auroral region. The sequential 2‐D images reveal that the auroral pulsations result from the repetitive formation of faint, diffuse auroral patches, propagating poleward at a speed of ∼1.5 km s−1. Interestingly, no obviously similar magnetic pulsations were found at SPA. The results differ fundamentally from the ground optical and magnetic signatures expected for a standing field line resonance. On the other hand, the co‐located riometer and VLF receiver observed clearly synchronized pulsations, suggesting that tens‐of‐keV electrons interact with modulated chorus waves and then are scattered down to the auroral pulsation region. During the same interval, the THEMIS‐D spacecraft detected corresponding Pc5 oscillations in the dayside outer magnetosphere (9–10REand ∼15 MLT). The compressional component of the magnetospheric Pc5 waves, presumably driven by an external source, exhibited a good correspondence to the daytime Pc5 auroral pulsations. The simultaneous SPA–THEMIS observations highlight the role of compressional Pc5 pulsations in the dayside outer magnetosphere in determining the periodicity of daytime high‐latitude diffuse auroral pulsations.

     
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  2. Abstract

    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.

     
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