TY - JOUR
T1 - Daytime Pc5 Diffuse Auroral Pulsations and Their Association With Outer Magnetospheric ULF Waves
AU - Motoba, T.
AU - Ogawa, Y.
AU - Ebihara, Y.
AU - Kadokura, A.
AU - Gerrard, A. J.
AU - Weatherwax, A. T.
N1 - Publisher Copyright:
© 2021. The Johns Hopkins University Applied Physics Laboratory.
PY - 2021/8
Y1 - 2021/8
N2 - 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 (9–10 RE and ∼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.
AB - 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 (9–10 RE and ∼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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U2 - 10.1029/2021JA029218
DO - 10.1029/2021JA029218
M3 - Article
AN - SCOPUS:85113812893
SN - 2169-9380
VL - 126
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
IS - 8
M1 - e2021JA029218
ER -