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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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Correspondence between the latitudinal ULF wave power distribution and auroral oval in conjugate ionospheres
We examine the Pc5 wave power latitudinal distribution in the morning sector along the conjugate magnetometer arrays in Greenland and Antarctica. These distributions are compared with the location of the auroral oval, reconstructed using the OVATION-prime model. This model makes it possible to reconstruct separately the spatial structures of diffuse and monoenergetic precipitation of auroral electrons. Mapping of the spectral power of narrowband Pc5 waves onto the auroral oval has shown that the wave power in the morning sector is localized inside the auroral oval, namely at the poleward edge of diffuse precipitation, but near the peak of monoenergetic precipitation. The case analysis results have been confirmed by a larger statistical study. This observational result confirms the effects earlier found in case studies: the spatial/temporal variations of Pc5 wave power are closely related to the location of the auroral electrojet and magnetospheric field-aligned currents. From the observed relationship between the wave power and the auroral boundaries, it may be concluded that the poleward edge of the diffuse precipitation, around the maximum of the monoenergetic precipitation, is preferred latitude of magnetospheric field-line resonance excitation. This effect is not taken into account by modern theories of ULF Pc5 waves.
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- Award ID(s):
- 1651263
- PAR ID:
- 10057802
- Date Published:
- Journal Name:
- Sun and geosphere
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 1819-0839
- Page Range / eLocation ID:
- 41-47
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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