Transpolar Arcs During a Prolonged Radial Interplanetary Magnetic Field Interval

Jong Sun Park, Quan Qi Shi, Motoharu Nowada, Jih Hong Shue, Khan Hyuk Kim, Dong Hun Lee, Qiu Gang Zong, Alexander W. Degeling, An Min Tian, Timo Pitkänen, Yongliang Zhang, I. Jonathan Rae, Marc R. Hairston

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4 Scopus citations


Transpolar arcs (TPAs) are believed to predominantly occur under northward interplanetary magnetic field (IMF) conditions with their hemispheric asymmetry controlled by the Sun-Earth (radial) component of the IMF. In this study, we present observations of TPAs that appear in both the northern and southern hemispheres even during a prolonged interval of radially oriented IMF. The Defense Meteorological Satellite Program (DMSP) F16 and the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellites observed TPAs on the dawnside polar cap in both hemispheres (one TPA structure in the southern hemisphere and two in the northern hemisphere) during an interval of nearly earthward-oriented IMF on October 29, 2005. The southern hemisphere TPA and one of the northern hemisphere TPAs are associated with electron and ion precipitation and mostly sunward plasma flow (with shears) relative to their surroundings. Meanwhile, the other TPA in the northern hemisphere is associated with an electron-only precipitation and antisunward flow relative to its surroundings. Our observations indicate the following: (a) the TPA formation is not limited to northward IMF conditions; (b) the TPAs can be located on both closed field lines rooted in the polar cap of both hemispheres and open field lines connected to the northward field lines draped over one hemisphere of the magnetopause. We believe that the TPAs presented here are the result of both indirect and direct processes of solar wind energy transfer to the high-latitude ionosphere.

Original languageEnglish
Article numbere2021JA029197
JournalJournal of Geophysical Research: Space Physics
Issue number6
StatePublished - Jun 2021


  • radial IMF
  • solar wind-magnetosphere-ionosphere coupling
  • transpolar arc


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