Height‐dependent ionospheric variations in the vicinity of nightside poleward expanding aurora after substorm onset

High‐latitude ionospheric variations at times near auroral substorms exhibit large temporal variations in both vertical and horizontal extents. Statistical analysis was made of data from the European Incoherent Scatter UHF radar at Tromsø, Norway, and International Monitor for Auroral Geomagnetic Effects magnetometer for finding common features in electron density, ion and electron temperatures and relating these to currents and associated heating. This paper particularly focused on the height dependencies. Results show clear evidences of large electric field with corresponding frictional heating and Pedersen currents located just outside the front of the poleward expanding aurora, which typically appeared at the eastside of westward traveling surge. At the beginning of the substorm recovery phase, the ionospheric density had a large peak in the E region and a smaller peak in the F region. This structure was named as C form in this paper based on its shape in the altitude‐time plot. The lower altitude density maximum is associated with hard auroral electron precipitation probably during pulsating aurora. We attribute the upper F region density maximum to local ionization by lower energy particle precipitation and/or long‐lived plasma that is convected horizontally into the overhead measurement volume from the dayside hemisphere.

[1]  M. Hirahara,et al.  The source region and its characteristic of pulsating aurora based on the Reimei observations , 2011 .

[2]  J. Moen,et al.  On the entry and transit of high-density plasma across the polar cap , 2010 .

[3]  B. Ni,et al.  Scattering by chorus waves as the dominant cause of diffuse auroral precipitation , 2010, Nature.

[4]  M. Hirahara,et al.  Time of flight analysis of pulsating aurora electrons, considering wave-particle interactions with propagating whistler mode waves , 2010 .

[5]  Keisuke Hosokawa,et al.  Modulation of ionospheric conductance and electric field associated with pulsating aurora , 2010 .

[6]  S. Oyama,et al.  Relations between proton auroras, intense electric field, and ionospheric electron density depletion , 2009 .

[7]  R. Horne,et al.  Survey of upper band chorus and ECH waves: Implications for the diffuse aurora , 2009 .

[8]  S. Oyama,et al.  Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance , 2008 .

[9]  B. Ni,et al.  Resonant scattering of plasma sheet electrons by whistler‐mode chorus: Contribution to diffuse auroral precipitation , 2008 .

[10]  Mitsuteru Sato,et al.  Generation region of pulsating aurora obtained simultaneously by the FAST satellite and a Syowa‐Iceland conjugate pair of observatories , 2004 .

[11]  Harald U. Frey,et al.  Substorm onset observations by IMAGE-FUV , 2004 .

[12]  R. Horne,et al.  Diffuse auroral electron scattering by electron cyclotron harmonic and whistler mode waves during an isolated substorm , 2003 .

[13]  C. Lathuillère,et al.  Winds in the high‐latitude lower thermosphere: Dependence on the interplanetary magnetic field , 2003 .

[14]  C. Owen,et al.  Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere , 2001, Nature.

[15]  J. Olson,et al.  Assimilated observations of thermospheric winds, the aurora, and ionospheric currents over Alaska , 2001 .

[16]  V. Trakhtengerts.  A generation mechanism for chorus emission , 1999 .

[17]  J. Davies,et al.  Heating of the high-latitude ionospheric plasma by electric fields , 1997 .

[18]  Asko Huuskonen,et al.  General incoherent scatter analysis and GUISDAP , 1996 .

[19]  Mariko Sato,et al.  Comparison between Electron Spectra Calculated from EISCAT Electron Density Profiles and Those Observed by the DMSP Satellites. , 1995 .

[20]  D. Klumpar,et al.  Observations in the vicinity of substorm onset: Implications for the substorm process , 1995 .

[21]  R. Greenwald,et al.  A new mechanism for polar patch formation , 1994 .

[22]  A. Demekhov,et al.  A mechanism of formation of pulsating aurorae , 1994 .

[23]  S. Quegan,et al.  The role of ion drift in the formation of ionisation troughs in the mid- and high-latitude ionosphere—a review , 1992 .

[24]  A. Brekke,et al.  Auroral ionospheric conductances during disturbed conditions , 1989 .

[25]  K. Kaila,et al.  Coordinated photometer and incoherent scatter radar measurement of pulsating arcs with high time resolution , 1989 .

[26]  R. Livingston,et al.  Polar cap F layer patches: Structure and dynamics , 1986 .

[27]  M. Lockwood,et al.  EISCAT observations of plasma convection and the high-latitude, winter F-region during substorm activity , 1984 .

[28]  J. Samson,et al.  Polarization characteristics of Pi 2 pulsations and implications for their source mechanisms: Influence of the westward travelling surge , 1983 .

[29]  J. St.‐Maurice,et al.  Anomalous heating of the polar E region by unstable plasma waves 1. Observations , 1981 .

[30]  R. Lundin,et al.  Rocket observations of precipitating electrons over a pulsating aurora , 1980 .

[31]  R. McPherron,et al.  The ground signatures of the expansion phase during multiple onset substorms , 1976 .

[32]  A. Brekke,et al.  Incoherent scatter measurements of E region conductivities and currents in the auroral zone , 1974 .

[33]  C. Meng,et al.  Dynamics of the aurora—V: Poleward motions , 1966 .

[34]  C. Meng,et al.  Dynamics of the aurora—IV: Polar magnetic substorms and westward traveling surges , 1966 .

[35]  M. Rees,et al.  Auroral ionization and excitation by incident energetic electrons , 1963 .

[36]  Seongryong Kim,et al.  American Geophysical Union. All Rights Reserved. Evidence of Volatile-Induced Melting , 2022 .