Auroras in the cusp and its poleward vicinity: a case study

V V Safargaleev,T I Sergienko

doi:10.30758/0555-2648-2018-64-2-141-156

Abstract

Summary We present a case study of the dayside aurora observed simultaneously with optical instruments from the ground and with auroral particle spectrometers aboard the DMSP F16 and F17 satellites. Optical observations were carried out with an all-sky camera at the Polar Geophysical Institute (PGI) observatory Barentsburg on Svalbard. The aurora as a whole moved equatorward in response to negative turning of the IMF Bz component and then the distinct faint rayed arc intensified, moved to the north and faded. Satellite DMSP F17 crossed the cusp twenty minutes after Bz turned southward. Joint analysis of optical and satellite data showed that faint auroral structures are embedded into the cusp precipitations and correspond to the bursts of electron precipitations with energy below 100 eV. The next satellite crossed the camera field-of-view ten minutes later and the data showed that the source of the faded poleward moving rayed arc was located, most probably, on the non-closed magnetic field lines. This finding and the presence of ion-energy dispersion in the DMSP data allows us to make the conclusion that the dayside reconnection may be considered as the reason for this kind of aurora activity. In this study we also estimated the altitude and horizontal scale of auroral rays in the cusp.

Highlights

Investigation of geophysical processes in the cusp and adjacent magnetospheric domains — the mantle (MANT) and the low latitude boundary layer (LLBL) — is important for understanding the physical mechanisms responsible for solar-terrestrial interaction
Indirect comparison of the location of auroras with regions of dayside precipitation was done in [10]. Using statistical distribution both of auroras and particle precipitation regions, the author showed that discrete dayside auroral forms are embedded into the boundary plasma sheet whereas diffuse luminosity is associated with rather hard precipitations from the central plasma sheet (CPS)
Sharp changing of the IMF Bz component from positive to negative values caused the partial reconstruction of the dayside magnetosphere so that the aurora activity of a poleward moving auroral form (PMAF)-like type was shifted southward and the cusp moved to the zenith of the all-sky camera at the Barentsburg observatory, i.e. southward of its statistical position ([2])

Summary

INTRODUCTION

Investigation of geophysical processes in the cusp and adjacent magnetospheric domains — the mantle (MANT) and the low latitude boundary layer (LLBL) — is important for understanding the physical mechanisms responsible for solar-terrestrial interaction. Using statistical distribution both of auroras and particle precipitation regions, the author showed that discrete dayside auroral forms are embedded into the boundary plasma sheet whereas diffuse luminosity is associated with rather hard precipitations from the central plasma sheet (CPS) Note that for their analysis they used the approximating formulas ([11]) instead of the direct simultaneous measurements. An analysis of the literature shows that direct simultaneous optical/satellite measurements aimed at locating of the near-noon auroras relative to magnetospheric domains (cusp, LLBL, MANT) are very rare, and the nature of near-cusp auroras, as well as the drivers of aurora dynamics, are still uncertain issues of solar wind/magnetopause interaction.

INSTRUMENTATION AND METHODOLOGICAL ISSUES

DISCUSSION

CONCLUSION