Hybrid-Vlasov simulation of auroral proton precipitation in the cusps: Comparison of northward and southward interplanetary magnetic field driving

Maxime Grandin,Minna Palmroth,Maxime Dubart,Lucile Turc,Urs Ganse,Markus Battarbee,Yann Pfau-Kempf,Andreas Johlander

doi:10.5194/egusphere-egu2020-3023

Abstract

&lt;p&gt;We present the first hybrid-Vlasov simulations of proton precipitation in the polar cusps. We use two runs from the Vlasiator model to compare cusp proton precipitation fluxes during southward and northward interplanetary magnetic field (IMF) driving. The simulations reproduce well-known features of cusp precipitation, such as a reverse dispersion of precipitating proton energies, with proton energies increasing with increasing geomagnetic latitude under northward IMF driving, and a nonreversed dispersion under southward IMF driving. The cusp location is also found more poleward in the northward IMF simulation than in the southward IMF simulation. In addition, we find that the precipitation takes place in the form of successive bursts during southward IMF driving, those bursts being associated with the transit of flux transfer events in the vicinity of the cusp. In the northward IMF simulation, dual lobe reconnection takes place. As a consequence, in addition to the high-latitude precipitation footprint associated with the lobe reconnection from the same hemisphere, we observe lower-latitude precipitating protons which originate from the opposite hemisphere&amp;#8217;s lobe reconnection site. The proton velocity distribution functions along the newly closed dayside magnetic field lines exhibit multiple proton beams travelling parallel and antiparallel to the magnetic field direction, which is consistent with observations with the Cluster spacecraft. We suggest that precipitating protons originating from the opposite hemisphere&amp;#8217;s lobe reconnection site, albeit infrequent, could be observed in a situation of dual lobe reconnection.&lt;/p&gt;

Highlights

The precipitation of particles from near-Earth space into the upper atmosphere is one of the sources of disruption of telecommunication and navigation signals (Smith et al, 2008; Jin et al, 2017), and carries field-aligned currents which find their closure in the ionosphere and may lead to Joule heating in the lower thermosphere (e.g., Sarris et al, 2020) and to the formation of geomagnetically induced currents in the ground, threatening power grids
This paper presents a comparison of auroral proton precipitation in the cusps during northward interplanetary magnetic field (IMF) and southward IMF driving in self-consistent kinetic simulations with the Vlasiator model
We find wave vectors that are within 30° from the mean magnetic field direction, consistent with the growth rate of EMIC waves maximising along the magnetic field vector (Gary & Schriver, 1987)

Summary

Introduction

The precipitation of particles from near-Earth space into the upper atmosphere is one of the sources of disruption of telecommunication and navigation signals (Smith et al, 2008; Jin et al, 2017), and carries field-aligned currents which find their closure in the ionosphere and may lead to Joule heating in the lower thermosphere (e.g., Sarris et al, 2020) and to the formation of geomagnetically induced currents in the ground, threatening power grids (e.g., de Villiers et al, 2017). Particle precipitation can durably affect the chemical composition of the upper atmosphere, leading for instance to ozone destruction and HOx and NOx species formation in the stratosphere and mesosphere (e.g., Andersson et al, 2014; Seppälä et al, 2015). As such, it is a major aspect of the space weather chain, linking in particular the magnetosphere (perturbed by solar driving) to the atmosphere and ionosphere. Particle precipitation predominantly takes place in the auroral ovals and affects the high latitudes, both on the dayside and on the nightside, for which observations and numerical simulations are needed to improve space weather forecasting (Robinson et al, 2019; Heelis & Maute, 2020).

Results

Discussion

Conclusion