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

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

doi:10.1051/swsc/2020053

Abstract

Particle precipitation is a central aspect of space weather, as it strongly couples the magnetosphere and the ionosphere and can be responsible for radio signal disruption at high latitudes. 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 is also found more polewards in the northward IMF simulation than in the southward IMF simulation. In addition, we find that the bursty precipitation during southward IMF driving is 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 spot associated with the lobe reconnection from the same hemisphere, we observe lower-latitude precipitating protons which originate from the opposite hemisphere’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 previously reported observations with the Cluster spacecraft. In both runs, clear electromagnetic ion cyclotron waves are generated in the cusps and might further increase the calculated precipitating fluxes by scattering protons to the loss cone in the low-altitude cusp. Global kinetic simulations can improve the understanding of space weather by providing a detailed physical description of the entire near-Earth space and its internal couplings.

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 (e.g., de Villiers et al, 2017)
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
Considering first the southward IMF simulation, we calculate the differential number fluxes of protons precipitating into the northern and southern cusps by analysing the velocity distribution function (VDF) at the two locations indicated with black circles in Figure 1 between t = 1350 s and the end of the simulation at t = 2150 s

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).

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Discussion

Conclusion