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Abstract
Abstract. Particle precipitation plays a key role in the coupling of the terrestrial magnetosphere and ionosphere by modifying the upper atmospheric conductivity and chemistry, driving field-aligned currents, and producing aurora. Yet quantitative observations of precipitating fluxes are limited, since ground-based instruments can only provide indirect measurements of precipitation, while particle telescopes aboard spacecraft merely enable point-like in situ observations with an inherently coarse time resolution above a given location. Further, orbit timescales generally prevent the analysis of whole events. On the other hand, global magnetospheric simulations can provide estimations of particle precipitation with a global view and higher time resolution. We present the first results of auroral (∼1–30 keV) proton precipitation estimation using the Vlasiator global hybrid-Vlasov model in a noon–midnight meridional plane simulation driven by steady solar wind with a southward interplanetary magnetic field. We first calculate the bounce loss-cone angle value at selected locations in the simulated nightside magnetosphere. Then, using the velocity distribution function representation of the proton population at those selected points, we study the population inside the loss cone. This enables the estimation of differential precipitating number fluxes as would be measured by a particle detector aboard a low-Earth-orbiting (LEO) spacecraft. The obtained differential flux values are in agreement with a well-established empirical model in the midnight sector, as are the integral energy flux and mean precipitating energy. We discuss the time evolution of the precipitation parameters derived in this manner in the global context of nightside magnetospheric activity in this simulation, and we find in particular that precipitation bursts of <1 min duration can be self-consistently and unambiguously associated with dipolarising flux bundles generated by tail reconnection. We also find that the transition region seems to partly regulate the transmission of precipitating protons to the inner magnetosphere, suggesting that it has an active role in regulating ionospheric precipitation.
Highlights
The terrestrial atmosphere and ionosphere are known to be affected by the precipitation of particles coming from the magnetosphere and the solar wind
We present an overview of nightside proton precipitation in a global magnetospheric hybrid-Vlasov simulation under southward interplanetary magnetic field (IMF) conditions, using the Vlasiator model
It can be seen that, at virtual spacecraft S1, broad-energy proton precipitation above 1 keV starts at around t = 1360 s, as the magnetic field line observed by S1 becomes slightly stretched
Summary
The terrestrial atmosphere and ionosphere are known to be affected by the precipitation of particles coming from the magnetosphere and the solar wind. Lin and Hoffman, 1982), the acceleration (or deceleration) of auroral-energy precipitating protons by parallel electric fields resulting from a field-aligned potential drop is negligible (Liang et al, 2013). Contrary to precipitating electrons which may be significantly affected by parallel electric fields in the auroral acceleration region This enables a mapping of the proton aurora in the ionosphere to the magnetospheric region from which the particles originate. This enables a mapping of the proton aurora in the ionosphere to the magnetospheric region from which the particles originate. Frey et al (2003) used this property to produce evidence of continuous magnetic reconnection at the magnetopause, as a proton
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