Highlight articles

Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard

This study analyses the observations of a new type of small-scale aurora-like feature, which is further referred to as fragmented aurora-like emission(s) (FAEs). One possible explanation for this is Farley–Buneman instabilities of strong local currents. In the present study, we provide an overview of the observations and discuss their characteristics and potential generation mechanisms.

Lower-thermosphere response to solar activity: an empirical-mode-decomposition analysis of GOCE 2009–2012 data

Forecasting the thermosphere (atmosphere’s uppermost layer from 90 to 800 km altitude) is crucial to space mission design, spacecraft operations and space surveillance. The thermosphere is controlled by the Sun through variable solar extreme-ultraviolet radiation and the solar wind. We show how the solar indices Mg II and Ap may be used in forecasting thermospheric density at 260 km, a very low altitude, where the GOCE satellite operated from 2009 to 2013, during the full rise of solar cycle 24.

On the alignment of velocity and magnetic fields within magnetosheath jets

Jets of solar-wind plasma commonly hit the Earth’s magnetosphere. Using data from the four Magnetospheric Multiscale (MMS) spacecraft, we show statistically that within jets the magnetic field is more aligned with the plasma flow direction than outside of these jets. Our study confirms prior simulation results, but it also shows that the average effect is moderate. The jets’ magnetic field is important with respect to their impact on space weather.

Terrestrial ion escape and relevant circulation in space

Terrestrial ion transport and total escape are synthesized, with stress on the high-latitude polar region and the inner magnetosphere where Custer significantly improved knowledge. After estimating the outflow flux and destinations, complicated ion dynamics in the inner magnetosphere was classified and summarized, through which more than half the O+ is finally lost to space. Together with direct escapes, total O+ escape is high enough to influence the evolution of the biosphere.

Electron pairing in mirror modes: surpassing the quasi-linear limit

The mirror mode starts as a zero-frequency ion fluid instability and saturates quasi-linearly at very low magnetic level, while forming extended magnetic bubbles. These trap the adiabatically bouncing electron component which forms pairs near the mirror points. The large pair anisotropy causes further growth beyond quasilinear level. Including pressure equilibrium gives and estimate of the required pair density.

Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions

When the terrestrial magnetic field is disturbed, particles from the near-Earth space can precipitate into the upper atmosphere. This work presents, for the first time, numerical simulations of proton precipitation in the energy range associated with the production of aurora (∼1–30 keV) using a global kinetic model of the near-Earth space: Vlasiator. We find that nightside proton precipitation can be regulated by the transition region between stretched and dipolar geomagnetic field lines.

Converging photospheric vortex flows close to the polarity inversion line of a fully emerged active region

We describe a technique used to locate and classify critical points in 2-D flow fields at the solar photosphere obtained from the evolution of the line-of-sight magnetic field in a region close to the magnetic polarity inversion line of a fully emerged active region. We apply this technique to locate a particular kind of critical point associated to vortex flows, which are considered important, since they can twist and interweave the foot points of flux tubes and generate magnetic reconnection.

Solar wind and kinetic heliophysics

This paper originated from the lecture I gave as the Hannes Alfvén medalist at the EGU General Assembly in Vienna in spring 2018. The paper reviews various aspects of modern solar wind physics and elucidates the role Alfvén waves play in solar wind acceleration and turbulence, which prevail in the low corona and inner heliosphere. Our understanding of the solar wind has recently made considerable progress based on remote sensing, in situ measurements, kinetic simulation and fluid modeling.

Sporadic auroras near the geomagnetic equator: in the Philippines, on 27 October 1856

A record has been found of an “aurora” observed on 27 October 1856 in the Philippines, practically at the magnetic equator. An analysis of this report indicates that it could belong to a “sporadic aurora” because of low magnetic activity at that time. We provide a possible physical mechanism that could explain the appearance of this sporadic, low-latitude aurora, according to the analyses on the observational report and magnetic observations at that time.

The mirror mode: a “superconducting” space plasma analogue

The physics of the magnetic mirror mode in its final state of saturation, the thermodynamic equilibrium, is re-examined to demonstrate that the mirror mode is the classical analogue of a superconducting effect in an anisotropic-pressure space plasma. Three different spatial correlation scales are identified which control the behaviour of its evolution into large-amplitude chains of mirror bubbles.

PS Planetary and Solar System Sciences Highlight articles

Highlight articles

Characteristics of fragmented aurora-like emissions (FAEs) observed on Svalbard

Lower-thermosphere response to solar activity: an empirical-mode-decomposition analysis of GOCE 2009–2012 data

On the alignment of velocity and magnetic fields within magnetosheath jets

Terrestrial ion escape and relevant circulation in space

Electron pairing in mirror modes: surpassing the quasi-linear limit

Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions

Converging photospheric vortex flows close to the polarity inversion line of a fully emerged active region

Solar wind and kinetic heliophysics

Sporadic auroras near the geomagnetic equator: in the Philippines, on 27 October 1856

The mirror mode: a “superconducting” space plasma analogue

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