MSSL Space Plasma Science Highlights

Seasonal and Temporal Variations of Field‐Aligned Currents and Ground Magnetic Deflections During Substorms

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Figure 3 from Forsyth et al. [2018]. Superposed epoch analysis results with respect to substorm onset of the substorm FACs (SU‐MLT and SD‐MLT) from AMPERE, calculated by removing the median current in the hour before onset. The top and bottom rows show the upward substorm FAC (SU) and downward substorm FAC (SD), respectively, in each MLT sector. As per the above, the results are subdivided into seasons of 90 days centered on the solstices and equinoxes.

Earth is surrounded by electrical currents flowing in space. These currents, which can be 10,000 times greater than domestic electrical supplies, can flow along the Earth's magnetic field and into the upper atmosphere and are linked to aurora. The size of this current depends on atmospheric conditions, with the upper atmosphere being a better conductor when it is sunlit, and the interaction between particles flowing from the Sun and the Earth's magnetic field. During space weather events known as substorms, which happen several times per day on average, the aurora brightens massively and the currents flowing into the upper atmosphere increase. Using data from the Iridium communications satellites, measured these currents during substorms.

The Role of Proton Cyclotron Resonance as a Dissipation Mechanism in Solar Wind Turbulence

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The solar wind contains turbulent fluctuations that are part of a continual cascade of energy from large scales down to smaller scales. At ion-kinetic scales, some of this energy is dissipated, resulting in a steepening in the spectrum of magnetic field fluctuations and heating of the ion velocity distributions, however, the specific mechanisms are still poorly understood. Understanding these mechanisms in the collisionless solar wind plasma is a major outstanding problem in the field of heliophysics research.

NHDS: Calculating the properties of plasma waves

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NHDS: The New Hampshire Dispersion relation Solver

Waves are a very important mechanism to transfer energy in a plasma and to heat the particles efficiently. These processes occur in astrophysical, space, and laboratory plasmas. Like all electric charges, the plasma particles react on electric and magnetic fields, while they also change the electric and magnetic fields themselves. This makes plasmas a lot more complicated than normal (neutral) gases. As a consequence of this behaviour, there are many different types of waves that can exist in a plasma, while a gas like the air we are breathing only carries one type of wave (the sound wave). 

Understanding Waves and Instabilities in Collisionless Plasmas with ALPS

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ALPS Logo.

The solar wind is a plasma in which collisions are very rare. Many plasmas in the universe are in this so-called "collisionless" state. This applies, for example, to a common type of accretion disks around black holes in the centres of galaxies, the very dilute medium between galaxies, magnetospheres around planets and comets, as well as pulsar winds in supernova remnants. In all collisionless plasmas, the behaviour of plasma waves, which are the fundamental building blocks of many important plasma processes, is more complicated to understand than in a collision-dominated plasma. Therefore, we have to rely on computer models to calculate the properties of plasma waves. With their help, it is also possible to calculate whether the plasma is in a stable or unstable state, a question of great importance for understanding the plasma behaviour.

The role of localised compressional Ultra-Low Frequency waves in energetic electron precipitation

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Global-scale electromagnetic wave activity known as Ultra-Low Frequency (ULF) waves have been historically discussed as playing an indirect role in the acceleration and loss of radiation belt electrons. This is primarily due to the fact that ULF waves cannot easily interact with the gyration of electrons causing acceleration, or their bounce motion causing them to be lost. However, certain assumptions on the global-scale nature of these ULF wave fields are made to arrive at this conclusion. In this paper, we explore the validity of the assumptions that go into our current thinking, and provide a thought experiment on how a localised, large-amplitude electromagnetic wave field could interact with relativistic particles and play a direct role in radiation belt losses as a result. We conclude that localized ULF wave fields may provide an additional and, importantly, complementary means to more established processes that are known to precipitate electrons from the radiation belts during geomagnetic storms.

Variations of high-latitude geomagnetic pulsation frequencies: A comparison of time-of-flight estimates and IMAGE magnetometer observations

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The terrestrial magnetosphere is subjected to an abundance of perturbations, both externally from the solar wind and internal plasma dynamics, which result in oscillations of the magnetic field lines at their given natural frequencies. These resonant oscillations of the field lines are a fundamental mechanism for the transfer of energy and momentum within the magnetosphere. Therefore, it is valuable to understand how these oscillation frequencies vary spatially throughout the magnetosphere.

How 'Coronal' Are Solar Wind Electrons?

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We aim to understand the link between the Sun's atmosphere, the corona, and the constant stream of plasma which escapes it, the solar wind. To do so we test how similar energetic electron populations (the isotropic 'halo' and the beamed 'strahl') in the solar wind are to their expected earlier state in the corona. Models for the formation of these electron populations in the corona suggest that their energy content should depend on the local temperature, for which we can use solar wind oxygen ionisation state measurements as a proxy. Comparing electron halo temperature and strahl energy content to these ionisation states, we find only a very weak link which varies with the type of solar wind stream and the 11-year solar cycle. We find minor evidence to suggest that this is due to solar wind processing during its outward flow.

The structure of PSBL during an storm-time intense reconnection

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The transition region lying between the plasma sheet and the lobe, is called the plasma sheet boundary layer (PSBL).  This layer is formed by magnetic reconnection operating farther down the magnetotail, which drives the accelerated electron and ion beams along the magnetic field towards the Earth. The information that electrons and ions carry in PSBL, is essential to understanding the temporal and spatial variation at the reconnection site. We aim to utilise these information including energy dispersion and pitch angle of particles in the highest cadence possible to analyse the dynamics of the reconnection site.

A magnetospheric plasma mass density model for varying geomagnetic activity

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A figure showing the spatial distribution of electron density, average ion mass, and mass density for quiet (bottom) and active (top) conditions.

The terrestrial magnetosphere, a region around the Earth where the motion of positively and negative charged particles (plasma) is largely controlled by the geomagnetic field, is a highly variable and structured environment. The variations in the density and composition of the plasma is an important factor in shaping how the global magnetic field responds to perturbations and how energy propagates throughout the system. A key phenomenon associated with the variability is the geomagnetic storm. In this study, observations of the plasma are used to construct a model describing how the number density, composition, and mass density of the magnetospheric plasma changes in response to storm conditions.

Electromagnetic waves and their respective roles in driving substorm onset

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Substorm onset is marked in the ionosphere by the rapid and poleward expansion of the aurora around local midnight and corresponds to a huge amount of energy release in the stretched tail of Earth’s magnetic environment. With the auroral display, a repeatable signature of substorm onset is the launching of electromagnetic waves across all frequencies, that at lower frequencies are invoked to carry the required electrical currents, and at higher frequencies are implicated in auroral particle acceleration.

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