Space Plasma Research at UCL/MSSL

We are active in a number of areas of Space Plasmas Research, driven by our current and future participation in international space science missions for which we have, or will provide instrument hardware.  These include interests in the solar wind, and the terrestrial and planetary magnetospheres.  

Illustration of the proposed model for the polar hole origin of the fast solar wind by Tu & Marsch (2005)

The solar wind is a continuous supersonic outflow of plasma from the Sun that fills the space between the planets. The solar wind is turbulent, and collisions between solar-wind particles are very rare. This leads to many effects that are counter-intuitive to our everyday experience with neutral gases like the air. Although we know that the solar wind is launched in the solar corona, the acceleration mechanisms, the heating of the solar wind, the role of non-equilibrium physics, as well as the effects of waves and turbulence are still areas of very active research. 

Members of the Space Plasma Physics group at MSSL work on answering these questions using spacecraft measurements of the particles and the electromagnetic fields in the solar wind as well as plasma theory and simulations. We want to understand the origin of the solar wind, its propagation through interplanetary space, and its interaction with celestial bodies. 

We are the principal investigator institute for the Solar Wind Analyser (SWA) instrument suite on board the upcoming Solar Orbiter mission. This mission will launch in 2020 and investigate the connection between the Sun and the solar wind in great detail. In addition to leading the SWA consortium, we built the Electron Analyser System (EAS) for SWA at MSSL. We also use data from past and present space missions such as Helios, Cluster, Wind, and MMS to study the solar wind.

We work in close collaboration with the UCL/MSSL Solar Physics group in order to better our understanding between phenomena on the Sun and their propagation into the solar system.

Artist's impression of plasma regions of the magnetosphere

Earth's magnetosphere describes the region around our planet controlled by the global magnetic field. This region, populated by plasma from both the lower atmosphere and the solar wind, is a highly complex and variable system. The magnetosphere responds strongly to external driving from the solar wind and internal dynamics. How dynamic processes, such as storms and substorms, are driven, and the response of the system to these processes are current open questions for the field. 

Through use of spacecraft and ground based observations, we are exploring the features of the magnetosphere and the key processes that occur. In particular, we study the source and loss processes of the radiation belt population during geomagnetic storms, the triggering of the substorm process and the substorm energy budget. 

The principal tool we use for magnetospheric research is data from the ESA 4-spacecraft Cluster mission and China/ESA 2-spacecraft Double Star mission. UCL/MSSL is the Principal Investigator Institute for the Electron Spectrometer instrument (PEACE) flown on all 6 of these spacecraft.  We also use data from the GOES, THEMIS and the Van Allen Probes, and from a range of ground based instruments (e.g. the CARISMA magnetometer array).

Artist impression of Jupiter and its moons. Image courtesy John Spencer

Often in close collaboration with members of the UCL/MSSL Planetary Group, members of the Space Plasmas Group regularly participate in studies of the plasma environments (magnetospheres, ionospheres, plasma wakes, etc.) of other solar system bodies.

Our expertise in studying the plasma environment around the Earth and the abundance of data available allow us to study the similarities and differences between the different planetary systems throughout the solar system. Through these comparisons, we can further our understanding of the fundamental physics of plasmas. 

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MSSL Space Plasma Science Highlights

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

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. More...


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

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. More...


How 'Coronal' Are Solar Wind Electrons?

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. More...


The structure of PSBL during an storm-time intense reconnection

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. More...

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

A magnetospheric plasma mass density model for varying geomagnetic activity

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. More...

Page last modified on 08 sep 11 09:26