There is a growing interest in the Earth’s environment and in the physical processes which govern such factors as its composition, energy distribution, turbulence and stability. The Radio & Space Plasma Physics Group is engaged in studies of the Earth’s ionosphere and its interactions with the regions both above and below it. Above, it couples with the magnetosphere, the solar wind and the interplanetary magnetic field. The most intense of these interactions occurs at high latitudes and results in the spectacular displays of the aurora or ‘Northern Lights’. Coupling of the ionosphere and upper atmosphere through its lower boundary to the middle and lower atmosphere is also a major interest. This research is undertaken using a combination of ground-based experimental facilities, measurements by Earth-orbiting spacecraft, computer modelling, and theory. Some of the work involves experimental campaigns at high polar latitudes, in which research students have the opportunity to participate.
Early theories of the origin of the aurora were somewhat fanciful, but in 1600 William Gilbert published "De Magneta" in which he proposed that the Earth acted as a magnet
Major ground based facilities have been established and many satellite borne experiments flown to study the Earth’s aerospace environment. Extensive use is made of radar facilities such as the European Incoherent Scatter (EISCAT) radar located in Northern Scandinavia and satellites such as Cluster and Polar. In addition to studies of the geophysical phenomena, the group is also involved in using the ionosphere as a giant plasma laboratory, in which a wide range of plasma irregularities and waves can be investigated without the constraints imposed by laboratory conditions. We also study the ionospheres and magnetospheres of other planets in our solar system, and are participating in the analysis of data from the Cassini Saturn orbiter space mission. Studies of a more applied nature are also in progress. The limitations imposed by the propagation medium are important factors in the design of a wide range of space to ground communications and navigation systems and the ionosphere is a key factor in conventional long-range broadcasting and communications. A Radio Systems Laboratory has been established jointly by the Physics and Engineering Departments for these investigations.
The RSPPG is internationally-renowned as a leader in the observational and theoretical understanding of solar system plasma environments. At present, the Group comprises approximately 40 people, including Academic Staff (~10), Research Fellows and Associates (~6), PhD students (~15), and Administrative and Technical Staff (~8). The Group has world-class computing facilities and operates several ionospheric radar systems around the world.
Vacancies exist for Science and Technology Facilities Council (STFC)- and Natural Environment Research Council (NERC)-funded PhD studentships within the Radio and Space Plasma Physics Group starting in October of each year. Early application is recommended to ensure consideration for these places. Alternative funding sources may also be available.
Details of currently available projects can be found at the Department of Physics and Astronomy Postgraduate Research page.
The Radio and Space Plasma Physics Group offers PhD projects in the following broad areas of research. Exact details of the projects on offer differ from year to year. More details can be found by following the links below.
All members of academic staff in the Radio and Space Plasma Physics Group are available to supervise PhD projects. Current members of staff (and their main area(s) of interest) are:
The solar wind plasma blows outwards from the Sun at speeds of 500 km/s, and flows continuously past the Earth on its way out towards interstellar space. The interaction between this wind and the Earth’s magnetic field confines the field to the interior of a cavity surrounding the planet, called the Earth’s magnetosphere. The position of the outer boundary of this magnetic cavity, the magnetopause, is determined mainly by pressure balance between the ram pressure of the solar wind on one side, and the magnetic pressure of the compressed planetary field on the other. On the dayside, this boundary is usually found at distances from Earth of about 10 Earth radii (about 64,000 km), while on the nightside the Earth’s magnetic field is pulled out by the solar wind into a long tail, rather like a comet’s tail, which extends to distances of at least 1000 Earth radii.
The region of space surrounding the Earth is separated into different regions by the interaction between the heliospheric magnetic field, carried by the solar wind, and the terrestrial magnetic field
The separation between the solar wind and the Earth’s magnetosphere is not perfect, however, and processes occur at the boundary which allow the transfer of mass and momentum across it. The most important of these is magnetic reconnection, which allows a direct connection between the geomagnetic and interplanetary magnetic fields. These processes, which are electromagnetic in nature, result in the transport of Earth’s magnetic flux from the dayside to the tail in the outer regions of the magnetosphere. The magnetic flux eventually returns to the dayside through the central part of the magnetosphere. A large-scale cyclical flow of plasma is therefore set up in the magnetospheric cavity due to the solar wind interaction, the total flow cycle time being about 12 hours. This, combined with sources of plasma from the solar wind on the outside and from the ionosphere on the inside, produces highly structured plasma populations inside the cavity.
This sequence of false-colour images taken from a spacecraft shows that the Earth's auroral rings are highly variable and dynamic
There are many aspects of such a complex system which are studied by a large number of research groups world-wide. In the Radio & Space Plasma Group at Leicester we concentrate on studies of the main interaction regions of the magnetosphere, the magnetopause and the tail, where the key processes take place which result in large-scale flow. An unprecedented opportunity to study these regions is currently in progress using data from the ESA Cluster space mission. Four identical spacecraft are flying in formation through these regions, measuring the electromagnetic field and the plasma populations. The Group has direct access to the magnetic field data from these spacecraft, and through this involvement to the data from other instruments. Using these measurements, studies are in progress on the nature of the field and plasma structures which occur in these regions, and their evolution with time. The recently-launched NASA THEMIS mission is also key to the Group's studies of magnetotail dynamics.
Cluster, and other space missions, provide in-situ observations of the magnetosphere
These space-based studies interface directly with the Group’s ground-based research programme since it is the flow generated in the magnetosphere, transferred along the magnetic field lines into the ionosphere, which is principally detected by the Group’s CUTLASS radars. The Group is therefore centrally placed to undertake unique coordinated space-ground observations using Cluster, THEMIS and CUTLASS at the present time.
The CUTLASS radars, part of the SuperDARN network, are central to the solar-terrestrial physics research within the RSPPG
The CUTLASS radars, located in Iceland and Finland, view the ionosphere over the northern polar regions. These radars were built and deployed by the Group, and have accumulated a large volume of data on ionospheric flows since the start of operations in 1995. Research is undertaken in conjunction with other ground-based facilities, such as the EISCAT Svalbard Radar which can measure a range of ionospheric parameters, optical instruments which observe auroras, and magnetic measurements which sense the effects of overhead ionospheric currents.
Radar experiments are also co-ordinated internationally with rocket shots from Svalbard, and satellite over-passes. The Group also operates vertical and oblique radio sounders in the northern polar regions, and a Doppler system called DOPE, which is designed to study ultra low-frequency waves propagating in the magnetosphere-ionosphere plasma.
CUTLASS forms part of SuperDARN, an international network of similar radars covering over 180˚ longitude in the northern hemisphere and including conjugate stations in the Antarctic. This network offers, for the first time, a truly global atmospheric monitoring which is so important if we are to understand our planetary environment.
Examples of research projects in this area include:
Like the Earth, most of the planets generate magnetic fields in their interiors. Direct measurements from spacecraft flybys have shown that this is true of Mercury, Jupiter, Saturn, Uranus, and Neptune (Pluto-Charon has yet to be visited). In this case the solar wind, composed of charged particles, interacts directly with the planetary magnetic field. The size of the resulting magnetospheric cavity depends on the strength of the planetary magnetic field, and varies from a structure which barely rises above the planet's surface in the case of Mercury, to the giant system which surrounds Jupiter, which is five times larger than the Sun. The plasma populations which occur inside these magnetospheres are also very varied, depending on the nature of the sources of plasma which are present, and the nature of the plasma transport mechanisms. At Mercury the interior flow is driven mainly by coupling to the solar wind, and the latter also forms the main source of plasma for the interior. At Jupiter and Saturn, on the other hand, the flows are driven principally by planetary rotation, and the plasma is mainly derived from the atmospheres or surfaces of moons which circle inside the magnetosphere.
The ultraviolet aurora of Jupiter and Saturn
Other bodies are unmagnetised, such as Venus and (to a first approximation) Mars, and the comets. In this case the solar wind interacts more directly with the atmosphere of the body, or with its outer conducting layer, the ionosphere. Then the magnetic field in the solar wind becomes draped over the ionosphere on the dayside of the planet, and stretched out into a long "induced" magnetic tail on the nightside. In the case of comets, however, the atmosphere extends for millions of kilometres around the nucleus due to the low gravity, and atmospheric particles are picked up and carried along by the solar wind flow as soon as they become ionised by solar ultraviolet light.
Group involvement in the Cassini mission makes the magnetosphere of Saturn a key area of research in the RSPPG
At present our work concentrates on the gas giant planets Jupiter and Saturn, and on theoretical and data analysis studies of the coupling of rotational energy between the atmosphere and the magnetosphere. Our analysis work centres on data from the Cassini spacecraft, on which we are co-investigators on the magnetic field experiment.
Research topics in the next few years will include:
While the CUTLASS radars work routinely by scattering radio waves from naturally-occurring irregularities in the ionosphere, which may or may not be present, in 1997 we discovered that irregularities can be generated artificially by injecting high-power radio waves from the ground, and that these can be used as artificial targets. Furthermore, because of the properties of these irregularities, the velocity data derived from CUTLASS scattering is of far higher precision than that obtained from natural scatter. As a consequence of these discoveries, we were awarded a grant of £2.4 M to build a new high-power radio wave injection facility on Svalbard, called SPEAR, which became operational in 2005. This facility not only produces targets for CUTLASS, but is also able to undertake a range of novel experiments on wave and particle injection into the magnetosphere.
The SPEAR radar probes the upper atmosphere with high power radio waves
SPEAR-related research projects which are currently being undertaken include:
Building on our long-standing expertise in the fields of ionospheric and magnetospheric physics, the group has been able to address several fundamental questions concerning the role that the Earth’s near-space environment plays in modifying the climate system. To be able to attribute human influences in climate change, it is essential that we can understand the principal nature causes. Solar activity has been identified as being one such agent of change. In particular, we have shown that wave processes in the stratosphere are able to modify strongly the winter polar stratosphere in response to external forcing from solar ultraviolet radiation and charged particle fluxes in the upper atmosphere.
Effects of solar variability on the stratosphere and hence climate
The group has initiated the development of a series of three-dimensional models of the atmosphere between 10 – 200 km to investigate the dynamical coupling of the different atmospheric regions. Planetary scale disturbances, known as Rossby waves, that are responsible for carrying frontal weather systems across the Atlantic to Britain, transport heat and momentum to the polar night regions that remain in darkness throughout the winter months. Solar-induced changes to the global circulation have been found to disrupt this process, also resulting in changes to ozone levels around the Arctic and Antarctic. We have access to world class supercomputing facilities in the department to perform the many numerical calculations that are needed by the models. There are extensive collaborations with a number of groups in Europe through an EU Framework 5 programme entitled ‘Coupling of Atmospheric Layers’, as well as with researchers in the UK and the US.
We are currently leading a team to design a micro-satellite mission to investigate further the role that space plasmas have on climate. ‘Chapman’, named after a British pioneer in upper atmosphere and magnetosphere research, would be roughly the size of a fridge. It is being designed to be able to monitor high energy particles that can penetrate the Earth’s atmosphere down to the cloud base and observe transient optical phenomena such as aurora and sprites (upper atmosphere lightning) at close quarters. It will also be able to measure stratospheric clouds that are responsible for the large-scale destruction of ozone and monitor mesospheric clouds, whose increasing frequency of occurrence may be an early indicator of long term climate change.
In depth localised measurements of the upper mesosphere and lower thermosphere region are currently being carried out with the CUTLASS and EISCAT radars. These observations allow us to assess the contributions made by relatively small scale phenomena, such as atmospheric gravity waves, to the atmospheric circulation on timescales ranging from minutes to a number of years. Linking a number of these radars together (e.g. SuperDARN) allows us to consider the global significance of such processes.
Projects in this area will include: