The work of the Group is concerned with the solar wind, the magnetosphere, the ionosphere, and the atmosphere of the Earth (and planets), and their strong mutual interactions. The primary focus of the work is on the fundamental plasma physical processes which occur in these systems, processes which have wide applicability in astrophysics, but which can only be addressed by in situ experimental investigation in the solar system context. Areas of particular interest in the Group concern boundary and current sheet phenomena including magnetic reconnection, large-scale instabilities and non-linear dynamics, communication mechanisms between tenuous collision-free and dense collisional plasmas, MHD waves and resonances, wave-particle interactions and non-linear transport, and atmospheric modulation mechanisms. At the same time, our work also contributes to knowledge of the properties and behaviour of the regions surrounding the Earth which are important for modern technological systems (e.g. applications spacecraft and communications). Consequently the research area may also be considered to be an increasingly significant branch of environmental science. This practical relevance provides the motivation for our programme of applied research.
The CUTLASS Radar System
The basis of the Groups internationally-recognised programme lies in its technical expertise in the design, construction, and operation of radio and radar systems for the study of the ionosphere and upper atmosphere, and in the scientific exploitation of the data which these facilities return. At present a central focus of our programme is exploitation of data from the Co-Operative UK Twin Located Auroral Sounding System (CUTLASS) radars, a bistatic pair of HF coherent-scatter radars sited in Iceland and Finland, with a common field-of-view over Svalbard. This system was built and deployed by the Group, and has been successfully operated (now as a National Facility) since 1995. Over the last few years, the system has proven to be very productive (as of April 2001 over 99 refereed papers since operations began) as well as being reliably used by a number of UK and international groups. The radars also form the easternmost pair of the northern hemisphere chain of SuperDARN, a network of similar radars in both hemispheres. These radars measure three main parameters, backscatter power, line of sight velocity and spectral width. As the fields of view of the two CUTLASS radars overlap, the line of sight velocities from the two radars can be merged to form 2-dimensional velocity vectors perpendicular to the magnetic field. The radars have proven ideal to study a range of scientific topics, including solar wind magnetosphere coupling, magnetosphere ionosphere coupling, magnetospheric substorms, MHD waves, atmospheric gravity waves, the irregularities from which the radar signal is backscattered, artificially generated irregularities, and mesosphere winds and temperatures. However, the full potential of such data is only realised when combined with data from other sources, both space-based and ground-based. In the recent past, for example, we have undertaken co-ordinated research with the EquatorS and Polar spacecraft, sounding rocket flights, the EISCAT Svalbard and mainland radars, the EISCAT heater, ground-based optical and magnetometer arrays, as well as with the international SuperDARN radars of similar type. We are also beginning to make a significant contribution to the exploitation of data from the four-spacecraft ESA Cluster mission, for which the Group has Co-Investigator status, by combining data from CUTLASS with data from Cluster. Cluster science operations began in February 2001. Much of the Groups research involves collaboration at an international level.
The New SPEAR Radar
SPEAR (Space Plasma Exploration by Active Radar) is a revolutionary new concept in ground-based radar design which is intended to provide a versatile HF system for solar-terrestrial physics research at very high latitudes. SPEAR is not only a radar system in its own right which will provide a major new capability for diagnosing plasma dynamics in the polar ionosphere by means of HF scatter, but also, by exploiting high power radio technology in a new way, will have an active capability of artificially stimulating VLF and ULF electromagnetic waves, as well as short-scale electrostatic plasma density waves and irregularities in the ionosphere and magnetosphere. These artificially generated waves and irregularities, once injected into the space plasma, will be detected by other ground-based radars and magnetometers, and by satellite-borne instruments in a controlled and co-ordinated manner which will significantly enhance our present diagnostic capabilities. Thus, coherent radars, such as the Group's CUTLASS system, and ground-based magnetometer networks will no longer have to rely entirely on sporadically occurring natural waves and irregularities to sound the ionosphere and magnetosphere. Furthermore, SPEAR will be able to inject waves whose refractive properties keep them confined to geomagnetic field lines, which can then be detected by satellite-borne instruments, such as those on board Cluster. The identification of common field lines along which the ionosphere and magnetosphere communicate will lead to an enormous improvement in our understanding of the fundamental coupling processes.
SPEAR is a multipurpose diagnostic which offers a number of exiting new possibilities for STP research, ranging from well tried and tested methods in the unique new (to STP activities) plasma environment of the polar cap, to more speculative new techniques which have the potential to deliver spectacular improvements in our understanding. SPEAR has a very flexible design, which will enable upgrades to be implemented at later stages, if and when new funding becomes available. Even with the basic system, however, as now approved by the PPARC, much outstanding new science is guaranteed, but perhaps more exciting is the possibility of unprecedented new gains. For a relatively modest cost, the UK will have a truly world-class space plasma physics tool for the 21st century which will address the key outstanding issues in STP. SPEAR will be a focus for UK ground-based STP activities and will operate in conjunction with coherent and incoherent scatter radars, magnetometer networks, riometers, and optical facilities which the UK has access to. Construction of the SPEAR system began early in 2000, with deployment on Svalbard (Spitzbergen) expected in 2003.
Solar Variability and Climate
Wave processes play a crucial role in redistributing energy and momentum around the upper atmosphere in response to external forcing from solar electromagnetic radiation and charged particle fluxes. In recent years, we have made significant contributions to the understanding of the fundamental mechanisms by which the upper atmosphere can influence the stratosphere and potentially the climate system as a whole. To consolidate these achievements, we have instigated a balanced programme of experimental observations of internal gravity waves and planetary (Rossby) waves, using both radar and satellite data sets, theoretical research, and numerical modelling. In particular, we intend to fully exploit the enhanced capabilities provided by the recent upgrades to the CUTLASS radars operated by the Group. As part of a chain of similar radars distributed along the auroral zone, we can undertake the simultaneous monitoring of large-scale atmospheric waves at a number of locations. The new purpose-built Aberystwyth-Leicester meteor radar will complement this network by providing measurements of upper atmosphere winds within the polar cap.
Part of our research into the coupling of the lower and upper atmosphere overlaps with activities traditionally associated with NERC. Interdisciplinary links have been built up over the years with a number of groups within the UK and beyond. The work has particular relevance to our understanding of natural climate variability and the near-Earth space environment. We have recently been allocated of a substantial fraction of a new PPARC High Performance Computer (the GRAND computer). In conjunction with the computational and data storage facilities within the Group, we are now in a position to tackle important, new scientific issues in solar/climate variability that were previously beyond reach.
Auroral Imager Development Project
It is part of the Group's medium-term strategy to develop a technical capability in imaging the Earth's aurora from space. There are three factors which render this aspiration scientifically appropriate, technically feasible, and politically desirable. The first of these is the scientific synergy with CUTLASS and the SuperDARN radar network with which the Group is presently centrally involved. The SuperDARN network provides the capability of "imaging" the flow over wide areas of the polar ionosphere with good temporal and spatial resolution, thus in effect also imaging the flow dynamics over wide volumes of the Earth's magnetosphere, and its coupling to the solar wind. An auroral imager correspondingly offers the unique capability of being able to image the dynamics of magnetospheric plasma populations over broad areas, with similar temporal and spatial resolutions. Coordinated observations of ionospheric flow using SuperDARN and auroral precipitation using a space-borne imager, will provide information on magnetospheric dynamics and solar wind-magnetosphere-ionosphere coupling of great diagnostic power. The second factor which makes this aspiration feasible is the great expertise which resides within the Space Research Centre (SRC) at Leicester University in the design and fabrication of UV and X-ray imaging systems for spacecraft, previously directed mainly towards astronomical objectives. The auroral imager project draws directly upon this expertise. Third, although a number of auroral imager systems have been flown on spacecraft to date, such as Dynamics Explorer, Viking, Freja, and Polar, no imager has yet been flown originating from a European group (except for the scanning photometers recently flown on the Swedish Astrid-2 spacecraft). There thus appears to be a clear niche for a European "product".
In the past two years, we have undertaken with PPARC support a design study for an imager which could be flown on a small satellite in near-Earth orbit. A compact low-mass design has been proposed based on novel microchannel plate optics. The next step is to develop a functional laboratory prototype, for which funding will be requested from the PPARC in due course.
Planetary Plasma Physics
Interest in the magnetospheres, ionospheres, and atmospheres of other planets is a natural and growing extension of our previous terrestrial studies, especially as these systems provide access to environments which possess conditions very different to those found near the Earth. Experimental studies have also been stimulated in recent years by growing European involvement in planetary space missions, particularly via the NASA/ESA Ulysses Jupiter fly-by and Cassini Saturn-orbiter missions. We at Leicester are co-investigators on instruments on both these spacecraft, and consequently are mainly involved at present in studies of the environments of these gas giant planets. Both generate immense magnetospheres which are bounded by the solar wind as at Earth, but the main sources of mass and momentum lie within. The plasma in these systems originates mainly from the surfaces and atmospheres of internal moons, producing an exotic sulphur-oxygen plasma from the atmosphere of Io in the case of Jupiter, while the main flow is maintained by planetary rotation. We have recently been investigating the dynamics of Jupiters magnetosphere preparatory to the Cassini fly-by in December 2000, specifically studying the mechanism by which the rotation of the Jupiter is imposed on the magnetospheric plasma at large distances. This is accomplished by a large-scale system of currents which flows between the magnetosphere and ionosphere. We have shown that this current system is directly connected with Jupiters main auroral oval. The current flowing out of the ionosphere requires magnetospheric electrons to flow in, and these have to be accelerated to high energies to carry the necessary current. We also suggest that it is these same electrons which form the energy source of much of Jupiters radio emissions.
Studies of the ionosphere and magnetosphere by radio and radar techniques require a detailed knowledge of the propagation characteristics of electromagnetic waves in these media. The Group has successfully developed this expertise over a number of years and now has an extensive range of experimental and analysis facilities at is disposal. Exactly the same facilities are required for the design of any technological system which depends on radio/radar signals traversing these regions of the geospace environment.
The Group has undertaken extensive studies on behalf of several governmental and commercial agencies. These range for example, from the propagation of VLF waves in the Earth-ionosphere wave-guide for navigation, communications, and prospecting purposes, to extensive measurements of the effects of the polar ionosphere on the accuracy of HF direction-finding systems. Currently we have a major study in progress on the influence of the ionosphere on the performance of over-the-horizon radars. These collaborative research projects, which depend critically on the basic science programme supported by PPARC, have attracted considerable research funds, and also the sponsorship of several CASE studentships.