Rolling Grant Support for a Programme of Research in Solar-Planetary and Atmospheric Physics at the University of Leicester

We propose a broadly-based programme of research on the outer environments of the Earth and planets, shaped by the interactions that take place between the planetary magnetic field, the solar wind on the outside, and the planetary atmosphere on the inside. The programme will consist of experimental work, data analysis, theory, and computer modelling, and can be described most simply in terms of four interactive elements. The first element consists of research in 'solar terrestrial physics' in which ground- and space-based experimental facilities will be used to examine the response of the Earth's magnetosphere to the highly-variable inputs from the interplanetary medium, namely the solar wind and embedded interplanetary magnetic field (IMF). The direction of the IMF is known to be a principal determinant of the interaction, but the solar wind ram pressure also plays a role. How the fundamental processes that occur within the outer regions vary in response to these inputs will be investigated, together with the transmission of the resulting effects along outer magnetic field lines into the Earth's polar ionosphere and atmosphere. Experimental research will focus on data from the SuperDARN radar array, the ESA Cluster space mission, and the new NASA THEMIS mission. A second area of study will consider related phenomena in the outer plasma environments of the planets, where similar considerations apply but under very different conditions. Results thus inform and are informed by understanding of the terrestrial system. Planetary research will initially focus on Jupiter and Saturn, using auroral data from the Hubble Space Telescope and in situ data from the Cassini space mission. Later, work will also begin on Mars in preparation for the ESA ExoMars orbiter mission, and on Mercury in preparation for BepiColombo. This work will also inform later studies on the outer environments of extra-solar planets. In the third research area novel active experiments will be undertaken in the terrestrial environment using the SPEAR, Tromso, and HAARP high-power radar facilities. These will first be used to study natural phenomena through the production of artificial scatter that can be detected by the SuperDARN radars. Secondly, they will also be used to artificially excite waves and oscillations in the Earth's ionosphere and magnetosphere in a controlled manner. Such wave excitation can 'tag' magnetic field lines connected to the radar deep into the Earth's magnetosphere, where they can be detected by spacecraft. Through these means the highly uncertain paths that magnetic field lines take through the outer environment of the Earth can be experimentally pinned down for the first time. The fourth area finally considers the impact that the space environment has on the upper atmosphere of the Earth, and the onward consequences at lower altitudes that may effect Earth's climate. This work will be undertaken principally through sophisticated computer modelling of the middle and upper atmosphere, and its responses to changes in the forcing at low altitudes and in the boundary conditions at high altitudes. Substantial development of existing computer models is required to do this. The work will also inform future studies of the atmospheres of extra-solar planets.