The physics controlling radiation belt dynamics

This research will investigate the physical processes governing 'Space Weather' effects within the regions of near-Earth space known as the inner and outer radiation belts. Times when the energetic particle content of the Earth's radiation belts becomes dramatically enhanced are of great 'Space Weather' interest. The adverse consequences of radiation belt enhancements for both satellite infrastructure operating within the radiation belts and to ground-based systems which magnetically map to these regions can have a significant socio-economic impact. The UK National Risk Register for Civil Emergencies has classified Space Weather as a new risk with relatively high chance of occurrence and high impact on UK society. According to senior science advisors to the UK Prime Minister and the US President, the potential cost of an extreme Space Weather event is estimated as $2 Trillion in the following year, in the U.S. alone, with a projected need for a 4-10 year recovery period. Moreover, particles escaping from the radiation belts during these disturbed periods are also predicted to have some impact on atmospheric chemistry and as a result global temperature by altering Nitrogen Oxide levels in the upper atmosphere. Thus research into physical processes governing Space Weather effects in general and the dynamics of the Earth's inner and outer radiation belts in particular is required to not only learn how to mitigate the socio-economic impact of these disturbances but also to more fully understand global climate change.

During disturbed Space Weather events the radiation belts may become energised, depleted or completely disappear, and sometimes simply move toward or away from the Earth. In fact, observations demonstrate that during certain events a third belt can form. These abrupt and dramatic changes are thought to be the result of electromagnetic waves trapping particles in the radiation belts, transporting particles through the belts, and scattering particles into the Earth's atmosphere. At present, none of these processes are fully understood, and the links and interactions between the various drivers of these processes need to be better quantified in order to move our understanding of the dynamics of the radiation belts forward.

The ultimate goal of this research is thus to determine the types of electromagnetic waves which control particle dynamics in the radiation belts and to discover the conditions under which these interactions lead to the energisation, depletion, and/or movement of the belts. This research will allow the development predictive physics-based models which can forecast the state of the radiation belts in order to help develop strategies to mitigate the effects of space weather on modern society.

As discussed in the Academic Beneficiaries section, there are numerous institutions that will benefit from this research. The overarching objective, to determine the power spectra, and thus relative effect, of all waves in the magnetosphere that can take part in radiation belt dynamics as a function of external and internal driving conditions and local time, is of paramount importance to those institutions engaged in predictive simulations of radiation belt dynamics. At present, many assumptions about wave characteristics at specific frequencies are made in order to try to include the effects of these waves into state-of-the-art radiation belt diffusion models. The result of this work will be a parameterisation of wave power as a function of frequency, across all relevant frequencies, in a single functional form. No wave frequency range will be excluded; indeed, previously excluded wave modes that may also interact with radiation belt particles will be incorporated This project will also identify whether there is significantly more wave power in any single wave mode during storms that accelerate, transport or empty the radiation belts, which will be of great interest to those same institutions. New state-of-the-art wave generation models will also be able to be tested using the results from this study.

Space Weather is now included in the UK National Risk Register for Civil Emergencies. Providing information directly relevant to predictive space weather modelling efforts is the first step towards providing advance warning for low-frequency, but high-consequence events such as those identified by the top UK and US Science Advisors (Holdren and Beddington, 2010) who warn "The potential total cost of an extreme Space Weather event is estimated as $2 Trillion in year 1 in the U.S. alone, with a 4-10 year recovery period". The Meteorological Office is responsible for providing space weather predictive capability and will directly benefit from the improved knowledge of the radiation belts that this project will provide. The Global Positioning System (GPS), and their European counterparts in Galileo, may be a primary benefactor of our research. The combination of large-amplitude electromagnetic waves and loss of particles from the radiation belts into the ionosphere leads to large and currently unpredictable changes in the density of the ionosphere. The accuracy of location information provided by GNSS is significantly degraded during periods of rapid ionospheric change that result from the direct action of radiation belt dynamics. Many industries rely upon GPS for their remarkable precision timing to 100 billionths of a second, synchronizing networks, computers or instruments. GPS technology is also used heavily in precision farming, including spraying and harvest, for snow removal in the US, and for vessels to determine their location precisely at sea anywhere on the globe. More generally, the effects of space weather can be felt in all activities that use space-related assets. For example, during the October-November 2003 geomagnetic storms the effects of space weather were included in a (US) National Weather Service report for the first time.

This proposed research will contribute to the reaching UK policy goals and enhancing UK economic competitiveness by providing crucial missing information on the dynamics and causes of radiation belt events. Realistic goals for the project will be the characterisation of all waves that contribute to radiation belt dynamics, crucial inputs into predictive radiation belt dynamics models essential for prediction of low frequency, high consequence events such as the Carrington storm of 1859 and the Halloween storms in October-November 2003. The research and professional skills that the PDRA will develop during this project will be in computational programming, the processing large datasets and clear scientific reasoning, which are all applicable to many employment sectors.