A new UK-built neutron monitor aims to detect high-energy particles from solar storms that can knock out power grids and force aircraft to divert. The prototype network, called GLEEM, will be deployed at a meteorological field site to test whether a cheaper, more compact design can match the performance of the ageing global network of 50 monitors—none of which are in the UK. These ground-level enhancement events, which occur roughly once per year and last up to 12 hours, pose a recognised risk to national infrastructure, including aviation, rail, satellite communications, and safety-critical electronics. The Met Office currently lacks the capability to provide adequate radiation hazard warnings because existing monitors rely on toxic or expensive detector materials and have changed little since the 1940s. If the GLEEM prototype works, it could re-establish monitoring in the UK, feed real-time data into the Met Office Space Weather Operations Centre, and support airborne radiation models being developed in the SWIMMR programme. The design uses helium-3 detectors optimised for cost and compactness, and is intended for unattended operation in remote locations. Success would enable a major expansion of the global monitoring network at significantly lower cost, giving forecasters better warning of solar radiation storms that disrupt the systems modern society depends on.
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The risks posed by space weather are becoming more widely recognised, and they are now listed on the UK National Risk Register. In particular, hard solar energetic particle (SEP) events containing a substantial flux of particles with energies greater than 300 MeV pose a considerable risk. Ground level neutron monitors detect such solar events, termed ground level enhancement (GLE) events, at the Earth's surface and have done so since the 1940s. Typically there is around one GLE event per year and they have durations from 1 to 12 hours, the largest event observed with instruments was measured in Leeds on 23 February 1956. Besides other ground-detectable space weather phenomena, GLE events have the potential to disrupt critical national infrastructures, such as the power grid, transport (aviation and rail), satellite applications and communications, and safety critical electronic control systems. Deducing space weather radiation at the top of the Earth's atmosphere from measurements made by neutron monitors on the Earth's surface requires a globally distributed network of monitors and models that simulate the physics of particle interactions in the Earth's atmosphere. The Met Office is responsible for reporting space weather risks to government departments and civil aviation, among others, and has recognised that it does not have sufficient capabilities to provide the necessary services for space weather radiation hazards. For example there are only 50 ground level neutron monitors worldwide still operational, none of these are located in the UK. The design of existing monitors and their instrumentation have changed very little over the last sixty years, they rely on detector materials that are either highly toxic (boron trifluoride) or expensive (helium-3), and are large and bulky instruments containing lead shielding. Concerns over the use of these materials in other applications involving neutron detection has led to the development of a plethora of alternative detection technologies. Despite the wide range of alternative neutron detectors now available, very few are suitable for the specific application requirements of ground-level neutron monitoring, where high detection efficiency and several decades of stability are essential. During the design phase, GLEEM evaluated an alternative detector technology (boron coated straws) that promised the greatest potential to fulfil these specific application requirements. This detector technology was developed for unattended safeguards monitoring, among other applications, where similar challenges exist. Our findings showed that, currently, fully modernised helium-3 detectors remain the most viable option. Our new design is optimised for cost savings, compactness and most efficient use of helium-3. It is designed to produce comparable results to a typical monitor in the existing network and is suited for unattended operation in relatively remote locations. The GLEEM implementation phase now aims to commission and demonstrate a prototype network of the new monitor design. The monitor will be deployed and tested at an existing meteorological field site to verify that such instruments can produce comparable results to those from existing ground level neutron monitors, and potentially enhance existing global capabilities. As proof of concept, a network of one complete instrument and one partial instrument will be demonstrated as part of a test deployment, to provide a compatible data stream for incorporation into the Met Office Space Weather Operations Centre (MOSWOC) and feed into the airborne radiation models being developed as part of SWIMMR N2, the NERC funded SWIMMR Aviation Risk Modelling (SWARM) project. Ultimately, GLEEM aims to construct and operate a significantly cheaper instrument, re-introduce monitoring in the UK and facilitate a major increase in space weather monitoring worldwide.
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