A multi-instrument exploration of the cusp ionosphere

At near-noon local times, at locations in the high arctic near 80 degrees North and South, the magnetic fields which originate in the conducting core of our planet extend upwards and are magnetically connected to the dayside magnetopause. This subsolar magnetopause is the point where the magnetic field of the Earth first touches the highly supersonic solar wind flow, and the interplanetary magnetic field of solar origin which is embedded in it. This creates the magnetospheric cusps, which are the primary entry points for energy of solar wind origin into the regions of space controlled by the terrestrial magnetic field, and the atmospheric regions which underlie them. This energy transfer occurs through a process called magnetic reconnection. As such, this crucial region of near-Earth space is fundamental to understanding the flow of energy, mass and momentum throughout the Earth's magnetosphere, ionosphere and upper atmosphere, and hence in our understanding of "space weather". The magnetospheric cusps are longstanding areas of research interest, but their highly variable nature, in both space and time, makes them a highly challenging region to fully understand. Here we describe a multi-instrument research programme based around an exciting new NASA space mission, TRACERS, due for launch in late 2022, on which the proposal PI is a named collaborator. The TRACERS programme relies on coordination with ground-based instrumentation. Of particular interest for TRACERS is the Svalbard region, an area of the high arctic uniquely well instrumented with, for example, numerous optical instruments and the NERC-funded EISCAT Svalbard radar. Around northern winter solstice Svalbard is in darkness at noon, and for ~10 days the moon is below the horizon. Such conditions offer a unique opportunity for multi-instrument cusp experiments involving cusp auroral optical observations. Our multi-instrument research programme requires the construction and deployment of a new state-of-the art digital imaging radar system, the Hankasalmi auroral imaging radar system (HAIRS). HAIRS will look northwards from Hankasalmi in Finland, having a field of view centred over the Svalbard region, revealing the ionospheric cusp region electrodynamics at high spatial and temporal resolution over a ~1 million square kilometre region of the ionosphere.

In this programme, low earth orbit measurements of energetic ions precipitating from the cusp region taken by the twin TRACERS spacecraft will provide measurements of the temporal and spatial structuring of the cusp reconnection processes. Magnetically conjugate measurements of the footprint of the reconnection line from HAIRS and associated ground-based instrumentation, will measure the length and the location of the reconnection line. HAIRS will provide an analysis of the boundary motion, and of the convection velocities detected near the boundary, allowing a calculation of the reconnection rate mapped down to the ionosphere. Such a combination of instrumentation will provide an unprecedented opportunity to understand the temporal and spatial behaviour of cusp reconnection and its role in controlling terrestrial space weather.

Outside of the science programme described here, HAIRS will offer vital complementary datasets to support the upcoming NERC-funded EISCAT 3D radar system at lower latitudes in Scandinavia, coming on stream in 2021 which will also lie in the HAIRS field of view. HAIRS will also directly complement the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE), launching in 2023, a joint mission between the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS). The innovative SMILE wide-field Soft X-ray Imager (SXI), provided by the UK Space Agency and other European institutions, will obtain unique measurements of the regions where the solar wind impacts the magnetosphere, regions which are directly magnetically connected to the area under study in this programme.

The proposal described here is focussed on the fundamental physics of magnetic reconnection, and reconnection at the magnetospheric cusps is of central importance in the large scale flow of energy, mass and momentum through the terrestrial magnetosphere-ionosphere-atmosphere system. Magnetic reconnection is the ultimate driver of terrestrial space weather, and its influences on the lower atmosphere. Space Weather is now recognised as a significant potential hazard to the UK's technological infrastructure following its inclusion in the National Risk Register for Civil Emergencies (NRR) published in January 2012. Both the advances in understanding of the drivers of space weather arising from this research programme, and the new dataset recorded by the HAIRS system, will directly contribute to our understanding of, and ability to forecast, space weather, benefiting Space Weather Service Providers such as the UK Met. Office. Other direct beneficiaries of the impact of this research includes HF Communications Users, Over the Horizon (OTHR) Radar Users, GNSS Users and Space Infrastructure Operators.

HF Users. Our work will provide information on the space weather impacts on the ionospheric plasma from the dataset resulting from the HF signals used by HAIRS. Such an HF propagation database will allow OTHR users to benefit from improved geolocation knowledge. A dataset of the presence of irregularities will also provide information on the ionospheric clutter received by these systems, enabling improved system performance.

GNSS Users. The SuperDARN radars such as HAIRS receive scatter from irregularities in the ionosphere which are related to those irregularities which are the source of the scintillation of the signals which propagate through the ionosphere in GNSS systems. Scintillation is a major source of error in GNSS. HAIRS will provide new information on when and where the GNSS signals may become severely impacted at auroral latitudes.

Space Infrastructure Operators. Atmospheric variability leads to variability in atmospheric drag on satellites in low Earth orbits, perturbing the satellite orbital motion, and decreasing the orbit predictability. The cusp is known to show strong atmospheric heating processes, and this research will contribute to our understanding of the effects of this heating on orbit predictability for polar LEO spacecraft.

Engagement with these groups

We will present our research results at international conferences with broad inter-disciplinary atmospheric science aims so as to maximise a two-way dialogue. We will continue to initiate and maintain new collaborations with industrial and other partners in order to maximise knowledge exchange and to seek contract income, focussing on our close relationship with Space Park Leicester, opening in 2021. We will publish our research in a wide range of journals, particularly those appropriate to the applications of the research (for example AGU's "Space Weather") in order to foster future collaborative ventures with new user groups. We will provide data and any required visualisation tools to the NERC British Atmospheric Data Centre to maximise its accessibility to the UK space community. We will host a workshop to facilitate UK stakeholders to take full advantage of the flexibility of the new digital radar system.

Wider user interest

The group has an ongoing, wide and diverse range of outreach activities, which actively promote our research to selected audiences and the general public. Outreach activities are closely coordinated with the National Space Centre, and Space School UK, a week-long residential programme run by our department to bring secondary school children closer to space science and astronomy. Real time data and system control of HAIRS and orbital data from TRACERS obtained through the University of Leicester ground station will provide new opportunities for space education.