EISCAT_3D-Based Reconstruction of Ionosphere-Thermosphere Electrodynamics

The E3D-BRITE project tackles one of the most exciting and challenging areas within ionospheric physics: Understanding the ionosphere and atmosphere over our heads at ~80–200 km altitude as a truly 3D system. Our current understanding is mostly based on conceptual models that treat the ionosphere as an infinitely thin, two-dimensional electrically conducting sheet. The ionosphere is indeed an electrically conducting plasma, but it is as three-dimensional as the world we experience on a day-to-day basis. So why would scientists treat it as a 2D sheet? Because we don't yet have the information we need to do anything different: the instruments we have historically used to measure ionospheric properties — for example, satellites, rockets, balloons, and radars — are all ill suited to creating a 3D picture of the ionosphere: At these altitudes the air is too thin for balloons to stay afloat and too dense for satellites to maintain a stable orbit, and rockets traverse the ionosphere only briefly during their flight. This situation is about to change. With sites in Norway, Sweden, and Finland, the upcoming EISCAT_3D phased array incoherent scatter radar will allow us to make 3D maps of ionospheric densities and temperatures, and ionospheric plasma convection. However, EISCAT_3D measurements are only one important part of the puzzle. We need a set of tools for combining EISCAT_3D measurements into a unified, 3D picture of ionospheric and atmospheric dynamics that is consistent with basic laws of physics. The E3D-BRITE team is well-posed to design and publish such tools: our team consists of experts in radar design, radar theory, physics modeling, statistics, inverse theory, and other areas of advanced mathematics. The E3D-BRITE project is dedicated to creating and using these tools to help us move away from the 2D paradigm, and toward a truly 3D understanding of the overlapping ionosphere-atmosphere system.

The EISCAT3D-Based Reconstruction of Ionosphere-Thermosphere Electrodynamics (E3D-BRITE) project addresses a grand challenge in space physics: How do electric currents in Earth's ionosphere evolve in time within a three-dimensional volume and on spatial scales smaller than 100 km? This question has been impossible to answer because of a lack of truly 3D measurements of the coupled ionosphere-thermosphere system. Using the trailblazing EISCAT_3D facility, I propose to address three fundamental questions directly related to this challenge: Q1: What is the role of small-scale (10s of km), 3D ionospheric currents in the development of meso- and large-scale auroral ionospheric current systems? Q2: How are the 3D properties of the ionosphere and thermosphere modified in the presence of an auroral arc? Q3: How does the neutral wind impact energy dissipation and ionospheric conductivities? Answering these questions, however, requires tools and techniques that do not currently exist. Drawing on our expertise on ionosphere-thermosphere (IT) physics, data assimilation techniques, empirical modeling, and radar systems, my team and I will (i) Create and disseminate an open-source reconstruction technique that uses EISCAT_3D measurements to reconstruct a coherent picture of 3D IT electrodynamics on scale sizes of several kilometers, far beyond the current state of the art; (ii) Design and implement an EISCAT_3D experiment that is optimized for investigating 3D small-scale structures on the shortest timescales achievable with EISCAT_3D over the altitude range ~90–150 km. I will use this technique to carry out the following scientific studies that answer Q1, Q2, and Q3 above: •"Comparison and validation of 3D volumetric current estimation methods" •"Generation and dissipation of kilometer-scale 3D ionospheric currents" •"Auroral current closure in the presence of 3D conductivity gradients" •"Neutral wind modification of plasma instabilities in the 3D auroral ionosphere"