LIPS: The Lifetimes of Ionospheric Plasma Structures

This project, called LIPS for short, set out to understand the turbulent breakup of plasma structures in the Earth's upper atmosphere. This abstract goal was intended to provide a better, more holistic understanding of electrostatic turbulence in these layers of plasma. For what good is it to understand the emergence of turbulence without knowledge of how that turbulence dissipates? To understand this turbulence is, at the same time, to understand more about how energy moves, in waves so to speak, from the sun into Earth's near space, where it creates auroras and other electrical activity. A deeper understanding of plasma turbulence itself will enable humanity to better protect technological assets in space, as well as better predict disruptions in GPS navigation. Among the results that the project fruitfully provided was proving that plasma structures around Earth's equator (the most turbulent part of Earth's near space) destroy themselves through a 'turbulent cascade,' with the effect that aspects of the plasma structures at various degrees of magnification dissipate simultaneously, and this is in clear contrast to a collisional understanding of the plasma. In other words, an ordinary understanding of how magnetized plasma structures should disappear in space does not agree with the theoretical basis, a major discovery in a small field of physics. This builds on a broader understanding of such turbulent dissipation of energy in Earth's near space. This non-linear aspect of space physics, which cannot be treated by the ordinary linear models that usually build our understanding of the large movements that energy takes in space, namely the interaction between Earth's magnetosphere and the Sun's large magnetic field, is important. By shedding light on the non-linear aspect of plasma physics, LIPS has made a contribution to the advancement of science.

The outcomes of my work during the project are divided into two themes, of which the original goal are an integral part of the the first category: 1. Turbulent Energy Dissipation The prevailing theories regarding plasma structure decay were largely based on ambipolar diffusion, with limited support from space observations. By using large datasets of in-situ plasma observations from the ionosphere, my research has altered our understanding of this process: a) While a single prior study hinted at the possibility, I provided the first definite evidence that low-latitude F-region irregularities tend to decay scale-independenty (DOI 10.1029/2024GL109441). This conclusion stands in stark contrast to previous expectations based on ambipolar diffusion. b) My work on the cusp region demonstrated that the particle energy flux from the solar wind decreases when the turbulent dissipation of irregularities maximizes (DOI 10.1029/2023JA031849). This altogether surprising result indicates that the growth of plasma turbulence in the cusp may be mostly influenced by factors other than soft electrons from the solar wind. c) I continued the investigation into the E-region's effect on F-region plasma irregularities, finding that the intense, diffuse aurorae that occur at night in the polar regions are simultaneously a source of local irregularity production and a sink of unstable plasma energy. (DOI 10.3389/fspas.2024.1309136). 2. Novel Methods for Characterizing Auroral Electric Fields Using Coherent Scatter Radar After moving to Canada I have been working with the Canadian 3D radar ICEBEAR, leading to discoveries in the field of radar-based remote sensing of the ionosphere: a) Using data analysis techniques borrowed from observational cosmology, I demonstrated that plasma irregularities in the E-region tend to exhibit a preferred scale of organization (DOI 10.1029/2022JA031233), and that this preferred scale is also observed in field-aligned current filamentation (DOI 10.1029/2023JA032310). This finding provides insights into the critical link between the lower ionosphere and the magnetosphere. b) Based on unsupervised machine learning, I developed a new point-cloud clustering and tracking algorithm for radar interferometry, breaking with long-held radar conventions (DOI 10.1103/PhysRevE.110.045207). The importance of this innovation is reflected in the attention it received from the American Physical Society, through being highlighted with an attendant popular-scientific article. c) I developed a novel method that allows, for the first time in decades, the unambiguous determination of electric fields using E-region coherent radars (DOI 10.1029/2024JA033060). This breakthrough overcomes a long-standing challenge in E-region remote sensing and opens up exciting new possibilities for monitoring space weather. The paper was highlighted by the American Geophysical Union, and the metadata service Altmetric placed the paper in the top 5% research outputs globally.

LIPS intends to shed light on plasma structure decay in the upper ionosphere, in both the polar and equatorial regions, by performing direct measurements of structure lifetimes, using a novel set of multi-point plasma measurements. In the ionosphere, plasma structure lifetimes are a result of chemical recombination and plasma diffusion. Whereas the growth of plasma irregularities have been paid considerable attention, their decay have largely not been studied, and plasma structure lifetime has consequently been paid little attention in the scientific literature. However, the topic is important, as every technological problem associated with plasma irregularities (radio scintillations, e.g.) are directly impacted by the lifetimes of those irregularities. LIPS identifies three main challenges in the field of F-region plasma structure lifetime. First, the measured scale-dependency in high-latitude plasma structure lifetime deviates strongly from the theoretical predictions. Second, measurements of equatorial F-region plasma structure lifetimes yield results that are completely scale-independent, suggesting that the mechanisms are not fully understood. Third, small-scale plasma structures result from instabilities, meaning the growth of turbulence can badly offset structure lifetime calculations. LIPS will resolve these issues by use of completely new multi-point plasma measurements performed by the Korean SNIPE satellite mission, which will be launched in 2021. A constellation of four satellites will orbit in tightly controlled formations. Whereas researchers performing power spectral density analyses on conventional satellite data have to contend with treating 3D plasma structure projections to 1 dimension, LIPS will be able to approach plasma structures without this simplification. The methodology we propose has real potential as a tool to scrutinize scale-dependent physical phenomena in ionospheric plasma, paving the way for future scale-dependent investigations.