Abstract: The Earth’s magnetic field maintains a pressure balance with the charged particle flow from the Sun (solar wind), forming a protective cavity, called the magnetosphere. When the magnetosphere is strongly perturbed by transient features in the solar wind, energetic electrons in the magnetosphere can move out of their trapped orbits and precipitate into the upper atmosphere, lighting up the aurora. Electron precipitation has significant space weather impacts, such as enhancing atmospheric drag for satellites at low Earth orbit (LEO), as well as producing ozone-depleting catalysts. These practical applications constantly drive the development of new theoretical and observational techniques to understand the process of electron precipitation. It is recognized in the early days of space physics research that interactions between natural magnetospheric electromagnetic waves and electrons are one of the dominant causes of electron precipitation. Modern conjugate measurements of waves in the equatorial magnetosphere and electron precipitation in LEO confirm the critical role of wave-particle interactions, but also bring forth substantial new questions awaiting resolution. In this colloquium, I will review the basic physics of resonant wave-particle interactions, and its application to relativistic electron precipitation by one of the most powerful electromagnetic emissions, electromagnetic ion cyclotron (EMIC) waves. I will present a generalization of classical theory to include a process which has been traditionally neglected, namely nonresonant interactions, and thereby solve the longstanding problem of sub-relativistic electron precipitation by EMIC waves, which should not be present according to classical resonant interactions. Finally, I will review new challenges for the classical theory to quantify electron precipitation by observed wave characteristics and realistic magnetic field configurations. I will discuss possible approaches to resolve these challenges with new theoretical tools and support from the growing fleet of rockets and CubeSats in LEO performing electron precipitation measurements.
***Join before the Colloquium at 3:00 pm for coffee, cookies and brownies from Lou's in Wilder 103!***
Hosted by Professor Yi-Hsin Liu
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