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Colloquium

27
JAN

Hong Zhao: Unraveling Mysteries behind Energy-Dependent Dynamics of Energetic Particles in Earth's Magnetosphere

2:30pm @ White Hall G09

The Earth’s magnetosphere is filled with charged particles of a wide range of energies, spanning from ~eV in cold, dense plasmasphere to relativistic energies in the radiation belts. In particular, ~10s of keV to ~10s of MeV electrons, trapped by the geomagnetic field in the radiation belts while azimuthally drifting around the Earth, exhibit energy-dependent acceleration, transport, and loss processes. These energetic particles pose potential threats to both spacecraft and humans in space and technical systems on the ground. Thus,understanding and eventually predicting the Earth’s radiation environment is of both scientific interests and practical needs. Utilizing measurements from past and current missions,combined with numerical modeling, the physical mechanisms responsible for the energy-dependent acceleration, transport, and loss of energetic particles have been revealed. This talk will feature some recent advances in the understanding of energy-dependent dynamics of radiation belt particles. First, a newly-discovered, reversed energy spectrum of radiation belt electrons generated by the plasmaspheric hiss waves highlights the critical role of wave-particle interaction in causing energy-dependent losses of energetic particles. Then, the importance of electric fields in energy-dependent transport of energetic particles will be demonstrated through multi-spacecraft observations and numerical modeling. Last but not least, the energy-dependent acceleration of relativistic electrons reveals the underlying physical mechanisms while also raises questions that point to the need for a future space mission. These results aid in a deeper understanding of energy-dependent particle dynamics in the Earth’s magnetosphere and shed light on future directions toward the prediction of Earth’s radiation environment.

22
JAN

Katherine Goodrich - Shocks Under the Microscope: Examining the Microphysics of Collisionless Shocks with High Resolution, Multi-point Space Plasma Measurements

2:30pm @ White Hall G09

Collisionless shocks are an important and universal phenomenon in astrophysical plasmas. Shocks form when a supersonic plasma flow interacts with an impermeable obstacle. Examples of such interactions include galactic jets or supernova remnants interacting with the interstellar medium, or plasma wind from stars encountering stellar system bodies, such as planets, comets and moons. The shock performs the necessary function of converting kinetic energy to thermal energy, heating the originally supersonic plasma flow until its speed is reduced and it can flow around the obstacle. The energy conversion processes that take place inside collisionless shocks, however, are not not well established and have thus been a subject of interest for several decades.