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Space Physics Seminar - spring-2024

Local generation of Alfvénic turbulence through the outer radiation belt

April 5, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Chris Chaston - University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, USA
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A recurrent feature of the outer radiation belt during intervals of enhanced geomagnetic activity is the occurrence of broad spectrum low frequency electromagnetic fluctuations. These fluctuations while primarily Alfvénic are not well characterized as plane waves. Reconstructions of observed wave spectra from Van Allen Probes observations using a generalized polarization technique show these fluctuations to be composed of an ensemble of vortices and filamentary currents. While similar observations at high latitudes are generally attributed to wave sources in the plasma sheet and its boundary layers, at lower L-shells and through the outer radiation belt the connection to such a source is perhaps less convincing. In this presentation it is shown how flow channels existing on closed field-lines in the inner magnetosphere and outside the plasmapause may self-generate a broad spectrum of fluctuations that are best described as Alfvénic turbulence. Observations of one such channel observed from the Van Allen Probes and populated by Alfvénic fluctuations is used to define a numerical simulation based on a fluid-kinetic approach to examine the stability of these flow channels. It is shown that the channel is unstable to a Kelvin-helmholtz instability which establishes a system of counter-propagating Alfven waves or eigenmodes along the geomagnetic field that non-linearly interact to drive a cascade down to kinetic scales. Continual driving of the channel by magnetospheric convection generates an intensified and persistent spectrum of fluctuations with properties similar to those observed. These features may be related to the popular low latitude auroral forms termed STEVEs. Time permitting some implications of this process for radiation belt electron transport, scattering and energization may be discussed.

Stratospheric space weather on Jupiter: auroral-driven heating, chemistry and dynamics

April 12, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

  • Dr. James Sinclair - JPL, Caltech
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Jupiter has the largest and strongest planetary magnetosphere in our solar system. Energy from the magnetosphere and solar wind are ultimately deposited as deep as the middle atmosphere, thereby modulating the stratospheric thermal structure, hydrocarbon chemistry and dynamics at altitudes significantly deeper and at magnitudes larger than analogous processes on other planets. Using mid-infrared imaging and spectroscopy of Jupiter’s auroral regions from Earth-based telescopes and spacecraft, a radiative transfer analysis will be presented to quantify this “stratospheric space weather” and the physical processes driving it.

Signatures of atmospheric escape in the exoplanet population

April 19, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

  • Hilke Schlichting, PhD. - Professor of Exoplanets & Planetary Science, Associate Dean for Research, Physical Sciences, Department of Earth, Planetary & Space Sciences, UCLA, Los Angeles, CA
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Hydrodynamic models of atmospheric escape successfully explain a variety of population level features seen in the small, close-in exoplanet population. In my talk I will briefly review the leading atmospheric escape models and their expected observational signatures. I will then show how for a small sub-set of exoplanets atmospheric escape can be detected directly through Lyman-alpha observations of their transits, and present the first of such a detection for a small close-in sub-Neptune exoplanet.