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.
Mercury’s Dynamic Magnetosphere: Insights from MESSENGER Measurements
April 26, 2024
3:30 p.m. - 4:30 p.m.
Slichter Hall 3853
Presented By:
- Dr. Weijie Sun - Space Sciences Laboratory, University of California, Berkeley
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Mercury is the planet closest to the Sun and does not have a significant atmosphere. Instead, it has a surface-bounded exosphere. Mercury also has a global intrinsic magnetic field that interacts with the solar wind to form a small magnetosphere. The magnetopause near the subsolar point is about one thousand kilometers above Mercury’s surface. The solar wind near Mercury’s orbit is stronger than that near Earth, with higher dynamic pressure and stronger interplanetary magnetic field intensity. In this presentation, we introduce our current understanding of Mercury’s magnetosphere based on the analysis of measurements from the MESSENGER spacecraft. We focus on the processes and couplings of solar wind, magnetosphere, surface, and exosphere. We present the Dungey cycle, flux transfer event showers on Mercury’s dayside magnetopause, Kelvin-Helmholtz waves, variations in planetary ions, and Mercury’s magnetosphere under extreme solar wind conditions. By summarizing these findings, we aim to enhance our understanding of Mercury’s magnetosphere and contribute to the broader field of planetary magnetospheric research.
Predicting the Radiation Belts and Precipitation with the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) Model
May 2, 2024
3:30 p.m. - 4:30 p.m.
Slichter Hall 3853
Presented By:
- Dr. Mei-Ching Fok - Geospace Physics Laboratory, NASA Goddard Space Flight Center
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Investigations of the dynamics of energetic particle fluxes in the Earth’s radiation belts and the associated precipitation have ample scientific significance and space weather applications. Data analysis and numerical simulation are two types of approaches commonly used to understand the radiation belt variations. In this presentation, we focus on simulation studies of the energetic particles in the inner magnetosphere and their precipitation into the ionosphere. Our main modeling tool is the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. CIMI can predict the cold plasma density, and the energetic ion and electron fluxes in space in the energy range from keV to MeV. Furthermore, CIMI is capable of predicting the Region 2 field-aligned currents, penetration electric field, energetic electron and ion precipitation and magnetospheric heat flux in the ionosphere. The CIMI model includes a realistic magnetic field configuration with a combination of an internal field and an external field. The internal field is usually assumed to be a dipole. Recently, the International Geomagnetic Reference Field (IGRF) has been implemented to replace the simple dipole field. This new capability enables studies of north-south and longitudinal dependences in particle precipitation and heat flux, as well as the corresponding asymmetries in ionospheric and thermospheric responses. In this talk, we will describe the current status of the CIMI model, including the new implementation of the IGRF model, and its applications in the study of the radiation belt precipitation.