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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.

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.

Remote-Sensing Magnetotail Dynamics from Low Earth Orbit with CINEMA

May 10, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Robyn Millan - Department of Physics and Astronomy, Dartmouth, Hanover, NH
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CINEMA (Cross-scale INvestigation of Earth’s Magnetotail and Aurora) is a NASA Small Explorer mission concept with the overarching goal to understand the role of plasma sheet structure and evolution in Earth’s multiscale magnetospheric convection cycle. How the magnetotail maintains steady convection, and when and how it decides to explosively release stored energy, are major unsolved mysteries of space physics. A significant challenge is the intrinsically multiscale nature of magnetotail convection; energy in the magnetotail flows between the largest (system-size) scales and smallest (kinetic) scales, mediated by mesoscale dynamics. Mesoscale flows (BBFs) play a particularly important role, responsible for much of the earth- ward plasma transport and for returning the magnetic field to a more dipolar configuration. CINEMA’s nine satellites in low-Earth polar orbits each carry an on-board imager, particle sensors, and magnetometers, and quickly traverse the low-altitude footprint of the magnetotail, capturing its evolution at different scales. CINEMA obtains information about the structure of the magnetotail remotely through its imprint on particle pitch-angle distributions, providing an unprecedented view of particle isotropy boundaries. Mesoscale aurora and bursty energetic particle precipitation serve as tracers of specific mesoscale and kinetic-scale dynamics. Field- aligned currents (FACs) that connect the magnetotail to the ionosphere are sensed by measuring magnetic field variations at each satellite. Combining remote sensing of plasma sheet structure and evolution with auroral imaging and measurements of FACs, CINEMA will provide key observations needed to understand magnetotail convection.

Ion escape from Mars and Venus: different worlds, different problems

May 17, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Shannon Curry - Laboratory for Atmospheric and Space Physics, CU Boulder, Boulder CO
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Both Mars and Venus are weakly magnetized planets, lacking a dipole magnetic field. Consequently, their upper atmospheres are directly exposed to the solar wind; neutrals get ionized and can escape as ions through a number of channels. While both planets formed at similar times and have CO2 atmospheres, they have evolved drastically differently. A number of missions have studied atmospheric escape at both planets, including the Mars Atmosphere and Volatile EvolutioN (MAVEN), Mars Express (MEX), Venus Express (VEX), Pioneer Venus Orbiter (PVO) and more recently the Parker Solar Probe (PSP) Venus flyby campaign. All of the missions except for MEX carried magnetometers and electrostatic analyzers to observe the magnetic fields and light and heavy ions, respectively. We will compare observed inputs from the Sun (EUV, solar wind, energetic particles and IMF) with the observed response of escaping atmospheric ions. We will specifically compare the physics of ion escape at Mars and Venus, including variables such as solar cycle, planetary size and artifacts of the observations themselves. Finally, I will discuss future missions and open questions. Understanding the dynamics of the Martian and Venusian atmosphere has significant implications for exoplanets and their atmospheres’ interaction with their host star, so these observations are important for the planetary, Heliophysics and astrophysics communities.

Plasma sheet electron scattering and precipitation driven by time domain structures

May 24, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Yangyang Shen - EPSS, UCLA
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Magnetospheric substorms are dynamic phenomena characterized by the global reconfiguration of the geomagnetic field and the violent release of stored solar energy, resulting in various forms of auroral displays in the nightside atmosphere. These energy releases are accompanied by fast plasma flows, magnetic flux transport, and particle acceleration, leading to complex, energy-dependent anisotropic distributions. The buildup of such anisotropy must necessarily be limited by plasma instabilities and wave-particle interactions. These plasma waves cause electron pitch-angle scattering and precipitation into the ionosphere, generating diffuse auroras from the plasma sheet and leading to loss of killer/relativistic electrons from the radiation belt. The wide energy range of precipitation, spanning from a few tens of eV to several MeV, suggests the operation of multiple mechanisms that aggregately scatter electrons into the loss cone. Recent advancements in observations and theory have shed new light on one such mechanism: electron scattering by time domain structures (TDS). TDSs appear as broadband electrostatic fluctuations in the frequency domain and manifest as electrostatic Debye-scale structures of electron phase space holes and double layers in the time domain. In this talk, we will discuss the characteristics of TDSs based on observations from THEMIS, Van Allen Probes, and MMS. We will explore how these structures contribute to electron scattering and precipitation through quasilinear analysis, and assess their significance in generating diffuse/diffuse-like auroral precipitation from the plasma sheet, by examining magnetically-conjugate observations between the magnetosphere and ionosphere.

The Science Case for the Magnetospheric Auroral Asymmetry eXplorer

May 31, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Michael Liemohn - Professor, University of Michigan | UMich · Climate and Space Sciences and Engineering College of Engineering
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Observations of the aurora have been used as a window to probe and understand the dynamics of the solar wind-magnetosphere-ionosphere (SWMI) system. A major limitation in our current understanding of the SWMI system is the nearly-exclusive northern-hemisphere view of the energy transfer processes. The Magnetospheric Auroral Asymmetry eXplorer (MAAX), a concept in Phase A study with the Heliophysics Small Explorer Program, would make a major leap forward in determining how magnetosphere-ionosphere electrodynamic coupling regulates multi-scale auroral energy cow through the near-Earth space environment. MAAX would comprise two observatories in circular high-altitude polar orbits for viewing of the full auroral ovals in both hemispheres. The motivation and major science objectives of MAAX will be presented and discussed.

Interpretation of the Geospace Plume Evolution by the MAGE Model

June 7, 2024
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

  • Dr. Shanshan Bao - Rice University | RiceU· Center for Geospace Storms, Houston, TX
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During geomagnetic storm times, multiscale dynamic processes establish throughout the geospace in response to the solar wind driving. The geospace plume, referring to the combined processes of the plasmaspheric and the ionospheric storm-enhanced density (SED)/total electron content (TEC) plumes, is one of the unique features of geomagnetic storms. The apparent spatial overlap and joint temporal evolution between the plasmaspheric plume and the equatorial mapping of the SED/TEC plume indicate strong magnetospheric-ionospheric coupling. To comprehensively investigate the driving factors for the geospace plume development, we employ the whole geospace model, Multiscale Atmosphere Geospace Environment (MAGE). In this talk, we will introduce the components and coupling scheme of the MAGE model, which are crucial for understanding the geospace plume from a coupled magnetosphere-ionosphere- thermosphere perspective. We will present the simulation results of the geospace plume in March 31, 2001 superstorm and unveil the major role of SAPS in shaping the geospace plume, as well as the self-consistent relationships among important storm- time dynamics, including the ring current buildup, SAPS and the geospace plume development.