Space Physics Seminar - winter-2023


Magnetosphere-Ionosphere Coupling Between North-South Propagating Streamers and High-Speed Earthward Flows

Jan. 13, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • James Weygand, - UCLA
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The magnetosphere-ionosphere coupling between the high-speed earthward flows and the north-south oriented streamers in the ionosphere has been discussed for decades, but to date, no one has examined the formation of that coupling from the start of the streamer to the end. We investigate the formation and development of the magnetosphere-ionosphere coupling using THEMIS observations of high-speed earthward flows within the magnetotail, simultaneous auroral all-sky images, and ionospheric equivalent current maps derived from ground magnetometer measurements. We show the formation of a downward field-aligned current on the dawnside of the north-south streamer and the upward current on the duskside, as well as the vortices within the equivalent currents around the field-align-like currents from the poleward boundary to the equatorward edge of the auroral oval for two substorm streamer events. By removing the background Birkeland current system, we can determine the current densities uniquely associated with the streamer current wedge and demonstrate that the downward and upward currents within the streamer are approximately balanced for one event. Furthermore, we find that the longitudinal size of the streamer current wedge is more transient and localized, and does not change, whereas the substorm current wedge is larger and expands during the first part of the substorm.


Characterizing auroral precipitation and ionospheric conductance with the Multiscale Atmosphere-Geospace Environment model

Jan. 20, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • Dong Lin - HAO/NCAR
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Auroral precipitation plays an important role in the magnetosphere-ionosphere-thermosphere (MIT) coupling. Various precipitation spectra have been observed and they are driven by different physical mechanisms. In this study, we report the characterization of auroral precipitation in the Multiscale Atmosphere-Geospace Environment (MAGE) model, a newly developed fully coupled whole geospace model. Diffuse electron precipitation is derived with a drift-physics based ring current model, in which electron lifetime due to interactions with chorus and hiss waves is obtained with an empirical table and electron loss rate is informed by drift physics and IGRF magnetic field. Mono-energetic electron precipitation is derived from large-scale field-aligned currents and their relationship with electrostatic potential drop. Broadband electron precipitation is derived from a statistical relationship between field-aligned Alfvénic Poynting flux and the precipitation energy flux and number flux. Auroral ionospheric conductance is self-consistently calculated by simulating the ionization profiles of auroral precipitation in an IT general circulation model that is two-way coupled with the magnetosphere-ring current model. I will also discuss how different types of auroral precipitation impact ionospheric conductance and their roles in MIT coupling


High-frequency electrostatic waves driven by electron crescents in electron diffusion regions

Jan. 27, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • Wenya Li - National Space Science Center, Chinese Academy of Sciences
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Magnetic reconnection is a fundamental and universal process, which transfers energy stored in the magnetic field to kinetic and thermal energies of charged particles. NASA’s Magnetospheric Multiscale (MMS) mission was designed to investigate the electron-scale physics of reconnection in the Earth’s magnetosphere. The four MMS spacecraft have encountered tens of electron diffusion regions (EDRs) at the magnetopause and in the magnetotail, and various types of plasma waves, including lower-hybrid and whistler waves, have been reported in and near EDRs. Recent studies reveal that two types of high-frequency electrostatic waves (upper-hybrid waves and electron Bernstein waves) can be driven by the crescent-shaped agyrotropic electron distribution functions in several EDR events. The large-amplitude electrostatic waves can thermalize electrons and change the electron pressure tensor. Therefore, the electrostatic waves have capability to modify the balance of reconnection electric field and have feedback on the reconnection process.


Magnetic Topology at Mars and Venus

Feb. 3, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • Shaosui Xu - Space Sciences Laboratory, University of California, Berkeley
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The Venus and Mars interactions with the solar wind are often compared because both planets lack a substantial intrinsic global magnetic field, and both have CO2-dominated atmospheres thick enough to form an ionosphere (ionized atmospheric layer). To first order, their magnetospheres are mainly induced in nature, with draped interplanetary magnetic fields (IMF) dominating their topology. However, this simple picture can be complicated by the magnetization of the ionosphere at Venus and Mars’s localized crustal field magnetism. An important property of these planet-solar wind interactions is the magnetic field’s connectivity to the collisional ionosphere/atmosphere, and possibly the planet's surface. This can provide insights into the induced magnetization state of their ionospheres, the possible particle and energy exchange between their ionospheres and the solar wind, and the impact Mars’s crustal fields have on its near-space environment. Suprathermal (>1 eV) electrons are easily magnetized and excellent tracers of magnetic topology. In this talk, we describe the use of combined electron energy and pitch angle distributions measured by Venus Express and Mars Atmospheric Volatile and EvolutioN (MAVEN) to infer magnetic topology at Venus and Mars, respectively. The results highlight the contribution of Mars’s crustal fields to its ‘hybrid’ magnetosphere, and shed new light on Venus’s not-so-simple induced magnetosphere.


On the evolution of Saturn’s ring-moon system and Ocean World Enceladus

Feb. 10, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • Sean Hsu - CU Boulder
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Seminar Description coming soon.

The Science Surprise of Juno’s Stellar Reference Unit – how a low-light engineering camera became a high-profile science instrument on NASA’s Juno mission at Jupiter

Feb. 17, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • Heidi Becker - JPL
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Extreme Plasma Heating and Flows in Earth’s Ionosphere

March 3, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • David Knudsen - Univ. of Calgary
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During quiet times, Earth’s ionosphere is relatively cool by space standards, with temperatures of 2,000 K (~0.2 eV) or less. However, the ionosphere can be highly disturbed in the presence of the aurora, which during active periods deposits hundreds of GW into the high-latitude atmosphere via the ionosphere. This energy comes from the magnetosphere in the form charged particle precipitation, Joule or frictional heating in the lower ionosphere, and wave-particle interactions at higher altitudes. The latter pathway can result in ion temperatures of the order of a million K – comparable the temperature of the solar corona. While such extremes have been measured for many decades in the magnetosphere, until recently they were not reported below 500 km altitude – within the main ionosphere – due to damping and dissipation caused by collisional interaction with the neutral atmosphere. High-time-resolution imaging of particle distribution functions made possible by recent satellite missions has in fact revealed the presence of extreme temperatures within the main ionosphere - typically in highly localized regions of the order or less than 1 km wide, which are traversed in only a fraction of a second in low Earth orbit. This talk will describe a new generation of particle instrument that has made possible the detection and characterization of these extreme regions, and their importance to geophysics and plasma physics.


Remote Sensing of Galilean Satellites

March 10, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • Katherine de Kleer - Caltech
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Solar Wind and CMEs

March 17, 2023
3:30 p.m. - 5:30 p.m.
Slichter 3853

Presented By:

  • Meng Jin - LM/SETI
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Seminar Description coming soon.