Category: Space Physics
Date: 2025-12-05 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Sheng Tian
Abstract:
Alfvén waves, named after the Nobel laureate Hannes Alfvén, are a fundamental mode in magnetized plasmas. It has long been established that they play a key role in the energy circulation of the magnetosphere-ionosphere (M–I) coupling system. However, their dissipation on meso- and small-scales is much less well understood. Here, we examine how Alfvén waves drive several common meso-scale structures, including the auroral arcs, auroral beads, and the magnetospheric cusp. We find that Alfvén waves, although being the common energy source, are dissipated differently among these structures. In the auroral arcs, Alfvén waves power a quasi-static parallel electric field that accelerates ions away from and electrons toward the ionosphere. In the auroral beads, electrons are accelerated directly by the wave’s own parallel electric field. In the cusp, Alfvén waves significantly energize the outflowing ions, presumably through perpendicular heating. These distinct energy conversion processes we have unveiled are important in understanding the meso-scale M–I coupling on Earth and other planets. Our results also raise important questions for future studies: How are these Alfvén waves generated? What additional dissipation mechanisms may be operating? Why are Alfvén waves dissipated differently, and what are the controlling factors?
Date: 2025-11-21 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Rebecca L Bishop
Abstract:
TBA
Date: 2025-11-14 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Yangyang Shen
Abstract:
TBA
Date: 2025-11-07 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Stephen Fuselier
Abstract:
Magnetic reconnection occurs continuously along long X-lines at the Earth’s magnetopause. The maximum magnetic shear model provides accurate predictions for the locations of these long X-lines for a wide range of upstream solar wind conditions. One of the more perplexing observational results is that these X-lines appear to be stationary, even on the near-flank magnetopause in the presence of significant magnetosheath plasma bulk flow. An alternate possibility is that X-lines form in the location predicted by the maximum magnetic shear model but then immediately propagate with the magnetosheath plasma bulk flow away from this location. If the X-line reformation cadence is high enough and some other conditions are valid, then these multiple propagating X-lines could appear as a single quasi-stationary X-line at the location predicted by the maximum magnetic shear model. Magnetospheric multiscale observations are used to perform initial tests of this alternate possibility. Results from these initial tests show that there may be multiple X-lines near the predicted location of the X-line, and therefore this alternate possibility may have merit. This alternate possibility may have implications for the magnetospheric cusps. Magnetic reconnection at the magnetopause produces distinct energy-latitude ion dispersion features in the cusps. Multiple reconnection X-lines may produce overlapping dispersion features depending on how they are formed. Therefore, under the right solar wind conditions, there may be many instances of overlapping dispersion features. Observations from the Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) are used to investigate this possibility.
Date: 2025-10-31 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Sachin Reddy
Abstract:
Jupiter’s moon Europa is thought to possess a subsurface ocean that could have the right conditions to harbor life. It will be visited by the Europa Clipper mission starting in 2030. To characterize this ocean and answer questions about habitability, the complex and highly variable plasma environment must be accounted for. In this talk, I will introduce a novel machine learning framework, including both forward and inverse modeling, to better understand the environment. Crucially, our model can reproduce the magnetic field, helping us define the depth, salinity, and conductivity of a potential subsurface ocean. These findings benefit both the upcoming missions to Europa and proposed missions to other planetary bodies such as those at Uranus or Neptune.
Date: 2025-10-24 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Stuart Bale
Abstract:
TBA
Date: 2025-10-17 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Leonid Olifer
Abstract:
TBA
Date: 2025-10-10 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Craig DeForest
Abstract:
The Polarimeter to Unify the Corona and Heliosphere (PUNCH) is a constellation of four smallsats launching in Spring 2025 to image the solar corona and solar wind as a single unified system. The four satellites work together to form a single “virtual coronagraph” with a 90° field of view centered on the Sun. One satellite carries a coronagraph (the Narrow Field Imager) that captures the outer corona at apparent distances between 6 solar radii and 32 solar radii from the Sun. The other three carry heliospheric imagers with 42° wide fields of view, extending from 12 solar radii to 180 solar radii from the Sun. All instruments view visible light scattered by free electrons in the corona and solar wind and use linear polarization to generate 3D information about density structures in the plasma. In this talk, I will briefly describe some of the key background science and the mission itself, then discuss the enabling technologies of deep signal separation and polarimetric inversion to reveal 3D structure before presenting and discussing recent data from the constellation and how to obtain the data for your own use.
Date: 2025-10-03 00:00:00
Time: 3:30 – 4:30pm
Location: 3853 Slichter Hall
Presented By:
Zac Milby
Abstract:
The optical aurorae of Jupiter’s Galilean satellites are generated and maintained through a variety of processes. On Io, a combination of volcanism and sublimation produces its SO₂-dominated atmosphere. On the icy satellites Europa, Ganymede, and Callisto, sublimation and sputtering produce O₂-dominated atmospheres. Unfortunately, in situ observations have been limited to brief spacecraft flybys by missions focusing on Jupiter or those just passing through the system. Consequently, most of our knowledge of their atmospheric compositions has come from Earth-based UV observations using the Hubble Space Telescope. However, its small mirror size and orbital properties limit the signal-to-noise achievable and prevent HST observations from revealing short-timescale variability.
For the past four years, we have been observing Jupiter’s Galilean satellites using the HIRES instrument on the Keck I telescope at the summit of Maunakea, Hawaii. This instrument’s wavelength sensitivity allows us to simultaneously observe a variety of bright optical auroral emissions, and the large mirror of the Keck I telescope enables high-cadence observations with good signal-to-noise. In comparison to the UV emissions observable with HST, the larger number of optical lines allows us to place more robust constraints on atmospheric composition. We must also take the observations in eclipse to suppress reflected sunlight from their icy surfaces, as this limits the excitation of the auroral emissions by magnetospheric electrons, providing a remote-sensing window into the interaction between the satellites and their local plasma environment. In this talk, I will discuss what these observations have revealed about each satellite’s atmosphere and provide insights into the properties of the electrons exciting their auroral emissions.