This Seminar is Cancelled,
University of Michigan
Our recent modeling work reconstructed the thermodynamic evolution of several plasma structures (prominence, prominence-coronal transition region, and coronal-like plasma) within the radial expansion of a coronal mass ejection (CME) by examining heliopsheric ion composition within the ejecta. This study suggested that the components experienced rapid, continuous, and non-uniform heating as they travelled away from the Sun. The work indicated that comprehensive CME studies require multi-wavelength plasma observations along with a wide off-limb field of view to capture the extent of the evolution. However, the dynamic nature of the eruption makes it difficult to capture the plasma’s temporal and spatial evolution with a single narrowband imager or high resolution spectrometer
National Solar Observatory
Even after decades of detailed study, many mysteries about the solar chromosphere remain. Making progress on these questions will be a key focus of solar physics in the coming years. In this talk, I will show recent work in this area combining imaging spectroscopy in the optical using the Interferometric Bidimensional Spectrometer (IBIS) and millimeter diagnostics from the Atacama Large Millimeter Array (ALMA). Using these instruments, we can probe the chromospheric temperature structure and dynamics on time scales of tens of seconds and at spatial scales of a few 100 km. We find evidence that spectral-line parameters of H-alpha and Ca II are closely correlated with the ALMA brightness temperatures. I will discuss how this changes our understanding of chromospheric dynamics and the interpretation of the observed spectral intensities. Finally, I will provide an overview of advances we expect on these questions from the soon-to-be-operational DKI Solar Telescope (DKIST).
Dipolarizing flux bundles (DFBs) are flux tubes in Earth’s magnetotail, which have larger Bz than the background. These bundles are most likely generated by near-earth tail reconnection. After they are generated, they propagate earthward (as bursty bulk flows) and carry strong electric fields. Their strong electric field can energize particles. If DFBs can bring these energized particles into the inner magnetosphere, they can impact the particle population of the ring current and the radiation belt. Even if a DFB cannot reach the inner magnetosphere, it may still impact the particle population there by sending ultra-low-frequency waves. In this talk, I explore the possible ways that DFBs can transport their energy to the inner magnetosphere.
Because solar wind plasma flow transports the entire spectrum of magnetic field fluctuations (from low-frequency inertial range to electron kinetic range), it is a natural laboratory for plasma turbulence investigation. Among the various wave modes and coherent plasma structures that contribute to this spectrum, one of the most important solar wind elements is ion-scale solar wind discontinuities. These structures, which carry very intense current, have been considered as a free energy source for plasma instabilities that contribute to solar wind heating. Investigations of such discontinuities have been mostly focused on their magnetic field signatures; much less is known about plasma kinetics around them. This presentation discusses statistics of such discontinuities observed around the Earth (~1 AU) by ARTEMIS and MMS mission and around the Mars (~1.5AU) by Maven mission. The main focus is on their kinetic structure and force balance.
University of Michigan
Dipolarizations in Earth’s magnetotail play a major role in plasma and magnetic flux transport, particle heating and acceleration, and substorm current wedge formation. Mercury, whose magnetosphere closely resembles Earth’s topologically, also experiences dipolarizations despite Mercury’s shorter spatiotemporal scales and lack of an ionosphere. In light of these magnetospheric differences, we investigate the nature of dipolarizations at Mercury using MESSENGER spacecraft observations. We discuss how differences between the magnetospheres influence dipolarization dynamics and how the implications of our results may shape our understanding of the substorm process at terrestrial planets.