Throughout the Spring Semester Space Science and CSPAR will be conducting a Colloquium. We invite both faculty and students to join us! Refreshments for the audience are served after the talk. Check for dates, speakers, and topics below. For further information on the Colloquium, please contact space_science_colloquium@uah.edu.
Important
Covid must be test negative. Masks are required for in-person Colloquium. In-person Colloquium will be held Fridays at 12:00pm in Cramer Hall (CRH), room 4078 and on dates provided for each speaking engagement. View Campus Map.
Parking: Visitors need to sign in at the Cramer Hall front desk and have their ID in order to get a parking pass. View Campus Map.
Date: 2/3/23
Speaker: Robert D. Preece, Professor, UAH
Title: Lessons Learned from Time-resolved Spectroscopy of Gamma-Ray Bursts
For 50 years, gamma-ray bursts (GRBs) have eluded answering some very important questions: What powers them? What is the emission mechanism? and What is the composition of their jets? I believe that there are clues to finding the answers to these questions in GRB time-resolved spectroscopy. I will outline what we know from spectroscopic studies, what we can infer and conclude with some well-informed guesses.
Date: 2/17/23
Speaker: Nikolai Pogorelov, Distinguished Professor of Space Science, UAH
Title: Heliosphere in the Local Interstellar Medium
The Sun moves with respect to the local interstellar medium (LISM) and modifies its properties to heliocentric distances as large as 1 pc. The solar wind (SW) is affected by penetration of the LISM neutral particles, especially H and He atoms. Charge exchange between the LISM atoms and SW ions creates pickup ions (PUIs) and secondary neutral atoms that can propagate deep into the LISM. Neutral atoms measured at 1 au can provide us with valuable information on the properties of pristine LISM. Voyager 1 and 2 spacecraft perform in situ measurements of the LISM perturbed by the presence of the heliosphere and relate them to the unperturbed region. We discuss observational data and numerical simulations that shed light onto the mutual influence of the SW and LISM. Physical phenomena accompanying the SW–LISM interaction are discussed, including the coupling of the heliospheric and interstellar magnetic field at the heliopause.
Date: 3/24/23
Speaker: William Matthaeus, Distinguished Professor of Physics, University of Delaware
Title: Dissipation in Space Plasmas
When collisions are strong in a magnetized plasma, standard closures provide simple representations of dissipation in terms of coefficients of viscosity and resistivity. In the opposite limit of weak collisions, the same underlying physical effects that lead to dissipation are present, but the simple approximations to describe them, the closures, are not available in general. But how different are these relationships when collisions are absent? We review a formalism based on the Vlasov-Maxwell equations that demonstrates the pathways of energy conversion among different forms. We highlight the production of internal energy by pressure-strain and pressure-dilatation interactions. These terms can also be scale filtered to study transfer across scales. Here we inquire as to whether the collisionless case admits statistical relationships analogous to the viscous and resistive closures found in collisional plasma theory plasma. We employ kinetic PIC simulation in two and a half and three dimensions, as well as MMS observations in the magnetosheath, to examine analogous viscous-like and resistive-like scalings in the weakly collisional regime.
Date: 3/31/23
Speaker: Jakobus Le Roux, Professor, UAH
Title: Modeling the Interaction of Energetic Particles with Small Scale Magnetic
Flux Rope Structures in the Inner Heliosphere
Evidence is mounting that the intermittent turbulent nature in the solar wind can partly be explained because small-scale magnetic flux ropes (SMFRs), as part of a non-propagating quasi-2D MHD turbulence component, have a strong presence in the inner heliosphere, as has been predicted for many years. The PDF of the magnetic field component increments of these nonlinear structures is characterized by non-Gaussian power-law statistics with strong tails generated by abrupt SMFR boundaries separated by secondary small-scale current sheets. By implication, induced or motional electric field components are expected to have the same statistical features. Thus, there is good reason to think that energetic particles interacting with SMFRs in the solar wind should exhibit disturbed particle trajectories displaying non-Gaussian power-law statistics. This should result in anomalous diffusive energetic particle transport on intermediate time scales when particles follow magnetic field lines with a transition to normal diffusive behavior at later times. In this talk I will present newly developed focused and Parker-type tempered fractional diffusion-advection equations derived from first principles that model the anomalous diffusive propagation and energization of energetic particles in a dynamic SMFR field on intermediate time scales as well as the later time transition to more normal diffusive states. I will discuss explorative solutions of the fractional Parker transport equation to investigate (1) superdiffusive shock acceleration of energetic particles at a parallel shock imbedded in a SMFR field, and (2) acceleration of energetic particles by dynamic SMFRs when both parallel spatial transport and acceleration are time-fractional superdiffusive processes.
Date: 4/7/23
Speaker: Yu Lin, Professor of Physics, Auburn University
Title: Magnetopause reconnection viewed from global hybrid simulation: magnetic flux ropes and ion precipitation
Magnetic flux ropes exist widely in solar and space plasmas. In the terrestrial magnetosphere, they are generated during magnetic reconnection at the magnetopause (causing flux transfer events (FTEs)) and in the magnetotail, and are believed to play essential roles in transport of plasma and electromagnetic energy between the solar wind and the magnetosphere. In the solar atmosphere, twisted flux ropes are a fundamental structure in pre-eruption magnetic field and the eruptions.
In this talk, I will discuss the physics of flux ropes at the magnetopause based on 3D global hybrid (fully kinetic ions + electron fluid) simulations of the magnetosphere, in its dynamic interaction with the solar wind. Specifically, I will discuss the formation of flux ropes by time-dependent reconnection, as well as their global configuration and dynamic interaction. The simulation results of electromagnetic field structures and ion velocity distributions will be compared with in-situ observations from NASA’s Magnetospheric Multiscale (MMS) mission. In addition, reconnection leads to direct entry of charged particles from the solar wind into the cusp magnetosphere and ionosphere. A dispersive signature of low energy cutoff is observed in the energy spectrum of the cusp precipitating particles. Such signature is believed to be a fingerprint of the magnetopause reconnection. Using the global hybrid simulation that treats ions in the particle-in-cell manner, ion acceleration in reconnection and the particle global trajectories can be traced self-consistently. I will discuss how our global hybrid simulations will provide a theoretical support to the Tandem Reconnection And Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission, in which two spacecraft will fly through the cusp to determine the spatial and temporal natures of reconnection at the magnetopause.
