Throughout the Fall 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 before the talk. Check for dates, speakers, and topics below. For further information on the Colloquium, please contact space_science_colloquium@uah.edu.
Important
In-person Colloquium will be held Fridays at 12:30pm in Cramer Hall (CRH), room 2096 and on dates provided for each speaking engagement. Refreshments are served for the audience at 12:00pm in the 2nd floor lobby. View Campus Map.
Covid-19 may be weakening, but it has not come to an end. Attendees of the colloquium have the option of wearing masks. If you have tested positive for Covid-19 or have been exposed to the virus, please follow the guidelines provided by the Centers for Disease Control and Prevention (CDC).
Parking: Visitors need to sign in at the Cramer Hall (CRH) front desk and have their ID in order to get a parking pass.
Date: 9/1/2023
Speaker: Vladimir Florinski, Professor, UAH
Title: Magnetic trapping of galactic cosmic rays in the VLISM and their preferential entry into the heliosphere
Abstract:
The subject of my presentation is the region of interstellar space adjacent to the heliopause, which is the magnetic boundary of the solar system. The distinctive draping pattern of the interstellar magnetic field around the heliopause creates an usual cosmic ray transport environment. A region of weaker magnetic field of about 300 au in size exists in the northern hemisphere that acts as a giant magnetic trap affecting the propagation of galactic cosmic rays. It is expected that a ring current is established consisting of energetic ions drifting around the interior of the magnetic trap, similar to that in planetary magnetospheres. The magnetic trap region is also a preferred site where cosmic rays penetrate into the heliosphere. I will also discuss cosmic-ray scattering and diffusion in a weakly turbulent magnetic field that includes a compressive component. Despite its remoteness, the region of the magnetic trap holds promise of new discoveries, and could potentially become a target of future multi-spacecraft missions, especially those using nuclear propulsion.
Date: 9/15/2023
Speaker: Qiang Hu, Professor, UAH
Title: Topology and Formation of Magnetic Flux Ropes
Abstract:
Magnetic flux rope is a type of magnetic field structure in space plasmas, especially as manifested in large-scale solar eruptions of coronal mass ejections. We provide a brief report on our recent event studies of its magnetic field configuration based on in-situ spacecraft measurements. We illustrate the complexity in its field-line topology by presenting three event studies employing a unique analysis method. In particular, we demonstrate the feasibility and challenges for advanced modeling approaches to combine/comply with two or more in-situ spacecraft datasets and additional multiple observations. We discuss the implications of our study for the formation of magnetic flux ropes across space plasma regimes.
Date: 10/13/2023
Speaker: Gary Webb, Principle Research Scientist, CSPAR, UAH
Title: Particle Acceleration in Relativistic Jet Shear Flows
Abstract:
A steady-state analytical model for particle acceleration owing to cosmic ray viscosity and fluid velocity shear in relativistic radio jets is investigated. Analysis of the work of Webb et al. (2018,2019,2020,2023) on particle acceleration by this mechanism is discussed. The flow velocity profile of the jet u=u(r) ez is directed along the z-axis of the jet, and depends only on cylindrical radius r about the jet axis, and u(r) is a monotonic decreasing function of r. The mean scattering time τ is a power law in momentum p, where p is the particle momentum in the scattering frame or fluid frame: τ= τ0 (p/p0)^α. Here α is a constant. The Green’s function solutions of the transport equation are obtained as an eigen-function expansion in terms of J0 Bessel functions (which depend on r) and power law
functions of p. The solutions are used to discuss particle acceleration by shear in jets. A leaky box model of electron acceleration by shear acceleration in jets developed by Rieger and Duffy (2019) and Wang et al, (2021) is used to discuss a cut-off momentum, beyond which the particle energy losses exceed the particle energy gains. The particle energy losses are due to synchrotron and inverse Compton losses. The competition between particle energy gains due to momentum space diffusion and synchrotron losses is studied. The spectral redistribution and flow lines of the accelerated particles are discussed.
Date: 11/3/2023
Speaker: Robert D. Preece, CSPAR Adjunct Professor, UAH
Title: The Spectroscopy of Gamma-Ray Bursts
Abstract:
For 50+ years, the study of gamma-ray bursts (GRBs) has eluded attempts to answer 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: 11/17/2023
Speaker: Jiong Qiu, Professor, Montana State University
Host: Qiang Hu
Title: Properties and energetics of three-dimensional magnetic reconnection in
two-ribbon flares
Abstract:
Energy release in solar flares is governed by magnetic reconnection, through which free magnetic energy is converted to heat, particle kinetic energy, and bulk motion. Some properties of flare reconnection can be
inferred from radiation signatures in the flaring chromosphere, in a way similar to the practice of tracking auroral rings in the ionosphere to infer properties of magnetic reconnection in the magnetosphere.
A large fraction of reconnection released energy is used to heat plasmas in post-reconnection flare loops, and hydrodynamic modeling constrained by spatially resolved, multiple-wavelength flare observations (particularly
by the Solar Dynamics Observatory) from the chromosphere through the corona allows us to quantify the amount of heating in post-reconnection flare loops. The results show that the efficiency of flare heating (and sometimes energy partition) varies during the evolution of the flare, and we explore whether and/or how this efficiency
is governed by three-dimensional properties of flare reconnection, such as those reflected in the strong-to-weak shear evolution of post-reconnection
flare loops in two-ribbon flares.
Date: 12/15/2023
Speaker: Andreas Shalchi, Professor, University of Manitoba Japan
Host: Lingling Zhao, G. P. Zank
Title: Transport of Energetic Particles: Simulations, Heuristic Arguments, and Analytical Theories
