Colloquia are held in DeMeritt Hall Rm 240 at 4:00pm on Mondays, unless otherwise noted
Dynamo process and momentum transport in astrophysical
disks
Fatima Ebrahimi, University of New Hampshire
Monday, January 25, 2010
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 pm
Abstract
Accretion, the inflow of matter into a central object, is an important process
in astrophysical plasmas. With matter collapsing into a rotating disk around a
compact object, such as a black hole or young stellar object, angular momentum
is rapidly transported outward. Collisional hydrodynamic viscosity alone is not
enough to explain the accretion process in disks and the associated momentum
transport. One possible source of anomalous viscosity is turbulence resulting
from the Magneto-Rotational Instability (MRI) [Velikhov 1959; Balbus and
Hawley 1991]. We show that stresses arising from MHD instabilities, flow-driven
and current-driven, can contribute to rapid transport of angular momentum in
astrophysical disks. It will also be shown that the transport process and MHD
dynamo (generation of large-scale magnetic field through complex flows) are
inseparable. We investigate the possibility of magnetic field generated by MRI
and whether the combination of differential rotation and a weak magnetic field
can produce an MHD dynamo. We discuss small-scale dynamo action in an
MRI-driven turbulent state using 3-D nonlinear computations. In a rotating
disk the saturation mechanism of the MRI through the generation of large-scale
magnetic field will also be presented.
The Evolving Three-Dimensional Heliosphere
Professor Nathan Schwadron, Boston University
Monday, February 1, 2010
DeMeritt Hall, Room 240
DeMeritt Hall, Room 240
Talk: 4:00 - 5:00 PM
Abstract
Through observations of the Sun and the protective heliosphere surrounding our solar system we have uncovered an increasingly sophisticated understanding of how the Sun changes through the solar cycle and how those changes influence the space environment. Relatively recent observations suggest the existence of universal behavior that applies not only at our own Sun but at stars and in plasmas throughout the universe. Moreover, we have started to uncover general behavior in the long-term evolution of solar wind, its relationship to the global heliosphere, to energetic particles and to galactic cosmic rays. These new developments push into new territory concerning the long-term evolution of the coupled solar-heliospheric system. Thus, we explore the realm of the evolving three-dimensional heliosphere and its growing implications for our understanding of our home in the galaxy.
A Most Peculiar Solar Minumum
Professor Toni Galvin, University of New Hampshire
Monday, February 8, 2010
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 pm
Abstract
The Sun is a variable magnetic star that exhibits changes on multiple time scales, ranging from the tick of a quantum clock to millennia.
Variations of interest to us as a societal species range from several minutes in the case of explosive events that create “space weather”, to the 11-year solar cycle and variations in that cycle over hundreds of
years that may be linked to climate effects. Studying the sun and its
effects on Earth and near-Earth space, understanding causes of the Sun’s variability, and predicting that variability are primary scientific objectives for a number of space and earth science missions and investigations. Today’s constellation of heliophysics missions, including SOHO, STEREO, Hinode, Wind, ACE, and (until recently) Ulysses provide unprecedented remote imaging of the Sun and multi-point measurements of the solar wind, fields, and solar energetic particles.
Modeling of the solar dynamo and modeling of solar wind propagation are quite sophisticated. Yet the length and depth of this recent “peculiar”
solar minimum and its effects on the Sun-Earth system caught nearly everyone by surprise. We will look at the Sun and its variability in both the recent and historical context, and how this exceptional minimum is furthering our understanding and appreciation of “living with a star”.
The Ins and Outs of Martian Mini-Magnetospheres
Dr. Dave Brain, UC Berkeley
Monday, February 15, 2010
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 pm
Abstract
Measurements of magnetic fields and charged particles near Mars made over the past four decades have taught us about its plasma environment, upper atmosphere, near-surface radiation environment, subsurface, and deep interior. The upper atmosphere and plasma environment of Mars are of interest because they are the sites of energy exchange between the planet and its surroundings, dominated by the Sun and solar wind. For this reason they may have played a critical role in martian climate evolution. A number of recent spacecraft observations demonstrate that the exchange of particles and energy between the solar wind and atmosphere is particularly dynamic at Mars because strong localized crustal magnetic fields form mini-magnetospheres that rotate with the planet, influencing the motion of charged particles. I will discuss two observed influences of crustal fields on particle motion near Mars and their implications: episodic escape of atmospheric particles via detached crustal fields and localized energy deposition characterized by ultraviolet aurora on the Martian night side.
Remote Sensing - It's Not Just for Photons Anymore
Dr. Eileen Chollet, Cal Tech
Monday, February 22, 2010
DeMeritt Hall, Room 240
Coffee: 3:30 pm - Physics Common
Talk: 4:00 - 5:00 pm
Abstract
Photons are only one type of highly-mobile particle that can be used for remote sensing, and both light observations and particle observations give information about environments that are too distant to be sampled directly. In this talk, I will present observations and numerical models of energetic ions and electrons in a variety of solar system environments to demonstrate how energetic particles can be used to find the topology of distant magnetic fields. Since particle properties at the observer reflect their entire lifetime, they can be used to study the source regions where particles are accelerated to high speeds as well as the plasma structures between the observer and the source. I will demonstrate both of these capabilities using examples from the solar wind and the Jovian magnetosphere. Energetic particles can be used as a new and unique remote sensing tool in an astrophysicist's toolkit.
Collisionless Shocks in the Heliosphere and Beyond
Professor Harald Kucharek, University of New Hampshire
Monday, March 1, 2010
DeMeritt Hall, Room 240
Coffee: 3:30 pm - Physics Common
Talk: 4:00 - 5:00 pm
Abstract
Shock waves are a very central feature of astrophysical plasmas, ranging from the Sun, to the heliosphere, and distant galaxies. Shocks transfer large amounts of energy from directed plasma flows into thermal ion motions. Space plasmas are usually collisionless, and the physics of the shock involves a wide range of plasma phenomena, some of which are imperfectly understood. Collisionless processes at the shock not only heat the plasma passing through the shock, but they also result in a significant fraction of the fluid flow energy being put into energetic particles. These resulting energetic particles are ubiquitous in space, and are a significant hazard to the exploration of space. Charged particle energization by shock waves generated during supernova explosions is believed to provide the main acceleration mechanism for cosmic rays. These energetic particles have other important effects on the Earth’s environment in space. For several decades the near-Earth environment was our in-house laboratory to study these collisionless processes. Multi-spacecraft missions such as Cluster have provided many new insights into the physics of collisionless shocks. With Voyager’s I and II in-situ measurements at the termination shock and the data being returned by the Interstellar Boundary EXplorer (IBEX), a new frontier has been reached to study these collisionless plasma phenomena at larger objects, such as the heliospheric termination shock, and thus build a bridge to astrophysical settings .
Astronomical Optical Interferometry with the Navy Prototype Optical Interferometer
Professor Anders Jorgensen, New Mexico Tech
Thursday, March 4, 2010
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 pm
Abstract
Stars are small. When seen from the Earth with traditional astronomical telescopes virtually all stars are completely unresolved That means that most of the information we obtain about stars are obtained only from their spectra, not from direct observations of their shapes and sizes. Estimates of diameters and surface features can be made based on second order effects in the spectra, but there is a limit to how far such information can be pushed. An alternative is to use much larger telescopes. The resolution of a telescope is inversely proportional to its diameter such that larger telescopes can resolve smaller angular sizes. However, to resolve a typical bright star requires a telescope mirror with a diameter of well over 100 m. On top of that, such a mirror must be actively corrected to compensate for atmospheric turbulence, making it a extremely costly and complicated proposition. An alternative is to use a stellar interferometer, which consists of an array of much smaller telescopes. The first stellar interferometer was used by Michelson and Pease on the Mount Wilson 100 inch telescope to measure the diameter of several stars. Since then a number of of interferometers have been built, almost all of them experimental or prototypes. Only very recently are service observatories being built and operated. The developments are taking much longer than for radio interferometers because of the complications associated with the atmosphere, very low SNR, real-time control systems, and the sheer cost of such specialized observatories. In this talk I will review the basics of astronomical optical interferometry, including why optical interferometry is so difficult, discuss examples of developments at existing and pending observatories, and then discuss my own work in stellar optical interferometry.
Aurora - Its Complexity and Scientific Importance
Dr. Marc Lessard, University of New Hampshire
Thursday, March 4, 2010
DeMeritt Hall, Room 240
Coffee: 4:00 pm - Physics Common
Talk: 4:30 - 5:00 pm
Abstract
Dr. Marc Lessard of UNH Physics Department and Space Science Center and a candidate for the Sub Orbital Faculty position will present Auroral displays are essentially the final step in complicated sequences of events involving the transfer of energy from the solar wind to the upper atmopshere. While the basic processes that excite aurora have been well−understood for decades (i.e., electrons and protons colliding with the particles in the upper atmosphere), new discoveries about how these processes develop and subsequently evolve, as well as how they relate to the broader questions of magnetosphere-ionosphere coupling, are continually emerging. Electrons and protons that excite aurora can originate from within many regions in the magnetosphere (or even the ionosphere) under different conditions, a fact that highlights two aspects of auroral research. One is that the different processes that drive aurora can be quite complex and can span a wide range of spatial and temporal scales, complicating efforts to understand these processes. The other question is, essentially, how to use auroral displays to reveal, in part, how the magnetosphere evolves in response to different solar wind drivers.
Historically, perhaps the most effective tool for carrying out auroral research has been the sounding rocket. Rocket platforms provide opportunities to conduct highly targeted research in the sense that their instrumentation, launch sites, trajectories and launch conditions can all be aimed at specific science problems. In this presentation, an overview of different types of auroral forms will be discussed, as well as recent results from various sounding rocket missions.
TBA
Professor Jian-Ming Tang, University of New Hampshire
Monday, March 29, 2010
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 pm
TBA
Professor Olof Echt, University of New Hampshire
Monday, April 5, 2010
DeMeritt Hall, Room 240
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 pm
TBA
Professor Marcelo Gleiser, Dartmouth University
Monday, May 10, 2010
DeMeritt Hall, Room 112
Coffee: 3:40 pm - Physics Common
Talk: 4:00 - 5:00 pm
