Space Physics Seminar

semester, 2018


Tuesday, January 16th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Tuesday, January 23rd 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
To be announced.

Tuesday, January 30th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Oleksiy Agapitov, Space Sciences Laboratory, University of California, Berkeley
Subject: Nonlinear wave-particle and wave-wave interactions in the outer radiation belt: physical mechanisms and observational effects

Tuesday, February 6th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Dr. Ricky Egeland, High Altitude Observatory, National Center for Atmospheric Research.
Subject: A Critical Rossby Number for Sun-Like Variability

Despite centuries of observation and decades of theoretical work, the ~11 year solar magnetic sunspot cycle remains one of the longest-standing unsolved problems in astrophysics. Additional insights can be made using synoptic observations of proxies for magnetism in other stars, where the varied stellar properties set the conditions for separate "dynamo experiments." We examine the decadal-scale variability in Ca II H & K emission of the Sun and a set of 26 solar analog stars within ~5% of the solar effective temperature but with varied mean rotation. Using a quantitative metric for determining cycle quality, we find that cycles of the highest quality—like the Sun's—occur in the stars with slower rotation and lower mean activity. Reexamining the results of a larger set of ~100 stars from the Baliunas et al. 1995 study of Mount Wilson H & K emission, we find again that the highest quality cycles occur for low activity and high Rossby number, the ratio of the rotation period to the convective turnover time. Guided by these observations, we propose the hypothesis that Sun-like variability—either a clean, monoperiodic cycle or flat activity analogous to the Maunder Minimum—occurs in G- and K- type main-sequence stars if and only if the Noyes et al. 1984 semi-empirical Rossby number is larger than 1.5, or equivalently if the star is on the low-activity side of the Vaughan-Preston gap. These results demonstrate the critical role of the Rossby number in determining the behavior of stellar dynamos.


Tuesday, February 13th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Tuesday, February 20th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Pat Meyers, University of Minnesota
Subject: Extremely low frequency electromagnetic waves and gravitational-wave detectors

The current generation of gravitational-wave (GW) detectors has already made phenomenal discoveries. One of the next frontiers of GW astrophysics is a measurement of the stochastic gravitational-wave background (SGWB). The SGWB is a superposition of many unresolvable stellar sources of GWs and potentially GWs from the earliest epochs of the Universe. Current searches for an SGWB rely on long cross-correlation measurements made with data from detectors separated by thousands of kilometers. The most likely source of correlated noise between detectors this far apart is extremely low frequency, persistent, electromagnetic waves like Schumann resonances. I'll discuss how these waves are produced, some recent measurements made using a global network of magnetometers, and how the waves can couple into GW detectors. Finally, I'll discuss development of methods to budget for and potentially subtract them from the GW data.


Tuesday, February 27th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Practice Talks for the upcoming Chapman Conference on Particle Dynamics in the Earth's Radiation Belts.

Tuesday, March 6th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Tuesday, March 13th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
No Seminar this week, spring break

Tuesday, March 20th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: David Malaspina, LASP, University of Colorado
Subject: Plasma Boundaries: Bridging Macro-Scale and Micro-Scale Plasma Physics

Plasma physics research is frequently focused on either macro-scale or micro-scale processes, often treating them as independent. Yet recent advances in spacecraft instrumentation, simulation, and laboratory studies are breaking down that paradigm, demonstrating that interactions between large and small scales are critical to understand and predict the behavior of systems as diverse as laboratory plasmas, the solar wind, and the terrestrial magnetosphere. In each of these systems, plasma boundaries act as a bridge between scales. Macro-scale plasma motions drive boundary formation, micro-scale instabilities develop or are spatially sorted as a consequence of these boundaries, and finally, the aggregate effect of many micro-scale interactions modifies the macro-scale system. Examples of interaction between macro- and micro-scale physical processes mediated by plasma boundaries in laboratory plasmas, the solar wind and the terrestrial inner magnetosphere will be discussed, with a focus on observational data.


Wednesday, March 28th 2018
3:30 pm:
Space Physics Seminar in Physics 201-20
Speaker: Barry Mauk, APL
Subject: Comparing the energetic particle populations of planetary magnetospheres

We compare planetary magnetospheres in different ways. Do we observe the same phenomenology? Are the same physical processes in play? It is, in fact, a challenge to compare planetary space environments quantitatively in a fashion that leads to a more predictive understanding. I examine here the differences and similarities of the strongly magnetized planetary magnetospheres of the solar system by examining their most energetic particle populations. For both trapped electron radiation and energetic ions comprising ring current populations, updated and extended versions of the classic Kennel-Petschek theory provide reasonable metrics for quantitatively comparing the populations of all of the strongly magnetized planetary magnetospheres. These comparisons are substantially revealing with regard to the character and states of the space environments of the respective planets. Comparisons between Earth and Jupiter are of particular interest in that these two environments are representative of the extremes of magnetospheric conditions; one the canonical solar-wind-driven magnetosphere and the other the canonical rotationally-driven magnetosphere. And yet, both are extremely active and energetic in their own ways.

Faculty Host: Robert Lysak

Tuesday, April 3rd 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Xianzhe Jia, University of Michigan, Dept. of Climate and Space Physics and Engineering
Subject: Global MHD Simulations of Saturn’s Magnetosphere

At Saturn’s orbital distance of ~ 9.5 AU, the low solar wind dynamic pressure and weak interplanetary magnetic field interact with the planet to create a magnetosphere that dwarfs Earth’s magnetosphere. While the form of Saturn’s magnetospheric cavity is still the result of solar wind stresses, many properties of the Kronian magnetosphere are determined largely by internal processes associated with the planet’s rapid rotation and the stresses arising from internal plasma sources dominated by the icy moon, Enceladus. Coupling between the planetary ionosphere and the magnetosphere through electric currents plays a vital role in determining the global configuration and dynamics of Saturn’s magnetosphere. To understand the large-scale behavior of the solar wind-magnetosphere-ionosphere interaction, we have applied the global MHD model, BATSRUS, to Saturn that couples the solar wind, the magnetosphere, and the ionosphere and incorporates key mass-loading processes associated with Enceladus and its extended neutral cloud. Here we present results from our global simulations carried out to understand how the various internally and externally driven processes influence Saturn’s magnetosphere, and discuss their implications for interpreting Cassin in-situ observations. We will also show results from an atmospheric vortex model we have developed that offers valuable insight into the physical processes that drive the ubiquitous periodic modulations of particles and fields properties observed by Cassini throughout the Saturnian magnetosphere.


Tuesday, April 10th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Tuesday, April 17th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Kendra Bergstedt, University of Minnesota
Subject: An Investigation of the Dayside Response of the Magnetosphere to Interplanetary Shocks: Dependence on Shock Parameters and Interplanetary Magnetic Field
This is the honors thesis presentation for Ms. Bergstedt
Faculty Host: Cynthia Cattell

Tuesday, April 24th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Speaker: Zac Cohen, University of Minnesota
Subject:  STEREO Observations of Waves in the Ramp Regions of Interplanetary Shocks
This is seminar is also the public portion of Mr. Cohen's Masters' Thesis Defense.

Tuesday, May 1st 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Tuesday, May 8th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

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