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.


Wednesday, March 28th 2018
3:30 pm:
Space Physics Seminar in Physics 201-20
Speaker: Barry Mauk, APL
Subject: TBD
Faculty Host: Robert Lysak

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