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Upcoming Seminars

Solar Activity and Dynamics in a Stellar Context April 13, 2021
Travis Metcalfe, Space Science Institute
Nearly half a century has passed since the initial indications that stellar rotation slows while chromospheric activity weakens with a power-law dependence on age, the so-called Skumanich relations. This coupled evolution is ultimately driven by angular momentum loss from a stellar wind entrained in the large-scale magnetic field produced by global dynamo action. Recent observational evidence suggests that the global dynamo begins to shut down near the middle of a star’s main-sequence lifetime, leading to a disruption in the production of large-scale magnetic field, a dramatic reduction in angular momentum loss, and a decoupling of further evolution in rotation and activity. For solar-type stars this transition appears to occur near the age of the Sun, when rotation becomes too slow to imprint Coriolis forces on the global convective patterns, reducing the shear induced by differential rotation, and disrupting the large-scale dynamo. I will review the latest evidence for this new understanding of magnetic stellar evolution, including recent constraints on the rate of solar angular momentum loss and measurements of sun-like stars that place solar variability in context.
Solaris - TBD May 11, 2021
Sarah Gibson, High Altitude Observatory

Past Seminars

Machine-learning Framework for Solar Data Processing March 9, 2021
Egor Illarionov, Lomonosov Moscow State University
Machine learning assumes working with large datasets. It is a common situation where the datasets do not fit into memory. To iterate and process datasets of arbitrary size, one needs a specific framework. In the seminar we discuss the key concepts of such frameworks that include data indexing, batch processing and pipelines construction. As a particular implementation we consider the framework and show how it helps to implement unified pipelines for synoptic maps construction and coronal holes segmentation using SDO and SOHO data. We also discuss the questions related to Python code optimization and acceleration.
Lessons Learned from Stellar Simulation Feb 9, 2021
Alan Wray, NASA Ames Research Center
The lessons are of course many. This talk will emphasize numerical and modeling techniques, both successful and failed ones, and the reasons for the choices made. Topics include: equations solved, space and time discretization, boundary conditions, conservation, radiation, subgrid turbulence modeling, shock capturing, MHD methodology, scaling and other speed issues, and results both technical and graphical. Enhancements in-progress will also be mentioned.
How Good Is the Bipolar Approximation of ARs for Surface Flux Transport? Jan 13, 2021
Anthony Yeates, Durham University
We investigate how representing active regions with bipolar magnetic regions (BMRs) affects the end-of-cycle polar field predicted by the surface flux transport model. Our study is based on a new database of BMRs derived from the SDO/HMI active region patch data between 2010 and 2020. An automated code is developed for fitting each active region patch with a BMR, matching both the magnetic flux and axial dipole moment of the region and removing repeat observations of the same region. By comparing the predicted evolution of each of the 1090 BMRs with the predicted evolution of their original active region patches, we show that the bipolar approximation leads to a 24% overestimate of the net axial dipole moment, given the same flow parameters. This is caused by neglecting the more complex multipolar and/or asymmetric magnetic structures of many of the real active regions, and may explain why previous flux transport models had to reduce BMR tilt angles to obtain realistic polar fields. Our BMR database and the Python code to extract it are freely available.
The Emergence of Magnetic Structures from the Deep Solar Interior Sep 1, 2020
Nicholas Brummell, University of California Santa Cruz
In this informal talk, I will address potential explanations for the origin of the magnetic structures that we observe as active regions and sunspots. I will try to point to some of the deeper questions that COFFIES could address on this topic, using (as an excuse) some work that we (here at UCSC) have been doing recently on a theory for the origin of the solar hemispheric helicity rules. This particular subject combines many aspects of COFFIES and I think is one avenue of study that has substantial potential for collaboration leading to a significant enhancement of understanding.
A Biased View on 20+ Years of Global Helioseismology Aug 4, 2020
Sylvain G. Korzennik, Center for Astrophysics | Harvard & Smithsonian
We have by now over two decades of nearly uninterrupted high quality and high cadence global helioseismogical data. GONG has been producing science quality data since 1995, MDI started in 1996 and HMI took over in 2010. Fundamental new constraints have been imposed by helioseismic inferences, yet global helioseismology seems frozen in time in some of its methodologies and has, at times, claimed to have detected what ended up being spurious features. I will present a biased - i.e. partial and personal - review of  the current state of global helioseismology, with some emphasis on issues and challenges presented by mode fitting, inversion techniques and the hunt for the residual systematic errors.

For more information contact us at: coffies-info at sun dot stanford dot edu