Scientific Colloquium
February 8, 2013
"Magnetism and the Invisible Man: The Mysteries of Coronal Cavities"

Magnetism defines the complex and dynamic solar corona.  Twists and tangles in coronal magnetic fields build up energy and ultimately erupt, hurling plasma into interplanetary space.  These coronal mass ejections (CMEs) are transient riders on the ever-outflowing solar wind, which itself possesses a three-dimensional morphology shaped by the global coronal magnetic field.  Coronal magnetism is thus at the heart of any understanding of the origins of space weather at the Earth.   However, we have historically been limited by the difficulty of directly measuring the magnetic fields of the corona, and have turned to observations of coronal plasma to trace out magnetic structure.  This approach is complicated by the fact that plasma temperatures and densities vary among coronal magnetic structures, so that looking at any one wavelength of light only shows part of the picture.  In fact, in some regimes it is the lack of plasma that is a significant indicator of the magnetic field.  Such a case is the coronal cavity: a dark, elliptical region in which strong and twisted magnetism dwells.  I will elucidate these enigmatic features by presenting observations of coronal cavities in multiple wavelengths and from a variety of observing vantages, including unprecedented coronal magnetic field measurements now being obtained by the Coronal Multichannel Polarimeter (CoMP).  These observations demonstrate the presence of twisted magnetic fields within cavities, and also provide clues to how and why cavities ultimately erupt as CMEs. 

About the speaker:
Dr. Sarah Gibson is a Scientist III in the High Altitude Observatory (HAO) Division of the National Center for Atmospheric Research, and Section Head of HAO’s Coronal and Heliospheric Section. Dr. Gibson received her Bachelor’s Degree in Physics from Stanford University, and her Masters and Doctoral Degrees in Astrophysics from the University of Colorado. Dr. Gibson’s research centers on solar drivers of the terrestrial environment, from short-term space weather drivers such as coronal mass ejections (CMEs), to long-term solar cycle variation with emphasis on the Sun-Earth system at solar minimum. She has led and coordinated international working groups on these subjects. Dr. Gibson uses theoretical models to understand the origins of CMEs and related space weather phenomena. A particular focus is observations and models of coronal prominence cavities, which are long-lived structures in the Sun’s atmosphere that store the magnetic energy liberated in CMEs. Dr. Gibson recently led an International Space Science Institute (Switzerland) International Team on Prominence Cavities. Dr. Gibson was also a leader of the international Whole Sun Month and Whole Heliosphere Interval coordinated observing and modeling efforts to characterize the three-dimensional, interconnected solar-heliospheric-planetary system at solar minimum. She currently leads an International Astronomical Union Working Group on Comparative Solar Minima, which promotes analyses of the degree and nature of variations within and between minima. Dr. Gibson was the recipient of the American Astronomical Society – Solar Physics Division 2005 Karen Harvey Prize. She was a Scientific Editor for the Astrophysical Journal and has served on many national and international committees. At present she serves on the National Research Council’s Solar and Space Physics Decadal Survey Steering Committee and is vice-chair of the Association of Universities for Research in Astronomy (AURA) Solar Observatories Council. Dr. Gibson is committed to education and public outreach. She has been a scientific mentor to several graduate and undergraduate students, and has presented multiple times at the American Association of University Women's Expanding your Horizon conference for middle-school girls. She gave the first of NCAR’s 50th anniversary public lectures, and has co-written an article on the Sun for the encyclopedia Space Science for Students.
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