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Astrophysics Luncheon Seminar

Solar Coronal Science from Ground to Space
Presented by Amir Caspi
Southwest Research Institute

Monday, November 12, 2018
12:00 noon in 169-336

Abstract
The solar corona, at temperatures of 1-2 million Kelvin (MK), is 100 times hotter than the underlying photosphere and chromosphere. During solar flares, coronal temperatures can rise even further, to 30-50 MK in the most intense events. Despite nearly 80 years of focused research, exactly how the corona is heated to these temperatures is still poorly understood. During flares, reconfiguration of the complex magnetic field ("magnetic reconnection") explosively releases energy, which can heat plasma directly and/or accelerate particles to high energies, which then thermalize through collisions and deposit additional heat. During quiescence, small flare-like processes ("nanoflares") are thought to heat the plasma around active regions; wave-like processes may be a global heating phenomenon. However, the specific physical mechanisms underlying these processes are still not well known or characterized.

We discuss a few recent missions to better understand these coronal heating processes through remote sensing from spacecraft, sounding rockets, balloons, and airplanes. New X-ray spectrometers using silicon drift detectors, flown on sounding rockets and on the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat, provided spectrally-resolved solar irradiance in soft X-rays (~0.5-20 keV) with the best-yet resolution (~0.15 keV FWHM) from such instruments. MinXSS-1 observed dozens of solar flares and much quiescent emission during its 1-year mission (May 2016-2017), and MinXSS-2 will launch in November 2018 for an estimated 4-year mission to provide unprecedented data for studying high-temperature plasma in solar flares and quiescent heating. Hard X-ray detectors, both cadmium-telluride and germanium, were flight-tested on the NASA GRIPS balloon during a 12-day mission over Antarctica (Jan 2016). More recently, two NASA WB-57 high-altitude research aircraft were deployed to observe the 2017 total solar eclipse using two ~220-cm visible (5303 ± 50 Å) and near-infrared (3-5 μm) telescopes to study the inner and middle corona with an unprecedented combination of temporal (30 Hz) and spatial (3 arcsec/pixel) resolutions. The two aircraft obtained a total of >7.5 minutes of contiguous totality, nearly a 3-fold increase over stationary observers, with ideal seeing conditions. The resulting high-speed movies enable a search for fast, coherent motion in the corona, such as would be expected from Alfvén or other wave phenomena, nanojets, or post-nanoflare reconfiguration, to better understand coronal heating and the stability of magnetic structures in the corona.

JPL Contact: Varoujan Gorjian (4-2068)


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