Session C03: Solar Eruptions

Understanding and Predicting Solar Eruptions with High Resolution Observations and Machine Learning

In this talk, I first review recent fundamental discoveries in the subject of solar flares, using high resolution observations from the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory. (1) Flare ribbon fronts, as well as pre- and post-flare loops are in the scale of about 100 km, which are much smaller than previously thought. (2) In some special wavelengths, flare front may appear as narrow dark bands instead of normal brightening. (3) Eruption in low density higher atmosphere can cause back reaction in dense photosphere. I will then introduce the work of machine learning to process the above data, and carry out near real time forecasting of solar eruptions.   

Trigger Shy? A "Rosetta-Stone" Solar Eruption

Solar eruptions are an active field with a broad range of accepted phenomena, and an even broader range of proposed mechanisms that cause them. This talk reports observations of an event that connects the major eruption classes, and could provide a holistic explanation for all of them. The event originated in a filament channel overlying a circular polarity inversion line and occurred on 2013 March 13 during the extended decay phase of the active region designated NOAA 12488/12501. This event was especially well-observed by multiple spacecraft and was seen to have the well-studied null-point topology. We analyze all aspects of the eruption using SDO AIA, HMI, STEREO-A, and SOHO LASCO imagery. One section of the filament undergoes a classic failed eruption with cool plasma subsequently draining onto the section that did not erupt, but a complex structured CME/jet is clearly observed by SOHO LASCO C2 shortly after the failed filament eruption. We cover the >30 hour buildup to eruption; the lack of obvious trigger; and the immediate reappearance of the filament after the event. The unique mixture of major eruption properties that are observed in this event places severe constraints on the structure of the filament channel field and, consequently, on the possible eruption mechanism.   

Exploring Electron Energy Distribution in the SEP-associated Radio CME of 2012 July 17

We present the modeling of the possible gyrosynchrotron (GS) emission from the CME associated with SEP event that started on 2012 July 17 17:15UT. We find that the legs of an erupting CME responsible for this SEP event appear bright in 150 MHz to 450 MHz radio images from Nancay Radio Heliograph. Upon further inspection, we find that some of the spatially-resolved radio spectra along these legs show characteristic shapes of GS emission from nonthermal electrons. We use 3D magnetic field model produced by thermodynamic MHD code, Magnetohydrodynamics Around a Sphere (MAS), place nonthermal electron population at where the GS emission is observed within the erupting CME geometry, and forward-fit the observed GS emission by performing the numerical calculation of GS emission and solving the radiative transfer equation along the line-of-sight. As a result, we obtain the spatial and energy distribution of nonthermal electrons in an erupting CME. We constrain the model by using white-light observation of the CME which can be used to estimate the plasma density distribution within the CME. We discuss the implication of the nonthermal electron distribution in terms of their acceleration mechanism during a CME eruption, and further explore their role as SEP seed particles by extending the modeling dynamically to pre-eruption time.   

Imaging Spectroscopy of CME-Associated Solar Radio Bursts

We present first results of a solar radio event observed with the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection (CME) and an M2.1 GOES soft X-ray flare from 2015 September 20. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. The event is imaged at multiple frequencies and source centroids are used to obtain the velocity for the outward motion. Spatial and temporal comparison with observations of the CME in white light from the LASCO(C2) coronagraph, indicates an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell (GCS) reconstruction of the CME, we constrain the density in the volume. Based on low density for plasma emission, source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral fitting techniques to estimate the evolving physical conditions during the outward motion of this burst source.