Virtual Meeting Abstracts

Tuesday July 7

Talk: RHESSI and STIX update – Krucker

Abstract: In this opening talk of our virtual RHESSI meeting, the activities of the RHESSI mission after decommissioning are presented. In the second part, a summary is given of the successful commissioning of the STIX hard X-ray imaging spectrometer onboard Solar Orbiter. 

Talk: The "Final" RHESSI Mission Archive – Schwartz/Tolbert

Abstract: We'll report on progress in creating the Final Mission Archive for the RHESSI mission. Specifically we are creating processed images for all flare time intervals above a meaningful threshold using a suite of imaging methodologies together with image plots, time series, as well as scripts to facilitate user modifications as needed. Supporting this are enhancements to the software and various databases that support both imaging and spectroscopy. Another processed database supporting future work is the visibility archive at both coarse energy binning and fine binning. Supporting this we are integrating the software to combine visibility energy and time intervals as needed. We'll also report on progress in migrating our ancillary databases to their future homes and describe how some of our toolset is being migrated to Python.

Talk: EOVSA update – Gary

Abstract: The Expanded Owens Valley Solar Array (EOVSA) continues to observe the Sun daily to provide microwave images and spatially-resolved spectral diagnostics of accelerated electrons in solar flares as well as thermal diagnostics of coronal plasma and coronal magnetic field in active regions.  During the extended period of quiet Sun during the past several years, EOVSA's pipeline has produced daily multifrequency full-disk images sensitive to coronal column emission measure even in the absence of spotted regions.  Even tiny B-class soft X-ray events can be usefully studied during this solar minimum period while we await the return of activity.  In addition, we still have a large backlog of events from 2017 that remain to be fully analyzed, including many with RHESSI coverage.  In addition to summarizing recent published science results from EOVSA, this talk also describes the improvements in EOVSA capabilities we have made during the past two years, including extension of frequency coverage down to 1 GHz, improving the bandwidth to eliminate gaps in frequency, and increasing the number of frequencies measured each second from 134 to 451 frequencies.  The Sun is showing signs of increased activity and the improved EOVSA will provide even more complete and valuable microwave diagnostics in the Solar Orbiter and Parker Solar Probe era.


Talk: Measuring solar flare hard X-ray (HXR) directivity with prospective stereoscopic and polarization missions – Jeffrey

Abstract: Solar flare particle acceleration is an extremely efficient process and understanding the acceleration mechanism remains a major challenge in solar physics. Hard X-ray (HXR) observations provide a direct link to flare-accelerated electrons and HXR directivity is a measure of the electron angular distribution, a prime diagnostic of the unknown electron acceleration mechanism, and various transport properties. However, to-date, HXR directivity has been difficult to measure, with different methods providing conflicting and often unreliable results. In this talk, I will discuss the importance of measuring electron directivity during flares, review different measurement methods (e.g. HXR stereoscopy, polarization) and discuss upcoming stereoscopic measurements with Solar Orbiter/STIX and a new X-ray fleet at Earth, and finally discuss prospective HXR polarization measurements.

Talk: Initiation and Early Kinematic Evolution of Solar Eruptions – Cheng

Abstract: Solar eruptions include coronal mass ejections (CMEs) and solar flares that are the most energetic eruptive phenomena in the solar system and are able to produce severe impacts on human high-tech activities in outer space. Nevertheless, the key questions of how and when CMEs/flares are initiated are still puzzled. In this talk, I will present a detailed analysis of the early kinematics of 12 solar eruptions, which yields three main conclusions: (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height-time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. But, a delayed onset of the impulsive flare phase is found in the majority of the filament eruptions. This delay, and its trend to be larger for slower eruptions, favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events, suggesting that this instability initiates and possibly drives the main acceleration.

Wednesday July 8

Talk: NuSTAR Solar Observations in the PSP/SO era – Glesener

Abstract: The NuSTAR hard X-ray telescope has observed the Sun occasionally for almost six years. It offers higher sensitivity than any other hard X-ray imager ever made, but can do so only at relatively quiet times since it is an astrophysicalinstrument and has limited throughput. Some of NuSTAR’s most notable solar results pertain to the faintest flares that can be observed individually on the Sun. NuSTAR has examined faint transient brightenings inside and outside active regions, allowing the study of their energetic and thermal properties and the investigation of how flare properties scale down in flare energy. NuSTAR has observed the Sun near the times of three Parker Solar Probe perihelia, with one of those during the Solar Orbiter / STIX calibration phase. This talk will review NuSTAR’s microflare science and will discuss the plans to continue these investigations in the PSP and SO eras.


Talk: High-Energy Observations of Solar Flares During Solar Cycle 24th with the Fermi Large Area Telescope – Omodei

Abstract: The Fermi Large Area Telescope (LAT) observations of the active Sun provide the largest sample of solar flares with emission greater than 30 MeV to date. These include detections of impulsive emission coincident with hard X-rays and hours-long sustained emission associated with GOES soft X-ray flares as well as very fast Coronal Mass Ejections (CME). Of particular interest is the first detection of >100 MeV gamma-ray emission from three solar flares whose positions behind the limb were confirmed by the STEREO spacecrafts and the 2017 September 10 X8.2 flare associated with Ground Level Enhancement 72. Fermi-LAT detections of solar flares at high energy present a unique opportunity to explore the mechanisms of high-energy emission and particle acceleration and transport in solar flares. We will present the Fermi-LAT Solar Flare Catalog, which includes observation of 45 solar flares during Solar Cycle 24. We will discuss correlation studies with CMEs and their byproducts Solar Energetic Particles (SEP) and Type II radio emissions, and highlight future prospects. These results indicate a closer relation of high-energy radiation producing particles and the CMEs.


Talk: Radio Propagation Diagnostics of the Inner Heliosphere in the Era of the Parker Solar Probe – Bastian

Abstract: A variety of radio propagation techniques can be used to probe regions in the corona and solar wind that are otherwise inaccessible to direct observation. One of these is angular broadening observations, which allow the wave structure function D(s) of solar wind to be measured rather directly. This, in turn, allows properties of the spatial spectrum of electron density fluctuations to be determined on small spatial scales, including the power law index, the degree of anisotropy, the presence of an inner scale, and the orientation of the local magnetic field. I present observations made by the Jansky VLA during the 3rd perihelion encounter of the Parker Solar Probe (PSP) during Aug-Sep 2019 to illustrate their potential for deducing properties of solar wind turbulence in the outer corona and the inner heliosphere, providing broader context within which to interpret in situ measurements made by PSP. A second radio propagation phenomenon is interplanetary scintillation (IPS). I will also briefly touch on IPS observations made by the Low Frequency Array (LOFAR) in support of PSP perihelia.


Talk: Current and Future Instrumentation – Martinez Oliveros

Abstract: In this talk I will present a review of the current and future of instrumentation for Solar physics.


Talk: The FIERCE mission concept – Shih

Abstract: The Fundamentals of Impulsive Energy Release in the Corona Explorer (FIERCE) mission concept – recently proposed to NASA – would make unprecedented X-ray and EUV observations to address open questions about how energy is suddenly released and transformed at the Sun in flares, CMEs, and even the quiescent Sun.  In particular, a major science goal is to understand the physical origins of space-weather events:  How are solar eruptive events initiated?   How do transient phenomena produce the energetic particles in the heliosphere that are observed in situ by missions such as Parker Solar Probe and Solar Orbiter?  The FIERCE instrument suite consists of a focusing hard X-ray spectroscopic imager, a soft X-ray spectrometer, and a high-resolution EUV imager optimized for flares.  If selected, FIERCE would launch in 2025, near the peak of the next solar cycle.