Radio Observations of Coronal Mass Ejections: Space Weather Aspects

The structure of the upper solar atmosphere, on all observable scales, is intimately governed by the magnetic field. The same holds for a variety of solar phenomena that constitute solar activity, from tiny transient brightening to huge Coronal Mass Ejections. Due to inherent difficulties in measuring magnetic field effects on atoms (Zeeman and Hanle effects) in the corona, radio methods sensitive to electrons are of primary importance in obtaining quantitative information about its magnetic field. In this review we explore these methods and point out their advantages and limitations. After a brief presentation of the magneto-ionic theory of wave propagation in cold, collisionless plasmas, we discuss how the magnetic field affects the radio emission produced by incoherent emission mechanisms (free-free, gyroresonance, and gyrosynchrotron processes) and give examples of measurements of magnetic filed parameters in the quiet sun, active regions and radio CMEs. We proceed by discussing how the inversion of the sense of circular polarization can be used to measure the field above active regions. Subsequently we pass to coherent emission mechanisms and present results of measurements from fiber bursts, zebra patterns, and type II burst emission. We close this review with a discussion of the variation of the magnetic field, deduced by radio measurements, from the low corona up to ~ 10 solar radii and with some thoughts about future work.

Section: Gyrosynchrotron Emissionmentioning

confidence: 99%

Radio Measurements of the Magnetic Field in the Solar Chromosphere and the Corona

Alissandrakis

Gary

2021

“…CMEs are the major drivers of space weather, as they are capable of producing shock waves and interplanetary disturbances (Gosling et al, 1991;Gosling, 1993), where the height of formation of the shock wave can often be estimated from the radio observations (Gopalswamy et al, 2013). Recently, Vourlidas et al (2020) have outlined the role of radio observations of CMEs during different stages of the CME eruption and its subsequent propagation in the heliosphere. Thus it is important to understand the kinematics of CMEs.…”

Section: Introductionmentioning

confidence: 99%

Investigating Width Distribution of Slow and Fast CMEs in Solar Cycles 23 and 24

Pant

Majumdar

Patel

et al. 2021

Coronal Mass Ejections (CMEs) are highly dynamic events originating in the solar atmosphere, that show a wide range of kinematic properties and are the major drivers of the space weather. The angular width of the CMEs is a crucial parameter in the study of their kinematics. The fact that whether slow and fast CMEs (as based on their relative speed to the average solar wind speed) are associated with different processes at the location of their ejection is still debatable. Thus, in this study, we investigate their angular width to understand the differences between the slow and fast CMEs. We study the width distribution of slow and fast CMEs and find that they follow different power law distributions, with a power law indices (α) of –1.1 and –3.7 for fast and slow CMEs respectively. To reduce the projection effects, we further restrict our analysis to only limb events as derived from manual catalog and we find similar results. We then associate the slow and fast CMEs to their source regions, and classified the sources as Active Regions (ARs) and Prominence Eruptions. We find that slow and fast CMEs coming from ARs and PEs, also follow different power laws in their width distributions. This clearly hints toward a possibility that different mechanisms might be involved in the width expansion of slow and fast CMEs coming from different sources.These results are also crucial from the space weather perspective since the width of the CME is an important factor in that aspect.

“…Again, the best viewing locations for SWx operations are off-SEL, which would necessitate the development of small volume/simple spectrograph and coronagraph concepts. Radio spectroscopy can play an important role in this area by tracking interplanetary shocks in the kHz-MHz range or probing CME magnetic fields via Faraday rotation measurements (e.g., Vourlidas et al, 2020b). Carley et al (2020) reviews extensively the SWx-related radio infrastructure upgrades under way.…”

Section: Path Forwardmentioning

confidence: 99%

Improving the Medium-Term Forecasting of Space Weather: A Big Picture Review From a Solar Observer's Perspective

Vourlidas

2021

Self Cite

We have improved considerably our scientific understanding of the key solar drivers of Space Weather, i.e., Coronal Mass Ejections, flares, in the last 20+ years thanks to a plethora of space missions and modeling advances. Yet, a major breakthrough in assessing the geo-effectiveness of a given CME and associated phenomena still escapes us, holding back actionable medium-term (up to 7 days) forecasting of Space Weather. Why is that? I adopt a two-pronged approach to search for answers. First, I assess the last 20+ years of research on solar drivers by identifying lessons-learned and paradigm shifts in our view of solar activity, always in relation to Space Weather concerns. Then, I review the state of key observation-based quantities used in forecasting to isolate the choke points and research gaps that limit medium-term forecasting performance. Finally, I outline a path forward along three vectors—breakthrough capabilities, geo-effective potential, and actionable forecast—with the strongest potential to improve space weather forecasting horizon and robustness.