Search Publications
Quasi-Periodic Pulsations in Solar and Stellar Flares. Review
Kolotkov, Dmitrii; Kupriyanova, Elena; Nakariakov, Valery +1 more
This paper provides an overview of the state-of-the-art studies of oscillatory processes in solar and stellar flares, based on modern observational data from ground-based and space-borne instruments with high temporal, spatial, and spectral resolution in different bands of the electromagnetic spectrum. We examine the mecha-nisms that generate flar…
Microwave Spectral Imaging of an Erupting Magnetic Flux Rope: Implications for the Standard Solar Flare Model in Three Dimensions
Reeves, Katharine K.; Chen, Bin; Yu, Sijie +1 more
We report microwave spectral imaging observations of an erupting magnetic flux rope during the early impulsive phase of the X8.2-class limb flare on 2017 September 10, obtained by the Expanded Owens Valley Solar Array. A few days prior to the eruption, when viewed against the disk, the flux rope appeared as a reverse S-shaped dark filament along t…
Hot Plasma Flows and Oscillations in the Loop-top Region During the 2017 September 10 X8.2 Solar Flare
Reeves, Katharine K.; Polito, Vanessa; Chen, Bin +4 more
In this study, we investigate motions in the hot plasma above the flare loops during the 2017 September 10 X8.2 flare event. We examine the region to the south of the main flare arcade, where there is data from the Interface Region Imaging Spectrograph (IRIS) and the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. We find that there are …
Hinode/EIS Measurements of Active-region Magnetic Fields
Landi, E.; Li, W.; Hutton, R. +1 more
The present work illustrates the potential of a new diagnostic technique that allows the measurement of the coronal magnetic field strength in solar active regions by utilizing a handful of bright Fe X and Fe XI lines commonly observed by the high-resolution Hinode/EUV Imaging Spectrometer (EIS). The importance of this new diagnostic technique is …
The multi-thermal chromosphere. Inversions of ALMA and IRIS data
De Pontieu, B.; Leenaarts, J.; da Silva Santos, J. M. +4 more
Context. Numerical simulations of the solar chromosphere predict a diverse thermal structure with both hot and cool regions. Observations of plage regions in particular typically feature broader and brighter chromospheric lines, which suggests that they are formed in hotter and denser conditions than in the quiet Sun, but also implies a nonthermal…
Detection of the Strongest Magnetic Field in a Sunspot Light Bridge
Lagg, Andreas; Solanki, Sami K.; Castellanos Durán, J. S. +1 more
Traditionally, the strongest magnetic fields on the Sun have been measured in sunspot umbrae. More recently, however, much stronger fields have been measured at the ends of penumbral filaments carrying the Evershed and counter-Evershed flows. Superstrong fields have also been reported within a light bridge separating two umbrae of opposite polarit…
A First Spectroscopic Measurement of the Magnetic-field Strength for an Active Region of the Solar Corona
Brage, Tomas; Si, Ran; Li, Wenxian +3 more
For all involved in astronomy, the importance of monitoring and determining astrophysical magnetic-field strengths is clear. It is also a well-known fact that the corona magnetic fields play an important part in the origin of solar flares and the variations of space weather. However, after many years of solar corona studies, there is still no dire…
Imaging and Spectral Study on the Null Point of a Fan-spine Structure During a Solar Flare
Yang, Shuhong; Zhang, Jun; Zhong, Ze +3 more
Using the multi-instrument observations, we make the first simultaneous imaging and spectral study on the null point of a fan-spine magnetic topology during a solar flare. When magnetic reconnection occurs at the null point, the fan-spine configuration brightens in the (extreme-)ultraviolet channels. In the Hα images, the fan-spine structure is pa…
Sun-as-a-star Spectral Irradiance Observations of Transiting Active Regions
Toriumi, Shin; Cheung, Mark C. M.; DeRosa, Marc L. +3 more
Major solar flares are prone to occur in active-region (AR) atmospheres associated with large, complex, dynamically evolving sunspots. This points to the importance of monitoring the evolution of starspots, not only in visible but also in ultraviolet (UV) and X-rays, in understanding the origin and occurrence of stellar flares. To this end, we per…
The influence of NLTE effects in Fe I lines on an inverted atmosphere. I. 6301 Å and 6302 Å lines formed in 1D NLTE
Solanki, S. K.; van Noort, M.; Smitha, H. N. +1 more
Context. Ultraviolet overionisation of iron atoms in the solar atmosphere leads to deviations in their level populations based on Saha-Boltzmann statistics. This causes their line profiles to form in non-local thermodynamic equilibrium (NLTE) conditions. When inverting such profiles to determine atmospheric parameters, the NLTE effects are often n…