Search for: All records

Abstract Solar magnetic fields are responsible for solar coronal mass ejections and other eruptive phenomena that govern space weather. Today, most of our knowledge about the solar magnetic field topologies was derived from the measurements of the magnetic field of the solar photosphere. The solar chromosphere is dilute, and associated magnetic fields are weak, which makes them difficult to measure. To address this challenging issue, we propose the use of the HeID₃5876 Å line, together with the HeI10830 Å line, to measure the off-limb weak and moderate chromospheric magnetic fields in the Hanle effect regime. We show that the current approach of using the polarization amplitude or degree cannot reliably retrieve the magnetic fields. We demonstrated that by using the Stokes linear polarization profiles simultaneously with the 5876 and 10830 Å lines, without the use of the circular polarization, chromospheric magnetic fields as low as and down to a few gauss can be measured easily and reliably with today’s instruments. We further demonstrate the potential to measure the weak chromospheric magnetic fields with the Stokes linear polarization profiles by using the He 5876 Å line alone, which has not been fully investigated yet. This work will provide a new technique for future daily synoptic observations for the weak magnetic fields in the solar chromosphere for both the active and quiescent regions, which are still difficult to measure. 

Abstract We present a uniform analysis of compact CaiiK (3934 Å) brightenings that occur near flare kernels and assess their value as short-lead indicators of solar flare onset. Using high-cadence imaging from the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope, we examine eight flare sequences (seven C-class and one B-class) obtained between 2021 and 2025. Fixed, detector-coordinate regions of interest are used to generate mean-intensity light curves, which are detrended and smoothed to isolate impulsive brightenings. In every event, a compact CaiiK brightening is detected within or adjacent to the flaring region that peaks 10–45 minutes before the primary kernel and the corresponding rise in GOES 1–8 Å flux. The measured temporal offsets scale with the deprojected separation between the brightening and flare kernels, implying an apparent propagation speed of ∼30–35 km s⁻¹that is consistent with chromospheric reconnection. Complementary Spectropolarimeter for Infrared and Optical Regions spectropolarimetry for one event shows topological reconfiguration from closed to open or extended connectivity, supporting a reconnection-driven origin. These results demonstrate that compact CaiiK brightenings are reproducible, physically meaningful precursors to flare onset. Their simplicity and cadence make them attractive chromospheric indicators, and future work will evaluate their predictive skill alongside established UV/EUV and magnetic diagnostics. 

Abstract The Sunspot Solar Observatory Data Archive (SSODA) stores data acquired with the suite of instruments at the Richard B. Dunn Solar Telescope (DST) from February 2018 to the present. The instrumentation at the DST continues to provide high cadence imaging, spectroscopy, and polarimetry of the solar photosphere and chromosphere across a wavelength range from 3500 Å to 11,000 Å. At the time of writing, the archive contains approximately 374 TiB of data across more than 520 observing days (starting on February 1, 2018). These numbers are approximate as the DST remains operational, and is actively adding new data to the archive. The SSODA includes both raw and calibrated data. A subset of the archive contains the results of photospheric and chromospheric spectropolarimetric inversions using the Hazel-2.0 code to obtain maps of magnetic fields, temperatures, and velocity flows. The SSODA represents a unique resource for the investigation of plasma processes throughout the solar atmosphere, the origin of space weather events, and the properties of active regions throughout the rise of Solar Cycle 25. 

This white paper is on the HMCS Firefly mission concept study. Firefly focuses on the global structure and dynamics of the Sun's interior, the generation of solar magnetic fields, the deciphering of the solar cycle, the conditions leading to the explosive activity, and the structure and dynamics of the corona as it drives the heliosphere.