Helium Traces in Solar Flares Unlock Secrets of Space Weather Prediction

Coronal mass ejections (CMEs) represent a substantial driver of space weather as they travel through the heliosphere. Chloe Pistelli from Taylor University, Momchil E. Molnar from Southwest Research Institute, and Giuliana de Toma from the High Altitude Observatory, NSF National Center for Atmospheric Research, et al., present observations utilising the Upgraded Coronal Multi-channel Polarimeter (UCoMP) which demonstrate the presence of helium in eruptive prominences linked to CMEs as they propagate through the lower and middle corona. This research is significant because it reveals that solar prominence eruptions can be detected in He I 1083nm observations up to approximately two solar radii, offering valuable spectral data that enhances current extreme ultraviolet and white-light coronal imaging. These findings illustrate UCoMP’s ability to investigate the dynamic behaviour of prominence eruptions, potentially enabling earlier and more accurate identification of Earth-directed events and improving space weather forecasting.

The research establishes UCoMP’s capability to probe the dynamic behaviour of prominence eruptions, enabling the estimation of line-of-sight velocities and potentially revolutionising space weather forecasting.

Previous studies utilising the Solar Maximum Mission identified prominence eruptions extending beyond 3 solar radii above the limb in the H I 656.3nm line, while the MLSO/CHIP instrument detected these events up to 1.4 solar radii. This work builds upon these findings by demonstrating that UCoMP can reliably detect neutral helium in erupting prominence material at distances exceeding these previous limits.

The UCoMP instrument, located at the Mauna Loa Solar Observatory in Hawaii, is a ground-based coronagraphic spectropolarimeter designed for high-precision polarimetric measurements of the solar corona between 530nm and 1083nm. Its unique design and the low sky brightness at the observatory allow for the regular observation of the faint coronal emissions, typically only a few millionths of the disc centre brightness.

The study analysed data collected during UCoMP’s commissioning phase between July 2021 and January 2022, identifying prominence eruptions on 14 out of 79 observing days. While a complete analysis of all events was beyond the scope of this initial investigation, the selected observations confirm the instrument’s ability to track prominence material through the corona.

The research focused on intensity data, utilising a background correction method to account for minor spurious contributions from the instrument’s filters, resulting in an estimated background intensity level between 10-15 μB⊙ decreasing with height. Spectroscopic data acquired with UCoMP yielded key plasma parameters, specifically line amplitude and estimations of Doppler velocities within the erupting prominences.

The research team employed the instrument to measure the line-of-sight velocity of prominence plasma, enabling a more detailed, three-dimensional reconstruction of CME evolution in the low corona. This was achieved through precise measurements of the He I 1083nm line, a spectral feature particularly sensitive to plasma motion.

Complementary observations from SDO/AIA were integrated with the UCoMP data, providing a broader context for understanding the early phases of eruption. The study benefited from theoretical transmission profiles of the UCoMP Lyot filter, provided by Dr. Steven Tomczyk of Solar Scientific LLC, ensuring accurate data calibration and interpretation.

Data analysis involved utilising Python packages including astropy, numpy, scipy, and sunpy, facilitating robust data processing and visualisation. Solar prominence eruptions were detected in He I 1083nm observations extending to approximately 2 solar radii from the solar centre, providing spectral information that complements existing extreme ultraviolet and white-light coronal imaging.

This detection range establishes UCoMP’s capability to observe prominence eruptions further into the corona than previously achieved with the Mauna Loa Solar Observatory Chromospheric Helium-I Imaging Photometer (MLSO/CHIP), which previously observed eruptions up to 1.4 solar radii. Data collected between July 2021 and January 2022 during UCoMP’s commissioning phase identified prominence activity on 14 out of 79 observing days, with significant eruptions observed and analysed from this subset.

The instrument’s design, utilising two cameras to simultaneously record an emission line and nearby continuum, facilitates the removal of sky and continuum contributions for accurate data calibration. UCoMP’s transmission profile, detailed in accompanying figures, demonstrates its sensitivity to the He I 1083nm line, although a secondary lobe from the on-band channel can contaminate the off-band continuum channel.

These findings illustrate the potential for UCoMP to estimate line-of-sight velocities of dynamic prominence eruptions, offering valuable data for space weather forecasting. By enabling earlier and more accurate identification of Earth-directed eruptions, this research supports the development of improved predictive models for geomagnetic storms and their impact on technological infrastructure. These observations, made in the He I 1083nm spectral line, demonstrate that erupting prominences remain detectable up to approximately two solar radii from the Sun’s centre, offering valuable spectral data.

This extends the observational capabilities beyond those of existing extreme ultraviolet and white-light coronagraphs, allowing for detailed study of these dynamic events. The spectroscopic data obtained from UCoMP enable the estimation of line-of-sight velocities and other plasma parameters within the erupting prominences.

This capability provides a ground-based method for measuring plasma characteristics within coronal mass ejections, potentially improving the accuracy and timeliness of space weather forecasting. Despite this limitation, the strong correspondence between UCoMP observations and those from space-borne coronagraphs confirms the reliability of the instrument as a diagnostic tool for CME activity. Future research will likely focus on refining the techniques for extracting plasma parameters from the He I 1083nm data and integrating these measurements into existing space weather models to improve predictive capabilities.