AI-Based Coronal Hole Detection and Solar Wind Model Validation

Context. Our understanding of the solar magnetic coronal structure is tightly linked to the shape of open field regions, specifically coronal holes. A dynamically evolving coronal hole coincides with the local restructuring of open to closed magnetic field, which leads to changes in the interplanetary solar wind structure. Aims. By investigating the dynamic evolution of a fast-tilting coronal hole, we strive to uncover clues about what processes may drive its morphological changes, which are clearly visible in extreme ultraviolet (EUV) filtergrams. Methods. Using combined 193 Å and 195 Å EUV observations by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and the Extreme UltraViolet Imager on board the Solar Terrestrial Relations Observatory-Ahead, in conjunction with line-of-sight magnetograms taken by the Helioseismic and Magnetic Imager, also on board the Solar Dynamics Observatory, we tracked and analyzed a coronal hole over 12 days to derive changes in morphology, area, and magnetic field. We complemented this analysis by potential field source surface modeling to compute the open field structure of the coronal hole. Results. We find that the coronal hole exhibits an apparent tilting motion over time that cannot solely be explained by solar differential rotation. It tilts at a mean rate of ∼3.2° day−1 that accelerates up to ∼5.4° day−1. At the beginning of May the area of the coronal hole decreased by more than a factor of three over four days (from ∼13 × 109 km2 to ∼4 × 109 km2), but its open flux remained constant (∼2 × 1020 Mx). Furthermore, the observed evolution is not reproduced by modeling that assumes the coronal magnetic field to be potential. Conclusions. In this study we present a solar coronal hole that tilts at a rate that has yet to be reported in literature. The rate exceeds the effect of the coronal hole being advected by either photospheric or coronal differential rotation. Based on the analysis we find it likely that this is due to morphological changes in the coronal hole boundary caused by ongoing interchange reconnection and the interaction with a newly emerging ephemeral region in its vicinity.

In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre-Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO).

In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre-Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO).

Context. The energy release in eruptive flares and the kinematics of the associated coronal mass ejections (CMEs) are interlinked and require favorable observing positions as both on-disk and off–limb signatures are necessary to characterize these events. Aims. We combine observations from different vantage points to perform a detailed study of a long duration eruptive C7 class flare that occurred on 17 April 2021 and was partially occulted from Earth view. The dynamics and thermal properties of the flare-related plasma flows, the flaring arcade, and the energy releases and particle acceleration are studied together with the kinematic evolution of the associated CME in order to place this long duration event in context of previous eruptive flare studies. Methods. We use data from the Spectrometer-Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter to analyze the spectral characteristics, timing, and spatial distribution of the flare X-ray emission. Data from the Extreme Ultraviolet Imager (EUVI) onboard the Solar TErrestrial RElations Observatory-Ahead (STEREO-A) spacecraft are used for context images as well as to track the ejected plasma close to the Sun. With Atmospheric Imaging Assembly extreme ultraviolet (EUV) images from the Solar Dynamics Observatory, the flare is observed off–limb and differential emission measure maps are reconstructed. The coronagraphs onboard STEREO-A are used to track the CME out to around 8 R⊙. Results. The flare showed hard X-ray (HXR) bursts over the duration of an hour in two phases lasting from 16:04 UT to 17:05 UT. During the first phase, a strong increase in emission from hot plasma and impulsive acceleration of the CME was observed. The CME acceleration profile shows a three-part evolution of slow rise, acceleration, and propagation in line with the first STIX HXR burst phase, which is triggered by a rising hot (14 MK) plasmoid. During the CME acceleration phase, we find signatures of ongoing magnetic reconnection behind the erupting structure, in agreement with the standard eruptive flare scenario. The subsequent HXR bursts that occur about 30 min after the primary CME acceleration show a spectral hardening (from δ ≈ 7 to δ ≈ 4) but do not correspond to further CME acceleration and chromospheric evaporation. Therefore, the CME-flare feedback relationship may only be of significance within the first 25 min. of the event under study, as thereafter the flare and the CME eruption evolve independently of each other.

We compare magnetic field measurements taken by the FIELDS instrument on board Parker Solar Probe (PSP) during its first solar encounter to predictions obtained by potential field source surface (PFSS) modeling. Ballistic propagation is used to connect the spacecraft to the source surface. Despite the simplicity of the model, our results show striking agreement with PSP’s first observations of the heliospheric magnetic field from ∼0.5 au (107.5 R ⊙) down to 0.16 au (35.7 R ⊙). Further, we show the robustness of the agreement is improved both by allowing the photospheric input to the model to vary in time, and by advecting the field from PSP down to the PFSS model domain using in situ PSP/Solar Wind Electrons Alphas and Protons measurements of the solar wind speed instead of assuming it to be constant with longitude and latitude. We also explore the source surface height parameter (R SS) to the PFSS model, finding that an extraordinarily low source surface height (1.3–1.5 R ⊙) predicts observed small-scale polarity inversions, which are otherwise washed out with regular modeling parameters. Finally, we extract field line traces from these models. By overlaying these on extreme ultraviolet images we observe magnetic connectivity to various equatorial and mid-latitude coronal holes, indicating plausible magnetic footpoints and offering context for future discussions of sources of the solar wind measured by PSP.

Solar coronal mass ejections (CMEs) are sometimes deflected during their propagation. This deflection may be the consequence of an interaction between the CME and the ambient coronal field, for example, a coronal hole, or the solar wind. The coronal magnetic field configuration is computed from daily synoptic maps of magnetic field from SOHO/MDI and SDO/HMI using a Potential Field Source Surface model. We analyze 30 halo‐CMEs whose deflection angle exceeds 90° by comparing the ambient magnetic field configuration and the measurement position angles of the CMEs. We find that the deflection of 87% of the CMEs (26 of 30) is consistent with the ambient magnetic field configuration, agreeing with previous studies. Of these 26, 69% are deflected toward the heliospheric current sheet, the boundary between the magnetic field polarities, and 31% toward a pseudo‐streamer, the boundary between same‐polarity magnetic field regions. This implies that the ambient coronal magnetic field configuration plays an important role in the deflection of CMEs and that the current sheet configuration is more important than a pseudo‐streamer. Of the 26 CMEs, the average and standard deviation of the minimum values of the deflection angle in three dimensions relative to an initially radial trajectory are 28° and 14°, respectively.

A series of powerful solar flares and coronal mass ejections (CMEs) occurred between 10 and 14 May 2024. As these eruptions propagated through the corona, they generated multiple solar type II radio bursts, indicating the presence of shock waves. This study characterises a series of type II radio bursts associated with a CME that occurred on 14 May, focusing on the coronal conditions during the event and identifying the likely location of the shocks where the radio bursts are generated. The CME was tracked using a combination of white light and extreme ultraviolet observations of the solar corona taken by three instruments: the Geostationary Operational Environmental Satellite (GOES) Solar Ultraviolet Imager (SUVI) and two coronagraphs of the Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO), together with ground-based radio observations between 10-240 MHz from the Irish Low-Frequency Array (I-LOFAR). The radial distances of the radio sources were examined using a series of density models, with both potential field source surface and magnetohydrodynamic models used to examine the coronal plasma conditions. Four type II bursts were identified in the I-LOFAR radio dynamic spectrum over ∼15 minutes, exhibiting features such as band splitting, herringbones, and fragmentation. The shocks were found to have speeds ranging between ∼443-2075 km s -1 $, with drift rates of ∼-361 to -78 kHz s^-1. The shocks were found to have a M_A ≈ 3.21-3.57. indicating that they were super-Alfvénic. The first type II burst was triggered $∼18 minutes after the CME launch, with each burst appearing to have been generated at a different height in the corona. Analysis of the derived kinematics and modelling results suggests that the type II bursts were likely produced at the shoulders of the CME near the flanks, where open magnetic field lines and relatively low Alfvén speeds facilitated shock formation. This multi-instrument study shows that multiple type II bursts from a single CME originated at different coronal heights, with modelling indicating their generation near the CME flanks where low Alfvén speeds and open magnetic field lines facilitated shock formation. The findings highlight the role of coronal conditions, particularly the magnetic field configuration and the Alfvén speed distribution, in determining the heights and locations where these bursts originate. Our results reinforce the importance of continuous, multi-wavelength observations for understanding shock dynamics and improving constraints on coronal models.

The potential-field source-surface (PFSS) model of the solar corona is a widely used tool in the space weather research and operations. In particular, the PFSS model is used in solar wind forecast models which empirically associate solar wind properties with the numerically derived coronal magnetic field. In the PFSS model, the spherical surface where magnetic field lines are forced to open is typically placed at 2.5 solar radii. However, the results presented here suggest that setting this surface (the source-surface) to lower heights can provide a better agreement between observed and modelled coronal holes during the current solar cycle. Furthermore, the lower heights of the source-surface provide a better match between observed and forecasted solar wind speed.

The solar wind, a stream of charged particles originating from the Sun, poses significant risks to technology and astronauts. It is driven by large structures on the solar surface like coronal holes and active regions, which can be identified in extreme ultra-violet (EUV) solar images several days before they become geoeffective. In this work, we propose to use a distributional regression algorithm to forecast the solar wind speed at the Lagrange 1 point from solar images. Instead of predicting a single value, this method models the entire conditional distribution as a function of input features. It allows computing the uncertainty of predictions and specifying the probability of the solar wind speed exceeding certain thresholds, which is especially useful for extreme event predictions like coronal mass ejections and high-speed solar wind streams. We employ a convolutional neural network to encode solar images from multiple wavelength channels into unstructured low-dimensional representations. Using a semi-structured distributional regression approach, we couple the deep learning encoder with structured physical input parameters, such as past solar wind properties and solar cycle information. Thereby, we incorporate physical knowledge into the model and enhance explainability. We predict the solar wind speed distributions with a one-hour cadence four days in advance. We train and evaluate our method using cross-validation on 15 years of data and compare it to current state-of-the-art models. We find that it provides an accurate forecast and especially models the heavy-tailed solar wind speed distribution well. We further show the advantages over standard regression approaches and how to use the predicted conditional quantiles to improve extreme event predictions, highlighting the potential for operational space weather forecasts.

The trajectories of coronal mass ejection (CME) are often observed to deviate from radial propagation from the source while within the coronagraph field of view (\(\mbox{R} <15\,\mbox{--}\,30~\mbox{R}_{\mathrm{sun}}\)). To better understand nonradial propagation within the corona, we first analyze the trajectories of five CMEs for which both the source and 3D trajectory (latitude, longitude, and velocity) can be well determined from solar imaging observations, primarily using observations from the twin Solar TErrestrial RElations Observatory (STEREO) spacecraft. Next we analyze the cause of any nonradial propagation using a potential field source surface (PFSS) model to determine the direction of the magnetic pressure forces exerted on the CME at various heights in the corona. In two cases, we find that the CME deviation from radial propagation primarily occurs before it reaches the coronagraph field of view (below 1.5 solar radii). Based on the observations and the magnetic pressure forces calculated from the PFSS model, we conclude that for these cases the deviation is the result of strong active-region fields causing an initial asymmetric expansion of the CME that gives rise to the apparent rapid deflection and nonradial propagation from the source. Within the limitations of the PFSS model, the magnetic fields for all five cases appear to guide the CMEs out of the corona through the weak-field region around the heliospheric current sheet even when the current sheet is inclined and warped.

Coronal holes are areas on the Sun with open magnetic field lines. They are a source region of the solar wind, but how the wind emerges from coronal holes is not known. We observed a coronal hole using the Extreme Ultraviolet Imager on the Solar Orbiter spacecraft. We identified jets on scales of a few hundred kilometers, which last 20 to 100 seconds and reach speeds of ~100 kilometers per second. The jets are powered by magnetic reconnection and have kinetic energy in the picoflare range. They are intermittent but widespread within the observed coronal hole. We suggest that such picoflare jets could produce enough high-temperature plasma to sustain the solar wind and that the wind emerges from coronal holes as a highly intermittent outflow at small scales.

Hot channels (HCs) are prevalent in the solar corona and play a critical role in driving flares and coronal mass ejections (CMEs). In this paper, we estimate the energy content of an X1.4 eruptive flare with a fast CME generated by an HC eruption on 2011 September 22. Originating from NOAA Active Region 11302, the HC is the most dramatic feature in 131 and 94 Å images observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The flare is simultaneously observed by SDO/AIA, the Reuven Ramaty High-energy Solar Spectroscopic Imager, and the Extreme-ultraviolet Imager on board the “behind” Solar Terrestrial Relations Observatory (STEREO). The CME is simultaneously detected by the white-light coronagraphs of the Large Angle Spectroscopic Coronagraph on board the Solar and Heliospheric Observatory and the COR1 coronagraph on board the behind STEREO. Using multiwavelength and multiview observations of the eruption, various energy components of the HC, flare, and CME are calculated. The thermal and kinetic energies of the HC are (1.77 ± 0.61) × 1030 erg and (2.90 ± 0.79) × 1030 erg, respectively. The peak thermal energy of the flare and total radiative loss of the soft X-ray–emitting plasma are (1.63 ± 0.04) × 1031 erg and (1.03–1.31) × 1031 erg, respectively. The ratio between the thermal energies of the HC and flare is 0.11 ± 0.03, suggesting that the thermal energy of the HC is not negligible. The kinetic and potential energies of the CME are (3.43 ± 0.94) × 1031 erg and (2.66 ± 0.49) × 1030 erg, yielding a total energy of (3.69 ± 0.98) × 1031 erg for the CME. Continuous heating of the HC is required to balance the rapid cooling by heat conduction, which probably originates from intermittent magnetic reconnection at the flare current sheet. Our investigation may provide insight into the buildup, release, and conversion of energies in large-scale solar eruptions.

A significant number of interplanetary shocks (∼17%) during cycle 23 were not followed by drivers. The number of such “driverless” shocks steadily increased with the solar cycle with 15%, 33%, and 52% occurring in the rise, maximum, and declining phase of the solar cycle. The solar sources of 15% of the driverless shocks were very close the central meridian of the Sun (within ∼15°), which is quite unexpected. More interestingly, all the driverless shocks with their solar sources near the solar disk center occurred during the declining phase of solar cycle 23. When we investigated the coronal environment of the source regions of driverless shocks, we found that in each case there was at least one coronal hole nearby, suggesting that the coronal holes might have deflected the associated coronal mass ejections (CMEs) away from the Sun‐Earth line. The presence of abundant low‐latitude coronal holes during the declining phase further explains why CMEs originating close to the disk center mimic the limb CMEs, which normally lead to driverless shocks due to purely geometrical reasons. We also examined the solar source regions of shocks with drivers. For these, the coronal holes were located such that they either had no influence on the CME trajectories, or they deflected the CMEs toward the Sun‐Earth line. We also obtained the open magnetic field distribution on the Sun by performing a potential field source surface extrapolation to the corona. It was found that the CMEs generally move away from the open magnetic field regions. The CME–coronal hole interaction must be widespread in the declining phase and may have a significant impact on the geoeffectiveness of CMEs.

The Sun may be less boisterous now than it was in 1989 or than it will be in 2000, but it is anything but quiet. In fact, the first images returned this spring from the Solar and Heliospheric Observatory (SOHO) reveal a Sun that is quite active even though it has waned to its solar minimum.“Movies made from SOHO ultraviolet data show that there is continuous motion and action everywhere on the Sun,” said Joseph Gurman, an astrophysicist from NASA's Goddard Space Flight Center and coinvestigator for SOHO's extreme ultraviolet imaging telescope (EIT). “Even at the quietest places on the Sun, including the so‐called coronal holes, there is a tremendous amount of activity… a general twinkling everywhere we look.”

A solar flare was observed on 1997 April 7 with the Soft X-ray Telescope (SXT) on Yohkoh. The flare was associated with a "halo" coronal mass ejection (CME). The flaring region showed areas of reduced soft X-ray (SXR) brightness—"dimmings"—that developed prior to the CME observed in white light and persisted for several hours following the CME. The most prominent dimming regions were located near the ends of a preflare SXR S-shaped (sigmoid) feature that disappeared during the event, leaving behind a postflare SXR arcade and cusp structure. Based upon these and similar soft X-ray observations, it has been postulated that SXR dimming regions are the coronal signatures (i.e., remnants) of magnetic flux ropes ejected during CMEs. This Letter reports new observations of coronal dimming at extreme-ultraviolet (EUV) wavelengths obtained with the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO). A series of EIT observations in the 195 Å Fe XII wavelength band were obtained simultaneously with SXT during the 1997 April 7 flare/CME. The EIT observations show that regions of reduced EUV intensity developed at the same locations and at the same time as SXR dimming features. The decrease in EUV intensity (averaged over each dimming region) occurred simultaneously with an increase in EUV emission from flaring loops in the active region. We interpret these joint observations within the framework of flux-rope eruption as the cause of EUV and SXR coronal dimmings, and as the source of at least part of the CME.