The research, led by Yutong Li of Dezhou University together with colleagues at Dezhou University and Purple Mountain Observatory of the Chinese Academy of Sciences, focuses on a noise storm observed on 24 December 2023. The team combined dynamic radio spectra from the ORFEES spectrograph and the RSTN San Vito station with radio imaging from the Nançay Radioheliograph in France, and paired these with extreme-ultraviolet and magnetogram data from NASA’s Solar Dynamics Observatory, including its Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager. X-ray measurements from the GOES 16 satellite provided the flare timeline. This multiwavelength approach allowed the researchers to track, nearly simultaneously, where the radio source sat in the corona, how its intensity evolved, and what the magnetic field was doing below it.

The radio source turned out to be co-spatial with active region 3529, a magnetically complex area on the solar disk. One of the study’s technically revealing findings concerns the spatial structure of the emission: the source showed frequency-dependent spatial dispersion, meaning that emission at different radio frequencies originated from slightly different locations above the active region. Because the frequency of plasma emission is tied directly to the local electron density, which generally decreases with height in the corona, this dispersion maps out the density stratification of the closed magnetic loops that host the storm. It confirms that the emission arises from electrons trapped within overlying closed structures rather than from freely propagating streams far from the flare site.

The pivotal moment came with an M2.9-class flare from the same active region. As the flare began, the noise-storm intensity did not surge; instead, it dropped. The emission then recovered after the flare’s impulsive phase, and, strikingly, the storm shifted to higher frequencies. In the language of plasma physics, a shift to higher emission frequencies implies a shift to higher electron densities, which in turn suggests that the radio source moved to lower altitudes or that denser plasma became involved in the emission process. The authors interpret this as the signature of the flare-driven magnetic reconfiguration compressing or reshaping the loop system in which the nonthermal electrons were trapped.

What kept the storm alive before the flare? Based on the multiwavelength evidence, the researchers propose that small-scale magnetic reconnection occurring below the storm source, in the period leading up to the eruption, supplied a continuous resupply of nonthermal electrons into the overlying closed magnetic structures. These energetic electrons, injected upward into loops where they became magnetically trapped, sustained the plasma emission that observers record as chains of type I bursts. This picture ties the longevity of noise storms to a steady engine of low-level reconnection rather than to a single impulsive acceleration event, a distinction that has long been debated in solar radio physics.

During the flare itself, the observations captured dramatic evidence of reconnection in progress above the active region. The radio spectra showed type III bursts with bidirectional frequency drifts, the hallmark of electron beams accelerated at a reconnection site and streaming simultaneously upward and downward along magnetic field lines. Because the drift rate of a type III burst encodes the density gradient the beam traverses, the direction and rate of drift reveal where the acceleration happened. Even more telling, the starting frequency of these bidirectional bursts gradually decreased over time. Since a lower starting frequency corresponds to a lower ambient density and therefore a greater height, the authors suggest that the reconnection site itself was moving upward through the corona as the flare progressed, consistent with the rising geometry of an erupting magnetic system.

The flare’s most consequential effect on the noise storm was magnetic rather than radiative. The reconnection event ejected plasma bidirectionally, restructuring the coronal magnetic field above the active region. In the pre-flare configuration, closed loops had provided the magnetic cages that confined nonthermal electrons long enough for them to generate coherent type I emission through plasma processes, a mechanism first outlined in the classic work of Ginzburg and Zhelezniakov in 1958 and refined by many theorists since. Once the flare scrambled those loops, the trapping efficiency collapsed. Electrons that would otherwise have bounced back and forth along closed field lines escaped or were precipitated, the supply of confined energetic particles was interrupted, and the storm was suppressed. The quieting of the radio emission was therefore not a simple absence of energy but the destruction of the magnetic architecture required to store it.

Recovery followed a logical sequence. As post-flare magnetic reconnection subsided and the coronal field relaxed back toward a closed, stable configuration, conditions favorable for electron trapping were re-established. New or re-formed closed loops once again confined nonthermal electrons, the plasma emission mechanism resumed, and the noise storm returned, now at higher frequencies reflecting the altered density structure of the rebuilt loop system. The full cycle, suppression at flare onset, recovery afterward, and a frequency shift tracking the magnetic evolution, provides a coherent narrative in which the flare acts as a modulator of the storm through magnetic restructuring rather than as a simple amplifier or destroyer of radio emission.

The broader significance of the result extends beyond a single event. Noise storms are among the most common manifestations of nonthermal activity in the solar corona, and their occurrence is known to be closely linked to the local magnetic configuration and to the acceleration of nonthermal electrons. By demonstrating that a moderate M-class flare can visibly reorganize the trapping structures of a storm in near real time, the study provides an observational benchmark for models that connect coronal magnetic evolution to radio diagnostics. Because meter-wave radio emission probes densities and heights that are difficult to access with extreme-ultraviolet imaging alone, noise storms serve as sensitive barometers of coronal change, and flare-induced modulations of the kind documented here could become a routine diagnostic for tracking magnetic reconfiguration during eruptions.

The work also carries practical weight for space-weather research. Radio bursts in the meter wavelength range can interfere with terrestrial and satellite communications systems, and understanding what controls their onset, persistence, and cessation improves the physical basis for forecasting disruptive solar radio events. The datasets underpinning the study, including the ORFEES and Nançay Radioheliograph observations available through the Radio Solar dataBase at Nançay, the RSTN San Vito spectra archived by NOAA’s National Centers for Environmental Information, and the SDO and GOES 16 measurements, are all publicly accessible, allowing other researchers to test the proposed sequence of pre-flare electron supply, flare-driven disruption, and post-flare recovery in additional events. If the pattern holds more generally, forecasters may one day read the rise and fall of a noise storm as a live record of magnetic reconnection reshaping the corona above an active region.

Subject of Research: Modulation of type I solar radio noise storms by flare-driven magnetic reconnection above an active region

Article Title: Type I Solar Radio Bursts Modulated by Solar Flares

Article References: Li, Y., Li, C., Tang, Y., Gai, N., Li, Z., Cui, Z., Gao, Y., Wang, Y., Xu, X., & Huo, X. (2026). Type I Solar Radio Bursts Modulated by Solar Flares. Solar Physics, 301(10), Article 150. https://doi.org/10.1007/s11207-026-02736-9

Image Credits: AI Generated

DOI: 10.1007/s11207-026-02736-9

Keywords: type I radio bursts, noise storms, solar flares, magnetic reconnection, solar corona, active region 3529, nonthermal electrons, type III bursts, plasma emission, Nançay Radioheliograph, SDO, space weather

The Extreme-ultraviolet Variability Experiment, or EVE, was never designed to measure Doppler velocities. Its mission is to track how the Sun’s extreme ultraviolet output varies over time, information that matters because that radiation is the primary energy input to Earth’s ionosphere and thermosphere. EVE observes the full solar disk from 6 to 106 nanometers with a spectral resolution of just 0.1 nanometers, using its Multiple EUV Grating Spectrographs, known as MEGS. At that modest resolution, detecting the tiny wavelength shifts produced by moving plasma would seem impossible. Yet two fortunate circumstances changed the calculus: the SDO spacecraft holds its solar pointing with exceptional stability, and its geosynchronous orbit provides an unusually stable thermal environment, keeping the instrument’s wavelength scale steady enough to capture genuine solar motions.

The new data product fits Gaussian profiles to 70 carefully selected emission features, each originating from a distinct layer of the solar atmosphere. Roughly half of the lines come from the transition region, a thin boundary layer where temperatures climb from about 25,000 kelvin to 0.6 million kelvin, and half come from the corona above, where temperatures exceed 0.6 million kelvin and can surpass 6 million kelvin during flares. The fitting algorithm models each feature of interest with a Gaussian plus two additional Gaussians for blended neighboring lines and a linear background, yielding fitted values for intensity, wavelength center, and line width. When the GOES X-Ray Sensor detects a flare, the algorithm automatically subtracts a pre-flare spectrum to isolate the flare’s own spectral signature, flagging those events in the data product.

Converting wavelength shifts to velocities is straightforward in principle: the shift between the flare spectrum and the pre-flare spectrum, multiplied by the speed of light and divided by the reference wavelength, gives the line-of-sight velocity. Positive values are red shifts, indicating plasma receding from the observer, which for flares near disk center means downflow. Negative values are blue shifts, indicating approaching plasma, or upflow. The team emphasizes that measured pre-flare wavelengths, rather than theoretical values from the CHIANTI spectral database, must serve as the reference, because small systematic offsets in the instrument’s wavelength scale would otherwise contaminate the result.

Not every spectral line is trustworthy for this work. Many EUV features are blends of multiple emissions at MEGS resolution, and different lines dominate at different plasma temperatures, so a blended feature can shift spuriously as solar activity changes. The team used CHIANTI model spectra for quiet Sun, active region, and flare conditions to estimate this blend uncertainty for each of the 70 features, expressing it as a velocity error. Forty-two lines, nine from MEGS-A and thirty-three from MEGS-B, came in below the 30 kilometers-per-second threshold and are flagged as the best choices for studying flare dynamics. The rest carry blend errors large enough to swamp any genuine solar signal.

Perhaps the most technically demanding part of the study involved disentangling an optical artifact from real solar physics. The MEGS-B instrument uses two Rowland-circle spectrographs in tandem, and because its CCD sensor is flat rather than curved along the Rowland circle, most wavelengths are slightly out of focus. That defocus makes the measured wavelength scale sensitive to where an active region sits on the solar disk. Raytrace modeling of the original optical design confirmed that active regions near the east limb produce wavelength shifts in one direction, west-limb regions in the opposite direction, with the sign flipping between central and outer wavelengths. Earlier reports of surprisingly fast prograde-rotation velocities of about 50 kilometers per second in coronal lines, published by Hudson and colleagues in 2022, turn out to be an artifact of this optical behavior rather than a genuine solar flow.

To validate and calibrate the correction, the team exploited a rare window in April 2019 near the minimum of solar cycle 24, when a single active region, NOAA 12738, crossed the disk alone over six days. By subtracting a spectrum from a spotless day to remove the full-disk contribution, and then fitting the remaining active-region spectrum, the researchers measured wavelength shifts that matched a tuned raytrace model remarkably well. The tuning revealed that the Sun’s center sits about 2.5 arc-minutes east of MEGS-B’s optical center, a misalignment inherited from the compromise positioning of EVE’s three channels and the jolts of launch. The resulting correction equations, expressed as parabolic functions of wavelength scaled by flare position, are now available for users of the data product, though the corrections are not applied automatically because the processing pipeline does not know each flare’s location.

The payoff comes in the flare statistics. For the X2.2 flare of 15 February 2011, the first X-class event of the SDO mission, all chromospheric, transition region, and cool coronal features below 1 million kelvin showed maximum red shifts averaging 75 plus or minus 24 kilometers per second, while hotter coronal lines showed blue shifts averaging minus 114 plus or minus 75 kilometers per second, with the Fe XIV line at 21.14 nanometers reaching an extraordinary minus 213 kilometers per second. The X9.0 flare of 3 October 2024 told a similar story, with downflows averaging 37 plus or minus 16 kilometers per second and upflows averaging minus 94 plus or minus 58 kilometers per second. In both cases, and across a broader sample of 15 disk-center X-class flares, the velocity maxima almost always occurred during the impulsive phase, the brief interval when magnetic reconnection releases energy most furiously.

These patterns match the standard picture of flare physics, often called the CSHKP model, in which reconnection drives chromospheric evaporation upward into hot coronal loops while cooler material drains downward. The transition from red shifts to blue shifts between 1 and 2 million kelvin, first noted by Milligan and Dennis in 2009 using Hinode data, appears clearly in the EVE results. The findings also align with earlier EVE-based analyses, including Hudson and colleagues’ 2011 report of a 50 kilometers-per-second red shift in He II and a 100 kilometers-per-second blue shift in Fe XXIV, and Otsu and Asai’s 2024 detection of a dramatic minus 400 kilometers-per-second blue shift during a filament eruption. For limb flares, the team found that even after location corrections, coronal lines still blue-shift by about 150 kilometers per second relative to the gradual phase, hinting at non-radial outflows that may accompany coronal mass ejections.

The practical lesson for solar physicists is that the EVE Level 4 Lines product, despite the instrument’s modest resolution and full-disk field of view, opens a routine path to measuring flare plasma dynamics across an entire solar cycle. Users must apply the optical wavelength-shift correction based on flare location for anything away from disk center, or risk mistaking instrumental artifacts for solar flows of 50 to 200 kilometers per second. But with 42 X-class flares already analyzed for MEGS-A and 103 for MEGS-B, and countless smaller events awaiting study, the new data product promises to deepen understanding of the magnetic explosions that drive space weather, disturb satellite orbits, and occasionally paint auroras across skies far from the poles.

Subject of Research: Measurement of solar flare Doppler velocities using the SDO EVE Level 4 Lines data product

Article Title: Solar Doppler Velocity Results from the SDO EVE Level 4 Lines Data Product

Article References: Solar Doppler Velocity Results from the SDO EVE Level 4 Lines Data Product. (n.d.). https://doi.org/10.1007/s11207-026-02727-w

Image Credits: AI Generated

DOI: 10.1007/s11207-026-02727-w

Keywords: solar flares, Doppler velocity, SDO, EVE, extreme ultraviolet, corona, transition region, space weather, magnetic reconnection, spectroscopy, Solar Dynamics Observatory, MEGS