Science nuggets - Solar Orbiter

Solar Orbiter Community building Webinars

Solar Orbiter community building webinars are aimed at the solar and space physics communities as a whole.
They aim is to provide recent news and insights on the Solar Orbiter operations and science.

They will be held on Webex every 1st Wednesday of every month, at 2:00pm European Central Time.

Click here for the Webinars registration

Future webinars

Webinar #10, 2nd July 2025 (30'): The dynamic Sun in high-resolution, from nanoflares to prominences. With Susanna Parenti (Institut d'Astrophysique Spatiale)

The new program from Fall 2025 is currently under preparation. To provide your feedback on the first series of webinars, find the link here.

Past webinars

Webinar #1, 2nd October 2024 (1h): Introduction to the Solar Orbiter mission: the science, the data, and the SunPy ecosystem. With Daniel Müller (ESA/ESTEC) and Laura Hayes (ESA/ESTEC)

Link to Daniel Müller's presentation

Link to Laura Hayes's presentation

Link to the form request for the webinar #1 recordings

(Notice: All information provided in the form request are treated confidentially and are only used for anonymised statistics.)

Webinar #2, 6th November 2024 (30'): Small-scale heating and relation to the solar wind: a review of Solar Orbiter observations. With Pradeep Chitta (MPS)

Link to Pradeep Chitta's presentation

Link to the form request for the webinar #2 recordings

(Notice: All information provided in the form request are treated confidentially and are only used for anonymised statistics.)

Webinar #3 was rescheduled to Webinar #5 due to a technical issue.

Webinar #4, 8th January 2025 (30'): Synergies between in situ and remote-sensing science with Solar Orbiter. With Daniel Verscharen (MSSL/UCL)

Link to Daniel Verscharen's presentation

Link to the form request for the webinar #4 recording

Webinar #5, 5th February 2025 (30'): Solar Wind connectivity with Solar Orbiter. With Stephanie Yardley (Northumbria University) (Rescheduled from 4th December 2024)

Link to Steph Yardley's presentation

Link to the form request for the webinar #5 recording

Webinar #6, 5th March 2025 (30'): Combining in-situ and remote-sensing data from Solar Orbiter to study particle acceleration and transport in the heliosphere. With Alexander Warmuth (AIP)

Link to Alexander Warmuth's presentation

Link to the form request for the webinar #6 recording

Webinar #7, 2nd April 2025 (30'): What can we learn from looking at the corona with Solar Orbiter. With Clementina Sasso (INAF)

Link to Clemetina Sasso's presentation

Link to the form request for the webinar #7 recording

Webinar #8, 7th May 2025 (30'): Observations of solar energetic particle events with Solar Orbiter and friends: new results and open-source analysis tools. With Nina Dresing (Turku University)

Link to Nina Dresing's presentation

Link to the form request for the webinar #8 recording

Webinar #9, 4th June 2025 (30'): A Tale of Two Spacecraft: How Solar Orbiter and Parker Solar Probe are Working Together to Revolutionize our View of the Sun. With Yeimy Rivera (Center for Astrophysics, Harvard)

Link to Yeimy Rivera's presentation

Link to the form request for the webinar #9 recording

Upcoming Events

2 July 2025 14:00 CEST: 10th Solar Orbiter community building webinar (see here)

8-10 July 2025: SOWG-27 at ESAC (hybrid meeting)

Nuggets archive

A prolific flare factory: Nearly continuous monitoring of an active region nest with Solar Orbiter

(Solar Orbiter Nugget #61 by Adam J. Finley¹, A. Sacha Brun¹, Antoine Strugarek¹, Barbara Perri¹)

1. Introduction

ESA's Solar Orbiter mission provides a unique opportunity to study the Sun's magnetic activity across its entire surface as it spends a few months each year observing the far side from Earth [1]. This vantage point complements Earth-based observations allowing for nearly continuous monitoring of solar activity. Magnetic activity on the Sun’s far side can have significant consequences for predicting space weather [2]. In this study, we used observations from Solar Orbiter along with data from the Solar Dynamics Observatory and GOES satellites to investigate the distribution of magnetic activity on the Sun. We focused on regions where intense magnetic fields frequently emerge in close proximity to one another, forming so-called active region (AR) nests.

2. Active Region Nesting

During the solar cycle, magnetic flux emerges in latitudinal bands that progress towards the equator in each hemisphere [3,4]. Longitudinal patterns in flux emergence are also present, called active longitudes or nests, but their long-term evolution is obscured from Earth alone. AR nests can remain active over several solar rotations due to localised and repeated flux emergence events. Figure 1 shows an AR nest from 2022, where the clustering of magnetic activity was evident in extreme-ultraviolet observations. Until recently, we have lacked the observations required to constrain their properties. Now, during favourable alignments with Earth, Solar Orbiter facilitates nearly continuous monitoring of the magnetic activity and flaring from AR nests.

Figure 1: Active region nesting. Left: Averaged extreme-ultraviolet from SDO in 2022, with persistent hot spots of activity highlighted. Right: Time-evolution of EUV activity in the northern hemisphere. Activity in the “region of interest” is continuous throughout 2022.

3. Flare Factory

In this study, we focused on the AR nest from Figure 1. This region was continuously observed by Earth and Solar Orbiter from April to October 2022. Observations from Solar Orbiter/EUI [5] were combined with SDO/AIA, and magnetic field measurements from Solar Orbiter/PHI [6] with SDO/HMI. An example of this is shown in Figure 2. X-ray flares statistics were taken from GOES and Solar Orbiter/STIX [7].

Figure 2: Combined map of the solar surface in extreme-ultraviolet from SDO, STEREO-A, and Solar Orbiter (on the far side) from May 2022. The AR nest is highlighted with a white contour.

Figure 3 shows two examples of solar flares observed during this period, highlighting the advantage of Solar Orbiter's far side position in capturing events not visible from Earth. Panel a) shows a flare seen by both GOES (near-Earth) and STIX (Solar Orbiter), while the flare in panel b) was only observed by STIX on the far side.

Figure 3: Example of two large solar flares from the AR nest during 2022. Panel (a) shows a solar eruption visible to both Earth (SDO/AIA image with GOES lightcurve) and Solar Orbiter (SolO/EUI image with STIX lightcurve). Panel (b) shows an eruption from the nest captured by Solar Orbiter on the far side to Earth.

Using these observations, we were able to study the distribution of solar flares from this AR nest, summarised in Figure 4. The two right panels show the peak flux distribution of solar flares from the AR nest during the eight Carrington rotations with nearly continuous observations (CR 2255 to 2262). We fit a power-law distribution with the exponent α, ranging from -1.6 to -2.1 with an average value of −1.86±0.18. This is consistent with previously derived exponents for soft x-ray flares [8]. During this time, the AR nest produced between 50-70% of all eruptions over the entire solar surface, including some of the strongest solar flares (X-class events). The repeated emergence of magnetic flux created complex active regions (as defined by the Hale classification system) that were more likely to produce strong solar flares [9]. In total, the AR nest contained 10 of the 17 complex flaring ARs recorded in 2022. Our work suggests that AR nests may act like assembly lines for the production of complex ARs, with new magnetic flux emerging into pre-existing flux [10].

Figure 4: Combined solar flare statistics for the AR nest using GOES and STIX. Left: Histogram of solar flare class (peak x-ray flux) versus time in 2022. From April to October the AR nest was near-continuously monitored. Right: Frequency of solar flares as a function of peak x-ray flux over the entire Sun for each solar rotation (28 days).

4. Conclusions

In 2022, an AR nest appeared in the Sun’s northern hemisphere and dominated solar activity over the entire solar surface for several months. A better understanding of the formation, evolution, and flaring characteristics of AR nests, facilitated by missions like Solar Orbiter, is crucial for improving space weather forecasts in the short to medium term. By providing a more complete picture of solar magnetic activity, including events on the far side, this research helps to predict and mitigate the potential impacts of solar eruptions on Earth.

This nugget is based on the following paper: Finley, A. J., et al. 2025, A&A, 697, A217

Affiliations
(1) Department of Astrophysics, Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191, Gif-sur-Yvette, France

References

[1] Finley, A. J., et al. 2025, A&A, 697, A217 https://doi.org/10.1051/0004-6361/202554323
[2] Perri, B., et al. 2024, A&A, 687, A10 https://doi.org/10.1051/0004-6361/202349040
[3] Hathaway, D. H. 2011, Solar Phys., 273, 221 https://doi.org/10.1007/s11207-011-9837-z
[4] Brun, A.S. & Browning, M., 2017, LRSP, 14, 4 https://doi.org/10.1007/s41116-017-0007-8
[5] Rochus, P., et al. 2020, A&A, 642, A8 https://doi.org/10.1051/0004-6361/201936663
[6] Solanki, S. K., et al. 2020, A&A, 642, A11 https://doi.org/10.1051/0004-6361/201935325
[7] Krucker, S., et al. 2020, A&A, 642, A15 https://doi.org/10.1051/0004-6361/201937362
[8] Aschwanden, M. J., et al. 2016, Space Sci. Rev., 198, 47 https://doi.org/10.1007/s11214-014-0054-6
[9] Sammis, I., et al. 2000, ApJ, 540, 583 https://doi.org/10.1086/309303
[10] Jaeggli, S. A. & Norton, A. A. 2016, ApJL, 820, L11 https://doi.org/10.3847/2041-8205/820/1/L11

Multi-spacecraft Radio Observations Trace the Heliospheric Magnetic Field

(Solar Orbiter Nugget #60 by Daniel L. Clarkson¹, Eduard P. Kontar¹, Nicolina Chrysaphi^1,2, A. Gordon Emslie³, Natasha L. S. Jeffrey⁴, Vratislav Krupar^5,6 & Antonio Vecchio^7,8)

1. Introduction

Solar flares accelerate energetic electrons that escape into interplanetary space, guided by the Parker spiral magnetic field, and are responsible for the generation of the interplanetary Type III solar radio bursts. With multiple spacecraft now in orbit around the Sun, we are in a unique position of observing the propagation of radio emission through the heliosphere from multiple vantage points.

2. Results

In this study, we demonstrate that the magnetic field not only guides the emitting electrons, but also directs radio waves via anisotropic scattering from density irregularities in the magnetised plasma of the interplanetary space.

Figure 1. Overview of a type III burst observed by four spacecrafts: PSP, SolO, Stereo-A, and Wind. (a) Dynamic spectra. (b) Time profiles at four frequencies with intensity scaled to 1 au. (c) Intensity peaks from panel (b) and directivity fitting. (d) Longitudes of the fitted maximum intensity. The symbols show the spacecraft positions in the heliosphere.

To address this effect across large distances in the heliosphere, we use observations of 20 Type III bursts between ~0.9-0.2 MHz from Parker Solar Probe, Solar Orbiter, STEREO-A and WIND spacecraft that were distributed around the Sun. Figure 1 shows an example event where the same burst is observed by spacecraft separated by ~180 degrees, with the brightest intensity observed by Solar Orbiter.

To reproduce the observations, we performed simulations to follow radio-waves. The simulations show that the radio-waves are guided by the heliospheric magnetic field via anisotropic scattering (Figure 2).

Figure 2. Polar plots of the time-averaged simulated photon propagation in the heliosphere for (a) a fundamental emitter (blue star) and (b) a harmonic emitter (green star). The coloured histograms show the photon positions with the average wavevector at a given location shown by the black arrows. The inset shows the approximate directivity at a distance where the scattering rate is significantly lower.

3. Conclusions

The paper concludes that the magnetic field guides only the emitting electrons whilst the radiation is weakly scattered cannot explain the directivity pattern in multi-spacecraft observations without invoking a much steeper curvature of the Parker spiral. Therefore, the emitted radio waves are also guided along the interplanetary field due to anisotropic scattering, affecting the radiation received by observers that are spatially separated around the Sun. The eastward deviation of the type III radio burst intensity with decreasing frequency (increasing distance) allows for the magnetic field to be traced to distances greater than that of the emitter path, offering a powerful diagnostic tool for space weather studies and a potentially wide-ranging diagnostic of the magnetic field structure of different astrophysical environments in which radio sources are embedded.

This nugget is based on the recent paper Clarkson, D.L., et al. Tracing the heliospheric magnetic field via anisotropic radio-wave scattering, Science Reports, 15, 11335 (2025). ). DOI: 10.1038/s41598-025-95270-w

Affiliations

(1) School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK
(2) Ecole Polytechnique, InstitutePolytechnique de Paris, CNRS, Laboratoire de Physique des Plasmas (LPP), Sorbonne Université, 4 Place Jussieu, 75005 Paris, France.
(3) Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101, USA.
(4) Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle upon Tyne NE1 8ST, UK.
(5) Goddard Planetary Heliophysics Institute, University of Maryland, Baltimore County,Baltimore, MD 21250, USA.
(6) Heliospheric Physics Laboratory, Heliophysics Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
(7) Radboud Radio Lab - Department of Astrophysics, Radboud University, Nijmegen, The Netherlands.
(8)LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France

Acknowledgements
This work is supported by UKRI/STFC grants ST/T000422/1 and ST/Y001834/1. N.C. acknowledges funding support from the Initiative Physique des Infinis (IPI), a research training program of the Idex SUPER at Sorbonne Université. A.G.E. was supported by NASA’s Heliophysics Supporting Research Program through grant 80NSSC24K0244, and by NASA award number 80NSSC23M0074, the NASA Kentucky EPSCoR Program, and the Kentucky Cabinet for Economic Development. V.K. was supported by the STEREO/WAVES and Wind/WAVES projects and by the NASA grant 19-HSR-19_2-0143. The authors thank the PSP/RFS, SolO/RPW, STEREO/WAVES, and Wind/WAVES teams for making the data available. Solar Orbiter49 is a mission of international cooperation between ESA and NASA, operated by ESA. The FIELDS experiment on the Parker Solar Probe spacecraft50 was designed and developed under NASA contract NNN06AA01C. This research has made use of the Astrophysics Data System, funded by NASA under Cooperative Agreement 80NSSC21M00561.