Science nugget: Multi-source connectivity drives heliospheric solar wind variability - Solar Orbiter
Multi-source connectivity drives heliospheric solar wind variability
(Solar Orbiter Nugget #35 by Stephanie L. Yardley1,2,3,4, David H. Brooks5, Raffaella D’Amicis6, Christopher J. Owen3, David M. Long7, et al. )
Introduction
The solar wind is the continuous outflow of tenuous, magnetised plasma into the heliosphere that originates from multiple sources in the solar corona. The solar wind is generally classified into two different types: relatively fast (>= 500 km/s), smooth and continuous streams from coronal holes, and slow (< 500 km/s), highly variable streams whose origins are still under debate [1,2,3]. One of the main goals of the ESA/NASA Solar Orbiter mission [4] is to determine the origin of solar wind plasma and what drives its heliospheric variability.
Promising source regions of the slow solar wind are the boundaries between open and closed magnetic fields such as (but not limited to) the edges of active regions [5,6] and coronal holes [7,8,9] where interchange reconnection can take place in order to release plasma into the solar wind [10,11,12]. Previous works have used plasma composition diagnostics to trace solar wind plasma detected in situ at 1au by ACE back to observations of outflows at AR boundaries taken by Hinode [13], although small-scale variability is often lost at large distances from the Sun due to transport processes.
Solar Orbiter Remote-sensing Observations
The remote-sensing observations and in situ measurements utilized in this analysis were taken as part of the Slow Solar Wind Connection Science Solar Orbiter Observing Plan (SOOP) (see more details of in [14], and other recent results in [15,16]). The Slow Wind SOOP operated for the first time during Solar Orbiter’s close perihelion passage in March 2022 (from 3 March 2022 06:00 UT until 6 March 2022 18:30 UT), when Solar Orbiter was at a close distance of approximately 0.5au. Figure 1 shows an example of the high-resolution remote-sensing observations taken at the beginning of the window on 3 March 2022.
Figure 1: Solar Orbiter remote-sensing observations taken on 3 March 2022 during the Slow Wind SOOP. (a) The EUI/FSI 174 Å image with the partial disk EUI/HRI 174 Å and PHI/HRT overlayed, where the green (blue) contours represent positive (negative) polarity magnetic field of the AR complex with a saturation of +(-)500) G. The active region numbers are labelled in white. (b-c) A close-up of (a) with the SPICE Mg VIII/Ne VIII intensity map overplotted. The points represent the connectivity points taken from the magnetic connectivity tool [17] corresponding to the in situ times of 3 March 2022 (b) and 7 March 2022 (c) where the colourbar gives the probability of the connectivity points. R1 and R2 are the regions where the composition was determined by applying spectroscopic techniques to the SPICE data.
To connect in situ measurements of solar wind plasma back to the remote-sensing observations of its solar origins requires the source location to be estimated by using the magnetic connectivity tool [17]. The magnetic connectivity of Solar Orbiter around the time of the Slow Wind SOOP moves across a dark channel that later merges with the large equatorial coronal hole (visible in SDO/AIA 193Å, not shown here) and the active region complex (from the negative polarities of AR 12961 to AR 12957) as seen in Figure 1(b-c). During this period, continuous flux emergence was observed (visible in SDO/HMI and PHI/HRT) in the region along with large-scale coronal fan loops (as seen in EUI/HRI 174 Å) associated with the negative polarities of the AR complex. By using a potential field extrapolation, we found that the large-scale coronal fan loops were associated with open magnetic fields whereby coronal plasma could potentially escape as the solar wind and be detected in situ by Solar Orbiter a few days later.
The composition of solar wind plasma varies depending on its solar origin. We applied spectroscopic techniques to SPICE data to determine that there was a clear difference in the plasma composition between the areas associated with the two negative polarities (R1 and R2 in Figure 1c) of the AR complex. A larger Mg/Ne abundance ratio suggesting coronal or strong coronal composition was found in the region associated with the negative polarity of AR 12961 (R1) compared to a smaller ratio suggesting photospheric or weak coronal composition in the region associated with the negative polarity of AR 12957 (R2).
In situ measurements
During 1 to 9 March 2022, SWA/PAS detected three fast and two slow-speed solar wind streams originating from the CH-AR complex (Figure 2a,b). MAG measured Sunward directed radial magnetic field (Figure 2c), which was consistent with the sources, namely the negative polarities of the CH and the two active region leading polarities. The VB correlation coefficient, a measure of Alfvénicity, is high during the fast streams and the subsequent Alfvénic slow stream but shows a poor correlation during the final typical (i.e. non-Alfvénic) slow wind stream (Figure 2d).
The electron strahl, which is a field-aligned beam of electrons propagating away from the solar corona, provides a direct probe of the magnetic connectivity and is measured by SWA/EAS (Figure 2e). For most of the period, the electron strahl is streaming outwards, directed anti-parallel to the magnetic field. There are numerous small periods of bidirectional strahl that are associated with the boundaries of the fast solar wind streams originating from the different sections of the CH. There is a long period of asymmetric bidirectional strahl beginning on 5 March 2022, suggesting that the magnetic field was locally connected back to different locations on the Sun, indicative of closed expanding field associated with the emerging AR complex.
Heavy ion measurements taken by SWA/HIS (Figure 3f,g), which can be linked to the spectroscopic data from SPICE, are also consistent with the magnetic connectivity moving across the CH-AR complex. Initially the Fe/O and O7+/O6+ ratios are low, indicative of plasma with photospheric abundance and temperatures originating from the CH. The Fe/O and O7+/O6+ ratios then increase, indicative of coronal and high temperature plasma from the leading edge of the AR complex. This coincides with the period of high Alfvénicity and bidirectional electron strahl. The Fe/O ratio decreases again while the O7+/O6+ ratio remains increased and variable suggesting that the slow wind arriving at SO originates from the leading polarity of the second AR in the complex.
Conclusions
By combining the magnetic field modelling and spacecraft connectivity, the spectroscopic analysis with the remote-sensing observations and in situ measurements from Solar Orbiter we have shown that Solar Orbiter detects three fast and two solar wind streams originating from the CH-AR complex. These results strongly support the scenario that the variability of the solar wind is driven by the transition of the magnetic connectivity of Solar Orbiter across the CH-AR complex, where the magnetic configuration is also altered due to interchange reconnection occurring between open and closed magnetic fields within the AR complex. We have shown that through coupling high-resolution remote-sensing observations and in situ measurements taken at close distances from the Sun that the solar wind still exhibits the footprints of its multiple solar sources. More cases should be investigated to determine whether similar in situ signatures are observed at close distances from the Sun taking advantage of measurements other close-in missions such as Parker Solar Probe.
This article has been published in Nature Astronomy with DOI: https://doi.org/10.1038/s41550-024-02278-9
Acknowledgments
S.L.Y. is grateful to the Science Technology and Facilities Council for the award of an Ernest Rutherford Fellowship (ST/X003787/1), for funding via the consolidated grant (STFC ST/V000497/1), and NERC for the SWIMMR Aviation Risk Modeling (SWARM) project grant (NE/V002899/1). The work of D.H.B. was performed under contract to the Naval Research Laboratory and was funded by the NASA Hinode program. D.M.L. is grateful to the Science Technology and Facilities Council for the award of an Ernest Rutherford Fellowship (ST/R003246/1). D.B. is funded under Solar Orbiter EUI Operations grant number ST/X002012/1 and Hinode Ops Continuation 2022-25 grant number ST/X002063/1. R.M.D. acknowledges support from NASA grant 80NSSC22K0204. N.N. is supported by STFC PhD studentship grant ST/W507891/1 and UCL Studentship. Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. The SO/EUI instrument was built by CSL, IAS, MPS, MSSL/UCL, PMOD/WRC, ROB, LCF/IO with funding from the Belgian Federal Science Policy Office (BELSPO/PRODEX PEA 4000134088); the Centre National d’Etudes Spatiales (CNES); the UK Space Agency (UKSA); the Bundesministerium für Wirtschaft und Energie (BMWi) through the Deutsches Zentrum für Luft- und Raumfahrt (DLR); and the Swiss Space Office (SSO). The German contribution to SO/PHI is funded by the BMWi through DLR and by MPG central funds. The Spanish contribution is funded by FEDER/AEI/MCIU (RTI2018-096886-C5), a “Center of Excellence Severo Ochoa” award to IAA-CSIC (SEV-2017-0709), and a Ramón y Cajal fellowship awarded to DOS. The French contribution is funded by CNES. The development of SPICE has been funded by ESA member states and ESA. It was built and is operated by a multi-national consortium of research institutes supported by their respective funding agencies: STFC RAL (UKSA, hardware lead), IAS (CNES, operations lead), GSFC (NASA), MPS (DLR), PMOD/WRC (Swiss Space Office), SwRI (NASA), UiO (Norwegian Space Agency). Solar Orbiter Solar Wind Analyser (SWA) data are derived from scientific sensors which have been designed and created, and are operated under funding provided in numerous contracts from the UK Space Agency (UKSA), the UK Science and Technology Facilities Council (STFC), the Agenzia Spaziale Italiana (ASI), the Centre National d’Etudes Spatiales (CNES, France), the Centre National de la Recherche Scientifique (CNRS, France), the Czech contribution to the ESA PRODEX programme and NASA. Solar Orbiter SWA work at UCL/MSSL is currently funded under STFC grants ST/W001004/1 and ST/X/002152/1. Solar Orbiter magnetometer operations are funded by the UK Space Agency (grant ST/T001062/1). Funding for SwRI was provided by NASA contract NNG10EK25C. Funding for the University of Michigan was provided through SwRI subcontract A99201MO.
Full list of authors: Stephanie L. Yardley1,2,3,4, David H. Brooks5, Raffaella D’Amicis6, Christopher J. Owen3, David M. Long7, Deb Baker3, Pascal Démoulin8,9, Matt Owens2, Mike Lockwood2, Teodora Mihailescu3, Jesse T. Coburn3, Ryan M. Dewey10, Daniel Müller11, Gabriel H.H. Suen3, Nawin Ngampoopun3, Philippe Louarn12, Stefano Livi13,10, Sue Lepri10, Andrzej Fludra14, Margit Haberreiter15 and Udo Schuehle16
Affiliations
1 Department of Mathematics, Physics and Electrical Engineering, Northumbria University, UK
2 Department of Meteorology, University of Reading, UK
3 Department of Space and Climate Physics, UCL Mullard Space Science Laboratory, UK
4 Donostia International Physics Center (DIPC), Spain
5 Department of Physics & Astronomy, George Mason University, USA.
6 INAF-Istituto di Astrofisica e Planetologia Spaziali, Italy
7 School of Physical Sciences, Dublin City University, Ireland
8 LESIA, Observatoire de Paris, Université PSL, CNRS, France
9 Laboratoire Cogitamus, France
10 Climate and Space Sciences and Engineering, University of Michigan, USA
11 European Space Agency, ESTEC, The Netherlands
12 Institut de Recherche en Astrophysique et Planétologie, France
13 Southwest Research Institute, USA
14 RAL Space, UKRI STFC Rutherford Appleton Laboratory, UK
15 Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Switzerland
16 Max-Planck-Institut für Sonnensystemforschung, Germany
References
[1] Abbo, L., Ofman, L., & Antiochos, S. K. et al. 2016, SSRs, 201, 55
[2] Cranmer, S. R., Gibson, S. E., & Riley, P. 2017, SSRs, 212, 1345
[3] Viall, N. M., & Borovsky, J. E. 2020, JGR, 125(7), 26005
[4] Müller, D., St. Cyr, O. C., Zouganelis, I. et al. 2020, A&A, 642, 1
[5] Hinode Review Team, Al-Janabi, K., Antolin, P., & Baker, D. et al. 2019, Pub. Of the Astron. Soc. Of Japan, 71(5), 1
[6] Tian, H., Harra, L., & Baker, D et al. 2021, Sol. Phys., 296(3), 47
[7] Abbo, L., Antonucci, E., & Mikíc et al. 2010, AdSR, 46(11), 1400
[8] Brooks, D. H., Ugarte-Urra, I., & Warren, H. P. et al. 2015, Nat. Comms., 6, 5947
[9] Macneil, A. R., Owen, C. J., & Baker et al. 2019, ApJ, 887(2), 146
[10] Fisk, L. A. 2002, JGR, 108(A4), 1157
[11] Edmondson, J. K., Antiochos, S. K., & DeVore, C. R. et al. 2010, ApJ, 714(1), 517
[12] Crooks, N. U. & Owens, M. J. 2012, SSRs, 172(1), 201
[13] Brooks, D. H. & Warren H. P. 2011, ApJL, 727(1), 13
[14] Yardley, S. L., Owen, C.J, & Long, D. M. et al 2023, ApJS, 267(1), 19
[15] Baker, D., Démoulin, Yardley, S. L. et al. 2022, ApJ, 950(1), 65
[16] Ngampoopun, N., Long, D. M., Baker. D et al. 2022, ApJ, 950(2), 150
[17] Rouillard, A. P., Pinto, R. F., Vourlidas, A. et al. 2020, A&A, 642, 2
[18] Yardley, S. L., Brooks, D. H., D’Amicis, R. et al. 2024, Nat. Astr., 8, 953
Nuggets archive
2024
25/09/2024: All microflares that accelerate electrons to high-energies are rooted in sunspots
25/09/2024: Connecting Solar Orbiter and L1 measurements of mesoscale solar wind structures to their coronal source using the Adapt-WSA model
18/09/2024: Modelling the global structure of a coronal mass ejection observed by Solar Orbiter and Parker Solar Probe
28/08/2024: Coordinated observations with the Swedish 1m Solar Telescope and Solar Orbiter
21/08/2024: Multi-source connectivity drives heliospheric solar wind variability
14/08/2024: Composition Mosaics from March 2022
19/06/2024: Coordinated Coronal and Heliospheric Observations During the 2024 Total Solar Eclipse
22/05/2024: Real time space weather prediction with Solar Orbiter
15/05/2024: Hard X ray and microwave pulsations: a signature of the flare energy release process
01/02/2024: Relativistic electrons accelerated by an interplanetary shock wave
11/01/2024: Modelling Two Consecutive Energetic Storm Particle Events observed by Solar Orbiter
2023
14/12/2023: Understanding STIX hard X-ray source motions using field extrapolations
16/11/2023: EUI data reveal a "steady" mode of coronal heating
09/11/2023: A new solution to the ambiguity problem
02/11/2023: Solar Orbiter and Parker Solar Probe jointly take a step forward in understanding coronal heating
25/10/2023: Observations of mini coronal dimmings caused by small-scale eruptions in the quiet Sun
18/10/2023: Fleeting small-scale surface magnetic fields build the quiet-Sun corona
27/09/2023: Solar Orbiter reveals non-field-aligned solar wind proton beams and its role in wave growth activities
20/09/2023: Polarisation of decayless kink oscillations of solar coronal loops
23/08/2023: A sharp EUI and SPICE look into the EUV variability and fine-scale structure associated with coronal rain
02/08/2023: Solar Flare Hard Xrays from the anchor points of an eruptive filament
28/06/2023: 3He-rich solar energetic particle events observed close to the Sun on Solar Orbiter
14/06/2023: Observational Evidence of S-web Source of Slow Solar Wind
31/05/2023: An interesting interplanetary shock
24/05/2023: High-resolution imaging of coronal mass ejections from SoloHI
17/05/2023: Direct assessment of far-side helioseismology using SO/PHI magnetograms
10/05/2023: Measuring the nascent solar wind outflow velocities via the doppler dimming technique
26/04/2023: Imaging and spectroscopic observations of EUV brightenings using SPICE and EUI on board Solar Orbiter
19/04/2023: Hot X-ray onset observations in solar flares with Solar Orbiter/STIX
12/04/2023: Multi-scale structure and composition of ICME prominence material from the Solar Wind Analyser suite
22/03/2023: Langmuir waves associated with magnetic holes in the solar wind
15/03/2023: Radial dependence of the peak intensity of solar energetic electron events in the inner heliosphere
08/03/2023: New insights about EUV brightenings in the quiet sun corona from the Extreme Ultraviolet Imager