Multi-Spacecraft Observations of the 2022 March 25 CME and EUV Wave: An Analysis of their Propagation and Interrelation

(Solar Orbiter nugget #23 by A. Liberatore¹, P. C. Liewer¹, A. Vourlidas², C. R. Braga³, M. Velli^4,5,1, O. Panasenco⁶, D. Telloni⁷, and S. Mancuso⁷)

Introduction

EUV waves are large-scale wave-like coronal disturbances visible in extreme ultraviolet (EUV) light [1]. EUV waves arise from active regions (ARs) and are almost always associated with Coronal Mass Ejections (CMEs) [2]. The nature of EUV waves and their interrelation with CMEs is still debated [3,4]. In the following, we investigate the nature of these phenomena through a multi-spacecraft analysis of an EUV wave associated with a CME observed on 2022 March 25. At that time Solar Orbiter (SolO) was at its first close perihelion and in near quadrature with the Solar Terrestrial Relations Observatory (STEREO-A).

Figure 1. Left: Relative position of the spacecraft on March 25, 2022 at 05:00 am UTC [5]. STEREO-A (red square) and Solar Orbiter (blue square) are near quadrature. Right: Selection of frames showing the CME evolution as observed by SolO/FSI-174 (top, initial phases), and by combing SolO/FSI-174 + Metis + SoloHI (bottom, interplanetary evolution).

Observation of the 2022 March 25 CME and EUV wave

On 2022 March 25 at 05:00 UTC multiple spacecraft observed a CME originating from AR 12974. SolO followed the CME during its entire evolution from the low corona to large heliocentric distances (> 55 R⊙) by combining three remote sensing instruments on board (Figure 1): the Full Sun Imager (FSI-174) [6], the coronagraph Metis [7], and the Solar Orbiter Heliospheric Imager (SoloHI) [8].

During the evolution of this CME, both STEREO-A/Extreme Ultraviolet Imager (EUVI-195) and SolO/FSI-174 observed a EUV wave propagating away from the same AR (Figure 2). Because the AR is almost at the center of the solar disk as observed by STEREO-A/EUVI, we were able to trace the evolution of the EUV wavefront at various position angles through a “point-and-click” method.

Figure 2. The image on the left shows the propagation of the EUV wavefront (as observed by EUVI) in the FSI field of view. Top: EUV wave (orange arrows) as observed by SolO/FSI-174. Each image is the difference between two consecutive frames. Due to the different wavelength, the EUV wave is not as clearly visible as in EUVI-195. However, it is possible to clearly observe the front of the CME in its early stage (not visible by STEREO or other spacecraft). Bottom: Selection of frames showing the EUV wave evolution as observed by STEREO-A/EUVI-195. Each frame is processed via a wavelet filter [9,10] and subtracted by the previous one. The EUV wave starts between 05:02:50 and 05:05:00 UTC and is visible until ≈ 06:00:00 UTC with a temporal resolution of 2.5 minutes (An animation of this figure is available).

EUV wave - CME propagation and interrelation

[3] reviews various interpretations of the nature of EUV waves as pseudo-waves, magneto-hydrodynamic (MHD) waves, or hybrid (i.e., a combination of the previous ones). The pseudo-wave interpretation suggests that EUV waves are the disk projection of the CME’s expanding envelope and not a true wave phenomenon [11]. The fast-/slow-mode MHD wave mode speeds can be described by the following equation:

where v_A = local Alfven speed, c_s = sound speed, and θ = inclination between wave vector and magnetic field. The slow-mode phase velocity (v_s) has a strong dependence on the propagation angle and goes to zero at θ = 90° (i.e., it cannot propagate perpendicularly to the magnetic field lines). For this reason, and considering the large scales of these phenomena, this interpretation is often rejected. Eq. 1 shows also that a fast magnetosonic wave must have a speed > v_A. Another interpretation is given by [12] and [13]: EUV waves can be interpreted as waves initially driven by a fast lateral expansion of the CME, then transitioning to a fast magnetosonic wave, at a lower velocity, after the rapid initial expansion slows. The observation of this kinematic behavior is almost impossible without high cadence imaging since the initial high-speed propagation and the decoupling phase tend to develop within 5 mins or so.

The strategic position between SolO and STEREO-A, and the high cadence of the EUVI acquisitions (2.5 minutes) allows us to compare, frame-by-frame, the CME and EUV wave early phase evolution to deconstruct the nature of the wave and its interrelation with the CME.

The kinematics study of the EUV wave, derived via visual identification of the fronts using the STEREO-A data, shows a change in velocity at about 05:20 UTC (Figure 3a). At that time, FSI images show the last fast lateral expansion of the CME (Figure 1 top, and Figure 2 top). At the same moment, the EUV wave shows a double front (green square in Figure 2 bottom). These two fronts may be an indication of the decoupling moment between the expanding CME and EUV wave as suggested by [12] and [13]. Additional insights come from the Type II radio burst associated to this event. The expanding CME caused a type II radio emission [14,15]. When the expansion slows (≈ 05 : 20 UTC), the radio emission stops, and at the same time, the EUV wave becomes freely propagating.

Finally, comparing the EUV speed to the local magnetic field using standard models of the solar corona, we can notice how the EUV wave, once free to propagate, avoids strong magnetic field regions. This behavior is consistent with a fast-mode magnetosonic wave.

Figure 3. a-b): Evolution of the EUV wave front in time (a) and space (b). Different colors are different position angles. The right image (b) shows the front projected on an EUVI-195 image at a fixed time. A type II radio burst is observed in the range of time delimited by the two dotted vertical lines in the time-distance plot (a). c): EUV wavefront evolution observed on a Carrington map showing the contour of magnetic field strength calculated from a Potential Field Source Surface model for 2022 March 25 at 12:04 UTC, 1.2R⊙; Rss = 2.5. Different colors correspond to different times. The wave avoids strong magnetic field regions (top and top left regions) while being free to propagate through the low field regions (right-side regions).

Conclusion and Discussion

In this work we investigated the nature of EUV waves in relation to the CME evolution through the analysis of the multi-spacecraft remote sensing observations of the 2022 March 25 CME-EUV wave event. We performed a detailed analysis of this event making use of the strategic relative position of SolO and STEREO-A (near quadrature). The large amount of evidence summarized in this study (i.e., imaging, kinematic, radio analysis, comparison with B, etc.), gives further support to the hybrid interpretation of EUV waves proposed by [3] and [13].

Movie 1. The Stereo-A data clearly displaying the EUV wave discussed here.

This study has been published in Alessandro Liberatore, et al. 2023 ApJ, 957, 110 https://doi.org/10.3847/1538-4357/acf8bf

Acknowledgements

The work of A.L. and P.C.L. was conducted at the Jet Propulsion Laboratory, California Institute of Technology under a contract from NASA (80NM0018D0004). A.V. is supported by NASA grants 80NSSC22K1028 and 80NSSC22K0970. C.R.B. acknowledges the support from the NASA STEREO/SECCHI (NNG17PP27I) program and NASA HGI (80NSSC23K0412) grant. M.V. was supported by ISSI via the J. Geiss fellowship and NASA contracts NNN06AA01C and the NASA Parker Solar Probe Observatory Scientist grant NNX15AF34G.

Affiliations

¹ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

² The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA

³ George Mason University, Fairfax, VA 22030, USA

⁴ Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, 90095 USA 

⁵ International Space Science Institute, 3012 Bern, Switzerland

⁶ Advanced Heliophysics, Pasadena, CA 91106, USA

⁷ National Institute for Astrophysics, Astrophysical Observatory of Turin, 10025, Pino To.se, Turin, Italy

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