Mode Conversion of a Solar Extreme-ultraviolet Wave over a Coronal Cavity

Feng

et al. 2018

ApJL

Extreme ultraviolet (EUV) waves, spectacular horizontally propagating disturbances in the low solar corona, always trigger horizontal secondary waves (SWs) when they encounter ambient coronal structure. We present a first example of upward SWs in a streamer-like structure after the passing of an EUV wave. The event occurred on 2017 June 1. The EUV wave happened during a typical solar eruption including a filament eruption, a CME, a C6.6 flare. The EUV wave was associated with quasi-periodic fast propagating (QFP) wave trains and a type II radio burst that represented the existence of a coronal shock. The EUV wave had a fast initial velocity of ∼1000 km s −1 , comparable to high speeds of the shock and the QFP wave trains. Intriguingly, upward SWs rose slowly (∼80 km s −1 ) in the streamer-like structure after the sweeping of the EUV wave. The upward SWs seemed to originate from limb brightenings that were caused by the EUV wave. All the results show the EUV wave is a fast-mode magnetohydrodynamic shock wave, likely triggered by the flare impulses. We suggest that part of the EUV wave was probably trapped in the closed magnetic fields of streamer-like structure, and upward SWs possibly resulted from the release of trapped waves in the form of slow-mode. It is believed that an interplay of the strong compression of the coronal shock and the configuration of the streamer-like structure is crucial for the formation of upward SWs.

Section: Conclusion and Discussionmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

An Extreme-ultraviolet Wave Generating Upward Secondary Waves in a Streamer-like Solar Structure

Zheng

Feng

et al. 2018

ApJL

“…Since the converted slowmode wave propagates along the closed magnetic loops, and cannot run across the nearly vertical magnetic field lines, it looks like a stationary front when seen from above. The limb event studied by Zong & Dai (2017) provided the first support for the mode-conversion model.…”

Section: Discussionmentioning

confidence: 87%

Observations of Two Successive EUV Waves and Their Mode Conversion

Chandra

Joshi

et al. 2018

ApJ

In this paper, we present the observations of two successive fast-mode extreme ultraviolet (EUV) wave events observed on 2016 July 23. Both fast-mode waves were observed by the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO) satellite, with a traveling speed of ≈675 and 640 km s −1 , respectively. These two wave events were associated with two filament eruptions and two GOES M-class solar flares from the NOAA active region 12565, which was located near the western limb. The EUV waves mainly move toward the south direction. We observed the interaction of the EUV waves with a helmet streamer further away in the south. When either or one of the EUV waves penetrates into the helmet streamer, a slowly propagating wave with a traveling speed of ≈150 km s −1 is observed along the streamer. We suggest that the slowly-moving waves are slow-mode waves, and interpret this phenomenon as the magnetohydrodynamic (MHD) wave mode conversion from the fast mode to the slow mode. Besides, we observed several stationary fronts in the north and south of the source region.

“…Despite the debate on the nature of slow component of EUV waves, it is widely accepted that the fast component of EUV waves, especially when faster than 500 km s −1 , is a fast-mode magnetoacoustic wave or shock wave Long et al 2017b). Their wave nature can be inferred by various observational features, such as reflection (e.g., Long et al 2008;Gopalswamy et al 2009;Shen & Liu 2012c;Li et al 2012;Olmedo et al 2012;Yang et al 2013), transmission (e.g., Liu et al 2012;Olmedo et al 2012;Shen et al 2013a), refraction (e.g., Shen & Liu 2012a;Shen et al 2013a), and mode conversion (e.g., Chen et al 2016;Zong & Dai 2017;Chandra et al 2018). In particular, Shen et al (2013a) observed many of these features in a single EUV wave event, which clearly demonstrated the wave nature of EUV waves.…”

Section: Introductionmentioning

confidence: 99%

First Unambiguous Imaging of Large-scale Quasi-periodic Extreme-ultraviolet Wave or Shock

Shen

Liu

et al. 2019

ApJ

We report the first unambiguous quasi-periodic large-scale extreme-ultraviolet (EUV) wave or shock that was detected by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. During the whip-like unwinding eruption of a small filament on 2012 April 24, multiple consecutive large-scale wavefronts emanating from AR11467 were observed simultaneously along the solar surface and a closed transequatorial loop system. In the meantime, an upward propagating dome-shaped wavefront was also observed, whose initial speed and deceleration are about 1392 km s −1 and 1.78 km s −2 , respectively. Along the solar surface, the quasi-peridoic wavefronts had a period of about 163±21 seconds and propagated at a nearly constant speed of 747±26 km s −1 ; they interacted with active region AR11469 and launched a sympathetic upward propagating secondary EUV wave. The wavefronts along the loop system propagated at a speed of 897 km s −1 , and they were reflected back at the southern end of the loop system at a similar speed. In addition to the propagating waves, a standing kink wave was also present in the loop system simultaneously. Periodicity analysis reveals that the period of the wavefronts was consistent with that of the unwinding helical structures of the erupting filament. Based on these observational facts, we propose that the observed quasi-periodic EUV wavefronts were most likely excited by the periodic unwinding motion of the filament helical structures. In addition, two different seismological methods are applied to derive the magnetic field strength of the loop system, and for the first time the reliability of these inversion techniques are tested with the same magnetic structure.