Multi-Wavelength Observations of Two Explosive Events and Their Effects on the Solar Atmosphere

Research Paper J. Astron. Space Sci. 33(3), 197-205 (2016) http://dx.doi.org/10.5140/JASS.2016.33.3.197

Multi-wavelength Observations of Two Explosive Events and Their Effects on the Solar Atmosphere

Agustinus G. Admiranto†, Rhorom Priyatikanto Space Science Center, National Institute of Aeronautics and Space, Bandung 40173, Indonesia

We investigated two flares in the solar atmosphere that occurred on June 3, 2012 and July 6, 2012 and caused propagation of Moreton and EIT waves. In the June 3 event, we noticed a filament winking which presumably was caused by the wave propagation from the flare. An interesting feature of this event is that there was a reflection of this wave by a coronal hole located alongside the wave propagation, but not all of this wave was transmitted by the coronal hole. Using the running difference method, we calculated the speed of Moreton and EIT waves and we found values of 926 km/s before the reflection and 276 km/s after the reflection (Moreton wave) and 1,127 km/s before the reflection and 46 km/s after the reflection (EIT wave). In the July 6 event, this phenomenon was accompanied by type II and type III solar radio bursts, and we also performed a running difference analysis to find the speed of the Moreton wave, obtaining a value of 988 km/s. The speed derived from the analysis of the solar radio burst was 1,200 km/s, and we assume that this difference was caused by the different nature of the motions in these phenomena, where the solar radio burst was caused by the propagating particles, not waves.

Keywords: flare, Moreton wave, EIT wave, coronal hole, solar radio bursts

1. INTRODUCTION Athay & Moreton 1961), where the flare explosion triggers a shock wave that propagates along the chromosphere. There are many events in the solar atmosphere that Uchida (1968) modeled the Moreton wave mechanism. In his are considered as explosive events, and usually they have model, a solar flare initiates a coronal shock disturbance that some impacts that can be detected on Earth (Daglis 2001; propagates as a hydromagnetic fast-mode wave whose front Bothmer & Daglis 2007). Although these phenomena have has a circular intersection line with the upper chromosphere. been studied extensively, there are still some unsolved The chromospheric (Moreton) wave is then treated as an problems. Flares, coronal mass ejections, and coronal holes acoustic wave due to the refraction of the coronal wave at this are some of the phenomena that could exert considerable intersection. Since Moreton waves were observed on only one influence toward the Earth. Often, these eruptive processes side of the flare, Uchida suggested that this asymmetry was trigger waves that propagate across the solar surface and due to a limited-directivity explosion of the flare. Nevertheless, can be observed in several wavelengths, mainly in Hα and there are some arguments that go against this because there extreme ultraviolet. The first observation of these waves was were some flares that occur with no Moreton waves observed. conducted in Hα wavelength by Moreton (1960). Subsequent Cliver et al. (1999) argued that the source of the Moreton waves observations revealed that such waves propagate with is coronal mass ejections, not flares. velocities of 500-1,500 km/s with angular extent of 90-270° The advent of space-borne observations enabled solar (Warmuth et al. 2004; Balasubramaniam et al. 2010). Moreton physicists to look beyond the optical window to the ultra violet waves usually occur after a large solar flare (Moreton 1960; and extreme ultra violet, and to see that there are similar waves

This is an Open Access article distributed under the terms of the Received 23 DEC 2015 Revised 14 JUN 2016 Accepted 16 JUN 2016 Creative Commons Attribution Non-Commercial License (http:// †Corresponding Author creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, E-mail: [email protected], ORCID: 0000-0003-1003-1583 provided the original work is properly cited. Tel: +62-22-601-2602, Fax: +62-22-601-4998

in the extreme ultra violet band. These waves are called EIT and coronal mass ejection that occured on February 15, (extreme ultraviolet imaging telescope) waves because they 2012. They found that the wave that passed through the were first observed using the EIT onboard the SOHO spacecraft coronal hole was accelerated and from this they inferred in 195 nm wavelength (Zhukov et al. 2009). The speed and that this wave is a real wave that obeys the law of reflection angular extent of the EIT waves are different from those of and transmission through a medium. Similar proof was Moreton waves. EIT waves propagate with speed of about provided by Gopalswamy et al. (2009) when they analyzed 170-350 km/s (Klassen et al. 2000). Some other researchers an EUV wave that was related with a fast CME (speed ~950 observed that the EIT propagates with speed in a range of 200- km/s) and a long-duration flare (GOES X-ray class B9.5) 400 km/s with an average of 270 km/s (Wills-Davey & Attrill that occured on May 19, 2007 from the active region NOAA 2009). The angular extent of these waves is usually wider than 10956. This phenomenon occured near a coronal hole that of the Moreton waves, being somewhat isotropical (Asai and they found that the resulting EUV wave from this flare et al. 2012). EIT waves occur more frequently than Moreton interacted with this coronal hole. waves, and accordingly have been more extensively studied. The speed analysis of the EUV waves showed that there In addition, in contrast with Moreton waves, EIT waves can was a change of speed and reflection of this wave after be observed through many channels using the atmospheric encountering the coronal hole. They argued that the speed imaging assembly on the solar dynamic observatory (SDO/ change and reflection of the wave support the notion that AIA, Lemen et al. 2012), whereas Moreton waves can be the EUV wave is a real wave, not a signature of a propagating observed in the Hα channel only. perturbation related to magnetic field line opening in the The observational differences between Moreton and wake of the associated CME (Veronig et al. 2006). They also EIT waves have sustained arguments about the nature of found that the resulting wave from the flare interacted with these waves. Although Moreton waves are observed in Hα, a coronal hole was decelerated by the coronal hole and they Balasubramaniam et al. (2007) argued that these waves also proved that the wave obeys the laws of reflection and propagate in the corona, not in the chromosphere. Furthermore, transmission and hence can be considered a real wave. the large discrepancies between the angular extent of the This paper reports our investigation of two Moreton waves, Moreton waves with that of EIT waves indicates that these waves where one is accompanied with an EIT wave. We consider are very different, both in terms of the mechanisms and the these two waves in detail because they were very different nature of their propagation. At present, the nature of Moreton from each other and seek to gain some insight into this and EIT waves is still a source of heated debate. The main points elusive wave from this very marked difference. These two of the debate are whether the EIT waves are: events occurred on June 3 and July 6, 2012, respectively, soon a) indeed coronal counterparts of Moreton waves (e.g. after the occurrence of M3.3 flare (June 3, 2012) and X1.1 flare Klassen et al. 2000; Thompson et al. 2000; Warmuth et (July 6, 2012) and coronal mass ejections. The phenomena al. 2001; Eto et al. 2002; Khan & Aurass 2002; Narukage that occurred on July 6 were accompanied by type II and et al. 2002; Vršnak et al. 2002; Gilbert et al. 2004; III solar radio bursts. Preliminary analyses regarding these Warmuth et al. 2004; Veronig et al. 2006); events have been reported in Admiranto & Priyatikanto (2015) b) caused by a flare’s explosive energy release or by an and Admiranto et al. (2014) while the present paper presents erupting CME (e.g. Warmuth et al. 2001; Biesecker a thorough analysis. Section 2 reviews the multi-wavelength et al. 2002; Hudson et al. 2003; Warmuth et al. 2004; data to be analyzed. Section 3 discusses the data analysis and Zhukov & Auchére 2004; Cliver et al. 2005; Vršnak et al. the results of this analysis. Section 4 provides a discussion of 2006); the results, and a summary is given in Section 5. c) not waves at all but rather propagating disturbances related to magnetic field line opening and restructuring associated with the CME lift-off (e.g. Delannée & 2. DATA Aulanier 1999; Wills-Davey & Thompson 1999; Delannée 2000; Wang 2000; Warmuth et al. 2001; Wu et al. 2001; In this study, we focus on two flaring events that occurred Chen et al. 2002; Vršnak et al. 2002; Ballai et al. 2005; on June 3, 2012 and July 6, 2012. The first event occurred at Attrill et al. 2007; Zhukov et al. 2009). NOAA 11496 (N16E38) and reached maximum X-ray flux of In some cases, the Moreton and EIT waves interacted with M3.3 at 17:55 UT. The second event occurred on July 6, 2012 coronal holes during their propagation. These interactions and occurred in the active region NOAA 11515 (S17W41) sometimes are used to prove the nature of these waves as with maximum X-ray flux of X1.1 at 23:01 UT. a real wave. Olmedo et al. (2012) investigated a X2.2 flare To better understand the Moreton wave resulting from http://dx.doi.org/10.5140/JASS.2016.33.3.197 198 Agustinus G. Admiranto & Rhorom Priyatikanto Multi-wavelength Observation of Two Explosive Events

those events, we analyzed a number of Hα images from the as a wave that moved in the chromospheric region. From global oscillation network group (GONG, Harvey et al. 1996) the movie of the sequence of Hα images, we also noticed a coordinated by the National Solar Observatory. The images winking filament which can be attributed to the motion of the were recorded with time resolution of about 20 seconds. In wave emanating from the flare location. total, we use 36 images for the first event and 30 images for We made a running difference analysis from the Hα and the second. We have used GONG data because the network one can see the filament moving away from the center of includes many observatories to observe the chromosphere the flare site. Looking at a sequence of pictures and making in high cadence so that the data completeness is more an animation of those pictures we can see that after the reliable. A couple of images are not of high quality and occurence of the bright features there was a propagating propagating wave features were not clearly detected. brightness enhancement that can be interpreted as a We chose only the data that can be used in our running propagation of a wave. Fig. 1 shows the wave motion and we difference analysis (will be described below). can see that this wave spanned angle of about 40°. From this EUV images from SDO/AIA (Lemen et al. 2012) were motion, we also derived the speed of the wave propagation used to investigate the behavior of EIT waves that occur based on the position of the wave in time. The diagram below in the corona. We used images from the 304 nm channel (Fig. 2) depicts the position of the wavefronts versus time, and because this channel gave the most pronounced features, from this diagram, we derived the speed of the Moreton wave and hence the running difference analysis was much easier. as 988 ±70 km/s. Additionally, to support our analysis, we also used coronal hole images obtained from the 171 nm channel. 3.2 EIT Wave of June 3

Observational data in EIT waves were obtained from 3. ANALYSIS SDO in several wavelengths, i.e. 94, 131, 193, 211, 304, and 335 , but more clear features can be observed in 304 . 3.1 Moreton Wave of June 3 The running differences analyses was conducted for the Å Å acquired SDO images. This technique will enhance any From the Hα images, we obtained some bright features subtle differences between two consecutive images, and that usually occur accompanying a flare. After the flare thus any motion of material caused by the flare can be easily started, some bright filaments occured near the flare location. detected. We tried to obtain the running difference between We followed the evolution of the active region since the two images in which the time distance between consecutive beginning of the flare. We noticed several interesting features images is 5 min to gain insight into the dynamics of the in these image sequences during the progression toward filament, and we found the differences in images taken from its maximum (Fig. 1). From this data, we can clearly see the 17:48 UT till 18:18 UT. moving density enhancement which can be interpreted

500 km) 3 150 r (10 17:51 17:52 17:53

0 0 2 4 6 8 10 t (minutes) Fig. 2. Radial distance of the wavefronts versus time derived from 17:54 17:55 17:56 the running differences of Hα and EIT images. One can see the abrupt Fig. 1. Sequence of Hα images of NOAA 11496 region. There is change of speed in both the Moreton wave and EIT the wave. Filled progression of brightness enhancements that occurred before the and empty symbols represent the measured value from Hα and EUV flare explosion, and one can also see the filament winking (arrow), observations, respectively. Triangles and circles represent the observed which was presumably caused by a wave propagation. propagated and reflected waves.

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(a) 17:48 – 17:53 (b) 17:53 – 17:58 (c) 17:58 - 18:03

(d) 18:03 – 18:08 (e) 18:08 – 18:13 (f) 18:13 – 18:18

Fig. 3. Running differences for images taken between 17:48 UT and 18:18 UT with 5 min time differences. Note the upward motion of the filament (dashed arrow) and the propagated wave (solid arrow).

If we look closely at the results of this technique, which was applied to the active region images, some filament motion began at about 17:53 UT and this motion ended at about 17:58 UT. The beginning of the filament motion occured later than the beginning of the flare, and it ended just after the maximum time of the flare. As seen in Fig. 3, the running differences technique employed for these images reveals some interesting features, there were some brightness changes in the images and presumably some reflection of wave caused by a coronal hole located at the right of the flare explosion. From the images shown in Figs. 3(c) and 3(d), it appears that the filament was moved upwards and hence this give the impression that the coronal hole reflected the incoming wave caused by the flare. To obtain the effect of the flare explosion toward its surrounding, we tried to obtain a broader view of the Sun and made a running difference analysis of the images taken consecutively from 17:53 UT till 17:58 UT with a time step of 1 min, and the results are shown in Fig. 4. These images were adjusted in terms of contrast and brightness, and hence the subtler image differences can be more clearly distinguished. From the images, one can see that there are two waves that Fig. 4. Running differences of two consecutive images. The contrast and originated from the flare explosion, and closer inspection brightness were adjusted between 17:53 UT-17:58 UT. The motion of the wave is observed in two directions. reveals that these two waves were related to the coronal hole; this coronal hole reflected and tranmitted the incoming wave. This reflection and transmission of the wave was proven in was absorbed by the coronal hole. speed analysis of the waves. As clearly seen in Fig. 2, the speed An interesting feature of the wave observed in these wavelengths of the transmitted wave is much less than that of the reflected is the existence of a coronal hole by which the wave was reflected. wave, and it appears that the energy of the transmitted wave The speed and direction of the EIT wave are influenced by this http://dx.doi.org/10.5140/JASS.2016.33.3.197 200 Agustinus G. Admiranto & Rhorom Priyatikanto Multi-wavelength Observation of Two Explosive Events

coronal hole, as shown in Fig. 5. It appears that the two movements, and computed more easily. Fig. 6 below shows the results as observed in Fig. 4, were caused by the existence of this coronal of running difference analysis for inverted images in the hole, in which one part of the wave was reflected by the coronal region. hole and the other part was transmitted with reduced velocity. Using these images, we made a plot of location versus time to obtain the speed of wave propagation along the 3.3 Moreton Wave of July 6 chromosphere, and the results can be seen in Fig. 7 below. The results show that the speed of the Moreton wave is From Fig. 6 we conclude that the winking filament that about 988 ± 70 km/s. can be observed in the June 3 phenomenon was not present The Moreton wave speed derived from the July 6 phenomenon in this event. On the other hand, we see a portion of wave is not substantially different from that of the June 3 phenomenon. motion caused by the flare explosion, which caused some These values are consistent with those previously found for other brightness changes, as can be seen in the Fig. 6 sequence. similar phenomena (Balasubramaniam et al. 2007, 2010; Muhr et As done for the June 3 phenomenon, we try to analyze al. 2010; Asai et al. 2012). the speed of the wave motion caused by the flare. To this end, we cropped and inverted the images and performed 3.4 EIT Wave of July 6 a running average analysis to enhance the differences among the images so that the wave motion can be detected A similar running difference analysis was also conducted for the EUV images taken by SDO. We also analyzed the

300 km)

3 150 r (10

0 0 1 2 3 4 5 6 t (minutes) Fig. 5. The movement direction of a wave reflected by the coronal Fig. 7. The speed of Moreton wave derived from the wavefront hole near the flare location(Courtesy of www://helioviewer.org). position in the chromosphere versus time.

Fig. 6. Running difference of inverted Hα images. Note the arcs that delineate the wave motion in the chromosphere.

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304 channel, which can be seen in Fig. 8. From this interaction with a coronal hole. analysis it was shown that there was no wave observed in Speed analyses from the observed density enhancement Å EUV channel. Presumably it existed, but because of the in Hα images give the speed of the Moreton wave for the June projection effect due to the location of the flare, which is 3 event as about 926 km/s. The same analysis was conducted near the limb, it was not possible to see it. for the EIT images from SDO/AIA, in which the cadence is On the other hand, related to the flare, type II and III about 12 seconds, and the speed of the shock wave was 1,127 solar radio bursts occurred right after the flare, as shown in km/s. This resulting speed of the EIT wave exceeds the speed Fig. 9 below. Type III occurred just after the flare, and type II of the Moreton wave. This is not trivial since the common EIT occurred about 5 min later. waves have much lower speed. The nature of the observed Type II and III solar radio bursts of the X-class flare of July moving features (both in chromosphere and lower corona 6 were recorded in Culgoora observatory. The other event layers) is still in question. is beyond the observation window of this observatory. The For the event of July 6, the obtained speed is 988 km/s and type III bursts started to occur at 23:05 UT, while the type II the flare was accompanied by a type III burst that occurred radio bursts started at 23:10 UT. A frequency analysis of the at 23:05 UT, about 4 min late compared to the peak-time of type II bursts yields a rising velocity of about 1,200 km/s. the X-ray flare. However, the radio burst time was still inside the range of the abrupt increase of X-ray intensity. A type II radio burst occurred at 23:10 UT after the ejected material 4. DISCUSSION AND CONCLUSIONS reached a higher and denser region of the corona. The reflection and transmission phenomena by a coronal hole Although the flares that occured on June 6 and July 3, that occured on the June 3 event proves that the Moreton wave 2012 both resulted in two kinds of waves, Moreton and EIT (at least in this event) was a real wave (it obeys transmission waves, these phenomena are very different from each other. and reflection laws). This phenomenon was also discussed by The Moreton wave that occurred on June 6 interacted with Gopalswamy et al. (2009), and they concluded that this reflection a coronal hole but there was no corresponding solar radio caused some dimming of the wave. A similar result was obtained burst. On the other hand, the phenomenon that occured on from our work, with the observation of the deceleration of both July 6, 2012 gave rise to a solar radio burst but there was no the Moreton and EIT waves, as can be seen in Fig. 2. Further

Fig. 8. Running difference analysis of EIT images taken in the 304 Å channel. Note that the filament moves upward (arrow), not in the direction of the Moreton wave. http://dx.doi.org/10.5140/JASS.2016.33.3.197 202 Agustinus G. Admiranto & Rhorom Priyatikanto Multi-wavelength Observation of Two Explosive Events

Fig. 9. Type II and type III solar radio burst that occured just after the July 6, 2012 flare. evidence that this is a wave can be seen from the filament Moreton waves and EIT waves related to the flare events winking in Hα that occured just after the flare (Fig. 1). of June 3, 2012 and July 6, 2012, Proceedings of the 5th Some interesting events related to these phenomena are the Internatioanl Conference on Mathematics and Natural occurrences of coronal mass ejection (CME), which happened Sciences, Bandung, Indonesia, 2-3 November 2014. just after the occurrence of the flares, where the CME data Asai A, Ishii TT, Isobe H, Kitai R, Ichimoto K, et al., First were obtained from the SOHO LASCO CME catalog (cdaw. simultaneous observation of an Hα Moreton wave, EUV gsfc.nasa.gov/CME_list). The CME that occurred on June 3 was wave, and filament/prominence oscillations, Astrophys. a partial halo with a maximum speed of 605 km/s. On the other J. Lett. 745, L18 (2012). http://dx.doi.org/10.1088/2041- hand, the CME related with the July 6 event was a halo event 8205/745/2/L18 with a maximum speed of 1,828 km/s. Wang (2000) argued Athay RG, Moreton GE, Impulsive phenomena of the solar that the initiation of a CME/flare could trigger an EUV wave. atmosphere. I. some optical events associated with flares Chen (2016) argued that there are two kinds of EUV waves, fast showing explosive phase, Astrophys. J. 133, 935-945 (1961). ones and slow ones, where the fast EUV waves are related with http://dx.doi.org/10.1086/147098 a solar radio burst. With respect to Chen (2016)’s argument, Attrill GDR, Harra LK, van Driel-Gesztelyi L, Démoulin P, both EUV waves were fast waves, but there are some questions Wülser JP, Coronal “wave”: a signature of the mechanism related with the waves that occurred on June 3 because on this making CMEs large-scale in the low corona?, Astron. day a solar radio burst was not observed. Nachr. 328, 760-763 (2007). http://dx.doi.org/10.1002/ asna.200710794 Balasubramaniam KS, Pevtsov AA, Neidig DF, Are Moreton ACKNOWLEDGMENTS waves coronal phenomena?, Astrophys. J. 658, 1372-1379 (2007). http://dx.doi.org/10.1086/512001 This study was initiated during a research visit of Agustinus Balasubramaniam KS, Cliver EW, Pevtsov A, Temmer M, Henry G. Admiranto to the Yunnan observatory during November- TW, et al., On the origin of the solar Moreton wave of 2006 December 2014, hosted by Dr. Jun Lin. This visit was supported December 6, Astrophys. J. 723, 587-601 (2010). http:// by the Ministry of Research Technology and Higher Education dx.doi.org/10.1088/0004-637X/723/1/587 of Indonesia. Assistance for figures correction by Nenik Ballai I, Erdélyi R, Pintér B, On the nature of coronal EIT waves, Nurjannah is greatly appreciated. Astrophys. J. Lett. 633, L145-L148 (2005). http://dx.doi. org/10.1086/498447 Biesecker DA, Myers DC, Thompson BJ, Hammer DM, REFERENCES Vourlidas A, Astrophys. J. Solar phenomena associated with “EIT waves”, Astrophys. J. 569, 1009-1015 (2002). Admiranto AG, Priyatikanto R, Moreton waves related to the http://dx.doi.org/10.1086/339402 solar eruption occurred on 3 June 2012 and 6 July 2012, Bothmer V, Daglis IA, Space weather - physics and effects Pub. Korean Astron. Soc. 30, 57-58 (2015). http://dx.doi. (Springer-Verlag Berlin Heidelberg, Berlin, 2007). org/10.5303/PKAS.2015.30.2.057 Chen PF, Wu ST, Shibata K, Fang C, Evidence of EIT and Admiranto AG, Priyatikanto R, Yus’an U, Puspitaningrum E, Moreton waves in numerical simulations, Astrophys. J. Lett.

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