Flare Monitoring Telescope Research Articles

A three-dimensional velocity of an erupting prominence prior to a coronal mass ejection

Abstract We present a detailed three-dimensional (3D) view of a prominence eruption, coronal loop expansion, and coronal mass ejections (CMEs) associated with an M4.4 flare that occurred on 2011 March 8 in the active region NOAA 11165. Full-disk Hα images of the flare and filament ejection were successfully obtained by the Flare Monitoring Telescope (FMT) following its relocation to Ica University, Peru. Multiwavelength observation around the Hα line enabled us to derive the 3D velocity field of the Hα prominence eruption. Features in extreme ultraviolet were also obtained by the Atmospheric Imager Assembly onboard the Solar Dynamic Observatory and the Extreme Ultraviolet Imager on board the Solar Terrestrial Relations Observatory - Ahead satellite. We found that, following collision of the erupted filament with the coronal magnetic field, some coronal loops began to expand, leading to the growth of a clear CME. We also discuss the succeeding activities of CME driven by multiple interactions between the expanding loops and the surrounding coronal magnetic field.

Dynamic Processes of the Moreton Wave on 2014 March 29

Abstract On 2014 March 29, an intense solar flare classified as X1.0 occurred in active region 12017. Several associated phenomena accompanied this event, among them a fast-filament eruption, large-scale propagating disturbances in the corona and the chromosphere including a Moreton wave, and a coronal mass ejection. This flare was successfully detected in multiwavelength imaging in the Hα line by the Flare Monitoring Telescope (FMT) at Ica University, Peru. We present a detailed study of the Moreton wave associated with the flare in question. Special attention is paid to the Doppler characteristics inferred from the FMT wing (Hα ± 0.8 Å) observations, which are used to examine the downward/upward motion of the plasma in the chromosphere. Our findings reveal that the downward motion of the chromospheric material at the front of the Moreton wave attains a maximum velocity of 4 km s−1, whereas the propagation speed ranges between 640 and 859 km s−1. Furthermore, using the weak-shock approximation in conjunction with the velocity amplitude of the chromospheric motion induced by the Moreton wave, we derive the Mach number of the incident shock in the corona. We also performed the temperature-emission measure analysis of the coronal wave based on the Atmospheric Imaging Assembly observations, which allowed us to derive the compression ratio, and to estimate Alfvén and fast-mode Mach numbers on the order of 1.06–1.28 and 1.05–1.27. Considering these results and the magnetohydrodynamics linear theory, we discuss the characteristics of the shock front and the interaction with the chromospheric plasma.

“Dandelion” Filament Eruption and Coronal Waves Associated with a Solar Flare on 2011 February 16

Abstract Coronal disturbances associated with solar flares, such as Hα Moreton waves, X-ray waves, and extreme ultraviolet (EUV) coronal waves, are discussed herein in relation to magnetohydrodynamic fast-mode waves or shocks in the corona. To understand the mechanism of coronal disturbances, full-disk solar observations with high spatial and temporal resolution over multiple wavelengths are of crucial importance. We observed a filament eruption, whose shape is like a “dandelion,” associated with the M1.6 flare that occurred on 2011 February 16 in Hα images taken by the Flare Monitoring Telescope at Ica University, Peru. We derive the three-dimensional velocity field of the erupting filament. We also identify winking filaments that are located far from the flare site in the Hα images, whereas no Moreton wave is observed. By comparing the temporal evolution of the winking filaments with those of the coronal wave seen in the EUV images data taken by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory and by the Extreme Ultraviolet Imager on board the Solar Terrestrial Relations Observatory-Ahead, we confirm that the winking filaments were activated by the EUV coronal wave.

Propagation of Moreton Waves

Abstract With the Flare-Monitoring Telescope (FMT) and Solar Magnetic Activity Research Telescope (SMART) at Hida observatory of Kyoto University, 13 events of Moreton waves were captured at H$\alpha$ center, H$\alpha$$\pm$0.5 Å, and H$\alpha$$\pm$0.8 Å wavebands since 1997. With such samples, we have studied the statistical properties of the propagation of Moreton waves. Moreton waves were all restricted in sectorial zones with a mean value of 92$^\circ$. However, their accompanying EIT waves, observed simultaneously with SOHO/EIT at extreme-ultraviolet wavelength, were very isotropic with a quite extended scope of 193$^\circ$. The average propagation speeds of the Moreton waves and the corresponding EIT waves were 664 km s$^{-1}$ and 205 km s$^{-1}$, respectively. Moreton waves propagated either under large-scale close magnetic flux loops, or firstly in the sectorial region where two sets of magnetic loops separated from each other and diverged, and then stopped before the open magnetic flux region. The location swept by Moreton waves had a relatively weak magnetic field as compared to the magnetic fields at their sidewalls. The ratio of the magnetic flux density between the sidewall and the path falls in the range of 1.4 to 3.7 at a height of 0.01 solar radii. Additionally, we roughly estimated the distribution of the fast magnetosonic speed between the propagating path and sidewalls in an event on 1997 November 3, and found a relatively low-fast magnetosonic speed in the path. We also found that the propagating direction of Moreton waves coincided with the direction of filament eruption in a few well-observed events. This favors an interpretation of the “Piston” model, although further studies are necessary for any definitive conclusion.

The CHAIN-Project and Installation of Flare Monitoring Telescopes in Developing Countries

The Flare Monitoring Telescope (FMT) was constructed in 1992 at Hida Observatory in Japan to investigate the long-term variation of solar activity and explosive events. It has five solar imaging telescopes that simultaneously observe the full-disk Sun at different wavelengths around the H-alpha absorption line or in different modes. Therefore, the FMT can measure the three-dimensional velocity field of moving structures on the full solar disk. The science target of the FMT is to monitor solar flares and erupting filaments continuously all over the solar disk and to investigate correlation between the characteristics of the erupting phenomena and the geoeffectiveness of the corresponding coronal mass ejections (CMEs). We are planning to start up a new worldwide project, the Continuous H-alpha Imaging Network (CHAIN) project, as an important IHY project of our observatories. As part of this project, we are examining the possibility of installing telescopes similar to the FMT in developing countries. We have selected Peru and Algeria as the countries where the first and second overseas FMTs will be installed, and we are aiming to start operation of these FMTs by the end of 2010 before the maximum phase of solar cycle 24. To create such an international network, it will be necessary to improve the information technologies applied in our observation-system. In this paper, we explain the current status and future areas of work regarding our system.

Large-Amplitude Oscillation of an Erupting Filament as Seen in EUV, Hα, and Microwave Observations

We present multiwavelength observations of a large-amplitude oscillation of a polar-crown filament on 15 October 2002, which has been reported by Isobe and Tripathi (Astron. Astrophys.449, L17, 2006). The oscillation occurred during the slow rise (≈1 km s−1) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than a propagating wave. The amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about 5 km s−1 and 15 000 km, respectively. The period of oscillation was about two hours and did not change significantly during the oscillation. The oscillation was also observed in Hα by the Flare Monitoring Telescope at the Hida Observatory. We determine the three-dimensional motion of the oscillation from the Hα wing images. The maximum line-of-sight velocity was estimated to be a few tens of kilometers per second, although the uncertainty is large owing to the lack of line-profile information. Furthermore, we also identified the spatial displacement of the oscillation in 17-GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium and oscillated.

Large amplitude oscillation of a polar crown filament in the pre-eruption phase

We report observation of a large-amplitude filament oscillation followed by an eruption. This is used to probe the pre-eruption condition and the trigger mechanism of solar eruptions. We used the EUV images from the Extreme-Ultraviolet Imaging Telescope on board SOHO satellite and the H-alpha images from the Flare Monitoring Telescope at Hida Observatory. The observed event is a polar crown filament that erupted on 15 Oct. 2002. The filament clearly exhibited oscillatory motion in the slow-rising, pre-eruption phase. The amplitude of the oscillation was larger than 20 km/s, and the motion was predominantly horizontal. The period was about 2 hours and seemed to increase during the oscillation, indicating weakening of restoring force. These results strongly indicate that, even in the slow-rise phase before the eruption, the filament retained equilibrium and behaved as an oscillator, and the equilibrium is stable to nonlinear perturbation. Moreover, the transition from such nonlinear stability to either instabilities or a loss of equilibrium that leads to the eruption occurred in the Alfven time scale. This suggests that the onset of the eruption was triggered by a fast magnetic reconnection that stabilized the pre-eruption magnetic configuration, rather than by the slow shearing motion at the photosphere.

Evolution of Barb Angle and Filament Eruption

Hα observations of a quiescent U-shaped filament were obtained at Big Bear Solar Observatory and at Hida Observatory with the Flare Monitoring Telescope. The filament was located in the southern hemisphere on 1998 November 4. We study the evolution of the angle of a barb with respect to the axis of the filament and find the evolution can be divided into two phases: a rise from the acute phase to the obtuse phase and a fall. Thus, this indicates that the chirality of this barb changes with time. Moreover, in the process of evolution, we find that interconnection of the part of the filament bearing the barb with the whole filament became either weakened or strengthened. We impute the final eruption of the filament to the chirality evolution of the barb.

Observations of an Emerging Flux Region Surge: Implications for Coronal Mass Ejections Triggered by Emerging Flux

It is well known that coronal mass ejections (CMEs) are often associated with flares and filament eruptions. Previous studies of CMEs, however, have not established any association between CMEs and surges. In this paper, we present a detailed analysis of a large emerging flux region (EFR) surge and a jetlike CME, both observed on 1998 April 16. Our analysis shows a close temporal and spatial relationship between the two. Using observations from the Large Angle and Spectrometric Coronagraph (LASCO) and Hida Flare Monitoring Telescope (Hα, Hα ± 0.8 A), we found that the CME's onset time and central position angle were coincident with the surge features. Magnetograms and Hα filtergrams showed that the surge resulted from the successive emergence of a bipolar sunspot group, NOAA Active Region 8203, which was the only active region in the northern hemisphere. The surge was impulsively accelerated at around the peak time of the GOES SXR flux. The associated CME appeared in the field of view of LASCO C2 16 minutes after the surge disappeared. Importantly, observations from the EUV Imaging Telescope at λ195 A clearly demonstrate topological changes in the coronal field due to its interaction with the EFR. An initially closed EFR-loop system opened up during the surge. There was no filament involved in this surge-CME event. We propose that the onset of the CME resulted from the significant restructuring of the large-scale coronal magnetic field as a result of flux emergence in the active region. This surge-CME event strongly suggests that emerging flux may not only trigger a surge but also simultaneously trigger a CME by means of small-scale reconnection in the lower atmosphere.

A Study On Surges: I. Automatic Detection Of Dynamic Hα Dark Features From High-Cadence Full-Disk Observations

We present a new method for the automatic identification and classification of dynamic Hα dark features found in time series of full-disk solar images at three Hα wavelengths (center, and ± 0.8 A). The simultaneous Hα observations are obtained by the multi-channel Flare Monitoring Telescope (FMT) at Hida Observatory. The program was developed in order to replace the present visual detection and classification of the phenomena. Usually, an obvious dark feature found in the Hα −0.8 A observations probably corresponds to some phenomenon such as a surge or chromospheric network enhancement, or filament activity. Thus, one of our aims in this program is to distinguish each phenomenon by its own properties and key parameters. We optimized the threshold values of the key parameters such as the area and darkness of the transiently darkening features in Hα −0.8 A so that the computer can reasonably identify surges and filament activations. In comparison, for a 7-day observation period, the number of dark events detected by the program contains 89% of the events recognized visually. However, 10 times more events are detected automatically. The missing events are mainly caused by the deletion of data with poor visibility. It is found that the dark events can be identified with more precise starting and ending times by a machine than by a human. Some statistical studies of surges or other activities can be carried out based on the computer-produced database. With some modifications the program can be applied to monitor real-time dynamic features on disk, including flare ribbons.

Filament Oscillations and Moreton Waves Associated with EIT Waves

In this paper we compare EUV Imaging Telescope (EIT) waves with simultaneous phenomena seen in Hα in order to address the question of what an EIT wave is. We surveyed the events associated with solar flares larger than GOES M-class in 1999-2002. The Hα data are taken with the Flare-monitoring Telescope (FMT) at the Hida Observatory of Kyoto University. Among 14 simultaneous observations of EIT waves and Hα, 11 were found to have filament eruptions, three were associated with Moreton waves, and one was found to have only filament oscillations. This shows that we cannot see clear wave fronts in Hα even if EIT waves exist, but that it is possible to recognize invisible waves by means of filament oscillations. The nature of filament oscillations and Moreton waves associated with EIT waves is examined in detail, and it is found that the filament oscillations were caused by EIT waves.

A Method for the Determination of 3-D Velocity Fields of Disappearing Solar Filaments

Abstract The 3-D velocity fields of disappearing filaments (Disparition Brusques: DBs) on the solar disk were extensively studied in order to determine their 3-D velocity fields. Applying Beckers’ cloud model to 5 DB events observed in the $\mathrm{H}\alpha$ line center and $\mathrm{H}\alpha \pm 0.8 \,$Å with the Flare Monitoring Telescope (FMT) at Hida Observatory, we developed a method to derive the complete 3-D velocity field of DBs. The line-of-sight velocity is obtained (i) by calculating the $\mathrm{H}\alpha$ line profile of the filament, and (ii) by measuring the Doppler shift which best fits to the observed temporal variations of contrasts of the filament. The tangential velocity is obtained by tracing the motions of the internal structures on the successive images. In this method, corrections for the effective filter bandwidths of the instrument, stray lights, and Doppler brightening effect are performed. We also discuss the velocity errors which arise from the intrinsic variations of the filament plasma during its activation, the fluctuations in intensities of the background chromosphere, and the choice of different forms of the spread function for estimating the stray light. It is emphasized that the calculation of three-dimensional vector trajectories of a disappearing filament with our method can enhance the quality of a space weather forecast with better certainty.

Relation between a Moreton Wave and an EIT Wave Observed on 1997 November 4

We consider the relationship between two flare-associated waves, a chromospheric Moreton wave and a coronal EIT wave, based on an analysis of an X-class flare event in AR 8100 on 1997 November 4. A Moreton wave was observed in $\mathrm{H}\alpha$, $\mathrm{H}\alpha {+} 0.8\,$$Å$, and $\mathrm{H}\alpha-0.8\,$$Å$ with the Flare-Monitoring Telescope (FMT) at the Hida Observatory. An EIT wave was observed in EUV with the Extreme ultraviolet Imaging Telescope (EIT) on board SOHO. The propagation speeds of the Moreton wave and the EIT wave were approximately $715 \,\mathrm{km} \,\mathrm{s}^{-1}$ and $202 \,\mathrm{km} \,\mathrm{s}^{-1}$, respectively. The times of visibility for the Moreton wave did not overlap those of the EIT wave, but the continuation of the former is indicated by a filament oscillation. Data on the speed and location clearly show that the Moreton wave differed physically from the EIT wave in this case. The Moreton wave preceded the EIT wave, which is inconsistent with an identification of the EIT wave with a fast-mode MHD shock.

Simultaneous Observation of a Moreton Wave on 1997 November 3 in Hα and Soft X-Rays

We report the observation of a Moreton wave in Hα (line center and ±0.8 A) with the Flare Monitoring Telescope at the Hida Observatory of Kyoto University at 4:36-4:41 UT on 1997 November 3. The same region (NOAA Active Region 8100) was simultaneously observed in soft X-rays with the soft X-ray telescope on board Yohkoh, and a wavelike disturbance (X-ray wave) was also found. The position of the wave front as well as the direction of propagation of the X-ray wave roughly agree with those of the Moreton wave. The propagation speeds of the Moreton wave and the X-ray wave are about 490 ± 40 and 630 ± 100 km s-1, respectively. Assuming that the X-ray wave is an MHD fast-mode shock, we can estimate the propagation speed of the shock, on the basis of MHD shock theory and the observed soft X-ray intensities ahead of and behind the X-ray wave front. The estimated fast shock speed is 400-760 km s-1, which is in rough agreement with the observed propagation speed of the X-ray wave. The fast-mode Mach number of the X-ray wave is also estimated to be about 1.15-1.25. These results suggest that the X-ray wave is a weak MHD fast-mode shock propagating through the corona and hence is the coronal counterpart of the Moreton wave.

A filament eruption and accompanying coronal field changes on November 5, 1992

An Hα filament eruption on November 5, 1992 was fully observed in Hα with the Hida Flare Monitoring Telescope, while Yohkoh's Soft X-ray Telescope observed the pre- and post-eruption evolution of the coronal magnetic fields. From the Hα data, including the red and blue wings, we have reconstructed the rise of the filament, including trajectory, velocity, and acceleration. In combination with the Yohkoh data this reconstruction suggests that the filament had several interactions with other coronal magnetic fields during the eruption. The Yohkoh data also shows pre-eruption changes in the coronal fields and several post-eruption bright coronal structures. The pre-eruption changes are interpreted as a partial opening of the corona, indicating that it is not necessary to have a complete opening of the corona in order for a filament to erupt and we discuss the several possible contributions from emerging flux. The post-event bright coronal structures are compared with theory and with a cleaner filament eruption event on July 31, 1992. These comparisons suggest that, although there are many similarities, it is hard to completely reconcile the observations with the existing theory.