Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFine Structures of an EUV Wave Event from Multi-Viewpoint Observations
81
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In this study, we investigate an extreme ultraviolet (EUV) wave event on 2010 February 11, which occurred as a limb event from the Earth viewpoint and a disk event from the STEREO--B viewpoint. We use the data obtained by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) in various EUV channels. The EUV wave event was launched by a partial prominence eruption. Similar to some EUV wave events in previous works, this EUV wave event contains a faster wave with a speed of $sim$445$pm$6 km s$^{-1}$, which we call coronal Moreton wave, and a slower wave with a speed of $sim$298$pm$5 km s$^{-1}$, which we call EIT wave. The coronal Moreton wave is identified as a fast-mode wave and the EIT wave is identified as an apparent propagation due to successive field-line stretching. We also observe a stationary front associated with the fast mode EUV wave. This stationary front is explained as mode conversion from the coronal Moreton wave to a slow-mode wave near a streamer.
rate research
Read More
EUV (Extreme-Ultraviolet) waves are globally propagating disturbances that have been observed since the era of the SoHO/EIT instrument. Although the kinematics of the wave front and secondary wave components have been widely studied, there is not much known about the generation and plasma properties of the wave. In this paper we discuss the effect of an EUV wave on the local plasma as it passes through the corona. We studied the EUV wave, generated during the 2011 February 15 X-class flare/CME event, using Differential Emission Measure diagnostics. We analyzed regions on the path of the EUV wave and investigated the local density and temperature changes. From our study we have quantitatively confirmed previous results that during wave passage the plasma visible in the Atmospheric Imaging Assembly (AIA) 171A channel is getting heated to higher temperatures corresponding to AIA 193A and 211A channels. We have calculated an increase of 6 - 9% in density and 5 - 6% in temperature during the passage of the EUV wave. We have compared the variation in temperature with the adiabatic relationship and have quantitatively demonstrated the phenomenon of heating due to adiabatic compression at the wave front. However, the cooling phase does not follow adiabatic relaxation but shows slow decay indicating slow energy release being triggered by the wave passage. We have also identified that heating is taking place at the front of the wave pulse rather than at the rear. Our results provide support for the case that the event under study here is a compressive fast-mode wave or a shock.
Context. The remote observations of solar flare ion acceleration are rather limited. There are theoretical predictions for signatures of ion acceleration in EUV line profiles. Previous tests involve observations of flares with no evidence for energetic ions. Aims. We aim to examine a source flare of impulsive (or 3He-rich) solar energetic particle events with EUV line spectroscopy. Methods. We inspect all (90+) reported 3He-rich flares of previous solar cycle 23 and find only four (recurrent) jets in the field of view of SOHO CDS. The jet with the most suitable spatial and temporal coverage is analyzed in detail. Results. Two enhanced (non-thermal) line broadenings are observed in the cooler chromospheric / transition-region lines and they are localized near the site where the closed magnetic loops reconnect with the open magnetic field lines. Both enhanced broadenings are found in the sites with redshifts in the lines, surrounded by the region with blueshifts. One enhanced line broadening is associated with a small flare without energetic particle signatures while another occurs just after the particle acceleration signatures of the main flare terminated. Conclusions. The observed excess broadening appears to be not directly related to the energetic ion production and motions. Further investigations where the critical impulsive phase of the flare is covered are required, ideally with high-resolution spectrometers intentionally pointed to the 3He-rich solar energetic particle source.
On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white light a large-scale dome-shaped expanding coronal transient with perfectly connected off-limb and on-disk signatures. Veronig et al. (2010, ApJL 716, 57) concluded that the dome was formed by a weak shock wave. We have revealed two EUV components, one of which corresponded to this transient. All of its properties found from EUV, white light, and a metric type II burst match expectations for a freely expanding coronal shock wave including correspondence to the fast-mode speed distribution, while the transient sweeping over the solar surface had a speed typical of EUV waves. The shock wave was presumably excited by an abrupt filament eruption. Both a weak shock approximation and a power-law fit match kinematics of the transient near the Sun. Moreover, the power-law fit matches expansion of the CME leading edge up to 24 solar radii. The second, quasi-stationary EUV component near the dimming was presumably associated with a stretched CME structure; no indications of opening magnetic fields have been detected far from the eruption region.
We present first observations of a dome-shaped large-scale EUV coronal wave, recorded by the EUVI instrument onboard STEREO-B on January 17, 2010. The main arguments that the observed structure is the wave dome (and not the CME) are: a) the spherical form and sharpness of the domes outer edge and the erupting CME loops observed inside the dome; b) the low-coronal wave signatures above the limb perfectly connecting to the on-disk signatures of the wave; c) the lateral extent of the expanding dome which is much larger than that of the coronal dimming; d) the associated high-frequency type II burst indicating shock formation low in the corona. The velocity of the upward expansion of the wave dome ($v sim 650$ km s$^{-1}$) is larger than that of the lateral expansion of the wave ($v sim 280$ km s$^{-1}$), indicating that the upward dome expansion is driven all the time, and thus depends on the CME speed, whereas in the lateral direction it is freely propagating after the CME lateral expansion stops. We also examine the evolution of the perturbation characteristics: First the perturbation profile steepens and the amplitude increases. Thereafter, the amplitude decreases with r$^{-2.5 pm 0.3}$, the width broadens, and the integral below the perturbation remains constant. Our findings are consistent with the spherical expansion and decay of a weakly shocked fast-mode MHD wave.
The EUV (100-912 {AA}) is a spectral region notoriously difficult to observe due to attenuation by neutral hydrogen gas in the interstellar medium. Despite this, hundreds to thousands of nearby stars of different spectral types and magnetic activity levels are accessible in the EUV range. The EUV probes interesting and complicated regions in the stellar atmosphere like the lower corona and transition region that are inaccessible from other spectral regions. In this white paper we describe how direct EUV observations, which require a dedicated grazing-incidence observatory, cannot yet be accurately substituted with models and theory. Exploring EUV emission from cool dwarf stars in the time domain can make a major contribution to understanding stellar outer atmospheres and magnetism, and offers the clearest path toward detecting coronal mass ejections on stars other than the Sun.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
