MHD-Oscillations of Coronal Loops and Diagnostics of Flare Plasma (original) (raw)
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The Astrophysical Journal, 2003
The evolution of a GOES class X1.1 solar flare, which occurred in NOAA Active Region 8910 on 2000 March 22, is discussed using observations from the Owens Valley Solar Array (OVSA), Big Bear Solar observatory (BBSO), Transition Region and Coronal Explorer (TRACE), and the Michelson Doppler Imager (MDI) on board Solar and Heliospheric Observatory (SOHO). During the impulsive phase, a set of coronal loops are visible in the TRACE 171 Å ($1 Â 10 6 K) wavelength band, which is confined to a small volume in the center of the large -type active region. This is rapidly followed by the emergence of bright H ribbons that coincide with the EUV emission. Radio images show a single source encompassing the H ribbons at 5 GHz, but at higher frequencies a double source is seen within the area bounded by the compact H and EUV emissions. We interpret the observation under the idea of the confined flare in contrast with the more commonly cited, eruptive flare. We use a schematic magnetic reconnection geometry based on the MDI magnetogram to suggest that the EUV loops show some parts of a separatrix, and that the radio and H sources coincide with the whole part of the separatrix and its footpoints, respectively. First of all, it explains why this flare lacks the separating motion of H ribbons, a signature for eruptive flares. Second, the very short duration of microwave bursts in spite of the large amount of soft X-ray flux is explicable under this scenario, since energy release via spontaneous reconnection in a confined magnetic structure can be very rapid. Third, the confined magnetic geometry is also considered favorable for preserving chromospheric evaporation and plasma turbulence as inferred from the OVSA microwave spectrum. In addition, a coronal mass ejection as detected in the LASCO coronagraph after this flare is briefly discussed in relation to the above flare model.
Multiwavelength Analysis of a Solar Flare on 2002 April 15
The Astrophysical Journal, 2005
We carried out a multiwavelength analysis of the solar limb flare on 2002 April 15. The observations all indicate that the flare occurred in an active region with an asymmetric dipole magnetic conguration. The earlier conclusion that magnetic reconnection is occurring in a large-scale current sheet in this flare is further supported by these observations: (1) Several blob-like sources, seen in RHESSI 12-25 keV X-ray images later in the flare, appeared along a line above the flare loops. These indicate the continued presence of the current sheet and are likely to be magnetic islands in the stretched sheet produced by the tearing-mode instability. (2) A cusp-like structure is seen in NoRH 34 GHz microwave images around the time of the peak flare emission. We quantitatively demonstrate that the X-ray emitting thermal plasma seen with RHESSI had a higher temperature than the microwave emitting plasma seen with NoRH. Since the radio data preferentially see cooler thermal plasma, this result is consistent with the picture in which energy release occurs at progressively greater heights and the hard X-rays see hot new loops while the radio sees older cooling loops. The kinetic energy of the coronal mass ejection (CME) associated with this flare was found to be about one order of magnitude less than both the thermal energy in the hot plasma and the nonthermal energy carried by the accelerated electrons in the flare, as deduced from the RHESSI observations. This contrasts with the higher CME kinetic energies typically deduced for large flares.
We investigate the solar flare of 20 October 2002. The flare was accompanied by quasi-periodic pulsations (QPP) of both thermal and nonthermal hard X-ray emissions (HXR) observed by RHESSI in the 3-50 keV energy range. Analysis of the HXR time profiles in different energy channels made with the Lomb periodogram indicates two statistically significant time periods of about 16 and 36 seconds. The 36-second QPP were observed only in the nonthermal HXR emission in the impulsive phase of the flare. The 16-second QPP were more pronounced in the thermal HXR emission and were observed both in the impulsive and in the decay phases of the flare. Imaging analysis of the flare region, the determined time periods of the QPP and the estimated physical parameters of magnetic loops in the flare region allow us to interpret the observations as follows. 1) In the impulsive phase energy was released and electrons were accelerated by successive acts with the average time period of about 36 seconds in d...
Study of Flare Related Intense Geomagnetic Storms with Solar Radio Burst
2017
We have studied X and M-Class X -Ray solar flares related intense geomagnetic storms observed during the period of 2000-2006 with halo and partial halo coronal mass ejections, solar radio bursts and disturbances in solar wind plasma parameters. We have found that 82.45% X and M-Class X-Ray solar flare related intense geomagnetic storms are associated with halo and partial halo coronal mass ejections. The association rate of halo and partial halo coronal mass ejections are found 78.72 % and 21.27 % respectively. Further we have observed that 71.92% X and M-Class X-Ray solar flare related intense geomagnetic storms are associated with solar radio bursts. The association rate of type IV and type II radio bursts have been found 60.97 % and 39.03% respectively. From the study of X and M-Class XRay solar flare related intense geomagnetic storms with jump in interplanetary magnetic field, we have determined positive co-relation with co-relation co-efficient, 0.71 between magnitude of X and...
Structure of the impulsive phase of solar flares from microwave observations
The Astrophysical Journal, 1982
Variation of the microwave intensity and spectrum due to gyro-synchrotron radiation from semi-relativistic particles injected at the top of a closed magnetic loop has been described. Using the recent high spatial resolution x-ray observations from the MIS experiment of the SMM and from observations by the VLA, it is shown that the high microwave brightness observed at the top of the flare loop can come about if i) the magnetic field from top to footpoints of the loop does not increase very rapidly, and iij the accelerated particles injected in the loop have a nearly isotropic pitch angle distribution. The limits on the rate of increase of the magnetic field and/or the average pitch angle depend on the geometry and location of the loop on the solar disk.
Detection of Hα Intensity Oscillations in Solar Flares
1998
We report here the first direct evidence for detection of Hα intensity oscillations in two extended flares of 15 November 1989 and 20 April 1991. The relative intensity variations measured with time at 18 different flare and chromospheric locations were analysed to obtain the oscillation modes. The analysis shows prominent 5-and 3-min modes in flares in addition to their existence in the chromosphere. However, there exists a frequency difference between the flare and chromospheric modes. This frequency deviation of about 300 µHz is proposed as an influence of higher magnetic field, location of the measurements (height) in chromosphere, and high temperature in the flare.
Spatial Characterization of a Flare Using Radio Observations and Magnetic Field Topology
Solar Physics, 2007
Using magnetograms, EUV and Hα images, Owens Valley Solar Array microwave observations, and 212-GHz flux density derived from the Solar Submillimeter Telescope data, we determine the spatial characteristics of the 1B/M6.9 flare that occurred on November 28, 2001, starting at 16:26 UT in active region (AR) NOAA 9715. This flare is associated with a chromospheric mass ejection or surge observed at 16:42 UT in the Hα images. We compute the coronal magnetic field under the linear force-free field assumption, constrained by the photospheric data of the Michelson Doppler Imager and loops observed by the Extreme Ultraviolet Imaging Telescope. The analysis of the magnetic field connectivity allows us to conclude that magnetic field reconnection between two different coronal/chromospheric sets of arches was at the origin of the flare and surge, respectively. The optically thick microwave spectrum at peak time shows a shape compatible with the emission from two different sites. Fitting gyrosynchrotron emission to the observed spectrum, we derive parameters for each source.
Coronal Loop Oscillations and Flare Shock Waves
The Astrophysical Journal, 2004
A statistical analysis of coronal loop oscillations observed by the Transition Region and Coronal Explorer (TRACE) shows that 12 of 28 cases were associated with metric type II bursts. The timing is consistent with the idea that in many cases the loop oscillations result from the passage of a large-scale wave disturbance originating in a flare in the nearby active region. The GOES classifications for these flares range from C4.2 to X20. Typically, the oscillating structures are not disrupted, implying that the disturbance has passed through the medium, which has returned to an equilibrium near that seen prior to the event. This is consistent with the Uchida interpretation of the disturbance as a weak fast-mode blast wave (i.e., a simple wave at a low Alfvénic Mach number) propagating in the ambient corona. We note that all 12 of the associated events were also associated with coronal mass ejections (CMEs) and conclude that the CME eruptions in these cases corresponded to only partial openings of the active-region magnetic fields.
RADIO EMISSION FROM ACCELERATION SITES OF SOLAR FLARES
The Astrophysical Journal, 2009
The Letter takes up a question of what radio emission is produced by electrons at the very acceleration site of a solar flare. Specifically, we calculate incoherent radio emission produced within two competing acceleration models-stochastic acceleration by cascading MHD turbulence and regular acceleration in collapsing magnetic traps. Our analysis clearly demonstrates that the radio emission from the acceleration sites: (i) has sufficiently strong intensity to be observed by currently available radio instruments and (ii) has spectra and light curves which are distinctly different in these two competing models, which makes them observationally distinguishable. In particular, we suggest that some of the narrowband microwave and decimeter continuum bursts may be a signature of the stochastic acceleration in solar flares.
First light detection of solar burst type IV in Malaysia in the region of 260 MHz till 380 MHz has been successfully detected on 5 th March 2012. This significant solar burst variations is associated with solar flare type M level 2.0 occurred from 0412UT. Due to the effect, strong bursts that caused by extraordinary solar flares due to magnetic reconnection effect potentially induced in the near-Earth magneto tail. One possible reason behind the formation of this very complex long duration of this loop is the magnetic reconnection and disruption of the loops which is observed during flare maximum. Sunspot 1429 active region was a site of several intense in several days. In Malaysia, monitoring solar burst in radio region is just in beginning by involved the project under International Space Weather Initiative (ISWI) since 2011. We also analyzed multi wavelength observation from different sites as continuity of the phenomenon. Observations presented in this paper confirmed that Malaysia can be one of the potential countries to focus on solar monitoring solar radio emission at lowbroadband frequency (45-870) MHz using ground-based telescope due to 12 hours per day throughout a year.