The Solar Physics E-Print Archive is an on-line, searchable archive of links to on-line preprints and unpublished work of broad interest to researchers in solar and heliospheric physics. This archive has been created to make it quick and easy to discover, and obtain copies of, submissions to journals around the world. http://mithra.physics.montana.edu/cgi-bin/eprint/index.pl http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16223 With the observations from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory, we statistically investigate the ephemeral regions (ERs) in the quiet Sun. We find that there are two types of ERs: normal ERs (NERs) and self-cancelled ERs (SERs). Each NER emerges and grows with separation of its opposite polarity patches which will cancel or coalesce with other surrounding magnetic flux. Each SER also emerges and grows and its dipolar patches separate at first, but a part of magnetic flux of the SER will move together and cancel gradually, which is described with the term ''self-cancellation'' by us. We identify 2988 ERs among which there are 190 SERs, about 6.4% of the ERs. The mean value of self-cancellation fraction of SERs is 62.5%, and the total self-cancelled flux of SERs is 9.8% of the total ER flux. Our results also reveal that the higher the ER magnetic flux is, (i) the easier the performance of ER self-cancellation is, (ii) the smaller the self-cancellation fraction is, and (iii) the more the self-cancelled flux is. We think that the self-cancellation of SERs is caused by the submergence of magnetic loops connecting the dipolar patches, without magnetic energy release. Wed, 16 May 2012 09:06:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16223 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16221 We present the results of studying the proton flare 2B/X4.8, observed with the Large Solar Vacuum Telescope (LSVT) at the Baikal Astrophysical Observatory in a spectropolarimetric mode with high spatial and spectral resolution. We have found some evidence for H?? line impact linear polarization in several cases, predominantly, during the initial moments of the flare. Of the ???? line 606 cuts made along the dispersion in 53 spectrograms, a polarizing signal was found more or less confidently in 60 cuts (13 spectrograms). Mainly, polarization was observed in one kernel of flare. A typical feature of this kernel was that ???? line was observed with a reversal in the central part of this kernel that created a dip in the kernel center in a photometric cut. The size of these dips and the size of sites with the linear polarization coincide and are equal to 3 ?C 6 arc sec. The maximum polarization degree in this kernel reached 15%. The polarization direction in the kernel is radial except for the first two frames with the polarization direction was both radial and tangential. Thus, there is an analogy of the effects observed at the chromospheric level in this kernel (polarization and depression in line ????) with the temporal variation of the HXR sources. Tue, 15 May 2012 19:56:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16221 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16220 We investigate the relationship between the main acceleration phase of coronal mass ejctions (CMEs) and the particle acceleration in the associated flares as evidenced in RHESSI non-thermal X-rays for a set of 37 impulsive flare-CME events. Both CME peak velocity and peak acceleration yield distinct correlations with various parameters characterizing the flare-accelerated electron spectra. The highest correlation coefficient is obtained for the relation of the CME peak velocity and the total energy in accelerated electrons (c = 0.85), supporting the idea that the acceleration of the CME and the particle acceleration in the associated flare draw their energy from a common source, probably magnetic reconnection in the current sheet behind the erupting structure. In general, the CME peak velocity shows somewhat higher correlations with the non-thermal flare parameters than the CME peak acceleration, except for the spectral index of the accelerated electron spectrum which yields a higher correlation with the CME peak acceleration (c = -0.6), indicating that the hardness of the flare-accelerated electron spectrum is tightly coupled to the impulsive acceleration process of the rising CME structure. We also obtained high correlations between the CME initiation height h0 and the non-thermal flare parameters, with the highest correlation of h0 to the spectral index of flare-accelerated electrons (c = 0.8). This means that CMEs erupting at low coronal heights, i.e. in regions of stronger magnetic fields, are accompanied with flares which are more efficient to accelerate electrons to high energies. In the majority of events (~80%), the non-thermal flare emission starts after the CME acceleration, on average delayed by ~6 min, in line with the standard flare model, where the rising flux rope stretches the field lines underneath until magnetic reconnection sets in. We find that the current sheet length at the onset of magnetic reconnection is 21 +/- 7 Mm. The flare HXR peaks are well synchronized with the peak of the CME acceleration profile, in 75% of the cases they occur within 5 min. Our findings provide strong evidence for the tight coupling between the CME dynamics and the particle acceleration in the associated flare in impulsive events, with the total energy in accelerated electrons being closely correlated to the peak velocity (and thus the kinetic energy) of the CME, whereas the number of electrons acclerated to high energies is decisively related to the CME peak acceleration and the height of the pre-eruptive structure. Mon, 14 May 2012 04:23:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16220 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16218 We present analysis of plasma parameters during the initial phase of the 12 June 2010 flare (SOL2010-06-12T00:57). Peculiarity of the flare was detection of gamma-emission that is unusual for the such weak and short event. The analysis revealed the flare precursor detected about 5 minute before the flare onset on 94 A images which spatially coincided with Neutral Line associated Source (NLS) indicated by the non-polarized MW source at 17 GHz (NORH). A comparison of results obtained from microwave (MW) data by the Nobeyama Radio Polarimeter and the Siberian Solar Radio Telescope (the new 10-antenna radio heliograph prototype at 4.6 and 6.4 GHz) and hard X-ray (HXR) observations by the Fermi Gamma-ray Space Telescope reveal presence of accelerated electrons at the initial phase the flare development. The analysis of MW and HXR spectra also confirms presence of accelerated particles. Moreover a good temporal correlation between several lightcurves of HXR energy bands and MW frequencies indicates to generation of both HXR and MW emission by the common populations of accelerated electrons. Detection of accelerated particles during the initial phase of the flare and SHH (soft-hard-harder) behaviour of the spectra points to several episodes of particle acceleration and confirms the non-impulsive type of the flare evolution. Sun, 13 May 2012 21:11:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16218 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16201 Evidence is beginning to be put forward that demonstrates the role of the chromosphere in supplying energy and mass to the corona. We aim to asses the role of chromospheric jets in active region dynamics}{Using a combination of the {Hinode/SOT} Ca II H and TRACE 1550 {AA} and 1600 {AA} filters we examine chromospheric jets situated at the edge of a sunspot.}{Analysis reveals a near continuous series of jets, that raise chromospheric material into the low corona above a sunspot. The jets have average rise speeds of 30 km,s^{-1} and a range of 10-100km,s^{-1}. Enhanced emission observed at the jets leading edge suggests the formation of a shock front. Increased emission in TRACE bandpasses above the sunspot and the disappearance of the jets from the Ca II filter suggests that some of the chromospheric jet material is at least heated to sim0.1MK. The evidence suggests that the jets could be a mechanism which provides a steady, low-level heating for active region features. Fri, 11 May 2012 02:32:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16201 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16194 Application of the magnetic-reconnection theory onto large-scale events, such as solar flares, requires formation of very thin (kinetic-scale) current sheets within the rather thick flare current layer. Hence, some fragmentation/filamentation mechanisms has to be in action. We aim at identifying fragmentation mechanisms for magnetic field and current density structures. Namely, we focus at detailed study of the processes during the merging of plasmoids that had been formed in the current layer. A 2.5-D electromagnetic Particle-In-Cell model is used and its results analysed. It is shown that the merging process of plasmoids is not a simple process as presented in some previous studies. On the contrary, this process leads to a complex fragmentation. We found two types of fragmentation processes: a) fragmentation in the current sheet generated between the merging plasmoids and b) fragmentation at the boundary of plasma outflow from the reconnection between these plasmoids. While the first type of fragmentation is generated by the tearing-mode (plasmoid) instability of the secondary current sheet, the second one looks to be connected with an increase of the plasma beta parameter during these processes. Thus, sheared high-beta plasma flows produce this additional fragmentation. The fragmentation and energy transport from large to small scales in a large-scale magnetic reconnection seem to be the result of interplay and positive feedback between instabilities driven by high gradients in both magnetic (intense current density) and velocity (high vorticity) fields. Wed, 09 May 2012 06:33:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16194 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16191 Long-term variations of solar differential rotation and sunspot activity are investigated through re-analyzing the data on parameters of the differential rotation law obtained by Makarov, Tlatov, and Callebaut (1997), Javaraiah, Bertello, and Ulrich (2005a, b), and Javaraiah et al. (2009). Our results indicate that the solar surface rotation rate at the Equator (indicated by the A parameter of the standard solar rotation law) shows a secular decrease since cycle 12 onwards, given by about $1,-,1.5 imes10^{-3}$($deg day^{-1} year^{-1}$). The B parameter of the standard differential rotation law seems to also show a secular decrease since cycle 12 onwards, but of weak statistical significance. The rotation rate averaged on latitudes ($0^{o},--,40^{o}$) does not show a secular trend of statistical significance. Moreover, the average sunspot area shows a secular increase of statistical significance since cycle 12 onwards, while a negative correlation is found between the level of sunspot activity (indicated by the average sunspot area) and the solar equatorial rotation in the long run. Tue, 08 May 2012 18:17:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16191 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16184 Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. Alfven waves and magneto-sonic waves are particular classes of MHD waves. These wave modes are clearly different and have pure properties in uniform plasmas of infinite extent only. Due to plasma non-uniformity MHD waves have mixed properties and cannot be classified as pure Alfven or magneto-sonic waves. However, vorticity is a quantity unequivocally related to Alfven waves as compression is for magneto-sonic waves. Here, we investigate MHD waves superimposed on a one-dimensional non-uniform straight cylinder with constant magnetic field. For a piecewise constant density profile we find that the fundamental radial modes of the non-axisymmetric waves have the same properties as surface Alfven waves at a true discontinuity in density. Contrary to the classic Alfveen waves in a uniform plasma of infinite extent, vorticity is zero everywhere except at the cylinder boundary. If the discontinuity in density is replaced with a continuous variation of density, vorticity is spread out over the whole interval with non-uniform density. The fundamental radial modes of the non-axisymmetric waves do not need compression to exist unlike the radial overtones. In thin magnetic cylinders the fundamental radial modes of the non-axisymmetric waves with phase velocities between the internal and the external Alfven velocities can be considered as surface Alfven waves. On the contrary, the radial overtones can be related to fast-like magneto-sonic modes. Mon, 07 May 2012 03:28:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16184 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16183 From August 16 to 21, 2010, a northern (~ N60) polar crown filament was observed by Solar Dynamics Observatory (SDO). Employing the six day SDO/AIA data, we identify 69 barbs, and select 58 of them, which appeared away from the western solar limb (≤ W60), as our sample. We systematically investigate the evolution of filament barbs. Three different types of apparent formation of barbs are detected, including (1) the convergence of surrounding moving plasma condensations, comprised 55.2% of our sample, (2) the flows of plasma condensations from the filament, composed 37.9%, and (3) the plasma injections from the neighboring brightening regions, comprised 6.9%. We also find three different ways of barb disappearance, involving: (i) the bi-lateral movements (44.8%), and (ii) the outflowing (27.6%), of barb plasma results in the barb disappearance, as well as (iii) the barb disappearance is associated with the neighboring brightening (27.6%). The evolutions of the magnetic fields, e.g. magnetic emergences, and magnetic cancelations and disappearances, may cause the formation and disappearance of the barb magnetic structures. Barbs exchange plasma condensations with the surrounding atmosphere, filament, and nearby brightening regions, leading to the formation and disappearance of barb material. Furthermore, we find that all the barbs underwent oscillations. The average oscillating period, amplitude and velocity are 30 min, 2.4 Mm and 5.7 km/s, respectively. Besides the oscillations, 21 (36%) barbs manifested sideward motions having an average speed of 0.45 km/s. Small-scale wave-like propagating disturbances caused by small-scale brightening are detected, and the barb oscillations associated with the disturbances are also found. We propose that the kinematics of barbs may be caused by the evolution of the neighboring photospheric magnetic fields. Mon, 07 May 2012 01:21:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16183 http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16169 Solar cycle 23 witnessed the most complete set of observations of coronal mass ejections (CMEs) associated with the Ground Level Enhancement (GLE) events. We present an overview of the observed properties of the GLEs and those of the two associated phenomena, viz., flares and CMEs, both being potential sources of particle acceleration. Although we do not find a striking correlation between the GLE intensity and the parameters of flares and CMEs, the solar eruptions are very intense involving X-class flares and extreme CME speeds (average ~2000 km/s). An M7.1 flare and a 1200 km/s CME are the weakest events in the list of 16 GLE events. Most (80%) of the CMEs are full halos with the three non-halos having widths in the range 167 to 212 degrees. The active regions in which the GLE events originate are generally large: 1290 msh (median 1010 msh) compared to 934 msh (median: 790 msh) for SEP-producing active regions. For accurate estimation of the CME height at the time of metric type II onset and GLE particle release, we estimated the initial acceleration of the CMEs using flare and CME observations. The initial acceleration of GLE-associated CMEs is much larger (by a factor of 2) than that of ordinary CMEs (2.3 km/s2 vs.1 km/s2). We confirmed the initial acceleration for two events for which CME measurements are available in the inner corona. The GLE particle release is delayed with respect to the onset of all electromagnetic signatures of the eruptions: type II bursts, low frequency type III bursts, soft X-ray flares and CMEs. The presence of metric type II radio bursts some 17 min (median: 16 min; range: 3 to 48 min) before the GLE onset indicates shock formation well before the particle release. The release of GLE particles occurs when the CMEs reach an average height of ~3.09 Rs (median: 3.18 Rs; range: 1.71 to 4.01 Rs) for well-connected events (source longitude in the range W20 ? W90). For poorly connected events, the average CME height at GLE particle release is ~66% larger (mean: 5.18 Rs; median: 4.61 Rs; range: 2.75 ? 8.49 Rs). The longitudinal dependence is consistent with shock accelerations because the shocks from poorly connected events need to expand more to cross the field lines connecting to an Earth observer. On the other hand, the CME height at metric type II burst onset has no longitudinal dependence because electromagnetic signals do not require magnetic connectivity to the observer. For several events, the GLE particle release is very close to the time of first appearance of the CME in the coronagraphic field of view, so we independently confirmed the CME height at particle release. The CME height at metric type II burst onset is in the narrow range 1.29 to 1.8 Rs, with mean and median values of 1.53 and 1.47 Rs. The CME heights at metric type II burst onset and GLE particle release correspond to the minimum and maximum in the Alfven speed profile. The increase in CME speed between these two heights suggests an increase in Alfv?nic Mach number from 2 to 3. The CME heights at GLE particle release are in good agreement with those obtained from the velocity dispersion analysis (Reames, 2009a,b) including the source longitude dependence. We also discuss the implications of the delay of GLE particle release with respect to complex type III bursts by ~18 min (median: 16 in; range: 2 to 44 min) for the flare acceleration mechanism. A similar analysis is also performed on the delay of particle release relative to the hard X-ray emission. Thu, 03 May 2012 19:32:00 MST http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=16169