We report on the detection of EUV wave reflection from a coronal hole, as observed by the Solar TErrestrial RElations Observatory (STEREO) mission.The EUV wave was associated with a coronal mass ejection (CME) erupting near the disk center. It was possible to measure the kinematics of the reflected waves for the first time. The reflected waves were generally slower than the direct wave. One of the important implications of the wave reflection is that the EUV transients are truly a wave phenomenon. The EUV wave reflection has implications for CME propagation, especially during the declining phase of the solar cycle when there are many low-latitude coronal holes.Subject headings: sun: euv -sun: coronal waves -sun: coronal mass ejections suggested in the literature (Delanee and Aulanier, 1999;Attrill et al. 2007). The secondary reflection from the south polar coronal hole further confirms the wave nature of the EUV disturbances. Finally, the metric type II burst is also a clear evidence of a fast mode shock, which must have formed due to the steepening of the magnetosonic wave.

We present detailed angle-dependent single crystal electron paramagnetic resonance (EPR) data for field rotations in the hard plane of the S=10 single molecule magnet Mn(12)-acetate. A clear fourfold variation in the resonance positions may be attributed to an intrinsic fourth-order transverse anisotropy (O(4)/(4)). Meanwhile, a fourfold variation of the EPR line shapes confirms a recently proposed model wherein disorder associated with the acetic acid of crystallization induces a locally varying quadratic (rhombic) transverse anisotropy [O (2)/(2) identical with E(S (2)/(x)-S(2)/(y))]. These findings explain most aspects of the magnetic quantum tunneling observed in Mn(12)-acetate.

An extended data set of extreme ultraviolet images of the solar corona provided by the SOHO spacecraft are analyzed using statistical methods common to studies of self-organized criticality (SOC) and to intermittent turbulence (IT). The data exhibits simultaneous hallmarks of both regimes, namely power law avalanche statistics as well as multiscaling of structure functions for spatial activity. This implies that both SOC and IT may be manifestations of a single complex dynamical process entangling avalanches of magnetic energy dissipation with turbulent particle flows.PACS numbers: 05.65+b, 52.35.Ra, 96.60.qe SOC and IT represent two paths to dynamical complexity in driven, extended nonlinear systems. In classical fluid turbulence, scaling is often associated with a hierarchical structure of eddies extending over the inertial range [1], while in SOC, avalanches of localized instabilities organize the system toward a steady state exhibiting long-range correlations up to the system size [2]. Some authors have argued that SOC and IT are distinct, unrelated phenomena [3,4,5], while others have suggested a fundamental connection [6,7,8,9,10]. In fact, Bak and co-workers have speculated that turbulence in the limit of high Reynolds number (HRN) may itself be a SOC phenomenon [6,11,12], with dynamical transitions observed in HRN turbulence being critical avalanches of dissipation. It has also been shown [10] that, in contrast to earlier claims [3], SOC and IT cannot be distinguished by analyzing interoccurrence times between bursts: once a finite observation threshold (unavoidable in any physical measurement) is introduced, even the ordinary BTW sandpile exhibits scale free waiting time statistics [10] indicative of turbulent systems.We propose that SOC and IT can coexist in magnetized plasmas. One scenario for this to occur is localized instabilities [13,14] switching the plasma between states dominated by convection and rapid diffusion of magnetic field lines. This process resembles stick-slip or depinning transitions of SOC models [15,16] and is to some extent analogous to rice pile dynamics [17], where kinetic energy of grains releases stored potential energy. Signatures of SOC and IT have also been obtained in MHD simulations [18,19] with a stationary forcing mimicking photospheric motions of magnetic loops in the corona. However, the explicit complementarity between SOC and IT in astrophysical observations has not been demonstrated.In order to clarify this issue, we present direct observational evidence for coexistence of SOC and IT in the magnetized plasma of the solar corona. Using a single high resolution data set, we apply two different analysis methods -one for analyzing avalanche statistics of the emission field and the other for analyzing structure functions of the same field. The energy, area and lifetime statistics of avalanches detected in this data set obey robust scaling laws. Unlike previous studies of flare statistics, we use a spatiotemporal event detection algorithm compatible with the usual defin...

We present for the first time a three-dimensional reconstruction of the electron density in the corona at distances from 1.5R to 4R using COR1 STEREO observations. The reconstruction is performed using a regularized tomography inversion method for two biweekly periods corresponding to Carrington Rotations 2058 and 2066. Images from the two STEREO spacecraft are used to compare the reconstructed density structures with coronal features located by triangulation. We find that the location of a bright tip of a helmet streamer obtained from the tomographic reconstruction is in good agreement with the location obtained by triangulation. The reconstructed density structure of the equatorial streamer belt is largely consistent with the variation of the current sheet derived from a potential magnetic field extrapolation for most of the equatorial region and for an MHD model of the corona. A zero-value density region in the reconstruction is identified with a low-density region seen in an EUVI image below the reconstruction domain.