Propagating slow magnetoacoustic waves in coronal loops observed by Hinode/EIS

We present the first Hinode/EIS observations of 5 min quasi-periodic oscillations detected in a transition-region line (He II) and five coronal lines (Fe X, Fe XII, Fe XIII, Fe XIV, and Fe XV) at the footpoint of a coronal loop. The oscillations exist throughout the whole observation, characterized by a series of wave packets with nearly constant period, typically persisting for 4-6 cycles with a lifetime of 20-30 min. There is an approximate in-phase relation between Doppler shift and intensity oscillations. This provides evidence for slow magnetoacoustic waves propagating upwards from the transition region into the corona. We find that the oscillations detected in the five coronal lines are highly correlated, and the amplitude decreases with increasing temperature. The amplitude of Doppler shift oscillations decrease by a factor of about 3, while that of relative intensity decreases by a factor of about 4 from Fe X to Fe XV. These oscillations may be caused by the leakage of the photospheric p-modes through the chromosphere and transition region into the corona, which has been suggested as the source for intensity oscillations previously observed by TRACE. The temperature dependence of the oscillation amplitudes can be explained by damping of the waves traveling along the loop with multithread structure near the footpoint. Thus, this property may have potential value for coronal seismology in diagnostic of temperature structure in a coronal loop.Comment: 13 pages, 11 color figures, 4 tables, Astrophys.J, May 2009 - v696 issue, (in press

Characterization of the human omega-oxidation pathway for omega-hydroxy-very-long-chain fatty acids

Very-long-chain fatty acids (VLCFAs) have long been known to be degraded exclusively in peroxisomes via beta-oxidation. A defect in peroxisomal beta-oxidation results in elevated levels of VLCFAs and is associated with the most frequent inherited disorder of the central nervous system white matter, X-linked adrenoleukodystrophy. Recently, we demonstrated that VLCFAs can also undergo omega-oxidation, which may provide an alternative route for the breakdown of VLCFAs. The omega-oxidation of VLCFA is initiated by CYP4F2 and CYP4F3B, which produce omega-hydroxy-VLCFAs. In this article, we characterized the enzymes involved in the formation of very-long-chain dicarboxylic acids from omega-hydroxy-VLCFAs. We demonstrate that very-long-chain dicarboxylic acids are produced via two independent pathways. The first is mediated by an as yet unidentified, microsomal NAD(+)-dependent alcohol dehydrogenase and fatty aldehyde dehydrogenase, which is encoded by the ALDH3A2 gene and is deficient in patients with Sjogren-Larsson syndrome. The second pathway involves the NADPH-dependent hydroxylation of omega-hydroxy-VLCFAs by CYP4F2, CYP4F3B, or CYP4F3A. Enzyme kinetic studies show that oxidation of omega-hydroxy-VLCFAs occurs predominantly via the NAD(+)-dependent route. Overall, our data demonstrate that in humans all enzymes are present for the complete conversion of VLCFAs to their corresponding very-long-chain dicarboxylic acids

SDO/AIA Observation of Kelvin-Helmholtz Instability in the Solar Corona

We present observations of the formation, propagation and decay of vortex- shaped features in coronal images from the Solar Dynamics Observatory (SDO) associated with an eruption starting at about 2:30UT on Apr 8, 2010. The series of vortices formed along the interface between an erupting (dimming) region and the surrounding corona. They ranged in size from several to ten arcseconds, and traveled along the interface at 6-14 km/s. The features were clearly visible in six out of the seven different EUV wavebands of the Atmospheric Imaging Assembly (AIA). Based on the structure, formation, propagation and decay of these features, we identified these features as the first observations of the Kelvin-Helmholtz (KH) instability in the corona in EUV. The interpretation is supported by linear analysis and by MHD model of KH instability. We conclude that the instability is driven by the velocity shear between the erupting and closed magnetic field of the Coronal Mass Ejection (CME). The shear flow driven instability can play an important role in energy transfer processes in coronal plasma

Flare-generated acoustic oscillations in solar and stellar coronal loops

Long period longitudinal oscillations of a flaring coronal loop are studied numerically. In the recent work of Nakariakov et al. (2004) it has been shown that the time dependence of density and velocity in a flaring loop contain pronounced quasi-harmonic oscillations associated with the 2nd harmonic of a standing slow magnetoacoustic wave. In this work we investigate the physical nature of these oscillations in greater detail, namely, their spectrum (using the periodogram technique) and how heat positioning affects mode excitation. We found that excitation of such oscillations is practically independent of the location of the heat deposition in the loop. Because of the change of the background temperature and density, the phase shift between the density and velocity perturbations is not exactly a quarter of the period; it varies along the loop and is time dependent, especially in the case of one footpoint (asymmetric) heating

Hinode/EIS observations of propagating low-frequency slow magnetoacoustic waves in fan-like coronal loops

We report the first observation of multiple-periodic propagating disturbances along a fan-like coronal structure simultaneously detected in both intensity and Doppler shift in the Fe XII 195 A line with the EUV Imaging Spectrometer (EIS) onboard Hinode. A new application of coronal seismology is provided based on this observation. We analyzed the EIS sit-and-stare mode observation of oscillations using the running difference and wavelet techniques. Two harmonics with periods of 12 and 25 min are detected. We measured the Doppler shift amplitude of 1-2 km/s, the relative intensity amplitude of 3%-5% and the apparent propagation speed of 100-120 km/s. The amplitude relationship between intensity and Doppler shift oscillations provides convincing evidence that these propagating features are a manifestation of slow magnetoacoustic waves. Detection lengths (over which the waves are visible) of the 25 min wave are about 70-90 Mm, much longer than those of the 5 min wave previously detected by TRACE. This difference may be explained by the dependence of damping length on the wave period for thermal conduction. Based on a linear wave theory, we derive an inclination of the magnetic field to the line-of-sight about 59$\pm$8 deg, a true propagation speed of 128$\pm$25 km/s and a temperature of 0.7$\pm$0.3 MK near the loop's footpoint from our measurements.Comment: 4 pages and 4 figures, with 3 online figures and 1 online table; Astron & Astrophys Letter, in pres

High-frequency Alfven waves in multi-ion coronal plasma : observational implications

We investigate the effects of high-frequency (of order ion gyrofrequency) Alfvén and ion-cyclotron waves on ion emission lines by studying the dispersion of these waves in a multi-ion coronal plasma. For this purpose we solve the dispersion relation of the linearized multifluid and Vlasov equations in a magnetized multi-ion plasma with coronal abundances of heavy ions. We also calculate the dispersion relation using nonlinear one-dimensional hybrid kinetic simulations of the multi-ion plasma. When heavy ions are present the dispersion relation of parallel propagating Alfvén cyclotron waves exhibits the following branches (in the positive Ω − k quadrant): right-hand polarized nonresonant and left-hand polarized resonant branch for protons and each ion. We calculate the ratio of ion to proton velocities perpendicular to the direction of the magnetic field for each wave modes for typical coronal parameters and find strong enhancement of the heavy ion perpendicular fluid velocity compared with proton perpendicular fluid velocity. The linear multifluid cold plasma results agree with linear warm plasma Vlasov results and with the nonlinear hybrid simulation model results. In view of our findings we discuss how the observed nonthermal line broadening of minor ions in coronal holes may relate to the high-frequency wave motions

Quasi-periodic Fast-mode Wave Trains Within a Global EUV Wave and Sequential Transverse Oscillations Detected by SDO/AIA

We present the first unambiguous detection of quasi-periodic wave trains within the broad pulse of a global EUV wave (so-called "EIT wave") occurring on the limb. These wave trains, running ahead of the lateral CME front of 2-4 times slower, coherently travel to distances $>R_{sun}/2$ along the solar surface, with initial velocities up to 1400 km/s decelerating to ~650 km/s. The rapid expansion of the CME initiated at an elevated height of 110 Mm produces a strong downward and lateral compression, which may play an important role in driving the primary EUV wave and shaping its front forwardly inclined toward the solar surface. The waves have a dominant 2 min periodicity that matches the X-ray flare pulsations, suggesting a causal connection. The arrival of the leading EUV wave front at increasing distances produces an uninterrupted chain sequence of deflections and/or transverse (likely fast kink mode) oscillations of local structures, including a flux-rope coronal cavity and its embedded filament with delayed onsets consistent with the wave travel time at an elevated (by ~50%) velocity within it. This suggests that the EUV wave penetrates through a topological separatrix surface into the cavity, unexpected from CME caused magnetic reconfiguration. These observations, when taken together, provide compelling evidence of the fast-mode MHD wave nature of the {\it primary (outer) fast component} of a global EUV wave, running ahead of the {\it secondary (inner) slow} component of CME-caused restructuring.Comment: 17 pages, 12 figures; accepted by ApJ, April 24, 201

On the period ratio P₁/2P₂ in the oscillations of coronal loops

<p>Aims. With strong evidence of fast and slow magnetoacoustic modes arising in the solar atmosphere there is scope for improved determinations of coronal parameters through coronal seismology. Of particular interest is the ratio P<sub>1</sub>/2P<sub>2</sub>between the period P<sub>1</sub> of the fundamental mode and the period P<sub>2</sub> of its first harmonic; in an homogeneous medium this ratio is one, but in a more complex configuration it is shifted to lower values.</p> <p>Methods. We consider analytically the effects on the different magnetohydrodynamic modes of structuring and stratification, pointing out that transverse or longitudinal structuring or gravitational stratification modifies the ratio P<sub>1</sub>/2P<sub>2</sub>.</p> <p>Results. The deviations caused by gravity and structure are studied for the fast and slow modes. Structure along the loop is found to be the dominant effect.</p> <p>Conclusions. The departure of P<sub>1</sub>/2P<sub>2</sub> from unity can be used as a seismological tool in the corona. We apply our technique to the observations by Verwichte et al. (2004), deducing the density scale height in a coronal loop.</p&gt

Coronal Loop Oscillations Observed with AIA - Kink-Mode with Cross-Sectional and Density Oscillations

A detailed analysis of a coronal loop oscillation event is presented, using data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) for the first time. The loop oscillation event occurred on 2010 Oct 16, 19:05-19:35 UT, was triggered by an M2.9 GOES-class flare, located inside a highly inclined cone of a narrow-angle CME. This oscillation event had a number of unusual features: (i) Excitation of kink-mode oscillations in vertical polarization (in the loop plane); (ii) Coupled cross-sectional and density oscillations with identical periods; (iii) no detectable kink amplitude damping over the observed duration of four kink-mode periods ($P=6.3$ min); (iv) multi-loop oscillations with slightly ($\approx 10$) different periods; and (v) a relatively cool loop temperature of $T\approx 0.5$ MK. We employ a novel method of deriving the electron density ratio external and internal to the oscillating loop from the ratio of Alfv\'enic speeds deduced from the flare trigger delay and the kink-mode period, i.e., $n_e/n_i=(v_A/v_{Ae})^2=0.08\pm0.01$. The coupling of the kink mode and cross-sectional oscillations can be explained as a consequence of the loop length variation in the vertical polarization mode. We determine the exact footpoint locations and loop length with stereoscopic triangulation using STEREO/EUVI-A data. We model the magnetic field in the oscillating loop using HMI/SDO magnetogram data and a potential field model and find agreement with the seismological value of the magnetic field, $B_{kink}=4.0\pm0.7$ G, within a factor of two.Comment: ApJ (in press, accepted May 10, 2011