Limb Event Brightenings and Fast Ejection Using IRIS Mission Observations

The Interface Region Imaging Spectrograph (IRIS) of the NASA small explorer mission provides significantly more complete and higher resolution spectral coverage of the dynamical conditions inside the chromosphere and transition region (TR) than has heretofore been available. Near the solar limb high temporal, spatial (0.3") and spectral resolution observations from the ultraviolet IRIS spectra reveal high-energy limb event brightenings (LEBs) at low chromospheric heights, around 1 Mm above the limb. They can be characterized as explosive events producing jets. We selected two events showing spectra of a confined eruption just off or near the quiet Sun limb, the jet part showing obvious moving material with short duration large Doppler shifts in three directions identified as macrospicules on slit-jaw (SJ) images in Si IV and He II 304 A. The events are analyzed from a sequence of very close rasters taken near the central meridian and the South pole limb. The processed SJ images and the simultaneously observed fast spectral sequences having large Doppler shifts, with a pair of red shifted elements together with a faster blue shifted element from almost the same position, are analyzed. Shifts correspond to velocities of up to 100 km/s in projection on the plane of the sky. The occurrence of erupting spicules and macrospicules from these regions is noticed from images taken before and after the spectra. The cool low first ionization potential (FIP) element simultaneous line emissions of the MgII h and k resonance lines do not clearly show a similar signature due to optical thickness effects but the Si IV broad-band SJ images do. The bidirectional plasma jets ejected from a small reconnection site are interpreted as the result of coronal loop-loop interactions leading to reconnection in nearby sites.Comment: 24 pages, 16 figures., Accepted in Sol. Phy

Polar Coronal Plumes as Tornado-Like Jets

We examine the dynamical behavior of white light polar plume structures in the inner corona that are observed from the ground during total solar eclipses, based on their EUV hot and cool emission line counterparts observed from space. EUV observations from SDO/AIA of a sequence of rapidly varying coronal hole structures are analyzed. Evidence of events showing acceleration in the 1.25 Mk line of Fe XII at 193 A is given. The structures along the plume show an outward velocity of about 140 kms-1 that can be interpreted as an upwards propagating wave in the 304 A and 171 A lines; higher speeds are seen in 193 A (up to 1000 km/s). The ejection of the cold He II plasma is delayed by about 4 min in the lowest layer and more than 12 min in the highest level compared to the hot 193 A behavior. A study of the dynamics using time-slice diagrams reveals that a large amount of fast ejected material originates from below the plume, at the footpoints. The release of plasma material appears to come from a cylinder with quasi-parallel edge-enhanced walls. After the initial phase of a longitudinal acceleration, the speed substantially reduces and the ejecta disperse into the environment. Finally, the detailed temporal and spatial relationships between the cool and hot components were studied with simultaneous multi-wavelength observations, using more AIA data. The outward-propagating perturbation of the presumably magnetic walls of polar plumes supports the suggestion that Alfven waves propagate outwardly along these radially extended walls.Comment: 17 pages, 10 figures, accepted in Ap

About the directional properties of Solar Spicules from Hough Transform analysis

Spicules are intermittently rising above the surface of the Sun eruptions; EUV jets are now also reported in immediately above layers. The variation of spicule orientation with respect to the solar latitude, presumably reflecting the confinement and the focusing of ejecta by the surrounding global coronal magnetic field, is an important parameter to understand their dynamical properties. A wealth of high resolution images of limb spicules are made available in H CaII emission from the SOT Hinode mission. Furthermore, the Hough transform is applied to the resulting images for making a statistical analysis of spicule orientations in different regions around the solar limb, from the pole to the equator. Results show a large difference of spicule apparent tilt angles in: (i) the solar pole regions, (ii) the equatorial regions, (iii) the active regions and (iv) the coronal hole regions. Spicules are visible in a radial direction in the polar regions with a tilt angle (less than 200). The tilt angle is even reduced to 10 degrees inside the coronal hole with open magnetic field lines and at the lower latitude the tilt angle reaches values in excess of 50 degree. Usually, which is in close resemblance to the rosettes made of dark mottles and fibrils in projection on the solar disk. The inference of these results for explaining the so-called chromospheric prolateness observed at solar minimum of activity in cool chromospheric lines is considered.Comment: 13 pages, 6 figure

Improved SOT (Hinode mission) high resolution solar imaging observations

We consider the best today available observations of the Sun free of turbulent Earth atmospheric effects, taken with the Solar Optical Telescope (SOT) onboard the Hinode spacecraft. Both the instrumental smearing and the observed stray light are analyzed in order to improve the resolution. The Point Spread Function (PSF) corresponding to the blue continuum Broadband Filter Imager (BFI) near 450 nm is deduced by analyzing i/ the limb of the Sun and ii/ images taken during the transit of the planet Venus in 2012. A combination of Gaussian and Lorentzian functions is selected to construct a PSF in order to remove both smearing due to the instrumental diffraction effects (PSF core) and the large-angle stray light due to the spiders and central obscuration (wings of the PSF) that are responsible for the parasitic stray light. A Max-likelihood deconvolution procedure based on an optimum number of iterations is discussed. It is applied to several solar field images, including the granulation near the limb. The normal non-magnetic granulation is compared to the abnormal granulation which we call magnetic. A new feature appearing for the first time at the extreme- limb of the disk (the last 100 km) is discussed in the context of the definition of the solar edge and of the solar diameter. A single sunspot is considered in order to illustrate how effectively the restoration works on the sunspot core. A set of 125 consecutive deconvolved images is assembled in a 45 min long movie illustrating the complexity of the dynamical behavior inside and around the sunspot.Comment: 15 pages, 22 figures, 1 movi

Alfvenic waves in polar spicules

Context. For investigating spicules from the photosphere to coronal heights, the new Hinode/SOT long series of high resolution observations from Space taken in CaII H line emission offers an improved way to look at their remarkable dynamical behavior using images free of seeing effects. They should be put in the context of the huge amount of already accumulated material from ground-based instruments, including high- resolution spectra of off-limb spicules. Results. The surge-like behavior of solar polar region spicules supports the untwisting multi-component interpretation of spicules exhibiting helical dynamics. Several tall spicules are found with (i) upward and downward flows similar at lower and middle-levels, the rate of upward motion being slightly higher at high levels; (ii) the left and right-hand velocities are also increasing with height; (iii) a large number of multi-component spicules show shearing motion of both left-handed and right-handed senses occurring simultaneously, which might be understood as twisting (or untwisting) threads. The number of turns depends on the overall diameter of the structure made of components and changes from at least one turn for the smallest structure to at most two or three turns for surge-like broad structures; the curvature along the spicule corresponds to a low turn number similar to a transverse kink mode oscillation along the threads.Comment: 8 pages, 10 figures, Accepted in Astronomy and Astrophysic

Chromospheric peculiar off-limb dynamical events from IRIS observations

To study motions and oscillations in the solar chromosphere and at the transition region (TR) level we analyze some extreme Doppler shifts observed off-limb with the Interface Region Imaging Spectrograph (IRIS). Raster scans and slit-jaw imaging observations performed in the near-ultraviolet (NUV) channels were used. Large transverse oscillations are revealed by the far wings profiles after accurately removing the bulk average line profiles of each sequence. Different regions around the Sun are considered. Accordingly, the cool material of spicules is observed in Mg II lines rather dispersed up to coronal heights. In the quiet Sun and especially in a polar coronal hole, we study dynamical properties of the dispersed spicules-material off-limb using a high spectral, temporal and spatial resolutions IRIS observations. We suggest that numerous small-scale jet-like spicules show rapid twisting and swaying motions evidenced by the large distortion and dispersion of the line profiles, including impressive periodic Doppler shifts. Most of these events repeatedly appear in red- and blue-shifts above the limb throughout the whole interval of the observation datasets with an average swaying speed of order +/-35 kms-1 reaching a maximum value of 50 km s-1 in the polar coronal hole region, well above the 2.2 Mm heights. We identified for the 1st time waves with a short period of order of 100 sec and less and transverse amplitudes of order of +/- 20 to 30 km s-1 with the definite signature of Alfven waves. No correlation exists between brightness and Doppler shift variations; the phase speed of the wave is very large and cannot definitely be determined from the spectral features seen along the quasi-radial features. Even shorter periods waves are evidenced, although their contrast is greatly attenuated by the overlapping effects along the line of sight.Comment: 15 pages, 9 figs. accepted in Ap

Oscillations and waves related to sunspots

In order to study umbral oscillations, running penumbral waves and the relationship between them, we analyzed CCD, high-resolution, sunspot observations obtained at the center and the wings of the Hα line and the Fe I 5576 ˚A line using a UBF filter. We produced “space/time slice images” which show that there is not a clear relationship between umbral oscillations and running penumbral waves as they observed in upper chromospheric layers. We found that the running penumbral waves are observable at least up to the formation height of the Hα±0.5 ˚A line, but not in the Hα±0.75 ˚A or the Fe I±0.12 ˚A. The correlation between umbral oscillations at various atmospheric heights and running penumbral waves strongly indicates that the latter are excited by photospheric umbral oscillations and not the chromospheric ones

Evaluation of a method for the resolution improvement of near limb solar images

We present a methodology, based onthe correctionfor the limb darkening and the use of a directionally sensitive operator the “MadMax”, for the image processing of observations obtained near the solar limb. Our image processing method substantially enhances near-limb observations and permits an insight into the studies of the very fine chromospheric structures, over higher-resolution images. Space/time images produced from filtergrams processed with our method indicate that polar surges and spicules are probably related to different physical mechanisms

A model of the prolate chromosphere formation at the solar minimum

Detailed observations in different chromospheric lines of a solar diameter in polar and equatorial directions showed that the polar chromosphere at the minimum phase of solar cycle looks more extended than the low-latitude chromosphere. We propose a simple geometric model to explainthe effect of the prolateness of the solar chromosphere. A specific dynamical part of the solar atmosphere above the 2 Mm level is assumed to be a mixture of moving up and down jets of chromospheric matter with the coronal plasma between them. Due to the dynamic nature of this layer, the magnetic field is considered to play a very important role in the density distribution with the height, guiding the mass flows along the field lines. The difference of the magnetic-field topology in the polar and the equatorial regions leads to different heights of the chromospheric limb