Causal Relationships between Eruptive Prominences and Coronal Mass Ejections

A close association between eruptive prominences and CMEs, both slow and fast CMEs, was reported in many studies. Sometimes it is possible to follow the material motion starting from the prominence (filament) activation to the CME in the high corona. Remnants of the prominence were found in the bright core of CMEs. However, detailed comparisons of the two phenomena reveal problems in explaining CMEs as a continuation of filament eruptions in the upper corona. For example, the heliolatitudes of the disappeared filaments and subsequent coronal ejections sometimes differ by tens of degrees. In order to clear up the problems of EP-CME association we tentatively analyse the more general question of the dynamics of a magnetic flux rope. Prominences and filaments are the best tracers of the flux ropes in the corona long before the beginning of the eruption. A twisted flux rope is held by the tension of field lines of photospheric sources until parameters of the system reach critical values and a catastrophe happens. We suggest that the associated flux rope height above the photosphere is one of these parameters and it is revealed by the height of the filament. 80 filaments were analysed and we found that eruptive prominences were near the so-called limit of stability a few days before their eruptions. We suggest that a comparison of the real heights of prominences with the calculated critical heights from magnetograms could be systematically used to predict filament eruptions and the corresponding CMEs.Comment: 20 pages and 8 figures Invited paper presented at SoHO-20 in Gent (Aug. 2007), in press in Ann. Geophysica

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

Proper Motions of Sunspots' Umbral Dots at High Temporal and Spatial Resolution

To deepen the analysis of the photometric properties of the umbra of a sunspot, we study proper motions of small features such as umbral dots (UDs) inside a single sunspot observed by the Solar Optical Telescope of Hinode close to the disk center. We consider horizontal flows with high precision and details to study the transient motion behavior of UDs in short time intervals. Blue continuum images were first deconvolved with the point-spread function, such that the stray light is precisely removed and the original resolution is improved. Several images were co-added to improve the signal-to-noise ratio, keeping a reasonable temporal resolution and checking that the results are reproducible. The Fourier local correlation tracking technique is applied to the new corrected time sequence of images, and horizontal velocity maps were obtained both for the whole umbra and for a high-resolution small region of the umbra to study the smallest details of the velocity fields. We used two different Gaussian tracking windows (0.8arcsec and 0.2arcsec), which reveals two types of horizontal motions for umbral features. First, a global inner penumbra and peripheral umbra inward motion directed to the central parts is revealed as an overall proper motion of bright peripheral fine structures. Second, motions matching small cells inside the darkest parts of the umbra with apparent sink and source areas are revealed, suggesting possible upflows and downflows appearing in different bright and dark locations without a definite answer regarding their brightness identification with a convective or a buoyant cell

Spectral atlases of the Sun from 3980 to 7100 {\AA} at the center and at the limb

In this work, we present digital and graphical atlases of spectra of both the solar disk-center and of the limb near the Solar poles using data taken at the UTS-IAP & RIAAM (the University of Tabriz Siderostat, telescope and spectrograph jointly developed with the Institut d'Astrophysique de Paris and Research Institute for Astronomy and Astrophysics of Maragha). High resolution and high signal-to-noise ratio (SNR)CCD-slit spectra of the sun for 2 different parts of the disk, namely for $\mu$~=~1.0 (solar center) \& for $\mu$~=~ 0.3 solar limb) are provided and discussed. While there are several spectral atlases of the solar disk-center, this is the first spectral atlas ever produced for the solar limb at this spectral range. The resolution of the spectra is about \emph{R}~$\sim$~70 000 ($\Delta\lambda$~$\sim$~0.09 {\AA} with the signal-to-noise ratio (SNR) of 400$-$600. The full atlas covers the 3980 to 7100 {\AA} spectral regions and contains 44 pages with three partial spectra of the solar spectrum put on each page to make it compact. The difference spectrum of the normalized solar disk-center and the solar limb is also included in the graphic presentation of the atlas to show the difference of line profiles, including far wings. The identification of the most significant solar lines is included in the graphic presentation of the atlas. Telluric lines are producing a definite signature on the difference spectra which is easy to notice. At the end of this paper we present only two sample pages of the whole atlas while the graphic presentation of the whole atlas along with its ASCII file can be accessed via the ftp server of the CDS in Strasbourg via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via this link \footnote{\url{http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/other/ApSS}}.Comment: Accepted for publication in Ap&SS journal. 11 pages, 10 figures. The full atlas can be accessed via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/other/ApS

Refraction and scattering in the atmosphere of the planet Venus: The Lomonossov arc

The main observations of 1761 by M. Lomonossov and those that followed are recalled by extending the discussion to other remarkable visual observations of the passages, then with more and more powerful imagers producing images in profusion. The modern treatment of parasitic effects is briefly recalled by focusing on the expert observation of 1761 which has recently been widely commented on and criticized. It included a spurious effect called the "black drop effect". The shell or aureole or atmospheric ring of Venus observed outside the solar disk is considered with reference to the today parameters of the Venus atmosphere. The contacts during the transit are discussed taking into account effects of scattering, absorption and the dominant effects of the refraction at the small angular distances found to be comparable to a fraction of the angular dimension of the planet. Modern observations of the 2004 and the 2012 transit are tentatively discussed to elucidate what is the arc of Lomonossov?Comment: 40 pages, 14 Figures. For the special issue on "Refraction atmospherique et astronomie" of the Compte-Rendus Physique Acad. Sc. Paris, Ed. L. Dettwiller and P. L\'en

The 2008 August 1 Eclipse Solar-Minimum Corona Unraveled

We discuss results stemming from observations of the white-light and [Fe XIV] emission corona during the total eclipse of the Sun of 2008 August 1, in Mongolia (Altaj region) and in Russia (Akademgorodok, Novosibirsk, Siberia). Corresponding to the current extreme solar minimum, the white-light corona, visible up to 20 solar radii, was of a transient type with well-pronounced helmet streamers situated above a chain of prominences at position angles 48, 130, 241 and 322 degrees. A variety of coronal holes, filled with a number of thin polar plumes, were seen around the poles. Furthering an original method of image processing, stars up to 12 magnitude, a Kreutz-group comet (C/2008 O1), and a coronal mass ejection (CME) were also detected, with the smallest resolvable structures being of, and at some places even less than, 1 arcsec. Differences, presumably motions, in the corona and prominences are seen even with the 19-min time difference between our sites. In addition to the high-resolution coronal images, which show the continuum corona (K-corona) that results from electron scattering of photospheric light, images of the overlapping green-emission-line (530.3 nm, [Fe XIV]) corona were obtained with the help of two narrow-passband filters (centered on the line itself and for the continuum in the vicinity of 529.1 nm, respectively), each with FWHM of 0.15 nm. Through solar observations, on whose scheduling and details we consulted, with the Solar and Heliospheric Observatory, Hinode's XRT and SOT, TRACE, and STEREO, as well as Wilcox Solar Observatory and SOHO/MDI magnetograms, we set our eclipse observations in the context of the current unusually low and prolonged solar minimum.Comment: Accepted in The Astrophysical Journal, 6 July 200