Observations of photospheric magnetic structure below a dark filament using the Hinode Spectro-Polarimeter

The structure of the photospheric vector magnetic field below a dark filament on the Sun is studied using the observations of the Spectro-Polarimeter attached to the Solar Optical Telescope onboard Hinode. Special attention is paid to discriminating between two suggested models, a flux rope or a bent arcade. “Inverse polarity” orientation is possible below the filament in a flux rope, whereas “normal polarity” can appear in both models. We study a filament in the active region NOAA 10930, which appeared on the solar disk during 2006 December. The transverse field perpendicular to the line of sight has a direction almost parallel to the filament spine with a shear angle of 30°, the orientation of which includes the 180° ambiguity. To know whether it is in the normal orientation or in the inverse one, the center-to-limb variation is used for the solution under the assumption that the filament does not drastically change its magnetic structure during the passage. When the filament is near the east limb, we found that the line-of-site magnetic component below the filament is positive, while it is negative near the west limb.This change of sign indicates that the horizontal photospheric field perpendicular to the polarity inversion line beneath the filament has an “inverse-polarity”, which indicates a flux-rope structure of the filament supporting field.

Structure and Dynamics of an Eruptive Prominence on the Quiet Sun

We present preliminary results on the investigation of one polar crown prominence that erupted on 2012 March 11. This prominence is viewed at the east limb by SDO/AIA and displays a simple vertical-thread structure. A bright U-shape (double horn-like) structure is observed surrounding the upper portion of the prominence before the eruption and becomes more prominent during the eruption. When viewed on the disk, STEREO_B shows that this prominence is composed of series of vertical threads and displays a loop-like structure during the eruption. We focus on the magnetic support of the prominence by studying the structure and dynamics before and during the eruption using observations from SDO and STEREO. We will also present preliminary DEM analysis of the cavity surrounding the prominence.

Column Density Measurements of a Prominence Observed by AIA

We present column density measurements of a polar crown prominence observed on March 9th, 2012 by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. The structure was viewed on the east limb by AIA and erupted about 30 hours after the observations shown here. We estimate column density by approximating the obscured background emission to obtain an optical depth. This can then be combined with the absorption cross sections of neutral hydrogen and helium, along with the He:H abundance ratio, to calculate column density. We perform this calculation for the 171, 193, 211, and 335 Å AIA passbands.

Microwave observations with the RATAN-600 radio telescope: detection of the thermal emission sources

We report on two off-limb radio sources of microwave emission which were detected in one-dimensional RATAN-600 solar scans of the post-eruptive loops: on December 2, 2003 (off west limb) and January 25, 2007 (east limb). The microwave spectra showed that the thermal emission was predominant at the early stage of the arcade formation with a small contribution of non-thermal emission. There were no high-energy particles in these events. The microwave spectra of the radio sources associated with the tops of postflare loops show the predominant thermal emission during one hour after the eruption. In case of a small contribution from accelerated particles to the microwave emission, there is a large amount of hot plasma in the region of the loop tops after the eruption.

Before the Frank Slide

The Frank Slide occurred on the east limb of the Turtle Mountain Anticline, which was thrust up along the folded and splayed Turtle Mountain Fault. Easterly dipping, Paleozoic limestones and dolomites then rested on sheared, weaker, Mesozoic clastic rocks and coal strata. Cordilleran glaciers steepened the eastern flank of Turtle Mountain but left buttressing kame moraines. These were eroded by the Crowsnest River, which was pushed against Turtle Mountain between its North and South Peaks by the growth of the alluvial fan of Gold Creek. Blairmore Group mudstones and shales beneath the moraines were susceptible to toppling. Photographs of the east slope of Turtle Mountain before the Frank Slide show disturbed vegetation, uneven topography, steep slopes, and rock fall deposits, all consistent with active slope movements. The Frank Slide may have been triggered by the freezing of melting snow in rock joints and by coal mining. Our calculations show that, while individual stopes may have been unstable, the mine pillars and the coal mine itself were stable. Numerical simulations of the coal mining in the Frank Mine suggest mining reduced the strength of the east slope of Turtle Mountain by less than 10% before the Frank Slide.Key words: Rocky Mountains, Frank Slide, coal mining, river erosion, toppling.

Seismic Forecasting of Solar Activity

Computational seismic holography, applied to Solar Oscillations Investigation -Michelson Doppler Imager (SOI-MDI) data fromSOHO, has recently given us the first images of an active region on the far side of the Sun(Lindsey & Braun 2000). The advent of phase-coherent seismic imaging is now allowing us quite literally to look into the solar interior from a local perspective, indeed to see through the solar interior acoustically to its far surface. Solar activity is critical to near-Earth space weather. A great deal of effort has been invested towards the prediction of flares and CMEs, based on the formidable presence of active regions on the near solar surface. Active regions can emerge rapidly from beneath the photosphere or appear on the east limb with relatively little warning. Because of this, the ability to anticipate the appearances of active regions will contribute substantially to forecasts of space weather on time scales of more than about a day. In collaboration with Dr. Phil Scherrer and the MDI team at Stanford University we are currently deriving far-side images from the lower resolution “medium-l” SOI-MDI Dopplergrams, which are obtained continuously through the year and arrive at MDI headquarters within 24 hours of their acquisition by theSOHOspacecraft. We are therefore already capable of locating large far-side active regions and predicting their appearance on the east solar limb to within a few hours more than a week in advance. In addition, ground-based networks such as GONG will soon have the capability for “real-time helioseismology”, and will be routinely monitoring the far surface of the Sun, and perhaps beneath the near surface, for emerging solar activity.

Observation of Reconnection Inflow of a Solar Flare

We find an important piece of evidence for magnetic reconnection inflow in a flare on March 18, 1999. The flare occurred on the north-east limb, displaying a nice cusp-shaped soft X-ray loop and a plasmoid ejection typical for the long-duration-events. As the plasmoid is ejected, magnetic reconnection occurs at the disconnecting point. A clear ingoing pattern toward the magnetic X-point is seen. The velocity of this apparent motion is about 5 km sec−1, which is an upper limit on reconnection inflow speed. Based on this observation, we derive the reconnection rate as MA = 0.001 − 0.03, where MA is a Alfvén Mach number of the inflow.

Dynamical Fine Structure of Filaments and Prominences

We observed a quiescent prominence on the east limb of the Sun, on June 7, 1988 (Mein P. et al 1990) and a quiescent filament (N 5, W 5) on June 17, 1986 (Schmieder et al 1991). These two observations are made with the Multichannel Subtractive Double Pass spectrograph of the turret dome refractor of the Pic du Midi Observatory, providing simultaneous 2D pictures in 9 channels for Hα.