Louise K. Harra

Coronal wave : Magnetic footprint of a coronal mass ejection?

We investigate the properties of two classical EUV Imaging Telescope (EIT) coronal waves. The two source regions of the associated coronal mass ejections (CMEs) possess opposite helicities, and the coronal waves display rotations in opposite senses. We observe deep core dimmings near the flare site and also widespread diffuse dimming, accompanying the expansion of the EIT wave. We also report a new property of these EIT waves, namely, that they display dual brightenings: persistent ones at the outermost edge of the core dimming regions and simultaneously diffuse brightenings constituting the leading edge of the coronal wave, surrounding the expanding diffuse dimmings. We show that such behavior is consistent with a diffuse EIT wave being the magnetic footprint of a CME. We propose a new mechanism where driven magnetic reconnections between the skirt of the expanding CME magnetic field and quiet-Sun magnetic loops generate the observed bright diffuse front. The dual brightenings and the widespread diffuse dimming are identified as innate characteristics of this process.

Continuous plasma outflows from the edge of a solar active region as a possible source of solar wind

The Sun continuously expels a huge amount of ionized material into interplanetary space as the solar wind. Despite its influence on the heliospheric environment, the origin of the solar wind has yet to be well identified. In this paper, we report Hinode X-ray Telescope observations of a solar active region. At the edge of the active region, located adjacent to a coronal hole, a pattern of continuous outflow of soft-x-ray–emitting plasmas was identified emanating along apparently open magnetic field lines and into the upper corona. Estimates of temperature and density for the outflowing plasmas suggest a mass loss rate that amounts to ∼1/4 of the total mass loss rate of the solar wind. These outflows may be indicative of one of the solar wind sources at the Sun.

Coronal Plasma Motions near Footpoints of Active Region Loops Revealed from Spectroscopic Observations with Hinode EIS

The solar active region 10938 has been observed from the disk center to the west limb with the Hinode EUV Imaging Spectrometer. In the disk-center observation, subsonic upflow motions of tens of km s -->−1 and enhanced nonthermal velocities have been found near the footpoints of the active region loops assuming a single Gaussian approximation for the emission-line profiles. When the same part of the active region is observed near the limb, both upflows and enhanced nonthermal velocities essentially decrease. There is a strong correlation between Doppler velocity and nonthermal velocity. Significant deviations from a single Gaussian profile are found in the blue wing of the line profiles for the upflows. These suggest that there are unresolved high-speed upflows. We discuss the implications for coronal heating mechanisms.

EUV Emission Lines and Diagnostics Observed with Hinode/EIS

Quiet Sun and active region spectra from the Hinode/EIS instrument are presented, and the strongest lines from different temperature regions discussed. A list of emission lines recommended to be included in EIS observation studies is presented based on analysis of blending and diagnostic potential using the CHIANTI atomic database. In addition we identify the most useful density diagnostics from the ions covered by EIS.

Material Outflows from Coronal Intensity "Dimming Regions" During Coronal Mass Ejection Onset

One signature of expulsion of coronal mass ejections (CMEs) from the solar corona is the appearance of transient intensity dimmings in coronal images. These dimmings have generally been assumed to be due to discharge of CME material from the corona, and thus the dimming regions are thought of as an important signature of the sources of CMEs. We present spectral observations of two dimming regions at the time of expulsion of CMEs, using the Coronal Diagnostic Spectrometer (CDS) on the SOHO satellite. One of the dimming regions is at the solar limb and associated with a CME traveling in the plane of the sky, while the other region is on the solar disk and associated with an Earth-directed halo CME. From the limb event, we see Doppler signatures of ≈30 km s-1 in coronal (Fe XVI and Mg IX) emission lines, where the enhanced velocities coincide with the locations of coronal dimming. This provides direct evidence that the dimmings are associated with outflowing material. We also see larger (≈100 km s-1) Doppler velocities in transition region (O V and He I) emission lines, which are likely to be associated with motions of a prominence and loops at transition region temperatures. An EIT wave accompanies the disk event, and a dimming region behind the wave shows strong blueshifted Doppler signatures of ≈100 km s-1 in O V, suggesting that material from the dimming regions behind the wave may be feeding the CME.

Imaging and Spectroscopic Investigations of a Solar Coronal Wave: Properties of the Wave Front and Associated Erupting Material

Using spectral data from the Coronal Diagnostic Spectrometer (CDS) instrument on the Solar and Heliospheric Observatory spacecraft, we observe a coronal wave feature (often referred to as an EIT wave) that occurred in association with a solar eruption and. are on 1998 June 13. EUV images from the Transition Region and Coronal Explorer (TRACE) satellite show that the coronal wave consists of two aspects: (1) a bright wave, which shows up prominently in the TRACE difference images, moves with a velocity of approximately 200 km s(-1), and is followed by a strong dimming region behind it and (2) a weak wave, which is faint in the TRACE images, has a velocity of about 500 km s(-1), and appears to disperse out of the bright wave. The weak wave passes through the CDS field of view but shows little or no line-of-sight motions in CDS spectra (velocities less than about 10 km s(-1)). Only a small portion of the bright wave passes the CDS field of view, with the spectral lines showing insignificant shifts. A high-velocity CDS feature, however, occurs after the weak wave passes, which appears to correspond to ejection of cool, filament-like material in TRACE images. Our observations have similarities with a numerical simulation model of coronal waves presented by Chen et al., who suggest that coronal waves consist of a faster propagating, piston-driven portion and a more slowly propagating portion due to the opening of field lines associated with an erupting filament.

The onset and association of CMEs with sigmoidal active regions

Previous studies of active regions characterised by Soft X-ray S or inverse-S morphology (Canfield et al., 1999), have found these regions to possess a higher probabil- ity of eruption. In such cases, CME launch has been inferred using X-ray proxies to indicate eruption. Active regions ob- served during 1997, previously categorised as both sigmoidal and eruptive (Canfield, 1999), have been selected for further study, incorporating SoHO-LASCO, SoHO-EIT and ground based H-alpha data. Our results allow re-classification into three main categories; sigmoidal, non-sigmoidal and active regions appearing sigmoidal due to the projection of many loops. Although the reduced dataset size prevents a statisti- cal measure of significance, we note that regions comprising a single S (or inverse-S) shaped structure are more frequently associated with a CME than those classed as non-sigmoidal. This motivates the study of a larger dataset and highlights the need for a quantitative observational definition of the term sigmoid.

PLASMA MOTIONS AND HEATING BY MAGNETIC RECONNECTION IN A 2007 MAY 19 FLARE

Based on scanning spectroscopic observations with the Hinode EUV imaging spectrometer, we have found a loop-top hot source, a fast jet nearby, and an inflow structure flowing to the hot source that appeared in the impulsive phase of a long-duration flare at the disk center on 2007 May 19. The hot source observed in Fe XXIII and Fe XXIV emission lines has the electron temperature of 12 MK and density of 1 Multiplication-Sign 10{sup 10} cm{sup -3}. It shows excess line broadening, which exceeds the thermal Doppler width by {approx}100 km s{sup -1}, with a weak redshift of {approx}30 km s{sup -1}. We have also observed a blueshifted faint jet whose Doppler velocity exceeds 200 km s{sup -1} with an electron temperature of 9 MK. Coronal plasmas with electron temperature of 1.2 MK and density of 2.5 Multiplication-Sign 10{sup 9} cm{sup -3} that flow into the loop-top region with a Doppler velocity of 20 km s{sup -1} have been identified in the Fe XII observation. They disappeared near the hot source, possibly by being heated to the hotter faint jet temperature. From the geometrical relationships of these phenomena, we conclude that they provide evidence for magnetic reconnection that occurs nearmorexa0» the loop-top region. The estimated reconnection rate is 0.05-0.1, which supports the Petschek-type magnetic reconnection. Further supporting evidence for the presence of the slow-mode and fast-mode MHD shocks in the reconnection geometry is given based on the observed quantities.«xa0less

Twisting solar coronal jet launched at the boundary of an active region

Aims. A broad jet was observed in a weak magnetic eld area at the edge of active region NOAA 11106 that also produced other nearby recurring and narrow jets. The peculiar shape and magnetic environment of the broad jet raised the question of whether it was created by the same physical processes of previously studied jets with reconnection occurring high in the corona. Methods. We carried out a multi-wavelength analysis using the EUV images from the Atmospheric Imaging Assembly (AIA) and magnetic elds from the Helioseismic and Magnetic Imager (HMI) both on-board the SDO satellite, which we coupled to a high-resolution, nonlinear force-free eld extrapolation. Local correlation tracking was used to identify the photospheric motions that triggered the jet, and time-slices were extracted along and across the jet to unveil its complex nature. A topological analysis of the extrapolated eld was performed and was related to the observed features. Results. The jet consisted of many dierent threads that expanded in around 10 minutes to about 100 Mm in length, with the bright features in later threads moving faster than in the early ones, reaching a maximum speed of about 200 km s 1 . Time-slice analysis revealed a striped pattern of dark and bright strands propagating along the jet, along with apparent damped oscillations across the jet. This is suggestive of a (un)twisting motion in the jet, possibly an Alfv

New evidence for the role of emerging flux in a solar Filament's slow rise preceding its cme-producing fast eruption

We observe the eruption of a large-scale (� 300,000 km) quiet-region solar filament leading to an Earth-directed ‘‘halo’’ coronal mass ejection (CME), using data from EIT, CDS, MDI, and LASCO on SOHO and from SXT on Yohkoh. Initially the filament shows a slow (� 1k m s � 1 projected against the solar disk) and approximately constant velocityriseforabout6hr,beforeeruptingrapidly,reachingavelocityof � 8kms � 1 overthenext � 25minutes.CDS Doppler data show Earth-directed filament velocities ranging from <20 km s � 1 (the noise limit) during the slow-rise phase, to � 100 km s � 1 early in the eruption. Beginning within 10 hr prior to the start of the slow rise, localized new magneticfluxemergednearoneendofthefilament.Nearthestartofandduringtheslow-risephase,softX-ray(SXR) microflaring occurred repeatedly at the flux-emergence site, and the magnetic arcade over the filament progressively brightened in a fan of illumination in SXRs. These observations are consistent with ‘‘tether-weakening’’ reconnection occurring between the newly emerging flux and the overlying arcade field containing the filament, and apparently this reconnection is the cause of the filament’s slow rise. We cannot, however, discern whether the transition from slow rise to fast eruption was caused by a final episode of tether-weakening reconnection, or by one or some combination of otherpossiblemechanismsallowedbytheobservations.Intensity‘‘dimmings’’and‘‘brightenings’’occurringbothnear to and relatively far from the location of the filament are possible signatures ofthe expansion (‘‘opening’’) of the erupting field and its reconnection with overarching field during the eruption.