333 research outputs found
Long duration thermal hard X-ray sources observed in two eruptive flares
We present observations of two eruptive flares on 17 of December 2006 (C1.9) and 19 of May 2007 (B9.7) which had good coverage with both Hinode and RHESSI. In these flares we see a long lived, gradual thermal hard X-ray source of low emission measure and, relative to the loops observed with GOES and XRT, high temperature. The lack of a non-thermal hard X-ray component and impulsive behaviour is inconsistent with electron beam driven chromospheric evaporation
Granular-Scale Elementary Flux Emergence Episodes in a Solar Active Region
We analyze data from Hinode spacecraft taken over two 54-minute periods
during the emergence of AR 11024. We focus on small-scale portions within the
observed solar active region and discover the appearance of very distinctive
small-scale and short-lived dark features in Ca II H chromospheric filtergrams
and Stokes I images. The features appear in regions with close-to-zero
longitudinal magnetic field, and are observed to increase in length before they
eventually disappear. Energy release in the low chromospheric line is detected
while the dark features are fading. In time series of magnetograms a diverging
bipolar configuration is observed accompanying the appearance of the dark
features and the brightenings. The observed phenomena are explained as
evidencing elementary flux emergence in the solar atmosphere, i.e small-scale
arch filament systems rising up from the photosphere to the lower chromosphere
with a length scale of a few solar granules. Brightenings are explained as
being the signatures of chromospheric heating triggered by reconnection of the
rising loops (once they reached chromospheric heights) with pre-existing
magnetic fields as well as to reconnection/cancellation events in U-loop
segments of emerging serpentine fields. We study the temporal evolution and
dynamics of the events and compare them with the emergence of magnetic loops
detected in quiet sun regions and serpentine flux emergence signatures in
active regions. Incorporating the novel features of granular-scale flux
emergence presented in this study we advance the scenario for serpentine flux
emergence.Comment: 24 pages, 9 figures. Accepted for publication in Solar Physic
An investigation of the sources of Earth-directed solar wind during Carrington Rotation 2053
In this work we analyze multiple sources of solar wind through a full Carrington Rotation (CR 2053) by analyzing the solar data through spectroscopic observations of the plasma upflow regions and the in situ data of the wind itself. Following earlier authors, we link solar and in situ observations by a combination of ballistic backmapping and potential-field source-surface modeling. We find three sources of fast solar wind that are low-latitude coronal holes. The coronal holes do not produce a steady fast wind, but rather a wind with rapid fluctuations. The coronal spectroscopic data from Hinode's Extreme Ultraviolet Imaging Spectrometer show a mixture of upflow and downflow regions highlighting the complexity of the coronal hole, with the upflows being dominant. There is a mix of open and multi-scale closed magnetic fields in this region whose (interchange) reconnections are consistent with the up- and downflows they generate being viewed through an optically thin corona, and with the strahl directions and freeze-in temperatures found in in situ data. At the boundary of slow and fast wind streams there are three short periods of enhanced-velocity solar wind, which we term intermediate based on their in situ characteristics. These are related to active regions that are located beside coronal holes. The active regions have different magnetic configurations, from bipolar through tripolar to quadrupolar, and we discuss the mechanisms to produce this intermediate wind, and the important role that the open field of coronal holes adjacent to closed-field active regions plays in the process
A slow coronal mass ejection with rising X-ray source
An eruptive event, which occurred on 16th April 2002, is discussed. Using images from the Transition Region and Coronal Explorer ( TRACE) at 195 angstrom, we observe a lifting flux rope which gives rise to a slow coronal mass ejection ( CME). There are supporting velocity observations from the Coronal Diagnostic Spectrometer ( CDS) on the Solar and Heliospheric Observatory ( SOHO), which illustrate the helical nature of the structure. Additionally a rising coronal hard X- ray source, which is observed with the Reuven Ramaty High Energy Solar Spectroscopic Imager ( RHESSI), is shown to follow the flux rope with a speed of similar to 60 km s(-1). It is also sampled by the CDS slit, although it has no signature in the Fe XIX band. Following the passage of this source, there is evidence from the CDS for down- flowing ( cooling) material along newly reconnected loops through Doppler velocity observations, combined with magnetic field modeling. Later, a slow CME is observed with the Large Angle and Spectroscopic Coronagraph ( LASCO). We combine a height- time profile of the flux rope at lower altitudes with the slow CME. The rising flux rope speeds up by a factor of 1.7 at the start of the impulsive energy release and goes through further acceleration before reaching 1.5 solar radii. These observations support classical CME scenarios in which the eruption of a filament precedes flaring activity. Cusped flare loops are observed following the erupting flux rope and their altitude increases with time. In addition we find RHESSI sources both below and above the probable location of the reconnection region
Signatures of Interchange Reconnection: STEREO, ACE and Hinode Observations Combined
Combining STEREO, ACE and Hinode observations has presented an opportunity to
follow a filament eruption and coronal mass ejection (CME) on the 17th of
October 2007 from an active region (AR) inside a coronal hole (CH) into the
heliosphere. This particular combination of `open' and closed magnetic
topologies provides an ideal scenario for interchange reconnection to take
place. With Hinode and STEREO data we were able to identify the emergence time
and type of structure seen in the in-situ data four days later. On the 21st,
ACE observed in-situ the passage of an ICME with `open' magnetic topology. The
magnetic field configuration of the source, a mature AR located inside an
equatorial CH, has important implications for the solar and interplanetary
signatures of the eruption. We interpret the formation of an `anemone'
structure of the erupting AR and the passage in-situ of the ICME being
disconnected at one leg, as manifested by uni-directional suprathermal electron
flux in the ICME, to be a direct result of interchange reconnection between
closed loops of the CME originating from the AR and `open' field lines of the
surrounding CH.Comment: 13 pages, 13 figures, accepted Annales Geophysica
Flux cancellation and the evolution of the eruptive filament of 2011 June 7
We investigate whether flux cancellation is responsible for the formation of
a very massive filament resulting in the spectacular 2011 June 7 eruption. We
analyse and quantify the amount of flux cancellation that occurs in NOAA AR
11226 and its two neighbouring ARs (11227 & 11233) using line-of-sight
magnetograms from the Heliospheric Magnetic Imager. During a 3.6-day period
building up to the filament eruption, 1.7 x 10^21 Mx, 21% of AR 11226's maximum
magnetic flux, was cancelled along the polarity inversion line (PIL) where the
filament formed. If the flux cancellation continued at the same rate up until
the eruption then up to 2.8 x 10^21 Mx (34% of the AR flux) may have been built
into the magnetic configuration that contains the filament plasma. The large
flux cancellation rate is due to an unusual motion of the positive polarity
sunspot, which splits, with the largest section moving rapidly towards the PIL.
This motion compresses the negative polarity and leads to the formation of an
orphan penumbra where one end of the filament is rooted. Dense plasma threads
above the orphan penumbra build into the filament, extending its length, and
presumably injecting material into it. We conclude that the exceptionally
strong flux cancellation in AR 11226 played a significant role in the formation
of its unusually massive filament. In addition, the presence and coherent
evolution of bald patches in the vector magnetic field along the PIL suggests
that the magnetic field configuration supporting the filament material is that
of a flux rope.Comment: 18 pages, 7 figures. Submitted to ApJ in December 2015, accepted in
June 201
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