834 research outputs found
The magnetic field topology associated to two M flares
On 27 October, 2003, two GOES M-class flares occurred in the lapse of three
hours in active region NOAA 10486. The two flares were confined and their
associated brightenings appeared at the same location, displaying a very
similar shape both at the chromospheric and coronal levels. We focus on the
analysis of magnetic field (SOHO/MDI), chromospheric (HASTA, Kanzelhoehe Solar
Observatory, TRACE) and coronal (TRACE) observations. By combining our data
analysis with a model of the coronal magnetic field, we compute the magnetic
field topology associated to the two M flares. We find that both events can be
explained in terms of a localized magnetic reconnection process occurring at a
coronal magnetic null point. This null point is also present at the same
location one day later, on 28 October, 2003. Magnetic energy release at this
null point was proposed as the origin of a localized event that occurred
independently with a large X17 flare on 28 October, 2003, at 11:01 UT. The
three events, those on 27 October and the one on 28 October, are homologous.
Our results show that coronal null points can be stable topological structures
where energy release via magnetic reconnection can happen, as proposed by
classical magnetic reconnection models.Comment: 14 pages, 7 figure
Evidence of Twisted flux-tube Emergence in Active Regions
Elongated magnetic polarities are observed during the emergence phase of
bipolar active regions (ARs). These extended features, called magnetic tongues,
are interpreted as a consequence of the azimuthal component of the magnetic
flux in the toroidal flux-tubes that form ARs. We develop a new systematic and
user-independent method to identify AR tongues. Our method is based on
determining and analyzing the evolution of the AR main polarity inversion line
(PIL). The effect of the tongues is quantified by measuring the acute angle [
tau] between the orientation of the PIL and the direction orthogonal to the AR
main bipolar axis. We apply a simple model to simulate the emergence of a
bipolar AR. This model lets us interpret the effect of magnetic tongues on
parameters that characterize ARs ( e.g. the PIL inclination and the tilt
angles, and their evolution). In this idealized kinematic emergence model, tau
is a monotonically increasing function of the twist and has the same sign as
the magnetic helicity. We systematically apply our procedure to a set of
bipolar ARs that were observed emerging in line-of-sight magnetograms over
eight years. For most of the cases studied, the tongues only have a small
influence on the AR tilt angle since tongues have a much lower magnetic flux
than the more concentrated main polarities. From the observed evolution of tau,
corrected for the temporal evolution of the tilt angle and its final value when
the AR is fully emerged, we estimate the average number of turns in the
subphotospherically emerging flux-rope. These values for the 41 observed ARs
are below unity, except for one. This indicates that subphotospheric flux-ropes
typically have a low amount of twist, i.e. highly twisted flux-tubes are rare.
Our results demonstrate that the evolution of the PIL is a robust indicator of
the presence of tongues and constrains the amount of twist in emerging
flux-tube
Coronal mass ejections from the same active region cluster: Two different perspectives
The cluster formed by active regions (ARs) NOAA 11121 and 11123,
approximately located on the solar central meridian on 11 November 2010, is of
great scientific interest. This complex was the site of violent flux emergence
and the source of a series of Earth-directed events on the same day. The onset
of the events was nearly simultaneously observed by the Atmospheric Imaging
Assembly (AIA) telescope aboard the Solar Dynamics Observatory (SDO) and the
Extreme-Ultraviolet Imagers (EUVI) on the Sun-Earth Connection Coronal and
Heliospheric Investigation (SECCHI) suite of telescopes onboard the
Solar-Terrestrial Relations Observatory (STEREO) twin spacecraft. The
progression of these events in the low corona was tracked by the Large Angle
Spectroscopic Coronagraphs (LASCO) onboard the Solar and Heliospheric
Observatory (SOHO) and the SECCHI/COR coronagraphs on STEREO. SDO and SOHO
imagers provided data from the Earth's perspective, whilst the STEREO twin
instruments procured images from the orthogonal directions. This spatial
configuration of spacecraft allowed optimum simultaneous observations of the AR
cluster and the coronal mass ejections that originated in it. Quadrature
coronal observations provided by STEREO revealed a notably large amount of
ejective events compared to those detected from Earth's perspective.
Furthermore, joint observations by SDO/AIA and STEREO/SECCHI EUVI of the source
region indicate that all events classified by GOES as X-ray flares had an
ejective coronal counterpart in quadrature observations. These results have
direct impact on current space weather forecasting because of the probable
missing alarms when there is a lack of solar observations in a view direction
perpendicular to the Sun-Earth line.Comment: Solar Physics - Accepted for publication 2015-Apr-25 v2: Corrected
metadat
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
Topological Analysis of Emerging Bipole Clusters Producing Violent Solar Events
During the rising phase of Solar Cycle 24 tremendous activity occurred on the
Sun with fast and compact emergence of magnetic flux leading to bursts of
flares (C to M and even X-class). We investigate the violent events occurring
in the cluster of two active regions (ARs), NOAA numbers 11121 and 11123,
observed in November 2010 with instruments onboard the {\it Solar Dynamics
Observatory} and from Earth. Within one day the total magnetic flux increased
by with the emergence of new groups of bipoles in AR 11123. From all the
events on 11 November, we study, in particular, the ones starting at around
07:16 UT in GOES soft X-ray data and the brightenings preceding them. A
magnetic-field topological analysis indicates the presence of null points,
associated separatrices and quasi-separatrix layers (QSLs) where magnetic
reconnection is prone to occur. The presence of null points is confirmed by a
linear and a non-linear force-free magnetic-field model. Their locations and
general characteristics are similar in both modelling approaches, which
supports their robustness. However, in order to explain the full extension of
the analysed event brightenings, which are not restricted to the photospheric
traces of the null separatrices, we compute the locations of QSLs. Based on
this more complete topological analysis, we propose a scenario to explain the
origin of a low-energy event preceding a filament eruption, which is
accompanied by a two-ribbon flare, and a consecutive confined flare in AR
11123. The results of our topology computation can also explain the locations
of flare ribbons in two other events, one preceding and one following the ones
at 07:16 UT. Finally, this study provides further examples where flare-ribbon
locations can be explained when compared to QSLs and only, partially, when
using separatrices.Comment: 42 pages, 15 figure
El viaje de la fragata San Antonio en 1745 - 1756: reflexiones sobre los procesos políticos operados entre los indígenas pampeano-patagónicos.
El advenimiento de la dinastía borbónica en España en el siglo XVIII y las transformaciones que tuvieron lugar en el terreno de las relaciones internacionales, conllevaron modificaciones de la política colonial española en la región del Río de La Plata. En este contexto, la revaluación de la ruta del cabo de Hornos y las amenazas extranjeras contra el territorio de Patagonia --potenciales si no efectivas--, alentaron los viajes de exploración y las expediciones militares a los territorios meridionales. El viaje de la fragata española San Antonio a las costas meridionales de Patagonia en 1745-1746 fue resultado de ese nuevo interés. A pesar de que los viajeros no vieron indios, encontraron una tumba india en San Julián, cuya descripción podemos encontrar en los diarios de los viajeros. Este articulo analiza esa información y sus implicaciones para comprender las estructuras políticas y sociales indígenas
Simulations of Prominence Formation in the Magnetized Solar Corona by Chromospheric Heating
Starting from a realistically sheared magnetic arcade connecting
chromospheric, transition region to coronal plasma, we simulate the in-situ
formation and sustained growth of a quiescent prominence in the solar corona.
Contrary to previous works, our model captures all phases of the prominence
formation, including the loss of thermal equilibrium, its successive growth in
height and width to macroscopic dimensions, and the gradual bending of the
arched loops into dipped loops, as a result of the mass accumulation. Our
2.5-dimensional, fully thermodynamically and magnetohydrodynamically consistent
model mimics the magnetic topology of normal-polarity prominences above a
photospheric neutral line, and results in a curtain-like prominence above the
neutral line through which the ultimately dipped magnetic field lines protrude
at a finite angle. The formation results from concentrated heating in the
chromosphere, followed by plasma evaporation and later rapid condensation in
the corona due to thermal instability, as verified by linear instability
criteria. Concentrated heating in the lower atmosphere evaporates plasma from
below to accumulate at the top of coronal loops and supply mass to the later
prominence constantly. This is the first evaporation-condensation model study
where we can demonstrate how the formed prominence stays in a force balanced
state, which can be compared to the Kippenhahn-Schluter type magnetohydrostatic
model, all in a finite low-beta corona
Two successive partial mini-filament confined ejections
Active region (AR) NOAA 11476 produced a series of confined plasma ejections, mostly accompanied by flares of X-ray class M, from 08 to 10 May 2012. The structure and evolution of the confined ejections resemble that of EUV surges; however, their origin is associated to the destabilization and eruption of a mini-filament, which lay along the photospheric inversion line (PIL) of a large rotating bipole. Our analysis indicate that the bipole rotation and flux cancellation along the PIL have a main role in destabilizing the structure and triggering the ejections. The observed bipole emerged within the main following AR polarity. Previous studies have analyzed and discussed in detail two events of this series in which the mini-filament erupted as a whole, one at 12:23 UT on 09 May and the other at 04:18 UT on 10 May. In this article we present the observations of the confined eruption and M4.1 flare on 09 May 2012 at 21:01 UT (SOL2012-05-09T21:01:00) and the previous activity in which the mini-filament was involved. For the analysis we use data in multiple wavelengths (UV, EUV, X-rays, and magnetograms) from space instruments. In this particular case, the mini-filament is seen to erupt in two different sections. The northern section erupted accompanied by a C1.6 flare and the southern section did it in association with the M4.1 flare. The global structure and direction of both confined ejections and the location of a far flare kernel, to where the plasma is seen to flow, suggest that both ejections and flares follow a similar underlying mechanism.Fil: Poisson, Mariano. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Bustos, C.. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Lopez Fuentes, Marcelo Claudio. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mandrini, Cristina Hemilse. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Cristiani, Germán Diego. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
Temporal power spectra of the horizontal velocity of the solar photosphere
We have derived the temporal power spectra of the horizontal velocity of the
solar photosphere. The data sets for 14 quiet regions observed with the Gband
filter of Hinode/SOT are analyzed to measure the temporal fluctuation of the
horizontal velocity by using the local correlation tracking (LCT) method. Among
the high resolution (~0.2") and seeing-free data sets of Hinode/SOT, we
selected the observations whose duration is longer than 70 minutes and cadence
is about 30 s. The so-called k-{\omega} diagrams of the photospheric horizontal
velocity are derived for the first time to investigate the temporal evolution
of convection. The power spectra derived from k-omega diagrams typically have a
double power law shape bent over at a frequency of 4.7 mHz. The power law index
in the high frequency range is -2.4 while the power law index in the low
frequency range is -0.6. The root mean square of the horizontal speed is about
1.1 km/s when we use a tracer size of 0.4" in LCT method. Autocorrelation
functions of intensity fluctuation, horizontal velocity, and its spatial
derivatives are also derived in order to measure the correlation time of the
stochastic photospheric motion. Since one of possible energy sources of the
coronal heating is the photospheric convection, the power spectra derived in
the present study will be of high value to quantitatively justify various
coronal heating models.Comment: 17 pages, 5 figures, accepted for publication in Astrophysical
Journa
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