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Search Results: 1 - 10 of 714552 matches for " A. M. Title "
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Simulation of the Formation of a Solar Active Region
M. C. M. Cheung,M. Rempel,A. M. Title,M. Schüssler
Physics , 2010, DOI: 10.1088/0004-637X/720/1/233
Abstract: We present a radiative magnetohydrodynamics simulation of the formation of an Active Region on the solar surface. The simulation models the rise of a buoyant magnetic flux bundle from a depth of 7.5 Mm in the convection zone up into the solar photosphere. The rise of the magnetic plasma in the convection zone is accompanied by predominantly horizontal expansion. Such an expansion leads to a scaling relation between the plasma density and the magnetic field strength such that $B\propto\varrho^{1/2}$. The emergence of magnetic flux into the photosphere appears as a complex magnetic pattern, which results from the interaction of the rising magnetic field with the turbulent convective flows. Small-scale magnetic elements at the surface first appear, followed by their gradual coalescence into larger magnetic concentrations, which eventually results in the formation of a pair of opposite polarity spots. Although the mean flow pattern in the vicinity of the developing spots is directed radially outward, correlations between the magnetic field and velocity field fluctuations allow the spots to accumulate flux. Such correlations result from the Lorentz-force driven, counter-streaming motion of opposite-polarity fragments. The formation of the simulated Active Region is accompanied by transient light bridges between umbrae and umbral dots. Together with recent sunspot modeling, this work highlights the common magnetoconvective origin of umbral dots, light bridges and penumbral filaments.
Pathways of large-scale magnetic couplings between solar coronal events
C. J. Schrijver,A. M. Title,A. R. Yeates,M. L. DeRosa
Physics , 2013, DOI: 10.1088/0004-637X/773/2/93
Abstract: The high-cadence, comprehensive view of the solar corona by SDO/AIA shows many events that are widely separated in space while occurring close together in time. In some cases, sets of coronal events are evidently causally related, while in many other instances indirect evidence can be found. We present case studies to highlight a variety of coupling processes involved in coronal events. We find that physical linkages between events do occur, but concur with earlier studies that these couplings appear to be crucial to understanding the initiation of major eruptive or explosive phenomena relatively infrequently. We note that the post-eruption reconfiguration time scale of the large-scale corona, estimated from the EUV afterglow, is on average longer than the mean time between CMEs, so that many CMEs originate from a corona that is still adjusting from a previous event. We argue that the coronal field is intrinsically global: current systems build up over days to months, the relaxation after eruptions continues over many hours, and evolving connections easily span much of a hemisphere. This needs to be reflected in our modeling of the connections from the solar surface into the heliosphere to properly model the solar wind, its perturbations, and the generation and propagation of solar energetic particles. However, the large-scale field cannot be constructed reliably by currently available observational resources. We assess the potential of high-quality observations from beyond Earth's perspective and advanced global modeling to understand the couplings between coronal events in the context of CMEs and solar energetic particle events.
Transverse component of the magnetic field in the solar photosphere observed by Sunrise
S. Danilovic,B. Beeck,A. Pietarila,M. Schuessler,S. K. Solanki,V. Martinez Pillet,J. A. Bonet,J. C. del Toro Iniesta,V. Domingo,P. Barthol,T. Berkefeld,A. Gandorfer,M. Knoelker,W. Schmidt,A. M. Title
Physics , 2010, DOI: 10.1088/2041-8205/723/2/L149
Abstract: We present the first observations of the transverse component of photospheric magnetic field acquired by the imaging magnetograph Sunrise/IMaX. Using an automated detection method, we obtain statistical properties of 4536 features with significant linear polarization signal. Their rate of occurrence is 1-2 orders of magnitude larger than values reported by previous studies. We show that these features have no characteristic size or lifetime. They appear preferentially at granule boundaries with most of them being caught in downflow lanes at some point in their evolution. Only a small percentage are entirely and constantly embedded in upflows (16%) or downflows (8%).
Sparkling EUV bright dots observed with Hi-C
S. Regnier,C. E. Alexander,R. W. Walsh,A. R. Winebarger,J. Cirtain,L. Golub,K. E. Korreck,N. Mitchell,S. Platt,M. Weber,B. De Pontieu,A. Title,K. Kobayashi,S. Kuzin,C. E. DeForest
Physics , 2014, DOI: 10.1088/0004-637X/784/2/134
Abstract: Observing the Sun at high time and spatial scales is a step towards understanding the finest and fundamental scales of heating events in the solar corona. The Hi-C instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 11 July 2012, which exhibits several interesting features in the EUV line at 193\AA: one of them is the existence of short, small brightenings ``sparkling" at the edge of the active region; we call these EUV Bright Dots (EBDs). Individual EBDs have a characteristic duration of 25s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength, however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA suggesting a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty EBDs. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 10$^{26}$ erg.
Magnetic loops in the quiet Sun
Thomas Wiegelmann,Sami K Solanki,Juan Borrero,Valentin Martinez Pillet,J. C. del Toro Iniesta,Vicente Domingo,J. A. Bonet Navarro,Peter Barthol,Achim Gandorfer,Michael Knoelker,Wolfgang Schmidt,Alan M. Title
Physics , 2010, DOI: 10.1088/2041-8205/723/2/L185
Abstract: We investigate the fine structure of magnetic fields in the atmosphere of the quiet Sun. We use photospheric magnetic field measurements from {\sc Sunrise}/IMaX with unprecedented spatial resolution to extrapolate the photospheric magnetic field into higher layers of the solar atmosphere with the help of potential and force-free extrapolation techniques. We find that most magnetic loops which reach into the chromosphere or higher have one foot point in relatively strong magnetic field regions in the photosphere. $91%$ of the magnetic energy in the mid chromosphere (at a height of 1 Mm) is in field lines, whose stronger foot point has a strength of more than 300 G, i.e. above the equipartition field strength with convection. The loops reaching into the chromosphere and corona are also found to be asymmetric in the sense that the weaker foot point has a strength $B < 300$ G and is located in the internetwork. Such loops are expected to be strongly dynamic and have short lifetimes, as dictated by the properties of the internetwork fields.
Prominence Formation Associated with an Emerging Helical Flux Rope
Takenori J. Okamoto,Saku Tsuneta,Bruce W. Lites,Masahito Kubo,Takaaki Yokoyama,Thomas E. Berger,Kiyoshi Ichimoto,Yukio Katsukawa,Shin'ichi Nagata,Kazunari Shibata,Toshifumi Shimizu,Richard A. Shine,Yoshinori Suematsu,Theodore D. Tarbell,Alan M. Title
Physics , 2009, DOI: 10.1088/0004-637X/697/1/913
Abstract: The formation and evolution process and magnetic configuration of solar prominences remain unclear. In order to study the formation process of prominences, we examine continuous observations of a prominence in NOAA AR 10953 with the Solar Optical Telescope on the \emph{Hinode} satellite. As reported in our previous Letter, we find a signature suggesting that a helical flux rope emerges from below the photosphere under a pre-existing prominence. Here we investigate more detailed properties and photospheric indications of the emerging helical flux rope, and discuss their relationship to the formation of the prominence. Our main conclusions are: (1) A dark region with absence of strong vertical magnetic fields broadens and then narrows in Ca \textsc{ii} H-line filtergrams. This phenomenon is consistent with the emergence of the helical flux rope as photospheric counterparts. The size of the flux rope is roughly 30,000 km long and 10,000 km wide. The width is larger than that of the prominence. (2) No shear motion or converging flows are detected, but we find diverging flows such as mesogranules along the polarity inversion line. The presence of mesogranules may be related to the emergence of the helical flux rope. (3) The emerging helical flux rope reconnects with magnetic fields of the pre-existing prominence to stabilize the prominence for the next several days. We thus conjecture that prominence coronal magnetic fields emerge in the form of helical flux ropes that contribute to the formation and maintenance of the prominence.
Fully resolved quiet-Sun magnetic flux tube observed with the Sunrise IMaX instrument
A. Lagg,S. K. Solanki,T. L. Riethmueller,V. Martinez Pillet,M. Schuessler,J. Hirzberger,A. Feller,J. M. Borrero,W. Schmidt,J. C. del Toro Iniesta,J. A. Bonet,P. Barthol,T. Berkefeld,V. Domingo,A. Gandorfer,M. Knoelker,A. M. Title
Physics , 2010, DOI: 10.1088/2041-8205/723/2/L164
Abstract: Until today, the small size of magnetic elements in quiet Sun areas has required the application of indirect methods, such as the line-ratio technique or multi-component inversions, to infer their physical properties. A consistent match to the observed Stokes profiles could only be obtained by introducing a magnetic filling factor that specifies the fraction of the observed pixel filled with magnetic field. Here, we investigate the properties of a small magnetic patch in the quiet Sun observed with the IMaX magnetograph on board the balloon-borne telescope Sunrise with unprecedented spatial resolution and low instrumental stray light. We apply an inversion technique based on the numerical solution of the radiative transfer equation to retrieve the temperature stratification and the field strength in the magnetic patch. The observations can be well reproduced with a one-component, fully magnetized atmosphere with a field strength exceeding 1 kG and a significantly enhanced temperature in the mid- to upper photosphere with respect to its surroundings, consistent with semi-empirical flux tube models for plage regions. We therefore conclude that, within the framework of a simple atmospheric model, the IMaX measurements resolve the observed quiet-Sun flux tube.
Sunrise: instrument, mission, data and first results
S. K. Solanki,P. Barthol,S. Danilovic,A. Feller,A. Gandorfer,J. Hirzberger,T. L. Riethmueller,M. Schüssler,J. A. Bonet,V. Martínez Pillet,J. C. del Toro Iniesta,V. Domingo,J. Palacios,M. Kn?lker,N. Bello González,T. Berkefeld,M. Franz,W. Schmidt,A. M. Title
Physics , 2010, DOI: 10.1088/2041-8205/723/2/L127
Abstract: The Sunrise balloon-borne solar observatory consists of a 1m aperture Gregory telescope, a UV filter imager, an imaging vector polarimeter, an image stabilization system and further infrastructure. The first science flight of Sunrise yielded high-quality data that reveal the structure, dynamics and evolution of solar convection, oscillations and magnetic fields at a resolution of around 100 km in the quiet Sun. After a brief description of instruments and data, first qualitative results are presented. In contrast to earlier observations, we clearly see granulation at 214 nm. Images in Ca II H display narrow, short-lived dark intergranular lanes between the bright edges of granules. The very small-scale, mixed-polarity internetwork fields are found to be highly dynamic. A significant increase in detectable magnetic flux is found after phase-diversity-related reconstruction of polarization maps, indicating that the polarities are mixed right down to the spatial resolution limit, and probably beyond.
The Wave-Front Correction System for the Sunrise Balloon-Borne Solar Observatory
T. Berkefeld,W. Schmidt,D. Soltau,A. Bell,H. P. Doerr,B. Feger,R. Friedlein,K. Gerber,F. Heidecke,T. Kentischer,O. v. d. Lühe,M. Sigwarth,E. W?lde,P. Barthol,W. Deutsch,A. Gandorfer,D. Germerott,B. Grauf,R. Meller,A. Alvarez-Herrero,M. Kn?lker,V. Martinez Pillet,S. K. Solanki,A. M. Title
Physics , 2010, DOI: 10.1007/s11207-010-9676-3
Abstract: This paper describes the wave-front correction system developed for the Sunrise balloon telescope, and provides information about its in-flight performance. For the correction of low-order aberrations, a Correlating Wave-Front Sensor (CWS) was used. It consisted of a six-element Shack-Hartmann wave-front sensor (WFS), a fast tip-tilt mirror for the compensation of image motion, and an active telescope secondary mirror for focus correction. The CWS delivered a stabilized image with a precision of 0.04 arcsec (rms), whenever the coarse pointing was better than 90 arcsec peak-to-peak. The automatic focus adjustment maintained a focus stability of 0.01 waves in the focal plane of the CWS. During the 5.5 day flight, good image quality and stability was achieved during 33 hours, containing 45 sequences that lasted between 10 and 45 minutes.
Homologous Helical Jets: Observations by IRIS, SDO and Hinode and Magnetic Modeling with Data-Driven Simulations
Mark C. M. Cheung,B. De Pontieu,T. D. Tarbell,Y. Fu,H. Tian,P. Testa,K. K. Reeves,J. Martinez-Sykora,P. Boerner,J. P. Wuelser,J. Lemen,A. M. Title,N. Hurlburt,L. Kleint,C. Kankelborg,S. Jaeggli,L. Golub,S. McKillop,S. Saar,M. Carlsson,V. Hansteen
Physics , 2015, DOI: 10.1088/0004-637X/801/2/83
Abstract: We report on observations of recurrent jets by instruments onboard the Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory (SDO) and Hinode spacecrafts. Over a 4-hour period on July 21st 2013, recurrent coronal jets were observed to emanate from NOAA Active Region 11793. FUV spectra probing plasma at transition region temperatures show evidence of oppositely directed flows with components reaching Doppler velocities of +/- 100 km/s. Raster Doppler maps using a Si IV transition region line show all four jets to have helical motion of the same sense. Simultaneous observations of the region by SDO and Hinode show that the jets emanate from a source region comprising a pore embedded in the interior of a supergranule. The parasitic pore has opposite polarity flux compared to the surrounding network field. This leads to a spine-fan magnetic topology in the coronal field that is amenable to jet formation. Time-dependent data-driven simulations are used to investigate the underlying drivers for the jets. These numerical experiments show that the emergence of current-carrying magnetic field in the vicinity of the pore supplies the magnetic twist needed for recurrent helical jet formation.
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