Big Bear Solar Observatory

Dixon Lane-Meadow Creek, CA, United States

Big Bear Solar Observatory

Dixon Lane-Meadow Creek, CA, United States

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News Article | October 26, 2016
Site: www.eurekalert.org

While it often seems unvarying from our viewpoint on Earth, the sun is constantly changing. Material courses through not only the star itself, but throughout its expansive atmosphere. Understanding the dance of this charged gas is a key part of better understanding our sun - how it heats up its atmosphere, how it creates a steady flow of solar wind streaming outward in all directions, and how magnetic fields twist and turn to create regions that can explode in giant eruptions. Now, for the first time, researchers have tracked a particular kind of solar wave as it swept upward from the sun's surface through its atmosphere, adding to our understanding of how solar material travels throughout the sun. Tracking solar waves like this provides a novel tool for scientists to study the atmosphere of the sun. The imagery of the journey also confirms existing ideas, helping to nail down the existence of a mechanism that moves energy - and therefore heat - into the sun's mysteriously-hot upper atmosphere, called the corona. A study on these results was published Oct. 11, 2016, in The Astrophysical Journal Letters. "We see certain kinds of solar seismic waves channeling upwards into the lower atmosphere, called the chromosphere, and from there, into the corona," said Junwei Zhao, a solar scientist at Stanford University in Stanford, California, and lead author on the study. "This research gives us a new viewpoint to look at waves that can contribute to the energy of the atmosphere." The study makes use of the wealth of data captured by NASA's Solar Dynamics Observatory, NASA's Interface Region Imaging Spectrograph, and the Big Bear Solar Observatory in Big Bear Lake, California. Together, these observatories watch the sun in 16 wavelengths of light that show the sun's surface and lower atmosphere. SDO alone captures 11 of these. "SDO takes images of the sun in many different wavelengths at a high time resolution," said Dean Pesnell, SDO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "That lets you see the frequencies of these waves - if you didn't have such rapid-fire images, you'd lose track of the waves from one image to the next." Though scientists have long suspected that the waves they spot in the sun's surface, called the photosphere, are linked to those seen in the lowest reaches of the sun's atmosphere, called the chromosphere, this new analysis is the first time that scientists have managed to actually watch the wave travel up through the various layers into the sun's atmosphere. When material is heated to high temperatures, it releases energy in the form of light. The type, or wavelength, of that light is determined by what the material is, as well as its temperature. That means different wavelengths from the sun can be mapped to different temperatures of solar material. Since we know how the sun's temperature changes throughout the layers of its atmosphere, we can then order these wavelengths according to their height above the surface - and essentially watch solar waves as they travel upwards. The implications of this study are twofold - first, this technique for watching the waves itself gives scientists a new tool to understand the sun's lower atmosphere. "Watching the waves move upwards tells us a lot about the properties of the atmosphere above sunspots - like temperature, pressure, and density," said Ruizhu Chen, a graduate student scientist at Stanford who is an author on the study. "More importantly, we can figure out the magnetic field strength and direction." The effect of the magnetic field on these waves is pronounced. Instead of traveling straight upwards through the sun, the waves veer off, taking a curved path through the atmosphere. "The magnetic field is acting like railroad tracks, guiding the waves as they move up through the atmosphere," said Pesnell, who was not involved in this study. The second implication of this new research is for a long-standing question in solar physics - the coronal heating problem. The sun produces energy by fusing hydrogen at its core, so the simplest models suggest that each layer of the sun should be cooler as you move outward. However, the sun's atmosphere, called the corona, is about a hundred times hotter than the region below - counter to what you would expect. No one has as-yet been able to definitively pinpoint the source of all the extra heat in the corona, but these waves may play a small role. "When a wave travels upwards, a number of different things can happen," said Zhao. "Some may reflect back downwards, or contribute to heating - but by how much, we don't yet know." NASA Goddard built, operates and manages the SDO spacecraft for NASA's Science Mission Directorate in Washington. Lockheed Martin designed the IRIS observatory and manages the mission for NASA. The Big Bear Solar Observatory is operated by the New Jersey Institute of Technology in Newark, New Jersey.


Chae J.,Seoul National University | Chae J.,Big Bear Solar Observatory
Astrophysical Journal | Year: 2010

The existence and behavior of vertical fine structures of plasma - threads and knots - are a significant observational clue to understanding the magnetic structure and dynamics of quiescent prominences on the quiet Sun. Based on the equation of motion in ideal MHD, we reason that the non-hydrostatic support of plasma against gravity in general requires either the motion of plasma with a high value of downward acceleration (dynamical support) or the role of horizontal magnetic fields (magnetic support). By carefully tracking the motion of several bright threads seen in a hedgerow prominence observed by the Solar Optical Telescope aboard Hinode, we confirm that these threads are essentially static and stable, which negates the dynamic support. The application of the Kippenhahn-Schlüter solution suggests that they may be supported by sagged magnetic field lines with a sag angle of about 43°. We also track several bright descending knots and find that their descending speeds range from 10 to 30 km s-1, with a mean value of 16 km s-1, and their vertical accelerations from -0.10 to 0.10 km s-2, with a mean of practically zero. This finding suggests that these knots are basically supported by horizontal magnetic fields against gravity even when they descend, and the complex variations of their descending speeds should be attributed to small imbalances between gravity and the force of magnetic tension. Furthermore, some knots are observed to impulsively get accelerated downward from time to time. We conjecture that these impulsive accelerations are a result of magnetic reconnection and the subsequent interchange of magnetic configuration between a knot and its surrounding structure. It is proposed that this process of reconnection and interchange not only initiates the descending motion of the knots, but also allows knots to keep falling long distance through the medium permeated by horizontal magnetic fields. © 2010. The American Astronomical Society. All rights reserved.


Kellerer A.,Big Bear Solar Observatory
Astronomy and Astrophysics | Year: 2011

Context. Wavefront sensing in solar adaptive-optics is currently done with correlating Shack-Hartmann sensors, although the spatial- and temporal-resolutions of the phase measurements are then limited by the extremely fast computing required to correlate the sensor signals at the frequencies of daytime atmospheric-fluctuations. Aims. To avoid this limitation, a new wavefront-sensing technique is presented, that makes use of the solar brightness and is applicable to extended sources. Methods. The wavefront is sent through a modified Mach-Zehnder interferometer. A small, central part of the wavefront is used as reference and is made to interfere with the rest of the wavefront. Results. The contrast of two simultaneously measured interference-patterns provides a direct estimate of the wavefront phase, no additional computation being required. The proposed optical layout shows precise initial alignment to be the critical point in implementing the new wavefront-sensing scheme. © 2011 ESO.


Abramenko V.,Big Bear Solar Observatory | Yurchyshyn V.,Big Bear Solar Observatory | Goode P.,Big Bear Solar Observatory | Kilcik A.,Big Bear Solar Observatory
Astrophysical Journal Letters | Year: 2010

We present results of 2 hr non-interrupted observations of solar granulation obtained under excellent seeing conditions with the largest aperture ground-based solar telescope-the New Solar Telescope (NST)-of Big Bear Solar Observatory. Observations were performed with adaptive optics correction using a broadband TiO filter in the 705.7 nm spectral line with a time cadence of 10 s and a pixel size of 0.″0375. Photospheric bright points (BPs) were detected and tracked. We find that the BPs detected in NST images are cospatial with those visible in Hinode/SOT G-band images. In cases where Hinode/SOT detects one large BP, NST detects several separated BPs. Extended filigree features are clearly fragmented into separate BPs in NST images. The distribution function of BP sizes extends to the diffraction limit of NST (77 km) without saturation and corresponds to a log-normal distribution. The lifetime distribution function follows a log-normal approximation for all BPs with lifetime exceeding 100 s. A majority of BPs are transient events reflecting the strong dynamics of the quiet Sun: 98.6% of BPs live less than 120 s. The longest registered lifetime was 44 minutes. The size and maximum intensity of BPs were found to be proportional to their lifetimes. © 2010. The American Astronomical Society. All rights reserved.


Abramenko V.,Big Bear Solar Observatory | Yurchyshyn V.,Big Bear Solar Observatory
Astrophysical Journal | Year: 2010

We present the results of a study of intermittency and multifractality of magnetic structures in solar active regions (ARs). Line-of-sight magnetograms for 214 ARs of different flare productivity observed at the center of the solar disk from 1997 January until 2006 December are utilized. Data from the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory operating in the high resolution mode, the Big Bear Solar Observatory digital magnetograph, and the Hinode SOT/SP instrument were used. Intermittency spectra were derived from high-order structure functions and flatness functions. The flatness function exponent is a measure of the degree of intermittency. We found that the flatness function exponent at scales below approximately 10 Mm is correlated with flare productivity (the correlation coefficient is -0.63). The Hinode data show that the intermittency regime is extended toward small scales (below 2 Mm) as compared to the MDI data. The spectra of multifractality, derived from the structure functions and flatness functions, are found to be broader for ARs of higher flare productivity as compared to those of low flare productivity. The magnetic structure of high-flaring ARs consists of a voluminous set of monofractals, and this set is much richer than that for low-flaring ARs. The results indicate the relevance of the multifractal organization of the photospheric magnetic fields to the flaring activity. The strong intermittency observed in complex and high-flaringARs is a hint that we observe a photospheric imprint of enhanced sub-photospheric dynamics. © 2010. The American Astronomical Society. All rights reserved.


Abramenko V.,Big Bear Solar Observatory | Yurchyshyn V.,Big Bear Solar Observatory
Astrophysical Journal | Year: 2010

Line-of-sight magnetograms for 217 active regions (ARs) with different flare rates observed at the solar disk center from 1997 January until 2006 December are utilized to study the turbulence regime and its relationship to flare productivity. Data from the SOHO/MDI instrument recorded in the high-resolution mode and data from the BBSO magnetograph were used. The turbulence regime was probed via magnetic energy spectra and magnetic dissipation spectra. We found steeper energy spectra for ARs with higher flare productivity. We also report that both the power index, α, of the energy spectrum, E(k) ∼ k-α, and the total spectral energy, W = ∫E(k)dk, are comparably correlated with the flare index, A, of an AR. The correlations are found to be stronger than those found between the flare index and the total unsigned flux. The flare index for an AR can be estimated based on measurements of α and Was A = 10b(αW)c, with b = - 7.92 ±0.58 and c = 1.85 ±0.13. We found that the regimeof the fully developed turbulence occurs in decaying ARs and in emerging ARs (at the very early stage of emergence). Well-developed ARs display underdeveloped turbulence with strong magnetic dissipation at all scales. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


Kellerer A.,Big Bear Solar Observatory
Applied Optics | Year: 2012

First multiconjugate adaptive-optical (MCAO) systems are currently being installed on solar telescopes. The aim of these systems is to increase the corrected field of view with respect to conventional adaptive optics. However, this first generation is based on a star-oriented approach, and it is then difficult to increase the size of the field of view beyond 60-80 arc sec in diameter.We propose to implement the layeroriented approach in solar MCAO systems by use of wide-field Shack-Hartmann wavefront sensors conjugated to the strongest turbulent layers. The wavefront distortions are averaged over a wide field: the signal from distant turbulence is attenuated and the tomographic reconstruction is thus done optically. The system consists of independent correction loops, which only need to account for local turbulence: the subapertures can be enlarged and the correction frequency reduced. Most importantly, a star-oriented MCAO system becomes more complex with increasing field size, while the layer-oriented approach benefits from larger fields and will therefore be an attractive solution for the future generation of solar MCAO systems. © 2012 Optical Society of America.


Guerrero G.,Stanford University | Smolarkiewicz P.K.,European Center for Medium Range Weather Forecasts | Kosovichev A.G.,Stanford University | Kosovichev A.G.,Big Bear Solar Observatory | Mansour N.N.,NASA
Astrophysical Journal | Year: 2013

To explore the physics of large-scale flows in solar-like stars, we perform three-dimensional anelastic simulations of rotating convection for global models with stratification resembling the solar interior. The numerical method is based on an implicit large-eddy simulation approach designed to capture effects from non-resolved small scales. We obtain two regimes of differential rotation, with equatorial zonal flows accelerated either in the direction of rotation (solar-like) or in the opposite direction (anti-solar). While the models with the solar-like differential rotation tend to produce multiple cells of meridional circulation, the models with anti-solar differential rotation result in only one or two meridional cells. Our simulations indicate that the rotation and large-scale flow patterns critically depend on the ratio between buoyancy and Coriolis forces. By including a sub-adiabatic layer at the bottom of the domain, corresponding to the stratification of a radiative zone, we reproduce a layer of strong radial shear similar to the solar tachocline. Similarly, enhanced super-adiabaticity at the top results in a near-surface shear layer located mainly at lower latitudes. The models reveal a latitudinal entropy gradient localized at the base of the convection zone and in the stable region, which, however, does not propagate across the convection zone. In consequence, baroclinicity effects remain small, and the rotation isocontours align in cylinders along the rotation axis. Our results confirm the alignment of large convective cells along the rotation axis in the deep convection zone and suggest that such "banana-cell" pattern can be hidden beneath the supergranulation layer. © 2013. The American Astronomical Society. All rights reserved.


News Article | April 21, 2016
Site: www.sciencedaily.com

Scientists at NJIT's Big Bear Solar Observatory have captured unprecedented images of a recent solar flare, including bright flare ribbons seen crossing a sunspot followed by 'coronal rain,' plasma that condenses in the cooling phase shortly after the flare, showering the visible surface of the sun where it lands in brilliant explosions.


News Article | October 12, 2016
Site: phys.org

But a team of NJIT scientists now claims that flares in turn have a powerful impact on sunspots, the visible concentrations of magnetic fields on the sun's surface, or photosphere. In a paper published in Nature Communications this week, the researchers argue that flares cause sunspots to rotate at much faster speeds than are usually observed before they erupt. Their observations, based on high-resolution images captured through NJIT's 1.6 meter New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO), come as something of a surprise. The sun's outer layer, or corona, where flares are released, has a plasma density about a hundred million times smaller than that of the photosphere. "It's analogous to the tail wagging the dog. The lower-density regions are much less energetic and forceful," said Chang Liu, a research professor of physics at NJIT and the principal author of the study, "Flare differentially rotates sunspot on Sun's surface." "We do think the rotation of sunspots builds up magnetic energy that is released in form of solar flares, but we have also observed conclusively that flares can cause sunspots to rotate about 10 times faster," he added. "This highlights the powerful, magnetic nature of solar flares." Previous images captured by space solar missions at lower resolutions hinted at this phenomenon, the researchers said, but were inconclusive. "Our new images allow us to not only confirm it, but to also characterize the time-spatial dimension of the sunspot's rotation - to describe its progressive, non-uniform rotation - as the flare travels through it," Liu said. Haimin Wang, a distinguished professor of physics at NJIT and a co-author of the paper, said the observations will prompt scientists to revisit the mechanisms of flares - and the basic physics of the Sun - in a fundamental way. "We used to think that the surface's magnetic evolution drives solar eruptions. Our new observations suggest that disturbances created in the solar outer atmosphere can also cause direct and significant perturbations on the surface through magnetic fields, a phenomenon not envisioned by any major contemporary solar eruption models. This has immediate and far-reaching implications in understanding energy and momentum transportation in eruptions on the Sun and other stars," Wang said. "We will continue to study, and possibly re-interpret, the relationship between the different layers of the Sun." Images captured by NST, the world's largest ground-based solar telescope, are providing an unprecedented glimpse into the complex dynamics of the Sun's many layers, as well as insights into the massive eruptions originating in the solar atmosphere that are responsible for space weather. Last year, scientists at BBSO captured the first high-resolution images of magnetic fields and plasma flows originating deep below the Sun's surface, tracing the evolution of sunspots and magnetic flux ropes through the chromosphere before their dramatic appearance in the corona as flaring loops. Another recent set of images give a first-ever detailed view of the interior structure of umbrae - the dark patches in the center of sunspots - revealing dynamic magnetic fields responsible for the plumes of plasma that emerge as bright dots interrupting their darkness. The high-resolution images show the atmosphere above the umbrae to be finely structured, consisting of hot plasma intermixed with cool plasma jets as wide as 100 kilometers. Explore further: New solar telescope peers deep into the sun to track the origins of space weather More information: Chang Liu et al, Flare differentially rotates sunspot on Sun's surface, Nature Communications (2016). DOI: 10.1038/ncomms13104

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