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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 721 records · Page 40
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DOE OSTI2014

Uncorrelated volatile behavior during the 2011 apparition of comet C/2009 P1 Garradd

The High Resolution Instrument Infrared Spectrometer (HRI-IR) on board the Deep Impact Flyby spacecraft detected H{sub 2}O, CO{sub 2}, and CO in the coma of the dynamically young Oort Cloud comet C/2009 P1 (Garradd) post-perihelion at a heliocentric distance of 2 AU. Production rates were derived for the parent volatiles, Q {sub H2O} = 4.6 ± 0.8 × 10{sup 28}, Q {sub CO2} = 3.9 ± 0.7 × 10{sup 27}, and Q {sub CO} = 2.9 ± 0.8 × 10{sup 28} molecules s{sup –1}, and are consistent with the trends seen by other observers and within the error bars of measurements acquired during a similar time period. When compiled with other observations of Garradd's dominant volatiles, unexpected behavior was seen in the release of CO. Garradd's H{sub 2}O outgassing, increasing and peaking pre-perihelion and then steadily decreasing, is more typical than that of CO, which monotonically increased throughout the entire apparition. Due to the temporal asymmetry in volatile release, Garradd exhibited the highest CO to H{sub 2}O abundance ratio ever observed for any comet inside the water snow line at ∼60% during the HRI-IR observations. Also, the HRI-IR made the only direct measurement of CO{sub 2}, giving a typical cometary abundance ratio of CO{sub 2} to H{sub 2}O of 8% but, with only one measurement, no sense of how it varied with orbital position.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

EVIDENCE FOR COLLAPSING FIELDS IN THE CORONA AND PHOTOSPHERE DURING THE 2011 FEBRUARY 15 X2.2 FLARE: SDO/AIA AND HMI OBSERVATIONS

We use high-resolution Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly observations to study the evolution of the coronal loops in a flaring solar active region, NOAA 11158. We identify three distinct phases of the coronal loop dynamics during this event: (1) slow-rise phase: slow rising motion of the loop-tops prior to the flare in response to the slow rise of the underlying flux rope; (2) collapse phase: sudden contraction of the loop-tops, with the lower loops collapsing earlier than the higher loops; and (3) oscillation phase: the loops exhibit global kink oscillations after the collapse phase at different periods, with the period decreasing with the decreasing height of the loops. The period of these loop oscillations is used to estimate the field strength in the coronal loops. Furthermore, we also use SDO/Helioseismic and Magnetic Imager (HMI) observations to study the photospheric changes close to the polarity inversion line (PIL). The longitudinal magnetograms show a stepwise permanent decrease in the magnetic flux after the flare over a coherent patch along the PIL. Furthermore, we examine the HMI Stokes I, Q, U, V profiles over this patch and find that the Stokes-V signal systematically decreases while the Stokes-Q and U signals increase after the flare. These observations suggest that close to the PIL the field configuration became more horizontal after the flare. We also use HMI vector magnetic field observations to quantify the changes in the field inclination angle and find an inward collapse of the field lines toward the PIL by {approx}10 Degree-Sign . These observations are consistent with the 'coronal implosion' scenario and its predictions about flare-related photospheric field changes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

SECONDARY WAVES AND/OR THE 'REFLECTION' FROM AND 'TRANSMISSION' THROUGH A CORONAL HOLE OF AN EXTREME ULTRAVIOLET WAVE ASSOCIATED WITH THE 2011 FEBRUARY 15 X2.2 FLARE OBSERVED WITH SDO/AIA AND STEREO/EUVI

For the first time, the kinematic evolution of a coronal wave over the entire solar surface is studied. Full Sun maps can be made by combining images from the Solar Terrestrial Relations Observatory satellites, Ahead and Behind, and the Solar Dynamics Observatory, thanks to the wide angular separation between them. We study the propagation of a coronal wave, also known as the 'Extreme Ultraviolet Imaging Telescope' wave, and its interaction with a coronal hole (CH) resulting in secondary waves and/or reflection and transmission. We explore the possibility of the wave obeying the law of reflection. In a detailed example, we find that a loop arcade at the CH boundary cascades and oscillates as a result of the extreme ultraviolet (EUV) wave passage and triggers a wave directed eastward that appears to have reflected. We find that the speed of this wave decelerates to an asymptotic value, which is less than half of the primary EUV wave speed. Thanks to the full Sun coverage we are able to determine that part of the primary wave is transmitted through the CH. This is the first observation of its kind. The kinematic measurements of the reflected and transmitted wave tracks are consistent with a fast-mode magnetohydrodynamic wave interpretation. Eventually, all wave tracks decelerate and disappear at a distance. A possible scenario of the whole process is that the wave is initially driven by the expanding coronal mass ejection and subsequently decouples from the driver and then propagates at the local fast-mode speed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

NUMERICAL SIMULATIONS OF CORONAL MASS EJECTION ON 2011 MARCH 7: ONE-TEMPERATURE AND TWO-TEMPERATURE MODEL COMPARISON

During Carrington rotation (CR) 2107, a fast coronal mass ejection (CME; >2000 km s{sup -1}) occurred in active region NOAA 11164. This event is also associated with a solar energetic particle event. In this study, we present simulations of this CME with one-temperature (1T) and two-temperature (2T: coupled thermodynamics of the electron and proton populations) models. Both the 1T and 2T models start from the chromosphere with heat conduction and radiative cooling. The background solar wind is driven by Alfven-wave pressure and heated by Alfven-wave dissipation in which we have incorporated the balanced turbulence at the top of the closed field lines. The magnetic field of the inner boundary is set up using a synoptic map from Solar Dynamics Observatory/Helioseismic and Magnetic Imager. The Titov-Demoulin flux-rope model is used to initiate the CME event. We compare the propagation of fast CMEs and the thermodynamics of CME-driven shocks in both the 1T and 2T CME simulations. Also, the synthesized white light images are compared with the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph observations. Because there is no distinction between electron and proton temperatures, heat conduction in the 1T model creates an unphysical temperature precursor in front of the CME-driven shock and makes the shock parameters (e.g., shock Mach number, compression ratio) incorrect. Our results demonstrate the importance of the electron heat conduction in conjunction with proton shock heating in order to produce the physically correct CME structures and CME-driven shocks.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Physical properties of white-light sources in the 2011 February 15 solar flare

White-light flares (WLFs) are observational rarities, making them understudied events. However, optical emission is a significant contribution to flare energy budgets and the emission mechanisms responsible could have important implications for flare models. Using Hinode SOT optical continuum data taken in broadband red, green, and blue filters, we investigate WL emission from the X2.2 flare SOL2011-02-15T01:56:00. We develop a technique to robustly identify enhanced flare pixels and, using a knowledge of the RGB filter transmissions, determined the source color temperature and effective temperature. We investigated two idealized models of WL emission—an optically thick photospheric source, and an optically thin chromospheric slab. Under the optically thick assumption, the color temperature and effective temperature of flare sources in sunspot umbra and penumbra were determined as a function of time and position. Values in the range of 5000-6000 K were found, corresponding to a blackbody temperature increase of a few hundred kelvin. The power emitted in the optical was estimated at ∼10{sup 26} erg s{sup –1}. In some of the WL sources the color and blackbody temperatures are the same within uncertainties, consistent with a blackbody emitter. In other regions this is not the case, suggesting that some other continuum emission process is contributing. An optically thin slab model producing hydrogen recombination radiation is also discussed as a potential source of WL emission; it requires temperatures in the range 5500-25,000 K, and total energies of ∼10{sup 27} erg s{sup –1}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Observational evidence of torus instability as trigger mechanism for coronal mass ejections: The 2011 August 4 filament eruption

Solar filaments are magnetic structures often observed in the solar atmosphere and consist of plasma that is cooler and denser than their surroundings. They are visible for days—even weeks—which suggests that they are often in equilibrium with their environment before disappearing or erupting. Several eruption models have been proposed that aim to reveal what mechanism causes (or triggers) these solar eruptions. Validating these models through observations represents a fundamental step in our understanding of solar eruptions. We present an analysis of the observation of a filament eruption that agrees with the torus instability model. This model predicts that a magnetic flux rope embedded in an ambient field undergoes an eruption when the axis of the flux rope reaches a critical height that depends on the topology of the ambient field. We use the two vantage points of the Solar Dynamics Observatory (SDO) and the Solar TErrestrial RElations Observatory to reconstruct the three-dimensional shape of the filament, to follow its morphological evolution, and to determine its height just before eruption. The magnetograms acquired by SDO/Helioseismic and Magnetic Imager are used to infer the topology of the ambient field and to derive the critical height for the onset of the torus instability. Our analysis shows that the torus instability is the trigger of the eruption. We also find that some pre-eruptive processes, such as magnetic reconnection during the observed flares and flux cancellation at the neutral line, facilitated the eruption by bringing the filament to a region where the magnetic field was more vulnerable to the torus instability.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Magnetohydrodynamic simulation of the x2.2 solar flare on 2011 February 15. I. Comparison with the observations

We performed a magnetohydrodynamic (MHD) simulation using a nonlinear force-free field (NLFFF) in solar active region 11158 to clarify the dynamics of an X2.2-class solar flare. We found that the NLFFF never shows the dramatic dynamics seen in observations, i.e., it is in a stable state against the perturbations. On the other hand, the MHD simulation shows that when the strongly twisted lines are formed at close to the neutral line, which are produced via tether-cutting reconnection in the twisted lines of the NLFFF, they consequently erupt away from the solar surface via the complicated reconnection. This result supports the argument that the strongly twisted lines formed in NLFFF via tether-cutting reconnection are responsible for breaking the force balance condition of the magnetic fields in the lower solar corona. In addition to this, the dynamical evolution of these field lines reveals that at the initial stage the spatial pattern of the footpoints caused by the reconnection of the twisted lines appropriately maps the distribution of the observed two-ribbon flares. Interestingly, after the flare, the reconnected field lines convert into a structure like the post-flare loops, which is analogous to the extreme ultraviolet image taken by the Solar Dynamics Observatory. Eventually, we found that the twisted lines exceed a critical height at which the flux tube becomes unstable to the torus instability. These results illustrate the reliability of our simulation and also provide an important relationship between flare and coronal mass ejection dynamics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Magnetic field fluctuations observed in the heliosheath and interstellar magnetic field by Voyager 1 at 115.7-124.9 AU during 2011-2013

We discuss microscale fluctuations of the hour averages of the magnetic field B observed on a scale of one day by Voyager 1 (V1) from 2011.0 to 2012.3143 (when it was within the distant heliosheath, where the average magnetic field strength (B) = 0.17 nT) and during the interval from 2012.6503 to 2013.5855 (when it was within the interstellar plasma with (B) = 0.47 nT). In both regions, the fluctuations were primarily compressive fluctuations, varying along the average B (≈T direction in RTN coordinates). In the heliosheath, the average of the daily standard deviations (SDs) of the compressive and transverse components of B were (SD{sub c}) = 0.010 nT and (SD{sub t}) ≤ 0.005 nT (which is the limit of the measurement). In the distant heliosheath (SD{sub c})/(B) = 0.06, and the distributions of SD were skewed and highly kurtotic. The interstellar magnetic field (ISMF) strength was B = 0.48 nT, but the fluctuations were below the limit of measurement: (SD{sub c}) = 0.004 nT and (abs(SD{sub t})) = 0.004 nT. The distributions of these interstellar SDs have skewness and kurtosis consistent with a Gaussian noise distribution. We also discuss the fluctuations of 48 s averages of B on a scale of 1 day during a 30 day interval when V1 was observing the ISMF. For the fluctuations in all three components of B, SD = 0.010 nT, which gives an upper limit on the fluctuations of the ISMF on the scales observed by V1. This SD rules out the possibility that there is significant power in electromagnetic fluctuations generated by pickup ion ring instabilities at these scales, which strongly constrains models of the IBEX ribbon.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Mixed sneutrino dark matter in light of the 2011 XENON and LHC results

In the context of supersymmetric models in which small Dirac neutrino masses are generated by supersymmetry breaking, a mainly right-handed (RH) mixed sneutrino can be an excellent cold dark matter (DM) candidate. We perform a global analysis of the Minimal Supersymmetric Standard Model (MSSM)+RH neutrino parameter space by means of Markov Chain Monte Carlo sampling. We include all relevant constraints from collider and dark matter searches, paying particular attention to nuclear and astrophysical uncertainties. Two distinct cases can satisfy all constraints: heavy sneutrino DM with mass of order 100 GeV, as well as light sneutrino DM with mass of about 3–6 GeV. We discuss the implications for direct and indirect dark matter searches, as well as for SUSY and Higgs searches at the LHC for both, the light and the heavy sneutrino dark matter case. The light sneutrino case is excluded by the 125–126 GeV Higgs signal.

79 ASTRONOMY AND ASTROPHYSICS↗