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All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Three-dimensional hybrid simulation study of anisotropic turbulence in the proton kinetic regime

Three-dimensional numerical hybrid simulations with particle protons and quasi-neutralizing fluid electrons are conducted for a freely decaying turbulence that is anisotropic with respect to the background magnetic field. The turbulence evolution is determined by both the combined root-mean-square (rms) amplitude for fluctuating proton bulk velocity and magnetic field and by the ratio of perpendicular to parallel wavenumbers. This kind of relationship had been considered in the past with regard to interplanetary turbulence. The fluctuations nonlinearly evolve to a turbulent phase whose net wave vector anisotropy is usually more perpendicular than the initial one, irrespective of the initial ratio of perpendicular to parallel wavenumbers. Self-similar anisotropy evolution is found as a function of the rms amplitude and parallel wavenumber. Proton heating rates in the turbulent phase vary strongly with the rms amplitude but only weakly with the initial wave vector anisotropy. Even in the limit where wave vectors are confined to the plane perpendicular to the background magnetic field, the heating rate remains close to the corresponding case with finite parallel wave vector components. Simulation results obtained as a function of proton plasma to background magnetic pressure ratio β {sub p} in the range 0.1-0.5 show that the wave vector anisotropy also weakly depends on β {sub p}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A detailed photometric and spectroscopic study of the 2011 outburst of the recurrent nova T Pyxidis from 0.8 to 250 days after discovery

We investigated the optical light curve of T Pyx during its 2011 outburst by compiling a database of Solar Mass Ejection Imager (SMEI) and AAVSO observations. The SMEI light curve, providing unprecedented detail covering t = 1.5-49 days post-discovery, was divided into four phases based on the idealized nova optical light curve: the initial rise (1.5-3.3 days), the pre-maximum halt (3.3-13.3 days), the final rise (14.7-27.9 days), and the early decline (27.9+ days). The SMEI light curve contains a strongly detected period of 1.44 ± 0.05 days during the pre-maximum halt phase. These oscillations resemble those found in recent thermonuclear runaway models arising from instabilities in the expanding envelope. No spectral variations that mirror the light curve periodicity were found, however. The marked dip at t ∼ 22-24 days just before the light curve maximum at t = 27.9 days may represent the same (shorter duration) phenomenon seen in other novae observed by SMEI and present in some model light curves. The spectra from the 2 m Liverpool Telescope and SMARTS 1.5 m telescope were obtained from t = 0.8-80.7 and 155.1-249.9 days, covering the major phases of development. The nova was observed very early in its rise where a distinct high-velocity ejection phase was evident with initially derived V {sub ej} ∼ 4000 km s{sup –1}. A marked drop occurred at t = 5.7 days, and then a gradual increase in derived V {sub ej} to stabilize at ∼1500 km s{sup –1} at the pre-maximum halt. Here, we propose two different stages of mass loss, a short-lived phase occurring immediately after outburst and lasting ∼6 days, followed by a more steadily evolving and higher mass loss phase. The overall spectral development follows that typical of a classical nova and comparison with the photometric behavior reveals consistencies with the simple evolving pseudo-photosphere model of the nova outburst. Comparing optical spectra to X-ray and radio light curves, weak [Fe X] 6375 Å emission was marginally detected before the X-ray rise and was clearly present during the brightest phase of X-ray emission. If the onset of the X-ray phase and the start of the final decline in the optical are related to the cessation of significant mass loss, then this occurred at t ∼ 90-110 days.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Effect of wind turbine nacelle on turbine wake dynamics in large wind farms

Wake meandering, a phenomenon of large-scale lateral oscillation of the wake, has significant effects on the velocity deficit and turbulence intensities in wind turbine wakes. Previous studies of a single turbine (Kang et al. , J. Fluid. Mech. , vol. 774, 2014, pp. 374–403; Foti et al. , Phys. Rev. Fluids , vol. 1 (4), 2016, 044407) have shown that the turbine nacelle induces large-scale coherent structures in the near field that can have a significant effect on wake meandering. However, whether nacelle-induced coherent structures at the turbine scale impact the emergent turbine wake dynamics at the wind farm scale is still an open question of both fundamental and practical significance. We take on this question by carrying out large-eddy simulation of atmospheric turbulent flow over the Horns Rev wind farm using actuator surface parameterisations of the turbines without and with the turbine nacelle taken into account. While the computed mean turbine power output and the mean velocity field away from the nacelle wake are similar for both cases, considerable differences are found in the turbine power fluctuations and turbulence intensities. Furthermore, wake meandering amplitude and area defined by wake meanders, which indicates the turbine wake unsteadiness, are larger for the simulations with the turbine nacelle. The wake influenced area computed from the velocity deficit profiles, which describes the spanwise extent of the turbine wakes, and the spanwise growth rate, on the other hand, are smaller for some rows in the simulation with the nacelle model. Our work shows that incorporating the nacelle model in wind farm scale simulations is critical for accurate predictions of quantities that affect the wind farm levelised cost of energy, such as the dynamics of wake meandering and the dynamic loads on downwind turbines.

Mechanics↗
NASA NTRS2015

Lidar Sensor Performance in Closed-Loop Flight Testing of the Morpheus Rocket-Propelled Lander to a Lunar-Like Hazard Field

For the first time, a suite of three lidar sensors have been used in flight to scan a lunar-like hazard field, identify a safe landing site, and, in concert with an experimental Guidance, Navigation, and Control (GN&C) system, help to guide the Morpheus autonomous, rocket-propelled, free-flying lander to that safe site on the hazard field. The lidar sensors and GN&C system are part of the Autonomous Precision Landing and Hazard Detection and Avoidance Technology (ALHAT) project which has been seeking to develop a system capable of enabling safe, precise crewed or robotic landings in challenging terrain on planetary bodies under any ambient lighting conditions. The 3-D imaging Flash Lidar is a second generation, compact, real-time, aircooled instrument developed from a number of components from industry and NASA and is used as part of the ALHAT Hazard Detection System (HDS) to scan the hazard field and build a 3-D Digital Elevation Map (DEM) in near-real time for identifying safe sites. The Flash Lidar is capable of identifying a 30 cm hazard from a slant range of 1 km with its 8 cm range precision (1-s). The Flash Lidar is also used in Hazard Relative Navigation (HRN) to provide position updates down to a 250m slant range to the ALHAT navigation filter as it guides Morpheus to the safe site. The Navigation Doppler Lidar (NDL) system has been developed within NASA to provide velocity measurements with an accuracy of 0.2 cm/sec and range measurements with an accuracy of 17 cm both from a maximum range of 2,200 m to a minimum range of several meters above the ground. The NDLâ€"TM"s measurements are fed into the ALHAT navigation filter to provide lander guidance to the safe site. The Laser Altimeter (LA), also developed within NASA, provides range measurements with an accuracy of 5 cm from a maximum operational range of 30 km down to 1 m and, being a separate sensor from the Flash Lidar, can provide range along a separate vector. The LA measurements are also fed into the ALHAT navigation filter to provide lander guidance to the safe site. The flight tests served as the culmination of the TRL 6 journey for the ALHAT system and included launch from a pad situated at the NASA-Kennedy Space Center Shuttle Landing Facility (SLF) runway, a lunar-like descent trajectory from an altitude of 250m, and landing on a lunar-like hazard field of rocks, craters, hazardous slopes, and safe sites 400m down-range just off the North end of the runway. The tests both confirmed the expected performance and also revealed several challenges present in the flight-like environment which will feed into future TRL advancement of the sensors. Guidance provided by the ALHAT system was impeded in portions of the trajectory and intermittent near the end of the trajectory due to optical effects arising from air heated by the rocket engine. The Flash Lidar identified hazards as small as 30 cm from the maximum slant range of 450 m which Morpheus could provide; however, it was occasionally susceptible to an increase in range noise due to scintillation arising from air heated by the Morpheus rocket engine which entered its Field-of-View (FOV). The Flash Lidar was also susceptible to pre-triggering, during the HRN phase, on a dust cloud created during launch and transported down-range by the wind. The NDL provided velocity and range measurements to the expected accuracy levels yet it was also susceptible to signal degradation due to air heated by the rocket engine. The LA, operating with a degraded transmitter laser, also showed signal attenuation over a few seconds at a specific phase of the flight due to the heat plume generated by the rocket engine.

Roback, V. Eric↗
DOE OSTI2023

Developing a Vorticity-Velocity-Based Off-Body Solver to Perform Multifidelity Simulations of Wind Farms

Wind power has become a key player in satisfying the global energy needs. With increased market penetration, unanticipated unsteady loading induced failures, installation related reductions in power generation, and significant maintenance costs have underscored the need to predict the unsteady fluid-structure interactions related to turbine layout and off-design wind conditions. Contemporary turbine design tools are incapable of accounting for such loadings. As a result, researchers have started utilizing high-Performance-Computing (HPC) based Computational Fluid Dynamics (CFD) solvers, such as the U.S. Department of Energy sponsored ExaWind software package, to investigate these phenomena. Unfortunately, such HPC tools are computationally expensive for routine industrial use, often because of the sheer number of cells required to resolve the wake flowfield. This paper describes a preliminary effort to address this issue by developing a vorticity-velocity based CFD off-body solver, VorTran-M2-AMReX, that integrates directly with DOE's ExaWind wind turbine analysis system to perform accurate and reliable simulations of wind turbine/farm at a lower computational cost than ExaWind alone. This article summarizes work undertaken to date concerning the assembly of the proposed analysis tool, and provides preliminary validation and verification of the VorTran-M2-AMReX off-body solver.

adaptive mesh refinement↗
NASA NTRS1977

Application of laser velocimetry to aircraft wake-vortex measurements

The theory and use of a laser velocimeter that makes simultaneous measurements of vertical and longitudinal velocities while rapidly scanning a flow field laterally are described, and its direct application to trailing wake-vortex research is discussed. Pertinent measurements of aircraft wake-vortex velocity distributions obtained in a wind tunnel and water towing tank are presented. The utility of the velocimeter to quantitatively assess differences in wake velocity distributions due to wake dissipating devices and span loading changes on the wake-generating model is also demonstrated.

Ciffone, D. L.↗
DOE OSTI2014

Turbulence transport modeling of the temporal outer heliosphere

The solar wind can be regarded as a turbulent magnetofluid, evolving in an expanding solar wind and subject to turbulent driving by a variety of in situ sources. Furthermore, the solar wind and the drivers of turbulence are highly time-dependent and change with solar cycle. Turbulence transport models describing low-frequency magnetic and velocity fluctuations in the solar wind have so far neglected solar cycle effects. Here we consider the effects of solar cycle variability on a turbulence transport model developed by Zank et al. This model is appropriate for the solar wind beyond about 1 AU, and extensions have described the steady-state dependence of the magnetic energy density fluctuations, correlation length, and solar wind temperature throughout the outer heliosphere. We find that the temporal solar wind introduces a periodic variability, particularly beyond ∼10 AU, in the magnetic energy density fluctuations, correlation length, and solar wind temperature. The variability is insufficient to account for the full observed variability in these quantities, but we find that the time-dependent solutions trace the steady-state solutions quite well, suggesting that the steady-state models are reasonable first approximations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Common envelope ejection for a luminous red nova in M101

We present the results of optical, near-infrared, and mid-infrared observations of M101 OT2015-1 (PSN J14021678+5426205), a luminous red transient in the Pinwheel galaxy (M101), spanning a total of 16 years. The light curve showed two distinct peaks with absolute magnitudes M{sub r}⩽−12.4 and M{sub r}≃−12, on 2014 November 11 and 2015 February 17, respectively. The spectral energy distributions during the second maximum show a cool outburst temperature of ≈3700 K and low expansion velocities (≈−300 km s{sup −1}) for the H i, Ca ii, Ba ii, and K i lines. From archival data spanning 15–8 years before the outburst, we find a single source consistent with the optically discovered transient, which we attribute to being the progenitor; it has properties consistent with being an F-type yellow supergiant with L ∼ 8.7 × 10{sup 4} L{sub ⊙}, T{sub eff}≈7000 K, and an estimated mass of M1=18±1 M{sub ⊙}. This star has likely just finished the H-burning phase in the core, started expanding, and is now crossing the Hertzsprung gap. Based on the combination of observed properties, we argue that the progenitor is a binary system, with the more evolved system overfilling the Roche lobe. Comparison with binary evolution models suggests that the outburst was an extremely rare phenomenon, likely associated with the ejection of the common envelope of a massive star. The initial mass of the primary fills the gap between the merger candidates V838 Mon (5−10 M{sub ⊙}) and NGC 4490-OT (30 M{sub ⊙}).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

GALAXY INTERACTIONS IN COMPACT GROUPS. I. THE GALACTIC WINDS OF HCG16

Using the WiFeS integral field spectrograph, we have undertaken a series of observations of star-forming galaxies in compact groups. In this first paper dedicated to the project, we present the analysis of the spiral galaxy NGC 838, a member of the Hickson Compact Group 16, and of its galactic wind. Our observations reveal that the wind forms an asymmetric, bipolar, rotating structure, powered by a nuclear starburst. Emission line ratio diagnostics indicate that photoionization is the dominant excitation mechanism at the base of the wind. Mixing from slow shocks (up to 20%) increases further out along the outflow axis. The asymmetry of the wind is most likely caused by one of the two lobes of the wind bubble bursting out of its H I envelope, as indicated by line ratios and radial velocity maps. The characteristics of this galactic wind suggest that it is caught early (a few Myr) in the wind evolution sequence. The wind is also quite different from the galactic wind in the partner galaxy NGC 839 which contains a symmetric, shock-excited wind. Assuming that both galaxies have similar interaction histories, the two different winds must be a consequence of the intrinsic properties of NGC 838 and NGC 839 and their starbursts.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Environmental sensitivities of shallow-cumulus dilution – Part 2: Vertical wind profile

This second part of a numerical study on shallow-cumulus dilution focuses on the sensitivity of cloud dilution to changes in the vertical wind profile. Insights are obtained through large-eddy simulations of maritime and continental cloud fields. In these simulations, the speed of the initially uniform geostrophic wind and the strength of geostrophic vertical wind shear in the cloud and subcloud layer are varied. Increases in the cloud-layer vertical wind shear (up to 9 ms -1 km -1 ) lead to 40%–50% larger cloud-core dilution rates compared to their respective unsheared counterparts. When the background wind speed, on the other hand, is enhanced by up to 10 ms -1 and subcloud-layer vertical wind shear develops or is initially prescribed, the dilution rate decreases by up to 25%. The sensitivities of the dilution rate are linked to the updraft strength and the properties of the entrained air. Increases in the wind speed or vertical wind shear result in lower vertical velocities across all sets of experiments with stronger reductions in the cloud-layer wind shear simulation (27%–47%). Weaker updrafts are exposed to mixing with the drier surrounding air for a longer time period, allowing more entrainment to occur (i.e., the “core-exposure effect”). However, reduced vertical velocities, in concert with increased cloud-layer turbulence, also assist in widening the humid shell surrounding the cloud cores, leading to entrainment of more humid air (i.e., the “core–shell dilution effect”). In the experiments with cloud-layer vertical wind shear, the core-exposure effect dominates and the cloud-core dilution increases with increasing shear. Conversely, when the wind speed is increased and subcloud-layer vertical wind shear develops or is imposed, the core–shell dilution effect dominates to induce a buffering effect. The sensitivities are generally stronger in the maritime simulations, where weaker sensible heat fluxes lead to narrower, more tilted, and, therefore, more suppressed cumuli when cloud-layer shear is imposed. Moreover, in the experiments with subcloud wind shear, the weaker baseline turbulence in the maritime case allows for a larger turbulence enhancement, resulting in a widening of the transition zones between the cores and their environment, leading to the entrainment of more humid air.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2003

Sheet Flows, Avalanches, and Dune Evolution on Earth and Mars

This investigation is a collaboration between researchers at Cornell University, the University of Florida, and the University of Rennes 1, France. Flow modeling at Cornell University focused on mechanisms for the suspension and transport of wind-blown sand that are important in both terrestrial and Martian environments. These mechanisms include the saltation (or jumping) of grains, collisions between grains, and the interaction of grains with the velocity fluctuations of the turbulent wind. Of particular interest are sheet flows; these are relatively thin, highly concentrated regions of grains flowing near the ground under the influence of a strong turbulent wind. In them, the grains are suspended by interparticle collisions. Sheet flows may be relatively rare events, but they have the capacity to move great amounts of sand. In order to describe sheet flows, a turbulent mixture theory was formulated for particles in a fluid in which fluctuations in the volume fiaction of the particles take place on the scale of the turbulent eddies. Ensemble averaged equations for particle and fluid mass, momentum, and energy and fluid rate of dissipation were expressed in terms of Farve (concentration) averaged velocities and the associated velocity fluctuations. Correlations that describe the turbulent suspension of particles and dissipation of turbulent energy of both phases due to fluid particle interactions were modeled and boundary conditions at the bed and at the upper surface of the collisional flow were formulated. The boundary conditions at the upper surface were tested in a numerical simulation developed at the University of Florida. Steady and unsteady solutions for steady and unsteady fully-developed flows were obtained over a range of wind speeds fiom the lowest for which collisional between particles occurred to at which turbulent suspension is found to dominate collisional suspension. Below the value of the wind speed at which collisions between particles were unimportant, numerical solutions were obtained for the velocity distribution function and the resulting fields of concentration, particle and gas mean velocity, and particle shear stress for the steady two-dimensional saltation of spherical sand particles driven by a turbulent wind over a bed characterized by a simple relationship (the splash function) between the properties of incoming particles and those of the rebounding particles and other particles ejected fiom the bed. At the University of Rennes 1, experiments devoted to the characterization of the splash function for beds consisting of either random or ordered arrays of spheres in two- dimensions were completed. These indicated the role played by the packing geometry in the rebound and ejection of grains. Preliminary experiments on response of a three- dimensional collision bed to a collision with a single particle were performed. Data was taken with a single camera focused on the plane of collision. Here, for example, the decrease of the effective coefficient of restitution of the bed with an increase of the angle of incidence of the incoming particle has been measured. Other experiments on avalanches at Rennes studied the properties of the flows of particles that are responsible for the motion of the leeward side of a dune. In these, the dependence of the initiation of avalanches on the packing and depth of the particles was measured. Particle migration was studied in inclined flows of a binary mixture of disks and the mechanisms of diffision and segregation were isolated and characterized. The influence of side wall on dense, rapid inclined flows was measured and shown to be the reason why the angle of the free surface in such flows can exceed the static angle of repose. Future research will be devoted to a better understanding the transition between saltating (collisionless) and collisional flows as the wind speed the increases. This will involve the understanding of the evolution of the splash function as clisions with the bed become more numerous, more frequent, and more violent.

Source record↗
NASA NTRS1995

Diagnostic calculations of the circulation in the Martian atmosphere

The circulation of the Martian atmosphere during late southern summer is derived from atmospheric temperature and dust distributions retrieved from a subset of the Mariner 9 infrared interferometer spectrometer (IRIS) thermal emission spectra (LS = 343-348 deg) (Santee and Crisp, 1933). Zonal-mean zonal winds are calculated by assuming gradient wind balance and zero surface zonal wind. Both hemispheres have intense midlatitude westerly jets with velocities of 80-90 m/s near 50 km; in the southern tropics the winds are easterly with velocities of 40 m/s near 50 km. The net effect of the zonal-mean meridional circulation and large-scale waves can be approximated by the diabatic ciculation, which is defined from the atmospheric thermal structure and net radiative heating rates. The radiative transfer model described by Crisp (1990) and Santee (1993) is used to compute solar heating and thermal cooling rates from diurnal averages of the retrieved IRIS temperature and dust distributions. At pressures below 4 mbar, there are large net radiative heating rates (up to 5 K/d) in the equatorial region and large net radiative cooling rates (up to 12 K/d) in the polar regions. These net radiative heating rates are used in a diagnostic stream function model which solves for the meridonal and vertical components of the diabatic circulation simultaneously. We find a two cell circulation, with rising motion over the equator, poleward flow in both hemispheres, sinking motion over both polar regions, and return flow in the lowest atmospheric levels. The maximum poleward velocity is 3 m/s in the tropics at approximately 55 km altitude, and the maximum vertical velocity is 2.5 cm/s downward over the north pole at approximately 60 km altitude. If these large transport rates are sustained for an entire season, the Martian atmosphere above the 1-mbar level is overturned in about 38 days. This diabatic circulation is qualitatively similar to the terrestial diabatic circulation at the comparable season, but is more vigorous.

Santee, Michelle L.↗
NASA NTRS1995

Diagnostic calculations of the circulation in the Martian atmosphere

The circulation of the Martian atmosphere during late southern summer is derived from atmospheric temperature and dust distributions retrieved from a subset of the Mariner 9 infrared interferometer spectrometer (IRIS) thermal emission spectra (L(sub s) = 343-348 deg). Zonal-mean zonal winds are calculated by assuming gradient wind balance and zero surface zonal wind. Both hemispheres have intense midlatitude westerly jets with velocities of 80-90 m/s near 50 km; in the southern tropics the winds are easterly with velocities of 40 m/s near 50 km. The net effect of the zonal mean meridional circulation and large-scale waves can be approximated by the diabatic circulation, which is defined from the atmospheric thermal structure and net radiative heating rates. The radiative transfer model described by Crisp (1990) and Santee (1993) is used to compute solar heating and thermal cooling rates from diurnal averages of the retrieved IRIS temperature and dust distributions. At pressures below 4 mbar, there are large net radiative heating rates (up to 5 K/d) in the equatorial region and large net radiative cooling rates (up to 12 K/d) in the polar regions. These net radiative heating rates are used in a diagnostic stream function model which solves for the meridional and vertical components of the diabatic circulation simultaneously. We find a two-cell circulation, with rising motion over the equator, poleward flow in both hemispheres, sinking motion over both polar regions, and return flow in the lowest atmospheric levels. The maximum poleward velocity is 3 m/s in the tropics at approx. 55 km altitude, and the maximum vertical velocity is 2.5 cm/s downward over the north pole at approx. 60 km altitude. If these large transport rates are sustained for an entire season, the Martian atmosphere above the 1-mbar level is overturned in about 38 days. This diabatic circulation is qualitatively similar to the terrestrial diabatic circulation at the comparable season, but is more vigorous.

Santee, Michelle L.↗
NASA NTRS1987

Intrinsic frequency spectra of short gravity-capillary waves obtained from temporal measurements of wave height on a lake

Intrinsic frequency spectra of water waves in the range of 6-17 Hz were obtained as a function of both wind speed and wind stress from point measurements of wave height. In a lake with a limited fetch, there are two types of surface motions causing Doppler shift in the frequencies of short waves: orbital velocity of long waves and surface wind drift. The former was estimated from long-wave amplitude by using a linear wave theory. The error in this estimate is of the order of the long-wave slope, and for this work it is typically 10 percent. The latter was approximated by the friction velocity. The friction velocity could be either taken as 3 percent of the mean wind speed measured at a height of 10 m or obtained from direct measurements of the wind stress. The surface drift velocities obtained by these two approaches were found to be in close agreement. Doppler frequency shift can be corrected in either the frequency or the equivalent spatial domain. The two techniques were found to produce comparable results. Experimental results showed that the spectral energy of short waves rapidly increased in response to increasing winds and jumped up by an order of magnitude when wave breaking occurred.

Atakturk, S. S.↗
DOE OSTI2011

Surface rippling on bulk metallic glass under nanosecond pulse laser ablation

We report an interesting surface ripple patterns in the irradiated area of a Zr-based bulk metallic glass by nanosecond pulse laser with single shot. Such surface rippling phenomenon can be ascribed to the Kelvin-Helmholtz instability at the interface between the molten layer and the expanding plasma plume. The analytical instability criterion is obtained via a perturbation analysis. Furthermore, the model demonstrates that the characteristic spacing of the ripples is dominated by the density, transverse velocity of the plasma wind, and the surface tension of the molten layer. The predicted spacing agrees well with the experimentally observed values. The results are fundamentally useful for laser-processing bulk metallic glasses (BMGs) and even for understanding the nature of flow in BMGs.

36 MATERIALS SCIENCE↗
DOE OSTI2012

HELIOSHEATH MAGNETIC FIELDS BETWEEN 104 AND 113 AU IN A REGION OF DECLINING SPEEDS AND A STAGNATION REGION

We examine the relationships between the magnetic field and the radial velocity component V{sub R} observed in the heliosheath by instruments on Voyager 1 (V1). No increase in the magnetic field strength B was observed in a region where V{sub R} decreased linearly from 70 km s{sup -1} to 0 km s{sup -1} as plasma moved outward past V1. An unusually broad transition from positive to negative polarity was observed during a Almost-Equal-To 26 day interval when the heliospheric current sheet (HCS) moved below the latitude of V1 and the speed of V1 was comparable to the radial speed of the heliosheath flow. When V1 moved through a region where V{sub R} Almost-Equal-To 0 (the 'stagnation region'), B increased linearly with time by a factor of two, and the average of B was 0.14 nT. Nothing comparable to this was observed previously. The magnetic polarity was negative throughout the stagnation region for Almost-Equal-To 580 days until 2011 DOY 235, indicating that the HCS was below the latitude of V1. The average passage times of the magnetic holes and proton boundary layers were the same during 2009 and 2011, because the plasma moved past V1 during 2009 at the same speed that V1 moved through the stagnation region during 2011. The microscale fluctuations of B in the stagnation region during 2011 are qualitatively the same as those observed in the heliosheath during 2009. These results suggest that the stagnation region is a part of the heliosheath, rather than a 'transition region' associated with the heliopause.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

AN ANALYSIS OF THE ORIGIN AND PROPAGATION OF THE MULTIPLE CORONAL MASS EJECTIONS OF 2010 AUGUST 1

On 2010 August 1, the northern solar hemisphere underwent significant activity that involved a complex set of active regions near central meridian with, nearby, two large prominences and other more distant active regions. This activity culminated in the eruption of four major coronal mass ejections (CMEs), effects of which were detected at Earth and other solar system bodies. Recognizing the unprecedented wealth of data from the wide range of spacecraft that were available-providing the potential for us to explore methods for CME identification and tracking, and to assess issues regarding onset and planetary impact-we present a comprehensive analysis of this sequence of CMEs. We show that, for three of the four major CMEs, onset is associated with prominence eruption, while the remaining CME appears to be closely associated with a flare. Using instrumentation on board the Solar Terrestrial Relations Observatory spacecraft, three of the CMEs could be tracked out to elongations beyond 50 Degree-Sign ; their directions and speeds have been determined by various methods, not least to assess their potential for Earth impact. The analysis techniques that can be applied to the other CME, the first to erupt, are more limited since that CME was obscured by the subsequent, much faster event before it had propagated far from the Sun; we discuss the speculation that these two CMEs interact. The consistency of the results, derived from the wide variety of methods applied to such an extraordinarily complete data set, has allowed us to converge on robust interpretations of the CME onsets and their arrivals at 1 AU.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

OBSERVATIONS OF THE CRAB NEBULA'S ASYMMETRICAL DEVELOPMENT

We present the first Hubble Space Telescope Wide Field Planetary Camera-2 imaging survey of the entire Crab Nebula, in the filters F502N ([O III] emission), F673N ([S II]), F631N ([O I]), and F547M (continuum). We use our mosaics to characterize the pulsar wind nebula (PWN) and its three-dimensional structure, the ionizational structure in the filaments forming at its periphery, the speed of the shock driven by the PWN into surrounding ejecta (by inferring the cooling rates behind the shock), and the morphology and ionizational structure of the Rayleigh-Taylor (R-T) fingers. We quantify a number of asymmetries between the northwest (NW) and southeast (SE) quadrants of the Crab Nebula. The lack of observed filaments in the NW, and our observations of the spatial extent of [O III] emission lead us to conclude that cooling rates are slower, and therefore the shock speeds are greater, in the NW quadrant of the nebula, compared with the SE. We conclude that R-T fingers are longer, more ionizationally stratified, and apparently more massive in the NW than in the SE, and the R-T instability appears more fully developed in the NW.

79 ASTRONOMY AND ASTROPHYSICS↗

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