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Sample records for observing field lrc1

  1. Field observations and lessons learned

    SciTech Connect

    Nielsen, Joh B

    2010-01-01

    This presentation outlines observations and lessons learned from the Megaports program. It provides: (1) details of field and technical observations collected during LANL field activities at ports around the world and details of observations collected during radiation detections system testing at Los Alamos National Laboratory; (2) provides suggestions for improvement and efficiency; and (3) discusses possible program execution changes for more effective operations.

  2. Observations of Mercury's magnetic field

    NASA Technical Reports Server (NTRS)

    Ness, N. F.; Behannon, K. W.; Lepping, R. P.; Whang, Y. C.

    1975-01-01

    Magnetic field data obtained by Mariner 10 during the third and final encounter with the planet Mercury on 16 March 1975 were studied. A well developed bow shock and modest magnetosphere, previously observed at first encounter on 29 March 1974, were again observed. In addition, a much stronger magnetic field near closest approach, 400 gamma versus 98 gamma, was observed at an altitude of 327 km and approximately 70 deg north Mercurian latitude. Spherical harmonic analysis of the data provide an estimate of the centered planetary magnetic dipole of 4.7 x 10 to the 22nd power Gauss/cu cm with the axis tilted 12 deg to the rotation axis and in the same sense as Earth's. The interplanetary field was sufficiently different between first and third encounters that in addition to the very large field magnitude observed, it argues strongly against a complex induction process generating the observed planetary field. While a possibility exists that Mercury possesses a remanent field due to magnetization early in its formation, a present day active dynamo seems to be a more likely candidate for its origin.

  3. Observations of Interstellar Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Crutcher, R.; Heiles, C.; Troland, T.

    This article describes how interstellar magnetic fields are detected, measured, and mapped, the results of such observations, and the role played by interstellar magnetic fields in the physics of the interstellar medium. A goal of the observations is the measurement of the morphology and strengths of the uniform (Bu) and random (Br) components of magnetic fields. Observational techniques probe either the component of B parallel to the line of sight (B_parallel) or in the plane of the sky (B_⊥). Tracers of B_parallel are Faraday rotation of the position angle of linearly polarized radiation and Zeeman splitting of spectral lines. Tracers of B_⊥ are the strength of synchrotron radiation and linear polarization of syn chrotron radiation and of emission or absorption from dust and spectral lines. Starlight polarization shows that on large spatial scales the Galactic magnetic field is not heavily tangled (B_u/B_r ≈ 0.7 - 1.0), that the field is generally parallel to the Galactic plane near the plane, that the local field points approximately along the local spiral arm (pitch angle 9.4(°) , center of curvature 7.8 kpc distant towards ℓ ≈ -15.4(°) ), and that off the Galactic plane there is considerable small-scale structure to the field. Galactic synchrotron emission shows magnetic spiral arms with a total strength B_t ≈ 6 #55G and B_u ≈ 4 #55G. Pulsar data show evidence for reversals of the field direction with Galactic radius and yield B_r ≈ 5 #55G and B_u ≈ 1.5 #55G; the morphology of the large-scale mean field is consistent with dynamo generation. H I Zeeman detections for diffuse clouds yield B_parallel char 126 5 - 20 #55G with many limits B_parallel #55G. A recent survey of Galactic H I in absorption against extragalactic sources confirms the result that the fields in diffuse clouds are often quite weak. The critical parameter for evaluating the importance of magnetic fields in star formation is the ratio of the mass to the magnetic flux, M

  4. Observations of Si field evaporation.

    PubMed

    Thompson, Keith; Sebastian, Jason; Gerstl, Stephan

    2007-01-01

    Field evaporation studies of crystalline <100> Si were performed in a three-dimensional atom-probe, which utilized a local electrode geometry. Several distinct phenomena were observed. Si field evaporation rates showed: (1) no measurable dependence on temperature below 110K, (2) an exponential dependence on evaporation rate as a function of temperature above 110K, and (3) no dependence on substrate doping (i.e., electrical conductivity) as high as 10 Omega cm in the temperature range of 40-150K. Two distinct evaporation modes were observed. The first was associated with approximately 1at% H+ in the mass spectrum. Negligible amounts of H were detected in the mass spectra of the second mode. When the pulse fraction (pf) was increased from 5% to 30%, the presence of H+ in the mass spectra, i.e. operation in the first mode, was associated with a degradation in mass resolution by as much as 80% for the 10 Omega cm Si samples. Conversely, no loss in mass resolution was detected for the approximately 0.001 Omega cm samples over the pf range studied.

  5. Observations of faint field galaxies

    NASA Technical Reports Server (NTRS)

    Koo, David C.

    1987-01-01

    Number counts, colors, and angular correlations of field galaxies fainter than 20th mag are summarized. Resulting conclusions regarding the presence and nature of luminosity, spectral, and clustering evolution remain contraversial. Preliminary analysis of two major spectroscopic surveys near completion suggests that by z approximately 0.5, larger numbers of very blue galaxies of moderate luminosities are found than today. The skewer-like surveys also provide new probes of galaxy clustering on scales previously unexplored (larger than 200 Mpc) and over lookback times of several billion years.

  6. Magnetic field observations in Comet Halley's coma

    NASA Astrophysics Data System (ADS)

    Riedler, W.; Schwingenschuh, K.; Yeroshenko, Ye. G.; Styashkin, V. A.; Russell, C. T.

    1986-05-01

    During the encounter with Comet Halley, the magnetometer (MISCHA) aboard the Vega 1 spacecraft observed an increased level of magnetic field turbulence, resulting from an upstream bow wave. Both Vega spacecraft measured a peak field strength of 70-80 nT and observed draping of magnetic field lines around the cometary obstacle. An unexpected rotation of the magnetic field vector was observed, which may reflect either penetration of magnetic field lines into a diffuse layer related to the contact surface separating the solar-wind and cometary plasma, or the persistence of pre-existing interplanetary field structures.

  7. Entropy of local smeared field observables

    NASA Astrophysics Data System (ADS)

    Satz, Alejandro

    2017-01-01

    We re-conceptualize the usual entanglement entropy of quantum fields in a spatial region as a limiting case of a more general and well-defined quantity, the entropy of a subalgebra of smeared field observables. We introduce this notion, discuss various examples, and recover from it the area law for the entanglement entropy of a sphere in Minkowski space.

  8. Cosmic Magnetic Fields: Observations and Prospects

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    2011-09-01

    Synchrotron emission, its polarization and its Faraday rotation at radio frequencies of 0.2-10 GHz are powerful tools to study the strength and structure of cosmic magnetic fields. Unpolarized emission traces turbulent fields which are strongest in galactic spiral arms and bars (20-30 μG) and in central starburst regions (50-100 μG). Such fields are dynamically important, e.g. they can drive gas inflows in central regions. Polarized emission traces ordered fields which can be regular (uni-directional) or anisotropic random (generated from isotropic random fields by compression or shear). Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. The strongest ordered (mostly regular) fields of 10-15 μG strength are generally found in galactic interarm regions and follow the orientation of adjacent gas spiral arms. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several spiral galaxies reveal large-scale patterns, which are signatures of regular fields probably generated by a mean-field dynamo. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Ordered magnetic fields are also observed in radio halos around edge-on galaxies, out to large distances from the plane, with X-shaped patterns.--The strength of the total magnetic field in our Milky Way is about 6 μG near the solar radius, but several mG in dense clouds, pulsar wind nebulae, and filaments near the Galactic Center. Diffuse polarized radio emission and Faraday rotation data from pulsars and background sources show spiral fields with large-scale reversals, but the overall field structure in our Galaxy is still under debate.--Diffuse radio emission from the halos of galaxy clusters is mostly unpolarized because intracluster magnetic fields are turbulent, while cluster

  9. Fundamental implications of intergalactic magnetic field observations

    NASA Astrophysics Data System (ADS)

    Vachaspati, Tanmay

    2017-03-01

    Helical intergalactic magnetic fields at the ˜10-14 G level on ˜10 Mpc length scales are indicated by current gamma ray observations. The existence of magnetic fields in cosmic voids and their nontrivial helicity suggest that they must have originated in the early Universe and thus have implications for the fundamental interactions. We derive the spectrum of the cosmological magnetic field as implied by observations and MHD evolution, yielding order nano Gauss fields on kiloparsec scales and a "large helicity puzzle" that needs to be resolved by the fundamental interactions. The importance of C P violation and a possible crucial role for chiral effects or axions in the early Universe are pointed out.

  10. Precipitation properties observed during CHUVA Field Campaign

    NASA Astrophysics Data System (ADS)

    Morales, C.; Machado, L. A.; Angelis, C. F.; Silva Dias, M. A. F.; Fisch, G.; Carvalho, I. C.; Biscaro, T.; Sakuragi, J.; Neves, J. R.; Anselmo, E. M.; Lacerda, M.

    2012-04-01

    CHUVA is a Brazilian research program that seeks to depict the main precipitating systems observed in Brazil as a support for the Global Precipitation Measurement (GPM) mission. CHUVA is conducting a series of field campaigns in the time frame of 2010-2013 to sample raining systems that vary from maritime to continental regime and in polluted and clean environments. For this study, we will present initially the drop size distribution (DSD) variability observed in the field experiments of Alcantara (March/2010), Fortaleza (April/2011), Belém (June/2011) and Vale do Paraiba (November-December/2011). Secondly, with the help of the mobile X-Band and MRR-2, we will show the DSD differences observed on warm and cold phase clouds, and convective and stratiform precipitation. Finally, by employing the vertical electrical field and lightning measurements together with the weather radar, we will present the main vertical precipitation features observed in thunderstorms and non- thunderstorms, in addition to the different raining systems observed during the four field campaigns.

  11. LAMOST observations in the Kepler field

    NASA Astrophysics Data System (ADS)

    Molenda-Żakowicz, Joanna; De Cat, Peter; Fu, Jian-Ning; Yang, Xiao-Hu; Yang

    2014-02-01

    We present results of observations of 22 664 stars in the Kepler field of view acquired with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in the years 2011 - 2012, and provide a database of the atmospheric parameters derived from those data.

  12. CCD observations of old nova fields

    NASA Technical Reports Server (NTRS)

    Downes, Ronald A.; Szkody, Paula

    1989-01-01

    The discovery of CK Vulpeculae (Nova 1670) has prompted a major review of ideas concerning the long-term development of novae. Unfortunately, there are very few recovered novae old enough to provide confirmation (or rejection) of the new 'hibernation' scenario. CCD images of seven old nova fields, and R band photometry for four fields, have been obtained in an attempt to recover these objects in quiescence. A strong candidate for U Leonis, and a possible counterpart for T Bootis, are found. For three other fields, weak candidates have been found. Finding charts and colors are presented for the seven fields observed. The R light curves of U Leo, indicating an orbital period of 192.5 or 385.0 min, are shown.

  13. CCD observations of old nova fields

    SciTech Connect

    Downes, R.A.; Szkody, P.; Washington Uni., Seattle )

    1989-06-01

    The discovery of CK Vulpeculae (Nova 1670) has prompted a major review of ideas concerning the long-term development of novae. Unfortunately, there are very few recovered novae old enough to provide confirmation (or rejection) of the new hibernation scenario. CCD images of seven old nova fields, and R band photometry for four fields, have been obtained in an attempt to recover these objects in quiescence. A strong candidate for U Leonis, and a possible counterpart for T Bootis, are found. For three other fields, weak candidates have been found. Finding charts and colors are presented for the seven fields observed. The R light curves of U Leo, indicating an orbital period of 192.5 or 385.0 min, are shown. 14 refs.

  14. CCD observations of old nova fields

    NASA Technical Reports Server (NTRS)

    Downes, Ronald A.; Szkody, Paula

    1989-01-01

    The discovery of CK Vulpeculae (Nova 1670) has prompted a major review of ideas concerning the long-term development of novae. Unfortunately, there are very few recovered novae old enough to provide confirmation (or rejection) of the new 'hibernation' scenario. CCD images of seven old nova fields, and R band photometry for four fields, have been obtained in an attempt to recover these objects in quiescence. A strong candidate for U Leonis, and a possible counterpart for T Bootis, are found. For three other fields, weak candidates have been found. Finding charts and colors are presented for the seven fields observed. The R light curves of U Leo, indicating an orbital period of 192.5 or 385.0 min, are shown.

  15. MESSENGER observations of Mercury's magnetic field structure

    NASA Astrophysics Data System (ADS)

    Johnson, Catherine L.; Purucker, Michael E.; Korth, Haje; Anderson, Brian J.; Winslow, Reka M.; Al Asad, Manar M. H.; Slavin, James A.; Alexeev, Igor. I.; Phillips, Roger J.; Zuber, Maria T.; Solomon, Sean C.

    2012-12-01

    We present a baseline, time-averaged model for Mercury's magnetosphere, derived from MESSENGER Magnetometer data from 24 March to 12 December 2011, comprising the spacecraft's first three Mercury years in orbit around the innermost planet. The model, constructed under the approximation that the magnetospheric shape can be represented as a paraboloid of revolution, includes two external (magnetopause and magnetotail) current systems and an internal (dipole) field and allows for reconnection. We take advantage of the geometry of the orbital Magnetometer data to estimate all but one of the model parameters, and their ranges, directly from the observations. These parameters are then used as a priori constraints in the paraboloid magnetospheric model, and the sole remaining parameter, the dipole moment, is estimated as 190 nT RM3 from a grid search. We verify that the best fit dipole moment is insensitive to changes in the other parameters within their determined ranges. The model provides an excellent first-order fit to the MESSENGER observations, with a root-mean-square misfit of less than 20 nT globally. The results show that the magnetopause field strength ranges from 10% to 50% of the dipole field strength at observation locations on the dayside and at nightside latitudes north of 60°N. Globally, the residual signatures observed to date are dominated by the results of magnetospheric processes, confirming the dynamic nature of Mercury's magnetosphere.

  16. Dwarf Discoveries from Serendipitous Field Star Observations

    NASA Astrophysics Data System (ADS)

    Green, Wayne

    2016-05-01

    For the past two years, The University of Colorado, in collaboration with Las Cumbres Observatory Global Telescope Network (LCOGTN) has been taking Sloans r' and i' images of approximately 200 galaxies during each new moon period to provide ground data in support of the approximately 1100 hours of warm Spitzer time awarded to Dr. Mansi Kasliwal's Caltech SPIRITS program. Currently there are over 6,000 images in this archive. Small telescope scientists routinely image the same fields, building similar archives brimming with science potential. This paper reports the technique to develop serendipitous observations of dwarf field stars. Answers to questions surrounding the dwarf's early life in proximity to non-hierarchal multiple star groups, about how dwarfs not only survive but are so numerous are well within the capabilities of small telescope scientists. The role of the small telescope scientist is of vital importance in these (re)discovery, confirmation, monitoring and reporting tasks.

  17. Observation of Magnetic Fields Generated by Tsunamis

    NASA Astrophysics Data System (ADS)

    Manoj, Chandrasekharan; Maus, Stefan; Chulliat, Arnaud

    2011-01-01

    Tsunamis produce perturbations in the Earth's magnetic field by electromagnetic induction. Recent deployments of highly accurate magnetometers and the exceptionally deep solar minimum provided ideal conditions to observe these small signals from the tsunami resulting from the strong Chilean earthquake on 27 February 2010. Magnetic observatory measurements on Easter Island, 3500 kilometers west of the epicenter, show a periodic signal of 1 nanotesla, coincident in time with recordings from the local tide gauge. The detection of these magnetic signals represents a milestone in understanding tsunami-induced electromagnetic effects.

  18. Electric field observations of equatorial bubbles

    NASA Technical Reports Server (NTRS)

    Aggson, T. L.; Maynard, N. C.; Hanson, W. B.; Saba, Jack L.

    1992-01-01

    Results from the double floating probe experiment performed on the San Marco D satellite are presented, with emphasis on the observation of large incremental changes in the convective electric field vector at the boundary of equatorial plasma bubbles. Attention is given to isolated bubble structures in the upper ionospheric F regions; these observed bubble encounters are divided into two types - type I (live bubbles) and type II (dead bubbles). Type I bubbles show varying degrees of plasma depletion and large upward velocities range up to 1000 km/s. The geometry of these bubbles is such that the spacecraft orbit may cut them where they are tilting either eastward or (more often) westward. Type II bubbles exhibit plasma density depletion but no appreciable upward convection. Both types of events are usually surrounded by a halo of plasma turbulence, which can extend considerably beyond the region of plasma depletion.

  19. Electric field observations of equatorial bubbles

    NASA Astrophysics Data System (ADS)

    Aggson, T. L.; Maynard, N. C.; Hanson, W. B.; Saba, Jack L.

    1992-03-01

    Results from the double floating probe experiment performed on the San Marco D satellite are presented, with emphasis on the observation of large incremental changes in the convective electric field vector at the boundary of equatorial plasma bubbles. Attention is given to isolated bubble structures in the upper ionospheric F regions; these observed bubble encounters are divided into two types - type I (live bubbles) and type II (dead bubbles). Type I bubbles show varying degrees of plasma depletion and large upward velocities range up to 1000 km/s. The geometry of these bubbles is such that the spacecraft orbit may cut them where they are tilting either eastward or (more often) westward. Type II bubbles exhibit plasma density depletion but no appreciable upward convection. Both types of events are usually surrounded by a halo of plasma turbulence, which can extend considerably beyond the region of plasma depletion.

  20. Subduction dynamics: Constraints from gravity field observations

    NASA Technical Reports Server (NTRS)

    Mcadoo, D. C.

    1985-01-01

    Satellite systems do the best job of resolving the long wavelength components of the Earth's gravity field. Over the oceans, satellite-borne radar altimeters such as SEASAT provide the best resolution observations of the intermediate wavelength components. Satellite observations of gravity contributed to the understanding of the dynamics of subduction. Large, long wavelength geoidal highs generally occur over subduction zones. These highs are attributed to the superposition of two effects of subduction: (1) the positive mass anomalies of subducting slabs themselves; and (2) the surface deformations such as the trenches convectively inducted by these slabs as they sink into the mantle. Models of this subduction process suggest that the mantle behaves as a nonNewtonian fluid, its effective viscosity increases significantly with depth, and that large positive mass anomalies may occur beneath the seismically defined Benioff zones.

  1. Observations of the diffuse UV radiation field

    NASA Technical Reports Server (NTRS)

    Murthy, Jayant; Henry, R. C.; Feldman, P. D.; Tennyson, P. D.

    1989-01-01

    Spectra are presented for the diffuse UV radiation field between 1250 to 3100 A from eight different regions of the sky, which were obtained with the Johns Hopkins UVX experiment. UVX flew aboard the Space Shuttle Columbia (STS-61C) in January 1986 as part of the Get-Away Special project. The experiment consisted of two 1/4 m Ebert-Fastie spectrometers, covering the spectral range 1250 to 1700 A at 17 A resolution and 1600 to 3100 A at 27 A resolution, respectively, with a field of view of 4 x .25 deg, sufficiently small to pick out regions of the sky with no stars in the line of sight. Values were found for the diffuse cosmic background ranging in intensity from 300 to 900 photons/sq cm/sec/sr/A. The cosmic background is spectrally flat from 1250 to 3100 A, within the uncertainties of each spectrometer. The zodiacal light begins to play a significant role in the diffuse radiation field above 2000 A, and its brightness was determined relative to the solar emission. Observed brightnesses of the zodiacal light in the UV remain almost constant with ecliptic latitude, unlike the declining visible brightnesses, possibly indicating that those (smaller) grains responsible for the UV scattering have a much more uniform distribution with distance from the ecliptic plane than do those grains responsible for the visible scattering.

  2. Early Magnetic Field Observations from HMI

    NASA Astrophysics Data System (ADS)

    Hoeksema, Jon Todd; HMI Magnetic Field Team

    2010-05-01

    The Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) is beginning to produce a synoptic series of full-disk arc-second resolution magnetograms. Line-of-sight magnetograms are available every 45 seconds and the vector field will be routinely calculated every 12 minutes in automatically identified active region patches. Select quick-look products are available within minutes and definitive science data will be published within a day or two. The larger team has developed programs to routinely produce a comprehensive set of higher level products, including synoptic maps and frames, local surface-flow maps, a variety of local and global coronal field models, and time series of tracked active-region parameters - all useful in learning to forecast space weather events. Comparisons with AIA, EVE, MDI, SOLIS and other ground-based observations will ultimately help understand uncertainties in the observations. This work was supported by NASA through contract NAS5-02139 to Stanford University.

  3. Interpretation of Solar Magnetic Field Strength Observations

    NASA Astrophysics Data System (ADS)

    Ulrich, R. K.; Bertello, L.; Boyden, J. E.; Webster, L.

    2009-03-01

    This study based on longitudinal Zeeman effect magnetograms and spectral line scans investigates the dependence of solar surface magnetic fields on the spectral line used and the way the line is sampled to estimate the magnetic flux emerging above the solar atmosphere and penetrating to the corona from magnetograms of the Mt. Wilson 150-foot tower synoptic program (MWO). We have compared the synoptic program λ5250 Å line of Fe i to the line of Fe i at λ5233 Å since this latter line has a broad shape with a profile that is nearly linear over a large portion of its wings. The present study uses five pairs of sampling points on the λ5233 Å line. Line profile observations show that the determination of the field strength from the Stokes V parameter or from line bisectors in the circularly polarized line profiles lead to similar dependencies on the spectral sampling of the lines, with the bisector method being the less sensitive. We recommend adoption of the field determined with the line bisector method as the best estimate of the emergent photospheric flux and further recommend the use of a sampling point as close to the line core as is practical. The combination of the line profile measurements and the cross-correlation of fields measured simultaneously with λ5250 Å and λ5233 Å yields a formula for the scale factor δ -1 that multiplies the MWO synoptic magnetic fields. By using ρ as the center-to-limb angle (CLA), a fit to this scale factor is δ -1=4.15-2.82sin 2( ρ). Previously δ -1=4.5-2.5sin 2( ρ) had been used. The new calibration shows that magnetic fields measured by the MDI system on the SOHO spacecraft are equal to 0.619±0.018 times the true value at a center-to-limb position 30°. Berger and Lites (2003, Solar Phys. 213, 213) found this factor to be 0.64±0.013 based on a comparison using the Advanced Stokes Polarimeter.

  4. Hazardous gas model evaluation with field observations

    NASA Astrophysics Data System (ADS)

    Hanna, S. R.; Chang, J. C.; Strimaitis, D. G.

    Fifteen hazardous gas models were evaluated using data from eight field experiments. The models include seven publicly available models (AFTOX, DEGADIS, HEGADAS, HGSYSTEM, INPUFF, OB/DG and SLAB), six proprietary models (AIRTOX, CHARM, FOCUS, GASTAR, PHAST and TRACE), and two "benchmark" analytical models (the Gaussian Plume Model and the analytical approximations to the Britter and McQuaid Workbook nomograms). The field data were divided into three groups—continuous dense gas releases (Burro LNG, Coyote LNG, Desert Tortoise NH 3-gas and aerosols, Goldfish HF-gas and aerosols, and Maplin Sands LNG), continuous passive gas releases (Prairie Grass and Hanford), and instantaneous dense gas releases (Thorney Island freon). The dense gas models that produced the most consistent predictions of plume centerline concentrations across the dense gas data sets are the Britter and McQuaid, CHARM, GASTAR, HEGADAS, HGSYSTEM, PHAST, SLAB and TRACE models, with relative mean biases of about ±30% or less and magnitudes of relative scatter that are about equal to the mean. The dense gas models tended to overpredict the plume widths and underpredict the plume depths by about a factor of two. All models except GASTAR, TRACE, and the area source version of DEGADIS perform fairly well with the continuous passive gas data sets. Some sensitivity studies were also carried out. It was found that three of the more widely used publicly-available dense gas models (DEGADIS, HGSYSTEM and SLAB) predicted increases in concentration of about 70% as roughness length decreased by an order of magnitude for the Desert Tortoise and Goldfish field studies. It was also found that none of the dense gas models that were considered came close to simulating the observed factor of two increase in peak concentrations as averaging time decreased from several minutes to 1 s. Because of their assumption that a concentrated dense gas core existed that was unaffected by variations in averaging time, the dense gas

  5. Theoretical and observational analysis of spacecraft fields

    NASA Technical Reports Server (NTRS)

    Neubauer, F. M.; Schatten, K. H.

    1972-01-01

    In order to investigate the nondipolar contributions of spacecraft magnetic fields a simple magnetic field model is proposed. This model consists of randomly oriented dipoles in a given volume. Two sets of formulas are presented which give the rms-multipole field components, for isotropic orientations of the dipoles at given positions and for isotropic orientations of the dipoles distributed uniformly throughout a cube or sphere. The statistical results for an 8 cu m cube together with individual examples computed numerically show the following features: Beyond about 2 to 3 m distance from the center of the cube, the field is dominated by an equivalent dipole. The magnitude of the magnetic moment of the dipolar part is approximated by an expression for equal magnetic moments or generally by the Pythagorean sum of the dipole moments. The radial component is generally greater than either of the transverse components for the dipole portion as well as for the nondipolar field contributions.

  6. Simultaneous particle and field observations of field-aligned currents

    NASA Technical Reports Server (NTRS)

    Berko, F. W.; Hoffman, R. A.; Burton, R. K.; Holzer, R. E.

    1973-01-01

    Simultaneous measurements of low energy precipitating electrons and magnetic fluctuations from the low altitude polar orbiting satellite OGO-4 have been compared. Analysis of the two sets of experimental data for isolated events led to the classification of high latitude field-aligned currents as purely temporal or purely spatial variations. Magnetic field disturbances calculated using these simple current models and the measured particle fluxes were in good agreement with measured field values. While fluxes of greater than 1 keV electrons are detected primarily on the nightside, magnetometer disturbances indicative of field-aligned currents were seen at all local times, both in the visual auroral regions and dayside polar cusp. Thus electrons with energies less than approximately 1 keV are the prime charge carriers in high latitude dayside field-aligned currents. The satellite measurements are in good agreement with previously measured field-aligned current values and with values predicted from several models involving magnetospheric field-aligned currents.

  7. Balloon-borne radiometer profiler: Field observations

    SciTech Connect

    Shaw, W.J.; Whiteman, C.D.; Anderson, G.A.; Alzheimer, J.M.; Hubbe, J.M.; Scott, K.A.

    1995-03-01

    This project involves the development of the capability of making routine soundings of broadband radiative fluxes and radiative flux divergences to heights of 1500m AGL. Described in this document are radiometers carried on a stabilized platform in a harness inserted in the tetherline of a tethered balloon meteriological sounding system. Field test results are given.

  8. Annotated Observations: Field Notes and Reflections

    ERIC Educational Resources Information Center

    Thomas-Fair, Ursula

    2007-01-01

    Purpose: The purpose of this action research presentation is to invite discourse on the intersection of race, gender and instructional decisions in the classrooms of student teachers. The purpose of this study is to also examine the thoughts of a university supervisor during clinical observation with respect to her positionality as a woman of…

  9. Multisatellite Observations of Interplanetary Field Enhancements

    NASA Astrophysics Data System (ADS)

    Russell, C. T.; Weimer, D. R.; Jian, L. K.; Lai, H. R.; Luhmann, J. G.

    2008-12-01

    Interplanetary Field Enhancements (IFEs) are magnetic structures in the solar wind that have a cusp-shaped maximum in the field strength with a strong current sheet often near the central peak. These structures generally last an hour or more. They have a tendency to be seen more often at specific ecliptic longitudes, have been identified on occasion with particular small solar system bodies (asteroid 2201 Oljato and comet 122P/ De Vico) and attributed to the interaction of the solar wind with charged dust. On occasion they are detected nearly simultaneously by several spacecraft. Multispacecraft detection have been made with PVO, Venera-13 and Venera-14; with ISEE 1 and ISEE 3 and more recently with STEREO A and B, ACE and Wind. In this paper we use a delay matching algorithm developed by D. Weimer on the IFE of December 24, 2006 detected by 4 spacecraft. While the IFE is crossing the four spacecraft separated in Y by 90 Re and in X by 160 Re the measured delay was close to the calculated advection time. Along the apparent center line of the event the delay was close to 4 minutes. This event together with previous events are consistent with IFEs being magnetic structures that are convecting outward from the Sun with nearly, but slightly slower than, the solar wind velocity. We need to understand the occurrence rate of such structures and their physical cause because if this hypothesis is true, they may be responsible for accelerating dust out of the inner solar system.

  10. POLAR FIELD REVERSAL OBSERVATIONS WITH HINODE

    SciTech Connect

    Shiota, D.; Tsuneta, S.; Shimojo, M.; Orozco Suarez, D.; Ishikawa, R.; Sako, N.

    2012-07-10

    We have been monitoring yearly variation in the Sun's polar magnetic fields with the Solar Optical Telescope aboard Hinode to record their evolution and expected reversal near the solar maximum. All magnetic patches in the magnetic flux maps are automatically identified to obtain the number density and magnetic flux density as a function of the total magnetic flux per patch. The detected magnetic flux per patch ranges over four orders of magnitude (10{sup 15}-10{sup 20} Mx). The higher end of the magnetic flux in the polar regions is about one order of magnitude larger than that of the quiet Sun, and nearly that of pores. Almost all large patches ({>=}10{sup 18} Mx) have the same polarity, while smaller patches have a fair balance of both polarities. The polarity of the polar region as a whole is consequently determined only by the large magnetic concentrations. A clear decrease in the net flux of the polar region is detected in the slow rising phase of the current solar cycle. The decrease is more rapid in the north polar region than in the south. The decrease in the net flux is caused by a decrease in the number and size of the large flux concentrations as well as the appearance of patches with opposite polarity at lower latitudes. In contrast, we do not see temporal change in the magnetic flux associated with the smaller patches (<10{sup 18} Mx) and that of the horizontal magnetic fields during the years 2008-2012.

  11. Field Research: Learning through the Process of Observation

    ERIC Educational Resources Information Center

    Hartlep, Nicholas Daniel

    2009-01-01

    This paper reports on the process of a participant observation. Its focus is its process, not on what was observed. This report provides the following: (1) an overview of this observation, (2) the purpose of this observation, (3) the site and situation of this observation, (4) two samples of reflective field notes from this observation, and (5) an…

  12. Regional gravity field modelling from GOCE observables

    NASA Astrophysics Data System (ADS)

    Pitoňák, Martin; Šprlák, Michal; Novák, Pavel; Tenzer, Robert

    2017-01-01

    In this article we discuss a regional recovery of gravity disturbances at the mean geocentric sphere approximating the Earth over the area of Central Europe from satellite gravitational gradients. For this purpose, we derive integral formulas which allow converting the gravity disturbances onto the disturbing gravitational gradients in the local north-oriented frame (LNOF). The derived formulas are free of singularities in case of r ≠ R . We then investigate three numerical approaches for solving their inverses. In the initial approach, the integral formulas are firstly modified for solving individually the near- and distant-zone contributions. While the effect of the near-zone gravitational gradients is solved as an inverse problem, the effect of the distant-zone gravitational gradients is computed by numerical integration from the global gravitational model (GGM) TIM-r4. In the second approach, we further elaborate the first scenario by reducing measured gravitational gradients for gravitational effects of topographic masses. In the third approach, we apply additional modification by reducing gravitational gradients for the reference GGM. In all approaches we determine the gravity disturbances from each of the four accurately measured gravitational gradients separately as well as from their combination. Our regional gravitational field solutions are based on the GOCE EGG_TRF_2 gravitational gradients collected within the period from November 1 2009 until January 11 2010. Obtained results are compared with EGM2008, DIR-r1, TIM-r1 and SPW-r1. The best fit, in terms of RMS (2.9 mGal), is achieved for EGM2008 while using the third approach which combine all four well-measured gravitational gradients. This is explained by the fact that a-priori information about the Earth's gravitational field up to the degree and order 180 was used.

  13. Field Observed Salt Tolerance of California Pistachios

    NASA Astrophysics Data System (ADS)

    Sanden, Blake; Fergusion, Lousie; Kallsen, Craig

    2017-04-01

    The general concept of crop salt tolerance is over simplified: consisting of a single soil saturation extract salinity threshold with a "% relative yield" decline function. This approach minimizes the real world variability in actual tree growth and yield due to additional specific ion toxicity and soil texture/anoxia. The current salinity tolerance function for California pistachios is essentially the same as cotton. It was developed from a small plot study in an 8 to 13 year old orchard in northwestern Kern County from 1997-2002 with a threshold of 9.4 dS/m ECe and an 8.4% relative yield decline above that level. These values were confirmed for seedling growth in saline sand-tank studies at the USDA Salinity Lab in Riverside, California. A second large scale field study applied fresh and saline irrigation treatments (0.5 to 5.2 dS/m EC) from planting through 10th leaf. Trees were commercially harvested starting in 2011. Average 2011-14 root zone salinity ranged from 2.5 to 13.2 dS/m and caused a significant edible inshell yield reduction of 108 to 264 kg/ha (depending on rootstock) in the combined 4 year yield: a 1 to 3% decline for every unit EC (dS/m) increase over 6 ds/m. A greatly expanded salinity survey including 10 commercial fields (9th - 15th leaf) in western Kern County with 140 individual tree data points ranging from an average root zone (1.5 m depth) salinity of 1.6 to 20.5 dS/m resulted in a similar yield reduction of 162 to 394 kg/ha (3 year cumulative inshell yield) for every unit ECe > 6.5 dS/m.

  14. River Surface Velocity Fields Observed From Space

    NASA Astrophysics Data System (ADS)

    Kääb, A.; Prowse, T. D.

    2011-12-01

    Knowledge of water-surface velocities in rivers is useful for understanding a wide range of lotic processes and systems, such as water and ice fluxes and forces, mixing, solute and sediment transport, bed and bank stability, aquatic and riparian ecology, and extreme hydrologic events. In cold regions, river-ice break up and the associated downstream transport of ice debris is often the most important hydrological event of the year, producing flood levels that commonly exceed those for the open-water period and dramatic consequences for river infrastructure and ecology. Quantification of river surface velocity and currents has relied mostly on very scarce in situ measurements or particle tracking in laboratory models, with few attempts to cover entire river reaches. Accurate and complete surface-velocity fields on rivers have rarely been produced. In this study, we use river-ice debris as an index of surface water velocity, and track it over a time period of about one minute, which is the typical time lapse between the two or more images that form a stereo data set in spaceborne, along-track optical-stereo mapping. Using this novel approach, we measure and visualize for the first time the almost complete two-dimensional surface velocity fields over many tens of kilometers long river reaches. We present the types of short time-delay imagery suitable for the measurements and discuss application examples on a number of North-American (e.g. Figs. 1 and 2) and Siberian rivers, using a range of high and medium resolution imagery. The methodology and results of the novel approach will be valuable to a number of disciplines requiring detailed information about river flow, such as hydraulics, hydrology, river ecology and natural-hazard management.

  15. Seismological Field Observation of Mesoscopic Nonlinearity

    NASA Astrophysics Data System (ADS)

    Sens-Schönfelder, Christoph; Gassenmeier, Martina; Eulenfeld, Tom; Tilmann, Frederik; Korn, Michael; Niederleithinger, Ernst

    2016-04-01

    Noise based observations of seismic velocity changes have been made in various environments. We know of seasonal changes of velocities related to ground water or temperature changes, co-seismic changes originating from shaking or stress redistribution and changes related to volcanic activity. Is is often argued that a decrease of velocity is related to the opening of cracks while the closure of cracks leads to a velocity increase if permanent stress changes are invoked. In contrast shaking induced changes are often related to "damage" and subsequent "healing" of the material. The co-seismic decrease and transient recovery of seismic velocities can thus be explained with both - static stress changes or damage/healing processes. This results in ambiguous interpretations of the observations. Here we present the analysis of one particular seismic station in northern Chile that shows very strong and clear velocity changes associated with several earthquakes ranging from Mw=5.3 to Mw=8.1. The fact that we can observe the response to several events of various magnitudes from different directions offers the unique possibility to discern the two possible causative processes. We test the hypothesis, that the velocity changes are related to shaking rather than stress changes by developing an empirical model that is based on the local ground acceleration at the sensor site. The eight year of almost continuous observations of velocity changes are well modeled by a daily drop of the velocity followed by an exponential recovery. Both, the amplitude of the drop as well as the recovery time are proportional to the integrated acceleration at the seismic station. Effects of consecutive days are independent and superimposed resulting in strong changes after earthquakes and constantly increasing velocities during quiet days thereafter. This model describes the continuous observations of the velocity changes solely based on the acceleration time series without individually defined dates

  16. Interplanetary magnetic sector polarity inferred from polar geomagnetic field observations

    NASA Technical Reports Server (NTRS)

    Eriss-Christensen, E.; Lassen, K.; Wilcox, J. M.; Gonzalez, W.; Colburn, D. S.

    1971-01-01

    With the use of a prediction technique it is shown that the polarity (toward or away from the sun) of the interplanetary magnetic field can be reliably inferred from observations of the polar geomagnetic field.

  17. Null fields in the outer Jovian magnetosphere: Ulysses observations

    NASA Technical Reports Server (NTRS)

    Haynes, P. L.; Balogh, A.; Dougherty, M. K.; Southwood, D. J.; Fazakerley, A.; Smith, E. J.

    1994-01-01

    This paper reports on a magnetic field phenomenon, hereafter referred to as null fields, which were discovered during the inbound pass of the recent flyby of Jupiter by the Ulysses spacecraft. These null fields which were observed in the outer dayside magnetosphere are characterised by brief but sharp decreases of the field magnitude to values less than 1 nT. The nulls are distinguished from the current sheet signatures characteristic of the middle magnetosphere by the fact that the field does not reverse across the event. A field configuration is suggested that accounts for the observed features of the events.

  18. Null fields in the outer Jovian magnetosphere: ULYSSES observations

    NASA Astrophysics Data System (ADS)

    Haynes, P. L.; Balogh, A.; Dougherty, M. K.; Southwood, D. J.; Fazakerley, A.

    1994-03-01

    This paper reports on a magnetic field phenomenon, hereafter referred to as null fields, which were discovered during the inbound pass of the recent flyby of Jupiter by the Ulysses spacecraft. These null fields which were observed in the outer dayside magnetosphere are characterised by brief but sharp decreases of the field magnitude to values less than 1 nT. The nulls are distinguished from the current sheet signatures characteristic of the middle magnetosphere by the fact that the field does not reverse across the event. A field configuration is suggested that accounts for the observed features of the events.

  19. Interplanetary magnetic sector polarity inferred from polar geomagnetic field observations

    NASA Technical Reports Server (NTRS)

    Friis-Christensen, E.; Lassen, K.; Wilcox, J. M.; Gonzalez, W.; Colburn, D. S.

    1971-01-01

    In order to infer the interplanetary sector polarity from polar geomagnetic field diurnal variations, measurements were carried out at Godhavn and Thule (Denmark) Geomagnetic Observatories. The inferred interplanetary sector polarity was compared with the polarity observed at the same time by Explorer 33 and 35 magnetometers. It is shown that the polarity (toward or away from the sun) of the interplanetary magnetic field can be reliably inferred from observations of the polar cap geomagnetic fields.

  20. Rethinking Field Observations: Strengthening Teacher Education through INFORM

    ERIC Educational Resources Information Center

    Hoyt, Kristin; Terantino, Joe

    2015-01-01

    This article introduces the Instructional Field Observation Rounds Model (INFORM), drawn from the medical profession where resident interns make rounds with experienced physicians, as an alternative approach for conducting classroom observations in pre-service teacher education methods courses. INFORM centers on structured group observations in…

  1. Observations of Strong Magnetic Fields in Nondegenerate Stars

    NASA Astrophysics Data System (ADS)

    Linsky, Jeffrey L.; Schöller, Markus

    2015-10-01

    We review magnetic-field measurements of nondegenerate stars across the Hertzprung-Russell diagram for main sequence, premain sequence, and postmain sequence stars. For stars with complex magnetic-field morphologies, which includes all G-M main sequence stars, the analysis of spectra obtained in polarized vs unpolarized light provides very different magnetic measurements because of the presence or absence of cancellation by oppositely directed magnetic fields within the instrument's spatial resolution. This cancellation can be severe, as indicated by the spatially averaged magnetic field of the Sun viewed as a star. These averaged fields are smaller by a factor of 1000 or more compared to spatially resolved magnetic-field strengths. We explain magnetic-field terms that characterize the fields obtained with different measurement techniques. Magnetic fields typically control the structure of stellar atmospheres in and above the photosphere, the heating rates of stellar chromospheres and coronae, mass and angular momentum loss through stellar winds, chemical peculiarity, and the emission of high energy photons, which is critically important for the evolution of protoplanetary disks and the habitability of exoplanets. Since these effects are governed by the star's magnetic energy, which is proportional to the magnetic-field strength squared and its fractional surface coverage, it is important to measure or reliably infer the true magnetic-field strength and filling factor across a stellar disk. We summarize magnetic-field measurements obtained with the different observing techniques for different types of stars and estimate the highest magnetic-field strengths. We also comment on the different field morphologies observed for stars across the H-R diagram, typically inferred from Zeeman-Doppler imaging and rotational modulation observations,

  2. Intergalactic Magnetic Field Observations and their Fundamental Implications

    NASA Astrophysics Data System (ADS)

    Vachaspati, Tanmay

    2017-01-01

    I will review current observational evidence for helical intergalactic magnetic fields at the 10-14 G level on 10 Mpc length scales. The existence of magnetic fields in cosmic voids and their non-trivial helical structure suggest that they might have originated in the early universe due to CP violating fundamental interactions. The large helicity of the magnetic field suggests a possible crucial role for chiral MHD effects in the early universe. Supported by the DOE.

  3. Variations in the atmospheric electric field at mountainous observation points

    NASA Astrophysics Data System (ADS)

    Adzhiev, A. Kh.; Kupovykh, G. V.

    2015-05-01

    Study of unitary variation in the electric field of the near-surface atmosphere is a topical tasks of atmospheric electricity. This work substantiates the possible registration of global variations in the electric field intensity of the near-surface atmospheric layer at mountainous stations and discusses the results of observations in the Elbrus region.

  4. Synthetic Observations of Magnetic Fields in Protostellar Cores

    NASA Astrophysics Data System (ADS)

    Lee, Joyce W. Y.; Hull, Charles L. H.; Offner, Stella S. R.

    2017-01-01

    The role of magnetic fields in the early stages of star formation is not well constrained. In order to discriminate between different star formation models, we analyze 3D magnetohydrodynamic simulations of low-mass cores and explore the correlation between magnetic field orientation and outflow orientation over time. We produce synthetic observations of dust polarization at resolutions comparable to millimeter-wave dust polarization maps observed by the Combined Array for Research in Millimeter-wave Astronomy and compare these with 2D visualizations of projected magnetic field and column density. Cumulative distribution functions of the projected angle between the magnetic field and outflow show different degrees of alignment in simulations with differing mass-to-flux ratios. The distribution function for the less magnetized core agrees with observations finding random alignment between outflow and field orientations, while the more magnetized core exhibits stronger alignment. We find that fractional polarization increases when the system is viewed such that the magnetic field is close to the plane of the sky, and the values of fractional polarization are consistent with observational measurements. The simulation outflow, which reflects the underlying angular momentum of the accreted gas, changes direction significantly over over the first ∼0.1 Myr of evolution. This movement could lead to the observed random alignment between outflows and the magnetic fields in protostellar cores.

  5. Toroidal and poloidal magnetic fields at Venus. Venus Express observations

    NASA Astrophysics Data System (ADS)

    Dubinin, E.; Fraenz, M.; Woch, J.; Zhang, T. L.; Wei, Y.; Fedorov, A.; Barabash, S.; Lundin, R.

    2013-10-01

    Magnetic field and plasma measurements carried out onboard Venus Express during solar minimum conditions suggest the existence of two kinds of magnetic field configuration in the Venusian ionosphere. We interpret these as the manifestation of two different types of generation mechanisms for the induced magnetosphere. A different magnetic field topology (toroidal and poloidal) arises if the induced currents are driven either by the solar wind motional electric field or by the Faraday electric field—a conducting ionosphere sees the magnetic field carried by solar wind as a time-varying field. At the dayside, both driving agents produce a similar draping pattern of the magnetic field. However, different magnetic field signatures inherent to both induction mechanisms appear at lower altitudes in the terminator region. The conditions at low solar EUV flux when the ionosphere of Venus becomes magnetized seem to be favorable to distinguish between two different types of the induced fields. We present cases of both types of the magnetic field topology. The cases when the effects of the Faraday induction become well noticeable are especially interesting since they provide us with an example of solar wind interaction with a tiny induced dipole field immersed into the ionosphere. Another interesting case when poloidal magnetic fields are evidently displayed is observed when the IMF vector is almost aligned with the solar wind velocity. In general case, both mechanisms of induction probably complement each other.

  6. Inferring Lower Boundary Driving Conditions Using Vector Magnetic Field Observations

    NASA Technical Reports Server (NTRS)

    Schuck, Peter W.; Linton, Mark; Leake, James; MacNeice, Peter; Allred, Joel

    2012-01-01

    Low-beta coronal MHD simulations of realistic CME events require the detailed specification of the magnetic fields, velocities, densities, temperatures, etc., in the low corona. Presently, the most accurate estimates of solar vector magnetic fields are made in the high-beta photosphere. Several techniques have been developed that provide accurate estimates of the associated photospheric plasma velocities such as the Differential Affine Velocity Estimator for Vector Magnetograms and the Poloidal/Toroidal Decomposition. Nominally, these velocities are consistent with the evolution of the radial magnetic field. To evolve the tangential magnetic field radial gradients must be specified. In addition to estimating the photospheric vector magnetic and velocity fields, a further challenge involves incorporating these fields into an MHD simulation. The simulation boundary must be driven, consistent with the numerical boundary equations, with the goal of accurately reproducing the observed magnetic fields and estimated velocities at some height within the simulation. Even if this goal is achieved, many unanswered questions remain. How can the photospheric magnetic fields and velocities be propagated to the low corona through the transition region? At what cadence must we observe the photosphere to realistically simulate the corona? How do we model the magnetic fields and plasma velocities in the quiet Sun? How sensitive are the solutions to other unknowns that must be specified, such as the global solar magnetic field, and the photospheric temperature and density?

  7. Observational testing of magnetospheric magnetic field models at geosynchronous orbit

    SciTech Connect

    Weiss, L.A.; Thomsen, M.F.; Reeves, G.D.; McComas, D.J.

    1996-09-01

    Empirical mode which estimate the magnetic field direction and magnitude at any point within the magnetosphere under a variety of conditions play an important role in space weather forecasting. We report here on a number of different studies aimed at quantitatively evaluating these models, and in particular the Tsyganenko T89a model. The models are evaluated in two basic ways: (1) by comparing the range of magnetic field tilt angles observed at geosynchronous orbit with the ranges predicted for the same locations by the models; and (2) by comparing the observed magnetic field mapping between the ionosphere and geosynchronous orbit (using two-satellite magnetic field conjunctions) with the model predictions at the same locations. We find that while the T89a model predicts reasonably well the basic variation in tilt angle with local time and permits a range of field inclinations adequate to encompass the majority of observed angles on the dawn, dusk, and night sides, it is unable to reproduce the range of inclinations on the dayside. The model also predicts a smaller magnetic latitude range of geosynchronous field line footpoints than the observed two-satellite mapping indicate. Together, these results suggest that the next generation of field models should allow a greater range of stretching, especially in local time sectors away from midnight. It is important to note, however, that any increased range should encompass less-stretched configurations: although there are certainly cases where the models are not sufficiently stretched, we find that on average all magnetic field models tested, including T89a, are too stretched. Finally, in investigating how well the observed degree of field stretch was ordered by various magnetospheric indices, we find that the tilt of the field at geosynchronous orbit is a promising candidate for the incorporation into future models.

  8. Direct observations of field-induced assemblies in magnetite ferrofluids

    NASA Astrophysics Data System (ADS)

    Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil

    2015-03-01

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05-0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  9. Direct observations of field-induced assemblies in magnetite ferrofluids

    SciTech Connect

    Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil

    2015-03-14

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05–0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  10. Direct observations of field-induced assemblies in magnetite ferrofluids

    PubMed Central

    Mousavi, N. S. Susan

    2015-01-01

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05–0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity. PMID:25829566

  11. Direct observations of field-induced assemblies in magnetite ferrofluids.

    PubMed

    Mousavi, N S Susan; Khapli, Sachin D; Kumar, Sunil

    2015-03-14

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05-0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  12. Stellar magnetic fields from four Stokes parameter observations

    NASA Astrophysics Data System (ADS)

    Rusomarov, N.; Kochukhov, O.; Piskunov, N.

    2015-01-01

    Magnetic Doppler imaging (MDI) from observations of four Stokes parameters can uncover new information that is of interest to the evolution and structure of magnetic fields of intermediate and high-mass stars. Our MDI study of the chemically peculiar star HD 24712 from four Stokes parameter observations, obtained with the HARPSpol instrument at the 3.6-m ESO telescope, revealed a magnetic field with strong dipolar component and weak small-scale contributions. This finding gives evidence for the hypothesis that old Ap stars have predominantly dipolar magnetic fields.

  13. Magnetospheric-field distortions observed by OGO 3 and 5.

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Ledley, B. G.; Skillman, T. L.; Heppner, J. P.

    1971-01-01

    The rubidium vapor magnetometer data of the scalar magnetic-field intensity obtained by the OGO 3 and 5 satellites are analyzed to study the magnetospheric-field distortions in terms of the observed field magnitude under quiet and slightly disturbed conditions minus the magnitude of the reference geomagnetic field (delta B). Average contours of equal delta Bs are shown in the geomagnetic noon-midnight and dawn-dusk meridian planes for magnetically quiet and slightly disturbed conditions. The equatorial distribution of observed delta Bs as a function of geocentric distance differs substantially from that expected from the well-known models of the quiet-time ring current. Other findings suggest that there must be a population of low-energy particles with substantial total energy near the equator at distances of 2 to 5 earth radii that has not been recognized as having sufficient energy to inflate the magnetic field.

  14. The mean magnetic field of the sun: Observations at Stanford

    NASA Technical Reports Server (NTRS)

    Scherrer, P. H.; Wilcox, J. M.; Svalgaard, L.; Duvall, T. L., Jr.; Dittmer, P. H.; Gustafson, E. K.

    1977-01-01

    A solar telescope was built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field were made daily since May 1975. The typical mean field magnitude is about 0.15 gauss with typical measurement error less than 0.05 gauss. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (seen near the earth with a 4 day lag). The differences in the observed structures can be understood in terms of a warped current sheet model.

  15. Validating an Environmental Education Field Day Observation Tool

    ERIC Educational Resources Information Center

    Carlson, Stephan P.; Heimlich, Joe E.; Storksdieck, Martin

    2011-01-01

    Environmental Field Days (EFD) are held throughout the country and provide a unique opportunity to involve students in real world science. A study to assess the validity of an observation tool for EFD programs was conducted at the Metro Water Festival with fifth grade students. Items from the observation tool were mapped to students' evaluation…

  16. Constructing the Coronal Magnetic Field: by Correlating Parameterized Magnetic Field Lines with Observed Coronal Plasma Structures

    NASA Technical Reports Server (NTRS)

    Gary, G. A.

    1998-01-01

    The reconstruction of the coronal magnetic field is carried out using a perturbation procedure. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal fluxtubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures (1) that the normal component of the photospheric field remains unchanged, (2) that the field is given in the entire corona, (3) that the field remains divergence free, and (4) that electrical currents are introduced into the field. It is demonstrated that a simple radial parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 Nov 26. At a coronal height of 30 km, the resulting magnetic field is a non-force free magnetic field with the maximum Lorentz force being on the order of 2.6 x 10(exp -9) dyn resulting from an electric current density of $0.13 mu A/ sq m. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.

  17. Detecting Field-Aligned Current Signatures Using MAVEN Observations

    NASA Astrophysics Data System (ADS)

    Hanley, K.; Brain, D.; Weber, T. D.

    2016-12-01

    Currents aligned with magnetic field lines have been observed on multiple planets, including Mars, Mercury, Earth, Saturn, and Jupiter. As documented by Mars Global Surveyor, field-aligned currents occur at Mars near regions of moderate or strong crustal magnetic fields. These currents, identified by the magnetic field perturbations they cause, indicate the acceleration of charged particles toward the Martian atmosphere, which may result in atmospheric heating, ionization, and discrete aurora observed at ultraviolet wavelengths. It is likely that charged particles are removed from the atmosphere via these currents in magnetic cusp regions. At present, the locations and conditions for which field-aligned current systems can occur at Mars are not well understood. We use magnetic field measurements collected by MAVEN between December 2014 and September 2015 to investigate the incidence of low-altitude field-aligned currents on the nightside of the planet in regions of strong crustal fields. These currents have been found to cause perturbations in the magnetic field at magnitudes of 5 nT. We have automated the detection process in order to facilitate future study of field-aligned currents using MAVEN data. First, low-frequency signals caused by spacecraft motion are removed from the data, revealing short-term (1-5 seconds) perturbations. The disturbances due to field-aligned currents are recorded by finding areas where the filtered data exceeds a threshold value for multiple seconds. Current events are then mapped to the planet's surface. We report on the geographic distribution of field-aligned current signatures, as well as their distributions with respect to local time.

  18. Magnetic field observations during the ulysses flyby of jupiter.

    PubMed

    Balogh, A; Dougherty, M K; Forsyth, R J; Southwood, D J; Smith, E J; Tsurutani, B T; Murphy, N; Burton, M E

    1992-09-11

    The Jovian flyby of the Ulysses spacecraft presented the opportunity to confirm and complement the findings of the four previous missions that investigated the structure and dynamics of the Jovian magnetosphere and magnetic field, as well as to explore for the first time the high-latitude dusk side of the magnetosphere and its boundary regions. In addition to confirming the general structure of the dayside magnetosphere, the Ulysses magnetic field measurements also showed that the importance of the current sheet dynamics extends well into the middle and outer magnetosphere. On the dusk side, the magnetic field is swept back significantly toward the magnetotail. The importance of current systems, both azimuthal and field-aligned, in determining the configuration of the field has been strongly highlighted by the Ulysses data. No significant changes have been found in the internal planetary field; however, the need to modify the external current densities with respect to previous observations on the inbound pass shows that Jovian magnetic and magnetospheric models are highly sensitive to both the intensity and the structure assumed for the current sheet and to any time dependence that may be assigned to these. The observations show that all boundaries and boundary layers in the magnetosphere have a very complex microstructure. Waves and wave-like structures were observed throughout the magnetosphere; these included the longest lasting mirror-mode wave trains observed in space.

  19. Magnetic Fields Around the Heliosphere: Theory vs Observations

    NASA Astrophysics Data System (ADS)

    Pogorelov, Nikolai

    2016-07-01

    Voyager in situ measurements of the magnetic field around the heliosphere are the source of invaluable information about the interface between the solar wind (SW) and local interstellar medium (LISM). On the other hand, they are quite challenging for theoretical analysis unless accompanied by remote observations of neutral atoms the Interstellar Boundary Explorer (IBEX) and Ulysses missions. Of particular interest is the fine structure of the heliopause due to its instability and possible magnetic reconnection. Both phenomena may have contributed to the remarkable changes in the galactic and anomalous cosmic ray fluxes observed by Voyager 1 within a one-month period of 2012 after which the spacecraft penetrated into the LISM. Draping of the heliopause by the interstellar magnetic field affects the position of the bright ribbon of enhanced ENA flux observed by IBEX on the celestial sphere and 2-3 kHz radio emission caused by shock propagation through the outer heliosheath observed by Voyager 1. Interstellar magnetic field determines the structure of the bow wave in front of the heliopause. Moreover, magnetic fields define the orientation and shape of the heliotail, the features of which have been observed by IBEX. Recent numerical simulations show that the details of the large-scale interstellar magnetic field modification caused by the presence of the heliotail may be the source of the observed 1-10 TeV cosmic ray anisotropy studied in detail in numerous air shower measurements around the world. In this paper, an overview will be given of the recent theoretical and simulations results describing the magnetic field distribution around the heliosphere. The objective of the talk is to connect observational and theoretical results, and outline challenges that are going to inspire the heliospheric community in the coming years.

  20. Cosmic microwave background observables of small field models of inflation

    SciTech Connect

    Ben-Dayan, Ido; Brustein, Ram E-mail: ramyb@bgu.ac.il

    2010-09-01

    We construct a class of single small field models of inflation that can predict, contrary to popular wisdom, an observable gravitational wave signal in the cosmic microwave background anisotropies. The spectral index, its running, the tensor to scalar ratio and the number of e-folds can cover all the parameter space currently allowed by cosmological observations. A unique feature of models in this class is their ability to predict a negative spectral index running in accordance with recent cosmic microwave background observations. We discuss the new class of models from an effective field theory perspective and show that if the dimensionless trilinear coupling is small, as required for consistency, then the observed spectral index running implies a high scale of inflation and hence an observable gravitational wave signal. All the models share a distinct prediction of higher power at smaller scales, making them easy targets for detection.

  1. In the field: notes on observation in qualitative research.

    PubMed

    Mulhall, Anne

    2003-02-01

    Observation is used in research in two ways - structured and unstructured. Which of these methods to choose depends on the research question but will be defined predominantly by the paradigm underlying each study. Positivistic research generally uses structured observation and interpretist/naturalistic paradigms use unstructured observation. This paper is concerned with unstructured observation. To discuss the importance of unstructured observation as a research method and to examine critically the problems associated with both access and field notes. Although unstructured observation has been used in nursing research, it is less favoured than the interview. Furthermore, although some of the dilemmas concerned with observation such as the role of the researcher, covert research and informed consent have received attention in the nursing literature, other aspects remain relatively unexplored. In particular little has been written concerning access to the field and field notes. Both of these aspects have practical and theoretical considerations that require the attention of the researcher. This omission may partly explain nurses' apparent reluctance to use unstructured observation in their studies. This paper seeks to redress this situation.

  2. Swarm Observations of Field Aligned Currents during Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    Le, G.; Luhr, H.; Anderson, B. J.; Strangeway, R. J.; Russell, C. T.; Slavin, J. A.; Bromund, K. R.; Plaschke, F.; Magnes, W.; Fischer, D.; Nakamura, R.; Leinweber, H. K.; Torbert, R. B.; Le Contel, O.; Oliveira, D. M.; Raeder, J.; Kepko, L.

    2015-12-01

    Field-aligned currents connect the Earth's magnetosphere to the high latitude ionosphere, and provide a main channel for energy transfer from the magnetosphere to the ionosphere. They are driven by solar wind-magnetosphere interactions and respond dynamically to changes in the solar wind and interplanetary magnetic field. Enhanced interaction during geomagnetic storms significantly intensifies their strength and variability. In this paper, we review our recent observations of field-aligned currents (FACs) during geomagnetic storms using observations from polar orbiting Swarm constellation as well as the Active Magnetosphere and Polar Electrodynamics Response Experiment (AMPERE). Both temporal resolutions and spatial coverage of these observations provide new insights in understanding the FACs and the magnetosphere-ionosphere coupling. We will discuss their spatial and temporal evolutions, ionospheric closure currents, and hemispheric asymmetry during storms.

  3. On radial heliospheric magnetic fields: Voyager 2 observation and model

    NASA Astrophysics Data System (ADS)

    Wang, C.; Richardson, J. D.; Burlaga, L. F.; Ness, N. F.

    2003-05-01

    The heliospheric magnetic field (HMF) direction, on average, conforms well to the Parker spiral. However, numerous examples of events where the HMF is oriented in near-radial directions for many hours have been reported on the basis of observations inside 5 AU from spacecraft such as ISEE-3 and Ulysses. The magnetic field data observed by Voyager 2 from launch in 1977 through the end of 1982 (i.e., between 1 and ˜10 AU) were searched for all instances of radial fields with durations of 6 hours or more. Radial fields of significant durations at large distances are unusual as the Parker spiral is very tightly wound. The radial HMF events in the inner heliosphere typically occur at times when the solar wind speed is declining gradually, while they tend to be associated with steady wind speeds at distances beyond ˜6 AU. The durations of these events appear to be independent of distance and solar cycle, with an average duration of ˜11 hours. They generally are not associated with interplanetary coronal mass ejections (ICMEs). Possible generation mechanisms of the radial field events related to speed variations near the Sun are investigated by use of a MHD model. We find that a noticeable low-speed plateau of limited duration in solar wind speed near the Sun can produce radial field events having durations of the order of 10 hours in the heliosphere as observed by Voyager 2.

  4. Magnetic Field Observations near Mercury: Preliminary Results from Mariner 10.

    PubMed

    Ness, N F; Behannon, K W; Lepping, R P; Whang, Y C; Schatten, K H

    1974-07-12

    Results are presented from a preliminary analysis of data obtained near Mercury on 29 March 1974 by the NASA-GSFC magnetic field experiment on Mariner 10. Rather unexpectedly, a very well-developed, detached bow shock wave, which develops as the super-Alfvénic solar wind interacts with the planet, has been observed. In addition, a magnetosphere-like region, with maximum field strength of 98 gammas at closest approach (704 kilometers altitude), has been observed, contained within boundaries similar to the terrestrial magnetopause. The obstacle deflecting the solar wind flow is global in size, but the origin of the enhanced magnetic field has not yet been uniquely established. The field may be intrinsic to the planet and distorted by interaction with the solar wind. It may also be associated with a complex induction process whereby the planetary interior-atmosphere-ionosphere interacts with the solar wind flow to generate the observed field by a dynamo action. The complete body of data favors the preliminary conclusion that Mercury has an intrinsic magnetic field. If this is correct, it represents a major scientific discovery in planetary magnetism and will have considerable impact on studies of the origin of the solar system.

  5. Inferring effective field observables from a discrete model

    NASA Astrophysics Data System (ADS)

    Bény, Cédric

    2017-01-01

    A spin system on a lattice can usually be modeled at large scales by an effective quantum field theory. A key mathematical result relating the two descriptions is the quantum central limit theorem, which shows that certain spin observables satisfy an algebra of bosonic fields under certain conditions. Here, we show that these particular observables and conditions are the relevant ones for an observer with certain limited abilities to resolve spatial locations as well as spin values. This is shown by computing the asymptotic behaviour of a quantum Fisher information metric as function of the resolution parameters. The relevant observables characterise the state perturbations whose distinguishability does not decay too fast as a function of spatial or spin resolution.

  6. Polar Magnetic Fields Observed During the Last Four Solar Minima

    NASA Astrophysics Data System (ADS)

    Sun, X.; Liu, Y.; Hoeksema, J. T.

    2008-12-01

    The Sun's polar fields during the current minimum are the weakest in at least four solar cycles. The field strengths are fairly symmetric, unlike at least the two previous minima. We compare data from the Wilcox Solar Observatory (WSO) and Michelson Doppler Imager (MDI) to follow the polar field changes since 1976. The polar field is never observed well from Earth because the ecliptic lies near the Sun's equator, and each year the view of the north (south) is completely hidden for several months around March 7 (September 7). Analysis of the most favorably oriented MDI synoptic maps each year allows us to derive the fairly slowly evolving large-scale polar magnetic field pattern from 1996 to the present. We account for differential rotation and other geometric effects. The analysis allows us to provide a useful interpolated or extrapolated correction that can be smoothly incorporated into the global synoptic or synchronic maps above about 70 degrees latitude. The polar field is important in modeling the large-scale coronal and heliospheric field, particularly at minimum. Even though there has been extremely little solar activity over the last several months, at the current solar minimum the structure of the corona is much less equatorial than usual, in part because the polar fields are relatively weak.

  7. Constructing the Coronal Magnetic Field by Correlating Parameterized Magnetic Field Lines with Observed Coronal Plasma Structures

    NASA Technical Reports Server (NTRS)

    Allen, Gary G.; Alexander, David

    1999-01-01

    A method is presented for constructing the coronal magnetic field from photospheric magnetograms and observed coronal loops. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal flux tubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures that (1) the normal component of the photospheric field remains unchanged, (2) the field is given in the entire corona over an active region, (3) the field remains divergence-free, and 4electric currents are introduced into the field. It is demonstrated that a parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 November 26. The result is a non-force-free magnetic field with the Lorentz force being of the order of 10(exp -5.5) g per s(exp 2) resulting from an electric current density of 0.79 micro A per m(exp 2). Calculations show that the plasma beta becomes larger than unity at a strong non-radial currents requires low height of about 0.25 solar radii supporting the non-force-free conclusion. The presence of such strong non-radial currents requires large transverse pressure gradients fo maintain a magnetostatic atmosphere, required by the relatively persistent nature of the coronal structures observed in AR 7999. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.

  8. Ulysses observations of latitude gradients in the heliospheric magnetic field

    NASA Technical Reports Server (NTRS)

    Smith, E. J.; Balogh, A.; Lepping, R. P.; Neugebauer, M.; Phillips, J.; Tsurutani, B. T.

    1995-01-01

    Several parameters measured by Ulysses as it traveled southward to heliographic latitudes of -50 deg are presented and analyzed. The radial component of the magnetic field, averaged over 5 deg latitude increments and extrapolated back to 1 AU, is found to agree with baseline measurements provided by IMP-8. There is little, if any, evidence of a latitude gradient, a result consistent with the dominance of the magnetic field associated with the heliospheric current sheet and with recent models which include the effect of the current sheet as well as of source surface fields. Thus far, the spiral angle agrees with the Parker spiral assuming a rate of rotation of the field lines at the Sun equal to the equatorial value. No evidence is seen of either a change in rotation rate with latitude or an unwinding of the spiral as suggested by a recent analysis. Hourly variances in the field magnitude and in the sum of the variances in the components, normalized to the square of the observed field strenght, show the former to be independent of latitude while the latter shows a strong increase with latitude. These two observations are shown to be associated with Alfven waves that are continuously present at high latitudes. The waves have large amplitudes, extend to long periods, and have important implications for galactic cosmic rays and the solar wind.

  9. Polarimetric Radar and Electric Field Observations of a Multicell Storm

    NASA Astrophysics Data System (ADS)

    Bruning, E. C.; Rust, W. D.; Macgorman, D. R.; Schuur, T.; Straka, J.; Krehbiel, P.; Rison, W.

    2004-12-01

    Much prior thunderstorm electrification research uses one-dimensional analyses of vertical profiles of the thunderstorm electric field, often incorporating cloud-to-ground lighting strike data and radar reflectivity observations. New instrumentation has provided the opportunity to investigate thunderstorm electrification and lightning in greater spatial detail. We present data from the late stages of a multicellular storm occurring on 28-29 June 2004 during the Thunderstorm Electrification and Lightning Experiment (TELEX) field program in central Oklahoma. Three-dimensional (3-D) vector electric field (measured by balloon sounding), total lighting mapping, and polarimetric radar are utilized. The maximum measured electric field exceeded -150 kV m-1. Preliminary charge analysis using the electric field vectors indicates a positive layer below 0\\deg C, followed by a large negative layer just above the melting level. Another positive and negative layer follow this. Polarimetric radar signatures within the melting layer are examined in the context of the electric field observations. Mapped lightning flashes are used to clarify and support the inferred charge structure. An interactive 3-D display is used to combine these data sources. Temporal evolution of the storm is also considered.

  10. Screwworm ecology from field observations to satellite imagery

    USDA-ARS?s Scientific Manuscript database

    Screwworm fly, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae), in its larval stage is a parasite of warm-blooded animals. Screwworm has been successfully eradicated from the United Sates and Central America using the sterile insect technique. Here we present how the field observations o...

  11. Observational constraints on gauge field production in axion inflation

    SciTech Connect

    Meerburg, P.D.; Pajer, E. E-mail: enrico.pajer@gmail.com

    2013-02-01

    Models of axion inflation are particularly interesting since they provide a natural justification for the flatness of the potential over a super-Planckian distance, namely the approximate shift-symmetry of the inflaton. In addition, most of the observational consequences are directly related to this symmetry and hence are correlated. Large tensor modes can be accompanied by the observable effects of a the shift-symmetric coupling φF F-tilde to a gauge field. During inflation this coupling leads to a copious production of gauge quanta and consequently a very distinct modification of the primordial curvature perturbations. In this work we compare these predictions with observations. We find that the leading constraint on the model comes from the CMB power spectrum when considering both WMAP 7-year and ACT data. The bispectrum generated by the non-Gaussian inverse-decay of the gauge field leads to a comparable but slightly weaker constraint. There is also a constraint from μ-distortion using TRIS plus COBE/FIRAS data, but it is much weaker. Finally we comment on a generalization of the model to massive gauge fields. When the mass is generated by some light Higgs field, observably large local non-Gaussianity can be produced.

  12. The interplanetary magnetic field observed by Juno enroute to Jupiter

    NASA Astrophysics Data System (ADS)

    Gruesbeck, Jacob R.; Gershman, Daniel J.; Espley, Jared R.; Connerney, John E. P.

    2017-06-01

    The Juno spacecraft was launched on 5 August 2011 and spent nearly 5 years traveling through the inner heliosphere on its way to Jupiter. The Magnetic Field Investigation was powered on shortly after launch and obtained vector measurements of the interplanetary magnetic field (IMF) at sample rates from 1 to 64 samples/second. The evolution of the magnetic field with radial distance from the Sun is compared to similar observations obtained by Voyager 1 and 2 and the Ulysses spacecraft, allowing a comparison of the radial evolution between prior solar cycles and the current depressed one. During the current solar cycle, the strength of the IMF has decreased throughout the inner heliosphere. A comparison of the variance of the normal component of the magnetic field shows that near Earth the variability of the IMF is similar during all three solar cycles but may be less at greater radial distances.

  13. The Global Magnetic Field of Mercury from MESSENGER Orbital Observations

    NASA Astrophysics Data System (ADS)

    Anderson, Brian J.; Johnson, Catherine L.; Korth, Haje; Purucker, Michael E.; Winslow, Reka M.; Slavin, James A.; Solomon, Sean C.; McNutt, Ralph L.; Raines, Jim M.; Zurbuchen, Thomas H.

    2011-09-01

    Magnetometer data acquired by the MESSENGER spacecraft in orbit about Mercury permit the separation of internal and external magnetic field contributions. The global planetary field is represented as a southward-directed, spin-aligned, offset dipole centered on the spin axis. Positions where the cylindrical radial magnetic field component vanishes were used to map the magnetic equator and reveal an offset of 484 ± 11 kilometers northward of the geographic equator. The magnetic axis is tilted by less than 3° from the rotation axis. A magnetopause and tail-current model was defined by using 332 magnetopause crossing locations. Residuals of the net external and offset-dipole fields from observations north of 30°N yield a best-fit planetary moment of 195 ± 10 nanotesla-RM3, where RM is Mercury’s mean radius.

  14. Implications of observing and writing field notes through different lenses

    PubMed Central

    Hellesø, Ragnhild; Melby, Line; Hauge, Solveig

    2015-01-01

    Background From a philosophy of science perspective, the literature has posited that different research approaches influence field studies. Studies addressing interdisciplinary research have focused on the challenges of organizing and running interdisciplinary teams, cultural differences between and within disciplines, and constraints in conducting interdisciplinary research. Studies exploring and discussing the process and outcome of transferring observations to notes from an interdisciplinary point of view are not identified. The aim of this paper is to explore the characteristics of field notes created by researchers representing different disciplines and experiences. Methods A case study using a modified dynamic observation method was employed. The analyses were initiated by a researcher who had not been involved in the data collection. The field notes were analyzed using three main steps. Results The structures of both researchers’ field notes were characterized by similarities in their descriptions, but the notes’ foci and analytical levels differed. Conclusion The findings contribute new insights concerning the execution of interdisciplinary observational studies. Our findings demonstrate that entering the field with different lenses produced richer and more varied data, providing a broader platform from which to discuss and interpret a study’s findings. From a theoretical point of view, the findings enable a more nuanced discussion and a conceptual elaboration regarding how observational approaches should be pursued in future studies. On a practical level, the findings show that even if the researchers agree on what the overall focus in the observations should be, differences can occur in both their focus and analytical level throughout the study. PMID:25914543

  15. THE 2012 HUBBLE ULTRA DEEP FIELD (UDF12): OBSERVATIONAL OVERVIEW

    SciTech Connect

    Koekemoer, Anton M.; Ellis, Richard S.; Schenker, Matthew A.; McLure, Ross J.; Dunlop, James S.; Bowler, Rebecca A. A.; Rogers, Alexander B.; Curtis-Lake, Emma; Cirasuolo, Michele; Wild, V.; Targett, T.; Robertson, Brant E.; Schneider, Evan; Stark, Daniel P.; Ono, Yoshiaki; Ouchi, Masami; Charlot, Stephane; Furlanetto, Steven R.

    2013-11-01

    We present the 2012 Hubble Ultra Deep Field campaign (UDF12), a large 128 orbit Cycle 19 Hubble Space Telescope program aimed at extending previous Wide Field Camera 3 (WFC3)/IR observations of the UDF by quadrupling the exposure time in the F105W filter, imaging in an additional F140W filter, and extending the F160W exposure time by 50%, as well as adding an extremely deep parallel field with the Advanced Camera for Surveys (ACS) in the F814W filter with a total exposure time of 128 orbits. The principal scientific goal of this project is to determine whether galaxies reionized the universe; our observations are designed to provide a robust determination of the star formation density at z ∼> 8, improve measurements of the ultraviolet continuum slope at z ∼ 7-8, facilitate the construction of new samples of z ∼ 9-10 candidates, and enable the detection of sources up to z ∼ 12. For this project we committed to combining these and other WFC3/IR imaging observations of the UDF area into a single homogeneous dataset to provide the deepest near-infrared observations of the sky. In this paper we present the observational overview of the project and describe the procedures used in reducing the data as well as the final products that were produced. We present the details of several special procedures that we implemented to correct calibration issues in the data for both the WFC3/IR observations of the main UDF field and our deep 128 orbit ACS/WFC F814W parallel field image, including treatment for persistence, correction for time-variable sky backgrounds, and astrometric alignment to an accuracy of a few milliarcseconds. We release the full, combined mosaics comprising a single, unified set of mosaics of the UDF, providing the deepest near-infrared blank-field view of the universe currently achievable, reaching magnitudes as deep as AB ∼ 30 mag in the near-infrared, and yielding a legacy dataset on this field.

  16. Possible observation of the isotope effect during field evaporation

    NASA Astrophysics Data System (ADS)

    Golubev, O. L.; Blashenkov, N. M.

    2016-01-01

    The field evaporation of tungsten at high temperatures (T ~ 2000 K) has been studied using a magnetic mass spectrometer equipped with a field ion source. Only low-charge ions (W+2 and W+) have been observed in the course of evaporation for all tungsten isotopes. For singly charged ions only, the number of ions of the heaviest isotope, 186W+, was about one order of magnitude lower than that corresponding to the standard isotope ratio for natural tungsten. An explanation of this anomalous phenomenon is proposed.

  17. The observer's ghost: notes on a field space connection

    NASA Astrophysics Data System (ADS)

    Gomes, Henrique; Riello, Aldo

    2017-05-01

    We introduce a functional covariant differential as a tool for studying field space geometry in a manifestly covariant way. We then touch upon its role in gauge theories and general relativity over bounded regions, and in BRST symmetry. Due to the Gribov problem, we argue that our formalism — allowing for a non-vanishing functional curvature — is necessary for a global treatment of gauge-invariance in field space. We conclude by suggesting that the structures we introduce satisfactorily implement the notion of a (non-asymptotic) observer in gauge theories and general relativity.

  18. Magnetic Field Observation around Current Path by Magnetic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Saida, Daisuke; Takahashi, Takuji

    2004-07-01

    The magnetic field around a GaAs/AlGaAs mesa stripe induced by an AC current in the range of 0.3-15.6 μA was observed by magnetic force microscopy (MFM). To confirm the possibility of the vector decomposition of the current-induced magnetic field gradient, we compared the magnetic force signals in the cases of parallel and perpendicular configurations between the MFM cantilever and the current path. In addition, we proposed a novel way of eliminating some effects of electrostatic force, by which a good linearity in the magnetic force signals against the currents was achieved. The spatial resolution of this method was also discussed.

  19. Near-field observation of light propagation in nanocoax waveguides.

    PubMed

    Merlo, Juan M; Ye, Fan; Rizal, Binod; Burns, Michael J; Naughton, Michael J

    2014-06-16

    We report the observation of propagating modes of visible and near infrared light in nanoscale coaxial (metal-dielectric-metal) structures, using near-field scanning optical microscopy. Together with numerical calculations, we show that the propagated modes have different nature depending on the excitation wavelength, i.e., plasmonic TE11 and TE21 modes in the near infrared and photonic TE31, TE41 and TM11 modes in the visible. Far field transmission out of the nanocoaxes is dominated by the superposition of Fabry-Perot cavity modes resonating in the structures, consistent with theory. Such coaxial optical waveguides may be useful for future nanoscale photonic systems.

  20. Observations of magnetic fields on solar-type stars

    NASA Technical Reports Server (NTRS)

    Marcy, G. W.

    1982-01-01

    Magnetic-field observations were carried out for 29 G and K main-sequence stars. The area covering-factors of magnetic regions tends to be greater in the K dwarfs than in the G dwarfs. However, no spectral-type dependence is found for the field strengths, contrary to predictions that pressure equilibrium with the ambient photospheric gas pressure would determine the surface field strengths. Coronal soft X-ray fluxes from the G and K dwarfs correlate well with the fraction of the stellar surface covered by magnetic regions. The dependence of coronal soft X-ray fluxes on photospheric field strengths is consistent with Stein's predicted generation-rates for Alfven waves. These dependences are inconsistent with the one dynamo model for which a specific prediction is offered. Finally, time variability of magnetic fields is seen on the two active stars that have been extensively monitored. Significant changes in magnetic fields are seen to occur on timescales as short as one day.

  1. Estimating thermal performance curves from repeated field observations.

    PubMed

    Childress, Evan S; Letcher, Benjamin H

    2017-03-08

    Estimating thermal performance of organisms is critical for understanding population distributions and dynamics and predicting responses to climate change. Typically, performance curves are estimated using laboratory studies to isolate temperature effects, but other abiotic and biotic factors influence temperature-performance relationships in nature reducing these models' predictive ability. We present a model for estimating thermal performance curves from repeated field observations that includes environmental and individual variation. We fit the model in a Bayesian framework using MCMC sampling, which allowed for estimation of unobserved latent growth while propagating uncertainty. Fitting the model to simulated data varying in sampling design and parameter values demonstrated that the parameter estimates were accurate, precise, and unbiased. Fitting the model to individual growth data from wild trout revealed high out-of-sample predictive ability relative to laboratory-derived models, which produced more biased predictions for field performance. The field-based estimates of thermal maxima were lower than those based on laboratory studies. Under warming temperature scenarios, field-derived performance models predicted stronger declines in body size than laboratory-derived models, suggesting that laboratory-based models may underestimate climate change effects. The presented model estimates true, realized field performance, avoiding assumptions required for applying laboratory-based models to field performance, which should improve estimates of performance under climate change and advance thermal ecology. This article is protected by copyright. All rights reserved.

  2. Observation of Field-Emission Dependence on Stored Energy.

    PubMed

    Shao, Jiahang; Antipov, Sergey P; Baryshev, Sergey V; Chen, Huaibi; Conde, Manoel; Doran, Darrell S; Gai, Wei; Jing, Chunguang; Liu, Wanming; Power, John; Qiu, Jiaqi; Shi, Jiaru; Wang, Dan; Wang, Faya; Whiteford, Charles E; Wisniewski, Eric; Xiao, Liling

    2015-12-31

    Field emission from a solid metal surface has been continuously studied for a century over macroscopic to atomic scales. It is general knowledge that, other than the surface properties, the emitted current is governed solely by the applied electric field. A pin cathode has been used to study the dependence of field emission on stored energy in an L-band rf gun. The stored energy was changed by adjusting the axial position (distance between the cathode base and the gun back surface) of the cathode while the applied electric field on the cathode tip is kept constant. A very strong correlation of the field-emission current with the stored energy has been observed. While eliminating all possible interfering sources, an enhancement of the current by a factor of 5 was obtained as the stored energy was increased by a factor of 3. It implies that under certain circumstances a localized field emission may be significantly altered by the global parameters in a system.

  3. Observation of field emission dependence on stored energy

    SciTech Connect

    Shao, Jiahang; Antipov, Sergey P.; Baryshev, Sergey V.; Chen, Huaibi; Conde, Manoel; Doran, Darrell S.; Gai, Wei; Jing, Chunguang; Liu, Wanming; Power, John; Qiu, Jiaqi; Shi, Jiaru; Wang, Dan; Wang, Faya; Whiteford, Charles E.; Wisniewski, Eric; Xiao, Liling

    2015-12-23

    Field emission from a solid metal surface has been continuously studied for a century over macroscopic to atomic scales. It is general knowledge that, other than the surface properties, the emitted current is governed solely by the applied electric field. A pin cathode has been used to study the dependence of field emission on stored energy in an L-band rf gun. The stored energy was changed by adjusting the axial position (distance between the cathode base and the gun back surface) of the cathode while the applied electric field on the cathode tip is kept constant. Avery strong correlation of the field-emission current with the stored energy has been observed. While eliminating all possible interfering sources, an enhancement of the current by a factor of 5 was obtained as the stored energy was increased by a factor of 3. It implies that under certain circumstances a localized field emission may be significantly altered by the global parameters in a system.

  4. Estimating thermal performance curves from repeated field observations

    USGS Publications Warehouse

    Childress, Evan; Letcher, Benjamin H.

    2017-01-01

    Estimating thermal performance of organisms is critical for understanding population distributions and dynamics and predicting responses to climate change. Typically, performance curves are estimated using laboratory studies to isolate temperature effects, but other abiotic and biotic factors influence temperature-performance relationships in nature reducing these models' predictive ability. We present a model for estimating thermal performance curves from repeated field observations that includes environmental and individual variation. We fit the model in a Bayesian framework using MCMC sampling, which allowed for estimation of unobserved latent growth while propagating uncertainty. Fitting the model to simulated data varying in sampling design and parameter values demonstrated that the parameter estimates were accurate, precise, and unbiased. Fitting the model to individual growth data from wild trout revealed high out-of-sample predictive ability relative to laboratory-derived models, which produced more biased predictions for field performance. The field-based estimates of thermal maxima were lower than those based on laboratory studies. Under warming temperature scenarios, field-derived performance models predicted stronger declines in body size than laboratory-derived models, suggesting that laboratory-based models may underestimate climate change effects. The presented model estimates true, realized field performance, avoiding assumptions required for applying laboratory-based models to field performance, which should improve estimates of performance under climate change and advance thermal ecology.

  5. MESSENGER Observations of Induced Magnetic Fields at Mercury

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.; Winslow, R. M.; Anderson, B. J.; Korth, H.; Purucker, M. E.; Heyner, D.; Phillips, R. J.; Slavin, J. A.; Benna, M.; Solomon, S. C.

    2013-12-01

    We use orbital data from the Magnetometer (MAG) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft to study induction signals from Mercury's core. The weak dipole moment (190 nT-RM3, where RM is Mercury's radius) yields a mean subsolar magnetopause distance,RSS, from the dipole origin of 1.45 RM. Time variations in Mercury's magnetopause position, and hence in the magnetopause fields, are driven by changes in solar wind dynamic pressure, Pram, and induce currents in Mercury's interior, in particular at the top of the large, highly conductive core. Mercury's eccentric orbit leads to periodic, annual variations in Pram with an amplitude of ˜50% of the mean Pram. Shorter-timescale, higher-amplitude variations in Pram also occur due to variability in the solar wind. We use a model of Mercury's magnetosphere derived from MESSENGER observations together with a two-layer, radial conductivity model to calculate the expected geometry and magnitude of induced field signatures. The inducing field geometry is obtained via a spherical harmonic expansion of the model magnetopause field at distinct RSS values corresponding to the range observed in MESSENGER MAG data. For the two-layer model and time variations in the field with periods longer than ~1 h, the transfer function between the inducing and induced fields depends only on the spherical harmonic degree and on the ratio of the core radius to the planetary radius. We observe two lines of evidence for an annual induced signature at Mercury. First, RSS varies with heliocentric distance, Rh, as Rhb where b < 1/3. Second, a stronger planetary dipole moment is observed at perihelion than at aphelion. The magnitudes of the observed signals are consistent with the recent estimate of Mercury's core radius (2020 × 30 km) derived from gravity and spin-state data, and independently rule out a core radius less than ˜1900 km. Larger amplitude induced signals are observed in association with

  6. Probing the Earth's core with magnetic field observations from Swarm

    NASA Astrophysics Data System (ADS)

    Finlay, Christopher; Olsen, Nils; Kotsiaros, Stavros; Gillet, Nicolas; Tøffner-Clausen, Lars

    2016-07-01

    By far the largest part of the Earth's magnetic field is generated by motions taking place within our planet's liquid metal outer core. Variations of this core-generated field thus provide a unique means of probing the dynamics taking place in the deepest reaches of the Earth. In this contribution we present a new high resolution model of the core-generated magnetic field, and its recent time changes, derived from a dataset that includes more two years of observations from the Swarm mission. Resulting inferences regarding the underlying core flow, its dynamics, and the nature of the geodynamo process will be discussed. The CHAOS-6 geomagnetic field model, covering the interval 1999-2016, is derived from magnetic data collected by the three Swarm missions, as well as the earlier CHAMP and Oersted satellites, and monthly means data collected from 160 ground observatories. Advantage is taken of the constellation aspect of the Swarm mission by ingesting both scalar and vector field differences along-track and across track between the lower pair of Swarm satellites. The internal part of the model consists of a spherical harmonic (SH) expansion, time-dependent for degrees 20 and below. The model coefficients are estimated using a regularized, iteratively reweighted, least squares scheme involving Huber weights. At Earth's surface, CHAOS-6 shows evidence for positive acceleration of the field intensity in 2015 over a broad area around longitude 90deg E that is also seen at ground observatories such as Novosibirsk. At the core surface, we are able to map the secular variation (linear trend in the magnetic field) up to SH degree 16. The radial field acceleration at the core surface in 2015 is found be largest at low latitudes under the India-South East Asia region and under the region of northern South America, as well as at high northern latitudes under Alaska and Siberia. Surprisingly, there is also evidence for some acceleration in the central Pacific region, for example

  7. An explanation for parallel electric field pulses observed over thunderstorms

    NASA Astrophysics Data System (ADS)

    Kelley, M. C.; Barnum, B. H.

    2009-10-01

    Every electric field instrument flown on sounding rockets over a thunderstorm has detected pulses of electric fields parallel to the Earth's magnetic field associated with every strike. This paper describes the ionospheric signatures found during a flight from Wallops Island, Virginia, on 2 September 1995. The electric field results in a drifting Maxwellian corresponding to energies up to 1 eV. The distribution function relaxes because of elastic and inelastic collisions, resulting in electron heating up to 4000-5000 K and potentially observable red line emissions and enhanced ISR electron temperatures. The field strength scales with the current in cloud-to-ground strikes and falls off as r -1 with distance. Pulses of both polarities are found, although most electric fields are downward, parallel to the magnetic field. The pulse may be the reaction of ambient plasma to a current pulse carried at the whistler packet's highest group velocity. The charge source required to produce the electric field is very likely electrons of a few keV traveling at the packet velocity. We conjecture that the current source is the divergence of the current flowing at mesospheric heights, the phenomenon called an elve. The whistler packet's effective radiated power is as high as 25 mW at ionospheric heights, comparable to some ionospheric heater transmissions. Comparing the Poynting flux at the base of the ionosphere with flux an equal distance away along the ground, some 30 db are lost in the mesosphere. Another 10 db are lost in the transition from free space to the whistler mode.

  8. MESSENGER observations of induced magnetic fields in Mercury's core

    NASA Astrophysics Data System (ADS)

    Johnson, Catherine L.; Philpott, Lydia C.; Anderson, Brian J.; Korth, Haje; Hauck, Steven A.; Heyner, Daniel; Phillips, Roger J.; Winslow, Reka M.; Solomon, Sean C.

    2016-03-01

    Orbital data from the Magnetometer on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft allow investigation of magnetic fields induced at the top of Mercury's core by time-varying magnetospheric fields. We used 15 Mercury years of observations of the magnetopause position as well as the magnetic field inside the magnetosphere to establish the presence and magnitude of an annual induction signal. Our results indicate an annual change in the internal axial dipole term, g10, of 7.5 to 9.5 nT. For negligible mantle conductivity, the average annual induction signal provides an estimate of Mercury's core radius to within ±90 km, independent of geodetic results. Larger induction signals during extreme events are expected but are challenging to identify because of reconnection-driven erosion. Our results indicate that the magnetopause reaches the dayside planetary surface 1.5-4% of the time.

  9. Mapping the Frontier Fields with Chandra X-ray Observations

    NASA Astrophysics Data System (ADS)

    Jones, Christine

    2015-08-01

    Chandra has observed both the clusters and the parallel fields in four of the Frontier Fields. These observations allow us to dramatically improve our understanding of cluster mergers through the detailed mapping of the hot cluster gas compared with high resolution mass maps and, by mapping the gas temperature and pressure, identify merger shocks. A comparison of the lensing maps and the Chandra images allows us to identify subclusters and determine if these have been stripped of their hot gas. In addition the HST images show unusual galaxies (e.g. jellyfish) whose morphologies may have resulted from interactions with the hot intracluster medium. Finally, we will report on any close pairs of AGN, which are candidates for gravitationally lensed QSOs.

  10. Observation of Excited State Spin Ordering under Pulsed Magnetic Field

    NASA Astrophysics Data System (ADS)

    Amaya, Kiichi; Karaki, Yoshitomo; Yamada, Norikatsu; Haseda, Taiichiro

    1981-10-01

    Spin ordering among excited levels in NaNi Acac3\\cdotbenzene is observed in the course of pulsed adiabatic magnetization with sweep rate of 105 T/sec. For initial temperatures below 1 K, dM/dt signals give the characteristic double peaks around the field of 2.11 T where the excited singlet and the upper state of the ground doublet crosses.

  11. Cosmological observables in multi-field inflation with a non-flat field space

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Li, Tianjun; Shukla, Pramod

    2014-10-01

    Using δN formalism, in the context of a generic multi-field inflation driven on a non-flat field space background, we revisit the analytic expressions of the various cosmological observables such as scalar/tensor power spectra, scalar/tensor spectral tilts, non-Gaussianity parameters, tensor-to-scalar ratio, and the various runnings of these observables. In our backward formalism approach, the subsequent expressions of observables automatically include the terms beyond the leading order slow-roll expansion correcting many of the expression at subleading order. To connect our analysis properly with the earlier results, we rederive the (well) known (single field) expressions in the limiting cases of our generic formulae. Further, in the light of PLANCK results, we examine for the compatibility of the consistency relations within the slow-roll regime of a two-field roulette poly-instanton inflation realized in the context of large volume scenarios.

  12. Observation of Dirac monopoles in a synthetic magnetic field

    NASA Astrophysics Data System (ADS)

    Ray, M. W.; Ruokokoski, E.; Kandel, S.; Möttönen, M.; Hall, D. S.

    2014-01-01

    Magnetic monopoles--particles that behave as isolated north or south magnetic poles--have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac's 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin ices and other systems, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3 (refs 10, 11, 12, 13). Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose-Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.

  13. Observation of Dirac monopoles in a synthetic magnetic field.

    PubMed

    Ray, M W; Ruokokoski, E; Kandel, S; Möttönen, M; Hall, D S

    2014-01-30

    Magnetic monopoles--particles that behave as isolated north or south magnetic poles--have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac's 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin ices and other systems, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3 (refs 10-13). Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose-Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.

  14. Another Piece of the Elephant: Chromospheric Vector Field Observations

    NASA Astrophysics Data System (ADS)

    Leka, K. D.; Metcalf, T. R.; Mickey, D. L.

    2005-05-01

    As with most solar observational questions, investigating the structure and role of the chromosphere is one of remote sensing: many investigations describing their "piece of the elephant". The goal is, of course, to form a coherent picture of the state of the magnetized plasma which resides there (or passes through). In this presentation, recent efforts to understand the chromospheric magnetic field structure via direct observation, i.e. chromospheric vector magnetograms, will be presented. Since late 2003, the U. Hawai`i/Mees Solar Observatory's Imaging Vector Magnetograph has routinely acquired spectropolarimetry measurements of active regions across the Na-I 589.6nm line; from the polarization at the line's near-wings approximately 0.007nm from line center we deduce the vector magnetic field. The data are specific to active regions, with the focus being the structure, free energy storage and evolution at that low-chromospheric layer. I will present salient aspects of the observed chromospheric magnetic field structure, to compare and contrast with the picture formed by the other methods in this session.

  15. Magnetic fields in star-forming regions - Observations

    NASA Technical Reports Server (NTRS)

    Heiles, Carl; Goodman, Alyssa A.; Mckee, Christopher F.; Zweibel, Ellen G.

    1993-01-01

    We review the observational aspects of magnetic fields in dense, star-forming regions. First we discuss ways to observe the field. These include direct methods, which consist of the measurement of both linear and circular polarization of spectral line and continuum radiation; and indirect methods, consisting of the angular distribution of H2O masers on the sky and the measurement of ambipolar diffusion. Next we discuss selected observational results, focusing on detailed discussions of a small number of points rather than a generalized discussion that covers the waterfront. We discuss the Orion/BN-KL region in detail, both on the small and large scales. Next we discuss the derivation of the complete magnetic vector, including both the systematic and fluctuating component, from a large sample of Zeeman and linear polarization measurements for the L204 dark cloud. We examine the virial theorem as it applies to dark clouds in general and one dark cloud, Barnard 1, in particular. We critically discuss the numerous claims for alignment of cloud structural features with the plane-of-the-sky component of the magnetic field, and find that many of these have not been definitively established.

  16. Net field-aligned currents observed by Triad

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Potemra, T. A.

    1975-01-01

    From the Triad magnetometer observation of a step-like level shift in the east-west component of the magnetic field at 800 km altitude, the existence of a net current flowing into or away from the ionosphere in a current layer was inferred. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The field aligned currents observed by Triad are considered as being an important element in the electro-dynamical coupling between the distant magnetosphere and the ionosphere. The current density integrated over the thickness of the layer increases with increasing magnetic activity, but the relation between the current density and Kp in individual cases is not a simple linear relation. An extrapolation of the statistical relation to Kp = 0 indicates existence of a sheet current of order 0.1 amp/m even at extremely quiet times. During periods of higher magnetic activity an integrated current of approximately 1 amp/m and average current density of order 0.000001 amp/sq m are observed. The location and the latitudinal width of the field aligned current layer carrying the net current very roughly agree with those of the region of high electron intensities in the trapping boundary.

  17. Magnetic fields in star-forming regions - Observations

    NASA Technical Reports Server (NTRS)

    Heiles, Carl; Goodman, Alyssa A.; Mckee, Christopher F.; Zweibel, Ellen G.

    1993-01-01

    We review the observational aspects of magnetic fields in dense, star-forming regions. First we discuss ways to observe the field. These include direct methods, which consist of the measurement of both linear and circular polarization of spectral line and continuum radiation; and indirect methods, consisting of the angular distribution of H2O masers on the sky and the measurement of ambipolar diffusion. Next we discuss selected observational results, focusing on detailed discussions of a small number of points rather than a generalized discussion that covers the waterfront. We discuss the Orion/BN-KL region in detail, both on the small and large scales. Next we discuss the derivation of the complete magnetic vector, including both the systematic and fluctuating component, from a large sample of Zeeman and linear polarization measurements for the L204 dark cloud. We examine the virial theorem as it applies to dark clouds in general and one dark cloud, Barnard 1, in particular. We critically discuss the numerous claims for alignment of cloud structural features with the plane-of-the-sky component of the magnetic field, and find that many of these have not been definitively established.

  18. MESSENGER Observations of Internal and External Magnetic Fields at Mercury

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.; Anderson, B. J.; Purucker, M. E.; Alexeev, I. I.; Al Asad, M.; Korth, H.; Phillips, R. J.; Slavin, J. A.; Solomon, S. C.; Winslow, R. M.; Zuber, M. T.

    2011-12-01

    Orbital observations with the Magnetometer (MAG) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft allow global-scale modeling of Mercury's internal and external magnetic fields. We use a paraboloid model with a cross-tail current sheet to quantify the external magnetic fields and examine possible origins for any residual long-wavelength signals. Observations inside the magnetosphere extend from ~60°S to 86°N; those below 1000 km altitude are confined to the northern hemisphere, with global coverage in body-fixed longitude and in local time. We use MAG data to constrain the magnetopause sub-solar standoff distance, the dipole tilt and offset along the rotation axis, the tail field, and the distance to the inner edge of the tail current sheet. Additional parameters, including the dipole moment, are constrained by the goodness of fit of the model to the MAG data. Inbound and outbound magnetopause crossings are identified on each magnetosphere pass. The mean magnetopause shape for the first 120 days in orbit is modeled by a paraboloid of revolution having a subsolar standoff distance of 1.4 RM (where RM is Mercury's radius). Observations of Mercury's magnetic equator indicate a southward-directed dipole, offset northward along the rotation axis from the planetary center by 484 km, with a tilt of less than 2.5°. These observations constrain the dipole moment to be 195 ± 10 nT-RM3. The paraboloid model successfully matches the first-order global signature of the field, with residual amplitudes typically less than 50 nT. Residuals contain signatures from several different sources: (1) variations in the long-wavelength field that are slow relative to the magnetospheric transit time and which correspond to differences in the baseline magnetospheric currents; (2) multipolar contributions to the internal field of either core or crustal origin; (3) plasma and current systems within the magnetosphere that are not captured in the

  19. Coronal Magnetic Field Measurement Using CME-Driven Shock Observations

    NASA Technical Reports Server (NTRS)

    Gopalswarmy, Nat; Nitta, N.; Yashiro, S.; Makela, P.; Xie, H.; Akiyama, S.

    2012-01-01

    Collisionless shocks form ahead of coronal mass ejections (CMEs) when the CME speed exceeds the Alfven speed of the ambient plasma in the corona and interplanetary medium. The shock stands at a distance from the CME flux rope that depends on the shock Mach number, the geometry of the driver, and the adiabatic index. While the shock ahead of the CME has been observed for a long time in the in situ data, it has been identified recently near the Sun in the coronagraphic and EUV images. Unlike in situ observations, the imaging observations are two dimensional, so one can better discern the CME-shock relationship near the Sun. Gopalswamy and Yashiro demonstrated that the coronal magnetic field can be derived from the shock standoff distance measured in coronagraphic images. The method involves measuring the standoff distance, the radius of curvature of the flux rope, and assuming the value of the adiabatic index and deriving the Alfvenic Mach number. The next step is to derive the Alfvenic Mach number from the measured shock speed and an estimate of the local solar wind speed. The final step involves deriving the magnetic field from the Alfven speed by measuring the local plasma density either from coronagraphic (polarized brightness) images or from the band-splitting of type II radio bursts. In this paper, we derive the combined magnetic field profile from near the Sun to the edge of the LASCO field of view (1.5 to 30 solar radii) and compare it with the current model profiles.

  20. DMD-based programmable wide field spectrograph for Earth observation

    NASA Astrophysics Data System (ADS)

    Zamkotsian, Frédéric; Lanzoni, Patrick; Liotard, Arnaud; Viard, Thierry; Costes, Vincent; Hébert, Philippe-Jean

    2015-03-01

    In Earth Observation, Universe Observation and Planet Exploration, scientific return could be optimized in future missions using MOEMS devices. In Earth Observation, we propose an innovative reconfigurable instrument, a programmable wide-field spectrograph where both the FOV and the spectrum could be tailored thanks to a 2D micromirror array (MMA). For a linear 1D field of view (FOV), the principle is to use a MMA to select the wavelengths by acting on intensity. This component is placed in the focal plane of a first grating. On the MMA surface, the spatial dimension is along one side of the device and for each spatial point, its spectrum is displayed along the perpendicular direction: each spatial and spectral feature of the 1D FOV is then fully adjustable dynamically and/or programmable. A second stage with an identical grating recomposes the beam after wavelengths selection, leading to an output tailored 1D image. A mock-up has been designed, fabricated and tested. The micromirror array is the largest DMD in 2048 x 1080 mirrors format, with a pitch of 13.68μm. A synthetic linear FOV is generated and typical images have been recorded o at the output focal plane of the instrument. By tailoring the DMD, we could modify successfully each pixel of the input image: for example, it is possible to remove bright objects or, for each spatial pixel, modify the spectral signature. The very promising results obtained on the mock-up of the programmable wide-field spectrograph reveal the efficiency of this new instrument concept for Earth Observation.

  1. Observation Impact over the Antarctic During the Concordiasi Field Campaign

    NASA Technical Reports Server (NTRS)

    Boullot, Nathalie; Rabier, Florence; Langland, Rolf; Gelaro, Ron; Cardinali, Carla; Guidard, Vincent; Bauer, Peter; Doerenbecher, Alexis

    2014-01-01

    The impact of observations on analysis uncertainty and forecast performance was investigated for Austral Spring 2010 over the Southern polar area for four different systems (NRL, GMAO, ECMWF and Meteo-France), at the time of the Concordiasi field experiment. The largest multi model variance in 500 hPa height analyses is found in the southern sub-Antarctic oceanic region, where there are strong atmospheric dynamics, rapid forecast error growth, and fewer upper air wind observation data to constrain the analyses. In terms of data impact the most important observation components are shown to be AMSU, IASI, AIRS, GPS-RO, radiosonde, surface and atmospheric motion vector observations. For sounding data, radiosondes and dropsondes, one can note a large impact of temperature at low levels and a large impact of wind at high levels. Observing system experiments using the Concordiasi dropsondes show a large impact of the observations over the Antarctic plateau extending to lower latitudes with the forecast range, with a large impact around 50 to 70deg South. These experiments indicate there is a potential benefit of better using radiance data over land and sea-ice and innovative atmospheric motion vectors obtained from a combination of various satellites to fill the current data gaps and improve NWP in this region.

  2. Probing Intergalactic Magnetic Fields from gamma-Ray Observations

    NASA Astrophysics Data System (ADS)

    Chen, Wenlei

    The large-scaled magnetic fields in intergalactic space may contain detailed information of the primordial magnetic fields produced in the early Universe. The generation of the cosmological matter-antimatter asymmetry may produce helical magnetic fields via CP (charge conjugation and parity) violating interactions during matter-genesis. Thus, the study of the intergalactic magnetic field (IGMF) could provide a new window on early-Universe cosmology. IGMFs deflect the electron-positron pairs produced by TeV gamma-rays from blazars, resulting in broadened beams of cascade GeV gamma-rays known as pair halos. In the presence of helical IGMFs, cascade GeV gamma-rays at different energies from a distant source fall into patterns in the observation plane in the GeV gamma-ray sky that have a similar chirality. These signatures of the IGMF on the gamma-ray emission from extragalactic sources, i.e. pair halos and helical patterns, can be observed using data from the Fermi Large Area Telescope (Fermi-LAT). In this dissertation, I describe methods for probing the IGMF using gamma-ray observations. I report on the results of a search for gamma-ray pair halos with a stacking analysis of low-redshift blazars using data from Fermi-LAT. For this analysis we used a number of a priori selection criteria, including the spatial and spectral properties of the Fermi sources. The angular distribution of ˜ 1 GeV photons around 24 stacked isolated high-synchrotron-peaked BL Lacs with redshift z < 0.5 shows an excess over that of point-like sources. A frequentist test yields a p-value of p ˜ 0.01 for the extended emission against the point-source hypothesis. A Bayesian estimation provides the common logarithm of Bayes factors > 2, consistent with expectations for pair halos produced in the IGMF with strength of ˜ 10-17 to 10-15 Gauss. In addition, I present a search for parity violating signatures of helical IGMFs in the GeV gamma-ray sky. In this study, the IGMF helicity is examined by

  3. Electric earthquake precursors: from laboratory results to field observations

    NASA Astrophysics Data System (ADS)

    Vallianatos, Filippos; Triantis, Dimos; Tzanis, Andreas; Anastasiadis, Cimon; Stavrakas, Ilias

    The generation of transient electric potential prior to rupture has been demonstrated in a number of laboratory experiments involving both dry and wet rock specimens. Several different electrification effects are responsible for these observations, however, piezoelectricity cannot explain why quartz-free rocks can also generate precursory phenomena and electrokinetic phenomena are normally very weak to produce macro- and megascopic scale effects. Electrification is observed in dry, non-piezoelectric rocks meaning that additional, solid state mechanisms should be responsible. Herein we focus on a promising effect that is ubiquitous during brittle rock failure: the motion of charged edge dislocations (MCD) during crack opening and propagation (microfracturing). We report a series of laboratory experiments on dry marble samples and discuss their possible relationship to field observations of purported electric earthquake precursors (EEP). The experiments confirm the generation of pressure-stimulated currents (PSC) as expected by the MCD model. The PSC was linearly related to the stress rate, so long as the stressed material deformed elastically. Deviation from linearity arose when the applied stress drove the specimen into the plastic deformation range; this effect has been attributed to the dependence of the PSC on the stress rate and, ultimately, to the inverse of the changing (decreasing) Young's modulus. The emitted current appears very intense and non-linear just prior to failure, where massive crack propagation implies massive MCD processes. Repeated cycles of deformation are associated with progressively weaker current emission, indicating the strong dependence of electrification on the residual damage. Overall, the results are consistent with, and render support to the concept of electrification by MCD/microfracturing. Other mechanisms cannot be excluded of course but are rather considered to accompany and supplement the drastic MCD process. The experiments

  4. The NASA STORMS Sub-Payload electric field observations

    NASA Astrophysics Data System (ADS)

    Pratt, J.; Swenson, C. M.; Barjatya, A.; Sanderson, W.

    2008-12-01

    The NASA STORMS sounding rocket, 36.218, was launched at 00:10 LT on October 30, 2007 into a mid- latitude spread-F condition over Wallops Island. The rocket deployed instrumented main and sub-payloads. The sub payload instrument complement included a plasma impedance probe for measuring plasma density, a Langmuir probe for relative plasma density and temperature measurements and the daughter electric field experiment. Unfortunately the sub-payload coned badly upon deployment complicating the data reduction. Within this paper we present a description of our data reduction techniques which are based upon an all magnetic attitude solution for the sub-payload's complex motion. The attitude solution is used to present preliminary density and electric field observations within this mid-latitude spread-F event.

  5. Swarm Observations of Field-Aligned Currents: Case Studies

    NASA Astrophysics Data System (ADS)

    Le, G.; Chi, P. J.; Gjerloev, J. W.; Stolle, C.; Luhr, H.; Park, J.; Rauberg, J.

    2014-12-01

    In this paper, we report the results of a few case studies of multi-point magnetic field measurements of field-aligned currents (FACs) from Swarm constellation mission to understand their temporal and spatial characteristics. During the commissioning phase, the three Swarm spacecraft were in an identical polar orbit with a string-of-pearl configuration with small separations. During the science operational phase (since April, 2014), the three spacecraft were placed in slightly different polar orbits: one spacecraft in a higher altitude orbit (507km x 512km) and two side-by-side in lower altitude orbits (459km x 462km). We analyze a few FAC events in both orbital phases and during periods of active geomagnetic conditions. The multi-point observations enable us to examine the FACs' temporal evolution and separate their temporal and spatial variations.

  6. Singularities in the Transverse Fields of Electromagnetic Waves. II. Observations on the Electric Field

    NASA Astrophysics Data System (ADS)

    Hajnal, J. V.

    1987-12-01

    Electromagnetic waves propagating in free space contain three kinds of singularities called C lines, S surfaces and disclinations. The paper describes observations of these singularities in two different monochromatic microwave fields. The observations confirm all the theoretically predicted properties of the singularities that could be tested. As expected, the singularities were found to be prominent structural features of the fields and in consequence to provide an economical means of characterizing their structure. A notable result is the observation of both right-hand and left-hand C lines in a field that is nominally uniformly left-hand circularly polarized. This is in agreement with the previous assertion that, in general, electromagnetic wavefields contain both right-hand and left-hand polarized regions.

  7. 2010 BLASTPol Observations of Magnetic Fields in Lupus

    NASA Astrophysics Data System (ADS)

    Matthews, Tristan G.

    The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) was created by adding polarimetric capability to the BLAST experiment that was flown in 2003, 2005, and 2006. BLASTPol inherited BLAST's 1.8 m primary and its Herschel/SPIRE heritage focal plane that allows simultaneous observation at 250, 350, and 500 mum. We flew BLASTPol in 2010 and again in 2012. Both were long duration Antarctic flights. The main result presented here is polarimetry of the nearby filamentary dark cloud Lupus I obtained during the 2010 flight. Despite limitations imposed by the effects of a damaged optical component, we were able to clearly detect submillimeter polarization on degree scales. We compare the resulting BLASTPol magnetic field map with a similar map made via optical polarimetry. (The optical data were published in 1998 by J. Rizzo and collaborators.) The two maps partially overlap and are reasonably consistent with one another. We compare these magnetic field maps to the orientations of filaments in Lupus I, and we find that the dominant filament in the cloud is approximately perpendicular to the large-scale field, while secondary filaments appear to run parallel to the magnetic fields in their vicinities. This is similar to what is observed in Serpens South via near-IR polarimetry, and consistent with what is seen in MHD simulations by F. Nakamura and Z. Li. We have performed a similar analysis for Lupus IV and present initial results. The Lupus IV cloud has no clear dominant filament and we make no attempts to interpret these initial findings. Finally, detailed discussions of two of the dominant sources of error in the 2010 data are presented.

  8. A magnetospheric field model incorporating the OGO 3 and 5 magnetic field observations

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Poros, D. J.

    1973-01-01

    A magnetospheric field model is presented in which the usually assumed toroidal ring current is replaced by a circular disk current of finite thickness that extends from the tail to geocentric distances less than 3 earth radii. The drastic departure of this model from the concept of the conventional ring current lies in the fact that the current is continuous from the tail to the inner magnetosphere. This conceptual change was required to account for the recent results of analysis of the OGO 3 and 5 magnetic field observations. In the present model the cross-tail current flows along circular arcs concentric with the earth and completes circuit via surface currents on the magnetopause. Apart from these return currents in the tail magnetopause, Mead's model is used for the field from the magnetopause current. The difference scalar field, delta B, defined as the difference between the scalar field calculated from the present model and the magnitude of the dipole field is found to be in gross agreement with the observed delta B. An updated version of the delta B contours from the OGO 3 and 5 observations, which is used for the comparison, is presented.

  9. Geomorphology: Perspectives on observation, history, and the field tradition

    NASA Astrophysics Data System (ADS)

    Vitek, John D.

    2013-10-01

    Other than a common interest in form and process, current geomorphologists have little in common with those who established the foundations of this science. Educated people who had an interest in Earth processes during the nineteenth century cannot be compared to the scholars who study geomorphology in the twenty-first century. Whereas Earth has undergone natural change from the beginning of time, the human record of observing and recording processes and changes in the surface Is but a recent phenomena. Observation is the only thread, however, that connects all practitioners of geomorphology through time. As people acquired knowledge related to all aspects of life, technological revolutions, such as the Iron Age, Bronze Age, agricultural revolution, the atomic age, and the digital age, shaped human existence and thought. Technology has greatly changed the power of human observation, including inward to the atomic scale and outward into the realm of space.Books and articles describe how to collect and analyze data but few references document the field experience. Each of us, however, has experienced unique circumstances during field work and we learned from various mentors how to observe. The surface of Earth on which we practice the vocation of geomorphology may not be much different from a hundred years ago but many things about how we collect data, analyze it and disseminate the results have changed. How we function in the field, including what we wear, what we eat, how we get there, and where we choose to collect data, clearly reflects the complexity of the human system on Earth and the processes and forms that arouse our interest. Computers, miniaturization of electronics, satellite communications and observation platforms in space provide access to data to aid in our quest to understand Earth surface processes. Once, people lived closer to nature in primitive shelters in contrast with life in urban environments. But as urban life continues to expand and people

  10. Birotor dipole for Saturn's inner magnetic field from Cassini observations

    NASA Astrophysics Data System (ADS)

    Galopeau, Patrick

    2017-04-01

    The radio and plasma wave science (RPWS) experiment on board the Cassini spacecraft, orbiting around Saturn since July 2004, revealed the presence of two distinct and variable rotation periods in the Saturnian kilometric radiation (SKR). These two periods were attributed to the northern and southern hemispheres respectively. We suppose that the periodic time modulations present in the SKR are mainly due to the rotation of Saturn's inner magnetic field. The existence of a double period implies that the inner field is not only limited to a simple rotation dipole but displays more complex structures having the same time periodicities than the radio emission. In order to build a model of this complex magnetic field, it is absolutely necessary to know the accurate phases of rotation linked with the two periods. The radio observations from the RPWS experiment allow a continuous and accurate follow-up of these rotation phases, since the SKR emission is permanently observable and produced very close to the planetary surface. A continuous wavelet transform analysis of the intensity of the SKR signal received at 290 kHz between July 2004 and June 2012 was performed in order to calculate in the same time the different periodicities and phases. A dipole model was proposed for Saturn's inner magnetic field: this dipole presents the particularity to have North and South poles rotating around Saturn's axis at two different angular velocities; this dipole is tilted and not centered. 57 Cassini's revolutions, the periapsis of which is less than 5 Saturnian radii, have been selected for this study. For each of these chosen orbits, it is possible to fit with high precision the measurements of the MAG data experiment given by the magnetometers embarked on board Cassini. A nonrotating external magnetic field completes the model. This study suggests that Saturn's inner magnetic field is neither stationary nor fully axisymmetric. These results can be used as a boundary condition for

  11. Seismostatistical characterization of microseismicity observed at geothermal fields

    NASA Astrophysics Data System (ADS)

    Eto, T.; Asanuma, H.; Adachi, M.; Saeki, K.; Aoyama, K.; Ozeki, H.; Häring, M. O.

    2012-12-01

    Recently, occurrence of felt earthquakes has been recognized as one of the most critical environmental burdens associated with geothermal development. We have taken seismostatistical approach to evaluate characteristics of the microseismicity at geothermal fields to establish realtime and automated monitoring techniques of the reservoir changes and risk assessment of the felt earthquakes. In this study, we have introduced the Epidemic Type Aftershock Sequence (ETAS) model (Ogata, JASA, 1988) to statistically model the time series of occurrences and the magnitude of microseismic events from hydrothermal and EGS fields. Here maximum likelihood estimation has been employed to estimate optimum parameters of the ETAS model. We analyzed microseismic events observed at Yanaizu Nishiyama, one of the largest hydrothermal fields in Japan. In this field, four felt earthquakes with local magnitude larger than 3.0 occurred during production operation since 1996, although no clear correlation between the occurrence of the felt earthquakes and operation to the reservoir has been observed (Asanuma et al., Trans. GRC, 2011). We found that the occurrence rate of primary fluid signals, which are the events triggered by external forcing and have been interpreted to be independent from a series of aftershocks (Hainzl and Ogata, JGR, 2005), correlated to the reinjection rate (Fig. 1). However, no significant change in the other parameters in the ETAS model has been observed. We also analyzed microseismic events observed at Basel EGS site in Switzerland, where some felt earthquakes occurred during and after hydraulic stimulation. The estimated ETAS model demonstrated that there is a correlation between the occurrence rate of primary fluid signals and injection rate. We, however, found that there is limitation to fit the ETAS model to the induced seismic events and new seismostatistical model is required for microseismic reservoir monitoring.ig. 1 A relation among production

  12. Field observations of dilution on the Ipanema Beach outfall.

    PubMed

    Roldão, J; Carvalho, J L; Roberts, P J

    2001-01-01

    Field observations of the Ipanema Beach, Rio de Janeiro, ocean sewage outfall are presented. Measurements of dilution and other wastefield characteristics were obtained by adding dye tracer to the effluent and measuring in-situ. Simultaneous measurements of oceanographic conditions were made by Acoustic Doppler Current Profilers, thermistor strings, and profiling instruments. Four experiments were performed, two during unstratified conditions when the plume was surfacing, and two during conditions of strong stratification when the plume was submerged. The minimum dilution varied from 30 to 130. The measurements reflect the worst case conditions as the campaigns were all made for weak currents.

  13. Newly velocity field of Sulawesi Island from GPS observation

    NASA Astrophysics Data System (ADS)

    Sarsito, D. A.; Susilo, Simons, W. J. F.; Abidin, H. Z.; Sapiie, B.; Triyoso, W.; Andreas, H.

    2017-07-01

    Sulawesi microplate Island is located at famous triple junction area of the Eurasian, India-Australian, and Philippine Sea plates. Under the influence of the northward moving Australian plate and the westward motion of the Philippine plate, the island at Eastern part of Indonesia is collide and with the Eurasian plate and Sunda Block. Those recent microplate tectonic motions can be quantitatively determine by GNSS-GPS measurement. We use combine GNSS-GPS observation types (campaign type and continuous type) from 1997 to 2015 to derive newly velocity field of the area. Several strategies are applied and tested to get the optimum result, and finally we choose regional strategy to reduce error propagation contribution from global multi baseline processing using GAMIT/GLOBK 10.5. Velocity field are analyzed in global reference frame ITRF 2008 and local reference frame by fixing with respect alternatively to Eurasian plate - Sunda block, India-Australian plate and Philippine Sea plates. Newly results show dense distribution of velocity field. This information is useful for tectonic deformation studying in geospatial era.

  14. The gravity field observations and products at IGFS

    NASA Astrophysics Data System (ADS)

    Barzaghi, Riccardo; Vergos, George; Bonvalot, Sylvain; Barthelmes, Franz; Reguzzoni, Mirko; Wziontek, Hartmut; Kelly, Kevin

    2017-04-01

    The International Gravity Field Service (IGFS) is a service of the International Association of Geodesy (IAG) that was established in 2003 at the IAG/IUGG General Assembly in Sapporo (Japan). This service aims at coordinating the actions of the IAG services related to the Earth gravity field, i.e. the Bureau Gravimétrique International (BGI), the International Service for the Geoid (ISG), the International Geodynamics and Earth Tides Service (IGETS), the International Center for Global Earth Models (ICGEM) and the International Digital Elevation Model Service (IDEMS). Also, via its Central Bureau hosted at the Aristotle University of Thessaloniki (Greece), IGFS provides a link to the Global Geodetic Observing System (GGOS) bureaus in order to communicate their requirements and recommendations to the IGFS-Centers. In this work, a presentation is given on the recent activities of the service, namely those related to the contributions to the implementation of: the International Height Reference System/Frame; the Global Geodetic Reference System/Frame; the new Global Absolute Gravity Reference System/Frame. Particularly, the impact that these activities have in improving the estimation of the Earth's gravity field, either at global and local scale, is highlighted also in the framework of GGOS.

  15. Field experimental observations of highly graded sediment plumes.

    PubMed

    Jensen, Jacob Hjelmager; Saremi, Sina; Jimenez, Carlos; Hadjioannou, Louis

    2015-06-15

    A field experiment in the waters off the south-eastern coast of Cyprus was carried out to study near-field formation of sediment plumes from dumping. Different loads of sediment were poured into calm and limpid waters one at the time from just above the sea surface. The associated plumes, gravitating towards the seafloor, were filmed simultaneously by four divers situated at different depths in the water column, and facing the plume at different angles. The processes were captured using GoPro-Hero-series cameras. The high-quality underwater footage from near-surface, mid-depth and near-bed positions gives unique insight into the dynamics of the descending plume and near-field dispersion processes, and enables good understanding of flow and sediment transport processes involved from-release-to-deposition of the load in a non-scaled environment. The high resolution images and footages are available through the link provided herein. Observations support the development of a detailed multi-fractional sediment plume model. Copyright © 2015 Elsevier Ltd. All rights reserved.

  16. Insight into shark magnetic field perception from empirical observations.

    PubMed

    Anderson, James M; Clegg, Tamrynn M; Véras, Luisa V M V Q; Holland, Kim N

    2017-09-08

    Elasmobranch fishes are among a broad range of taxa believed to gain positional information and navigate using the earth's magnetic field, yet in sharks, much remains uncertain regarding the sensory receptors and pathways involved, or the exact nature of perceived stimuli. Captive sandbar sharks, Carcharhinus plumbeus were conditioned to respond to presentation of a magnetic stimulus by seeking out a target in anticipation of reward (food). Sharks in the study demonstrated strong responses to magnetic stimuli, making significantly more approaches to the target (p = < 0.01) during stimulus activation (S+) than before or after activation (S-). Sharks exposed to reversible magnetosensory impairment were less capable of discriminating changes to the local magnetic field, with no difference seen in approaches to the target under the S+ and S- conditions (p = 0.375). We provide quantified detection and discrimination thresholds of magnetic stimuli presented, and quantify associated transient electrical artefacts. We show that the likelihood of such artefacts serving as the stimulus for observed behavioural responses was low. These impairment experiments support hypotheses that magnetic field perception in sharks is not solely performed via the electrosensory system, and that putative magnetoreceptor structures may be located in the naso-olfactory capsules of sharks.

  17. A new approach to observe toroidal magnetic fields of magnetars

    NASA Astrophysics Data System (ADS)

    Murakami, H.; Makishima, K.; Enoto, T.; Nakano, T.; Furuta, Y.; Nakazawa, K.

    2016-06-01

    Over the last decade, observational evidence has amounted that magnetars harbor enormous surface dipole magnetic fields (MFs) of B_{d} = 10^{14-15} {G}. Theoretically, we expect even stronger toroidal MFs B_{t} (e.g., Takiwaki+2009), which is observationally supported by a discovery of low-B_{d} magnetars (e.g., SGR 0418+5729; Rea+2013). Here, we will present a new approach to access B_{t} more directly. Suzaku allows us to simultaneously observe a soft thermal component and a distinct hard X-ray tail of magnetars. Extensively analyzing two magnetars, 4U 0142+61 and 1E 1547.0-5408, we found that their hard X-ray pulses suffered from slow phase modulations (Makishima+2014, 2015). This can be interpreted as a manifestation of free precession, under an axial deformation by ˜0.01%. If this effect is attributed to the magnetic stress, B_{t}˜10^{16} G is inferred. We further found that, within 6 years observation of 4U 0142+61, the modulation periods remained constant, while the amplitude gradually increased from < 0.4 to ˜1.3 sec. These results suggest the shift of the hard X-ray emission region (or direction).

  18. Using Clocks and Atomic Interferometry for Gravity Field Observations

    NASA Astrophysics Data System (ADS)

    Müller, Jürgen

    2016-07-01

    New technology developed in the frame of fundamental physics may lead to enhanced capabilities for geodetic applications such as refined observations of the Earth's gravity field. Here, we will present new sensor measurement concepts that apply atomic interferometry for gravimetry and clock measurements for observing potential values. In the first case, gravity anomalies can be determined by observing free-falling atoms (quantum gravimetry). In the second case, highly precise optical clocks can be used to measure differences of the gravity potential over long distances (relativistic geodesy). Principally, also inter-satellite ranging between test masses in space with nanometer accuracy belongs to these novel developments. We will show, how the new measurement concepts are connected to classical geodetic concepts, e.g. geopotential numbers and clock readings. We will illustrate the application of these new methods and their benefit for geodesy, where local and global mass variations can be observed with unforeseen accuracy and resolution, mass variations that reflect processes in the Earth system. We will present a few examples where geodesy will potentially benefit from these developments. Thus, the novel technologies might be applied for defining and realizing height systems in a new way, but also for fast local gravimetric surveys and exploration.

  19. {Interball-1 Plasma, Magnetic Field, and Energetic Particle Observations}

    NASA Technical Reports Server (NTRS)

    Sibeck, David G.

    1998-01-01

    Funding from NASA was received in two installments. The first installment supported research using Russian/Czech/Slovak/French Interball-1 plasma, magnetic field, and energetic particles observations in the vicinity of the magnetopause. The second installment provided salary support to review unsolicited proposals to NASA for data recovery and archiving, and also to survey ISTP data provision efforts. Two papers were published under the auspices of the grant. Sibeck et al. reported Interball-1 observations of a wave on the magnetopause with an amplitude in excess of 5 R(sub E), the largest ever reported to date. They attributed the wave to a hot flow anomaly striking the magnetopause and suggested that the hot flow anomaly itself formed during the interaction of an IMF discontinuity with the bow shock. Nemecek et al. used Interball-1's VDP Faraday cup to identify large transient increases in the magnetosheath density. They noted large variations in simultaneous Wind observations of the IMF cone angle, but were unable to establish any relationship between the cone angle variations at Wind and the density variations at Interball-1. Funds from the second installment were used to review over 20 proposals from various researchers in the scientific community who sought NASA support to restore or archive past observations. It also supported a survey of ISTP data provisions which was used as input to a Senior Review of ongoing NASA ISTP programs.

  20. Inferences on Coronal Magnetic Fields from SOHO UVCS Observations

    NASA Technical Reports Server (NTRS)

    Poletto, G.; Romoli, M.; Suess, S. T.; Wang, A. H.; Wu, S. T.

    1996-01-01

    The characteristics of the magnetic field ubiquitously permeating the coronal plasma are still largely unknown. In this paper we analyze some aspects of coronal physics, related to the magnetic field behavior, which forthcoming SOHO UVCS observations can help better understand. To this end, three coronal structures will be examined: streamers, coronal mass ejections (CME's) and coronal holes. As to streamers and CME's, we show, via simulations of the Ly-alpha and white light emission from these objects, calculated on the basis of recent theoretical models, how new data from SOHO can help advancing our knowledge of the streamer/CME magnetic configuration. Our discussion highlights also those observational signatures which might offer clues on reconnection processes in streamers' current sheets. Coronal holes (CH's) are discussed in the last section of the paper. Little is known about CH flux tube geometry, which is closely related to the behavior of the solar wind at small heliocentric distances. Indirect evidence for the flux tube spreading factors, within a few solar radii, is here examined.

  1. A magnetospheric field model incorporating the OGO 3 and 5 magnetic field observations.

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Poros, D. J.

    1973-01-01

    A magnetospheric field model is presented in which the usually assumed toroidal ring current is replaced by a circular disk current of finite thickness that extends from the tail to geocentric distances less than 3 earth radii. The drastic departure of this model from the concept of the conventional ring current lies in that the current is continuous from the tail to the inner magnetosphere. This conceptual change was required to account for the recent results of analysis of the OGO 3 and 5 magnetic field observations. In the present model the cross-tail current flows along circular arcs concentric with the earth and completes circuit via surface currents on the magnetopause. Apart from these return currents in the tail magnetopause, Mead's (1964) model is used for the field from the magnetopause current. The difference scalar field, Delta B, defined as the difference between the scalar field calculated from the present model and the magnitude of the dipole field, is found to be in gross agreement with the observed Delta B.

  2. Near Field Ocean Surface Waves Acoustic Radiation Observation and Modeling

    NASA Astrophysics Data System (ADS)

    Ardhuin, F.; Peureux, C.; Royer, J. Y.

    2016-12-01

    The acoustic noise generation by nonlinearly interacting surface gravity waves has been studied for a long time both theoretically and experimentally [Longuet-Higgins 1951]. The associated far field noise is continuously measured by a vast network of seismometers at the ocean bottom and on the continents. It can especially be used to infer the time variability of short ocean waves statistics [Peureux and Ardhuin 2016]. However, better quantitative estimates of the latter are made difficult due to a poor knowledge of the Earth's crust characteristics, whose coupling with acoustic modes can affect large uncertainties to the frequency response at the bottom of the ocean.The pressure field at depths less than an acoustic wave length to the surface is made of evanescent modes which vanish away from their sources (near field) [Cox and Jacobs 1989]. For this reason, they are less affected by the ocean bottom composition. This near field is recorded and analyzed in the frequency range 0.1 to 0.5 Hz approximately, at two locations : at a shallow site in the North-East Atlantic continental shelf and a deep water site in the Southern Indian ocean, where pressure measurements are performed at the ocean bottom (ca. 100 m) and at 300 m water depth respectively. Evanescent and propagating Rayleigh modes are compared against theoretical predictions. Comparisons against surface waves hindcast based on WAVEWATCH(R) III modeling framework help assessing its performances and can be used to help future model improvements.References Longuet-Higgins, M. S., A Theory of the Origin of Microseisms, Philos. Trans. Royal Soc. A, 1950, 243, 1-3. Peureux, C. and Ardhuin, F., Ocean bottom pressure records from the Cascadia array and short surface gravity waves, J. Geophys. Res. Oceans, 2016, 121, 2862-2873. Cox, C. S. & Jacobs, D. C., Cartesian diver observations of double frequency pressure fluctuations in the upper levels of the ocean, Geophys. Res. Lett., 1989, 16, 807-810.

  3. Electric earthquake precursors: from laboratory results to field observations.

    NASA Astrophysics Data System (ADS)

    Vallianatos, F.; Triantis, D.; Tzanis, A.; Anastasiadis, C.; Stavrakas, I.

    2003-04-01

    The possibility of electrical earthquake precursors (EEP) has long been appreciated, but it has proven difficult to construct a solid theory to describe their generation and expected characteristics, or proven techniques to identify and discriminate true precursors from noise. To this end, a large number of laboratory experiments have been conducted, which have demonstrated the generation of transient electric potential prior to rupture in both dry and wet rock specimens. The principal mechanisms proposed to explain these observations are the piezo-electric and electrokinetic effects. The often quoted in the literature piezoelectric effect, cannot explain why non-piezoelectric rock specimens can also generate precursory electric phenomena. Streaming potential can be generated in many kinds of saturated rocks, but the fracturing of dry rocks also produces transient electric effects. Therefore, these two mechanisms may not be the basic contributors to the precursory phenomena observed in the laboratory (and to possible EEP signals). Herein we present a series of laboratory experiments on the microfracturing electrification of dry marble samples under stress, and discuss their possible relationship to field observations of purported EEP. The marble samples were subjected to constant and variable stress-rate uniaxial compression, in both the elastic and the plastic region. During the experiment, pressure stimulated currents (PSC) were observed, which show a clear dependence on the stress rate and mechanical state of the material (the Young modulus), decreasing in frequency and intensity with increasing damage during repeated loading cycles. Explanation of these observations is attempted with a theoretical model involving microfracturing and the motion of charged edge dislocations (MCD) as the primary electrification mechanism, after Tzanis and Vallianatos (Seismo Electromagnetics: Lithosphere-Atmosphere-Ionosphere Coupling, TERRAPUB, 2002). The PSC waveforms and mode

  4. Observations of field-aligned currents, waves, and electric fields at substorm onset

    NASA Technical Reports Server (NTRS)

    Smits, D. P.; Hughes, W. J.; Cattell, C. A.; Russell, C. T.

    1986-01-01

    Substorm onsets, identified Pi 2 pulsations observed on the Air Force Geophysics Laboratory Magnetometer Network, are studied using magnetometer and electric field data from ISEE 1 as well as magnetometer data from the geosynchronous satellites GOES 2 and 3. The mid-latitude magnetometer data provides the means of both timing and locating the substorm onset so that the spacecraft locations with respect to the substorm current systems are known. During two intervals, each containing several onsets or intensifications, ISEE 1 observed field-aligned current signatures beginning simultaneously with the mid-latitude Pi 2 pulsation. Close to the earth broadband bursts of wave noise were observed in the electric field data whenever field-aligned currents were detected. One onset occurred when ISEE 1 and GOES 2 were on the same field line but in opposite hemispheres. During this onset ISEE 1 and GOES 2 saw magnetic signatures which appear to be due to conjugate field-aligned currents flowing out of the western end of the westward auroral electrojets. The ISEE 1 signature is of a line current moving westward past the spacecraft. During the other interval, ISEE 1 was in the near-tail region near the midnight meridian. Plasma data confirms that the plasma sheet thinned and subsequently expanded at onset. Electric field data shows that the plasma moved in the opposite direction to the plasma sheet boundary as the boundary expanded which implies that there must have been an abundant source of hot plasma present. The plasma motion was towards the center of the plasma sheet and earthwards and consisted of a series of pulses rather than a steady flow.

  5. C/NOFS Observations of AC Electric Field Fields Associated with Equatorial Spread-F

    NASA Technical Reports Server (NTRS)

    Pfaff, R.; Liebrecht, C.

    2009-01-01

    The Vector Electric Field Investigation (VEFI) on the C/NOFS equatorial satellite provides a unique data set in which to acquire detailed knowledge of irregularities associated with the equatorial ionosphere and in particular with spread-F depletions. We present vector AC electric field observations, primarily gathered within the ELF band (1 Hz to 250 Hz) on C/NOFS that address a variety of key questions regarding how plasma irregularities, from meter to kilometer scales, are created and evolve. The data will be used to explore the anisotropy/isotropy of the waves, their wavelength and phase velocity, as well as their spectral distributions. When analyzed in conjunction with the driving DC electric fields and detailed plasma number density measurements, the combined data reveal important information concerning the instability mechanisms themselves. We also present high resolution, vector measurements of intense lower hybrid waves that have been detected on numerous occasions by the VEFI burst memory VLF electric field channels.

  6. Field observations using an AOTF polarimetric imaging spectrometer

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Hamilton, Mike; Mahoney, Colin; Reyes, George

    1993-01-01

    This paper reports preliminary results of recent field observations using a prototype acousto-optic tunable filter (AOTF) polarimetric imaging spectrometer. The data illustrate application potentials for geoscience. The operation principle of this instrument is different from that of current airborne multispectral imaging instruments, such as AVIRIS. The AOTF instrument takes two orthogonally polarized images at a desired wavelength at one time, whereas AVIRIS takes a spectrum over a predetermined wavelength range at one pixel at a time and the image is constructed later. AVIRIS does not have any polarization measuring capability. The AOTF instrument could be a complement tool to AVIRIS. Polarization measurement is a desired capability for many applications in remote sensing. It is well know that natural light is often polarized due to various scattering phenomena in the atmosphere. Also, scattered light from canopies is reported to have a polarized component. To characterize objects of interest correctly requires a remote sensing imaging spectrometer capable of measuring object signal and background radiation in both intensity and polarization so that the characteristics of the object can be determined. The AORF instrument has the capability to do so. The AOTF instrument has other unique properties. For example, it can provide spectral images immediately after the observation. The instrument can also allow observations to be tailored in real time to perform the desired experiments and to collect only required data. Consequently, the performance in each mission can be increased with minimal resources. The prototype instrument was completed in the beginning of this year. A number of outdoor field experiments were performed with the objective to evaluate the capability of this new technology for remote sensing applications and to determine issues for further improvements.

  7. Observations of the diffuse near-UV radiation field

    NASA Technical Reports Server (NTRS)

    Murthy, J.; Henry, R. C.; Feldman, P. D.; Tennyson, P. D.

    1990-01-01

    The diffuse radiation field from 1650-3100 A has been observed by spectrometer aboard the Space Shuttle, and the contributions of the zodiacal light an the diffuse cosmic background to the signal have been derived. Colors ranging from 0.65 to 1.2 are found for the zodiacal light with an almost linear increase in the color with ecliptic latitude. This rise in color is due to UV brightness remaining almost constant while the visible brightnesses drop by almost a factor of two. This is interpreted as evidence that the grains responsible for the UV scattering have much more uniform distribution with distance from the ecliptic plane than do those grains responsible for the visible scattering. Intensities for the cosmic diffuse background ranging from 300 units to 900 units are found which are not consistent with either a correlation with N(H I) or with spatial isotropy.

  8. Some field observations on OSI aerial photography scales

    SciTech Connect

    Geil, R.

    1981-03-16

    The US, UK and USSR are attempting to negotiate a Comprehensive Test Ban Treaty (CTBT) in Geneva. One of the verification procedures presently proposed provides for the possibility of conducting an On-Site Inspection (OSI) if a violation is suspected. According to the terms of the draft treaty, the OSI team would be provided with either (1) stereoscopic aerial photographs with a scale of 1:2,500, or equivalent topographic maps (US version) or (2) a large scale aerial photograph (USSR version). In order to gain a better understanding of the aerial photograph issue, EG and G was asked to take stereoscopic aerial photographs of two areas at the NTS at four different scales, 1:2,500, 1:5,000, 1:10,000 and 1:25,000. The purpose of this paper is to present some field observations on the use for OSI type purposes of these different scale photos.

  9. Los Azufres geothermal field: Observed response after 12-year exploitation

    SciTech Connect

    Maldonado, G.J.

    1995-12-31

    Exploitation of the Los Azufres Geothermal field was initiated in August 1982, with the electric power generation of five 5-MW wellhead units. Since then another 70 MW have been installed. A large amount of information has been compiled, including geologic, geochemical, production, and reservoir characteristics. The data were evaluated to detect the extent of observable changes in the main reservoir parameters over the twelve-year production period. Pressure and temperature measurements in Los Azufres wells show that geothermal fluid distribution is strongly influenced by the presence of permeable structures. Wellhead production and chemical analysis of the separated brine show that we are dealing with a highly heterogeneous reservoir, were the drawdown and enthalpy changes depend on the position of the well being studied.

  10. Comparison of St. Lawrence blue whale vocalizations with field observations

    NASA Astrophysics Data System (ADS)

    Berchok, Catherine; Bradley, David; Gabrielson, Thomas; Sears, Richard

    2003-04-01

    During four field seasons from 1998-2001, vocalizations were recorded in the presence of St. Lawrence blue whales using a single omni-directional hydrophone. Both long duration infrasonic calls (~18 Hz, 5-20 s) as well as short duration higher frequency calls (85-25 Hz, ~2 s) were detected and compared with field observations. Two trends were noted. First, the long infrasonic call series were concentrated primarily in the deep (300 m) channel. These call series appear to compare well with blue whale vocalizations recorded by others in the deep open ocean. Second, the shorter audible calls were more evenly distributed over bathymetry and seem to be a form of short distance communication with at least one case occurring during an agonistic interaction. A comparison of these calls with biological parameters such as density of whales in the area, percentages of paired versus single whales, and numbers of males versus females will also be discussed. [Project supported by ARL/PSU, NSF, and the American Museum of Natural History.

  11. Review of lightning properties from electron field and TV observations

    NASA Astrophysics Data System (ADS)

    Rakov, Vladimir A.; Uman, Martin A.; Thottappillil, Rajeev

    1994-05-01

    strokes are similar to or shorter than those preceding higher-order strokes. These observations indicate that channel conditions for the propagation of a subsequent leader are determined not just by the immediately preceding channel heating and cooling processes but rather by the entire channel history. In particular, the status of the channel apparently depends on the number of strokes that have participated in its cumulative conditioning. The overwhelming majority of long continuing currents, those with a duration longer than 40 ms, were initiated by subsequent strokes of multiple-stroke flashes as opposed to either the first stroke in a multiple-stroke flash or the only stroke in a single-stroke flash. Strokes that initiate such long continuing currents were (1) relatively small (in terms of both return-stroke field peak and, as determined from an independent study in New Mexico, stroke charge), (2) followed relatively short interstroke intervals, and (3) showed a tendency to be preceded by a relatively large stroke. Millisecond-scale K and M electric field changes appeared different in terms of both microsecond-scale pulse content and interevent time intervals. Often no microsecond-scale K and M field pulses were detected. When they were present, such pulses were highly variable and sometimes irregular in waveshape, as opposed to the alleged characteristic K-pulse waveform described by Arnold and Pierce (1964), which has been extensively used in atmospheric radio-noise studies. There is a remarkable similarity between many lightning characteristics in Florida and in New Mexico.

  12. Photometric Observations of 6000 Stars in the Cygnus Field

    NASA Technical Reports Server (NTRS)

    Borucki, W.; Caldwell, D.; Koch, D.; Jenkins, J.; Ninkov, Z.

    1999-01-01

    A small photometer to detect transits by extrasolar planets has been assembled and is being tested at Lick Observatory on Mt. Hamilton, California. The Vulcan photometer is constructed from a 30 cm focal length, F/2.5 AeroEktar reconnaissance lens and Photometrics PXL16800 CCD camera. A spectral filter is used to confine the pass band from 480 to 763 mn. It simultaneously monitors 6000 stars brighter than 12th magnitude within a single star field in the galactic plane. When the data are folded and phased to discover low amplitude transits, the relative precision of one-hour samples is about 1 part per thousand (10 x l0(exp -3)) for many of the brighter stars. This precision is sufficient to find jovian-size planets orbiting solar-like stars, which have signal amplitudes from 5 to 30 x l0(exp -3) depending on the inflation of the planet and the size of the star. Based on the frequency of giant inner-planets discovered by Doppler-velocity method, one or two planets should be detectable in a rich star field. The goal of the observations is to obtain the sizes of giant extrasolar planets in short-period orbits and to combine these with masses determined from Doppler velocity measurements to determine the densities of these planets. A further goal is to compare the measured planetary diameters with those predicted from theoretical models. From August 10 through September 30 of 1998, a forty nine square degree field in the Cygnus constellation centered at RA and DEC of 19 hr 47 min, +36 deg 55 min was observed. Useful data were obtained on twenty-nine nights. Nearly fifty stars showed some evidence of transits with periods between 0.3 and 8 days. Most had amplitudes too large to be associated with planetary transits. However, several stars showed low amplitude transits. The data for several transits of each of these two stars have been folded and been folded into 30 minute periods. Only Cygl433 shows any evidence of a flattened bottom that is expected when a small object

  13. Geopotential Field Anomaly Continuation with Multi-Altitude Observations

    NASA Technical Reports Server (NTRS)

    Kim, Jeong Woo; Kim, Hyung Rae; von Frese, Ralph; Taylor, Patrick; Rangelova, Elena

    2012-01-01

    Conventional gravity and magnetic anomaly continuation invokes the standard Poisson boundary condition of a zero anomaly at an infinite vertical distance from the observation surface. This simple continuation is limited, however, where multiple altitude slices of the anomaly field have been observed. Increasingly, areas are becoming available constrained by multiple boundary conditions from surface, airborne, and satellite surveys. This paper describes the implementation of continuation with multi-altitude boundary conditions in Cartesian and spherical coordinates and investigates the advantages and limitations of these applications. Continuations by EPS (Equivalent Point Source) inversion and the FT (Fourier Transform), as well as by SCHA (Spherical Cap Harmonic Analysis) are considered. These methods were selected because they are especially well suited for analyzing multi-altitude data over finite patches of the earth such as covered by the ADMAP database. In general, continuations constrained by multi-altitude data surfaces are invariably superior to those constrained by a single altitude data surface due to anomaly measurement errors and the non-uniqueness of continuation.

  14. Geopotential Field Anomaly Continuation with Multi-Altitude Observations

    NASA Technical Reports Server (NTRS)

    Kim, Jeong Woo; Kim, Hyung Rae; vonFrese, Ralph; Taylor, Patrick; Rangelova, Elena

    2011-01-01

    Conventional gravity and magnetic anomaly continuation invokes the standard Poisson boundary condition of a zero anomaly at an infinite vertical distance from the observation surface. This simple continuation is limited, however, where multiple altitude slices of the anomaly field have been observed. Increasingly, areas are becoming available constrained by multiple boundary conditions from surface, airborne, and satellite surveys. This paper describes the implementation of continuation with multi-altitude boundary conditions in Cartesian and spherical coordinates and investigates the advantages and limitations of these applications. Continuations by EPS (Equivalent Point Source) inversion and the FT (Fourier Transform), as well as by SCHA (Spherical Cap Harmonic Analysis) are considered. These methods were selected because they are especially well suited for analyzing multi-altitude data over finite patches of the earth such as covered by the ADMAP database. In general, continuations constrained by multi-altitude data surfaces are invariably superior to those constrained by a single altitude data surface due to anomaly measurement errors and the non-uniqueness of continuation.

  15. H-band observations of the Chandra Deep Field South

    NASA Astrophysics Data System (ADS)

    Moy, E.; Barmby, P.; Rigopoulou, D.; Huang, J.-S.; Willner, S. P.; Fazio, G. G.

    2003-05-01

    We report results of our H-band survey of the Chandra Deep Field South (CDFS). The observations, made with SofI on the NTT, cover 0.027 square degrees to H< 20.5 and 0.17 square degrees to H< 19.8 (50% completeness limits). In total, 4819 objects were detected, of which 80% are galaxies based on the SExtractor parameter ``stellarity index'' having a value less than 0.5. Our astrometric solutions are in good agreement with those of the Las Campanas Infrared Survey (LCIRS), the COMBO-17, and the ESO-EIS surveys. Our photometry compares satisfactorily with the LCIRS results as well as with GOODS data. Galaxy number counts are ~ 50 000 galaxies per square degree at H< 20.75, in good agreement with those of LCIRS. The object catalog is published electronically at the CDS. The whole catalog is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/403/493}. Based on observations collected at the European Southern Observatory, Chile under programs 66.A-0451 and 68.A-0375.

  16. Anomalous foreshock field-aligned beams observed by Cluster

    NASA Astrophysics Data System (ADS)

    Meziane, K.; Hamza, A. M.; Wilber, M.; Mazelle, C.; Lee, M. A.

    2011-10-01

    We report occasional observations of two simultaneously distinct ion foreshock components recorded by the Cluster spacecraft upstream of the Earth's bow shock. In most occurrences, the lower-energy population originates as a field-aligned beam (FAB) associated with quasi-perpendicular regions, which loses energy as the IMF rotates into oblique geometries. A second beam, with energies in excess of ~10 keV, appears sometimes in association with the onset of ultra-low frequency (ULF) waves, and sometimes ahead of the appearance of the latter. Measurements from the mass spectrometer indicate that both beams consist of protons. While the lower-speed beam is well-accounted for by a known reflection mechanism, the non-radial IMF orientations as well as other arguments seem to rule out magnetosheath or magnetospheric sources for the higher energy component. The wave characteristics are typical of the oblique foreshock and we have found that they are in cyclotron-resonance with the low speed beam (FAB). These observations constitute a theoretical challenge since conventional mechanisms described in the literature cannot account for the production of beams at two different energies.

  17. Comment on ``Observation of anticorrelation in incoherent thermal light fields''

    NASA Astrophysics Data System (ADS)

    Shapiro, Jeffrey H.; Lantz, Eric

    2012-05-01

    Recently, Chen [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.033835 84, 033835 (2011)] reported observation of anticorrelated photon coincidences in a Mach-Zehnder interferometer whose input light came from a mode-locked Ti:sapphire laser that had been rendered spatially incoherent by passage through a rotating ground-glass diffuser. They provided a quantum-mechanical explanation of their results, which ascribes the anticorrelation to two-photon interference. They also developed a classical-light treatment of the experiment and showed that it was incapable of explaining the anticorrelation behavior. Here we show that semiclassical photodetection theory, i.e., classical electromagnetic fields plus photodetector shot noise, does indeed explain the anticorrelation found by Chen The key to our analysis is properly accounting for the disparate time scales associated with the laser's pulse duration, the speckle-correlation time, the interferometer's differential delay, and the duration of the photon-coincidence gate. Our result is consistent with the long-accepted dictum that laser light which has undergone linear-optical transformations is classical-state light, so that the quantum and semiclassical theories of photodetection yield quantitatively identical results for its measurement statistics. The interpretation provided by Chen for their observations implicitly contradicts that dictum.

  18. Determining degree-day thresholds from field observations

    NASA Astrophysics Data System (ADS)

    Snyder, R. L.; Spano, Donatella; Cesaraccio, Carla; Duce, Pierpaolo

    This paper compares several methods for determining degree-day (°D) threshold temperatures from field observations. Three of the methods use the mean developmental period temperature and simple equations to estimate: (1) the smallest standard deviation in °D, (2) the least standard deviation in days, and (3) a linear regression intercept. Two additional methods use iterations of cumulative °D and threshold temperatures to determine the smallest root mean square error (RMSE). One of the iteration methods uses a linear model and the other uses a single triangle °D calculation method. The method giving the best results was verified by comparing observed and predicted phenological periods using 7 years of kiwifruit data and 10 years of cherry tree data. In general, the iteration method using the single triangle method to calculate °D provided threshold temperatures with the smallest RMSE values. However, the iteration method using a linear °D model also worked well. Simply using a threshold of zero gave predictions that were nearly as good as those obtained using the other two methods. The smallest standard deviation in °D performed the worst. The least standard deviation in days and the regression methods did well sometimes; however, the threshold temperatures were sometimes negative, which does not support the idea that development rates are related to heat units.

  19. Field aligned current observations in the polar cusp ionosphere

    NASA Technical Reports Server (NTRS)

    Ledley, B. G.; Farthing, W. H.

    1973-01-01

    Vector magnetic field measurements made during a sounding rocket flight in the polar cusp ionosphere show field fluctuations in the lower F-region which are interpreted as being caused by the payload's passage through a structured field aligned current system. The field aligned currents have a characteristic horizontal scale size of one kilometer. Analysis of one large field fluctuation gives a current density of 0.0001 amp/m sq.

  20. Modeling the Jovian magnetic field and its secular variation using all available magnetic field observations

    NASA Astrophysics Data System (ADS)

    Ridley, Victoria A.; Holme, Richard

    2016-03-01

    We present new models of Jupiter's internal magnetic field and secular variation from all available direct measurements from three decades of spacecraft observation. A regularized minimum norm approach allows the creation of smooth, numerically stable models displaying a high degree of structure. External field from the magnetodisk is modeled iteratively for each orbit. Jupiter's inner magnetosphere is highly stable with time, with no evidence for variation with solar activity. We compare two spherical harmonic models, one assuming a field constant in time and a second allowing for linear time variation. Including secular variation improves data fit with fewer additional parameters than increasing field complexity. Our favored solution indicates a ˜0.012% yr-1 increase in Jupiter's dipole magnetic moment from 1973 to 2003; this value is roughly one quarter of that for Earth. Inaccuracies in determination of the planetary reference frame cannot explain all the observed secular variation. Should more structure be allowed in the solutions, we find the northern hemispherical configuration resembles recent models based on satellite auroral footprint locations, and there is also evidence of a possible patch of reversed polar flux seen at the expected depth of the dynamo region, resembling that found at Earth and with implications for the Jovian interior. Finally, using our preferred model, we infer flow dynamics at the top of Jupiter's dynamo source. Though highly speculative, the results produce several gyres with some symmetry about the equator, similar to those seen at Earth's core-mantle boundary, suggesting motion on cylinders aligned with the rotation axis.

  1. Earthquake Rupture Complexity Evidence from Field Observations (Invited)

    NASA Astrophysics Data System (ADS)

    Hudnut, K. W.; Fletcher, J. M.; Rockwell, T. K.; Gonzalez-Garcia, J. J.; Teran, O.; Akciz, S. O.

    2010-12-01

    Field observations provide strong evidence for four intriguing aspects of rupture process complexity for the 4 April 2010 El Mayor - Cucapah - Indiviso earthquake. First, the southern “fork” of the rupture exhibits two splays just to the northwest of the event epicenter, both with nearly pure right-lateral faulting. Teleseismic source modeling by others indicates normal slip on deep fault surface preceded the shallow strike-slip faulting, and our field observations from the fork area indicate that the earliest phase of strike-slip faulting did not involve a significant normal faulting component. Second, as rupture propagated to the northwest along the Pescadores fault, slip ended abruptly on this fault and transferred across a complex zone to the Borrego fault (although the Pescadores fault continues farther and would have seemed an easier route to follow). This stepover is called the Puerta Accommodation Zone (PAZ) which extends 11 km along-strike within an elevated portion of the Cucapah massif and accommodates a left step (transpressional) that measures less than 2 km across-strike. Though partly obscured by rockfalls in the steep terrain here, only discontinuous faulting of up to one meter reached the ground surface, yet imagery differencing by others indicates several meters of continuous subsurface slip throughout this section. This 11 km region of reduced and discontinuous slip is one of the longest surface rupture jumps ever observed, with lengthy and continuous surface faulting on either side. The SE end of the stepover coincides spatially with the Canon Rojo embayment where the M7.2 1892 surface rupture propagated onto a second fault forming an abrupt corner in its surface trace. Hence, the surface rupture and slip distribution pattern in 2010 appears to have been influenced by stress changes induced by the 1892 event. Thirdly, from the NW end of the transition section, the Borrego fault continues to the NNW with strong east-down slip obliquity. Along

  2. Experimental evidence for seismoelectric observations at field scale

    NASA Astrophysics Data System (ADS)

    Holzhauer, Julia; Yaramanci, Ugur

    2010-05-01

    In the past decades, seismoelectric has concentrated a growing interest as a promising tool for hydrogeophysical studies. Resulting from an electrokinetic coupling in porous saturated media traversed by an acoustic wave, this method could ultimately offer a direct access to various hydraulic parameters ranging from porosity to permeability or fluids conductivity. In some other aspects it also occasionally showed some ability to thin-layer resolution. Within the development of the new test-site Schillerslage with typical north-German geology, consisting of two shallow quaternary aquifers separated by a till layer over cretaceous marl, we tested the observability of the seismoelectric signal along with various conventional (seismic, georadar, geoelectric) and unconventional (magnetic resonance sounding -MRS, spectral induced polarisation -SIP) geophysical methods as well as boreholes analysis. The special focus was on the converted seismoelectric signal, an electromagnetic wave acting as a vertical dipole which should theoretically display on the seismoelectrogram as a horizontal arrival. This converted wave appears when the incident acoustic wave meets a hydraulic discontinuity affecting the pore space in any geometrical or chemical manner. This electromagnetic signal fades out rapidly, due to its dipole nature and its weakness, so that its relevance is restricted to the near surface characterisation. In the given setting, such a wave could either initiate at the water table or originate from an abrupt transition from sand to till. Decision was made to record both seismic and seismoelectric signal concomitantly. To allow the detection of the later signal, the field layout was gradually adjusted. Considering the source, hammer-seismic was chosen for its precision in near surface application and automatic trigger-techniques producing major disturbances in the first 10 ms of the seismoelectrogram were abandoned in favour of manual triggering. To avoid any further noise

  3. Unifying inflation and dark matter with the Peccei-Quinn field: Observable axions and observable tensors

    NASA Astrophysics Data System (ADS)

    Fairbairn, Malcolm; Hogan, Robert; Marsh, David J. E.

    2015-01-01

    A model of high scale inflation is presented where the radial part of the Peccei-Quinn (PQ) field with a non-minimal coupling to gravity plays the role of the inflaton, and the QCD axion is the dark matter. A quantum fluctuation of O (H /2 π ) in the axion field will result in a smaller angular fluctuation if the PQ field is sitting at a larger radius during inflation than in the vacuum. This changes the effective axion decay constant, fa, during inflation and dramatically reduces the production of isocurvature modes. This mechanism opens up a new window in parameter space where an axion decay constant in the range 1 012 GeV ≲fa≲1 015 GeV is compatible with observably large r . The exact range allowed for fa depends on the efficiency of reheating. This model also predicts a minimum possible value of r =1 0-3. The new window can be explored by a measurement of r possible with SPIDER and the proposed CASPEr experiment search for high fa axions.

  4. Field Observations of Coastal Air-Sea Interaction

    NASA Astrophysics Data System (ADS)

    Ortiz-Suslow, D. G.; Haus, B. K.; Williams, N. J.; Graber, H. C.

    2016-12-01

    In the nearshore zone wind, waves, and currents generated from different forcing mechanisms converge in shallow water. This can profoundly affect the physical nature of the ocean surface, which can significantly modulate the exchange of momentum, heat, and mass across the air-sea interface. For decades, the focus of air-sea interaction research has been on the open ocean while the shallow water regime has been relatively under-explored. This bears implications for efforts to understand and model various coastal processes, such as mixing, surface transport, and air-sea gas flux. The results from a recent study conducted at the New River Inlet in North Carolina showed that directly measured air-sea flux parameters, such as the atmospheric drag coefficient, are strong functions of space as well as the ambient conditions (i.e. wind speed and direction). The drag is typically used to parameterize the wind stress magnitude. It is generally assumed that the wind direction is the direction of the atmospheric forcing (i.e. wind stress), however significant wind stress steering off of the azimuthal wind direction was observed and was found to be related to the horizontal surface current shear. The authors have just returned from a field campaign carried out within Monterey Bay in California. Surface observations made from two research vessels were complimented by an array of beach and inland flux stations, high-resolution wind forecasts, and satellite image acquisitions. This is a rich data set and several case studies will be analyzed to highlight the importance of various processes for understanding the air-sea fluxes. Preliminary findings show that interactions between the local wind-sea and the shoaling, incident swell can have a profound effect on the wind stress magnitude. The Monterey Bay coastline contains a variety of topographical features and the importance of land-air-sea interactions will also be investigated.

  5. Field Observations of the Effects of Explosives on Snow Properties

    NASA Astrophysics Data System (ADS)

    Wooldridge, R.; Hendrikx, J.; Miller, D. A.; Birkeland, K.

    2012-12-01

    Explosives are a critically important component of avalanche control programs. They are used to both initiate avalanches and to test snowpack instability by ski areas, highway departments and other avalanche programs around the world. Current understanding of the effects of explosives on snow is mainly limited to shock wave behavior demonstrated through stress wave velocities, pressures and attenuation. This study seeks to enhance current knowledge of how explosives physically alter snow by providing practical, field-based observations and analyses that quantify the effect of explosives on snow density, snow hardness and snow stability test results. Density, hardness and stability test results were evaluated both before and after the application of 0.9 kg cast pentolite boosters as air blasts. Changes in these properties were evaluated at specified distances up to 4 meters (m) from the blast center using a density gauge, hand hardness, Compression Tests (CTs), and Extended Column Tests (ECTs). Statistically significant density increases occurred out to a distance of 1.5 m from the blast center and down to a depth of 60 centimeters (cm). Statistically significant density increases were also observed at the surface (down to 20 cm) out to a distance of 4 m. Hardness increased slightly at the surface and at the bottom of the snowpack (depths of 80-100 cm), while decreasing slightly in the middle of the snowpack (depths of 30-60 cm). Results from CTs showed a decrease in the number of taps needed for column failure in the post explosive tests, while a smaller data set of ECT results showed no overall change in ECT score. The findings of this study provide a better understanding of the physical changes in snow following explosives, which may lead to more effective and efficient avalanche risk mitigation.

  6. In situ magnetic field observations of the AMPTE artificial comet

    NASA Technical Reports Server (NTRS)

    Luehr, H.; Kloecker, N.; Southwood, D. J.; Dunlop, M. W.; Mier-Jedrzejowicz, W. A. C.; Rijnbeek, R. P.; Six, M.; Haeusler, B.; Acuna, M.

    1986-01-01

    Magnetometers aboard the IRM and UKS spacecraft monitored the magnetic field during the AMPTE artificial comet experiment of Dec. 27, 1984. Rapid photoionization of the released barium vapor resulted in the formation of a magnetic cavity, shielded from the ambient magnetic field.The presence of this highly conductive obstacle caused draping and compression of the solar wind magnetic field.

  7. The linear model and experimentally observed resonant field amplification in tokamaks and reversed field pinches

    SciTech Connect

    Pustovitov, V. D.

    2011-01-15

    A review is given of the experimentally observed effects related to the resonant field amplification (RFA) and the Resistive Wall Mode (RWM) instability in tokamaks and reversed field pinches (RFPs). This includes the feedback rotation of RWM in RFX-mod RFP, dependence of the RWM growth rate on the plasma-wall separation observed in JT-60U, appearance of the slowly growing RWM precursors in JT-60U and similar phenomena in other devices. The experimental results are compared with theoretical predictions based on the model comprising the Maxwell equations, Ohm's law for the conducting wall, the boundary conditions and assumption of linear plasma response to the external magnetic perturbations. The model describes the plasma reaction to the error field as essentially depending on two factors: the plasma proximity to the RWM stability threshold and the natural rotation frequency of the plasma mode. The linear response means that these characteristics are determined by the plasma equilibrium parameters only. It is shown that the mentioned effects in different devices under different conditions can be described on a common basis with only assumption that the plasma behaves as a linear system. To extend the range of the model validation, some predictions are derived with proposals for experimental studies of the RFA dynamics.

  8. An observational test of magnetospheric field models at geosynchronous orbit

    SciTech Connect

    Thomsen, M.F.; Weiss, L.A.; McComas, D.J.; Moldwin, M.B.; Reeves, G.D.

    1994-07-01

    The configuration of the geomagnetic field is an indicator of the response of the magnetosphere to the solar wind input. A number of empirical magnetospheric field models are currently in use which estimate the magnetic field direction and magnitude at any point within the magnetosphere under a variety of conditions. Here, the global nature of the Tsyganenko 89 [Tsyganenko, 1989] magnetospheric magnetic field model is tested by comparison of the model-predicted field orientations with the field orientations derived simultaneously at two different locations in geosynchronous orbit from the axis of symmetry of the plasma electron distribution function (30 eV--40 keV). The results for the particular time interval studied are inconclusive because the Tsyganenko 89 model does not describe the field at one of the satellites well enough, but the procedure itself appears promising.

  9. CORONAL MAGNETIC FIELDS DERIVED FROM SIMULTANEOUS MICROWAVE AND EUV OBSERVATIONS AND COMPARISON WITH THE POTENTIAL FIELD MODEL

    SciTech Connect

    Miyawaki, Shun; Nozawa, Satoshi; Iwai, Kazumasa; Shibasaki, Kiyoto; Shiota, Daikou

    2016-02-10

    We estimated the accuracy of coronal magnetic fields derived from radio observations by comparing them to potential field calculations and the differential emission measure measurements using EUV observations. We derived line-of-sight components of the coronal magnetic field from polarization observations of the thermal bremsstrahlung in the NOAA active region 11150, observed around 3:00 UT on 2011 February 3 using the Nobeyama Radioheliograph at 17 GHz. Because the thermal bremsstrahlung intensity at 17 GHz includes both chromospheric and coronal components, we extracted only the coronal component by measuring the coronal emission measure in EUV observations. In addition, we derived only the radio polarization component of the corona by selecting the region of coronal loops and weak magnetic field strength in the chromosphere along the line of sight. The upper limits of the coronal longitudinal magnetic fields were determined as 100–210 G. We also calculated the coronal longitudinal magnetic fields from the potential field extrapolation using the photospheric magnetic field obtained from the Helioseismic and Magnetic Imager. However, the calculated potential fields were certainly smaller than the observed coronal longitudinal magnetic field. This discrepancy between the potential and the observed magnetic field strengths can be explained consistently by two reasons: (1) the underestimation of the coronal emission measure resulting from the limitation of the temperature range of the EUV observations, and (2) the underestimation of the coronal magnetic field resulting from the potential field assumption.

  10. Clustered or regular cumulus cloud fields - The statistical character of observed and simulated cloud fields

    NASA Technical Reports Server (NTRS)

    Ramirez, Jorge A.; Bras, Rafael L.

    1990-01-01

    The spatial distribution of cumulus clouds is assumed to be the result of the effects of convective activity on the thermodynamic environment. The effects can be parameterized in terms of a stabilization function representing the time rate of change of convective available potential energy. Using these results, a new inhibition hypothesis explaining the expected characteristics of the spatial distribution of cumulus clouds is postulated. This paper performs a verification of the inhibition hypothesis on real and simulated cloud fields. In order to do so, an objective measure of the spatial characteristics of cumulus clouds is introduced. Multiple cloud experiments are performed with a three-dimensional numerical cloud model. Skylab pictures of real cumuli are also used in the verification. Results of applying this measure to simulated and observed cumulus cloud fields confirm the inhibition hypothesis.

  11. Neotectonic stresses in Fennoscandia: field observations and modelling

    NASA Astrophysics Data System (ADS)

    Pascal, Christophe

    2013-04-01

    The present-day stress state of Fennoscandia is traditionally viewed as the combination of far field sources and residual glacial loading stresses. Investigations were conducted in different regions of Norway with the purpose of detecting and measuring stress-relief features and to derive from them valuable information on the crustal stress state. Stress-relief features are induced by blasting and sudden rock unloading in road construction and quarrying operations and are common in Norway and very likely in other regions of Fennoscandia. Stress relief at the Earth's surface is diagnostic of anomalously high stress levels at shallow depths in the crust and appears to be a characteristic of the formerly glaciated Baltic and Canadian Precambrian shields. The studied stress-relief features are, in general, indicative of NW-SE compression, suggesting ridge-push as the main source of stress. Our derived stress directions are also in excellent agreement with the ones derived from other kinds of stress indicators, including focal mechanisms from deep earthquakes, demonstrating that stress-relief features are valuable for neotectonic research. As a second step we applied numerical modelling techniques to simulate the neotectonic stress field in Fennoscandia with particular emphasis to southern Norway. A numerical method was used to reconstruct the structure of the Fennoscandian lithosphere. The numerical method involves classical steady-state heat equations to derive lithosphere thickness, geotherm and density distribution and, in addition, requires the studied lithosphere to be isostatically compensated at its base. The a priori crustal structure was derived from previous geophysical studies. Undulations of the geoid were used to calibrate the models. Once the density structure of the Fennoscandian lithosphere is reconstructed it is straightforward to quantify its stress state and compare modelling results with existing stress indicators. The modelling suggests that

  12. Kinetics of droplet growth observed in recent field campaigns

    NASA Astrophysics Data System (ADS)

    Mei, F.; Wang, J.

    2012-12-01

    Atmospheric aerosols can indirectly influence global climate budget by changing the microphysical structure, lifetime, and coverage of clouds. While it is generally agreed that aerosol indirect effects act to cool the Earth-atmosphere system by increasing cloud reflectivity and coverage, the magnitudes of the indirect effects are poorly understood. The formation of cloud droplets from aerosol particles is kinetically controlled by the availability of water vapor, equilibrium water vapor pressure above the growing droplet surface, and both the gas phase and aerosol phase mass transfer resistances. It has been hypothesized that the formation of surface organic films or the delay in dissolution of solute could significantly delay the growth of cloud droplets. Such delay could lead to a higher maximum supersaturation within a rising cloud parcel, therefore higher droplet number concentration and smaller droplet size at constant liquid water content. When only a subset of the droplets experiences significant growth delay, the overall droplet size spectrum will be broadened, which facilitates the formation of precipitation. During three recent field campaigns (CalNex-LA, CARES, and Aerosol Intensive Observation Period at Brookhaven National Laboratory), the CCN activity and droplet growth of size selected particles ranging from 25 to 320 nm were characterized by a CCN counter under supersaturations from 0.1% to 0.8%. The three campaigns allow us to examine the droplet growth for many representative organic aerosol types, including biogenic SOA, anthropogenic SOA, and organic aerosols from biomass burning. The droplet growth of size-selected ambient particles inside the CCN counter was found to be influenced by a number of parameters, including particle critical supersaturation, heterogeneity in particle composition, and particle concentration. For example, reduced droplet growth due to water vapor depletion was observed when particle concentration was higher than 200 cm

  13. Extended field observations of cirrus clouds using a ground-based cloud observing system

    NASA Technical Reports Server (NTRS)

    Ackerman, Thomas P.

    1994-01-01

    The evolution of synoptic-scale dynamics associated with a middle and upper tropospheric cloud event that occurred on 26 November 1991 is examined. The case under consideration occurred during the FIRE CIRRUS-II Intensive Field Observing Period held in Coffeyville, KS during Nov. and Dec., 1991. Using data from the wind profiler demonstration network and a temporally and spatially augmented radiosonde array, emphasis is given to explaining the evolution of the kinematically-derived ageostrophic vertical circulations and correlating the circulation with the forcing of an extensively sampled cloud field. This is facilitated by decomposing the horizontal divergence into its component parts through a natural coordinate representation of the flow. Ageostrophic vertical circulations are inferred and compared to the circulation forcing arising from geostrophic confluence and shearing deformation derived from the Sawyer-Eliassen Equation. It is found that a thermodynamically indirect vertical circulation existed in association with a jet streak exit region. The circulation was displaced to the cyclonic side of the jet axis due to the orientation of the jet exit between a deepening diffluent trough and building ridge. The cloud line formed in the ascending branch of the vertical circulation with the most concentrated cloud development occurring in conjunction with the maximum large-scale vertical motion. The relationship between the large scale dynamics and the parameterization of middle and upper tropospheric clouds in large-scale models is discussed and an example of ice water contents derived from a parameterization forced by the diagnosed vertical motions and observed water vapor contents is presented.

  14. Observing earthquakes triggered in the near field by dynamic deformations

    USGS Publications Warehouse

    Gomberg, J.; Bodin, P.; Reasenberg, P.A.

    2003-01-01

    We examine the hypothesis that dynamic deformations associated with seismic waves trigger earthquakes in many tectonic environments. Our analysis focuses on seismicity at close range (within the aftershock zone), complementing published studies of long-range triggering. Our results suggest that dynamic triggering is not confined to remote distances or to geothermal and volcanic regions. Long unilaterally propagating ruptures may focus radiated dynamic deformations in the propagation direction. Therefore, we expect seismicity triggered dynamically by a directive rupture to occur asymmetrically, with a majority of triggered earthquakes in the direction of rupture propagation. Bilaterally propagating ruptures also may be directive, and we propose simple criteria for assessing their directivity. We compare the inferred rupture direction and observed seismicity rate change following 15 earthquakes (M 5.7 to M 8.1) that occured in California and Idaho in the United States, the Gulf of Aqaba, Syria, Guatemala, China, New Guinea, Turkey, Japan, Mexico, and Antarctica. Nine of these mainshocks had clearly directive, unilateral ruptures. Of these nine, seven apparently induced an asymmetric increase in seismicity rate that correlates with the rupture direction. The two exceptions include an earthquake preceded by a comparable-magnitude event on a conjugate fault and another for which data limitations prohibited conclusive results. Similar (but weaker) correlations were found for the bilaterally rupturing earthquakes we studied. Although the static stress change also may trigger seismicity, it and the seismicity it triggers are expected to be similarly asymmetric only if the final slip is skewed toward the rupture terminus. For several of the directive earthquakes, we suggest that the seismicity rate change correlates better with the dynamic stress field than the static stress change.

  15. The Khoy ophiolite: new field observations, geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Lechmann, Anna; Burg, Jean-Pierre; Mohammadi, Ali; Faridi, Mohammad

    2017-04-01

    The tectonic assemblage at the junction of the Bitlis-Zagros and Izmir-Ankara-Erzincan suture zones is exposed in the region of the Khoy Ophiolitic Complex, in the Azerbaijan Province of NW Iran. We present new petrography, major and trace element analyses, LA-ICP-MS U-Pb zircon ages and Sr-Nd-Pb isotope data of mantle and crustal suites together with field observations and stratigraphic ages obtained from foraminifera-bearing sediments. Ultramafic rocks crop out as mappable (km-scale) continuous units with fault bounded contacts to neighbouring lithologies and as blocks (m-scale) within an olistostrome. They vary from fresh lherzolite, harzburgite and dunite tectonites with primary mantle structures to completely serpentinized and metasomatized (with metamorphic olivine) samples. Rodingite dikes with MORB-REE signatures are common. Gabbros, also with MORB signature, occur only in small volumes. Pillow basalts have either a MORB or a calc-alkaline signature depending on sample location. First results show that the Khoy Ophiolitic Complex formed during the Jurassic (152-159 Ma) and came in a supra-subduction position, with calc-alkaline magmatism showing negative Nb-Ta and Ti anomalies, in Albian (105-109 Ma) times. Heavy minerals including Cr-spinel and serpentine within the turbidites of the region indicate that the ophiolites were being eroded as early as the Late Cretaceous. An Early Miocene olistostrome, containing blocks of the ophiolitic sequences unconformably covers the ophiolitic complex and the Late-Cretaceous to Eocene turbiditic sequences. A tuff layer dated at 43 Ma within a fine-grained and thin-bedded sandstone block within the olistostrome witnesses continuing volcanic activity in Eocene times. The Khoy Ophiolite compares well with the Inner Zagros and North Makran ophiolites, recording Jurassic extension in the Iranian continental margin followed by Late Cretaceous subduction. This work is supported by SNF Research Grant (project 200021_153124/1).

  16. Application of relativistic mean field and effective field theory densities to scattering observables for Ca isotopes

    SciTech Connect

    Bhuyan, M.; Panda, R. N.; Routray, T. R.; Patra, S. K.

    2010-12-15

    In the framework of relativistic mean field (RMF) theory, we have calculated the density distribution of protons and neutrons for {sup 40,42,44,48}Ca with NL3 and G2 parameter sets. The microscopic proton-nucleus optical potentials for p+{sup 40,42,44,48}Ca systems are evaluated from the Dirac nucleon-nucleon scattering amplitude and the density of the target nucleus using relativistic-Love-Franey and McNeil-Ray-Wallace parametrizations. We have estimated the scattering observables, such as the elastic differential scattering cross section, analyzing power and the spin observables with the relativistic impulse approximation (RIA). The results have been compared with the experimental data for a few selective cases and we find that the use of density as well as the scattering matrix parametrizations are crucial for the theoretical prediction.

  17. A Case Study of Hogtown Creek: Justification for Field Observations.

    ERIC Educational Resources Information Center

    West, Felicia E.

    A case-study model of a field trip to a small creek was made to facilitate the use of field studies as a technique for involving students and teachers in studying the earth as it undergoes change. Methods and techniques of planning are presented which include familiarization with the area by the teacher, the development of goals and objectives,…

  18. Modified electron acoustic field and energy applied to observation data

    SciTech Connect

    Abdelwahed, H. G. E-mail: hgomaa-eg@mans.edu.eg; El-Shewy, E. K.

    2016-08-15

    Improved electrostatic acoustic field and energy have been debated in vortex trapped hot electrons and fluid of cold electrons with pressure term plasmas. The perturbed higher-order modified-Korteweg-de Vries equation (PhomKdV) has been worked out. The effect of trapping and electron temperatures on the electro-field and energy properties in auroral plasmas has been inspected.

  19. Field Science Ethnography: Methods For Systematic Observation on an Expedition

    NASA Technical Reports Server (NTRS)

    Clancey, William J.; Clancy, Daniel (Technical Monitor)

    2001-01-01

    The Haughton-Mars expedition is a multidisciplinary project, exploring an impact crater in an extreme environment to determine how people might live and work on Mars. The expedition seeks to understand and field test Mars facilities, crew roles, operations, and computer tools. I combine an ethnographic approach to establish a baseline understanding of how scientists prefer to live and work when relatively unemcumbered, with a participatory design approach of experimenting with procedures and tools in the context of use. This paper focuses on field methods for systematically recording and analyzing the expedition's activities. Systematic photography and time-lapse video are combined with concept mapping to organize and present information. This hybrid approach is generally applicable to the study of modern field expeditions having a dozen or more multidisciplinary participants, spread over a large terrain during multiple field seasons.

  20. Mariner 10 magnetic field observations of the Venus wake

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Behannon, K. W.

    1977-01-01

    Magnetic field measurements made over a 21-hour interval during the Mariner 10 encounter with Venus were used to study the down-stream region of the solar wind-Venus interaction over a distance of approximately 100 R sub v. For most of the day before closest approach the spacecraft was located in a sheath-like region which was apparently bounded by planetary bow shock on the outer side and either a planetary wake boundary or transient boundary-like feature on the inner side. The spacecraft made multiple encounters with the wake-like boundary during the 21-hour interval with an increasing frequency as it approached the planet. Each pass into the wake boundary from the sheath region was consistently characterized by a slight decrease in magnetic field magnitude, a marked increase in the frequency and amplitude of field fluctuations, and a systematic clockwise rotation of the field direction when viewed from above the plane of the planet orbit.

  1. Correlation between atmospheric electric fields and cloud cover using a field mill and cloud observation data

    NASA Astrophysics Data System (ADS)

    Nakamori, Kota; Suzuki, Yasuki; Ohya, Hiroyo; Takano, Toshiaki; Kawamura, Yohei; Nakata, Hiroyuki; Yamashita, Kozo

    2017-04-01

    It is known that lightning and precipitations of rain droplets generated from thunderclouds are a generator of global atmospheric electric circuit. In the fair weather, the atmospheric electric fields (AEF) are downward (positive), while they are upward (negative) during lightning and precipitations. However, the correlations between the AEF, and the cloud parameters such as cloud cover, weather phenomenon, have been not revealed quantitatively yet. In this study, we investigate the correlations between the AEF and the cloud parameters, weather phenomenon using a field mill, the 95 GHz-FALCON (FMCW Radar for Cloud Observations)-I and all-sky camera observations. In this study, we installed a Boltek field mill on the roof of our building in Chiba University, Japan, (Geographic coordinate: 35.63 degree N, 140.10 degree E, the sea level: 55 m) on the first June, 2016. The sampling time of the AEF is 0.5 s. On the other hand, the FALCON-I has observed the cloud parameters far from about 76 m of the field mill throughout 24 hours every day. The vertical cloud profiles and the Doppler velocity of cloud particles can be derived by the FALCON-I with high distance resolutions (48.8 m) (Takano et al., 2010). In addition, the images of the clouds and precipitations are recorded with 30-s sampling by an all-sky camera using a CCD camera on the same roof during 05:00-22:00 LT every day. The distance between the field mill and the all-sky camera is 3.75 m. During 08:30 UT - 10:30 UT, on 4 July, 2016, we found the variation of the AEF due to the approach of thundercloud. The variation consisted of two patterns. One was slow variation due to the movement of thunderclouds, and the other was rapid variation associated with lightning discharges. As for the movement of thunderclouds, the AEF increased when the anvil was located over the field mill, which was opposite direction of the previous studies. This change might be due to the positive charges in the upper anvil more than 14 km

  2. Laboratory Observation Of Magnetic Field Growth Driven By Shear Flow

    NASA Astrophysics Data System (ADS)

    Intrator, T.; Sun, X.; Dorf, L.; Sears, J.; Weber, T.; Lapenta, G.

    2012-12-01

    We have measured in the laboratory profiles of magnetic flux ropes, that include ion flow, magnetic field, current density, and plasma pressure. These data allow a complete screw pinch equilibrium with guide magnetic field to be reconstructed, and the electron flows to be inferred. We use this information to evaluate the Hall JxB term in a two fluid magnetohydrodynamic Ohms Law. The difference between ion and electron flows allows us to show experimentally and theoretically that the sheared electron flows can account for the generation of magnetic field. For example we show a measured quadrupole out of plane magnetic field B_z structure that occurs even in the absence of magnetic reconnection. This out of plane quadrupole pattern has historically been used as a signature of magnetic reconnection, especially with small to vanishing guide field. Recent theoretical analyses have pointed out that this presumption need not be true. *Supported by DOE Office of Fusion Energy Sciences under LANS contract DE-AC52-06NA25369, NASA Geospace NNHIOA044I, Basic

  3. Results from HST Observations of Six LMC Globular Cluster Fields

    NASA Astrophysics Data System (ADS)

    Olsen, K. A. G.; Hodge, P. W.; Mateo, M.; Olszewski, E. W.; Schommer, R. A.; Suntzeff, N. B.; Walker, A. R.

    We present deep HST color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, NGC 1898, NGC 1916, NGC 2005, and NGC 2019. Separate cluster and field star CMDs are shown. The time of formation of the LMC is studied from an analysis of the cluster CMDs. Based on a comparison of the CMDs with sequences of the Milky Way clusters M3, M5, and M55, we suggest that the LMC formed its first stars at the same time as the Milky Way to within 1 Gyr. We derive abundances and reddenings of the clusters that agree roughly with published values. Adopting our measured abundances, we find additional evidence that these LMC globular clusters are as old as the oldest Milky Way clusters through a comparison of our data with the horizontal branch evolutionary models of Lee, Demarque, and Zinn (1994). The evolution of the LMC following its formation is studied through an analysis of the field star CMDs. Through an automated comparison with stellar evolution models, we extract the star formation histories implied by the CMDs and luminosity functions. We explore the effects of varying the reddening, distance modulus, and IMF of the field stars on the derived star formation histories. We discuss the evidence for different star formation histories among the six fields.

  4. Faint Object Camera observations of a globular cluster nova field

    NASA Technical Reports Server (NTRS)

    Margon, Bruce; Anderson, Scott F.; Downes, Ronald A.; Bohlin, Ralph C.; Jakobsen, Peter

    1991-01-01

    The Faint Object Camera onboard Hubble Space Telescope has obtained U and B images of the field of Nova Ophiuchi 1938 in the globular cluster M14 (NGC 6402). The candidate for the quiescent nova suggested by Shara et al. (1986) is clearly resolved into at least six separate images, probably all stellar, in a region of 0.5 arcsec. Although two of these objects are intriguing as they are somewhat ultraviolet, the actual nova counterpart remains ambiguous, as none of the images in the field has a marked UV excess. Many stars within the 1.4 arcsec (2 sigma) uncertainty of the nova outburst position are viable counterparts if only astrometric criteria are used for selection. The 11 x 11 arcsec frames easily resolve several hundred stars in modest exposures, implying that HST even in its current optical configuration will be unique for studies of very crowded fields at moderate (B = 22) limiting magnitudes.

  5. Faint Object Camera observations of a globular cluster nova field

    NASA Technical Reports Server (NTRS)

    Margon, Bruce; Anderson, Scott F.; Downes, Ronald A.; Bohlin, Ralph C.; Jakobsen, Peter

    1991-01-01

    The Faint Object Camera onboard Hubble Space Telescope has obtained U and B images of the field of Nova Ophiuchi 1938 in the globular cluster M14 (NGC 6402). The candidate for the quiescent nova suggested by Shara et al. (1986) is clearly resolved into at least six separate images, probably all stellar, in a region of 0.5 arcsec. Although two of these objects are intriguing as they are somewhat ultraviolet, the actual nova counterpart remains ambiguous, as none of the images in the field has a marked UV excess. Many stars within the 1.4 arcsec (2 sigma) uncertainty of the nova outburst position are viable counterparts if only astrometric criteria are used for selection. The 11 x 11 arcsec frames easily resolve several hundred stars in modest exposures, implying that HST even in its current optical configuration will be unique for studies of very crowded fields at moderate (B = 22) limiting magnitudes.

  6. Multi-point Magnetic Field Observations of Field-Aligned Currents from Swarm Constellation Mission

    NASA Astrophysics Data System (ADS)

    Le, Guan; Chi, Peter; Lühr, Hermann; Gjerloev, Jesper; Stolle, Claudia; Park, Jaeheung; Rauberg, Jan

    2015-04-01

    In this paper, we report the results of case studies of multi-point magnetic field measurements of field-aligned currents (FACs) from Swarm constellation mission to understand their temporal characteristics and hemispheric asymmetry. For science operations (since April, 2014), the three spacecraft were placed in slightly different polar orbits: Swarm B spacecraft in a higher altitude orbit (507km x 512km) and Swarm A and C side-by-side in lower altitude orbits (459km x 462km). In the beginning of the science operational phase, the longitudinal separations of the orbital planes were small, and Swarm A/C pair and Swarm B were nearly out of phase in the orbit. This unique orbit configuration provides opportunities to study some new features of FACs. Specifically, the Swarm satellites make multiple crossings of a FAC region within a few hours. Such data enable us to study temporal variations in several time scales, from 1 minute up to about 3 hours. Furthermore, the three satellites make nearly simultaneous observations of FACs in northern and southern hemispheres, which provide us an opportunity to study the hemispheric asymmetry.

  7. Convective Systems Observed and Simulated During TRMM Field Campaigns

    NASA Technical Reports Server (NTRS)

    Tao, Wei-Kuo; Einaudi, Franco (Technical Monitor)

    2001-01-01

    Recently completed TRMM field campaigns (TEFLUN1998, SCSMEX-1998, TRMM.LBA-1999, and KWAJEX 1999) have obtained direct measurements of microphysical data associated with convective systems from various geographical locations. These TRMM field experiments were designed to contribute to fundamental understanding of cloud dynamics and microphysics, as well as for validation,, testing assumptions and error estimates of cloud-resolving models, forward radiative transfer models, algorithms used to estimate rainfall statistics and vertical structure of precipitation and latent heating from both surface-based radar and satellites.

  8. Reactivity to Systematic Observation with Film: A Field Experiment

    ERIC Educational Resources Information Center

    Smith, Richard L.; And Others

    1975-01-01

    The reluctance to use film and video equipment for systematic observation and recording can be partially attributed to an assumption of reactivity and internal invalidity. The results of the study discuss placement of the observer and the use of film in data collection. (Author/DEP)

  9. An improved Overhauser magnetometer for Earth's magnetic field observation

    NASA Astrophysics Data System (ADS)

    Fan, Shifang; Chen, Shudong; Zhang, Shuang; Guo, Xin; Cao, Qiong

    2016-09-01

    Overhauser magnetometer is a kind of high-precision devices for magnetostatic field measurement. It is widely used in geological survey, earth field variations, UXO detection etc. However, the original Overhauser magnetometer JOM-2 shows great shortcomings of low signal to noise ratio (SNR) and high power consumption, which directly affect the performance of the device. In order to increase the sensitivity and reduce power consumption, we present an improved Overhauser magnetometer. Firstly, compared with the original power board which suffers from heavy noise for improper EMC design, an improved power broad with 20mV peak to peak noise is presented in this paper. Then, the junction field effect transistor (JFET) is used as pre-amplifier in our new design, to overcome the higher current noise produced by the original instrumentation amplifier. By adjusting the parameters carefully low noise factor down to 0.5 dB can be obtained. Finally, the new architecture of ARM + CPLD is adopted to replace the original one with DSP+CPLD. So lower power consumption and greater flash memory can be realized. With these measures, an improved Overhauser magnetometer with higher sensitivity and lower power consumption is design here. The experimental results indicate that the sensitivity of the improved Overhauser magnetometer is 0.071nT, which confirms that the new magnetometer is sensitive to earth field measurement.

  10. Magnetic Field and Plasma Diagnostics from Coordinated Prominence Observations

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Levens, P.; Dalmasse, K.; Mein, N.; Mein, P.; Lopez-Ariste, A.; Labrosse, N.; Heinzel, P.

    2016-04-01

    We study the magnetic field in prominences from a statistical point of view, by using THEMIS in the MTR mode, performing spectropolarimetry of the He I D3 line. Combining these measurements with spectroscopic data from IRIS, Hinode/EIS as well as ground-based telescopes, such as the Meudon Solar Tower, we infer the temperature, density, and flow velocities of the plasma. There are a number of open questions that we aim to answer: - What is the general direction of the magnetic field in prominences? Is the model using a single orientation of magnetic field always valid for atypical prominences? %- Does this depend on the location of the filament on the disk (visible in Hα, in He II 304 Å) over an inversion line between weak or strong network ? - Are prominences in a weak environment field dominated by gas pressure? - Measuring the Doppler shifts in Mg II lines (with IRIS) and in Hα can tell us if there are substantial velocities to maintain vertical rotating structures, as has been suggested for tornado-like prominences. We present here some results obtained with different ground-based and space-based instruments in this framework.

  11. Space Technology 5 observations of auroral field-aligned currents

    NASA Astrophysics Data System (ADS)

    Slavin, James

    During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.6o) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness, and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the "standard method," based upon s/c velocity, but corrected for FAC current sheet motion, and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data set and expand to include horizontal ionospheric currents, ULF waves and geomagnetic field gradient analyses.

  12. Space Technology 5 Observations of Auroral Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Slavin, James

    2008-01-01

    During its three month long technology validation mission, Space Technology 5 (ST-5) returned high quality multi-point measurements of the near-Earth magnetic field. Its three micro-satellites were launched into a 300 x 4500 km, dawn - dusk, sun synchronous orbit (inclination = 105.60) orbit with a period of 138 min by a Pegasus launch vehicle on March 22, 2006. The spacecraft were maintained in a "pearls on a sting" constellation with controlled spacings ranging from just over 5000 km down to under 50 km. The individual micro-satellites were 48 cm tall octagons with diameters of 50 cm. They were spin-stabilized at approximately 20 rpm at deployment and slowly spun-down to about 15 rpm by the end of the mission. Each spacecraft carried a miniature tri-axial fluxgate magnetometer (MAG) provided by the University of California at Los Angeles mounted at the end of a ultra-low mass 72 cm boom. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of 10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness. and current density. Two multi-point methods for the inference of FAC current density that have not previously been possible in low-Earth orbit are demonstrated: 1) the -standard method." based upon s/c velocity, but corrected for FAC current sheet motion. and 2) the "gradiometer method" which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST-5 data sct and expand to include horizontal ionospheric currents. ULF waves and geomagnetic field gradient analyses.

  13. Observation of Parallel Electric Fields in a Reconnecting Magnetosheath Current Sheet

    NASA Astrophysics Data System (ADS)

    Wilder, Frederick; Ergun, Robert; Eriksson, Stefan; Ahmadi, Narges; Goodrich, Katherine; Phan, Tai; Newman, David; Trattner, Karlheinz; Burch, James; Torbert, Roy; Giles, Barbara; Strangeway, Robert

    2017-04-01

    We present observations of symmetric reconnection in the Earth's magnetosheath by the Magnetospheric Multiscale (MMS) mission. The observed event has a guide field of 0.5 times the reconnecting magnetic field. The observations suggest that three of the four spacecraft encountered an electron jet in the direction of the magnetic field reversal, as well as hall magnetic field and electric field signatures. Coincident with the electron jet is enhanced dissipation of approximately 8 nW/m2 and a parallel electric field of -4 mV/m. The parallel electric field is associated with electron phase space holes, suggesting that it is accelerating electrons in the electron jet.

  14. Sensor Technology Performance Characteristics- Field and Laboratory Observations

    EPA Science Inventory

    Observed Intangible Performance Characteristics RH and temperature impacts may be significant for some devices Internal battery lifetimes range from 4 to 24 hoursSensor packaging can interfere with accurate measurements (reactivity)Wireless communication protocols are not foolpr...

  15. Sensor Technology Performance Characteristics- Field and Laboratory Observations

    EPA Science Inventory

    Observed Intangible Performance Characteristics RH and temperature impacts may be significant for some devices Internal battery lifetimes range from 4 to 24 hoursSensor packaging can interfere with accurate measurements (reactivity)Wireless communication protocols are not foolpr...

  16. Observation of airplane flow fields by natural condensation effects

    NASA Technical Reports Server (NTRS)

    Campbell, James F.; Chambers, Joseph R.; Rumsey, Christopher L.

    1988-01-01

    In-flight condensation patterns can illustrate a variety of airplane flow fields, such as attached and separated flows, vortex flows, and expansion and shock waves. These patterns are a unique source of flow visualization that has not been utilized previously. Condensation patterns at full-scale Reynolds number can provide useful information for researchers experimenting in subscale tunnels. It is also shown that computed values of relative humidity in the local flow field provide an inexpensive way to analyze the qualitative features of the condensation pattern, although a more complete theoretical modeling is necessary to obtain details of the condensation process. Furthermore, the analysis revealed that relative humidity is more sensitive to changes in local static temperature than to changes in pressure.

  17. A Multipole Model of the Observed Cerebral Cortex Magnetic Field.

    DTIC Science & Technology

    1984-12-01

    extends out of the cortex to connect to other cortex areas or subcortical areas. Thus, while the stellate cells are primarily cortical interconnecting...between electrons 17 becomes more important than disordering thermal effects. As a result, the electrons bind together in pairs which appear to have the... relationship is established between the applied magnetic field and the current flowing around the loop. The sensitivity of a Josephson junction will be

  18. Microspacecraft and Earth observation: Electrical field (ELF) measurement project

    NASA Technical Reports Server (NTRS)

    Olsen, Tanya; Elkington, Scot; Parker, Scott; Smith, Grover; Shumway, Andrew; Christensen, Craig; Parsa, Mehrdad; Larsen, Layne; Martinez, Ranae; Powell, George

    1990-01-01

    The Utah State University space system design project for 1989 to 1990 focuses on the design of a global electrical field sensing system to be deployed in a constellation of microspacecraft. The design includes the selection of the sensor and the design of the spacecraft, the sensor support subsystems, the launch vehicle interface structure, on board data storage and communications subsystems, and associated ground receiving stations. Optimization of satellite orbits and spacecraft attitude are critical to the overall mapping of the electrical field and, thus, are also included in the project. The spacecraft design incorporates a deployable sensor array (5 m booms) into a spinning oblate platform. Data is taken every 0.1 seconds by the electrical field sensors and stored on-board. An omni-directional antenna communicates with a ground station twice per day to down link the stored data. Wrap-around solar cells cover the exterior of the spacecraft to generate power. Nine Pegasus launches may be used to deploy fifty such satellites to orbits with inclinations greater than 45 deg. Piggyback deployment from other launch vehicles such as the DELTA 2 is also examined.

  19. Laboratory observation of magnetic field growth driven by shear flow

    NASA Astrophysics Data System (ADS)

    Intrator, T. P.; Dorf, L.; Sun, X.; Feng, Y.; Sears, J.; Weber, T.

    2014-04-01

    Two magnetic flux ropes that collide and bounce have been characterized in the laboratory. We find screw pinch profiles that include ion flow vi, magnetic field B, current density J, and plasma pressure. The electron flow ve can be inferred, allowing the evaluation of the Hall J ×B term in a two fluid magnetohydrodynamic Ohm's Law. Flux ropes that are initially cylindrical are mutually attracted and compress each other, which distorts the cylindrical symmetry. Magnetic field is created via the ∇×ve×B induction term in Ohm's Law where in-plane (perpendicular) shear of parallel flow (along the flux rope) is the dominant feature, along with some dissipation and magnetic reconnection. We predict and measure the growth of a quadrupole out-of-plane magnetic field δBz. This is a simple and coherent example of a shear flow driven dynamo. There is some similarity with two dimensional reconnection scenarios, which induce a current sheet and thus out-of-plane flow in the third dimension, despite the customary picture that considers flows only in the reconnection plane. These data illustrate a general and deterministic mechanism for large scale sheared flows to acquire smaller scale magnetic features, disordered structure, and possibly turbulence.

  20. Laboratory Observation of Magnetic Field Growth Driven by Shear Flow

    NASA Astrophysics Data System (ADS)

    Intrator, Thomas; Dorf, L.; Sun, X.; Sears, J.; Weber, T.; Feng, Y.

    2013-04-01

    We have measured in the laboratory profiles of magnetic flux ropes, that include ion flow, magnetic field, current density, and plasma pressure. The electron flows v_e can therefore be inferred, and we use this information to evaluate the Hall J × B term in a two fluid magnetohydrodynamic Ohm’s Law. Mutually attracted and compressed flux ropes break the cylindrical symmetry. This simple and coherent example of shear flow supports magnetic field growth corresponding to non vanishing curl × v_e × B. In the absence of magnetic reconnection we measure and predict a quadrupole out of plane magnetic field δBz, even though this has historically been invoked to be the signature of Hall magnetic reconnection. This provides a natural and general mechanism for large scale sheared flows to acquire smaller scale magnetic features, disordered structure, and possibly turbulence. *Supported by DOE Office of Fusion Energy Sciences under LANS contract DE-AC52-06NA25369, NASA Geospace NNHIOA044I, Basic

  1. Laboratory observation of magnetic field growth driven by shear flow

    SciTech Connect

    Intrator, T. P. Feng, Y.; Sears, J.; Weber, T.; Dorf, L.; Sun, X.

    2014-04-15

    Two magnetic flux ropes that collide and bounce have been characterized in the laboratory. We find screw pinch profiles that include ion flow v{sub i}, magnetic field B, current density J, and plasma pressure. The electron flow v{sub e} can be inferred, allowing the evaluation of the Hall J×B term in a two fluid magnetohydrodynamic Ohm's Law. Flux ropes that are initially cylindrical are mutually attracted and compress each other, which distorts the cylindrical symmetry. Magnetic field is created via the ∇×v{sub e}×B induction term in Ohm's Law where in-plane (perpendicular) shear of parallel flow (along the flux rope) is the dominant feature, along with some dissipation and magnetic reconnection. We predict and measure the growth of a quadrupole out-of-plane magnetic field δB{sub z}. This is a simple and coherent example of a shear flow driven dynamo. There is some similarity with two dimensional reconnection scenarios, which induce a current sheet and thus out-of-plane flow in the third dimension, despite the customary picture that considers flows only in the reconnection plane. These data illustrate a general and deterministic mechanism for large scale sheared flows to acquire smaller scale magnetic features, disordered structure, and possibly turbulence.

  2. Microspacecraft and Earth observation: Electrical field (ELF) measurement project

    NASA Astrophysics Data System (ADS)

    Olsen, Tanya; Elkington, Scot; Parker, Scott; Smith, Grover; Shumway, Andrew; Christensen, Craig; Parsa, Mehrdad; Larsen, Layne; Martinez, Ranae; Powell, George

    The Utah State University space system design project for 1989 to 1990 focuses on the design of a global electrical field sensing system to be deployed in a constellation of microspacecraft. The design includes the selection of the sensor and the design of the spacecraft, the sensor support subsystems, the launch vehicle interface structure, on board data storage and communications subsystems, and associated ground receiving stations. Optimization of satellite orbits and spacecraft attitude are critical to the overall mapping of the electrical field and, thus, are also included in the project. The spacecraft design incorporates a deployable sensor array (5 m booms) into a spinning oblate platform. Data is taken every 0.1 seconds by the electrical field sensors and stored on-board. An omni-directional antenna communicates with a ground station twice per day to down link the stored data. Wrap-around solar cells cover the exterior of the spacecraft to generate power. Nine Pegasus launches may be used to deploy fifty such satellites to orbits with inclinations greater than 45 deg. Piggyback deployment from other launch vehicles such as the DELTA 2 is also examined.

  3. An observational test of magnetospheric magnetic field mapping

    SciTech Connect

    Weiss, L.A.; Thomsen, M.F.; Reeves, G.D.; Hones, E.W.; McComas, D.J.

    1994-07-01

    The distortion of the geomagnetic field is a key signature of the response of the magnetosphere to the solar wind input. A number of empirical models have been devised to estimate the magnetic field direction and magnitude at any point within the magnetosphere under a variety of conditions. We describe a technique whereby the field-line mapping predicted by such models is tested by matching measurements of magnetospheric plasma energy spectra obtained by Los Alamos instruments at geosynchronous orbit with spectra obtained by instruments on the polar-orbiting DMSP satellites (at an altitude of about 800 km) at times when the two satellites are in approximate magnetic conjugacy. With up to three geosynchronous satellites and as many as four DMSP satellites in operation at any given time, there are a very large number of such two-satellite conjunctions, allowing the model mappings to be tested under a wide range of local times and geomagnetic activity. Preliminary results from the application of this technique are presented for one week of data from March, 1991.

  4. Relationships between field-aligned currents, electric fields and particle precipitation as observed by dynamics Explorer-2

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Iyemori, T.; Hoffman, R. A.; Maynard, N. C.; Burch, J. L.; Winningham, J. D.

    1983-01-01

    The relationships between field-aligned currents, electric fields, and particle fluxes are determined using observations from the polar orbiting low-altitude satellite Dynamics Explorer-2. It is shown that the north-south electric field and the east-west magnetic field components are usually highly correlated in the field-aligned current regions. This proportionality observationally proves that the field-aligned current equals the divergence of the height-integrated ionospheric Pedersen current in the meridional plane to a high degree of approximation. As a general rule, in the evening sector the upward field-aligned currents flow in the boundary plasma sheet region and the downward currents flow in the central plasma sheet region. The current densities determined independently from the plasma and magnetic field measurements are compared. Although the current densities deduced from the two methods are in general agreement, the degree and extent of the agreement vary in individual cases.

  5. Relationships between field-aligned currents, electric fields, and particle precipitation as observed by Dynamics Explorer-2

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Iyemori, T.; Hoffman, R. A.; Maynard, N. C.; Burch, J. L.; Winningham, J. D.

    1984-01-01

    The relationships between field-aligned currents, electric fields, and particle fluxes are determined using observations from the polar orbiting low-altitude satellite Dynamics Explorer-2. It is shown that the north-south electric field and the east-west magnetic field components are usually highly correlated in the field-aligned current regions. This proportionality observationally proves that the field-aligned current equals the divergence of the height-integrated ionospheric Pedersen current in the meridional plane to a high degree of approximation. As a general rule, in the evening sector the upward field-aligned currents flow in the boundary plasma sheet region and the downward currents flow in the central plasma sheet region. The current densities determined independently from the plasma and magnetic field measurements are compared. Although the current densities deduced from the two methods are in general agreement, the degree and extent of the agreement vary in individual cases.

  6. HST Advanced Camera Observations of the Hubble Deep Fields

    NASA Astrophysics Data System (ADS)

    Illingworth, G. D.; Ford, H. C.; Franx, M.; Benitez, N.; Blakeslee, J. P.; Bouwens, R.; Broadhurst, T. J.; Gronwall, C.; Martel, A.; Miley, G.; Postman, M.; Rosati, P.; Tsvetanov, Z. I.; ACS Science Team

    2002-05-01

    The HST Advanced Camera (ACS) provides survey capability for characterizing distant galaxies that is ~10X better than WFPC2, through its greatly increased sensitivity, areal coverage and improved spatial resolution. The SDSS filter set also provides new opportunities for the study of distant galaxies --- for example, the detection of galaxies at very high redshifts through ``dropouts'' using the red `i'and `z' filters. Early observations of the HDF-N and HDF-S are being taken to tie the ACS data into the vast array of observations already carried out on the HDFs, and to demonstrate the capabilities of the ACS in this area. The first observations of the HDF-N and HDF-S will be shown. The support of NASA and the efforts of the HST project and Ball (BATC) will be acknowledged.

  7. VOYAGER OBSERVATIONS OF THE DIFFUSE FAR-ULTRAVIOLET RADIATION FIELD

    SciTech Connect

    Murthy, Jayant; Henry, Richard Conn; Holberg, Jay B.

    2012-03-01

    The two Voyager spacecraft have completed their planetary exploration mission and are now probing the outer realms of the heliosphere. The Voyager ultraviolet spectrometers continued to operate well after the Voyager 2 Neptune encounter in 1989. We present a complete database of diffuse radiation observations made by both Voyagers: a total of 1943 spectra (500-1600 A) scattered throughout the sky. These include observations of dust-scattered starlight, emission lines from the hot interstellar medium, and a number of locations where no diffuse radiation was detected, with the very low upper limit of about 25 photons cm{sup -2} s{sup -1} sr{sup -1} A{sup -1}. Many of these observations were from late in the mission when there was significantly less contribution from interplanetary emission lines and thus less contamination of the interstellar signal.

  8. A cumulus cloud field observed by Landsat Thematic Mapper

    NASA Technical Reports Server (NTRS)

    Hoffman, Ross N.; Isaacs, Ronald G.

    1986-01-01

    The development of a spatial coherence scene model which is to be utilized to determine cloud properties from TM data is described. The observed radiances are modeled in terms of ocean and cloud spectra, the cloud fraction, and a geometric factor. Consideration is given to saturation effects and the need to constrain the model. The conjugate gradient algorithm is utilized to fit the model. A one-dimensional simulation was performed in order to evaluate the model; it is observed that the model provides good fit.

  9. Field observations of artificial sand and oil agglomerates

    USGS Publications Warehouse

    Dalyander, Patricia (Soupy); Long, Joseph W.; Plant, Nathaniel G.; McLaughlin, Molly R.; Mickey, Rangley C.

    2015-01-01

    Oil that comes into the surf zone following spills, such as occurred during the 2010 Deepwater Horizon (DWH) blowout, can mix with local sediment to form heavier-than-water sand and oil agglomerates (SOAs), at times in the form of mats a few centimeters thick and tens of meters long. Smaller agglomerates that form in situ or pieces that break off of larger mats, sometimes referred to as surface residual balls (SRBs), range in size from sand-sized grains to patty-shaped pieces several centimeters (cm) in diameter. These mobile SOAs can cause beach oiling for extended periods following the spill, on the scale of years as in the case of DWH. Limited research, including a prior effort by the U.S. Geological Survey (USGS) investigating SOA mobility, alongshore transport, and seafloor interaction using numerical model output, focused on the physical dynamics of SOAs. To address this data gap, we constructed artificial sand and oil agglomerates (aSOAs) with sand and paraffin wax to mimic the size and density of genuine SOAs. These aSOAs were deployed in the nearshore off the coast of St. Petersburg, Florida, during a field experiment to investigate their movement and seafloor interaction. This report presents the methodology for constructing aSOAs and describes the field experiment. Data acquired during the field campaign, including videos and images of aSOA movement in the nearshore (1.5-meter and 0.5-meter water depth) and in the swash zone, are also presented in this report.

  10. Observability of atomic line features in strong magnetic fields

    NASA Technical Reports Server (NTRS)

    Wunner, G.; Ruder, H.; Herold, H.; Truemper, J.

    1981-01-01

    The physical properties of atoms in superstrong magnetic fields, characteristic of neutron stars, and the possibility of detecting magnetically strongly shifted atomic lines in the spectra of magnetized X-ray pulsars are discussed. It is suggested that it is recommendable to look for magnetically strongly shifted Fe 26 Lyman lines in rotating neutron stars of not too high luminosity using spectrometers working in the energy range 10 - 20 keV, with sensitivities to minus 4 power photons per sq cm and second, and resolution E/delta E approx. 10-100.

  11. Neptune's polar cusp region - Observations and magnetic field analysis

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Burlaga, L. F.; Lazarus, A. J.; Vasyliunas, V. M.; Szabo, A.; Steinberg, J.; Ness, N. F.; Krimigis, S. M.

    1992-01-01

    This paper confirms and extends the results of Szabo et al. (1991) (which demonstrated some similarities of the Neptune's polar cusp region to the earth's cusp), but uses a different approach requiring plasma and vector magnetic field quantities. In addition, various MHD properties of the cusp-magnetopause boundary, which separates the cusp from the magnetosheath allowing thermal anisotropy, are obtained, including the magnetopause (MP) normal, mass, and normal momentum flux, the boundary speed (and thickness), and their relationships. Results demonstrate that the MP velocity is composed of two components: a propagation speed and the other component consistent with the rotational motion of the magnetosphere.

  12. Situational Evidence: Strategies for Causal Reasoning From Observational Field Notes

    ERIC Educational Resources Information Center

    Katz, Jack

    2015-01-01

    There is unexamined potential for developing and testing rival causal explanations in the type of data that participant observation is best suited to create: descriptions of in situ social interaction crafted from the participants' perspectives. By intensively examining a single ethnography, we can see how multiple predictions can be derived from…

  13. Observations and Opinions of Student Teachers while in the Field.

    ERIC Educational Resources Information Center

    Masztal, Nancy; Singleton, Dorothy

    This study surveyed teacher education students during their student teaching assignments in order to determine their perspectives on their preparedness for the classroom and their observations or use of effective teaching strategies during their student teaching experiences. Responses were obtained from 31 preservice teachers, 26 elementary and 6…

  14. Programs for the Field Collection of Observational Data.

    ERIC Educational Resources Information Center

    Roberts, William L.; Schill, Loreen G.

    The collection of observational data in natural settings and in real time requires equipment that is light and easily used, and programs that permit rapid and flexible encoding of data. This paper describes a set of four programs for collecting and analyzing continuous time sample, focal-individual data as described by J. Altmann (1974), using a…

  15. Time Series Vegetation Aerodynamic Roughness Fields Estimated from MODIS Observations

    NASA Technical Reports Server (NTRS)

    Borak, Jordan S.; Jasinski, Michael F.; Crago, Richard D.

    2005-01-01

    Most land surface models used today require estimates of aerodynamic roughness length in order to characterize momentum transfer between the surface and atmosphere. The most common method of prescribing roughness is through the use of empirical look-up tables based solely on land cover class. Theoretical approaches that employ satellite-based estimates of canopy density present an attractive alternative to current look-up table approaches based on vegetation cover type that do not account for within-class variability and are oftentimes simplistic with respect to temporal variability. The current research applies Raupach s formulation of momentum aerodynamic roughness to MODIS data on a regional scale in order to estimate seasonally variable roughness and zero-plane displacement height fields using bulk land cover parameters estimated by [Jasinski, M.F., Borak, J., Crago, R., 2005. Bulk surface momentum parameters for satellite-derived vegetation fields. Agric. For. Meteorol. 133, 55-68]. Results indicate promising advances over look-up approaches with respect to characterization of vegetation roughness variability in land surface and atmospheric circulation models.

  16. Time Series Vegetation Aerodynamic Roughness Fields Estimated from MODIS Observations

    NASA Technical Reports Server (NTRS)

    Borak, Jordan S.; Jasinski, Michael F.; Crago, Richard D.

    2005-01-01

    Most land surface models used today require estimates of aerodynamic roughness length in order to characterize momentum transfer between the surface and atmosphere. The most common method of prescribing roughness is through the use of empirical look-up tables based solely on land cover class. Theoretical approaches that employ satellite-based estimates of canopy density present an attractive alternative to current look-up table approaches based on vegetation cover type that do not account for within-class variability and are oftentimes simplistic with respect to temporal variability. The current research applies Raupach s formulation of momentum aerodynamic roughness to MODIS data on a regional scale in order to estimate seasonally variable roughness and zero-plane displacement height fields using bulk land cover parameters estimated by [Jasinski, M.F., Borak, J., Crago, R., 2005. Bulk surface momentum parameters for satellite-derived vegetation fields. Agric. For. Meteorol. 133, 55-68]. Results indicate promising advances over look-up approaches with respect to characterization of vegetation roughness variability in land surface and atmospheric circulation models.

  17. A physical interpretation of field observations that precede large earthquakes

    NASA Astrophysics Data System (ADS)

    Suyehiro, K.; Sacks, S. I.; Rydelek, P. A.; Smith, D. E.; Takanami, T.

    2016-12-01

    A cellular automaton model of earthquake faulting adopting Coulomb's failure criterion developed by Sacks and Rydelek (1995) successfully generates catalogs that satisfy Gutenberg-Richter's Law, the observed decreases in b-value before large events, as well as the propagation of the rupture front. Model runs indicate that redistributed stresses remain on the ruptured area and that some slips recur on the same cells forming dynamic asperities of high slips. We found that the observed magnitude-dependent seismicity quiescence can be explained by the introduction of dilatancy hardening into the model. Only a few % of the total number of model cells need be strengthened by a small amount. This indicates the difficulty of detecting their presence using seismic imaging. However, the observed long term ( years) temporal changes in seismicity, gravity, and electrical resistivity may be causally linked to the volume change from microfractures and the effect of pore pressure changes on fault strength. Our model predicts the process occurs at points sparcely distributed. Water migrations into unfilled microfractures act to lower the strength, thus promoting the occurrence of seismic slips. These slips may expel water that will influence aquifer levels, which may be observed at regional water wells. Drilling in seismic fault zones, such as at the 1995 Kobe earthquake fault, has revealed that the permeability on the main fault plane was many orders of magnitude higher than the surrounding rocks. We suggest the same water migration process at highly permeable zone can occur at short time scale to grow into a large magnitude slip or may manifest as a slow slip. The aftershock sequence of the 1978 Izu-Oshima earthquake shows that it overlaps the inferred slow slip on the fault following the main shock, thus suggesting that a fault can slip in various ways in the same time interval. We propose new observations that are sensitive to crustal water migration such as vertical

  18. Some Observations for Mean-Field Spin Glass Models

    NASA Astrophysics Data System (ADS)

    Starr, Shannon; Vermesi, Brigitta

    2008-03-01

    We obtain bounds to show that the pressure of a two-body, mean-field spin glass is a Lipschitz function of the underlying distribution of the random coupling constants, with respect to a particular semi-norm. This allows us to re-derive a result of Carmona and Hu, on the universality of the SK model, by a different proof, and to generalize this result to the Viana Bray model. We also prove another bound, suitable when the coupling constants are not independent, which is what is necessary if one wants to consider “canonical” instead of “grand canonical” versions of the SK and Viana Bray models. Finally, we review Viana Bray type models, using the language of Lévy processes, which is natural in this context.

  19. Overhauser magnetometer sensor design for magnetic field observation

    NASA Astrophysics Data System (ADS)

    Li, Zan; Chen, Shudong; Zhang, Shuang; Guo, Xin; Cao, Qiong

    2016-10-01

    The Overhauser magnetometer, with its unique set of advantages, such as low power consumption, high precision and fast recording ability has been widely used in geophysical mineral and oil exploration, archeology, environmental survey, ordnance and weapons detection (UXO) and other earth science applications. Compared with the traditional proton magnetometer, which suffers from high power consumption and low precision, the Overhauser magnetometer excite the free radical solution in a cavity with RF signal to enhance nuclear magnetic resonance (NMR). Thus, RF resonator plays a crucial role in reducing power consumption and improving the accuracy of Overhauser magnetometer. There are a wide variety of resonators, but only two of them are chosen for Overhauser magnetometer: birdcage coil and coaxial resonator. In order to get the best RF cavity for Overhauser magnetometer sensor, both resonators are investigated here. Firstly, parameters of two RF resonators are calculated theoretically and simulated with Ansoft HFSS. The results indicate that birdcage coil is characterized by linear polarization while coaxial resonator is characterized by circular polarization. Besides, all RF fields are limited inside of the coaxial resonator while distributed both inside and outside of the birdcage coil. Then, the two resonators are practically manufactured based on the theoretical design. And the S-parameter and Smith chart of these resonators are measured with Agilent 8712ES RF network analyzer. The measured results indicate that the coaxial resonator has a much higher Q value(875) than the birdcage coil(70). All these results reveal a better performance for coaxial resonator. Finally, field experimental shows 0.074nT sensitivity for Overhauser magnetometer with coaxial resonator.

  20. Field Observations of Meteotsunami in Kami-koshiki Island, Japan

    NASA Astrophysics Data System (ADS)

    Asano, T.; Yamashiro, T.; Nishimura, N.

    2012-12-01

    BACKGROUND Meteotsunami; atmospherically induced destructive ocean waves in the tsunami frequency band, are known in Japan by the local term "abiki", literally meaning "net-dragging waves" in Japanese. Large abiki occur in bays and harbors along the west coast of Kyushu almost every year during winter and early spring. On 24-25 February, 2009, Urauchi Bay, located on west coast of Kami-Koshiki Island on the southeast coast of Kyushu, was subjected to a destructive meteotsunami. In this event, a maximum sea surface height of 3.1 m was observed at the inner part of the bay. At least 18 boats capsized and eight houses were flooded. This event surpassed the previous record height for an abiki in Japan: 278 cm in Nagasaki Bay, also located west coast of Kyushu, in 1979. Generally, such an elongated inlet with narrow mouth as Urauchi bay provides calm water conditions even when offshore weather is stormy. Therefore, the area is regarded as a suitable place for the farming of large fish with a high market value. Possible damage to the extensive fish cage system as a result of meteotsunami events is of concern, especially because aquaculture is the main industry in the isolated islands. Forecasting of meteotsunami is a serious request from the local people. AIMS The objectives of the present study are to detect a meteotsunami event in Urauchi Bay and to clarify the meteorological and hydrodynamic conditions related to its occurrence. This work attempts to observe the whole process of a meteotsunami event: generation offshore, resonance while it propagates, and finally amplification in the bay. Observations were conducted over a period of 82 days; 12 January to 4 April, 2010, aiming to record large secondary oscillations. A comprehensive measuring system for sea level, current and barometric pressure fluctuations was deployed covering not only inside and near Urauchi Bay but also further offshore in the vicinity of Mejima in the East China Sea. MAIN RESULTS 1) Large

  1. LAMOST Observations of Flaring M Dwarfs in the Kepler Field

    NASA Astrophysics Data System (ADS)

    Chang, H.-Y.; Song, Y.-H.; Luo, A.-L.; Huang, L.-C.; Ip, W.-H.; Fu, J.-N.; Zhang, Y.; Hou, Y.-H.; Cao, Z.-H.; Wang, Y.-F.

    2017-01-01

    A sample of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope spectra of early-type M0-M3 dwarfs is compared with Kepler observations. It is found that M dwarfs with strong chromospheric emission in {{{H}}}α have large flare activity in general. The rotational periods derived from the Kepler measurements have close correlations with the sizes of the flares, the power-law distribution index, and the equivalent widths of the {{{H}}}α emission. A clear trend exists for higher magnetic activities being detected in faster-rotating M dwarfs (rotation periods < 20 days).

  2. Observations of polarization electric fields and plasma drifts associated with low-latitude TIDs

    NASA Astrophysics Data System (ADS)

    Huang, C.

    2015-12-01

    Ionospheric plasma structures and TIDs are often observed in the conjugate hemispheres. It is widely believed that the polarization electric field is responsible for the conjugacy. However, observed conjugate disturbances so far are mostly in plasma density and TEC, and there is almost no report of observations of polarization electric fields associated with TIDs. We present the C/NOFS measurements of TID-like disturbances in the plasma density and drift velocity. The plasma drift perpendicular to the geomagnetic field is manifestation of the polarization electric field. Plasma flow parallel to the geomagnetic field is highly correlated with the polarization electric field and is consistent with the prediction of TID theories, confirming that the polarization electric field is caused by TIDs. Surprisingly, the polarization electric field is observed not only at night but also during daytime, implying that the polarization electric field is not shorted out by the dayside E layers. The satellite data are compared with the Jicamarca radar data when C/NOFS is 20 degrees away from the radar but nearly at the same magnetic latitude (along the same field lines). This may be the first observation of polarization electric field associated with TIDs and verifies that the polarization electric field can be indeed transmitted thousands of kilometers along the geomagnetic field lines. The observations provide direct evidence for justifying the mechanism for the generation of similar ionospheric disturbances in the conjugate hemispheres.

  3. Applicability of sniffing team observations: experience of field measurements.

    PubMed

    Van Langenhove, H; Van Broeck, G

    2001-01-01

    Sniffing measurement campaigns are a commonly used technique in Flanders to estimate the impact of an odour emission source. The Department of Organic Chemistry at Ghent University has developed its own sniffing strategy throughout the last ten years. The method uses, in essence, the technique of plotting odour perception areas and calculation of total odour emission rates based on maximum odour perception distance. 566 sniffing measurements, executed from 1990 until 1999 around industrial and agricultural odour sources were collected in a database for statistical analysis. Short-term dispersion modelling was executed using four different models, two of them based on Bultynck-Malet dispersion parameters, and two based on Pasquill dispersion parameters. Results from this analysis demonstrate some causes of variance in calculated emissions and show the fitness of each model. From the results of the sniffing teams, which are expressed as sniffing units (SU) instead of odour units (OU, OUE) to underline the difference in methodological approach, the overall odorous emission can be calculated, using short-term atmospheric dispersion models. In a second step, long-term dispersion models can be used to calculate isopercentile contour plots. According to our experience the short-term atmospheric model is a source of "noise" in the method since calculated standard deviations on calculated emissions are larger than standard deviations in the observed maximum distance for odour perception. This will be illustrated by presenting results from the evaluation of composting plants and animal farm houses.

  4. Snapshots from deep magma chambers: decoding field observations

    NASA Astrophysics Data System (ADS)

    De Campos, Cristina P.

    2014-05-01

    mingling, between contrasting magmas generated from different sources and depths. When flow patterns from these plutonic structures are compared to those obtained from experiments and numerical modeling, vortex-like systems may be locally recognized with chaotic regions among concentric regular flow cells, separated by major flow shearing zones. These patterns may be in remarkable good agreement with less complex flow patterns obtained for simpler dynamic systems. Differences in the magma supply and flow regimes between distinct plutons, in time and space, depict frozen moments in their evolution and therefore may explain some of the discrepancies in the different hybridization degrees for different complexes. The combination of detailed mapping of flow patterns in the field, numerical modeling and experimental results using natural magmatic products as end-members may provide new insights into the dynamics of magma chambers, specially for shallow chambers in a volcanic environment. Due to high viscosities and non-Newtonian behavior during a long time-interval, the application of fluid dynamics to understanding magmatic processes, especially those taking place in the deep crust, is still a major challenge to Geosciences. Extrapolation for plutonic environments remains therefore a great defiance. This discussion aims to show that it is nevertheless worthwhile.

  5. An observation planning algorithm applied to multi-objective astronomical observations and its simulation in COSMOS field

    NASA Astrophysics Data System (ADS)

    Jin, Yi; Gu, Yonggang; Zhai, Chao

    2012-09-01

    Multi-Object Fiber Spectroscopic sky surveys are now booming, such as LAMOST already built by China, BIGBOSS project put forward by the U.S. Lawrence Berkeley National Lab and GTC (Gran Telescopio Canarias) telescope developed by the United States, Mexico and Spain. They all use or will use this approach and each fiber can be moved within a certain area for one astrology target, so observation planning is particularly important for this Sky Surveys. One observation planning algorithm used in multi-objective astronomical observations is developed. It can avoid the collision and interference between the fiber positioning units in the focal plane during the observation in one field of view, and the interested objects can be ovserved in a limited round with the maximize efficiency. Also, the observation simulation can be made for wide field of view through multi-FOV observation. After the observation planning is built ,the simulation is made in COSMOS field using GTC telescope. Interested galaxies, stars and high-redshift LBG galaxies are selected after the removal of the mask area, which may be bright stars. Then 9 FOV simulation is completed and observation efficiency and fiber utilization ratio for every round are given. Otherwise,allocating a certain number of fibers for background sky, giving different weights for different objects and how to move the FOV to improve the overall observation efficiency are discussed.

  6. Observations of improved confinement in field reversed configurations sustained by antisymmetric rotating magnetic fields

    SciTech Connect

    Guo, H.Y.; Hoffman, A.L.; Steinhauer, L.C.

    2005-06-15

    Rotating magnetic fields (RMF) have been employed to both form and sustain currents in field reversed configurations (FRC). A major concern about this method has been the fear of opening up magnetic field lines with even small ratios of vacuum RMF B{sub {omega}} to external confinement field B{sub e}. A recently proposed innovation was to use an antisymmetric arrangement of RMF, but vacuum calculations with full RMF penetration showed that very low values of B{sub {omega}}/B{sub e} would still be required to provide field-line closure. Recent comparisons of symmetric and antisymmetric RMF drive on the translation, confinement, and sustainment (TCS) facility [A. L. Hoffman, H. Y. Guo, J. T. Slough et al., Fusion Sci. Technol. 41, 92 (2002)] have shown strong improvements in the basic confinement properties of the FRCs when using antisymmetric drive, even with ratios of B{sub {omega}}/B{sub e} as high as 0.3. This is due to normal standard operation with only partial penetration of the RMF beyond the FRC separatrix. The uniform transverse RMF in vacuum is shielded by the conducting plasma, resulting in a mostly azimuthal field near the FRC separatrix with a very small radial component. Simple numerical calculations using analytical solutions for the partially penetrated antisymmetric RMF, superimposed on Grad-Shafranov solutions for the poloidal FRC fields, show good field-line closure for the TCS experimental conditions. The antisymmetric arrangement also leads to more efficient current drive and improved stabilization of rotational modes.

  7. Observations of Plasma Transient on the Lobe Field Line During the Substorm. Interball Tail Observations on October 3, 1995

    NASA Technical Reports Server (NTRS)

    Avanov, L. A.; Smimov, V. N.; Chandler, M. O.

    2004-01-01

    On October 3, 1995 Interball Tail spacecraft was located on tail lobe field lines. Solar wind conditions monitored by WIND and Getail spacecraft were quiet stable. During the time of operation of SCA-1 plasma spectrometer typical plasma mantle is observed. However, at approx. 15:07 UT strong plasma transient with duration of approx. 10 minutes was detected. We found that magnetic field profile of this plasma transient correlates well with ground based H component of magnetic field measured by Tixie Bay station. Ground base data indicates that this transient is observed during strong substorm. We argue that this transient is probably more dense mantle plasma which can be observed at the Interball Tail location provided that the current on the magnetopause is depressed. This depression probably reflects response of the tail magnetopause to changing of the global current system of the magnetosphere caused by the substorm.

  8. Correlation between magnetic and electric field perturbations in the field-aligned current regions deduced from DE 2 observations

    NASA Technical Reports Server (NTRS)

    Ishii, M.; Sugiura, M.; Iyemori, T.; Slavin, J. A.

    1992-01-01

    The satellite-observed high correlations between magnetic and electric field perturbations in the high-latitude field-aligned current regions are investigated by examining the dependence of the relationship between Delta-B and E on spatial scale, using the electric and magnetic field data obtained by DE 2 in the polar regions. The results are compared with the Pedersen conductivity inferred from the international reference ionosphere model and the Alfven wave velocity calculated from the in situ ion density and magnetic field measurements.

  9. Observation of magnetic field-induced contraction of fission yeast cells using optical projection microscopy

    NASA Astrophysics Data System (ADS)

    Yang, Xi; Beckwith, A. W.

    2005-03-01

    The charges in live cells interact with or produce electric fields, which results in enormous dielectric responses, flexoelectricity, and related phenomena. Here we report on a contraction of Schizosaccharomyces pombe (fission yeast) cells induced by magnetic fields, as observed using a phase-sensitive projection imaging technique. Unlike electric fields, magnetic fields only act on moving charges. The observed behavior is therefore quite remarkable, and may result from a contractile Lorentz force acting on diamagnetic screening currents. This would indicate extremely high intracellular charge mobilities. Besides, we observed a large electro-optic response from fission yeast cells.

  10. Guided Field Observations: Variables Related to Preservice Teachers' Knowledge about Effective Primary Reading Instruction

    ERIC Educational Resources Information Center

    Roehrig, Alysia D.; Guidry, Lisa O.; Bodur, Yasar; Guan, Qun; Guo, Ying; Pop, Margareta

    2008-01-01

    Relations between preservice teachers' guided field observations of primary literacy instruction and knowledge about effective beginning reading practices were explored. Preservice teachers (n = 48) participated in a Directed Field Experience course including instruction on and observations of exemplary teaching practices promoting student…

  11. Observations of broad-band circular polarization in sunspots - Magnetic field correspondence

    NASA Technical Reports Server (NTRS)

    Illing, R. M. E.; Landman, D. A.; Mickey, D. L.

    1974-01-01

    The present work proposes a general rule relating the polarity of broad-band (spectral range: 5250 A to 5350 A) circular polarization fields observed in sunspots to that of the corresponding magnetic fields. The rule is illustrated with observations of particular spots.

  12. Observing and modelling the poloidal and toroidal magnetic fields of the global dynamo

    NASA Astrophysics Data System (ADS)

    Cameron, Robert; Duvall, Thomas; Schüssler, Manfred; Schunker, Hannah

    2017-08-01

    The large scale solar dynamo is a cycle where poloidal flux is generated from toroidal flux, and toroidal flux is generated from poloidal flux. The toroidal and poloidal fields can be inferred from observations, and the Babcock-Leighton model shows how differential rotation and flux emergence explain the observed evolution of the fields.

  13. Guided Field Observations: Variables Related to Preservice Teachers' Knowledge about Effective Primary Reading Instruction

    ERIC Educational Resources Information Center

    Roehrig, Alysia D.; Guidry, Lisa O.; Bodur, Yasar; Guan, Qun; Guo, Ying; Pop, Margareta

    2008-01-01

    Relations between preservice teachers' guided field observations of primary literacy instruction and knowledge about effective beginning reading practices were explored. Preservice teachers (n = 48) participated in a Directed Field Experience course including instruction on and observations of exemplary teaching practices promoting student…

  14. The energy budget of stellar magnetic fields: comparing non-potential simulations and observations

    NASA Astrophysics Data System (ADS)

    Lehmann, L. T.; Jardine, M. M.; Vidotto, A. A.; Mackay, D. H.; See, V.; Donati, J.-F.; Folsom, C. P.; Jeffers, S. V.; Marsden, S. C.; Morin, J.; Petit, P.

    2017-03-01

    The magnetic geometry of the surface magnetic fields of more than 55 cool stars have now been mapped using spectropolarimetry. In order to better understand these observations, we compare the magnetic field topology at different surface scale sizes of observed and simulated cool stars. For ease of comparison between the high-resolution non-potential magnetofrictional simulations and the relatively low-resolution observations, we filter out the small-scale field in the simulations using a spherical harmonics decomposition. We show that the large-scale field topologies of the solar-based simulations produce values of poloidal/toroidal fields and fractions of energy in axisymmetric modes which are similar to the observations. These global non-potential evolution model simulations capture key magnetic features of the observed solar-like stars through the processes of surface flux transport and magnetic flux emergence. They do not, however, reproduce the magnetic field of M-dwarfs or stars with dominantly toroidal field. Furthermore, we analyse the magnetic field topologies of individual spherical harmonics for the simulations and discover that the dipole is predominately poloidal, while the quadrupole shows the highest fraction of toroidal fields. Magnetic field structures smaller than a quadrupole display a fixed ratio between the poloidal and toroidal magnetic energies.

  15. B fields in OB stars (BOB): Concluding the FORS 2 observing campaign

    NASA Astrophysics Data System (ADS)

    Schöller, M.; Hubrig, S.; Fossati, L.; Carroll, T. A.; Briquet, M.; Oskinova, L. M.; Järvinen, S.; Ilyin, I.; Castro, N.; Morel, T.; Langer, N.; Przybilla, N.; Nieva, M.-F.; Kholtygin, A. F.; Sana, H.; Herrero, A.; Barbá, R. H.; de Koter, A.; BOB Collaboration

    2017-03-01

    Aims: The B fields in OB stars (BOB) Collaboration is based on an ESO Large Programme to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. Methods: In the framework of this program, we carried out low-resolution spectropolarimetric observations of a large sample of massive stars using FORS 2 installed at the ESO VLT 8 m telescope. Results: We determined the magnetic field values with two completely independent reduction and analysis pipelines. Our in-depth study of the magnetic field measurements shows that differences between our two pipelines are usually well within 3σ errors. From the 32 observations of 28 OB stars, we were able to monitor the magnetic fields in CPD -57° 3509 and HD 164492C, confirm the magnetic field in HD 54879, and detect a magnetic field in CPD -62° 2124. We obtain a magnetic field detection rate of 6 ± 3% for the full sample of 69 OB stars observed with FORS 2 within the BOB program. For the preselected objects with a v sin i below 60 km s-1, we obtain a magnetic field detection rate of 5 ± 5%. We also discuss X-ray properties and multiplicity of the objects in our FORS 2 sample with respect to the magnetic field detections. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 191.D-0255(E,G).

  16. Investigation of Spatially Unresolved Magnetic Field Outside Sunspots Using Hinode/SOT Observations

    NASA Astrophysics Data System (ADS)

    Botygina, Olga; Gordovskyy, Mykola; Lozitsky, Vsevolod

    2017-06-01

    The structure of photospheric magnetic fields outside sunspots is investigated in three active regions using Hinode/Solar Optical Telescope(SOT) observations. We analyze Zeeman effect in FeI 6301.5 and FeI 6302.5 lines and determine the observed magnetic field value B eff for each of them. We find that the line ratio B eff(6301)/B eff(6302) is close to 1.3 in the range B eff < 0.2 kG, and close to 1.0 for 0.8 kG < B eff < 1.2 kG. We find that the observed magnetic field is formed by flux tubes with the magnetic field strengths 1.3 - 2.3 kG even in places with weak observed magnetic field fluxes. We also estimate the diameters of smallest magnetic flux tubes to be 15 - 20 km.

  17. Observations of the Ion Signatures of Double Merging and the Formation of Newly Closed Field Lines

    NASA Technical Reports Server (NTRS)

    Chandler, Michael O.; Avanov, Levon A.; Craven, Paul D.

    2007-01-01

    Observations from the Polar spacecraft, taken during a period of northward interplanetary magnetic field (IMF) show magnetosheath ions within the magnetosphere with velocity distributions resulting from multiple merging sites along the same field line. The observations from the TIDE instrument show two separate ion energy-time dispersions that are attributed to two widely separated (-20Re) merging sites. Estimates of the initial merging times show that they occurred nearly simultaneously (within 5 minutes.) Along with these populations, cold, ionospheric ions were observed counterstreaming along the field lines. The presence of such ions is evidence that these field lines are connected to the ionosphere on both ends. These results are consistent with the hypothesis that double merging can produce closed field lines populated by solar wind plasma. While the merging sites cannot be unambiguously located, the observations and analyses favor one site poleward of the northern cusp and a second site at low latitudes.

  18. Synergies between spectroscopic and time-series photometric surveys - LAMOST observations for the Kepler field and K2 fields

    NASA Astrophysics Data System (ADS)

    Fu, Jianning; De Cat, Peter; Smith, Martin

    2017-01-01

    Synergies between spectroscopic and time-series photometric surveys can provide valuable information for studies in Galactic archaeology. The Kepler satellite has provided unprecedented high duty-cycle, high-precision time-series photometric observations for a large number of stars. After a continuous monitoring of the Kepler field for 4 years, it started to observe K2 fields, which include multiple stellar populations, for about 80 days each. These observed fields are all good targets for Galactic archaeology, provided that spectroscopic observations can be made for hundreds of thousands of stars within these fields in a homogeneous way.In 2010, we initiated the LAMOST-Kepler project with the aim to collect low-resolution spectra for as many objects from the KIC10 catalogue as possible with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). This is a 4-m telescope equipped with 4,000 optical fibers covering a circular field of view with a diameter of 5 degrees on the sky. The observations since 2012 have resulted in 150,567 low-resolution spectra with the Signal-Noise-Ratio in r larger than 20. The stellar atmospheric parameters were derived and calibrated with the values determined from either high-resolution spectroscopy or asteroseismology. Since the end of 2015, five K2 fields have been observed with LAMOST and the qualified spectra were used to derive the stellar atmospheric parameters for 59,213 stars.In this presentation we introduce the LAMOST-Kepler project, whose data have a great potential for Galactic archaeology. It includes an update on the progress and a summary of the existing scientific works based on the data provided by this project.

  19. Direct observation of electric field induced pattern formation and particle aggregation in ferrofluids

    NASA Astrophysics Data System (ADS)

    Rajnak, Michal; Petrenko, Viktor I.; Avdeev, Mikhail V.; Ivankov, Olexandr I.; Feoktystov, Artem; Dolnik, Bystrik; Kurimsky, Juraj; Kopcansky, Peter; Timko, Milan

    2015-08-01

    Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and electrical body forces. The free charge and permittivity variation are considered to play a key role in the observed phenomenon. The corresponding changes in the ferrofluid structure have been found at nanoscale as well. By small-angle neutron scattering (SANS), we show that the magnetic nanoparticles aggregate in direct current (dc) electric field with a strong dependence on the field intensity. The anisotropic aggregates preferably orient in the direction of the applied electric field. Conducting SANS experiments with alternating current (ac) electric fields of various frequencies, we found a critical frequency triggering the aggregation process. Our experimental study could open future applications of ferrofluids based on insulating liquids.

  20. Predicting observational consequences of magnetic field effects in the Eagle Nebula

    NASA Astrophysics Data System (ADS)

    Ryutov1, D. D.; Kane1, J. O.; Mizuta2, A.; Pound3, M. W.; Remington1, B. A.

    2003-10-01

    Magnetic fields are thought to play a substantial role in photoevaporated molecular clouds, an example of which is the famous Eagle Nebula. On the other hand, any direct measurements of the magnetic fields in the Eagle Nebula are still absent. To help in developing the observational strategies, we consider two models of the magnetic field and discuss their general compatibility with the observed structures. We also consider other factors that can be used to derive the structure and the strength of the magnetic field. The two models are those of an initially quasi-homogeneous magnetic field permeating the cloud prior to the onset of hydrodynamic motion, and of a pre-existing "magnetostatic turbulence" [1]. We evaluate possible magnetic field strength in the ablated flow, magnetic field effects on the velocity distribution inside the cloud, and on the star formation. [1] D.D. Ryutov, B.A. Remington. PPCF, 44, B407, 2002.

  1. Direct observation of electric field induced pattern formation and particle aggregation in ferrofluids

    SciTech Connect

    Rajnak, Michal; Kopcansky, Peter; Timko, Milan; Petrenko, Viktor I.; Avdeev, Mikhail V.; Ivankov, Olexandr I.; Feoktystov, Artem; Dolnik, Bystrik; Kurimsky, Juraj

    2015-08-17

    Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and electrical body forces. The free charge and permittivity variation are considered to play a key role in the observed phenomenon. The corresponding changes in the ferrofluid structure have been found at nanoscale as well. By small-angle neutron scattering (SANS), we show that the magnetic nanoparticles aggregate in direct current (dc) electric field with a strong dependence on the field intensity. The anisotropic aggregates preferably orient in the direction of the applied electric field. Conducting SANS experiments with alternating current (ac) electric fields of various frequencies, we found a critical frequency triggering the aggregation process. Our experimental study could open future applications of ferrofluids based on insulating liquids.

  2. Modelling coronal electron density and temperature profiles based on solar magnetic field observations

    NASA Astrophysics Data System (ADS)

    Rodríguez Gómez, J. M.; Antunes Vieira, L. E.; Dal Lago, A.; Palacios, J.; Balmaceda, L. A.; Stekel, T.

    2017-10-01

    The density and temperature profiles in the solar corona are complex to describe, the observational diagnostics is not easy. Here we present a physics-based model to reconstruct the evolution of the electron density and temperature in the solar corona based on the configuration of the magnetic field imprinted on the solar surface. The structure of the coronal magnetic field is estimated from Potential Field Source Surface (PFSS) based on magnetic field from both observational synoptic charts and a magnetic flux transport model. We use an emission model based on the ionization equilibrium and coronal abundances from CHIANTI atomic database 8.0. The preliminary results are discussed in details.

  3. Observation of the Faraday effect via beam deflection in a longitudinal magnetic field

    SciTech Connect

    Ghosh, Ambarish; Hill, Winfield; Fischer, Peer

    2007-11-15

    We show that magnetic-field-induced circular differential deflection of light can be observed in reflection or refraction at a single interface. The difference in the reflection or refraction angles between the two circular polarization components is a function of the magnetic-field strength and the Verdet constant, and permits the observation of the Faraday effect not via polarization rotation in transmission, but via changes in the propagation direction. Deflection measurements do not suffer from n-{pi} ambiguities and are shown to be another means to map magnetic fields with high axial resolution, or to determine the sign and magnitude of magnetic-field pulses in a single measurement.

  4. Advanced Field Artillery Tactical Data System (AFATDS) Contextual Task Analysis and Observational Study

    DTIC Science & Technology

    2017-04-01

    Analysis and Observational Study by Charles L Hernandez and Pamela A Savage-Knepshield Approved for public release...US Army Research Laboratory Advanced Field Artillery Tactical Data System (AFATDS) Contextual Task Analysis and Observational Study by...System (AFATDS) Contextual Task Analysis and Observational Study 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S

  5. Forcing a Global, Offline Land Surface Modeling System with Observation-Based Fields

    NASA Technical Reports Server (NTRS)

    Rodell, Matthew; Houser, Paul R.; Jambor, U.; Gottschalck, J.; Radakovich, J.; Arsenault, K.; Meng, C.-J.; Mitchell, K. E.

    2002-01-01

    The Global Land Data Assimilation System (GLDAS) drives multiple uncoupled land surface models in order to produce optimal output fields of surface states in near-real time, globally, at 1/4 degree spatial resolution. These fields are then made available for coupled atmospheric model initialization and further research. One of the unique aspects of GLDAS is its ability to ingest both modeled and observation-derived forcing for running global scale land surface models. This paper compares results of runs forced by modeled and observed precipitation and shortwave radiation fields. Differences are examined and the impact of the observations on model skill is assessed.

  6. Reconstructing solar magnetic fields from historical observations. II. Testing the surface flux transport model

    NASA Astrophysics Data System (ADS)

    Virtanen, I. O. I.; Virtanen, I. I.; Pevtsov, A. A.; Yeates, A.; Mursula, K.

    2017-07-01

    Aims: We aim to use the surface flux transport model to simulate the long-term evolution of the photospheric magnetic field from historical observations. In this work we study the accuracy of the model and its sensitivity to uncertainties in its main parameters and the input data. Methods: We tested the model by running simulations with different values of meridional circulation and supergranular diffusion parameters, and studied how the flux distribution inside active regions and the initial magnetic field affected the simulation. We compared the results to assess how sensitive the simulation is to uncertainties in meridional circulation speed, supergranular diffusion, and input data. We also compared the simulated magnetic field with observations. Results: We find that there is generally good agreement between simulations and observations. Although the model is not capable of replicating fine details of the magnetic field, the long-term evolution of the polar field is very similar in simulations and observations. Simulations typically yield a smoother evolution of polar fields than observations, which often include artificial variations due to observational limitations. We also find that the simulated field is fairly insensitive to uncertainties in model parameters or the input data. Due to the decay term included in the model the effects of the uncertainties are somewhat minor or temporary, lasting typically one solar cycle.

  7. Reconstructing solar magnetic fields from historical observations: Testing the surface flux transport model

    NASA Astrophysics Data System (ADS)

    Virtanen, Iiro; Virtanen, Ilpo; Pevtsov, Alexei; Yeates, Anthony; Mursula, Kalevi

    2017-04-01

    We aim to use the surface flux transport model to simulate the long-term evolution of the photospheric magnetic field from historical observations. In this work we study the accuracy of the model and its sensitivity to uncertainties in its main parameters and the input data. We test the model by running simulations with different values of meridional circulation and supergranular diffusion parameters, and study how the flux distribution inside active regions and the initial magnetic field affect the simulation. We compare the results to assess how sensitive the simulation is to uncertainties in meridional circulation speed, supergranular diffusion and input data. We also compare the simulated magnetic field with observations. We find that there is generally good agreement between simulations and observations. While the model is not capable of replicating fine details of the magnetic field, the long-term evolution of the polar field is very similar in simulations and observations. Simulations typically yield a smoother evolution of polar fields than observations, that often include artificial variations due to observational limitations. We also find that the simulated field is fairly insensitive to uncertainties in model parameters or the input data. Due to the decay term included in the model the effects of the uncertainties are rather minor or temporary, lasting typically one solar cycle.

  8. Magnetic and Electric Field Diagnostics of Chromospheric Jets by Spectropolarimetric Observations of the HI Paschen Lines

    NASA Astrophysics Data System (ADS)

    Anan, T.; Casini, R.; Ichimoto, K.

    2014-10-01

    In order to study the magnetic and electric fields of chromospheric jets, we observed the full Stokes spectra of the Paschen series of neutral hydrogen in active region jets that took place at the solar limb on May 5, 2012. For the observations, we used the spectropolarimeter of the Domeless Solar Telescope at Hida observatory, Japan. Inversion of the Stokes spectra taking into account the effect of magnetic field on the energy structure and polarization of the hydrogen levels (including the Hanle effect and level-crossing effects) elucidates the magnetic field approximately aligned with the visible structure of the jets. In addition to the magnetic field, the energy structure and the polarization of the hydrogen levels is sensitive to electric field through the Stark effect, electric Hanle effect (analogous effect with the Hanle effect by magnetic field), and the level-crossing effects. Since, we found no definitive evidence of the polarization produced by the effect of electric field in the observed Stokes profiles, we derived upper limits of electric field felt by neutral atom moving across the magnetic field, and conclude that the velocity of the neutral atom perpendicular to the magnetic field was below several percents of the velocity bulk plasma motion.

  9. Magnetic fields in protoplanetary discs: from MHD simulations to ALMA observations

    NASA Astrophysics Data System (ADS)

    Bertrang, G. H.-M.; Flock, M.; Wolf, S.

    2017-01-01

    Magnetic fields significantly influence the evolution of protoplanetary discs and the formation of planets, following the predictions of numerous magnetohydrodynamic (MHD) simulations. However, these predictions are yet observationally unconstrained. To validate the predictions on the influence of magnetic fields on protoplanetary discs, we apply 3D radiative transfer simulations of the polarized emission of aligned aspherical dust grains that directly link 3D global non-ideal MHD simulations to Atacama Large Millimeter/submillimeter Array (ALMA) observations. Our simulations show that it is feasible to observe the predicted toroidal large-scale magnetic field structures, not only in the ideal observations but also with high-angular resolution ALMA observations. Our results show further that high-angular resolution observations by ALMA are able to identify vortices embedded in outer magnetized disc regions.

  10. In-situ Observation and Differential Thermal Analysis of MnBi in High Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Miyazaki, Daiki; Mitsui, Yoshifuru; Abematsu, Ken-ichi; Takahashi, Kohki; Watanabe, Kazuo; Uda, Satoshi; Koyama, Keiichi

    For investigating in-field process of melting and solidification visually and quantitatively, in-situ observation system with differential thermal analysis (DTA) utilized in high temperature and in high magnetic field was developed. Decomposition processes of the bulk sample of ferromagnetic MnBi were directly observed with collecting DTA data under high magnetic field of 10 T for the 290-770 K temperature range. When the temperature was over decomposition point (ferromagnetic MnBi → paramagnetic Mn1.08Bi + liquid), liquid phase appeared on the sample surface. Furthermore, when the temperature was over peritectic temperature (∼ 700 K: paramagnetic Mn1.08Bi → Mn + liquid), the sample surface was broken and a large quantity of the liquid phase appeared from the sample. The in-situ observation also suggested that the decomposition temperature increased from 620 K for a zero field to 638 K for a magnetic field of 10 T.

  11. Determination of magnetic fields in broad line region of active galactic nuclei from polarimetric observations

    NASA Astrophysics Data System (ADS)

    Piotrovich, Mikhail; Silant'ev, Nikolai; Gnedin, Yuri; Natsvlishvili, Tinatin; Buliga, Stanislava

    2017-02-01

    Magnetic fields play an important role in confining gas clouds in the broad line region (BLR) of active galactic nuclei (AGN) and in maintaining the stability of these clouds. Without magnetic fields the clouds would not be stable, and soon after their formation they would expand and disperse. We show that the strength of the magnetic field can be derived from the polarimetric observations. Estimates of magnetic fields for a number of AGNs are based on the observed polarization degrees of broad Hα lines and nearby continuum. The difference between their values allows us to estimate the magnetic field strength in the BLR using the method developed by Silant'ev et al. (2013). Values of magnetic fields in BLR for a number of AGNs have been derived.

  12. Nonoptically probing near-field microscopy for the observation of biological living specimens

    NASA Astrophysics Data System (ADS)

    Kawata, Yoshimasa; Murakami, Manabu; Egami, Chikara; Sugihara, Okihiro; Okamoto, Naomichi; Tsuchimori, Masaaki; Watanabe, Osamu; Nakamura, Osamu

    2001-04-01

    We present the observation of living specimens with subwavelength resolution by using the nonoptically probing near-field microscopy we have developed recently. In the near-field microscope, the optical field distributions near the specimens are recorded as the surface topography of a photosensitive film, and the topographical distributions are readout with an atomic-force microscopy. Since the near-field microscope does not require the scanning of a probe tip for illumination or detection or scattering of light, it is possible to observe moving biological specimens and fast phenomena. We demonstrate the observation of a moving paramecium and euglena gracilis with subwavelength resolution. The observation of the nucleus inside a euglena cell was also demonstrated.

  13. Observations of two-dimensional magnetic field evolution in a plasma opening switch

    NASA Astrophysics Data System (ADS)

    Shpitalnik, R.; Weingarten, A.; Gomberoff, K.; Krasik, Ya.; Maron, Y.

    1998-03-01

    The time dependent magnetic field distribution was studied in a coaxial 100-ns positive-polarity Plasma Opening Switch (POS) by observing the Zeeman effect in ionic line emission. Measurements local in three dimensions are obtained by doping the plasma using laser evaporation techniques. Fast magnetic field penetration with a relatively sharp magnetic field front (⩽1 cm) is observed at the early stages of the pulse (t≲25). Later in the pulse, the magnetic field is observed at the load-side edge of the plasma, leaving "islands" of low magnetic field at the plasma center that last for about 10 ns. The two-dimensional (2-D) structure of the magnetic field in the r,z plane is compared to the results of an analytical model based on electron-magneto-hydrodynamics, that utilizes the measured 2-D plasma density distribution and assumes fast magnetic field penetration along both POS electrodes. The model results provide quantitative explanation for the magnetic field evolution observed.

  14. Observational estimate of magnetic field and geodynamo parameters under the surface of the Earth's core

    NASA Astrophysics Data System (ADS)

    Starchenko, S. V.

    2015-09-01

    For the first time, estimates (averaged in latitude and longitude) of the radial derivatives of the vortex magnetic field hidden directly under the surface of the Earth's core were obtained on the basis of contemporary determinations of the electric conductivity and systematic observations of the geomagnetic dipole evolution, as well as Faraday's and Ohm's laws. This allows one to formulate the simplest, `almost dipole" model of the vortex field under the core surface and to estimate a characteristic scale of the field measurements, which determines the depth of the adequacy area of the proposed simplest model. According to this estimate, the spatial size of the field (around 60 km) is an order of magnitude less than its typical size, following from an extrapolation of the observable field to the mantle-core boundary. This agrees well with the modern theory of hydromagnetic dynamos of planets, making it possible to refine the typical values of the magnetic field, the convection rate, and specific power, together with other geodynamo parameters, on the basis of known scaling laws and observations. The proposed new approach to determining the surface characteristics of the vortex magnetic field hidden in the interior of a physical object from the observed evolution of the potential field may be used for both astrophysical and engineering objects with an inaccessible current system.

  15. Radio observations in the fields of COS-B gamma ray sources. IV - First quadrant sources

    NASA Technical Reports Server (NTRS)

    Ozel, M. E.; Schlickeiser, R.; Sieber, W.; Younis, S.

    1988-01-01

    The field of five COS-B gamma-ray sources in the first galactic quadrant have been mapped using the Effelsberg radio telescope at several frequencies. Candidate objects as potential radio counterparts of gamma-ray sources are discussed in the light of current observations; however, mostly being due to the crowded nature of the radio fields, no clear identification has been possible.

  16. Radio observations in the fields of COS-B gamma ray sources. IV - First quadrant sources

    NASA Technical Reports Server (NTRS)

    Ozel, M. E.; Schlickeiser, R.; Sieber, W.; Younis, S.

    1988-01-01

    The field of five COS-B gamma-ray sources in the first galactic quadrant have been mapped using the Effelsberg radio telescope at several frequencies. Candidate objects as potential radio counterparts of gamma-ray sources are discussed in the light of current observations; however, mostly being due to the crowded nature of the radio fields, no clear identification has been possible.

  17. Marine stratocumulus cloud parameters from GOES during the 1987 FIRE intensive field observation period

    NASA Technical Reports Server (NTRS)

    Young, David F.; Heck, Patrick W.; Minnis, Patrick; Harrison, Edwin F.

    1989-01-01

    GOES was used to perform the Marine Stratocumulus Intensive Field Observations (IFO) from June 29 to July 19, 1987. Preliminary results of an analysis of GOES data covering most of the IFO period are discussed. The large-scale cloud-field characteristics are derived, and then related to a longer period of measurements and to surface observations. Some preliminary point measurements taken from the surface are compared to regional-scale cloud parameters derived from satellite radiances.

  18. Larmor electric field observed at the Earth's magnetopause by Polar satellite

    SciTech Connect

    Koga, D. Gonzalez, W. D.; Silveira, M. V. D.; Mozer, F. S.; Cardoso, F. R.

    2014-10-15

    We present, for the first time, observational evidence of a kinetic electric field near the X-line associated with asymmetric reconnection at the Earth's dayside magnetopause using Polar observations. On March 29, 2003, Polar satellite detected an asymmetric collisionless reconnection event. This event shows a unipolar Hall electric field signature and a simple deviation from the guide field during the magnetopause crossing, with the absence of an ion plasma jet outflow indicating that the magnetopause crossing was near the X-line. As expected from particle-in-cell simulations by Malakit et al. (Phys. Rev. Lett. 111, 135001 (2013)), an earthward pointing normal electric field appears in the magnetospheric side of the ion diffusion region. The electric field satisfies two necessary conditions for the existence of the finite ion Larmor radius effect: (1) the ion Larmor radius (r{sub g2}) is larger than the distance between the stagnation point and the edge of the ion diffusion region in the strong magnetic field side (δ{sub S2}) and (2) the spatial extent of the kinetic electric field (δ{sub EL}) is of the order of the ion Larmor radius. Furthermore, it is shown that the peak value of the Larmor electric field is comparable to the predicted value. The observation of the Larmor electric field can be valuable in other analyses to show that the crossing occurred near the X-line.

  19. DC Electric Fields and Associated Plasma Drifts Observed with the C/NOFS Satellite

    NASA Technical Reports Server (NTRS)

    Pfaff, R.; Freudenreich, H.; Bromund, K.; Rowland, D.

    2009-01-01

    Initial DC electric field observations and associated plasma drifts are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite. We present statistical averages of the vector fields for the first year of operations that include both the zonal and radial components of the resulting E x B plasma flows at low latitudes. Magnetic field data from the VEFI science magnetometer are used to compute the plasma flows. The DC electric field detector reveals zonal and radial electric fields that undergo strong diurnal variations, typically displaying eastward and outward-directed fields during the day and westward and downward-directed fields at night. There is considerable variation in the large scale DC electric field data, in both the daytime and nighttime cases, with enhanced structures typically observed at night. In general, the measured zonal DC electric field amplitudes include excursions that extend within the 0.4 - 2 m V/m range, corresponding to E x B drifts of the order of 30-150 m/s. The average vertical or radial electric fields may exceed the zonal fields in amplitude by a factor of 1.5 to 2. Although the data compare well, in a general sense, with previous satellite observations and statistical patterns of vertical ion drifts, the E x B drifts we report from C/NOFS rarely show a pronounced pre-reversal enhancement after sunset. We attribute this to a combination of extreme solar minimum conditions and the fact that the C/NOFS orbit of 401 by 867 km carries the probes essentially above the lower altitude regions where the wind-driven dynamo might be expected to create enhanced upwards drifts in the early evening. Evidence for wavenumber 4 tidal effects and other longitudinal signatures have been detected and will be presented. We also discuss off-equatorial electric fields and their relation to the ambient plasma density.

  20. Quantitative comparison of lunar magnetic field observed by Kaguya and Lunar Prospector missions

    NASA Astrophysics Data System (ADS)

    Hayashida, A.; Shibuya, H.; Tsunakawa, H.; Takahashi, F.; Shimizu, H.; Matsushima, M.

    2009-12-01

    The magnetometer on board Kaguya (Kaguya-LMAG) has been almost continuously observed the magnetic field at about 100km altitude since October 29, 2007. The magnetic field observations are beautiful because of the very low solar activity, the crustal field is well observed at 100km altitude from the record in the lunar wake and the tail-lobe environments. As the lunar crustal magnetic field does not vary, those results are comparable with the Lunar Prospector magnetometer (LP-MAG). Such a comparison has been made between Apollo sub-satellite data and LP-MAG, but only qualitative similarity has been discussed, since the altitude effect to the intensity and shape of the magnetic field was not quantitatively evaluated. We have developed a method to recover the 3-d magnetic field from satellite field observations (EPR method which stands for Equivalent Pole Reduction; Toyoshima et al. 2008). Applying EPR to the LP-MAG data, we presented, at AGU 2008 meeting, the global magnetic anomaly map. As the EPR reduce the field observation to the magnetic monopole distribution, the magnetic field at the Kaguya track is also calculated, so that the quantitative comparison between the observations of the two missions becomes possible. The comparison in several strong magnetic anomaly regions, Abel, Descartes, Reiner Gamma, Rima Sirsalis, Crisium Antipode, Orientale Antipode and South Pole-Aitken regions, the EPR field and observation agree very well, considerably better than the previous mapping models. In some passes the discrepancy is less than 0.1nT though out the 20 span in latitude. This agreement indicates that the calibrations of both Kaguya and LP are very precisely consistent, and the EPR works very well to restore the magnetic field in three dimensions. It is also found in most of the areas that the radial component is more consistent than the other components. It might be due to the moon surface current generated by the varying interplanetary field. They are also

  1. Relationship of the interplanetary electric field to the high-latitude ionospheric electric field and currents Observations and model simulation

    NASA Technical Reports Server (NTRS)

    Clauer, C. R.; Banks, P. M.

    1986-01-01

    The electrical coupling between the solar wind, magnetosphere, and ionosphere is studied. The coupling is analyzed using observations of high-latitude ion convection measured by the Sondre Stromfjord radar in Greenland and a computer simulation. The computer simulation calculates the ionospheric electric potential distribution for a given configuration of field-aligned currents and conductivity distribution. The technique for measuring F-region in velocities at high time resolution over a large range of latitudes is described. Variations in the currents on ionospheric plasma convection are examined using a model of field-aligned currents linking the solar wind with the dayside, high-latitude ionosphere. The data reveal that high-latitude ionospheric convection patterns, electric fields, and field-aligned currents are dependent on IMF orientation; it is observed that the electric field, which drives the F-region plasma curve, responds within about 14 minutes to IMF variations in the magnetopause. Comparisons of the simulated plasma convection with the ion velocity measurements reveal good correlation between the data.

  2. Pioneer Venus observations of plasma and field structure in the near wake of Venus

    NASA Technical Reports Server (NTRS)

    Luhmann, J. G.; Russell, C. T.; Brace, L. H.; Knudsen, W. C.; Taylor, H. A.; Scarf, F. L.; Colburn, D. S.; Barnes, A.

    1982-01-01

    Ionospheric plasma density depletions or 'holes' are observed by the Pioneer Venus orbiter in association with radial magnetic fields in the near wake of Venus. This report presents examples of the collected observations of these unexpected features of the Venus nightside ionosphere obtained by the Langmuir probe, magnetometer, ion mass spectrometer, retarding potential analyzer, plasma analyzer, and electric field experiments. The connection between plasma density depletions and temperature changes, changes in ion composition, plasma wave emissions, and magnetic fields with a substantial radial component is illustrated. Mechanisms that may be responsible for the formation and maintenance of holes are suggested.

  3. Field-aligned currents observed in the vicinity of a moving auroral arc

    NASA Astrophysics Data System (ADS)

    Goertz, C. K.; Bruening, K.

    1984-09-01

    The sounding rocket Porcupine F4 was launched into an auroral arc and the field aligned currents were independently deduced from magnetic field measurements; the horizontal current deduced from the electric field measurements and height integrated conductivity calculations; and measurements of electron fluxes. Above the arc the different methods agree. The magnetosphere acts as generator and the ionosphere as load. North of the arc, the first two methods disagree, possibly due to an Alfven wave carrying the observed magnetic field perturbation. The energy flow is out of the ionosphere. Here the ionosphere acts as generator and the magnetosphere as load.

  4. Field-aligned currents observed in the vicinity of a moving auroral arc

    NASA Technical Reports Server (NTRS)

    Goertz, C. K.; Bruening, K.

    1984-01-01

    The sounding rocket Porcupine F4 was launched into an auroral arc and the field aligned currents were independently deduced from magnetic field measurements; the horizontal current deduced from the electric field measurements and height integrated conductivity calculations; and measurements of electron fluxes. Above the arc the different methods agree. The magnetosphere acts as generator and the ionosphere as load. North of the arc, the first two methods disagree, possibly due to an Alfven wave carrying the observed magnetic field perturbation. The energy flow is out of the ionosphere. Here the ionosphere acts as generator and the magnetosphere as load.

  5. Bridging the terahertz near-field and far-field observations of liquid crystal based metamaterial absorbers

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Ge, Shijun; Chen, Zhaoxian; Hu, Wei; Lu, Yanqing

    2016-09-01

    Metamaterial-based absorbers play a significant role in applications ranging from energy harvesting and thermal emitters to sensors and imaging devices. The middle dielectric layer of conventional metamaterial absorbers has always been solid. Researchers could not detect the near field distribution in this layer or utilize it effectively. Here, we use anisotropic liquid crystal as the dielectric layer to realize electrically fast tunable terahertz metamaterial absorbers. We demonstrate strong, position-dependent terahertz near-field enhancement with sub-wavelength resolution inside the metamaterial absorber. We measure the terahertz far-field absorption as the driving voltage increases. By combining experimental results with liquid crystal simulations, we verify the near-field distribution in the middle layer indirectly and bridge the near-field and far-field observations. Our work opens new opportunities for creating high-performance, fast, tunable, terahertz metamaterial devices that can be applied in biological imaging and sensing. Project supported by the National Basic Research Program of China (Grant No. 2012CB921803), the National Natural Science Foundation of China (Grants Nos. 61225026, 61490714, 11304151, and 61435008), the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK20150845 and 15KJB140004), the Open Foundation Project of National Laboratory of Solid State Microstructures, China (Grant No. M28003), and the Research Center of Optical Communications Engineering & Technology, Jiangsu Province, China.

  6. Interplanetary and Interstellar Dust Observed by the Wind/WAVES Electric Field Instrument

    NASA Technical Reports Server (NTRS)

    Malaspina, David; Horanyi, M.; Zaslavsky, A.; Goetz, K.; Wilson, L. B., III; Kersten, K.

    2014-01-01

    Observations of hypervelocity dust particles impacting the Wind spacecraft are reported here for the first time using data from the WindWAVES electric field instrument. A unique combination of rotating spacecraft, amplitude-triggered high-cadence waveform collection, and electric field antenna configuration allow the first direct determination of dust impact direction by any spacecraft using electric field data. Dust flux and impact direction data indicate that the observed dust is approximately micron-sized with both interplanetary and interstellar populations. Nanometer radius dust is not detected by Wind during times when nanometer dust is observed on the STEREO spacecraft and both spacecraft are in close proximity. Determined impact directions suggest that interplanetary dust detected by electric field instruments at 1 AU is dominated by particles on bound trajectories crossing Earths orbit, rather than dust with hyperbolic orbits.

  7. Coronal structure analysis based on the potential field source surface modeling and total solar eclipse observation

    NASA Astrophysics Data System (ADS)

    Muhamad, Johan; Mumtahana, Farahhati; Sutastio, Heri; Imaduddin, Irfan; Putri, Gerhana P.

    2016-11-01

    We constructed global coronal magnetic fields of the Sun during the Total Solar Eclipse (TSE) 9 March 2016 by using Potential Field Source Surface (PFSS) model. Synoptic photospheric magnetogram data from Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO) was used as a boundary condition to extrapolate the coronal magnetic fields of the Sun. This extrapolated structure was analyzed by comparing the alignment of the fields from the model with coronal structure from the observation. We also used observational data of coronal structure during the total solar eclipse to know how well the model agree with the observation. As a result, we could identify several coronal streamers which were produced by the large closed loops in the lower regime of the corona. This result verified that the PFSS extrapolation can be used as a tool to model the inner corona with several constraints. We also discussed how the coronal structure can be used to deduce the phase of the solar cycle.

  8. Comparison of inferred and observed interplanetary magnetic field polarities, 1970-1972

    NASA Technical Reports Server (NTRS)

    Wilcox, J. M.; Svalgaard, L.; Hedgecock, P. C.

    1975-01-01

    The inferred polarity (toward or away from the sun) of the interplanetary magnetic field at earth using polar observations of the geomagnetic field has been compared with spacecraft observations. A list published by Svalgaard (1974) of the inferred field polarities in the period from 1970 to 1972 is found to be correct on 82% of the days. A near real-time (same day) method of inferring the polarity of the interplanetary magnetic field using geomagnetic observations at Vostok and Thule is in use at the NOAA Space Environment Laboratory, Boulder, Colorado. During 1972, this method is found to be correct on 87% of the days. A list of 'well-defined' sector boundaries at earth from 1970 to 1972 is given.

  9. What Preservice Physical Educators Observe about Lessons in Progressive Field Experiences.

    ERIC Educational Resources Information Center

    Belka, David E.

    1988-01-01

    Freshmen through senior physical education majors' observation and interpretation of a videotaped soccer skill lesson indicated that over time they tended to observe the lesson more congruently with program goals and reflect the targeted teaching skills in the current field experience. The quality and clarity of responses improved as the subjects…

  10. Micropulsations in the electric field near the plasmapause, observed by ISEE-1

    NASA Technical Reports Server (NTRS)

    Moe, T. E.; Maynard, N. C.; Heppner, J. P.

    1979-01-01

    The occurrence of micropulsations near and inside the plasmapause was surveyed. The observed pulsations, classified as Pc3 and Pi2, are discussed. In addition one single event of Pc1 was observed. The frequencies in the Pc3 and Pi2 bands, the amplitude ranges, and the direction of rotation for the electric field vector are reported.

  11. Magnetic fields around evolved stars: further observations of H2O maser polarization

    NASA Astrophysics Data System (ADS)

    Leal-Ferreira, M. L.; Vlemmings, W. H. T.; Kemball, A.; Amiri, N.

    2013-06-01

    Context. A low- or intermediate-mass star is believed to maintain a spherical shape throughout the evolution from the main sequence to the asymptotic giant branch (AGB) phase. However, many post-AGB objects and planetary nebulae exhibit non-spherical symmetry. Several candidates have been suggested as factors that can play a role in this change of morphology, but the problem is still not well understood. Magnetic fields are one of these possible agents. Aims: We aim to detect the magnetic field and infer its properties around four AGB stars using H2O maser observations. The sample we observed consists of the following sources: the semi-regular variable RT Vir, and the Mira variables AP Lyn, IK Tau, and IRC+60370. Methods: We observed the 61,6 -52,3 H2O maser rotational transition in full-polarization mode to determine its linear and circular polarization. Based on the Zeeman effect, one can infer the properties of the magnetic field from the maser polarization analysis. Results: We detected a total of 238 maser features in three of the four observed sources. No masers were found toward AP Lyn. The observed masers are all located between 2.4 and 53.0 AU from the stars. Linear and circular polarization was found in 18 and 11 maser features, respectively. Conclusions: We more than doubled the number of AGB stars in which a magnetic field has been detected from H2O maser polarization. Our results confirm the presence of fields around IK Tau, RT Vir, and IRC+60370. The strength of the field along the line of sight is found to be between 47 and 331 mG in the H2O maser region. Extrapolating this result to the surface of the stars, assuming a toroidal field (∝ r-1), we find magnetic fields of 0.3-6.9 G on the stellar surfaces. If, instead of a toroidal field, we assume a poloidal field (∝ r-2), then the extrapolated magnetic field strength on the stellar surfaces are in the range between 2.2 and ~115 G. Finally, if a dipole field (∝ r-3) is assumed, the field

  12. MMS Multipoint Electric Field Observations of Small-Scale Magnetic Holes

    NASA Technical Reports Server (NTRS)

    Goodrich, Katherine A.; Ergun, Robert E.; Wilder, Frederick; Burch, James; Torbert, Roy; Khotyaintsev, Yuri; Lindqvist, Per-Arne; Russell, Christopher; Strangeway, Robert; Magnus, Werner

    2016-01-01

    Small-scale magnetic holes (MHs), local depletions in magnetic field strength, have been observed multiple times in the Earths magnetosphere in the bursty bulk flow (BBF) braking region. This particular subset of MHs has observed scale sizes perpendicular to the background magnetic field (B) less than the ambient ion Larmor radius (p(sib i)). Previous observations by Time History of Events and Macroscale Interactions during Substorms (THEMIS) indicate that this subset of MHs can be supported by a current driven by the E x B drift of electrons. Ions do not participate in the E x B drift due to the small-scale size of the electric field. While in the BBF braking region, during its commissioning phase, the Magnetospheric Multiscale (MMS) spacecraft observed a small-scale MH. The electric field observations taken during this event suggest the presence of electron currents perpendicular to the magnetic field. These observations also suggest that these currents can evolve to smaller spatial scales.

  13. Imaging Analysis of Near-Field Recording Technique for Observation of Biological Specimens

    NASA Astrophysics Data System (ADS)

    Moriguchi, Chihiro; Ohta, Akihiro; Egami, Chikara; Kawata, Yoshimasa; Terakawa, Susumu; Tsuchimori, Masaaki; Watanabe, Osamu

    2006-07-01

    We present an analysis of the properties of an imaging based on a near-field recording technique in comparison with simulation results. In the system, the optical field distributions localized near the specimens are recorded as the surface topographic distributions of a photosensitive film. It is possible to observe both soft and moving specimens, because the system does not require a scanning probe to obtain the observed image. The imaging properties are evaluated using fine structures of paramecium, and we demonstrate that it is possible to observe minute differences of refractive indices.

  14. Observational features of field line resonances excited by solar wind pressure variations on 4 September 1984

    NASA Technical Reports Server (NTRS)

    Warnecke, J.; Luehr, H.; Takahashi, K.

    1990-01-01

    The purpose of the study is to establish the most probable excitation mechanism of the magnetic storm occurred after an inverse sudden impulse on September 4, 1984. Geomagnetic pulsations in the Pc5-frequency range observed at magnetometer stations are evaluated. Attention is focused on two events of the enhanced activity: for the first one, conjugate observations on the ground are assessed and then compared with satellite-based observations on adjacent field lines; for the second event two hours later, data from an extended azimuthal range is employed. It is pointed out that the observations are consistent with the theory of filed-line resonance, and may be interpreted as excitations caused by pressure variations in the solar wind. Both magnetopause-surface waves and cavity resonances are excited; the cavity mode drives toroidal field-line oscillations at locations where its frequency matches the resonance frequency of the field lines.

  15. A Method for Observing Soil Re-Deposition and Soil Loss Rates in Large Field Experiments

    NASA Astrophysics Data System (ADS)

    Hsieh, Y. P.; Bugna, G. C.; Nemours, D.

    2014-12-01

    The lack of quality soil erosion field data, which is required for the verification and calibration of soil erosion models, has been one of the serious problems in the soil conservation modeling today. Observing soil erosion of a relatively large field under truly unobstructed runoff conditions has rarely been done and doccumented. Report here is the results of our observation of soil erosion in a 7.3 ha peanut-cotton cropping system in the Mears Farm of Grand Ridge, FL. We used the mesh-pad method to quantify soil loss from the field and soil re-deposition in the field over the cropping season of 2010. The main slope (1-3 %) of the field is about 210 m long. We show that the amount of soil re-deposition was 50-150 times of the soil loss from the slope. The corresponding organic matter, nitrogen, phosphorous and silt and clay contents of the lost soil, however, were 20.9%, 21%, 17.6% and 14.2%, respectively, of the total amounts re-deposited on the slope. The amounts of soil loss predicted by a SWAT model was 10-20 times greater than our observed values. Soil erosion process was quite heterogeneous, as shown by the mesh-pad method, even on a seemingly uniform cultivated field. Soil erosion models need to be verified and calibrated by extensive quality field data in order to improve their performance.

  16. Airborne observations of electric fields around growing and decaying cumulus clouds

    NASA Technical Reports Server (NTRS)

    Giori, K. L.; Nanevicz, J. E.

    1991-01-01

    Airborne electric field data were gathered in an atmospheric electrification study near Cape Canaveral, FL. A Learjet 36A was instrumented with eight electric field meters (mills) and five different particle probes. The local electric field enhancements at each field mill site were determined under lab conditions and verified using in-flight data. The overdetermined system of eight equations (one for each field mill) was solved using a weighted least squares algorithm to compute the magnitude and direction of the ambient electric field. The signal processing system allowed the measured data to be expressed in terms of earth coordinates, regardless of the attitude of the aircraft. Thus, it was possible to take maximum advantage of the Learjet's speed and maneuverability in studying the electric field structure in the vicinity of the clouds. Data gathered while circling just outside the boundary of a growing cumulus cloud show a nonsymmetric pattern of electric field strength. Field intensity grew rapidly over a period of less than 10 minutes. The observed direction of the ambient electric field vector can be explained by an ascending motion of the charge centers of a classic tripole model of a thunderstorm.

  17. 3D Global Coronal Density, Temperature, and Vector Magnetic Field Derived from Coronal Observation.

    NASA Astrophysics Data System (ADS)

    Kramar, M.; Lin, H.; Airapetian, V.; Tomczyk, S.

    2016-12-01

    Solar coronal magnetic fields play a key role in the energetics and dynamics of coronal heating, solar flares, coronal mass ejections (CME), filament eruptions, and determine space weather processes. Therefore, one of the central problems of solar physics is to measure the magnetic fields in the solar corona.The main techniques that are currently used to deduce the global magnetic structure of the solar corona include potential field, nonlinear force-free field (NLFFF), and magnetohydrodynamic (MHD) models. These methods are based on boundary conditions of the solar photospheric magnetic field that are derived directly from photospheric magnetograms. All of these methods are essentially extrapolation methods based on inner boundary conditions taken at the photosphere. However, the magnetic field at the photosphere and lower chromosphere is far from potential or force-free, because of the dominance of the plasma pressure there.We will present 3D reconstruction of the global coronal electron density, temperature during periods of minimum and maximum of solar activity cycle and derived from coronal STEREO/COR1 and EUVI observations. We find that the magnetic field configuration during maximum of solar activity (CR 2131) has a tendency to become radially open at heliocentric distances below 2.5 Rsun while during the solar minimum (CR 2066) they tend to open at higher distances.Moreover, the obtained 3D density and temperature has been used as additional input for recently developed vector tomography method to reconstruct the coronal vector magnetic field based on polarimetric observation of magnetically sensitive Fe XIII ion emission by Coronal Magnetic Polarimeter (CoMP). We validated the vector tomography inverted coronal magnetic fields with those constructed by MHD simulation based on observed photospheric magnetic fields as well as with the STEREO/EUVI 195 image and with the global 3D coronal electron density structure obtained by tomography based on STEREO/COR1

  18. Magnetic field inversions at 1 AU: Comparisons between mapping predictions and observations

    NASA Astrophysics Data System (ADS)

    Li, B.; Cairns, Iver H.; Owens, M. J.; Neudegg, D.; Lobzin, V. V.; Steward, G.

    2016-11-01

    Large-scale magnetic field configurations are important for the transport of solar wind strahl electrons, which are suprathermal and directed along the field outward from the Sun. Strahl electrons are routinely used to infer not only the field configurations between the Sun and Earth but also local field structures, i.e., field inversions, where the magnetic field is locally folded back or inverted. Using solar wind data from ACE observations and a 2-D data-driven solar wind model with nonzero azimuthal magnetic field at the solar wind source surface, magnetic field lines are mapped between the Sun and Earth and beyond, in the solar equatorial plane. Standard verification metrics are used to assess, for five solar rotations at different phases of solar cycle 23, the performance of the mapping predictions for observed inversions, which are inferred from solar wind suprathermal electrons and magnetic fields measured by ACE. The probability of detection is consistently ≈0.70 across the different phases. The success ratio, the Hanssen-Kuipers skill score, and the Heidke skill score are ≈0.55-0.70 for the four rotations in the rising, solar maximum, and declining phases, but ≈0.35-0.60 for the rotation near solar minimum, during which almost half of the samples have undetermined field configurations. Our analyses confirm the persistence of inversions throughout solar cycle 23, suggest for most observed inversions a solar/coronal origin at the wind's source surface or below, and predict that inversions should be less common for larger heliocentric distance r ˜> 3 AU than for smaller r.

  19. GPS Occultation Observations of Equatorial Scintillation: Dependence on Magnetic Field Orientation, Longitude, and Season

    NASA Astrophysics Data System (ADS)

    Anderson, P. C.; Straus, P. R.

    2004-12-01

    We analyzed GPS occultation data from the CHAMP, SAC-C, and PICOSat satellite for the entire year 2002 identifying radiowave scintillation occurrence from SNR measurements of the C/A code on the L1 frequency obtained at the 1-second rate cadence. Global distributions clearly indicate that we are observing equatorial scintillation and scintillation in the auroral zones and polar cap. Seasonal and magnetic local time distributions of the low-latitude observations are in good agreement with the known distributions of equatorial scintillation. Longitudinal distributions vary somewhat from the WBMOD climatological model, particularly in the African sector where scintillation is observed nearly all year. A strong dependence on the orientation of the occultation ray path with the magnetic field orientation is observed with a low probability of scintillation at ray path angles perpendicular to the magnetic field and high probability of observations at smaller angles. This is interpreted as the result of the orientation of the ionospheric bubbles responsible for the scintillation. The walls of the bubbles, on which the instabilities that cause the scintillation occur, are typically aligned with the magnetic field. Thus, occultation ray paths along the magnetic field pass along the edge of the bubbles and remain within the region of instabilities for a longer period that ray paths perpendicular to the magnetic field and the bubble walls.

  20. Solar coronal and magnetic field observations near the time of the 1988 March 18 solar eclipse

    SciTech Connect

    Sime, D.G.; Fisher, R.R.; Mickey, D.L.

    1988-10-01

    Observations made during the interval March 1-31, 1988, are presented which were designed to provide a synoptic context in which data from the March 18, 1988, total solar eclipse can be interpreted. Daily observations made with the Mark III K-coronameter and the H-alpha prominence monitor at the Mauna Loa Solar Observatory, along with photographic records of the Sun in H-alpha from the flare patrol at Mees Solar Observatory on Haleakala, Maui, are included. Observations of the longitudinal component of the photospheric magnetic field made at Mees Solar Observatory were also gathered around the period of the eclipse. Together with the white-light image of the corona at the eclipse, these coronal and magnetic field observations assembled into synoptic maps for this epoch, are presented. On the basis of these observations, an interpretation of the global density distribution of the corona at the time of the eclipse is constructed. 11 references.

  1. Solar coronal and magnetic field observations near the time of the 1988 March 18 solar eclipse

    NASA Technical Reports Server (NTRS)

    Sime, D. G.; Fisher, R. R.; Mickey, D. L.

    1988-01-01

    Observations made during the interval March 1-31, 1988, are presented which were designed to provide a synoptic context in which data from the March 18, 1988, total solar eclipse can be interpreted. Daily observations made with the Mark III K-coronameter and the H-alpha prominence monitor at the Mauna Loa Solar Observatory, along with photographic records of the Sun in H-alpha from the flare patrol at Mees Solar Observatory on Haleakala, Maui, are included. Observations of the longitudinal component of the photospheric magnetic field made at Mees Solar Observatory were also gathered around the period of the eclipse. Together with the white-light image of the corona at the eclipse, these coronal and magnetic field observations assembled into synoptic maps for this epoch, are presented. On the basis of these observations, an interpretation of the global density distribution of the corona at the time of the eclipse is constructed.

  2. MAVEN Observations of Energy-Time Dispersed Electron Signatures in Martian Crustal Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Harada, Y.; Mitchell, D. L.; Halekas, J. S.; McFadden, J. P.; Mazelle, C.; Connerney, J. E. P.; Espley, J.; Brain, D. A.; Larson, D. E.; Lillis, R. J.; Hara, T.; Livi, R.; DiBraccio, G. A.; Ruhunusiri, S.; Jakosky, B. M.

    2016-01-01

    Energy-time dispersed electron signatures are observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission in the vicinity of strong Martian crustal magnetic fields. Analysis of pitch angle distributions indicates that these dispersed electrons are typically trapped on closed field lines formed above strong crustal magnetic sources. Most of the dispersed electron signatures are characterized by peak energies decreasing with time rather than increasing peak energies. These properties can be explained by impulsive and local injection of hot electrons into closed field lines and subsequent dispersion by magnetic drift of the trapped electrons. In addition, the dispersed flux enhancements are often bursty and sometimes exhibit clear periodicity, suggesting that the injection and trapping processes are intrinsically time dependent and dynamic. These MAVEN observations demonstrate that common physical processes can operate in both global intrinsic magnetospheres and local crustal magnetic fields.

  3. Magnetospheric Multiscale Observations of the Electron Diffusion Region of Large Guide Field Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Eriksson, S.; Wilder, F. D.; Ergun, R. E.; Schwartz, S. J.; Cassak, P. A.; Burch, J. L.; Chen, Li-Jen; Torbert, R. B.; Phan, T. D.; Lavraud, B.; hide

    2016-01-01

    We report observations from the Magnetospheric Multiscale (MMS) satellites of a large guide field magnetic reconnection event. The observations suggest that two of the four MMS spacecraft sampled the electron diffusion region, whereas the other two spacecraft detected the exhaust jet from the event. The guide magnetic field amplitude is approximately 4 times that of the reconnecting field. The event is accompanied by a significant parallel electric field (E(sub parallel lines) that is larger than predicted by simulations. The high-speed (approximately 300 km/s) crossing of the electron diffusion region limited the data set to one complete electron distribution inside of the electron diffusion region, which shows significant parallel heating. The data suggest that E(sub parallel lines) is balanced by a combination of electron inertia and a parallel gradient of the gyrotropic electron pressure.

  4. Magnetic field observations as Voyager 1 entered the heliosheath depletion region.

    PubMed

    Burlaga, L F; Ness, N F; Stone, E C

    2013-07-12

    Magnetic fields measured by Voyager 1 (V1) show that the spacecraft crossed the boundary of an unexpected region five times between days 210 and ~238 in 2012. The magnetic field strength B increased across this boundary from ≈0.2 to ≈0.4 nanotesla, and B remained near 0.4 nanotesla until at least day 270, 2012. The strong magnetic fields were associated with unusually low counting rates of >0.5 mega-electron volt per nuclear particle. The direction of B did not change significantly across any of the five boundary crossings; it was very uniform and very close to the spiral magnetic field direction, which was observed throughout the heliosheath. The observations indicate that V1 entered a region of the heliosheath (the heliosheath depletion region), rather than the interstellar medium.

  5. Electric and magnetic field observations during a substorm of 24 February 1970

    NASA Technical Reports Server (NTRS)

    Gurnett, D. A.; Akasofu, S. I.

    1974-01-01

    A series of electric field measurements is reported which was obtained from the Injun 5 satellite along with a simultaneous magnetic disturbance observed in the interplanetary medium and on the ground during a magnetic substorm. The substorm analyzed took place on February 24, 1970. Prior to the onset of the substorm a greatly enhanced anti-sunward plasma flow was observed over the polar cap. The enhanced plasma flow occurred about 30 minutes after a switch in the direction of the interplanetary magnetic field from northward to southward. The electric fields across the polar cap immediately before and during the substorm were essentially unchanged indicating that an enhancement in the ionospheric conductivity rather than the electric field must be responsible for the large increase in the auroral electrojet current during the substorm.

  6. A biophysical observation model for field potentials of networks of leaky integrate-and-fire neurons.

    PubMed

    Beim Graben, Peter; Rodrigues, Serafim

    2012-01-01

    We present a biophysical approach for the coupling of neural network activity as resulting from proper dipole currents of cortical pyramidal neurons to the electric field in extracellular fluid. Starting from a reduced three-compartment model of a single pyramidal neuron, we derive an observation model for dendritic dipole currents in extracellular space and thereby for the dendritic field potential (DFP) that contributes to the local field potential (LFP) of a neural population. This work aligns and satisfies the widespread dipole assumption that is motivated by the "open-field" configuration of the DFP around cortical pyramidal cells. Our reduced three-compartment scheme allows to derive networks of leaky integrate-and-fire (LIF) models, which facilitates comparison with existing neural network and observation models. In particular, by means of numerical simulations we compare our approach with an ad hoc model by Mazzoni et al. (2008), and conclude that our biophysically motivated approach yields substantial improvement.

  7. MAVEN Observations of Energy-Time Dispersed Electron Signatures in Martian Crustal Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Harada, Y.; Mitchell, D. L.; Halekas, J. S.; McFadden, J. P.; Mazelle, C.; Connerney, J. E. P.; Espley, J.; Brain, D. A.; Larson, D. E.; Lillis, R. J.; hide

    2016-01-01

    Energy-time dispersed electron signatures are observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission in the vicinity of strong Martian crustal magnetic fields. Analysis of pitch angle distributions indicates that these dispersed electrons are typically trapped on closed field lines formed above strong crustal magnetic sources. Most of the dispersed electron signatures are characterized by peak energies decreasing with time rather than increasing peak energies. These properties can be explained by impulsive and local injection of hot electrons into closed field lines and subsequent dispersion by magnetic drift of the trapped electrons. In addition, the dispersed flux enhancements are often bursty and sometimes exhibit clear periodicity, suggesting that the injection and trapping processes are intrinsically time dependent and dynamic. These MAVEN observations demonstrate that common physical processes can operate in both global intrinsic magnetospheres and local crustal magnetic fields.

  8. Gauge-invariant observables and marginal deformations in open string field theory

    NASA Astrophysics Data System (ADS)

    Kudrna, Matěj; Masuda, Toru; Okawa, Yuji; Schnabl, Martin; Yoshida, Kenichiro

    2013-01-01

    The level-truncation analysis of open string field theory for a class of periodic marginal deformations indicates that a branch of solutions in Siegel gauge exists only for a finite range of values of the marginal field. The periodicity in the deformation parameter is thus obscure. We use the relation between gauge-invariant observables and the closed string tadpole on a disk conjectured by Ellwood to construct a map between the deformation parameter of the boundary conformal field theory and the parameter labeling classical solutions of open string field theory. We evaluate the gauge-invariant observables for the numerical solutions in Siegel gauge up to level 12 and find that our results qualitatively agree with the analysis by Sen using the energy-momentum tensor and are consistent with the picture that the finite range of the branch covers one fundamental domain of the periodic moduli space.

  9. Near-field observation of subwavelength confinement of photoluminescence by a photonic crystal microcavity.

    PubMed

    Louvion, Nicolas; Rahmani, Adel; Seassal, Christian; Callard, Ségolène; Gérard, Davy; de Fornel, Frédérique

    2006-07-15

    We present a direct, room-temperature near-field optical study of light confinement by a subwavelength defect microcavity in a photonic crystal slab containing quantum-well sources. The observations are compared with three-dimensional finite-difference time-domain calculations, and excellent agreement is found. Moreover, we use a subwavelength cavity to study the influence of a near-field probe on the imaging of localized optical modes.

  10. Cosmological backreaction for a test field observer in a chaotic inflationary model

    SciTech Connect

    Marozzi, Giovanni; Vacca, Gian Paolo; Brandenberger, Robert H. E-mail: vacca@bo.infn.it

    2013-02-01

    In an inhomogeneous universe, an observer associated with a particular matter field does not necessarily measure the same cosmological evolution as an observer in a homogeneous and isotropic universe. Here we consider, in the context of a chaotic inflationary background model, a class of observers associated with a ''clock field'' for which we use a light test field. We compute the effective expansion rate and fluid equation of state in a gauge invariant way, taking into account the quantum fluctuations of the long wavelength modes, and working up to second order in perturbation theory and in the slow-roll approximation. We find that the effective expansion rate is smaller than what would be measured in the absence of fluctuations. Within the stochastic approach we study the bounds for which the approximations we make are consistent.

  11. Dynamics of Tachyon Fields and Inflation - Comparison of Analytical and Numerical Results with Observation

    NASA Astrophysics Data System (ADS)

    Milošević, M.; Dimitrijević, D. D.; Djordjević, G. S.; Stojanović, M. D.

    2016-06-01

    The role tachyon fields may play in evolution of early universe is discussed in this paper. We consider the evolution of a flat and homogeneous universe governed by a tachyon scalar field with the DBI-type action and calculate the slow-roll parameters of inflation, scalar spectral index (n), and tensor-scalar ratio (r) for the given potentials. We pay special attention to the inverse power potential, first of all to V(x)˜ x^{-4}, and compare the available results obtained by analytical and numerical methods with those obtained by observation. It is shown that the computed values of the observational parameters and the observed ones are in a good agreement for the high values of the constant X_0. The possibility that influence of the radion field can extend a range of the acceptable values of the constant X_0 to the string theory motivated sector of its values is briefly considered.

  12. Ionospheric magnetic fields and currents at Mars and Venus. Perspectives from MEX and VEX observations.

    NASA Astrophysics Data System (ADS)

    Dubinin, E.; Fraenz, M.; Zhang, T.-L.; Wei, Y.; Woch, J.; Fedorov, A.; Barabash, S.; Lundin, R.; Duru, F.

    2012-09-01

    Mars Express and Venus Express spacecrafts have provided us a wealth of in-situ observations of characteristics of induced magnetospheres of Mars and Venus at low altitudes during solar minimum conditions. At such conditions large-scale magnetic fields are observed deeply in the ionospheres (magnetized ionospheres). The observations again raise a long-standing question about the origin of these fields. The problem is intimately related to issue of electric current system and their closure. Analysis of ASPERA-3, ASPERA-4, MARSIS and MAG data reveals a lot of features which require a more sophisticated view at the origin and topology of the ionospheric magnetic fields. Differing perspectives at this problem are widely discussed.

  13. Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm

    NASA Astrophysics Data System (ADS)

    Nakajima, A.; Shiokawa, K.; Seki, K.; Strangeway, R. J.; McFadden, J. P.; Carlson, C. W.

    2007-06-01

    Broadband electrons (BBEs) are remarkable flux enhancements (>1013 eV cm-2 s-1) of precipitating electrons over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. We show characteristics of particles (energy spectra and pitch angle distribution) and fields (electric field, magnetic field, and wave spectra) during a BBE event observed by the Fast Auroral SnapshoT (FAST) satellite. The BBEs were observed at an altitude of ˜2000 km at 59°-61° invariant latitudes (ILATs) and 21 h magnetic local time (MLT). The event was observed at ˜7 min after the onset of a substorm during the main phase of the Bastille Day geomagnetic storm (minimum Dst = -301 nT) on 15 July 2000. The precipitation region of the BBEs corresponded to a localized intensification of auroral emission, lasting ˜14 min, observed by the Polar UVI images at 50°-60° geomagnetic latitudes (MLATs) and 20-21 MLTs. These results suggest that rapid particle acceleration was occurring in the inner magnetosphere associated with a storm-time substorm. The pitch angle distribution of BBEs was isotropic except for a loss cone feature around the field-aligned upward direction at a higher energy range above ˜1 keV, while field-aligned electron fluxes were larger than the perpendicular fluxes below ˜1 keV. These results imply that a higher energy part of the BBEs originated from higher altitudes in the inner magnetosphere and that a lower energy part was accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields were observed during this BBE event. From these results, we discuss possible acceleration of the lower energy part of BBEs through wave-particle interaction.

  14. Interpolation of observed rainfall fields for flood forecasting in data poor areas

    NASA Astrophysics Data System (ADS)

    Rogelis Prada, M. C.; Werner, M. G. F.

    2010-09-01

    Observed rainfall fields constitute a crucial input for operational flood forecasting, providing boundary conditions to hydrological models for prediction of flows and levels in relevant forecast points. Such observed fields are derived through interpolation from available observed data from rain gauges. The reliability of the derived rainfall field depends on the density of the gauge network within the basin, as well as on the variability of the rainfall itself, and the interpolation method. In this paper interpolation methods to estimate rainfall fields under data- poor environments are researched, with the derived rainfall fields being used in operational flood warnings. Methods are applied in a small catchment in Bogotá, Colombia. This catchment has a complex climatology, which is strongly influenced by the inter-tropical convergence zone and orographic enhancement. As is common in such catchments in developing countries, the rainfall gauging network is sparse, while the need for reliable rainfall in flood forecasting is high. The extensive high flood risk zones in the lower areas of the catchment, where urbanization processes are characterized by unplanned occupation of areas close to rivers, is common in developing countries. Results show the sensitivity of interpolated rainfall fields to the interpolation methods chosen, and the importance of the use of indicator variables for improving the spatial distribution of interpolated rainfall. The value of these methods in establishing optimal new gauging sites for augmenting the sparse gauge network is demonstrated.

  15. Latitudinal variation of perturbation electric fields during magnetically disturbed periods - 1986 Sundial observations and model results

    NASA Technical Reports Server (NTRS)

    Fejer, B. G.; Spiro, R. W.; Wolf, R. A.; Foster, J. C.

    1990-01-01

    F-region incoherent scatter radar drift observations from Millstone Hill and Jicamarca, h-prime F observations from Huancayo, and high latitude ground-magnetometer measurements taken during the Sundial 1986 campaign are used to study the relationship between plasmaspheric electric field perturbations and high latitude currents during disturbed periods. The observations are in good agreement with numerical results from a Rice Covection Model run that involved a sharp increase in the polar cap potential drop followed by a subsequent decrease. The zonal disturbance electric field pattern is latitude independent, and the corresponding amplitudes change approximately as L exp n (where n is about 1.5). The meridional electric field patterns and amplitudes have larger latitudinal variations. The mid-, low, and equatorial electric fields from the Rice Convection Model are in good agreement with previous results from the semianalytic, Senior-Blanc (1987) model. Also discussed are three physical mechanisms (over-shielding, fossil winds, and magnetic reconfiguration) that contribute to the long lasting (1-2 h) equatorial zonal electric field perturbations associated with a sudden northward turning of the IMF. It is predicted that the penetration of high latitude electric fields to low latitudes should, in general, be closely related to the rate of motion of the shielding layer and the equatorward edge of the diffuse aurora.

  16. High performance field emission and Nottingham effect observed from carbon nanotube yarn

    NASA Astrophysics Data System (ADS)

    Choi, Young Chul; Kang, Jun-Tae; Park, Sora; Go, Eunsol; Jeon, Hyojin; Kim, Jae-Woo; Jeong, Jin-Woo; Park, Kyung-Ho; Song, Yoon-Ho

    2017-02-01

    Vertically aligned CNTs were synthesized on a four inch wafer, followed by the preparation of a CNT yarn. The yarn emitter was found to have an extremely high field enhancement factor, which was confirmed to have originated from multi-stage effect. In addition to superb field emission characteristics, the energy exchange during field emission, called Nottingham effect, was observed from the CNT yarn emitter. A CNT yarn was attached to the thermistor whose resistance depends on temperature. Then, the change of resistance was monitored during the field emission, which enabled us to calculate the energy exchange. It was found that the observed heating originated from both Nottingham and Joule heating. Nottingham heating was dominant at low current region while Joule heating became larger contribution at high current region. Very large Nottingham region of up to 33.35 mA was obtained, which is due presumably to the high performance field emission characteristics of a CNT yarn. This is believed to be an important observation for developing reliable field emission devices with suppressed Joule heating effect.

  17. Magnetic fields in Venus nightside ionospheric holes - Collected Pioneer Venus Orbiter magnetometer observations

    NASA Technical Reports Server (NTRS)

    Luhmann, J. G.; Russell, D. S.

    1992-01-01

    The magnetic fields detected by the Pioneer Venus Orbiter (PVO) magnetometer within the electron density depletions called 'holes' in the nightside ionosphere are typically larger and more organized than the fields in the surrounding ionosphere. Moreover, they have substantial sunward/antisunward components which cause them to appear as near-radial fields near the antisolar point. The collection of observations presented here illustrate the variety of appearances of the fields in holes. Some new results which summarize their average properties, their dependence on solar wind conditions, and their lack of geographical control are aslo presented. These results are potentially pertinent to the interpretation of data from the PVO entry at the end of 1992 and from the impending Mars Obsever mission, which will probe the magnetic fields in the low-altitude wake of weakly magnetized Mars.

  18. Observations of the magnetic field and plasma flow in Jupiter's magnetosheath

    NASA Technical Reports Server (NTRS)

    Lepping, R. P.; Burlaga, L. F.; Klein, L. W.; Jessen, J. M.; Goodrich, G. C.

    1980-01-01

    Large scale (many minutes to 10 hours) magnetic field structures consisting predominantly of nearly north-south field direction were discovered in Jupiter's magnetosheath from the data of Voyagers 1 and 2 and Pioneer 10 during their outbound encounter trajectories. The Voyager 2 data, and that of Voyager 1 to a lesser extent, show evidence of a quasi-period of 10 hours (and occasionally 5 hours) for these structures. The north-south components of the field and plasma velocity were strongly correlated in the outbound magnetosheath as observed by Voyagers 1 and 2, and the components orthogonal to the north-south direction showed weak correlations. For both Voyager encounters the sense (positive and negative) of the north-south correlations were directly related to the direction of the ecliptic plane component of the interplanetary magnetic field using the field and plasma measurements of the non-encountering spacecraft.

  19. Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field

    PubMed Central

    Piazza, L; Lummen, T.T.A.; Quiñonez, E; Murooka, Y; Reed, B.W.; Barwick, B; Carbone, F

    2015-01-01

    Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. This methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits. PMID:25728197

  20. Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field

    DOE PAGES

    Piazza, L.; Lummen, T. T. A.; Quiñonez, E.; ...

    2015-03-02

    Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinducedmore » near-field is imaged synchronously with its spatial interference pattern. In conclusion, this methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.« less

  1. Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field

    SciTech Connect

    Piazza, L.; Lummen, T. T. A.; Quiñonez, E.; Murooka, Y.; Reed, B. W.; Barwick, B.; Carbone, F.

    2015-03-02

    Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. In conclusion, this methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.

  2. Interaction of solar wind with Mercury and its magnetic field. [as observed by Mariner 10 space probe

    NASA Technical Reports Server (NTRS)

    Ness, N. F.; Behannon, K. W.; Lepping, R. P.; Whang, Y. C.

    1976-01-01

    A brief review is presented of magnetic field and solar wind electron observations by Mariner 10 spacecraft. The intrinsic magnetic field of the planet Mercury and the implications of such a field for the planetary interior are also discussed.

  3. Field trip report: Observations made at Yucca Mountain, Nye County, Nevada. Special report No. 2

    SciTech Connect

    Hill, C.A.

    1993-03-01

    A field trip was made to the Yucca Mountain area on December 5-9, 1992 by Jerry Frazier, Don Livingston, Christine Schluter, Russell Harmon, and Carol Hill. Forty-three separate stops were made and 275 lbs. of rocks were collected during the five days of the field trip. Key localities visited were the Bare Mountains, Yucca Mountain, Calico Hills, Busted Butte, Harper Valley, Red Cliff Gulch, Wahmonie Hills, Crater Flat, and Lathrop Wells Cone. This report only describes field observations made by Carol Hill. Drawings are used rather than photographs because cameras were not permitted on the Nevada Test Site during this trip.

  4. Future Observations of Cosmic Magnetic Fields with LOFAR, SKA and Its Precursors

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission from the Milky Way, galaxies and galaxy clusters, observed with the new Low Frequency Array (LOFAR) and the planned Square Kilometre Array (SKA), traces low-energy cosmic ray electrons and allows us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in halos and relics of clusters and in the Milky Way. Polarization at higher frequencies (1-10 GHz), to be observed with the SKA and its precursors Australia SKA Pathfinder (ASKAP) and the South African MeerKAT telescopes, will trace magnetic fields in the disks and central regions of galaxies and in cluster relics in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with ASKAP (project POSSUM) and the SKA are dedicated to measure magnetic fields in intervening galaxies, clusters and intergalactic filaments, and will be used to model the overall structure and strength of magnetic fields in the Milky Way. Cosmic magnetism is "key science" for LOFAR, ASKAP and the SKA.

  5. The magnetic field of the earth - Performance considerations for space-based observing systems

    NASA Technical Reports Server (NTRS)

    Webster, W. J., Jr.; Taylor, P. T.; Schnetzler, C. C.; Langel, R. A.

    1985-01-01

    Basic problems inherent in carrying out observations of the earth magnetic field from space are reviewed. It is shown that while useful observations of the core and crustal fields are possible at the peak of the solar cycle, the greatest useful data volume is obtained during solar minimum. During the last three solar cycles, the proportion of data with a planetary disturbance index of less than 2 at solar maximum was in the range 0.4-0.8 in comparison with solar minimum. It is found that current state of the art orbit determination techniques should eliminate orbit error as a problem in gravitational field measurements from space. The spatial resolution obtained for crustal field anomalies during the major satellite observation programs of the last 30 years are compared in a table. The relationship between observing altitude and the spatial resolution of magnetic field structures is discussed. Reference is made to data obtained using the Magsat, the Polar Orbiting Geophysical Observatory (POGO), and instruments on board the Space Shuttle.

  6. A quantitative study relating observed shear in photospheric magnetic fields to repeated flaring

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J.; Teuber, D.; West, E. A.; Smith, J. B.

    1984-01-01

    In this paper a quantitative evaluation of the shear in the magnetic field along the neutral line in an active region during an epoch of flare activity is presented. Shear is defined as the angular difference in the photosphere between the potential magnetic field, which fits the boundary conditions imposed by the observed line-of-sight field, and the observed magnetic field. For the active region studied, this angular difference (shear) is non-uniform along the neutral line with maxima occurring at the locations of repeated flare onsets. It is suggested that continued magnetic evolution causes the field's maximum shear to exceed a critical value of shear, resulting in a flare around the site of maximum shear. Evidently, the field at the site of the flare must relax to a state of shear somewhat below the critical value (but still far from potential), with subsequent evolution returning the field to the critical threshold. This inference is drawn because several flares occured at sites of maximum photospheric shear which were persistent in location.

  7. Observations of the dust radial velocity field in the F-corona on March 29, 2006

    NASA Astrophysics Data System (ADS)

    Shestakova, L. I.; Demchenko, B. I.; Rspaev, F. K.; Chalabaev, A.

    2011-12-01

    The results of interferometer observations of the dust radial velocity field in the F-corona during the total solar eclipse of March 29, 2006, are presented. The observations were performed in the Mugalzhar settlement, Aqtobe region, Kazakhstan. The observation results indicated that the dust orbital motion is opposite to the planetary motion and is inclined at an angle of about 105° with respect to the ecliptic plane. It is assumed that the observed dust is genetically related to Kreutz comets falling on the Sun and registered with the SOHO spacecraft on March 28 and 31, 2006.

  8. Modular model for Mercury's magnetospheric magnetic field confined within the average observed magnetopause

    PubMed Central

    Tsyganenko, Nikolai A.; Johnson, Catherine L.; Philpott, Lydia C.; Anderson, Brian J.; Al Asad, Manar M.; Solomon, Sean C.; McNutt, Ralph L.

    2015-01-01

    Abstract Accurate knowledge of Mercury's magnetospheric magnetic field is required to understand the sources of the planet's internal field. We present the first model of Mercury's magnetospheric magnetic field confined within a magnetopause shape derived from Magnetometer observations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft. The field of internal origin is approximated by a dipole of magnitude 190 nT RM 3, where RM is Mercury's radius, offset northward by 479 km along the spin axis. External field sources include currents flowing on the magnetopause boundary and in the cross‐tail current sheet. The cross‐tail current is described by a disk‐shaped current near the planet and a sheet current at larger (≳ 5 RM) antisunward distances. The tail currents are constrained by minimizing the root‐mean‐square (RMS) residual between the model and the magnetic field observed within the magnetosphere. The magnetopause current contributions are derived by shielding the field of each module external to the magnetopause by minimizing the RMS normal component of the magnetic field at the magnetopause. The new model yields improvements over the previously developed paraboloid model in regions that are close to the magnetopause and the nightside magnetic equatorial plane. Magnetic field residuals remain that are distributed systematically over large areas and vary monotonically with magnetic activity. Further advances in empirical descriptions of Mercury's magnetospheric external field will need to account for the dependence of the tail and magnetopause currents on magnetic activity and additional sources within the magnetosphere associated with Birkeland currents and plasma distributions near the dayside magnetopause. PMID:27656335

  9. Modular model for Mercury's magnetospheric magnetic field confined within the average observed magnetopause.

    PubMed

    Korth, Haje; Tsyganenko, Nikolai A; Johnson, Catherine L; Philpott, Lydia C; Anderson, Brian J; Al Asad, Manar M; Solomon, Sean C; McNutt, Ralph L

    2015-06-01

    Accurate knowledge of Mercury's magnetospheric magnetic field is required to understand the sources of the planet's internal field. We present the first model of Mercury's magnetospheric magnetic field confined within a magnetopause shape derived from Magnetometer observations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft. The field of internal origin is approximated by a dipole of magnitude 190 nT RM(3), where RM is Mercury's radius, offset northward by 479 km along the spin axis. External field sources include currents flowing on the magnetopause boundary and in the cross-tail current sheet. The cross-tail current is described by a disk-shaped current near the planet and a sheet current at larger (≳ 5 RM ) antisunward distances. The tail currents are constrained by minimizing the root-mean-square (RMS) residual between the model and the magnetic field observed within the magnetosphere. The magnetopause current contributions are derived by shielding the field of each module external to the magnetopause by minimizing the RMS normal component of the magnetic field at the magnetopause. The new model yields improvements over the previously developed paraboloid model in regions that are close to the magnetopause and the nightside magnetic equatorial plane. Magnetic field residuals remain that are distributed systematically over large areas and vary monotonically with magnetic activity. Further advances in empirical descriptions of Mercury's magnetospheric external field will need to account for the dependence of the tail and magnetopause currents on magnetic activity and additional sources within the magnetosphere associated with Birkeland currents and plasma distributions near the dayside magnetopause.

  10. Geology Structure Identification based on Polarimetric SAR (PolSAR) Data and Field Based Observation at Ciwidey Geothermal Field

    NASA Astrophysics Data System (ADS)

    Pradipta, R. A.; Saepuloh, A.; Suryantini

    2016-09-01

    Geological structure observation is difficult to be conducted at Quaternary volcanic field due to the classical problem at tropical region such as intensive erosion, dense vegetation covers, and rough terrain. The problem hampers the field observation especially for geological structures mapping. In order to overcome the problems, an active remote sensing technology based on Polarimetric Synthetic Aperture Radar (PolSAR) data was used in this study. The longer wavelength of microwave than optical region caused the SAR layer penetration higher than optics. The Ciwidey Geothermal Field, Indonesia was selected as study area because of the existence of surface manifestations with lack information about the control of geological structures to the geothermal system. Visual interpretation based on composite polarization modes was applied to identify geological structures at study area. The color composite Red-Green-Blue for HV-HH-VV polarizations provided highest texture and structural features among the other composite combination. The Linear Features Density (LFD) map was also used to interpret the fractures zones. The calculated LFD showed high anomaly about 3.6 km/km2 with two strike directions NW-SE and NE-SW. Interestingly, the surface geothermal manifestation agreed with the low anomaly of LFD. The geological structures consisted of ten faults were successfully detected and mapped. The faults type mainly are oblique-slip with strike directions NE-SW and NW-SE.

  11. FM 22. Mapping the Frontier Fields with Chandra X-ray Observations

    NASA Astrophysics Data System (ADS)

    Jones, C.; van Weeren, R.; Ogrean, G.; Forman, W.

    Chandra has deeply observed the clusters and parallel fields in four Frontier Fields. These observations allow us to dramatically improve our understanding of cluster mergers by comparing the detailed mapping of the hot cluster gas with high resolution mass maps and by identifying merger shocks and cold fronts. In merging clusters, relativistic particles can be re-accelerated to produce radio relics. A comparison of lensing maps and Chandra images allows us to determine the cluster morphology and dynamical state and if there are offsets between the dark matter and the hot gas.

  12. Rocket and satellite observations of electric fields and ion convection in the dayside auroral ionosphere

    NASA Technical Reports Server (NTRS)

    Marklund, G. T.; Heelis, R. A.; Winningham, J. D.

    1986-01-01

    The electric field and convection pattern of the dayside auroral ionosphere are analyzed using electric-field data from two high-altitude rocket flights in the polar cusp and satelltie observations of ion drifts and energetic particles. The geophysical conditions for December 1 and 13, 1981 are described. The flow reversals for the two events are studied, and a dayside convection pattern is characterized. It is observed that this convection pattern is in qualitative agreement with the predictions of a geometrical model of Crooker (1979), when the IMF is oriented towards dawn.

  13. Voyager 1 and 2 Observations of the Local Interstellar Magnetic Field and Heliosheath

    NASA Astrophysics Data System (ADS)

    Richardson, J. D.; Burlaga, L. F.; Ness, N. F.

    2015-12-01

    Voyager 1 (V1) observed compressive interstellar turbulence in the local interstellar medium (LISM) with a Kolmogorov spectrum from 2013.36 to 2014.64. Observations of the magnetic field by V1 during 2015 will be presented. Preliminary heliosheath observations by Voyager 2 (V2) indicate that the magnetic field strength (B) began to increase in mid-2011, possibly reaching 0.3 nT during mid-2012. A similar increase in B was observed by V1 shortly before it crossed the heliopause. However, it is possible that the strong magnetic fields observed by V2, if confirmed, were associated with increasing solar activity. The plasma speed was lowest during the middle of 2012, but there was no clear relationship between V and B. The magnetic flux continued to be conserved by V2 during 2011 and 2012, whereas the magnetic flux at V1 decreased in the heliosheath with increasing distance. At least 30 magnetic holes, magnetic humps and other microscale features were observed in the heliosheath by V2 during 2012. Such features were not observed by V1 in the LISM.

  14. OBSERVATIONS AND MAGNETIC FIELD MODELING OF A SOLAR POLAR CROWN PROMINENCE

    SciTech Connect

    Su Yingna; Van Ballegooijen, Adriaan

    2012-10-01

    We present observations and magnetic field modeling of the large polar crown prominence that erupted on 2010 December 6. Combination of Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and STEREO{sub B}ehind/EUVI allows us to see the fine structures of this prominence both at the limb and on the disk. We focus on the structures and dynamics of this prominence before the eruption. This prominence contains two parts: an active region part containing mainly horizontal threads and a quiet-Sun part containing mainly vertical threads. On the northern side of the prominence channel, both AIA and EUVI observe bright features which appear to be the lower legs of loops that go above then join in the filament. Filament materials are observed to frequently eject horizontally from the active region part to the quiet-Sun part. This ejection results in the formation of a dense-column structure (concentration of dark vertical threads) near the border between the active region and the quiet Sun. Using the flux rope insertion method, we create nonlinear force-free field models based on SDO/Helioseismic and Magnetic Imager line-of-sight magnetograms. A key feature of these models is that the flux rope has connections with the surroundings photosphere, so its axial flux varies along the filament path. The height and location of the dips of field lines in our models roughly replicate those of the observed prominence. Comparison between model and observations suggests that the bright features on the northern side of the channel are the lower legs of the field lines that turn into the flux rope. We suggest that plasma may be injected into the prominence along these field lines. Although the models fit the observations quiet well, there are also some interesting differences. For example, the models do not reproduce the observed vertical threads and cannot explain the formation of the dense-column structure.

  15. OBSERVATION OF A NON-RADIAL PENUMBRA IN A FLUX EMERGING REGION UNDER CHROMOSPHERIC CANOPY FIELDS

    SciTech Connect

    Lim, Eun-Kyung; Yurchyshyn, Vasyl; Goode, Philip; Cho, Kyung-Suk

    2013-05-20

    The presence of a penumbra is one of the main properties of a mature sunspot, but its formation mechanism has been elusive due to a lack of observations that fully cover the formation process. Utilizing the New Solar Telescope at the Big Bear Solar Observatory, we observed the formation of a partial penumbra for about 7 hr simultaneously at the photospheric (TiO; 7057 A) and the chromospheric (H{alpha} - 1 A) spectral lines with high spatial and temporal resolution. From this uninterrupted, long observing sequence, we found that the formation of the observed penumbra was closely associated with flux emergence under the pre-existing chromospheric canopy fields. Based on this finding, we suggest a possible scenario for penumbra formation in which a penumbra forms when the emerging flux is constrained from continuing to emerge, but rather is trapped at the photospheric level by the overlying chromospheric canopy fields.

  16. Observation of low field microwave absorption in co-doped ZnO system

    NASA Astrophysics Data System (ADS)

    Mahule, Tebogo S.; Srinivasu, Vijaya V.; Das, Jayashree

    2016-10-01

    Room temperature low field microwave absorption (LFMA) in magnetic materials find application in microwave absorbers and low field sensors. However not all the magnetic materials show LFMA and the phenomenon is not fully understood. We report on the observation of low field microwave absorption (LFMA) or the non-resonant microwave absorption (NRMA) in the transition metal (TM) co-doped ZnO samples of the composition Zn1-x(TM:TM)xO synthesized by solid state reaction technique. LFMA peaks and hysteresis matches very well with that of the magnetization hysteresis loop and the anisotropy fields at room temperature similar to the reports in the literature for other magnetic systems. However we show through our careful experiments that such a correlation between LFMA and the magnetization does not survive at low temperatures and particularly at 10 K the LFMA hysteresis collapses in our TM co-doped ZnO system; whereas the magnetization hysteresis loop becomes very big and anisotropy field becomes bigger in the range of kOe. We interpret the LFMA as field dependent surface impedance or eddy current losses, in terms of a possible role of anomalous hall resistivity that follows magnetization and the ordinary hall resistivity that only follows the applied field. We then argue that LFMA accordingly follows magnetization or applied field when AHE or OHE dominates respectively. Also we confirm the absence of LFMA signals in the rare earth co-doped ZnO system.

  17. Observation of magnetic field effects on transient fluorescence spectra of cryptochrome 1 from homing pigeons.

    PubMed

    Du, Xian-li; Wang, Jing; Pan, Wei-song; Liu, Qi-jun; Wang, Xiao-jie; Wu, Wen-jian

    2014-01-01

    Cryptochromes are suggested to be involved in the bird magnetoreception based on the radical pair mechanism (RPM), a well established theory of weak magnetic field effects on chemical reactions. Two members of cryptochrome/photolyase family were found to respond to magnetic field, however, no direct responses of bird cryptochrome to magnetic field as weak as the Earth's magnetic field have been obtained so far. In this study, we used transient fluorescence spectroscopy to characterize the weak magnetic field effects of bird cryptochromes. To do this, we cloned the cryptochrome 1 gene (clCRY1) from the retina of homing pigeons (Columba livia), expressed it in insect Sf9 cells and analyzed the transient fluorescence of purified clCRY1 by application of 45-300 μT magnetic fields. The flavin adenine dinucleotide (FADox ) and glucose oxidase (GOD) in PBS buffer were set as controls which could be excited by light to generate radicals, but would not be sensitive to magnetic field. We observed that the transient fluorescence spectra of clCRY1 were sensitive to the applied magnetic field at room temperature. Our result provides a new proof of the cryptochrome-based model of avian magnetoreception in vitro. © 2014 The American Society of Photobiology.

  18. Horizontal flow fields observed in Hinode G-band images. II. Flow fields in the final stages of sunspot decay

    NASA Astrophysics Data System (ADS)

    Verma, M.; Balthasar, H.; Deng, N.; Liu, C.; Shimizu, T.; Wang, H.; Denker, C.

    2012-02-01

    Context. Generation and dissipation of magnetic fields is a fundamental physical process on the Sun. In comparison to flux emergence and the initial stages of sunspot formation, the demise of sunspots still lacks a comprehensive description. Aims: The evolution of sunspots is most commonly discussed in terms of their intensity and magnetic field. Here, we present additional information about the three-dimensional flow field in the vicinity of sunspots towards the end of their existence. Methods: We present a subset of multi-wavelengths observations obtained with the Japanese Hinode mission, the Solar Dynamics Observatory (SDO), and the Vacuum Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain during the time period 2010 November 18-23. Horizontal proper motions were derived from G-band and Ca ii H images, whereas line-of-sight velocities were extracted from VTT echelle Hα λ656.28 nm spectra and Fe i λ630.25 nm spectral data of the Hinode/Spectro-Polarimeter, which also provided three-dimensional magnetic field information. The Helioseismic and Magnetic Imager on board SDO provided continuum images and line-of-sight magnetograms, in addition to the high-resolution observations for the entire disk passage of the active region. Results: We perform a quantitative study of photospheric and chromospheric flow fields in and around decaying sunspots. In one of the trailing sunspots of active region NOAA 11126, we observe moat flow and moving magnetic features (MMFs), even after its penumbra had decayed. We also detect a superpenumbral structure around this pore. We find that MMFs follow well-defined, radial paths from the spot all the way to the border of a supergranular cell surrounding the spot. In contrast, flux emergence near the other sunspot prevents the establishment of similar well ordered flow patterns, which could be discerned around a tiny pore of merely 2 Mm diameter. After the disappearance of the sunspots/pores, a coherent patch of abnormal

  19. High-resolution observations of the polar magnetic fields of the sun

    NASA Technical Reports Server (NTRS)

    Lin, H.; Varsik, J.; Zirin, H.

    1994-01-01

    High-resolution magnetograms of the solar polar region were used for the study of the polar magnetic field. In contrast to low-resolution magnetograph observations which measure the polar magnetic field averaged over a large area, we focused our efforts on the properties of the small magnetic elements in the polar region. Evolution of the filling factor (the ratio of the area occupied by the magnetic elements to the total area) of these magnetic elements, as well as the average magnetic field strength, were studied during the maximum and declining phase of solar cycle 22, from early 1991 to mid-1993. We found that during the sunspot maximum period, the polar regions were occupied by about equal numbers of positive and negative magnetic elements, with equal average field strength. As the solar cycle progresses toward sunspot minimum, the magnetic field elements in the polar region become predominantly of one polarity. The average magnetic field of the dominant polarity elements also increases with the filling factor. In the meanwhile, both the filling factor and the average field strength of the non-dominant polarity elements decrease. The combined effects of the changing filling factors and average field strength produce the observed evolution of the integrated polar flux over the solar cycle. We compared the evolutionary histories of both filling factor and average field strength, for regions of high (70-80 deg) and low (60-70 deg) latitudes. For the south pole, we found no significant evidence of difference in the time of reversal. However, the low-latitude region of the north pole did reverse polarity much earlier than the high-latitude region. It later showed an oscillatory behavior. We suggest this may be caused by the poleward migration of flux from a large active region in 1989 with highly imbalanced flux.

  20. High-resolution observations of the polar magnetic fields of the sun

    NASA Technical Reports Server (NTRS)

    Lin, H.; Varsik, J.; Zirin, H.

    1994-01-01

    High-resolution magnetograms of the solar polar region were used for the study of the polar magnetic field. In contrast to low-resolution magnetograph observations which measure the polar magnetic field averaged over a large area, we focused our efforts on the properties of the small magnetic elements in the polar region. Evolution of the filling factor (the ratio of the area occupied by the magnetic elements to the total area) of these magnetic elements, as well as the average magnetic field strength, were studied during the maximum and declining phase of solar cycle 22, from early 1991 to mid-1993. We found that during the sunspot maximum period, the polar regions were occupied by about equal numbers of positive and negative magnetic elements, with equal average field strength. As the solar cycle progresses toward sunspot minimum, the magnetic field elements in the polar region become predominantly of one polarity. The average magnetic field of the dominant polarity elements also increases with the filling factor. In the meanwhile, both the filling factor and the average field strength of the non-dominant polarity elements decrease. The combined effects of the changing filling factors and average field strength produce the observed evolution of the integrated polar flux over the solar cycle. We compared the evolutionary histories of both filling factor and average field strength, for regions of high (70-80 deg) and low (60-70 deg) latitudes. For the south pole, we found no significant evidence of difference in the time of reversal. However, the low-latitude region of the north pole did reverse polarity much earlier than the high-latitude region. It later showed an oscillatory behavior. We suggest this may be caused by the poleward migration of flux from a large active region in 1989 with highly imbalanced flux.

  1. Modeling electron density, temperature distribution in the solar corona based on solar surface magnetic field observations

    NASA Astrophysics Data System (ADS)

    Lago, A.; Rodríguez, J. M.; Vieira, L.; Coelho Stekel, T. R.; Costa, J. E. R.; Pinto, T. S. N.

    2015-12-01

    Magnetic fields constitute a natural link between the Sun, the Earth and the Heliosphere in general. The solar dynamo action maintains and strengthens the magnetic field in the solar interior. The structure of the solar corona is mostly determined by the configuration and evolution of the magnetic field. While open magnetic field lines carry plasma into the heliosphere, closed field lines confine plasma. Additionally, key physical processes that impact the evolution of Earth's atmosphere on time-scale from days to millennia, such as the soft X-ray and EUV emission, are also determined by the solar magnetic field. However, observations of the solar spectral irradiance are restricted to the last few solar cycles and are subject to large uncertainties. Here we present a physics-based model to reconstruct in near-real time the evolution of the solar EUV emission based on the configuration of the magnetic field imprinted on the solar surface and assuming that the emission lines are optically thin. The structure of the coronal magnetic field is estimated employing a potential field source surface extrapolation based on the synoptic charts. The coronal plasma temperature and density are described by a hydrostatic model. The emission is estimated to employ the CHIANTI database. The performance of the model is compared to the emission observed by EVE instrument on board SDO spacecraft. The preliminary results and uncertainties are discussed in details. Furthermore, we examine the possibility of delivery the reconstruction of the solar spectral irradiance in near-real time using the infrastructure provided by the Brazilian Space weather program (EMBRACE/INPE). This work is partially supported by CNPq/Brazil under the grant agreement no. 140779/2015-9.

  2. Cloud parameters derived from GOES during the 1987 marine stratocumulus FIRE Intensive Field Observation (IFO) period

    NASA Technical Reports Server (NTRS)

    Young, David F.; Minnis, Patrick; Harrison, Edwin F.

    1990-01-01

    The Geostationary Operational Environmental Satellite (GOES) is well suited for observations of the variations of clouds over many temporal and spatial scales. For this reason, GOES data taken during the Marine Stratocumulus Intensive Field Observations (IFO) (June 29 to July 19, 1987, Kloessel et al.) serve several purposes. One facet of the First ISCCP Regional Experiment (FIRE) is improvement of the understanding of cloud parameter retrievals from satellite-observed radiances. This involves comparisons of coincident satellite cloud parameters and high resolution data taken by various instruments on other platforms during the IFO periods. Another aspect of FIRE is the improvement of both large- and small-scale models of stratocumulus used in general circulation models (GCMs). This may involve, among other studies, linking the small-scale processes observed during the IFO to the variations in large-scale cloud fields observed with the satellites during the IFO and Extended Time Observation (ETO) periods. Preliminary results are presented of an analysis of GOES data covering most of the IFO period. The large scale cloud-field characteristics are derived, then related to a longer period of measurements. Finally, some point measurements taken from the surface are compared to regional scale cloud parameters derived from satellite radiances.

  3. Constraining magnetic fields morphologies using mid-IR polarization: observations and modeling

    NASA Astrophysics Data System (ADS)

    Zhang, Han; Li, Dan; Pantin, Eric; Telesco, Charles M.

    2016-01-01

    Polarization arises from aligned dust grains in magnetic fields, and thus the direction of polarization can trace the direction of B fields. We present the mid-IR imaging and spectropolarimetry observations made with the GTC's CanariCam of the Herbig Ae star WL 16. WL 16 is embedded in/behind the ρ Ophiuchus molecular cloud with visual extinction of ~31 mag. It exhibits large and extended (~900 AU) emission, which is believed to come from the emission of PAHs and very small dust grains. Uniform polarization vectors from imaging polarization and the absorption-dominated polarization profile from spectropolarimetry consistently indicate a uniform foreground magnetic field oriented at about 30 deg from the North.We also model the predicted polarization patterns expected to arise from different magnetic field morphologies, which can be distinguished by high-resolution observations. As an example, we present the mid-IR polarization modeling of AB Aur, a well-studied Herbig Ae star. We incorporate polarization from dichroic absorption, emission and scattering in the modeling. The observed polarization structures are well reproduced by two components: emissive polarization arising from a poloidal B field and scattering polarization by 0.01-1 μm dust grains.

  4. Radial profile of the inner heliospheric magnetic field as deduced from Faraday rotation observations

    NASA Astrophysics Data System (ADS)

    Mancuso, S.; Garzelli, M. V.

    2013-05-01

    Faraday rotation measures (RMs) of the polarized emission from extragalactic radio sources occulted by the coronal plasma were used to infer the radial profile of the inner heliospheric magnetic field near the solar minimum. By inverting LASCO/SOHO polarized brightness (pB) data taken during the observations in May 1997, we retrieved the electron density distribution along the lines of sight to the sources, which allowed us to separate the two plasma properties that contribute to the observed RMs. By comparing the observed RM values with those theoretically predicted by a power law model of the radial component of the coronal magnetic field using a best-fitting procedure, we found that the radial component of the inner heliospheric magnetic field can be nicely approximated by a power law of the form Br = 3.76 r-2.29 G in a range of heights from about 5 to 14 R⊙. Finally, our analysis suggests that the radial computation of the potential field source surface model from the Wilcox Solar Observatory is the preferred choice near solar minimum assuming a radial field in the photosphere and a source surface located at Rss = 2.5 R⊙.

  5. Making global map of the solar surface Br from the HMI vector magnetic field observations

    NASA Astrophysics Data System (ADS)

    Hayashi, K.; Liu, Y.; Sun, X.; Hoeksema, J. T.; Centeno, R.; Barnes, G.; Leka, K. D.

    2013-06-01

    The Helioseismic Magnetic Imager (HMI) has made full-disk vector magnetic field measurements of the Sun with cadence of 12 minutes. The three-component solar surface magnetic field vector data are from the HMI observations with the data process pipeline modules, VFISV (Very Fast Inversion of the Stokes Vector, Borrero et al., 2011) for Milne-Eddington inversion and the minimum-energy disambiguation algorithm (Metcalf 1994, Leka et al, 2009). The models of the global corona and solar wind, such as the PFSS (potential-field source-surface) model and the MHD simulations, often use the maps of solar surface magnetic field, especially the radial component (Br) as the boundary condition. The HMI observation can provide new Br data for these model. Because of weak magnetic signals at the quiet regions of the Sun, the limb darkening, and geometric effects near solar poles, we need to apply an assumption to make a whole-surface map. In this paper, we tested two assumptions for determining Br at weak-field regions. The coronal structures calculated by the PFSS model with the vector-based Br are compared with those with the magnetogram-based Br and the corona observed by the SDO/AIA (Atmospheric Imaging Assembly). In the tested period, CR 2098, the vector-based Br map gives better agreements than the line-of-sight magnetogram data, though we need further investigation for evaluation.

  6. On the reconstructing the coronal magnetic field from Fe XIII 10747 A emission line observations

    NASA Astrophysics Data System (ADS)

    Kramar, M.; Lin, H.; Inhester, B.

    2009-12-01

    Magnetic fields in the solar corona are the dominant fields that determine the static and dynamic properties of this outermost region of the solar atmosphere. It is within this tenuous region that the magnetic force dominates the gas pressure. Direct measurement of the coronal magnetic field is one of the most challenging problems in observational solar astronomy. To date, one of the promising measurement methods that have been successfully demonstrated is the spectropolarimetric measurement of the Fe XIII 10747 A forbidden emission line (CEL) (Lin, Penn, Tomczyk 2000; Lin, Kuhn, Coulter 2004; Tomczyk et al. 2007) formed due to Hanle and Zeeman effects. However, because coronal measurements are integrated over line-of-site (LOS), it is impossible to derive the configuration of the coronal magnetic field from a single observation (from a single viewing direction). Recent development in vector tomography techniques based on IR forbidden CEL polarization measurements from several viewing direction (Kramar, Inhester, Solanki 2006; Kramar, Inhester 2007) has the potential to resolve the 3D coronal magnetic field structure. In this paper, we will present a study of the effects of instrumental characteristics on the results of vector tomographic inversion using simulated data. We also investigate the sensitivity of the vector tomographic inversion to different coronal magnetic field configuration.

  7. DIRECT OBSERVATION OF SOLAR CORONAL MAGNETIC FIELDS BY VECTOR TOMOGRAPHY OF THE CORONAL EMISSION LINE POLARIZATIONS

    SciTech Connect

    Kramar, M.; Lin, H.; Tomczyk, S. E-mail: lin@ifa.hawaii.edu

    2016-03-10

    We present the first direct “observation” of the global-scale, 3D coronal magnetic fields of Carrington Rotation (CR) Cycle 2112 using vector tomographic inversion techniques. The vector tomographic inversion uses measurements of the Fe xiii 10747 Å Hanle effect polarization signals by the Coronal Multichannel Polarimeter (CoMP) and 3D coronal density and temperature derived from scalar tomographic inversion of Solar Terrestrial Relations Observatory (STEREO)/Extreme Ultraviolet Imager (EUVI) coronal emission lines (CELs) intensity images as inputs to derive a coronal magnetic field model that best reproduces the observed polarization signals. While independent verifications of the vector tomography results cannot be performed, we compared the tomography inverted coronal magnetic fields with those constructed by magnetohydrodynamic (MHD) simulations based on observed photospheric magnetic fields of CR 2112 and 2113. We found that the MHD model for CR 2112 is qualitatively consistent with the tomography inverted result for most of the reconstruction domain except for several regions. Particularly, for one of the most noticeable regions, we found that the MHD simulation for CR 2113 predicted a model that more closely resembles the vector tomography inverted magnetic fields. In another case, our tomographic reconstruction predicted an open magnetic field at a region where a coronal hole can be seen directly from a STEREO-B/EUVI image. We discuss the utilities and limitations of the tomographic inversion technique, and present ideas for future developments.

  8. Magnetospheric Multiscale Observations of Field-aligned Currents at the Magnetopause

    NASA Astrophysics Data System (ADS)

    Strangeway, R. J.; Russell, C. T.; Zhao, C.; Magnes, W.; Bromund, K. R.; Plaschke, F.; Fischer, D.; Anderson, B. J.; Le, G.; Chutter, M.; Slavin, J. A.; Nakamura, R.; Baumjohann, W.; Paterson, W. R.; Torbert, R. B.; Burch, J. L.

    2016-12-01

    Magnetospheric Multiscale (MMS) has demonstrated that the dayside magnetopause is usually highly structured, with multiple layers. Within these layers currents are observed to be flowing both parallel and perpendicular to the magnetic field. The parallel currents primarily act to bend or shear the magnetic field, while the perpendicular currents mainly change the field strength. We note that within the magnetopause MMS observes current densities that can be of the order of 100s of nAm-2. If these currents were to map to the ionosphere, then they would correspond to field-aligned current densities of the order of 100s of μAm-2, orders of magnitude larger than the observed low altitude field-aligned currents. A survey of several magnetopause crossings shows that the field-aligned currents on the magnetosphere side of the current layers can be flowing either parallel or anti-parallel to the magnetic field. On the magnetospheric side of the magnetopause current layers the plasma flows are generally in the -z direction (in GSM coordinates) for the events studied, suggesting that the observations are to the south of the reconnection site. If the currents were to correspond to Region-1 sense currents flowing into and out of the southern ionosphere, then the polarity of the currents would be ordered by local time, flowing parallel to the local magnetic field on the dusk-side of noon, and anti-parallel on the dawn-side of noon. But the current signatures are mixed, and sometimes the field-aligned currents reverse polarity within one crossing of the magnetopause. The issue is therefore how do we reconcile the local magnetopause field-aligned current signatures with what would be expected for the large-scale Region-1 currents that are typically associated with flow shears introduced through reconnection? Given the strength of the currents and their structure much of the current may be closed locally, with only a residual contributing to the large-scale currents.

  9. Observations of the longitudinal magnetic field in the transition region and photosphere of a sunspot

    NASA Technical Reports Server (NTRS)

    Henze, W., Jr.; Tandberg-Hanssen, E.; Hagyard, M. J.; West, E. A.; Woodgate, B. E.; Shine, R. A.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; West, E. A.

    1982-01-01

    The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission spacraft has observed for the first time the longitudinal component of the magnetic field by means of the Zeeman effect in the transition region above a sunspot. The data presented here were obtained on three days in one sunspot, have spatial resolutions of 10 arcsec and 3 arcsec, and yield maximum field strengths greater than 1000 G above the umbrae in the spot. The method of analysis, including a line-width calibration feature used during some of the observations, is described in some detail in an appendix; the line width is required for the determination of the longitudinal magnetic field from the observed circular polarization. The transition region data for one day are compared with photospheric magnetograms from the Marshall Space Flight Center. Vertical gradients of the magnetic field are compared from the two sets of data; the maximum gradients of 0.41 to 0.62 G/km occur above the umbra and agree with or are smaller than values observed previously in the photosphere and low chromosphere.

  10. Observations of the longitudinal magnetic field in the transition region and photosphere of a sunspot

    NASA Technical Reports Server (NTRS)

    Henze, W., Jr.; Tandberg-Hanssen, E.; Hagyard, M. J.; West, E. A.; Woodgate, B. E.; Shine, R. A.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; West, E. A.

    1982-01-01

    The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission spacraft has observed for the first time the longitudinal component of the magnetic field by means of the Zeeman effect in the transition region above a sunspot. The data presented here were obtained on three days in one sunspot, have spatial resolutions of 10 arcsec and 3 arcsec, and yield maximum field strengths greater than 1000 G above the umbrae in the spot. The method of analysis, including a line-width calibration feature used during some of the observations, is described in some detail in an appendix; the line width is required for the determination of the longitudinal magnetic field from the observed circular polarization. The transition region data for one day are compared with photospheric magnetograms from the Marshall Space Flight Center. Vertical gradients of the magnetic field are compared from the two sets of data; the maximum gradients of 0.41 to 0.62 G/km occur above the umbra and agree with or are smaller than values observed previously in the photosphere and low chromosphere.

  11. Inferring plasma flow velocities from photospheric vector magnetic field observations for the investigation of flare onsets

    NASA Astrophysics Data System (ADS)

    Santos, J. C.; Büchner, J.; Zhang, H.

    2008-09-01

    The amount of emergence and submergence of magnetized plasma and the horizontal motion of the footpoints of flux tubes might be crucial for the dynamics of the solar atmosphere. Although the rate of flux emergence and submergence can be observationally determined near the polarity inversion line (Chae et al., 2004), the same is not true for regions away from the PIL. Also, the horizontal motions cannot be directly measured in the solar photosphere. In this sense, the evolution of the photospheric magnetic field provides valuable information which can be used to estimate photospheric plasma flows since magnetic field and plasma are closely associated (frozen-in-condition). We used three methods to estimate the photospheric plasma motion from magnetic field observations. The methods were applied to photospheric vector magnetic field data of active region NOAA 9077, observed by the Huairou Solar Observing Station (HSOS) of the National Astronomical Observatories of China before and after the ‘Bastille Day’ flare on July 13th and 14th, 2000.

  12. Observations of ferrofluid flow under a uniform rotating magnetic field in a spherical cavity

    NASA Astrophysics Data System (ADS)

    Torres-Díaz, Isaac; Rinaldi, Carlos; Khushrushahi, Shahriar; Zahn, Markus

    2012-04-01

    Flow of a ferrofluid in spherical and cylindrical geometries were measured under the influence of a uniform rotating magnetic field produced by two perpendicular spherical coils, a so-called fluxball, excited by quadrature currents. Using an ultrasound velocity profile technique and a commercial oil based ferrofluid (EFH1, Ferrotec) we observed rotational flow around the z-axis. In comparison, the radial component of the flow was found to be negligible. Results show that the magnitude of the azimuthal velocity profile increases as the applied magnetic field amplitude increases. This behavior is also observed for ferrofluid in a cylindrical container placed inside the fluxball cavity and inside a two-pole stator winding. These results indicate that inhomogeneities in the magnetic field produced by slots and finite height of the stator winding used in prior experiments are not the source of previously observed flows produced by a two pole stator winding. The experiments reported here either point to the existence of non-uniform demagnetizing magnetic fields due to the finite height of the cylindrical container, the existence of couple stresses and spin viscosity in ferrofluids, or to the need to develop alternate governing and constitutive equations capable of describing the experimental observations.

  13. Precise calibration of CCD images with a small field of view. Application to observations of Phoebe

    NASA Astrophysics Data System (ADS)

    Peng, Q.; Vienne, A.; Han, Y. B.; Li, Z. L.

    2004-09-01

    A precise astrometric calibration method is presented for a CCD image with a small field of view. Its detailed computational formulae are given, and its feasibility and accuracy are tested by the observations of both the star and Phoebe, the 9th satellite of Saturn. This new method can also be applicable to other planetary satellites, asteroids and optical counterparts of extragalactic radio sources.

  14. Difficulties in Field-Based Observation among Pre-Service Teachers: Implications to Practice Teaching

    ERIC Educational Resources Information Center

    Abas, Maripaz C.

    2016-01-01

    Field-based observation has long been a central part of pre-service teacher education in many countries and is crucial for implementing effective practicum of pre-service teachers. This paper focused on the perspectives of graduating pre-service teachers regarding their difficulties related to administrative support, cooperating teachers, student…

  15. Direct observation of Oersted-field-induced magnetization dynamics in magnetic nanostripes

    SciTech Connect

    Uhlir, V.; Pizzini, S.; Rougemaille, N.; Ranno, L.; Fruchart, O.; Wagner, E.; Vogel, J.; Cros, V.; Jimenez, E.; Camarero, J.; Urbanek, M.; Gaudin, G.; Sirotti, F.

    2011-01-15

    We have used time-resolved x-ray photoemission electron microscopy to investigate the magnetization dynamics induced by nanosecond current pulses in NiFe/Cu/Co nanostripes. A large tilt of the NiFe magnetization in the direction transverse to the stripe is observed during the pulses. We show that this effect cannot be quantitatively understood from the amplitude of the Oersted field and the shape anisotropy. High-frequency oscillations observed at the onset of the pulses are attributed to precessional motion of the NiFe magnetization about the effective field. We discuss the possible origins of the large magnetization tilt and the potential implications of the static and dynamic effects of the Oersted field on current-induced domain-wall motion in such stripes.

  16. Radar observations of field-aligned plasma propagations associated with NASA's PMG experiment

    NASA Astrophysics Data System (ADS)

    Olson, Darren M.

    1994-09-01

    NASA's Plasma Motor Generator (PMG) tethered satellite mission was launched in June 1993 to verify the ability of hollow cathode plasma sources to couple electric currents from an electrodynamic tether into the ambient ionospheric plasma. This large-scale coupling process resulted in turbulent plasma signatures associated with the orbiting plasma generator, which propagated over great distances along the earth's geomagnetic field lines. VHF radars in Hilo, Hawaii and Jicamarca, Peru recorded observations of these field-aligned disturbances as part of the experiment. Based on analysis of these radar observations and tracking data of PMG's orbit, the effective propagation velocity of these traveling plasma waveforms was calculated to be of the order of 1000 meters per second. Detection of these disturbances, associated with PMG's passage overhead, supports the existence of a phantom current loop allowing current flow along the magnetic field lines of the earth and into the lower ionosphere from either end of an electrodynamic tether.

  17. Interplanetary Field Enhancements: Observations from 0.3 AU to 1 AU

    NASA Astrophysics Data System (ADS)

    Russell, C. T.; Jian, L. K.; Lai, H. R.; Zhang, T. L.; Wennmacher, A.; Luhmann, J. G.

    2010-03-01

    Interplanetary Field Enhancements are rare but very distinct increases in the magnetic field strength, reaching a nearly symmetric cusp-shaped peak. These increases are usually accompanied by a thin central current sheet. Their associations with the perihelion passages of the asteroid 2201 Oljato and with the comet De Vico have led to the hypothesis that these events are associated with the interaction of the solar wind with dust particles. In this paper we examine observations of these events with the Helios 1/2 spacecraft that flew as close to the Sun as 0.29 AU. These events are observed over the entire range of distances studied by Helios 1 and 2. The ponderomotive force exerted by the magnetic field strength decreases with radial distance roughly inversely proportional to the distance squared.

  18. A biophysical observation model for field potentials of networks of leaky integrate-and-fire neurons

    PubMed Central

    beim Graben, Peter; Rodrigues, Serafim

    2013-01-01

    We present a biophysical approach for the coupling of neural network activity as resulting from proper dipole currents of cortical pyramidal neurons to the electric field in extracellular fluid. Starting from a reduced three-compartment model of a single pyramidal neuron, we derive an observation model for dendritic dipole currents in extracellular space and thereby for the dendritic field potential (DFP) that contributes to the local field potential (LFP) of a neural population. This work aligns and satisfies the widespread dipole assumption that is motivated by the “open-field” configuration of the DFP around cortical pyramidal cells. Our reduced three-compartment scheme allows to derive networks of leaky integrate-and-fire (LIF) models, which facilitates comparison with existing neural network and observation models. In particular, by means of numerical simulations we compare our approach with an ad hoc model by Mazzoni et al. (2008), and conclude that our biophysically motivated approach yields substantial improvement. PMID:23316157

  19. Radar observations of field-aligned plasma propagations associated with nasa's PMG experiment. Master's thesis

    SciTech Connect

    Olson, D.M.

    1994-09-01

    NASA's Plasma Motor Generator (PMG) tethered satellite mission was launched in June 1993 to verify the ability of hollow cathode plasma sources to couple electric currents from an electrodynamic tether into the ambient ionospheric plasma. This large-scale coupling process resulted in turbulent plasma signatures associated with the orbiting plasma generator, which propagated over great distances along the earth's geomagnetic field lines. VHF radars in Hilo, Hawaii and Jicamarca, Peru recorded observations of these field-aligned disturbances as part of the experiment. Based on analysis of these radar observations and tracking data of PMG's orbit, the effective propagation velocity of these traveling plasma waveforms was calculated to be of the order of 1000 meters per second. Detection of these disturbances, associated with PMG's passage overhead, supports the existence of a phantom current loop allowing current flow along the magnetic field lines of the earth and into the lower ionosphere from either end of an electrodynamic tether.

  20. High-latitude dayside electric fields and currents during strong northward interplanetary magnetic field - Observations and model simulation

    NASA Technical Reports Server (NTRS)

    Clauer, C. Robert; Friis-Christensen, Eigil

    1988-01-01

    On July 23, 1983 the IMF turned strongly northward, becoming about 22 nT for several hours. Using a combined data set of ionospheric convection measurements made by the Sondre Stromfjord incoherent scatter radar and convection inferred from Greenland magnetometer measurements, the onset of the reconfiguration of the high-latitude ionospheric currents is found to occur about 3 min after the northward IMF encounters the magnetopause. The large-scale reconfiguration of currents, however, appears to evolve over a period of about 22 min. These observations and the results of numerical simulations indicate that the dayside polar-cap electric field observed during strong northward IMF is produced by a direct electrical current coupling with the solar wind.

  1. High-latitude dayside electric fields and currents during strong northward interplanetary magnetic field - Observations and model simulation

    NASA Technical Reports Server (NTRS)

    Clauer, C. Robert; Friis-Christensen, Eigil

    1988-01-01

    On July 23, 1983 the IMF turned strongly northward, becoming about 22 nT for several hours. Using a combined data set of ionospheric convection measurements made by the Sondre Stromfjord incoherent scatter radar and convection inferred from Greenland magnetometer measurements, the onset of the reconfiguration of the high-latitude ionospheric currents is found to occur about 3 min after the northward IMF encounters the magnetopause. The large-scale reconfiguration of currents, however, appears to evolve over a period of about 22 min. These observations and the results of numerical simulations indicate that the dayside polar-cap electric field observed during strong northward IMF is produced by a direct electrical current coupling with the solar wind.

  2. Multiscale Bayesian inversion of binary permeability fields from static and dynamic observations

    NASA Astrophysics Data System (ADS)

    Ray, J.; McKenna, S. A.; Marzouk, Y. M.; van Bloemenwaanders, B.

    2009-12-01

    Binary fields are a useful fine-scale representation of heterogeneous porous media. Averaged properties of these fields can characterize flow through porous media at the macroscale. These averaged properties are not easily measured, however, and direct upscaling poses a challenge. Upscaled properties can instead be inferred from indirect measurements at the coarse scale, using appropriate link functions or subgrid models to connect the disparate scales and to generate realizations of fine scale fields conditioned on all available data. Truncated Gaussian random fields provide a flexible geometrical model for binary media of inclusions embedded in a matrix. We utilize a recently developed subgrid model based on excursion sets of Gaussian random fields for upscaling binary permeability fields to a coarse (block) scale effective permeability. This subgrid model requires an estimate of the proportion of high permeability inclusions and associated parameters at the block scale. Computations of the upscaled properties are inexpensive and provide a robust link between fine and block scales. We employ the subgrid model in a multiscale Bayesian inversion process, thus conditioning the proportion and geometry of the latent binary field on coarse-scale observations of permeability and on tracer recovery data. In this inversion process, the variogram of the proportion field is assumed known. The proportion field is efficiently represented via its Karhunen-Loève expansion. From limited and noisy observations of static and dynamic data, we infer the posterior distribution of the coefficients of the Karhunen-Loève modes and associated geometrical parameters of the binary field. We then generate posterior realizations of the fine scale binary media and simulate tracer recovery with these fields; the resulting predictive distributions are compared to a predetermined “ground truth” response. Additionally, we evaluate the sensitivity of the posterior distribution to different

  3. Explaining Mercury's Magnetic Field Observables Using Dynamo Models with Stable Layers and Laterally Variable Heat Flux

    NASA Astrophysics Data System (ADS)

    Tian, Z.; Zuber, M. T.; Stanley, S.

    2013-12-01

    Mercury's surface magnetic field is unique among planetary fields for its weak intensity, spin-aligned axisymmetry, and large dipole offset (Anderson et al., 2011). Reproducing these features with dynamo models is challenging and requires additions to the 'standard' dynamo setup. Here we explain the magnetic field observables by a combination of two effects: (1) a stably-stratified layer at the top of the outer core, and (2) a low-degree spherical harmonic (SH) heat flux variation at the core-mantle boundary (CMB). A stably-stratified layer at the top of the outer core was proposed by Stevenson (1980,1982) to explain the weak intensity and axisymmetry of Saturn's magnetic field. Recent studies (Christensen, 2006, Christensen & Wicht, 2008) used a stable layer to produce the low-intensity and axisymmetric features of Mercury's magnetic field, but didn't typically produce a dipole offset similar to the observed value. Stratification in Mercury's upper core region can occur due to a sub-adiabatic heat flux or an enrichment of sulfur there. Mercury's equator-to-north pole crustal thinning trend suggests a low degree SH global crustal thickness pattern, which can result in heat flux variability at the CMB. We use the Kuang & Bloxham (1999) numerical dynamo scheme to model Mercury's magnetic field generation. We use an internal structure model for Mercury that has a stably-stratified layer at the top of the outer core. We also apply degree-1 SH heat flux variations at the CMB. We vary the stable layer thickness, the inner core size and the magnitude of the CMB heat flux variations. We find models that can produce surface magnetic fields with a weak intensity, high axisymmetry and a large offset, similar to the observed features of Mercury.

  4. EVIDENCE FOR QUASI-ISOTROPIC MAGNETIC FIELDS FROM HINODE QUIET-SUN OBSERVATIONS

    SciTech Connect

    Asensio Ramos, A.

    2009-08-20

    Some recent investigations of spectropolarimetric observations of the Zeeman effect in the Fe I lines at 630 nm carried out with the Hinode solar space telescope have concluded that the strength of the magnetic field vector in the internetwork regions of the quiet Sun is in the hG regime and that its inclination is predominantly horizontal. We critically reconsider the analysis of such observations and carry out a complete Bayesian analysis with the aim of extracting as much information as possible from them, including error bars. We apply the recently developed BAYES-ME code that carries out a complete Bayesian inference for Milne-Eddington atmospheres. The sampling of the posterior distribution function is obtained with a Markov Chain Monte Carlo scheme and the marginal distributions are analyzed in detail. The Kullback-Leibler divergence is used to study the extent to which the observations introduce new information in the inference process resulting in sufficiently constrained parameters. Our analysis clearly shows that only upper limits to the magnetic field strength can be inferred, with fields in the kG regime completely discarded. Furthermore, the noise level present in the analyzed Hinode observations induces a substantial loss of information for constraining the azimuth of the magnetic field. Concerning the inclination of the field, we demonstrate that some information is available to constrain it for those pixels with the largest polarimetric signal. The results also point out that the field in pixels with small polarimetric signals can be nicely reproduced in terms of a quasi-isotropic distribution.

  5. Cosmic Rays, Magnetic Fields and Diffuse Emissions: Combining Observations from Radio to Gamma Rays

    NASA Astrophysics Data System (ADS)

    Michelson, Peter

    With the advent of WMAP, Planck, and Fermi-LAT telescopes the diffuse emission from the Milky Way has received renewed attention. Observations of the different components of the diffuse emission reveal information on Cosmic Rays (CRs), magnetic fields (B-fields) and the interstellar medium. CRs interact with the interstellar medium and the B-fields in the Milky Way, producing diffuse emission from radio to gamma rays. The fundamental problem is that CRs, B-fields, and the interstellar medium are not precisely known. In fact, despite intensive studies, the B-field intensity and topology, and CR spectra and distribution throughout the Galaxy are still uncertain. As a consequence unequivocally disentangling and describing the diffuse components simultaneously using a single wavelength domain is impossible. Our approach to disentangling and describing the diffuse emission components is to simultaneously consider the diffuse emission in multiple frequency domains. We propose to exploit the entire database of the present radio surveys, microwave observations (WMAP and Planck), X-ray observations (INTEGRAL) and gamma-ray observations (COMPTEL and Fermi-LAT) in order to analyze their diffuse emission in a combined multi-wavelength approach. We will jointly infer information on the spectra and distribution of CRs in the Galaxy, and on Galactic B-fields, with unprecedented accuracy. Finally we will be able to describe the baseline Galactic diffuse emissions and characterize Milky Way structures and their emission mechanisms, which have attracted the attention of the scientific community recently. This project is innovative and essential for maximizing the scientific return from the presently available data in a multidisciplinary view and uses novel approaches. The results will benefit NASA-related science generally and the return from the named missions specifically.

  6. Cone of Darkness: Finding Blank-sky Positions for Multi-object Wide-field Observations

    NASA Astrophysics Data System (ADS)

    Lorente, N. P. F.

    2014-05-01

    We present the Cone of Darkness, an application to automatically configure blank-sky positions for a series of stacked, wide-field observations, such as those carried out by the SAMI instrument on the Anglo-Australian Telescope (AAT). The Sydney-AAO Multi-object Integral field spectrograph (SAMI) uses a plug-plate to mount its 13×61 core imaging fibre bundles (hexabundles) in the optical plane at the telescope's prime focus. To make the most efficient use of each plug-plate, several observing fields are typically stacked to produce a single plate. When choosing blank-sky positions for the observations it is most effective to select these such that one set of 26 holes gives valid sky positions for all fields on the plate. However, when carried out manually this selection process is tedious and includes a significant risk of error. The Cone of Darkness software aims to provide uniform blank-sky position coverage over the field of observation, within the limits set by the distribution of target positions and the chosen input catalogs. This will then facilitate the production of the best representative median sky spectrum for use in sky subtraction. The application, written in C++, is configurable, making it usable for a range of instruments. Given the plate characteristics and the positions of target holes, the software segments the unallocated space on the plate and determines the position which best fits the uniform distribution requirement. This position is checked, for each field, against the selected catalog using a TAP ADQL search. The process is then repeated until the desired number of sky positions is attained.

  7. Observation of Landau levels in potassium-intercalated graphite under a zero magnetic field

    PubMed Central

    Guo, Donghui; Kondo, Takahiro; Machida, Takahiro; Iwatake, Keigo; Okada, Susumu; Nakamura, Junji

    2012-01-01

    The charge carriers in graphene are massless Dirac fermions and exhibit a relativistic Landau-level quantization in a magnetic field. Recently, it has been reported that, without any external magnetic field, quantized energy levels have been also observed from strained graphene nanobubbles on a platinum surface, which were attributed to the Landau levels of massless Dirac fermions in graphene formed by a strain-induced pseudomagnetic field. Here we show the generation of the Landau levels of massless Dirac fermions on a partially potassium-intercalated graphite surface without applying external magnetic field. Landau levels of massless Dirac fermions indicate the graphene character in partially potassium-intercalated graphite. The generation of the Landau levels is ascribed to a vector potential induced by the perturbation of nearest-neighbour hopping, which may originate from a strain or a gradient of on-site potentials at the perimeters of potassium-free domains. PMID:22990864

  8. Observation of Self-Sustaining Relativistic Ionization Wave Launched by a Sheath Field

    NASA Astrophysics Data System (ADS)

    McCormick, M.; Arefiev, A. V.; Quevedo, H. J.; Bengtson, R. D.; Ditmire, T.

    2014-01-01

    We present experimental evidence supported by simulations of a relativistic ionization wave launched into a surrounding gas by the sheath field of a plasma filament with high energy electrons. Such a filament is created by irradiating a clustering gas jet with a short pulse laser (115 fs) at a peak intensity of 5×1017 W/cm2. We observe an ionization wave propagating radially through the gas for about 2 ps at 0.2-0.5 c after the laser has passed, doubling the initial radius of the filament. The gas is ionized by the sheath field, while the longevity of the wave is explained by a moving field structure that traps the high energy electrons near the boundary, maintaining a strong sheath field despite the significant expansion of the plasma.

  9. Observation of thermally driven field-like spin torque in magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Bose, Arnab; Shukla, Amit Kumar; Konishi, Katsunori; Jain, Sourabh; Asam, Nagarjuna; Bhuktare, Swapnil; Singh, Hanuman; Lam, Duc Duong; Fujii, Yuya; Miwa, Shinji; Suzuki, Yoshishige; Tulapurkar, Ashwin A.

    2016-07-01

    We report the thermally driven giant field-like spin-torque in magnetic tunnel junctions (MTJ) on application of heat current from top to bottom. The field-like term is detected by the shift of the magneto-resistance hysteresis loop applying temperature gradient. We observed that the field-like term depends on the magnetic symmetry of the MTJ. In asymmetric structures, with different ferromagnetic materials for free and fixed layers, the field-like term is greatly enhanced. Our results show that a pure spin current density of the order of 109 A/m2 can be produced by creating a 120 mK temperature difference across 0.9 nm thick MgO tunnelling barrier. Our results will be useful for writing MTJ and domain wall-based memories using thermally driven spin torque.

  10. Observation of thermally driven field-like spin torque in magnetic tunnel junctions

    SciTech Connect

    Bose, Arnab Jain, Sourabh; Asam, Nagarjuna; Bhuktare, Swapnil; Singh, Hanuman; Tulapurkar, Ashwin A.; Shukla, Amit Kumar; Konishi, Katsunori; Lam, Duc Duong; Fujii, Yuya; Miwa, Shinji; Suzuki, Yoshishige

    2016-07-18

    We report the thermally driven giant field-like spin-torque in magnetic tunnel junctions (MTJ) on application of heat current from top to bottom. The field-like term is detected by the shift of the magneto-resistance hysteresis loop applying temperature gradient. We observed that the field-like term depends on the magnetic symmetry of the MTJ. In asymmetric structures, with different ferromagnetic materials for free and fixed layers, the field-like term is greatly enhanced. Our results show that a pure spin current density of the order of 10{sup 9 }A/m{sup 2} can be produced by creating a 120 mK temperature difference across 0.9 nm thick MgO tunnelling barrier. Our results will be useful for writing MTJ and domain wall-based memories using thermally driven spin torque.

  11. Observation of Landau levels in potassium-intercalated graphite under a zero magnetic field.

    PubMed

    Guo, Donghui; Kondo, Takahiro; Machida, Takahiro; Iwatake, Keigo; Okada, Susumu; Nakamura, Junji

    2012-01-01

    The charge carriers in graphene are massless Dirac fermions and exhibit a relativistic Landau-level quantization in a magnetic field. Recently, it has been reported that, without any external magnetic field, quantized energy levels have been also observed from strained graphene nanobubbles on a platinum surface, which were attributed to the Landau levels of massless Dirac fermions in graphene formed by a strain-induced pseudomagnetic field. Here we show the generation of the Landau levels of massless Dirac fermions on a partially potassium-intercalated graphite surface without applying external magnetic field. Landau levels of massless Dirac fermions indicate the graphene character in partially potassium-intercalated graphite. The generation of the Landau levels is ascribed to a vector potential induced by the perturbation of nearest-neighbour hopping, which may originate from a strain or a gradient of on-site potentials at the perimeters of potassium-free domains.

  12. Theoretical and Observational Consequences of Rotation and Magnetic Fields in Stellar Winds

    NASA Astrophysics Data System (ADS)

    Ignace, Richard

    1996-05-01

    My dissertation concerns the study of stellar winds from theoretical modeling of the wind structure and the development of observational diagnostics. First, I have investigated the effects of stellar rotation for the wind structure of stars across the H-R Diagram. The effect of rotation is to increase the wind density at the equator while decreasing the density near the poles. The model, known as the Wind-Compressed Zone (WCZ) model, predicts that equatorial wind compressions are most likely to occur for stars with rapid rotation, low terminal speeds, and/or radial velocity distributions that increase gradually from the base of the wind. It is found that in favorable cases, stellar rotation can play a significant role in shaping the winds of Wolf Rayet stars, B supergiants, Asymptotic Giant Branch stars, and even some novae. The second major part of my thesis relates to the fact that the WCZ model will predict the magnetic field structure in the wind, if the field strength is relatively weak. However, there are generally no good diagnostics of stellar magnetic fields in the weak field limit, where Zeeman splitting is smaller than Doppler broadening. Thus, I have explored applications of the Hanle effect for probing magnetic fields in stellar winds. This effect (which has been used in studies of the solar atmosphere) deals with the modification of resonance line scattering polarization by a magnetic field. Solutions for the Hanle effect in optically thin axisymmetric extended stellar envelopes have been derived. Relative to the zero field case, the Hanle effect can result in significant changes of the line polarization, in some cases causing a position angle flip of 90(deg) . With multiline observations the Hanle effect is a viable diagnostic of stellar magnetic fields in the range 1-1000 Gauss. This thesis work was completed under the supervision of Joseph Cassinelli and in collaboration with Kenneth Nordsieck and Jon Bjorkman.

  13. Space Technology 5 Multipoint Observations of Temporal and Spatial Variability of Field-Aligned Currents

    NASA Technical Reports Server (NTRS)

    Le, G.; Wang, Y.; Slavin, J. A.; Strangeway, R. L.

    2009-01-01

    Space Technology 5 (ST5) is a constellation mission consisting of three microsatellites. It provides the first multipoint magnetic field measurements in low Earth orbit, which enables us to separate spatial and temporal variations. In this paper, we present a study of the temporal variability of field-aligned currents using the ST5 data. We examine the field-aligned current observations during and after a geomagnetic storm and compare the magnetic field profiles at the three spacecraft. The multipoint data demonstrate that mesoscale current structures, commonly embedded within large-scale current sheets, are very dynamic with highly variable current density and/or polarity in approx.10 min time scales. On the other hand, the data also show that the time scales for the currents to be relatively stable are approx.1 min for mesoscale currents and approx.10 min for large-scale currents. These temporal features are very likely associated with dynamic variations of their charge carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of mesoscale field-aligned currents are found to be consistent with those of auroral parallel electric field.

  14. The performance of field scientists undertaking observations of early life fossils while in simulated space suit

    NASA Astrophysics Data System (ADS)

    Willson, D.; Rask, J. C.; George, S. C.; de Leon, P.; Bonaccorsi, R.; Blank, J.; Slocombe, J.; Silburn, K.; Steele, H.; Gargarno, M.; McKay, C. P.

    2014-01-01

    We conducted simulated Apollo Extravehicular Activity's (EVA) at the 3.45 Ga Australian 'Pilbara Dawn of life' (Western Australia) trail with field and non-field scientists using the University of North Dakota's NDX-1 pressurizable space suit to overview the effectiveness of scientist astronauts employing their field observation skills while looking for stromatolite fossil evidence. Off-world scientist astronauts will be faced with space suit limitations in vision, human sense perception, mobility, dexterity, the space suit fit, time limitations, and the psychological fear of death from accidents, causing physical fatigue reducing field science performance. Finding evidence of visible biosignatures for past life such as stromatolite fossils, on Mars, is a very significant discovery. Our preliminary overview trials showed that when in simulated EVAs, 25% stromatolite fossil evidence is missed with more incorrect identifications compared to ground truth surveys but providing quality characterization descriptions becomes less affected by simulated EVA limitations as the science importance of the features increases. Field scientists focused more on capturing high value characterization detail from the rock features whereas non-field scientists focused more on finding many features. We identified technologies and training to improve off-world field science performance. The data collected is also useful for NASA's "EVA performance and crew health" research program requirements but further work will be required to confirm the conclusions.

  15. Electron diffusion region during magnetopause reconnection with an intermediate guide field: Magnetospheric multiscale observations

    NASA Astrophysics Data System (ADS)

    Chen, L.-J.; Hesse, M.; Wang, S.; Gershman, D.; Ergun, R. E.; Burch, J.; Bessho, N.; Torbert, R. B.; Giles, B.; Webster, J.; Pollock, C.; Dorelli, J.; Moore, T.; Paterson, W.; Lavraud, B.; Strangeway, R.; Russell, C.; Khotyaintsev, Y.; Lindqvist, P.-A.; Avanov, L.

    2017-05-01

    An electron diffusion region (EDR) in magnetic reconnection with a guide magnetic field approximately 0.2 times the reconnecting component is encountered by the four Magnetospheric Multiscale spacecraft at the Earth's magnetopause. The distinct substructures in the EDR on both sides of the reconnecting current sheet are visualized with electron distribution functions that are 2 orders of magnitude higher cadence than ever achieved to enable the following new findings: (1) Motion of the demagnetized electrons plays an important role to sustain the reconnection current and contributes to the dissipation due to the nonideal electric field, (2) the finite guide field dominates over the Hall magnetic field in an electron-scale region in the exhaust and modifies the electron flow dynamics in the EDR, (3) the reconnection current is in part carried by inflowing field-aligned electrons in the magnetosphere part of the EDR, and (4) the reconnection electric field measured by multiple spacecraft is uniform over at least eight electron skin depths and corresponds to a reconnection rate of approximately 0.1. The observations establish the first look at the structure of the EDR under a weak but not negligible guide field.

  16. Field and material stresses predict observable surface forces in optical and electrostatic manipulation

    NASA Astrophysics Data System (ADS)

    Kemp, Brandon A.; Sheppard, Cheyenne J.

    2016-09-01

    The momentum of light in media has been one of the most debated topics in physics over the past one hundred years. Originally a theoretical debate over the electrodynamics of moving media, practical applications have emerged over the past few decades due to interest in optical manipulation and nanotechnology. Resolution of the debate identifies a kinetic momentum as the momentum of the fields responsible for center of mass translations and a canonical momentum related to the coupled field and material system. The optical momentum resolution has been considered incomplete because it did not uniquely identify the full stress-energy-momentum (SEM) tensor of the field-kinetic subsystem. A consequence of this partial resolution is that the field-kinetic momentum could be described by three of the leading formulations found in the literature. The Abraham, Einstein-Laub, and Chu SEM tensors share the field-kinetic momentum, but their SEM tensors differ resulting in competing force densities. We can show now that the Abraham and Einstein-Laub formulations are invalid since their SEM tensors are not frame invariant, whereas the Chu SEM tensor satisfies relativistic principles as the field-kinetic formulation. However, a number of reports indicate that the force distribution in matter may not accurately represent experimental observations. In this correspondence, we show that the field-kinetic SEM tensor can be used along with the corresponding material subsystem to accurately predict experimental force and stress distributions. We model experimental examples from optical and static manipulation of particles and fluids.

  17. MAVEN MAG Observations of Magnetic Field Enhancements and Decreases in the Induced Magnetosphere of Mars

    NASA Astrophysics Data System (ADS)

    Soobiah, Y. I. J.; Espley, J. R.; Connerney, J. E. P.; DiBraccio, G. A.; Gruesbeck, J.; Halekas, J. S.; Mitchell, D. L.; McFadden, J. P.; Brain, D. A.; Jakosky, B. M.; Schneider, N. M.; Mazelle, C. X.; Andersson, L.; Ergun, R. E.; Jain, S.; Deighan, J.; McClintock, W. E.

    2015-12-01

    Recent results have shown the occurrence of a large-scale flux rope (enhancement in magnetic field strength and rotation in magnetic field vectors) on the dayside of Mars as associated with a dayside current sheet region forming at the proximity of strong crustal magnetic fields. This dayside current sheet region including the example of the large-scale flux rope occurred when the draped solar wind magnetic field showed a +By component in the MSO frame. All events involved similar anisotropic pitch angle distribution of electrons with low-energy field aligned electrons and higher-energy trapped electrons, indicating either the mixing of trapped magnetosheath electrons with low energy field aligned ionospheric electrons and/or the pitch angle diffusion of ionospheric electrons. During a time of weak draped field, the current sheet region became highly extended and was observed alongside a decrease in magnetic field strength and highly anisotropic plasma indicative of a mirror mode structure or magnetic hole. The occurrence of magnetic decreases or magnetic holes are an established feature of the solar wind and are often found in the terrestrial magnetosheath, and have also been observed near Jupiter, Venus and comets. More recently, mirror mode structures have been reported within the Earth's magnetosphere. The occurrence of the mirror mode instability could result in the excitation of ULF waves and has also been related to Alfvén waves that could cause heating of the local plasma. Hence, both the large-scale flux ropes and mirror mode structures of current sheet regions on the dayside of Mars may have an important role in ionospheric heating and atmospheric escape at Mars. Therefore, using an automated routine we will attempt to search for the occurrence of magnetic field enhancements and magnetic field decreases in measurements of magnetic field by the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite Magnetometer (MAG) instrument whilst comparing to the

  18. Evolution of magnetic fields in galaxies and future observational tests with the Square Kilometre Array

    NASA Astrophysics Data System (ADS)

    Arshakian, T. G.; Beck, R.; Krause, Marita; Sokoloff, D.

    2009-01-01

    Aims: In the context of models of galaxy formation and evolution, we investigate the cosmological evolution of large- and small-scale magnetic fields inside galaxies. Methods: We use the dynamo theory to derive the timescales of amplification and ordering of magnetic fields in disk and puffy galaxies. Turbulence in protogalactic halos generated by thermal virialization can drive an efficient turbulent dynamo. Results from simulations of hierarchical structure formation cosmology provide a tool to develop an evolutionary model of regular magnetic fields coupled with galaxy formation and evolution. Results: The turbulent (small-scale) dynamo was able to amplify a weak seed magnetic field in halos of protogalaxies to a few μG strength within a few 108 yr. This turbulent field served as a seed to the mean-field (large-scale) dynamo. Galaxies similar to the Milky Way formed their disks at z≈10 and regular fields of μG strength and a few kpc coherence length were generated within 2 Gyr (at z≈3), but field-ordering on the coherence scale of the galaxy size required an additional 6 Gyr (at z≈0.5). Giant galaxies formed their disks at z≈10, allowing more efficient dynamo generation of strong regular fields (with kpc coherence length) already at z≈4. However, the age of the Universe is short for fully coherent fields in giant galaxies larger than 15 kpc to have been achieved. Dwarf galaxies should have hosted fully coherent fields at z≈1. After a major merger, the strength of the turbulent field is enhanced by a factor of a few. Conclusions: This evolutionary scenario can be tested by measurements of polarized synchrotron emission and Faraday rotation with the planned Square Kilometre Array (SKA). We predict an anticorrelation between galaxy size and ratio between ordering scale and galaxy size. Weak regular fields (small Faraday rotation) in galaxies at z⪉3 are signatures of major mergers. Undisturbed dwarf galaxies should host fully coherent fields, giving

  19. Use of Unmanned Aircraft Systems in Observations of Glaciers, Ice Sheets, Sea Ice and Snow Fields

    NASA Astrophysics Data System (ADS)

    Herzfeld Mayer, M. U.

    2015-12-01

    Unmanned Aircraft Systems (UAS) are being used increasingly in observations of the Earth, especially as such UAS become smaller, lighter and hence less expensive. In this paper, we present examples of observations of snow fields, glaciers and ice sheets and of sea ice in the Arctic that have been collected from UAS. We further examine possibilities for instrument miniaturization, using smaller UAS and smaller sensors for collecting data. The quality and type of data is compared to that of satellite observations, observations from manned aircraft and to measurements made during field experiments on the ground. For example, a small UAS can be sent out to observe a sudden event, such as a natural catastrophe, and provide high-resolution imagery, but a satellite has the advantage of providing the same type of data over much of the Earth's surface and for several years, but the data is generally of lower resolution. Data collected on the ground typically have the best control and quality, but the survey area is usually small. Here we compare micro-topographic measurements made on snow fields the Colorado Rocky Mountains with airborne and satellite data.

  20. The Z3 model of Saturns magnetic field and the Pioneer 11 vector helium magnetometer observations

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Acuna, M. H.; Ness, N. F.

    1984-01-01

    Magnetic field observations obtained by the Pioneer 11 vector helium magnetometer are compared with the Z(sub 3) model magnetic field. These Pioneer 11 observations, obtained at close-in radial distances, constitute an important and independent test of the Z(sub 3) zonal harmonic model, which was derived from Voyager 1 and Voyager 2 fluxgate magnetometer observations. Differences between the Pioneer 11 magnetometer and the Z(sub 3) model field are found to be small (approximately 1%) and quantitatively consistent with the expected instrumental accuracy. A detailed examination of these differences in spacecraft payload coordinates shows that they are uniquely associated with the instrument frame of reference and operation. A much improved fit to the Pioneer 11 observations is obtained by rotation of the instrument coordinate system about the spacecraft spin axis by 1.4 degree. With this adjustment, possibly associated with an instrumental phase lag or roll attitude error, the Pioneer 11 vector helium magnetometer observations are fully consistent with the Voyager Z(sub 3) model.

  1. Hinode magnetic-field observations of solar flares for exploring the energy storage and trigger mechanisms

    NASA Astrophysics Data System (ADS)

    Shimizu, Toshifumi; Inoue, Satoshi; Kawabata, Yusuke

    2015-08-01

    Solar flares abruptly release the free energy stored as a non-potential magnetic field in the corona and may be accompanied by eruptions of the coronal plasma. Magnetic reconnection is considered as a physical process in which the magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration, but the location of magnetic reconnection is difficult to identify directly because of low emission measure at the reconnection region. We are still lack of observational knowledge on the 3D magnetic configuration and physical conditions for leading to flare trigger. Accurate measurements of vector magnetic fields at the solar photosphere, provided by the Solar Optical Telescope onboard Hinode, help us in exploring how the free energy is stored in the solar atmosphere and how the release of the energy is triggered. This presentation will review the magnetic field configuration and possible candidates for flare trigger primarily based on Hinode observations of some large flare events, which may include X5.4/X1.3 flares on 7 March 2012, X1.2 flare on 7 January 2014 and two M-class flares on 2 February 2014. The 7 March 2012 events were observed in an active region with delta-type sunspots, showing a strong shear in the entire magnetic system. For the sheared magnetic structure, the inclusion of a small-scale trigger field was identified near the polarity inversion line with excitation of a high-speed material flow in the horizontally oriented magnetic field formed nearly in parallel to the polarity inversion line. The observations suggest that gas dynamics at the solar surface play a vital role of leading to the onset of flares. The 7 January 2014 event is an exceptional event which most scientists would not be able to predict its occurrence. The flare unexpectedly happened apart from the sheared magnetic field region. The M-class flares on 2 February 2014 were observed in the magnetic field configuration, in which four magnetic domains were

  2. Cassini SAR, radiometry, scatterometry and altimetry observations of Titan's dune fields

    USGS Publications Warehouse

    Le, Gall A.; Janssen, M.A.; Wye, L.C.; Hayes, A.G.; Radebaugh, J.; Savage, C.; Zebker, H.; Lorenz, R.D.; Lunine, J.I.; Kirk, R.L.; Lopes, R.M.C.; Wall, S.; Callahan, P.; Stofan, E.R.; Farr, Tom

    2011-01-01

    Large expanses of linear dunes cover Titan's equatorial regions. As the Cassini mission continues, more dune fields are becoming unveiled and examined by the microwave radar in all its modes of operation (SAR, radiometry, scatterometry, altimetry) and with an increasing variety of observational geometries. In this paper, we report on Cassini's radar instrument observations of the dune fields mapped through May 2009 and present our key findings in terms of Titan's geology and climate. We estimate that dune fields cover ???12.5% of Titan's surface, which corresponds to an area of ???10millionkm2, roughly the area of the United States. If dune sand-sized particles are mainly composed of solid organics as suggested by VIMS observations (Cassini Visual and Infrared Mapping Spectrometer) and atmospheric modeling and supported by radiometry data, dune fields are the largest known organic reservoir on Titan. Dune regions are, with the exception of the polar lakes and seas, the least reflective and most emissive features on this moon. Interestingly, we also find a latitudinal dependence in the dune field microwave properties: up to a latitude of ???11??, dune fields tend to become less emissive and brighter as one moves northward. Above ???11?? this trend is reversed. The microwave signatures of the dune regions are thought to be primarily controlled by the interdune proportion (relative to that of the dune), roughness and degree of sand cover. In agreement with radiometry and scatterometry observations, SAR images suggest that the fraction of interdunes increases northward up to a latitude of ???14??. In general, scattering from the subsurface (volume scattering and surface scattering from buried interfaces) makes interdunal regions brighter than the dunes. The observed latitudinal trend may therefore also be partially caused by a gradual thinning of the interdunal sand cover or surrounding sand sheets to the north, thus allowing wave penetration in the underlying

  3. Magnetic field observations on DE-A and -B. [Dynamics Explorer A and B satellites

    NASA Technical Reports Server (NTRS)

    Farthing, W. H.; Sugiura, M.; Ledley, B. G.; Cahill, L. J., Jr.

    1981-01-01

    Magnetic field observations are conducted on each of the DE-A and -B satellites by a triaxial fluxgate magnetometer. In the basic mode the instrumental resolution is + or - 1.5 nT; in addition, the DE-A magnetometer has two modes of higher resolution: + or - 0.25 nT and + or - 20 pT. The sampling rate is 16 vector samples per second in all modes. The experiment objectives include observations of field-aligned currents, magnetospheric equatorial currents, and ULF waves. These observations, taking full advantage of the specifically selected orbits of the two spacecraft and of the unique combination of instruments, are performed to achieve a better understanding of the electrodynamic coupling within the atmosphere-ionosphere-magnetosphere system and of wave-particle interactions which contribute to the coupling processes.

  4. Lava flow surface textures - SIR-B radar image texture, field observations, and terrain measurements

    NASA Technical Reports Server (NTRS)

    Gaddis, Lisa R.; Mouginis-Mark, Peter J.; Hayashi, Joan N.

    1990-01-01

    SIR-B images, field observations, and small-scale (cm) terrain measurements are used to study lave flow surface textures related to emplacement processes of a single Hawaiian lava flow. Although smooth pahoehoe textures are poorly characterized on the SIR-B data, rougher pahoehoe types and the a'a flow portion show image textures attributed to spatial variations in surface roughness. Field observations of six distinct lava flow textural units are described and used to interpret modes of emplacement. The radar smooth/rough boundary between pahoehoe and a'a occurs at a vertical relief of about 10 cm on this lava flow. While direct observation and measurement most readily yield information related to lava eruption and emplacement processes, analyses of remote sensing data such as those acquired by imaging radars and altimeters can provide a means of quantifying surface texture, identifying the size and distribution of flow components, and delineating textural unit boundaries.

  5. Ground Observations of Artificial E Region Field-Aligned Irregularities Over HAARP

    NASA Astrophysics Data System (ADS)

    Nossa, E.; Hysell, D. L.

    2008-12-01

    Heating experiments were performed at HAARP intended to create E region field aligned plasma irregularities (FAIs) at midday in July of 2008 when the critical frequency of the E layer is a maximum. Field-aligned backscatter was observed using a 30 MHz imaging coherent scatter radar located close to Homer, Alaska. Three experiment modes were used, involving 1) heating alternately at zenith and magnetic zenith, 2) heating using triangular power modulation, and 3) heating slightly above and below the second electron gyroharmonic. Strong echoes were observed in all cases. Radar imaging and other diagnostic methods are used to examine the degree to which irregularities can be observed outside the Spitze angle, the possible effects of predonditioning on thermal parametric instability, and the effects of the double resonance on backscatter intensity and irregularity formation.

  6. Retrieval of Hydrometeor Drop Size Distributions from TRMM Field Campaign Profiler Doppler Velocity Spectra Observations

    NASA Technical Reports Server (NTRS)

    Williams, Christopher R.; Gage, Kenneth S.

    2003-01-01

    Consistent with the original proposal and work plan, this project focused on estimating the raindrop size distributions (DSDs) retrieved from vertically pointing Doppler radar profilers and analyzing the relationship of the retrieved DSDs with the dynamics of the precipitation processes. The first phase of this project focused on developing the model to retrieve the DSD from the observed Doppler velocity spectra. The second phase used this model to perform DSD retrievals from the profiler observations made during the TRMM Ground Validation Field Campaigns of TEFLUN-B, TRMM-LBA, and KWAJEX. The third phase of this project established collaborations with scientists involved with each field campaign in order to validate the profiler DSD estimates and to enable the profiler retrievals to be used in their research. Through these collaborations, the retrieved DSDs were placed into context with the dynamical processes of the observed precipitating cloud systems.

  7. Modeling human target reaching with an adaptive observer implemented with dynamic neural fields.

    PubMed

    Fard, Farzaneh S; Hollensen, Paul; Heinke, Dietmar; Trappenberg, Thomas P

    2015-12-01

    Humans can point fairly accurately to memorized states when closing their eyes despite slow or even missing sensory feedback. It is also common that the arm dynamics changes during development or from injuries. We propose a biologically motivated implementation of an arm controller that includes an adaptive observer. Our implementation is based on the neural field framework, and we show how a path integration mechanism can be trained from few examples. Our results illustrate successful generalization of path integration with a dynamic neural field by which the robotic arm can move in arbitrary directions and velocities. Also, by adapting the strength of the motor effect the observer implicitly learns to compensate an image acquisition delay in the sensory system. Our dynamic implementation of an observer successfully guides the arm toward the target in the dark, and the model produces movements with a bell-shaped velocity profile, consistent with human behavior data. Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. Squeezed bispectrum in the δ N formalism: local observer effect in field space

    NASA Astrophysics Data System (ADS)

    Tada, Yuichiro; Vennin, Vincent

    2017-02-01

    The prospects of future galaxy surveys for non-Gaussianity measurements call for the development of robust techniques for computing the bispectrum of primordial cosmological perturbations. In this paper, we propose a novel approach to the calculation of the squeezed bispectrum in multiple-field inflation. With use of the δ N formalism, our framework sheds new light on the recently pointed out difference between the squeezed bispectrum for global observers and that for local observers, while allowing one to calculate both. For local observers in particular, the squeezed bispectrum is found to vanish in single-field inflation. Furthermore, our framework allows one to go beyond the near-equilateral ("small hierarchy") limit, and to automatically include intrinsic non-Gaussianities that do not need to be calculated separately. The explicit computational programme of our method is given and illustrated with a few examples.

  9. A theory of electron cyclotron waves generated along auroral field lines observed by ground facilities

    NASA Technical Reports Server (NTRS)

    Wu, C. S.; Yoon, Peter H.; Freund, H. P.

    1989-01-01

    A generation mechanism for radio waves in the frequency range 150 - 700 kHz observed by ground facilities is suggested in terms of an electromagnetic electron cyclotron instability driven by auroral electrons. The excited waves can propagate downward along the ambient magnetic field lines and are thus observable with ground facilities. The trapped auroral electrons are supposed to play an important role in the generation process, because they give rise to a thermal anisotropy which consequently leads to the instability. The present work is a natural extension of the theory proposed earlier by Wu et al. (1983) which was discussed in a different context but may be used to explain the observed waves originated at low altitudes. This paper presents a possible wave generation mechanism valid in the entire auroral field-line region of interest.

  10. Gridded field observations of polybrominated diphenyl ethers and decabromodiphenyl ethane in the atmosphere of north China.

    PubMed

    Zhao, Yifan; Ma, Jin; Qiu, Xinghua; Lin, Yan; Yang, Qiaoyun; Zhu, Tong

    2013-08-06

    Brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs) are important pollutants, yet few data on ambient BFRs levels have been available for North China, one of the most developed regions of the country. In this study, we investigated levels and spatial distributions of BFRs based on gridded field observations coupled with passive air sampling in the aforementioned region. A model incorporating both point and nonpoint sources was developed to simulate the spatial distribution and to achieve source apportionment. Although high concentration was observed at an electronic-waste (e-waste) recycling site, the median level of the sum of tri-, tetra-, hepta-, hexa-, and hepta-PBDEs (∑10PBDEs) was 0.56 ng/sample, which was lower than those observed previously in mainland China. Source apportionment revealed that nonpoint emissions contributed nearly 78% of ∑10PBDEs observed in this study. In contrast, high levels of BDE-209 and DBDPE were observed, with median concentrations of 4.0 and 10.2 ng/sample, respectively. Point sources located in the region around Laizhou Bay, Shandong Province were the major sources, which contributed 31% of BDE-209 and 70% of DBDPE observed in this study, indicating that this manufacturing base was the most important source region for atmospheric deca-BFRs in North China. To our knowledge, this is the first study to report source apportionment of atmospheric BFRs based on gridded field observations.

  11. Magnetic fields in molecular clouds: Limitations of the analysis of Zeeman observations

    NASA Astrophysics Data System (ADS)

    Brauer, R.; Wolf, S.; Reissl, S.; Ober, F.

    2017-05-01

    Context. Observations of Zeeman split spectral lines represent an important approach to derive the structure and strength of magnetic fields in molecular clouds. In contrast to the uncertainty of the spectral line observation itself, the uncertainty of the analysis method to derive the magnetic field strength from these observations has so far not been well characterized. Aims: We investigate the impact of several physical quantities on the uncertainty of the analysis method, which is used to derive the line-of-sight (LOS) magnetic field strength from Zeeman split spectral lines. These quantities are the density, temperature, velocity, and magnetic field strength. Methods: We simulated the Zeeman splitting of the 1665 MHz OH line with the 3D radiative transfer (RT) extension ZRAD. This extension is based on the line RT code Mol3D and has been developed for the POLArized RadIation Simulator POLARIS. Results: Observations of the OH Zeeman effect in typical molecular clouds are not significantly affected by the uncertainty of the analysis method. However, some observations obtained a magnetic field strength of more than 300 μG, which may result in an uncertainty of the analysis method of > 10%. We derived an approximation to quantify the range of parameters in which the analysis method works accurately enough and provide factors to convert our results to other spectral lines and species as well. We applied these conversion factors to CN and found that observations of the CN Zeeman effect in typical molecular clouds are not significantly affected by the uncertainty of the analysis method. In addition, we found that the density has almost no impact on the uncertainty of the analysis method, unless it reaches values higher than those typically found in molecular clouds (nH ≫ 107 cm-3). Furthermore, the uncertainty of the analysis method increases if both the gas velocity and magnetic field show significant variations along the LOS. However, this increase should be

  12. Observations of a Newly "Captured" Magnetosheath Field Line: Evidence for "Double Reconnection"

    NASA Technical Reports Server (NTRS)

    Chandler, Michael O.; Avanov, Levon A.; Craven, Paul D.; Mozer, Forrest S.; Moore, Thomas E.

    2007-01-01

    We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. This region has been routinely sampled for about three months each year for the periods 1999-2001 and 2004-2006. The low-to-mid-energy ion instruments frequently observed dense, magnetosheath-like plasma deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. One such case, taken during a period of northward interplanetary magnetic field (IMF), shows magnetosheath ions within the magnetosphere with velocity distributions resulting from two separate merging sites along the same field lines. Cold ionospheric ions were also observed counterstreaming along the field lines, evidence that these field lines were closed. These results are consistent with the hypothesis that double merging can produce closed field .lines populated by solar wind plasma. Through the use of individual cases such as this and statistical studies of a broader database we seek to understand the morphology of the LLBL as it projects from the sub-solar region into the cusp. We will present preliminary results of our ongoing study.

  13. Magnetic field fluctuations observed by the Swarm constellation in the nighttime mid-latitude topside ionosphere

    NASA Astrophysics Data System (ADS)

    Park, J.; Luhr, H.; Kervalishvili, G.; Rauberg, J.; Michaelis, I.; Stolle, C.; Kwak, Y. S.

    2015-12-01

    Using single-satellite observations on Low-Earth-Orbits (LEO), some previous studies suggested that electric and magnetic field fluctuations observed in the nighttime mid-latitude ionosphere originate from medium-scale traveling ionospheric disturbances (MSTIDs). With the inherently 1-dimensional sampling, however, those studies could not confirm whether (1) the electric and magnetic field fluctuations are spatial structures rather than temporal variations, and (2) horizontal shapes of the field fluctuation regions generally have mirror symmetry with respect to the magnetic equator, just as MSTIDs do. In this presentation we analyze magnetic field data sampled by three identical Swarm satellites. The results support the idea of a close connection between mid-latitude magnetic fluctuations (MMFs) and MSTIDs in the nighttime sector. Combined with the relationship between MMFs and MSTIDs, the MMF climatology can be used for extending that of MSTIDs, which has been poorly investigated over oceans. In addition, we have conducted a scale size analysis and found that coherence lengths of MMFs are typically shorter than 150 km. We also discuss the possibility that the MMF regions are aligned with the background magnetic field.

  14. Multi-instrument observation of simultaneous polar cap auroras on open and closed magnetic field lines

    NASA Astrophysics Data System (ADS)

    Reidy, J. A.; Fear, R. C.; Whiter, D. K.; Lanchester, B. S.; Kavanagh, A. J.; Paxton, L. J.; Zhang, Y.; Lester, M.

    2017-04-01

    This paper presents observations of polar cap auroral features on 19 January 2008, evaluated using multiple instruments with near-simultaneous observations in both hemispheres. Analysis of the features indicates that there are at least two formation mechanisms/types of polar cap aurora occurring simultaneously on different magnetic field topologies (one on open and the other on closed magnetospheric field lines). Two high-latitude structures were observed on opposing sides of the northern hemisphere polar cap in the same time interval. The structure on the duskside was formed on closed field lines that protruded into the polar cap and was generated by the precipitation of electrons with energies varying between 2 and 11 keV consistent with an identified mechanism for the formation of transpolar arcs. However, the structure did not extend fully across to the dayside of the auroral oval but rather stayed at ˜80° magnetic latitude for a minimum duration of 40 min. Thus, this structure is an example of a "failed" transpolar arc. The structure on the dawnside of the polar cap was associated with low-energy electron precipitation (less than 1 keV) and no associated ion signatures, which is consistent with it being a common low-intensity arc formed by accelerated polar rain on open field lines. The two separate types of polar cap auroras formed during the same interval, demonstrating the complexity of the solar wind-magnetosphere coupling during the interval.

  15. Observational Analysis of the Relation between Coronal Loop Heating and Photospheric Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Katsukawa, Y.

    2007-10-01

    The solar corona and the photosphere are linked through magnetic field lines, and heating energy is supposed to be supplied from the footpoints of each coronal loop along magnetic field lines. Thus it is important to examine properties of photospheric magnetic fields at the footpoints of the coronal loops in order to understand heating of the coronal loops. We performed simultaneous observations of photospheric magnetic properties and coronal loop structures using the ground based telescopes and Transition Region And Coronal Explorer (TRACE). Footpoint locations were identified in the TRACE images, and the structure in the photosphere was examined by Advanced Stokes Polarimeter (ASP) or Dutch Open Telescope (DOT). Most of the coronal loops emanating from a sunspot had their footpoints around the boundary between the umbra and the penumbra. Furthermore, bright loops were revealed to have their footpoints at the locations where there was highly interlaced magnetic configuration. We observed fragmentation of an umbra and formation of a light bridge in decaying sunspots, and found possible association between such phenomena in the decaying spots and the coronal loops. These observational results suggest that spatial fluctuation of magnetic fields forms current sheets at the base of the corona, resulting in heating of the coronal loops.

  16. Magnetic field rotation at the dayside magnetopause: AMPTE/IRM observations

    NASA Astrophysics Data System (ADS)

    De Keyser, J.; Roth, M.

    1998-04-01

    Given the large-scale magnetosheath flow pattern around the magnetosphere, the tangential discontinuity magnetopause model of De Keyser and Roth predicts, for a prescribed magnetic field rotation angle and rotation sense, where equilibrium is possible on the dayside magnetopause surface and where it is not. In this paper we verify these predictions using 5 s time resolution magnetic field and plasma observations of the low-latitude dayside magnetospheric boundary acquired by the Active Magnetospheric Particle Tracer Explorers/Ion Release Module satellite. The model is confirmed by (1) the dominant presence of large positive magnetic field rotations among the dawnside crossings north of the equator, (2) the observation of positive and negative rotations near the stagnation point and at the duskside, and (3) the rare occurrence and questionable tangential discontinuity nature of low magnetic shear dawnside crossings. The absence of tangential discontinuity equilibrium in dawnside low shear crossings is consistent with the observation of increased dawnside low-latitude boundary layer thickness for northward magnetosheath field reported in the literature.

  17. Local magnetic field measurements and fault creep observations on the San Andreas fault

    NASA Astrophysics Data System (ADS)

    Johnston, M. J. S.; Smith, B. E.; Burford, R. O.

    1980-04-01

    Simultaneous creep and magnetic field records have been obtained for more than 60 episodic creep events since early 1974, no clear magnetic transients or offsets, as suggested by Breiner and Kovach (1968), are observed at or up to several days before the occurrence times of these events. Although some patterns of creep onset times at adjacent stations over periods of weeks to months appear to correspond to some periods of longer term change in local magnetic field, these changes do not always occur and other groups of creep events have no corresponding changes in local magnetic field. Changes in stress related to the surface expression of episodic fault creep on the San Andreas fault can be estimated from dislocation models fit to observations of simultaneous strains and tilts at points near the fault. These stress values are generally less than 1 bar. For these stress levels and with the apparent limited extent of surface failure, tectonomagnetic models of creep events indicate that simultaneous observations of related magnetic field variations at detectable levels of a gamma or so are unlikely. Slip at greater depth may occur more smoothly and would load the near-surface material to failure. These data also argue against large-scale dilatant cracking occurring along the region of the fault presently monitored.

  18. Local magnetic field measurements and fault creep observations on the San Andreas fault

    USGS Publications Warehouse

    Johnston, M.J.S.; Smith, B.E.; Burford, R.O.

    1980-01-01

    Simultaneous creep and magnetic field records have been obtained for more than 60 episodic creep events since early 1974, no clear magnetic transients or offsets, as suggested by Breiner and Kovach (1968), are observed at or up to several days before the occurrence times of these events. Although some patterns of creep onset times at adjacent stations over periods of weeks to months appear to correspond to some periods of longer term change in local magnetic field, these changes do not always occur and other groups of creep events have no corresponding changes in local magnetic field. Changes in stress related to the surface expression of episodic fault creep on the San Andreas fault can be estimated from dislocation models fit to observations of simultaneous strains and tilts at points near the fault. These stress values are generally less than 1 bar. For these stress levels and with the apparent limited extent of surface failure, tectonomagnetic models of creep events indicate that simultaneous observations of related magnetic field variations at detectable levels of a gamma or so are unlikely. Slip at greater depth may occur more smoothly and would load the near-surface material to failure. These data also argue against large-scale dilatant cracking occurring along the region of the fault presently monitored. ?? 1980.

  19. Electric Field and Lightning Observations in the Core of Category 5 Hurricane Emily

    NASA Technical Reports Server (NTRS)

    Blakeslee, Richard; Mach, Doug M.; Bateman, Monte G.; Bailey, Jeff C.

    2007-01-01

    Significant electric fields and lightning activity associated with Hurricane Emily were observed from a NASA high-altitude ER-2 aircraft on July 17, 2005 while this storm developed as a compact but intense category 5 hurricane in the Caribbean south of Cuba. The electrical measurements were acquired as part of the NASA sponsored Tropical Cloud Systems and Processes (TCSP) experiment. In addition to the electrical measurements, the aircraft's remote sensing instrument complement also included active radars, passive microwave, visible and infrared radiometers, and a temperature sounder providing details on the dynamical, microphysical, and environmental structure, characteristics and development of this intense storm. Cloud-to-ground lightning location data from Vaisala's long range lightning detection network were also acquired and displayed in real-time along with electric fields measured at the aircraft. These data and associated display also supported aircraft guidance and vectoring during the mission. During the observing period, flash rates in excess of 3 to 5 flashes per minute, as well as large electric field and field change values were observed as the storm appeared to undergo periods of intensification, especially in the northwest quadrant in the core eyewall regions. This is in contrast to most hurricanes that tend to be characterized by weak electrification and little or no lightning activity except in the outer rain bands. It should be noted that this storm also had significant lightning associated with its rain bands.

  20. Toward the Direct Measurement of Coronal Magnetic Fields: An Airborne Infrared Spectrometer for Eclipse Observations

    NASA Astrophysics Data System (ADS)

    Samra, J.; DeLuca, E. E.; Golub, L.; Cheimets, P.

    2014-12-01

    The solar magnetic field enables the heating of the corona and provides its underlying structure. Energy stored in coronal magnetic fields is released in flares and coronal mass ejections (CME) and provides the ultimate source of energy for space weather. Therefore, direct measurements of the coronal magnetic field have significant potential to enhance understanding of coronal dynamics and improve solar forecasting models. Of particular interest are observations of coronal field lines in the transitional region between closed and open flux systems, providing important information on the origin of the slow solar wind. While current instruments routinely observe only the photospheric and chromospheric magnetic fields, a proposed airborne spectrometer will take a step toward the direct observation of coronal fields by measuring plasma emission in the infrared at high spatial and spectral resolution. The targeted lines are four forbidden magnetic dipole transitions between 2 and 4 μm. The airborne system will consist of a telescope, grating spectrometer, and pointing/stabilization system to be flown on the NSF/NCAR High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) during the August 2017 total solar eclipse. The project incorporates several optical engineering challenges, centered around maintaining adequate spectral and spatial resolution in a compact and inexpensive package and on a moving platform. Design studies are currently underway to examine the tradeoffs between various optical geometries and control strategies for the pointing/stabilization system. The results will be presented and interpreted in terms of the consequences for the scientific questions. In addition, results from a laboratory prototype and simulations of the final system will be presented.

  1. Wide-field direct CCD observations supporting the Astro-1 Space Shuttle mission's Ultraviolet Imaging Telescope

    NASA Technical Reports Server (NTRS)

    Hintzen, Paul; Angione, Ron; Talbert, Freddie; Cheng, K.-P.; Smith, Eric; Stecher, Theodore P.

    1993-01-01

    Wide field direct CCD observations are being obtained to support and complement the vacuum-ultraviolet (VUV) images provided by Astro's Ultraviolet Imaging Telescope (UIT) during a Space Shuttle flight in December 1990. Because of the wide variety of projects addressed by UIT, the fields observed include (1) galactic supernova remnants such as the Cygnus Loop and globular clusters such as Omega Cen and M79; (2) the Magellanic Clouds, M33, M81, and other galaxies in the Local Group; and (3) rich clusters of galaxies, principally the Perseus cluster and Abell 1367. Ground-based observations have been obtained for virtually all of the Astro-1 UIT fields. The optical images allow identification of individual UV sources in each field and provide the long baseline in wavelength necessary for accurate analysis of UV-bright sources. To facilitate use of our optical images for analysis of UIT data and other projects, we plan to archive them, with the UIT images, at the National Space Science Data Center (NSSDC), where they will be universally accessible via anonymous FTP. The UIT, one of three telescopes comprising the Astro spacecraft, is a 38-cm f/9 Ritchey-Chretien telescope on which high quantum efficiency, solar-blind image tubes are used to record VUV images on photographic film. Five filters with passbands centered between 1250A and 2500A provide both VUV colors and a measurement of extinction via the 2200A dust feature. The resulting calibrated VUV pictures are 40 arcminutes in diameter at 2.5 arcseconds resolution. The capabilities of UIT, therefore, complement HST's WFPC: the latter has 40 times greater collecting area, while UIT's usable field has 170 times WFPC's field area.

  2. Generating wind fields that honour point observations and physical conservation laws

    NASA Astrophysics Data System (ADS)

    Schlabing, Dirk; Bárdossy, András

    2015-04-01

    Wind exhibits a strong spatial and temporal variability. In the application of lake modelling, these features are important for simulating water flows and stratification correctly, as mean and variance of wind speed determine the input of momentum into the lake. This makes a mere interpolation of point measurements an unsuitable method for producing model input. Additionally to concrete point measurements, more subtle aspects of wind fields are to be reproduced. It follows from the fact that wind vectors represent moving air that a wind field has to be divergency-free in order to be mass-conservative. Further, a temporal sequence of wind fields has to comply with the Navier-Stokes equation in order to conserve momentum. All these constraints can be met by representing the conditioned wind field as a linear combination of unconditioned, normally distributed random fields that individually possess the same spatial covariance structuref as observed wind fields. The aim of having the same covariance structure in the conditioned wind field is formulated as an optimization problem with respect to the weights used in the linear combination. With the help of Quadratic Programming (QP) and exploiting the convexity of the problem, feasible solutions can easily be found. In this QP problem, observations become linear constraints. Conservation laws can be incorporated by introducing control volumes in a similar fashion as they are used in fluid mechanics. Budgets of flows through these control volumes become integral conditions in the QP problem. The applicability of the approach will be shown using an artificial example and real-world data measured on shore and on a moving boat on Lake Constance.

  3. Effects of the Observed Meridional Flow Variations since 1996 on the Sun's Polar Fields

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.; Upton, Lisa

    2013-01-01

    The cause of the low and extended minimum in solar activity between Sunspot Cycles 23 and 24 was the small size of Sunspot Cycle 24 itself - small cycles start late and leave behind low minima. Cycle 24 is small because the polar fields produced during Cycle 23 were substantially weaker than those produced during the previous cycles and those (weak) polar fields are the seeds for the activity of the following cycle. The polar fields are produced by the latitudinal transport of magnetic flux that emerged in low-latitude active regions. The polar fields thus depend upon the details of both the flux emergence and the flux transport. We have measured the flux transport flows (differential rotation, meridional flow, and supergranules) since 1996 and find systematic and substantial variation in the meridional flow alone. Here we present experiments using a Surface Flux Transport Model in which magnetic field data from SOHO/MDI and SDO/HMI are assimilated into the model only at latitudes between 45-degrees north and south of the equator (this assures that the details of the active region flux emergence are well represented). This flux is then transported in both longitude and latitude by the observed flows. In one experiment the meridional flow is given by the time averaged (and north-south symmetric) meridional flow profile. In the second experiment the time-varying and north-south asymmetric meridional flow is used. Differences between the observed polar fields and those produced in these two experiments allow us to ascertain the effects of these meridional flow variations on the Sun s polar fields.

  4. Simulation of polarized optical speckle fields: effects of the observation scale on polarimetry.

    PubMed

    Dupont, Jan; Orlik, Xavier

    2016-05-16

    In this paper, we propose the simulation of polarized speckle fields using the Stokes formalism, which allows the description of partially polarized electromagnetic waves. We define a unique parameter which determines the partial decorrelation of the involved fields, allowing to simulate the polarized speckles produced by all types of scatterers, from simple to multiple scatterers. We validate this model by comparison with experimental measurements. We use that simulation model to study the impact of the imaging device parameters on polarimetric measurements: first we emphasize a limit of resolution on retardance measurements, then we study the spatial depolarization, which appears when an observer is measuring any space-variant polarization map.

  5. Observational Signatures and Non-Gaussianities ofGeneral Single Field Inflation

    SciTech Connect

    Chen, Xingang; Huang, Min-xin; Kachru, Shamit; Shiu, Gary

    2006-05-05

    We perform a general study of primordial scalar non-Gaussianities in single field inflationary models. We consider models where the inflaton Lagrangian is an arbitrary function of the scalar field and its first derivative, and the sound speed is arbitrary. We find that under reasonable assumptions, the non-Gaussianity is completely determined by 5 parameters. In special limits of the parameter space, one finds distinctive ''shapes'' of the non-Gaussianity. In models with a small sound speed, several of these shapes would become potentially observable in the near future. Different limits of our formulae recover various previously known results.

  6. Observation of Plasma Rotation Driven by Static Nonaxisymmetric Magnetic Fields in a Tokamak

    SciTech Connect

    Garofalo, A. M.; Burrell, K. H.; DeBoo, J. C.; DeGrassie, J. S.; Jackson, G. L.; Schaffer, M. J.; Strait, E. J.; Lanctot, M.; Reimerdes, H.; Solomon, W. M.

    2008-11-07

    We present the first evidence for the existence of a neoclassical toroidal rotation driven in a direction counter to the plasma current by nonaxisymmetric, nonresonant magnetic fields. At high beta and with large injected neutral beam momentum, the nonresonant field torque slows down the plasma toward the neoclassical 'offset' rotation rate. With small injected neutral beam momentum, the toroidal rotation is accelerated toward the offset rotation, with resulting improvement in the global energy confinement time. The observed magnitude, direction, and radial profile of the offset rotation are consistent with neoclassical theory predictions [A. J. Cole et al., Phys. Rev. Lett. 99, 065001 (2007)].

  7. Observation of Thermoelectric Currents in High-Field Superconductor-Ferromagnet Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Kolenda, S.; Wolf, M. J.; Beckmann, D.

    2016-03-01

    We report on the experimental observation of spin-dependent thermoelectric currents in superconductor-ferromagnet tunnel junctions in high magnetic fields. The thermoelectric signals are due to a spin-dependent lifting of the particle-hole symmetry, and are found to be in excellent agreement with recent theoretical predictions. The maximum Seebeck coefficient inferred from the data is about -100 μ V /K , much larger than commonly found in metallic structures. Our results directly prove the coupling of spin and heat transport in high-field superconductors.

  8. Field-aligned currents and magnetospheric convection - A comparison between MHD simulations and observations

    NASA Technical Reports Server (NTRS)

    Walker, Raymond J.; Ogino, Tatsuki

    1988-01-01

    A time-dependent three-dimensional MHD model was used to investigate the magnetospheric configuration as a function of the interplanetary magnetic field direction when it was in the y-z plane in geocentric solar magnetospheric coordinates. The model results show large global convection cells, tail lobe cells, high-latitude polarcap cells, and low latitude cells. The field-aligned currents generated in the model magnetosphere and the model convection system are compared with observations from low-altitude polar orbiting satellites.

  9. Voyager Observations of Magnetic Fields and Cosmic Rays in the Heliosheath

    NASA Technical Reports Server (NTRS)

    Burlaga, L. F.; Ness, N. F.; Stone, E.; McDonald, F. B.

    2011-01-01

    The major features of the profile of greater than 70 MeV/nuc cosmic ray intensity (CRI) observed by Voyager 1 (VI) in the heliosheath from 2005.8-2010.24 are described by the empirical "CR-B" relation as the cumulative effect of variations of the magnetic field strength B. The CRI profile observed by Voyager 2 (V2) from 2008.60 to 2010.28 in the heliosheath is also described by the CR-B relation. On a smaller scale, of the order of a hundred days, a sequence on CRI decreases observed by V 1 during 2006 was interpreted as the effect of a propagating interplanetary shock first interacting with the termination shock, then moving past V1, and finally reflecting from the heliopause and propagating back to V1. Our observations show that the second CRI decrease in this sequence began during the passage of a "Global Merged Interaction Region" (GMIR), 40 days after the arrival of the GMIR and its possible shock. The first and third CRI decreases in the sequence were associated with local enhancements of B. The magnetic field observations associated with the second sequence of 3 cosmic ray intensity decreases observed by V 1 in 2007/2008 are more difficult to reconcile with the scenario of Webber et al. (2009) and the CR-B relation. The discrepancy might indicate the importance of latitudinal effects

  10. Seasonal-scale nearshore morphological evolution: Field observations and numerical modeling

    USGS Publications Warehouse

    Ruggiero, P.; Walstra, D.-J.R.; Gelfenbaum, G.; van, Ormondt M.

    2009-01-01

    A coupled waves-currents-bathymetric evolution model (DELFT-3D) is compared with field measurements to test hypotheses regarding the processes responsible for alongshore varying nearshore morphological changes at seasonal time scales. A 2001 field experiment, along the beaches adjacent to Grays Harbor, Washington, USA, captured the transition between the high-energy erosive conditions of winter and the low-energy beach-building conditions typical of summer. The experiment documented shoreline progradation on the order of 10-20 m and on average approximately 70 m of onshore sandbar migration during a four-month period. Significant alongshore variability was observed in the morphological response of the sandbar over a 4 km reach of coast with sandbar movement ranging from 20 m of offshore migration to over 175 m of onshore bar migration, the largest seasonal-scale onshore migration event observed in a natural setting. Both observations and model results suggest that, in the case investigated here, alongshore variations in initial bathymetry are primarily responsible for the observed alongshore variable morphological changes. Alongshore varying incident hydrodynamic forcing, occasionally significant in this region due to a tidal inlet and associated ebb-tidal delta, was relatively minor during the study period and appears to play an insignificant role in the observed alongshore variability in sandbar behavior at kilometer-scale. The role of fully three-dimensional cell circulation patterns in explaining the observed morphological variability also appears to be minor, at least in the case investigated here. ?? 2009 Elsevier B.V.

  11. Voyager observations of magnetic fields and cosmic rays in the heliosheath

    NASA Astrophysics Data System (ADS)

    Burlaga, L. F.; Ness, N. F.; Stone, E.; McDonald, F. B.

    2011-12-01

    The major features of the profile of >70 MeV/nuc cosmic ray intensity (CRI) observed by Voyager 1 (V1) in the heliosheath from 2005.8-2010.24 are described by the empirical “CR-B” relation as the cumulative effect of variations of the magnetic field strength B. The CRI profile observed by Voyager 2 (V2) from 2008.60 to 2010.28 in the heliosheath is also described by the CR-B relation. On a smaller scale, of the order of a hundred days, a sequence of 3 CRI decreases observed by V1 during 2006 was interpreted as the effect of a propagating interplanetary shock first interacting with the termination shock, then moving past V1, and finally reflecting from the heliopause and propagating back to V1. Our observations show that the second CRI decrease in this sequence began during the passage of a “Global Merged Interaction Region” (GMIR), ˜40 days after the arrival of the GMIR and its possible shock. The first and third CRI decreases in the sequence were associated with local enhancements of B. The magnetic field observations associated with the second sequence of 3 cosmic ray intensity decreases observed by V1 in 2007/2008 are more difficult to reconcile with the scenario of Webber et al. (2009) and the CR-B relation. The discrepancy might indicate the importance of latitudinal effects.

  12. Clear widens the field for observations of the Sun with multi-conjugate adaptive optics

    NASA Astrophysics Data System (ADS)

    Schmidt, Dirk; Gorceix, Nicolas; Goode, Philip R.; Marino, Jose; Rimmele, Thomas; Berkefeld, Thomas; Wöger, Friedrich; Zhang, Xianyu; Rigaut, François; von der Lühe, Oskar

    2017-01-01

    The multi-conjugate adaptive optics (MCAO) pathfinder Clear on the New Solar Telescope in Big Bear Lake has provided the first-ever MCAO-corrected observations of the Sun that show a clearly and visibly widened corrected field of view compared to quasi-simultaneous observations with classical adaptive optics (CAO) correction. Clear simultaneously uses three deformable mirrors, each conjugated to a different altitude, to compensate for atmospheric turbulence. While the MCAO correction was most effective over an angle that is approximately three times wider than the angle that was corrected by CAO, the full 53'' field of view did benefit from MCAO correction. We further demonstrate that ground-layer-only correction is attractive for solar observations as a complementary flavor of adaptive optics for observational programs that require homogenous seeing improvement over a wide field rather than diffraction-limited resolution. We show illustrative images of solar granulation and of a sunspot obtained on different days in July 2016, and present a brief quantitative analysis of the generalized Fried parameters of the images. The movies associated to Fig. 1 are available at http://www.aanda.org

  13. Observations of ELF fields near the low-altitude CRRES chemical releases

    SciTech Connect

    Koons, H.C.; Roeder, J.L.

    1995-08-01

    The Combined Release and Radiation Effects Satellite (CRRES) performed a series of seven low altitude chemical releases between September 10, 1990, and August 12, 1991. Immediately following each chemical release, electric and magnetic fields were detected by the extremely low frequency wave analyzer sensors of the Low Altitude Satellite Studies of Ionospheric Irregularities (LASSII) experiment on the spacecraft. The time series and spectra of the two field components are quite similar for each of the releases but vary in detail from release to release. The index of refraction estimated from the ratio of the magnetic field to the electric field is too small by about 2 orders of magnitude for either the right hand wave or the extraordinary wave modes which are the only propagating electromagnetic modes in the detected band above the O+ ion gyrofrequency (about 30 Hz). ELF hiss observed at higher altitudes is found to be propagating in the extraordinary wave mode with the correct index of refraction. This confirms that the intensity measurements are being made correctly by the instrument and that an alternative explanation is required for the signals detected following the chemical releases. The authors show that the waves are primarily electrostatic and that the magnitude of the wave magnetic field is consistent with the transverse magnetic field component of ion acoustic waves.

  14. Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows

    NASA Astrophysics Data System (ADS)

    Huntington, C. M.; Fiuza, F.; Ross, J. S.; Zylstra, A. B.; Drake, R. P.; Froula, D. H.; Gregori, G.; Kugland, N. L.; Kuranz, C. C.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R.; Plechaty, C.; Remington, B. A.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Park, H.-S.

    2015-02-01

    Collisionless shocks can be produced as a result of strong magnetic fields in a plasma flow, and therefore are common in many astrophysical systems. The Weibel instability is one candidate mechanism for the generation of sufficiently strong fields to create a collisionless shock. Despite their crucial role in astrophysical systems, observation of the magnetic fields produced by Weibel instabilities in experiments has been challenging. Using a proton probe to directly image electromagnetic fields, we present evidence of Weibel-generated magnetic fields that grow in opposing, initially unmagnetized plasma flows from laser-driven laboratory experiments. Three-dimensional particle-in-cell simulations reveal that the instability efficiently extracts energy from the plasma flows, and that the self-generated magnetic energy reaches a few percent of the total energy in the system. This result demonstrates an experimental platform suitable for the investigation of a wide range of astrophysical phenomena, including collisionless shock formation in supernova remnants, large-scale magnetic field amplification, and the radiation signature from gamma-ray bursts.

  15. A 4-meter wide field coronagraph space telescope for general astrophysics and exoplanet observations

    NASA Astrophysics Data System (ADS)

    Tenerelli, Domenick; Angel, Roger; Burge, Jim; Guyon, Olivier; Zabludoff, Ann; Belikov, Ruslan; Pluzhnik, Eugene; Egerman, Robert

    2010-07-01

    The Wide Field Coronagraph Telescope (WFCT) is a 4-meter space telescope for general astrophysics and exoplanet observations that meets the 2000 Decadal Committee requirements. This paper presents a design for a 4-m diameter, off-axis space telescope that offers high performance in both wide field and coronagraphic imaging modes. A 3.8 x 3.3-m unobstructed elliptical pupil is provided for direct coronagraphic imaging of exoplanets and a 4-m diameter pupil for wide-field imaging from far-ultraviolet (UV) to near-infrared (IR). The off-axis wide-field optics are all reflective and designed to deliver an average of 12 nm wavefront aberrations over a 6 x 24 arcminute field of view (FOV), therefore providing diffraction-limited images down to 300 nm wavelength and 15 mas images down to a wavelength limit set only by the mirror coatings. The coronagraph with phase-induced amplitude apodization (PIAA) provides diffraction suppression around a 360-degree field with high Strehl and sensitivity at the 1e-10 level to an inner working angle of 2 λ/D (or 50 mas at 500 nm wavelength). This paper focuses on the optical design that allows the above imaging features to be combined in single telescope, and gives a preliminary spacecraft design and costing, assuming a distant trailing orbit.

  16. Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows

    SciTech Connect

    Huntington, C. M.; Fiuza, F.; Ross, J. S.; Zylstra, A. B.; Drake, R. P.; Froula, D. H.; Gregori, G.; Kugland, N. L.; Kuranz, C. C.; Levy, M. C.; Li, C. K.; Meinecke, J.; Morita, T.; Petrasso, R.; Plechaty, C.; Remington, B. A.; Ryutov, D. D.; Sakawa, Y.; Spitkovsky, A.; Takabe, H.; Park, H.-S.

    2015-01-19

    Collisionless shocks can be produced as a result of strong magnetic fields in a plasma flow, and therefore are common in many astrophysical systems. The Weibel instability is one candidate mechanism for the generation of su fficiently strong fields to create a collisionless shock. Despite their crucial role in astrophysical systems, observation of the magnetic fields produced by Weibel instabilities in experiments has been challenging. Using a proton probe to directly image electromagnetic fields, we present evidence of Weibel-generated magnetic fields that grow in opposing, initially unmagnetized plasma flows from laser-driven laboratory experiments. Three-dimensional particle-in-cell simulations reveal that the instability effi ciently extracts energy from the plasma flows, and that the self-generated magnetic energy reaches a few percent of the total energy in the system. Furthermore, this result demonstrates an experimental platform suitable for the investigation of a wide range of astrophysical phenomena, including collisionless shock formation in supernova remnants, large-scale magnetic field amplification, and the radiation signature from gamma-ray bursts.

  17. Observation of ionization enhancement in two-color circularly polarized laser fields

    NASA Astrophysics Data System (ADS)

    Mancuso, Christopher A.; Dorney, Kevin M.; Hickstein, Daniel D.; Chaloupka, Jan L.; Tong, Xiao-Min; Ellis, Jennifer L.; Kapteyn, Henry C.; Murnane, Margaret M.

    2017-08-01

    When atoms are irradiated by two-color circularly polarized laser fields the resulting strong-field processes are dramatically different than when the same atoms are irradiated by a single-color ultrafast laser. For example, electrons can be driven in complex two-dimensional trajectories before rescattering or circularly polarized high harmonics can be generated, which was once thought impossible. Here, we show that two-color circularly polarized lasers also enable control over the ionization process itself and make a surprising finding: the ionization rate can be enhanced by up to 700 % simply by switching the relative helicity of the two-color circularly polarized laser field. This enhancement is experimentally observed in helium, argon, and krypton over a wide range of intensity ratios of the two-color field. We use a combination of advanced quantum and fully classical calculations to explain this ionization enhancement as resulting in part due to the increased density of excited states available for resonance-enhanced ionization in counter-rotating fields compared with co-rotating fields. In the future, this effect could be used to probe the excited state manifold of complex molecules.

  18. Magnetospheric Response to Interplanetary Field Enhancements: Coordinated Space-based and Ground-based Observations

    NASA Astrophysics Data System (ADS)

    Chi, Peter; Russell, Christopher; Lai, Hairong

    2014-05-01

    In general, asteroids, meteoroids and dust do not interact with the plasma structures in the solar system, but after a collision between fast moving bodies the debris cloud contains nanoscale dust particles that are charged and behave like heavy ions. Dusty magnetic clouds are then accelerated to the solar wind speed. While they pose no threat to spacecraft because of the particle size, the coherency imposed by the magnetization of the cloud allows the cloud to interact with the Earth's magnetosphere as well as the plasma in the immediate vicinity of the cloud. We call these clouds Interplanetary Field Enhancements (IFEs). These IFEs are a unique class of interplanetary field structures that feature cusp-shaped increases and decreases in the interplanetary magnetic field and a thin current sheet. The occurrence of IFEs is attributed to the interaction between the solar wind and dust particles produced in inter-bolide collisions. Previous spacecraft observations have confirmed that IFEs move with the solar wind. When IFEs strike the magnetosphere, they may distort the magnetosphere in several possible ways, such as producing a small indentation, a large scale compression, or a glancing blow. In any event if the IFE is slowed by the magnetosphere, the compression of the Earth's field should be seen in the ground-based magnetic records that are continuously recorded. Thus it is important to understand the magnetospheric response to IFE arrival. In this study, we investigate the IFE structure observed by spacecraft upstream of the magnetosphere and the induced magnetic field perturbations observed by networks of ground magnetometers, including the THEMIS, CARISMA, McMAC arrays in North America and the IMAGE array in Europe. We find that, in a well-observed IFE event on December 24, 2006, all ground magnetometer stations observed an impulse at approximately 1217 UT when the IFE was expected to arrive at the Earth's magnetopause. These ground stations spread across many

  19. Structure of Mercury's Global Magnetic Field Determined from MESSENGER Orbital Observations

    NASA Astrophysics Data System (ADS)

    Anderson, B. J.; Johnson, C. L.; Korth, H.; Purucker, M. E.; Winslow, R. M.; Slavin, J. A.; Solomon, S. C.; McNutt, R. L.; Raines, J. M.; Zurbuchen, T.

    2011-12-01

    On 18 March 2011, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was inserted into a near-polar orbit about Mercury with a periapsis altitude of 200 km, an inclination of 82.5°, an apoapsis altitude of 15,300 km, and nominal orbit period of 12 hours. Magnetometer (MAG) data acquired since 23 March provide multiple circuits in solar local time and planetary longitude and yield extensive coverage of the planetary magnetic field sufficient to resolve the dominant magnetic fields of internal and external origin. Plasma pressures exceeding the magnetic pressure are commonly found within ±30° latitude of the equator and complicate solutions for the planetary field that use conventional spherical harmonic analysis. However, because the planetary field constrains the locations of external currents (e.g., the magnetopause and tail currents) to be symmetric about the magnetic equator, the location of that equator can be identified from the geometry of the magnetic field without the need to correct for local plasma pressures and external currents. We identify Mercury's magnetic equator from the orbital positions at which the cylindrical radial magnetic field component vanishes and find that the magnetic equator is offset north of the geographic equator by 484 ± 11 km. With this offset for the dipole we then analyze the tilt, position, and intensity of the best-fit dipole moment and find that the global planetary field is best represented as a southward-directed dipole, centered on the spin axis, tilted from that axis by less than 2.5°, and having a moment of 195 ± 10 nT-RM3, where RM is Mercury's radius. Mercury's axially symmetric but equatorially asymmetric field may imply lateral variations in heat flow at the planet's core-mantle boundary. This solution provides the basis for defining Mercury-solar-magnetospheric coordinates used to order observations of Mercury's magnetosphere, constructing a model for the magnetopause and

  20. Spontaneous Formation of Closed-Field Torus Equilibrium via Current Jump Observed in an Electron-Cyclotron-Heated Plasma

    SciTech Connect

    Yoshinaga, T.; Uchida, M.; Tanaka, H.; Maekawa, T.

    2006-03-31

    Spontaneous current jump resulting in the formation of closed field equilibrium has been observed in electron-cyclotron-heated toroidal plasmas under steady external fields composed of a toroidal field and a relatively weak vertical field in the low aspect ratio torus experiment device. This bridges the gap between the open field equilibrium maintained by a pressure-driven current in the external field and the closed field equilibrium at a larger current. Experimental results and theoretical analyses suggest a current jump model that is based on the asymmetric electron confinement along the field line appearing upon simultaneous transitions of field topology and equilibrium.

  1. Phase microscopy using light-field reconstruction method for cell observation.

    PubMed

    Xiu, Peng; Zhou, Xin; Kuang, Cuifang; Xu, Yingke; Liu, Xu

    2015-08-01

    The refractive index (RI) distribution can serve as a natural label for undyed cell imaging. However, the majority of images obtained through quantitative phase microscopy is integrated along the illumination angle and cannot reflect additional information about the refractive map on a certain plane. Herein, a light-field reconstruction method to image the RI map within a depth of 0.2 μm is proposed. It records quantitative phase-delay images using a four-step phase shifting method in different directions and then reconstructs a similar scattered light field for the refractive sample on the focus plane. It can image the RI of samples, transparent cell samples in particular, in a manner similar to the observation of scattering characteristics. The light-field reconstruction method is therefore a powerful tool for use in cytobiology studies.

  2. Observation of spectrum effect on the measurement of intrinsic error field on EAST

    NASA Astrophysics Data System (ADS)

    Wang, Hui-Hui; Sun, You-Wen; Qian, Jin-Ping; Shi, Tong-Hui; Shen, Biao; Gu, Shuai; Liu, Yue-Qiang; Guo, Wen-Feng; Chu, Nan; He, Kai-Yang; Jia, Man-Ni; Chen, Da-Long; Xue, Min-Min; Ren, Jie; Wang, Yong; Sheng, Zhi-Cai; Xiao, Bing-Jia; Luo, Zheng-Ping; Liu, Yong; Liu, Hai-Qing; Zhao, Hai-Lin; Zeng, Long; Gong, Xian-Zu; Liang, Yun-Feng; Wan, Bao-Nian; The EAST Team

    2016-06-01

    Intrinsic error field on EAST is measured using the ‘compass scan’ technique with different n  =  1 magnetic perturbation coil configurations in ohmically heated discharges. The intrinsic error field measured using a non-resonant dominated spectrum with even connection of the upper and lower resonant magnetic perturbation coils is of the order {{b}r2,1}/{{B}\\text{T}}≃ {{10}-5} and the toroidal phase of intrinsic error field is around {{60}{^\\circ}} . A clear difference between the results using the two coil configurations, resonant and non-resonant dominated spectra, is observed. The ‘resonant’ and ‘non-resonant’ terminology is based on vacuum modeling. The penetration thresholds of the non-resonant dominated cases are much smaller than that of the resonant cases. The difference of penetration thresholds between the resonant and non-resonant cases is reduced by plasma response modeling using the MARS-F code.

  3. Initial ISEE magnetometer results - Shock observation. [magnetic field profiles across terrestrial bow and interplanetary shocks

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Greenstadt, E. W.

    1979-01-01

    A selection of early measurements is used to illustrate the three advantages brought by ISEE to the study of natural collisionless shocks. These advantages are the ability to resolve most space/time ambiguity by means of simultaneous two-point measurements, instrumentation to make comprehensive field and particle observations covering all important quantities, and the capacity to record data at high time resolution. Magnetic-field records from shocks of various types are presented; the types of shock include laminar, supercritical, quasi-perpendicular, high-beta, and quasi-parallel. The spacing of the two spacecraft and the resolution of the system are employed to develop numerous kinematic descriptions of the shocks and the waves that compose and surround them. Data from a single particle experiment are correlated with field data for three cases to demonstrate the important role of comprehensive instrumentation.

  4. Field Emission and Consequences as Observed and Simulated for CEBAF Upgrade Cryomodules

    SciTech Connect

    Marhauser, Frank; Johnson, Rolland; Rodriguez, Rodolfo; Degtiarenko, Pavel; Hutton, Andrew; Kharashvili, George; Reece, Charles; Rimmer, Robert

    2013-09-01

    High gamma and neutron radiation levels were monitored at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Laboratory (JLab) after installation of new cavity cryomodules and initial test runs in the frame of the ongoing 12 GeV upgrade program. The dose rates scaled exponentially with cavity accelerating fields, but were independent of the presence of an electron beam in the accelerator. Hence, field emission (FE) is the source of origin. This has led to concerns regarding the high field operation (100 MV per cryomodule) in the future 12 GeV era. Utilizing supercomputing, novel FE studies have been performed with electrons tracked through a complete cryomodule. It provides a principal understanding of experimental observations as well as ways to mitigate FE as best as practicable by identification of problematic cavities.

  5. Observations of phase deformation of monomeric systems in electric fields and subsequent polymerization

    NASA Astrophysics Data System (ADS)

    Bentenitis, Nikolaos; Krause, Sonja

    2001-03-01

    When a droplet from one phase of a phase-separated solution of two immiscible homopolymers is injected in the matrix of the other phase and a homogeneous electric field is applied, the droplet can deform either parallel or perpendicular to the electric field direction. In this work one or the other phase consisted of a monomer, which could be polymerized after being distorted in an electric field. DGEBA and Epoxidized Linseed Oil (ELO) were used as monomers along with deionized water and various silicone oils. For example, using DGEBA as the matrix and ELO as the dispersed phase, polymerization of the DGEBA was achieved using a cationic UV-sensitive initiator, that was dissolved only in the DGEBA. In addition, the deformation cycle in 0.1 Hz of deionized water in ELO was observed and compared with theoretical predictions. (Supported by NSF, DMR-9521265)

  6. Land subsidence caused by the East Mesa geothermal field, California, observed using SAR interferometry

    USGS Publications Warehouse

    Massonnet, D.; Holzer, T.; Vadon, H.

    1997-01-01

    Interferometric combination of pairs of synthetic aperture radar (SAR) images acquired by the ERS-1 satellite maps the deformation field associated with the activity of the East Mesa geothermal plant, located in southern California. SAR interferometry is applied to this flat area without the need of a digital terrain model. Several combinations are used to ascertain the nature of the phenomenon. Short term interferograms reveal surface phase changes on agricultural fields similar to what had been observed previously with SEASAT radar data. Long term (2 years) interferograms allow the study of land subsidence and improve prior knowledge of the displacement field, and agree with existing, sparse levelling data. This example illustrates the power of the interferometric technique for deriving accurate industrial intelligence as well as its potential for legal action, in cases involving environmental damages. Copyright 1997 by the American Geophysical Union.

  7. Observation of field emission from GeSn nanoparticles epitaxially grown on silicon nanopillar arrays

    NASA Astrophysics Data System (ADS)

    Di Bartolomeo, Antonio; Passacantando, Maurizio; Niu, Gang; Schlykow, Viktoria; Lupina, Grzegorz; Giubileo, Filippo; Schroeder, Thomas

    2016-12-01

    We apply molecular beam epitaxy to grow GeSn-nanoparticles on top of Si-nanopillars patterned onto p-type Si wafers. We use x-ray photoelectron spectroscopy to confirm a metallic behavior of the nanoparticle surface due to partial Sn segregation as well as the presence of a superficial Ge oxide. We report the observation of stable field emission (FE) current from the GeSn-nanoparticles, with turn on field of 65 {{V}} μ {{{m}}}-{{1}} and field enhancement factor β ˜ 100 at anode-cathode distance of ˜0.6 μm. We prove that FE can be enhanced by preventing GeSn nanoparticles oxidation or by breaking the oxide layer through electrical stress. Finally, we show that GeSn/p-Si junctions have a rectifying behavior.

  8. Proto-Type Development of Optical Wide-field Patrol Network and Test Observation

    NASA Astrophysics Data System (ADS)

    Park, J.; Choi, Y.; Jo, J.; Moon, H.; Yim, H.; Park, Y.; Hae, Y.; Park, S.; Choi, J.; Son, J.

    2014-09-01

    We present a prototype system developed for optical satellite tracking and its early test observation results. The main objective of the OWL (Optical Wide-field patroL) network is to get orbital information for Korean domestic satellites using optical means only and to maintain their orbital elements. The network is composed of 5 small wide-field telescopes deployed over the world. Each observing station is operated in fully robotic manner from receiving observation schedule to reporting the result, and controlled by the headquarter located in Daejeon, Korea, where orbit calculation and observation strategy will be determined. We developed a compact telescope system for robotic observation and easy maintenance. The telescope is 0.5m of aperture diameter with Rechey-Cretian configuration and its field of view is 1.1 deg. It is equipped with 4K CCD with 9um pixel size, and its pixel scale is 1.2 arcsec/pixel. A chopper wheel with variable speed is adopted to get more points in a single shot. The CCD camera and all the rotating parts (chopper wheel, de-rotator, and filter wheel) are integrated into one compact component called a wheel station. Each observing station is equipped with a fully automatic dome and heavy duty environment monitoring system. We could get an image every 20 seconds and up to ~100 trail points in a single exposure. Each point is time-tagged by ~1/1000 second precision. For one of best cases, we could estimate satellite position with RMS ~ 0.5km accuracy in the along-track with only 4 exposures (~100 points). The first system was installed at the Mongolian site after completing verification test at the testbed site in Daejeon, Korea. The second and third system will be installed in the end of this year.

  9. Constraints on the Observed Zonal Flows from the Magnetic Fields in Giant Planets

    NASA Astrophysics Data System (ADS)

    Liu, J. J.; Stevenson, D. J.

    2003-05-01

    The zonal winds on the surface of the giant planets are very strong ( 100m/s ) and stable (on a decadal time scale). Observations by the Galileo probe suggest that the zonal flow might be deep seated. However, the magnitude of the zonal flow must be reduced to a small value in the interior of the giant planets because the flow is defined relative to the magnetic field frame of reference (System III) and very large zonal flows can not be tolerated in a high conductivity region. The mechanisms for reducing the magnitude of the zonal flow and the coupling between the zonal flow and magnetic field are unclear. Here we use a coupled Navier-Stokes equation and the magnetic induction equation in steady state to study this. From Navier-Stokes, we find that the zonal flow vth can be expressed in three parts: vth(s,z) = a(s) + Bth2/4μ0ρ Ω s + F(grad(ρ ),Bth)/4μ0ρ Ω s, where a(s) is an arbitrary function of cylindrical radius (s) only, z is the coordinate parallel to the rotation axis, Bth is the toroidal field, μ 0 is the permeability of free space, ρ (s,z) is the density, Ω is the planetary rotation and F is a function of the density gradient (grad(ρ )) and the toroidal magnetic field. The first part is the geostrophic flow consistent with the Taylor-Proudman theorem. The second part is due to the tensile force that arises from the curvature of the toroidal field, and always leads a prograde flow. The third part comes from the density variation and meridional gradient of the toroidal field, and may lead to the prograde flow or the retrograde flow. Whether the flow observed on the surface could be reduced to small values in the interior will depend on the direction of the flow, the density gradient and also the structure of the toroidal magnetic field. It can also be shown that the magnitude of the generated toroidal magnetic field in the interior of the giant planets is very large and around 10 Tesla for consistency with the observed zonal flow on the surface of

  10. Orbit and Gravity Field Solutions from Swarm GPS Observations - First Result

    NASA Astrophysics Data System (ADS)

    Jaeggi, A.; Dahle, C.; Arnold, D.; Bock, H.; Flechtner, F.

    2014-12-01

    Although ESA's Earth Explorer Mission Swarm is primarily dedicated to measure the Earth's magnetic field, it may also serve as a gravity field mission. Equipped with GPS receivers, accelerometers, star-tracker assemblies and laser retro-reflectors, the three Swarm satellites are potentially capable to be used as a high-low satellite-to-satellite tracking (hl-SST) observing system, following the missions CHAMP (first single-satellite hl-SST mission), GRACE (twin-satellite mission with additional ultra-precise low-low SST and GOCE (single-satellite mission additionally equipped with a gradiometer). GRACE, dedicated to measure the time-variability of the gravity field, is the only mission still in orbit, but its lifetime will likely end before launch of its follow-on mission GRACE-FO in August 2017 primarily due to aging of the onboard batteries after meanwhile more than 12 years of operation. Swarm is probably a good candidate to provide time-variable gravity field solutions and to close a potential gap between GRACE and GRACE-FO. Consisting of three satellites, Swarm also offers to use inter-satellite GPS-derived baselines as additional observations. However, as of today it is not clear if such information will substantially improve the gravity field solutions. Nevertheless, the properties of the Swarm constellation with two lower satellites flying in a pendulum-like orbit and a slightly differently inclined third satellite at higher altitude still represent a unique observing system raising expectations at least compared to CHAMP derived time-variable gravity field solutions. Whatever processing method will be applied for Swarm gravity field recovery, its success strongly depends on the quality of the Swarm Level 1b data as well as the quality of the derived Swarm orbits. With first Level 1b data sets available since mid of May 2014 (excluding accelerometer data), first results for Swarm orbits and baselines, as well as Swarm gravity field solutions are presented

  11. Finite field of view effects on inversion of limb thermal emission observations. [balloon sounding of stratosphere

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Guo, J.; Conrath, B. J.; Kunde, V. G.; Maguire, W. C.

    1985-01-01

    It is pointed out that the technique of thermal emission spectroscopy provides an effective means for remote sounding of stratospheric temperature structure and constituent distributions. One procedure for measuring the stratospheric infrared spectrum involves the conduction of observations along ray paths tangent to the stratospheric limb. Thermal emission limb tangent observations have certain advantages compared to other types of observations. The techniques for determining temperature and trace gas distributions from limb thermal emission radiances are based on the assumption that the bulk of opacity lies near the tangent point. Ideally, the field of view (FOV) of the observing instrument should be very small. The effect of a finite FOV is to reduce the spatial resolution of the retrieved temperature and constituent profiles. The present investigation is concerned with the effects of the FOV on the inversion of infrared thermal emission measurements for balloon platforms. Attention is given to a convenient method for determining the weighting functions.

  12. 1969 - 2010: Multicolor Photometric Observations of Population II Field Horizontal-Branch Stars

    NASA Astrophysics Data System (ADS)

    Philip, A. G. Davis

    2010-05-01

    From 1969 to 2010 I have been involved in a photometric study of Population II Field Horizontal-Branch stars. I started by making Stromgren four-color observations at Kitt Peak National Observatory and then Cerro Tololo Inter-American Observatory. I had taken spectral plates of all my selected areas on which I marked all the A-type stars. These stars were then observed photometrically. New FHB stars could be identified by their large c1 indices, caused by their greater (u-b) colors. Later four new filters were added ( U V B S ). With Richard Boyle of the Vatican Observatory we observed on Mt. Graham (Arizona) on the Vatican Advanced Technology Telescope.We plan follow-up observations of the new FHB stars found.

  13. 1969 to 2010: Multicolor Photometric Observations of Population II Field Horizontal-Branch Stars

    NASA Astrophysics Data System (ADS)

    Philip, A. G. D.

    2011-04-01

    From 1969 to 2010 I have been involved in a photometric study of Population II Field Horizontal-Branch Stars and published several papers on this topic in BOTT from 1967 thru 1972. I started by making Strömgren four-color observations at Kitt Peak National Observatory and then at Cerro Tololo Inter-American Observatory. I had taken spectral plates of all my selected areas on which I marked all the A-type stars. These stars were then observed photometrically. New FHB stars could be identified by their large c indices, caused by their greater (u-b) colors. Later four new filters were added (U, V, B, S). With Richard Boyle of the Vatican Observatory we observed on Mt. Graham (Arizona) on the Vatican Advanced Technology Telescope. We are making follow-up observations of the new FHB stars found.

  14. High-intensity geomagnetic field 'spike' observed at ca. 3000 cal BP in Texas, USA

    NASA Astrophysics Data System (ADS)

    Bourne, Mark D.; Feinberg, Joshua M.; Stafford, Thomas W.; Waters, Michael R.; Lundelius, Ernest; Forman, Steven L.

    2016-05-01

    By observing the fluctuations in direction and intensity of the Earth's magnetic field through time, we increase our understanding of the fluid motions of the Earth's outer core that sustain the geomagnetic field, the geodynamo. Recent archaeomagnetic studies in the Near East have found extremely rapid increases - 'spikes' - in geomagnetic field intensity at ca. 3000 yr cal BP. These observations have proved problematic for our current understanding of core-flow. However, until now, these geomagnetic spikes had not been observed outside of the Near East, where they have been preserved in metallurgical slag and fired, mud brick walls. We present a new, fully oriented, geomagnetic secular variation and relative palaeointensity (RPI) record for the last 17,000 yr from Hall's Cave, Texas, whose complete, >3.8 m thick sedimentary sequence spans from the present to 16 , 850 ± 110 RC yr BP (Modern to 20,600 cal BP). Within the stable, cool climate of the cave, pedogenic and bioturbation processes are negligible to non-existent, thereby limiting post-depositional physical and geochemical alteration of the magnetic record. The sub-aerial and subterranean setting of the sedimentary sequence in Hall's Cave enabled us to collect oriented palaeomagnetic cubes from a previously excavated stratigraphic section. The palaeomagnetic samples yielded high-quality vectors. An age model for the sequence, determined using 15 AMS 14C-dates on individual bones from microvertebrates, was combined with the palaeomagnetic data to construct a secular variation record. The record is in broad agreement with predictions by Holocene field models for the site's location. However, starting ca. 3000 yr ago, the RPI data indicate an almost four-fold increase in geomagnetic field intensity lasting several hundred years. This record presents well-dated evidence, obtained using conventional techniques, for the existence of a geomagnetic intensity spike in North America that is contemporaneous with the

  15. Magneto-frictional Modeling of Coronal Nonlinear Force-free Fields. II. Application to Observations

    NASA Astrophysics Data System (ADS)

    Guo, Y.; Xia, C.; Keppens, R.

    2016-09-01

    A magneto-frictional module has been implemented and tested in the Message Passing Interface Adaptive Mesh Refinement Versatile Advection Code (MPI-AMRVAC) in the first paper of this series. Here, we apply the magneto-frictional method to observations to demonstrate its applicability in both Cartesian and spherical coordinates, and in uniform and block-adaptive octree grids. We first reconstruct a nonlinear force-free field (NLFFF) on a uniform grid of 1803 cells in Cartesian coordinates, with boundary conditions provided by the vector magnetic field observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) at 06:00 UT on 2010 November 11 in active region NOAA 11123. The reconstructed NLFFF successfully reproduces the sheared and twisted field lines and magnetic null points. Next, we adopt a three-level block-adaptive grid to model the same active region with a higher spatial resolution on the bottom boundary and a coarser treatment of regions higher up. The force-free and divergence-free metrics obtained are comparable to the run with a uniform grid, and the reconstructed field topology is also very similar. Finally, a group of active regions, including NOAA 11401, 11402, 11405, and 11407, observed at 03:00 UT on 2012 January 23 by SDO/HMI is modeled with a five-level block-adaptive grid in spherical coordinates, where we reach a local resolution of 0\\buildrel{\\circ}\\over{.} 06 pixel-1 in an area of 790 Mm × 604 Mm. Local high spatial resolution and a large field of view in NLFFF modeling can be achieved simultaneously in parallel and block-adaptive magneto-frictional relaxations.

  16. Magnetic field observations in the near-field the 28 June 1992 Mw 7.3 Landers, California, earthquake

    USGS Publications Warehouse

    Johnston, M.J.; Mueller, R.J.; Sasai, Yoichi

    1994-01-01

    Recent reports suggest that large magnetic field changes occur prior to, and during, large earthquakes. Two continuously operating proton magnetometers, LSBM and OCHM, at distances of 17.3 and 24.2 km, respectively, from the epicenter of the 28 June 1992 Mw 7.3 Landers earthquake, recorded data through the earthquake and its aftershocks. These two stations are part of a differentially connected array of proton magnetometers that has been operated along the San Andreas fault since 1976. The instruments have a sensitivity of 0.25 nT or better and transmit data every 10 min through the GOES satellite to the USGS headquarters in Menlo Park, California. Seismomagnetic offsets of −1.2 ± 0.6 and −0.7 ± 0.7 nT were observed at these sites. In comparison, offsets of −0.3 ± 0.2 and −1.3 ± 0.2 nT were observed during the 8 July 1986 ML 5.9 North Palm Springs earthquake, which occurred directly beneath the OCHM magnetometer site. The observations are generally consistent with seismomagnetic models of the earthquake, in which fault geometry and slip have the same from as that determined by either inversion of the seismic data or inversion of geodetically determined ground displacements produced by the earthquake. In these models, right-lateral rupture occurs on connected fault segments in a homogeneous medium with average magnetization of 2 A/m. The fault-slip distribution has roughly the same form as the observed surface rupture, and the total moment release is 1.1 × 1020 Nm. There is no indication of diffusion-like character to the magnetic field offsets that might indicate these effects result from fluid flow phenomena. It thus seems unlikely that these earthquake-generated offsets and those produced by the North Palm Springs earthquake were generated by electrokinetic effects. Also, there are no indications of enhanced low-frequency magnetic noise before the earthquake at frequencies below 0.001 Hz.

  17. Surprises from the field: Novel aspects of aeolian saltation observed under natural turbulence

    NASA Astrophysics Data System (ADS)

    Martin, R. L.; Kok, J. F.; Chamecki, M.

    2015-12-01

    The mass flux of aeolian (wind-blown) sediment transport - critical for understanding earth and planetary geomorphology, dust generation, and soil stability - is difficult to predict. Recent work suggests that competing models for saltation (the characteristic hopping of aeolian sediment) fail because they do not adequately account for wind turbulence. To address this issue, we performed field deployments measuring high-frequency co-variations of aeolian saltation and near-surface winds at multiple sites under a range of conditions. Our observations yield several novel findings not currently captured by saltation models: (1) Saltation flux displays no significant lag relative to horizontal wind velocity; (2) Characteristic height of the saltation layer remains constant with changes in shear velocity; and (3) During saltation, the vertical profile of mean horizontal wind velocity is steeper than expected from the Reynolds stress. We examine how the interactions between saltation and turbulence in field settings could explain some of these surprising observations.

  18. Observation of Bose-Einstein condensation in a strong synthetic magnetic field

    NASA Astrophysics Data System (ADS)

    Kennedy, Colin J.; Burton, William Cody; Chung, Woo Chang; Ketterle, Wolfgang

    2015-10-01

    Extensions of Berry’s phase and the quantum Hall effect have led to the discovery of new states of matter with topological properties. Traditionally, this has been achieved using magnetic fields or spin-orbit interactions, which couple only to charged particles. For neutral ultracold atoms, synthetic magnetic fields have been created that are strong enough to realize the Harper-Hofstadter model. We report the first observation of Bose-Einstein condensation in this system and study the Harper-Hofstadter Hamiltonian with one-half flux quantum per lattice unit cell. The diffraction pattern of the superfluid state directly shows the momentum distribution of the wavefunction, which is gauge-dependent. It reveals both the reduced symmetry of the vector potential and the twofold degeneracy of the ground state. We explore an adiabatic many-body state preparation protocol via the Mott insulating phase and observe the superfluid ground state in a three-dimensional lattice with strong interactions.

  19. Chandra X-ray Observations of Young Clusters. Volume II; Orion Flanking Fields Data

    NASA Technical Reports Server (NTRS)

    Ramirez, Solange V.; Rebull, Luisa; Stauffer, John; Strom, Stephen; Hillenbrand, Lynne; Hearty, Thomas; Kopan, Eugene L.; Pravdo, Steven; Makidon, Russell; Jones, Burton

    2004-01-01

    We present results of Chandra observations of two flanking fields (FFs) in Orion, outside the Orion Nebula Cluster (ONC). The observations were taken with the ACIS-I camera with an exposure time of about 48 ks each field. We present a catalog of 417 sources, which includes X-ray luminosity, optical and infrared photometry, and X-ray variability information. We have found 91 variable sources, 33 of which have a flarelike light curve and 11 of which have a pattern of a steady increase or decrease over a 10 hr period. The optical and infrared photometry for the stars identified as X-ray sources are consistent with most of these objects being pre-main-sequence stars with ages younger than 10 Myr. We present evidence for an age difference among the X-ray-selected samples of NGC 2264, Orion FFs, and ONC, with NGC 2264 being the oldest and ONC being the youngest.

  20. The effect of the interplanetary magnetic field on sidereal variations observed at medium depth underground detectors

    NASA Technical Reports Server (NTRS)

    Humble, J. E.; Fenton, A. G.

    1985-01-01

    It has been known for some years that the intensity variations in sidereal time observed by muon detectors at moderate underground depths are sensitive to the polarity of the interplanetary magnetic field (ipmf) near the Earth. There are differences in the response to these anisotropies as observed in the Norhtern and southern hemispheres. When fully understood, the nature of the anisotropy seems likely to provide information on the 3-dimensional structure of the heliomagnetosphere, its time variations, and its linking with the local interstellar field. The summation harmonic dials for the sidereal diurnal variation during 1958 to 1982 show that there is a strong dependence on whether the ipmf near the Earth is directed outwards from the Sun or inwards it.

  1. Chandra X-ray Observations of Young Clusters. Volume II; Orion Flanking Fields Data

    NASA Technical Reports Server (NTRS)

    Ramirez, Solange V.; Rebull, Luisa; Stauffer, John; Strom, Stephen; Hillenbrand, Lynne; Hearty, Thomas; Kopan, Eugene L.; Pravdo, Steven; Makidon, Russell; Jones, Burton

    2004-01-01

    We present results of Chandra observations of two flanking fields (FFs) in Orion, outside the Orion Nebula Cluster (ONC). The observations were taken with the ACIS-I camera with an exposure time of about 48 ks each field. We present a catalog of 417 sources, which includes X-ray luminosity, optical and infrared photometry, and X-ray variability information. We have found 91 variable sources, 33 of which have a flarelike light curve and 11 of which have a pattern of a steady increase or decrease over a 10 hr period. The optical and infrared photometry for the stars identified as X-ray sources are consistent with most of these objects being pre-main-sequence stars with ages younger than 10 Myr. We present evidence for an age difference among the X-ray-selected samples of NGC 2264, Orion FFs, and ONC, with NGC 2264 being the oldest and ONC being the youngest.

  2. Low-frequency magnetic field fluctuations in comet P/Halley's magnetosheath - Giotto observations

    NASA Technical Reports Server (NTRS)

    Glassmeier, K. H.; Neubauer, F. M.; Acuna, M. H.; Mariani, F.

    1987-01-01

    The interaction region between comets and the solar wind is characterized by large amplitude, low frequency magnetic field fluctuations, both within the upstream region as well as in the magnetosheath. Magnetosheath observations of the magnetic field experiment onboard Giotto indicate values of delta B/B equal to about O(1). Power spectral peaks appear at frequencies of 10mHz with the spectrum exhibiting a power law dependence with an exponent of the order 2. Radial variation of the fluctuation level does not clearly increase with decreasing distance from the cometary nucleus as observed by the magnetometer onboard Vega-1 and as expected from quasi-linear theory. The entrance into the cometary bow shock is furthermore characterized by an order of magnitude increase of the fluctuation level, both on the in- and outbound pass of Giotto.

  3. Simulation of Satellite Observations of Induced Magnetic Fields using Scripted Finite Element Methods

    NASA Astrophysics Data System (ADS)

    Ribaudo, J. T.; Constable, C.; Parker, R. L.

    2009-12-01

    Scripted finite element methods allow flexible investigations of the influence of asymmetric external source fields and 3-dimensional (3D) internal electrical conductivity structure in the problem of global geomagnetic depth sounding. Our forward modeling is performed in the time and frequency domains via FlexPDE, a commercial finite element modeling package, and the technique has been validated against known solutions to 3D steady state and time-dependent problems. The induction problem is formulated in terms of the magnetic vector potential and electric scalar potential, and mesh density is managed both explicitly and through adaptive mesh refinement. We investigate the effects of 3D Earth conductivity on both satellite and ground-based magnetic field observations in the form of a geographically varying conductance map of the crust and oceans overlying a radially symmetric core and mantle. This map is used in conjunction with a novel boundary condition based on Ampere's Law to model variable near-surface induction without the computational expense of a 3D crust/ocean mesh and is valid for magnetic signals in the frequency range of interest for satellite induction studies. The simulated external magnetic field is aligned with Earth's magnetic pole, rather than its rotational pole, and increases in magnitude along the Earth/Sun axis. Earth rotates through this field with a period of 24 hours. Electromagnetic c-responses estimated from satellite data under the assumption that the primary and induced fields are dipolar in structure are known to be biased with respect to local time. We investigate the influence of Earth's rotation through the non-uniform external field on these c-responses, to determine whether this can explain the observed local time bias.

  4. Magnetic helicity estimations in models and observations of the solar magnetic field

    NASA Astrophysics Data System (ADS)

    Valori, Gherardo; Pariat, Etienne; Anfinogentov, Sergey; Chen, Feng; Georgoulis, Manolis; Guo, Yang; Liu, Yang; Moraitis, Kostas; Thalmann, Julia K.; Yang, Shangbin

    2017-04-01

    Magnetic helicity, as one of the few conserved quantities in magneto-hydrodynamics, is often invoked as the principle driving the generation and structuring of magnetic fields in a variety of environments, from dynamo models in stars and planets, to post-disruption reconfigurations of tokamak's plasmas. Most particularly magnetic helicity has raised the interest of solar physicists, since helicity is suspected to represent a key quantity for the understanding of solar flares and the generation of coronal mass ejections. In recent years, several methods of estimation of magnetic helicity have been proposed and already applied to observations and numerical simulations. However, no systematic comparison of accuracy, mutual consistency, and reliability of such methods has ever been performed. We present the results of the first benchmark of several finite-volume methods in estimating magnetic helicity in 3D test models. In addition to finite volume methods, two additional methods are also included that estimate magnetic helicity based either on the field line's twist, or on the field's values on one boundary and an inferred minimal volume connectivity. The employed model tests range from solutions of the force-free equations to 3D magneto-hydrodynamical numerical simulations. Almost all methods are found to produce the same value of magnetic helicity within few percent in all tests. However, methods show differences in the sensitivity to numerical resolution and to errors in the solenoidal property of input fields. Our benchmark of finite volume methods allows to determine the reliability and precision of estimations of magnetic helicity in practical cases. As a next step, finite volume methods are used to test estimation methods that are based on the flux of helicity through one boundary, in particular for applications to observation-based models of coronal magnetic fields. The ultimate goal is to assess if and how can helicity be meaningfully used as a diagnostic of

  5. Observation of enhanced field emission properties of Au/TiO2 nanocomposite

    NASA Astrophysics Data System (ADS)

    Patil, Girish P.; Bagal, Vivekanand S.; Suryawanshi, Sachin R.; Late, Dattatray J.; More, Mahendra A.; Chavan, Padmakar G.

    2016-05-01

    Simple and low-cost method of thermal annealing was used to decorate Gold (Au) nanoparticles on aligned TiO2 nanotubes. The aligned TiO2 nanotubes were decorated by Au nanoparticles with an average diameter of 9, 18 and 28 nm (aligned TiO2 nanotubes referred as specimen A and TiO2 nanotubes decorated by Au nanoparticles with average diameter of 9, 18 and 28 nm are referred as specimen B, C and D, respectively). The detailed characterization such as structural, morphological and elemental analysis of TiO2 and Au/TiO2 nanocomposite have been carried out using X-ray diffraction, field emission scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and Raman spectroscopy. Furthermore, the meticulous comparative field emission characteristics of the aligned TiO2 nanotubes and Au/TiO2 nanocomposite have been performed. The turn-on field defined for the current density of 10 μA/cm2 has been found to be 3.9, 2.8, 3.2 and 3.7 V/μm for specimen A, B, C and D, respectively. The observed low turn-on field of specimen B has been found to be superior than the other semiconducting nanocomposites reported in the literature. The emission current stability over a period of 3 h is found to be better for all the specimens. To the best of our knowledge, a systematic field emission study of Au/TiO2 nanocomposite has not been explored. The observed superior field emission study of Au/TiO2 nanocomposite indicates their possible use in micro/nanoelectronic devices.

  6. Kilometric radio waves generated along auroral field lines observed by ground facilities - A theoretical model

    NASA Technical Reports Server (NTRS)

    Ziebell, L. F.; Wu, C. S.; Yoon, Peter H.

    1991-01-01

    A theory of generation of radio waves observed by ground-based facilities in the frequency range 150-700 kHz is discussed. This work is a continuation of an earlier discussion (Wu et al., 1989) in which it was proposed that the trapped electrons along the auroral field lines can lead to a cyclotron instability which amplifies the whistler waves observed at ground level. The objective of the present study is to investigate the propagation effect on the wave amplification and to examine whether the proposed mechanism is indeed viable.

  7. Kilometric radio waves generated along auroral field lines observed by ground facilities - A theoretical model

    NASA Technical Reports Server (NTRS)

    Ziebell, L. F.; Wu, C. S.; Yoon, Peter H.

    1991-01-01

    A theory of generation of radio waves observed by ground-based facilities in the frequency range 150-700 kHz is discussed. This work is a continuation of an earlier discussion (Wu et al., 1989) in which it was proposed that the trapped electrons along the auroral field lines can lead to a cyclotron instability which amplifies the whistler waves observed at ground level. The objective of the present study is to investigate the propagation effect on the wave amplification and to examine whether the proposed mechanism is indeed viable.

  8. Observing the nonequilibrium dynamics of the quantum transverse-field Ising chain in circuit QED.

    PubMed

    Viehmann, Oliver; von Delft, Jan; Marquardt, Florian

    2013-01-18

    We show how a quantum Ising spin chain in a time-dependent transverse magnetic field can be simulated and experimentally probed in the framework of circuit QED with current technology. The proposed setup provides a new platform for observing the nonequilibrium dynamics of interacting many-body systems. We calculate its spectrum to offer a guideline for its initial experimental characterization. We demonstrate that quench dynamics and the propagation of localized excitations can be observed with the proposed setup and discuss further possible applications and modifications of this circuit QED quantum simulator.

  9. Field-aligned currents observed by the OGO 5 and Triad satellites

    NASA Technical Reports Server (NTRS)

    Sugiura, M.

    1975-01-01

    The existence of field-aligned currents in the polar cap boundary layer as a permanent feature of the magnetosphere is investigated. Magnetic field observations from Triad at 800 km altitude and from OGO 5 in the high-altitude magnetosphere are examined. Results indicate that in the morning half of the boundary layer, currents flow into the ionosphere, and that the current direction is reversed in the afternoon half of the layer. The Triad data further indicate that the net current is a maximum near 1500 MLT and that there may be a secondary maximum during early morning hours. According to the Isis 2 electron observations, the locations of these maximums of field-aligned net current roughly match those of two maximums in the isointensity contours for 150 ev electrons. It is proposed that the polar cap boundary current is driven by a current generator in the magnetotail, or ultimately in the solar wind. It is suggested that the large scale field-aligned currents in the polar cap boundary layer are associated with the dominance of protons on the morning side and of electrons on the afternoon side near the poleward edge of the precipitation zone along the auroral oval.

  10. Neural network integration of field observations for soil endocrine disruptor characterisation.

    PubMed

    Aitkenhead, M J; Rhind, S M; Zhang, Z L; Kyle, C E; Coull, M C

    2014-01-15

    A neural network approach was used to predict the presence and concentration of a range of endocrine disrupting compounds (EDCs), based on field observations. Soil sample concentrations of endocrine disrupting compounds (EDCs) and site environmental characteristics, drawn from the National Soil Inventory of Scotland (NSIS) database, were used. Neural network models were trained to predict soil EDC concentrations using field observations for 184 sites. The results showed that presence/absence and concentration of several of the EDCs, mostly no longer in production, could be predicted with some accuracy. We were able to predict concentrations of seven of 31 compounds with r(2) values greater than 0.25 for log-normalised values and of eight with log-normalised predictions converted to a linear scale. Additional statistical analyses were carried out, including Root Mean Square Error (RMSE), Mean Error (ME), Willmott's index of agreement, Percent Bias (PBIAS) and ratio of root mean square to standard deviation (RSR). These analyses allowed us to demonstrate that the neural network models were making meaningful predictions of EDC concentration. We identified the main predictive input parameters in each case, based on a sensitivity analysis of the trained neural network model. We also demonstrated the capacity of the method for predicting the presence and level of EDC concentration in the field, identified further developments required to make this process as rapid and operator-friendly as possible and discussed the potential value of a system for field surveys of soil composition. © 2013.

  11. Electric field observations of time constants related to charging and charge neutralization processes in the ionosphere

    NASA Technical Reports Server (NTRS)

    Maynard, N. C.; Evans, D. S.; Troim, J.

    1982-01-01

    The Polar 5 electric field results are reviewed, and the transients from Polar 3 are presented. The phenomena are discussed from the standpoint of space charge. On the basis of the Polar 5 results, the large magnitude of the electric field from Polar 3 is seen as indicating that the observed space charge was probably within a few km or less of the payload. Reference is made to Cole's prediction (1960) that charges in the ionosphere would reach equilibrium with a time constant of the order of a few microsec. The processes involved in the two cases presented here require time constants of the order of ms. If the sheath dimensions are taken to be between 50 and 100 m, which is not considered unreasonable in view of the electric field measurements, then a qualitative estimate of the neutralization time would be the transit time for ions across the sheath. Since the kinetic velocity of a 1-eV proton is approximately 14 m/s, it would traverse the distance in 4 to 8 ms, assuming freedom of movement across magnetic field lines. This is the order of the decay times observed on Polar 5.

  12. Observation of field-induced Fermi surface reconstruction in CeRhIn5

    NASA Astrophysics Data System (ADS)

    Yuan, Huiqiu; Jiao, Lin; Weng, Zongfa; Chen, Ye; Steglich, Frank; Graf, David; Singleton, John; Jaime, Marcelo; Bauer, Eric; Thompson, Joe

    2015-03-01

    CeRhIn5 provides a prototype compound for studying quantum criticality and its interplay with superconductivity. Application of pressure suppresses the antiferromagnetic (AF) order and gives rise to superconductivity. A sharp change of Fermi surface was observed just at the pressure-tuning AF quantum critical point (QCP), which was argued to support the scenario of local quantum criticality. By measuring the dHvA oscillations and specific heat in a pulsed magnetic field, we have demonstrated the existence of a field-induced AF QCP around Bc0 =50T in this compound. In this presentation, we will report the measurements of dHvA effect and Hall resistivity of CeRhIn5 performed by using the 45T hybrid magnet and the pulsed field magnet at NHMFL. Field-induced changes of the dHvA frequencies and Hall coefficient are observed around B* =31T. Detailed analyses suggest that the Fermi surface reconstruction at B* corresponds to a localized-itinerant transition of Ce 4f-electrons attributed to the Kondo effect. Our results indicate that multiple quantum phase transitions may exist in CeRhIn5 which can be classified by the measurements of Fermi surface topology.

  13. COMPARISON BETWEEN OBSERVATION AND SIMULATION OF MAGNETIC FIELD CHANGES ASSOCIATED WITH FLARES

    SciTech Connect

    Li Yixuan; Jing Ju; Wang Haimin; Fan Yuhong E-mail: jj4@njit.edu E-mail: yfan@ucar.edu

    2011-01-20

    It has been a long-standing question in solar physics how magnetic field structure changes with eruptive events (e.g., flares and coronal mass ejections). In this Letter, we present the eruption-associated changes in the magnetic inclination angle, the horizontal component of magnetic field vectors, and the Lorentz force. The analysis is based on the observation of the X3.4 flare on 2006 December 13 and in comparison to the numerical simulation of Fan. Both observation and simulation show that (1) the magnetic inclination angle in the decayed peripheral penumbra increases, while that in the central area close to the flaring polarity inversion line (PIL) deceases after the flare; (2) the horizontal component of magnetic field increases at the lower altitude near the flaring PIL after the flare. The result suggests that the field lines at the flaring neutral line turn to more horizontal near the surface, that is in agreement with the prediction of Hudson et al.

  14. Calculating Coronal Mass Ejection Magnetic Field at 1 AU Using Solar Observables

    NASA Astrophysics Data System (ADS)

    Chen, J.; Kunkel, V.

    2013-12-01

    It is well-established that most major nonrecurrent geomagnetic storms are caused by solar wind structures with long durations of strong southward (Bz < 0) interplanetary magnetic field (IMF). Such geoeffective IMF structures are associated with CME events at the Sun. Unfortunately, neither the duration nor the internal magnetic field vector of the ejecta--the key determinants of geoeffectiveness--is measurable until the observer (e.g., Earth) passes through the ejecta. In this paper, we discuss the quantitative relationships between the ejecta magnetic field at 1 AU and remotely observable solar quantities associated with the eruption of a given CME. In particular, we show that observed CME trajectories (position-time data) within, say, 1/3 AU of the Sun, contain sufficient information to allow the calculation of the ejecta magnetic field (magnitude and components) at 1 AU using the Erupting Flux Rope (EFR) model of CMEs. Furthermore, in order to accurately determine the size and arrival time of the ejecta as seen by a fixed observer at 1 AU (e.g., ACE), it is essential to accurately calculate the three-dimensional geometry of the underlying magnetic structure. Accordingly, we have extended the physics-based EFR model to include a self-consistent calculation of the transverse expansion taking into account the non-symmetric drag coupling between an expanding CME flux rope and the ambient solar wind. The dependence of the minor radius of the flux rope at 1 AU that determines the perceived size of the ejecta on solar quantities is discussed. Work supported by the NRL Base Program.

  15. Convulsive threshold in humans and rats and magnetic field changes: observations during total solar eclipse.

    PubMed

    Keshavan, M S; Gangadhar, B N; Gautam, R U; Ajit, V B; Kapur, R L

    1981-03-10

    Convulsive thresholds were measured in 26 psychiatric patients who were receiving electroconvulsive treatment, and in 8 rats subjects to electroconvulsive shocks, during the recent the recent total solar eclipse day (February 16th, 1980) and on control days. Our results showed that there was a significant reduction in the convulsive thresholds of both humans and rats at the time of solar eclipse, probably occurring due to the observed geomagnetic field variation of 19 Gammas.

  16. ESTIMATION OF MAGNETIC FIELD IN THE SOLAR CORONAL STREAMERS THROUGH LOW FREQUENCY RADIO OBSERVATIONS

    SciTech Connect

    Ramesh, R.; Kathiravan, C.; Sastry, Ch. V. E-mail: kathir@iiap.res.i

    2010-03-10

    The observations of circularly polarized thermal radio emission from solar coronal streamers at two low frequencies, viz., 77 and 109 MHz, are used to estimate the magnetic field strength (B) at their corresponding radial distances r{approx} 1.7 and 1.5 solar radii given by the electron density model of Newkirk. The estimated values of B at the above two distances are {approx}5 +- 1 G and 6 +- 2 G, respectively.

  17. Observations of Field Line Resonances by Low-Altitude ST-5 Satellites

    NASA Technical Reports Server (NTRS)

    Le, G.; Chi, P. J.; Strangeway, R. J.; Slavin, J. A.

    2010-01-01

    Space Technology 5 (ST-5) mission is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6deg inclination angle. Due to the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pe 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2- 3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that this unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

  18. TAOS Project: Searching for Variable Stars in the Selected TAOS Fields and Optical Followup Observations

    NASA Astrophysics Data System (ADS)

    Ngeow, Chow Choong; Chang, D.; Pan, K.; Chung, T.; Koptelova, E.; TAOS Collaboration

    2010-05-01

    The Taiwan-American Occultation Survey (TAOS) project is aimed to find Kuiper Belt Objects (KBO) and measure their size distribution using the occultation technique. The TAOS project employed four 20-inch wide-field (F/1.9, 3 degree-squared FOV) telescopes, equipped with a 2K x 2K CCD, to simultaneously monitor the same patch of the sky. All four TAOS telescopes, which can be operated automatically, were located at the Lulin Observatory in central Taiwan. The TAOS project has been continuously taking data since 2005. In addition of finding KBO, the dense sampling strategy employed in TAOS can also be used to find variable stars. We report the search of variable stars from selected TAOS fields at this Meeting. For example, we found about 50 candidate variables (out of 2600 stars) in TAOS 60 Field (RA: 04h48m00s, DEC: +20d46m20s, with limiting magnitudes about15 mag. at S/N=10), including three previously known variables, using sigma deviation and Stetson's J-index methods. The available data in this field spanned about 150 days in time. However, TAOS observations were conducted using a customized filter. We therefore initiated a followup program to observe and construct the light curves of these candidate variables in the BVRI bands, using the Lulin's One-Meter telescope, Lulin's SLT telescope (16-inch aperture) and 32-inch telescope from the Tenagra II Observatory. The multi-band optical followup observation will help in improving the classification of these candidates, estimate their BVRI mean magnitudes, colors as well as extinction. This will enable a wide range of research in astrophysics for these variables. We also present our preliminary results based on the first season of the followup observations. CCN acknowledges the support from NSC 98-2112-M-008-013-MY3.

  19. Estimation of rainfall field by combining radar data and raingauge observations: the modified conditional merging technique

    NASA Astrophysics Data System (ADS)

    Pignone, Flavio; Rebora, Nicola

    2014-05-01

    Estimation of rainfall field by combining radar data and raingauge observations: the modified conditional merging technique N. Rebora, F. Pignone, F. Silvestro The estimation of rainfall fields, especially its spatial distribution and position is a crucial task both for rainfall nowcasting and for modeling catchment response to rainfall. Some studies of literature about multisensor datafusion prove that combining data from raingauges and radar represents the best way to obtain an enhanced ad more reliable estimation of QPE and of the associated river discharge. Sinclair and Peagram (2004) have proposed the Conditional Merging (CM) technique, a merging algorithm which extract the information content from the observed data and use it within an interpolation method to obtain the rainfall maps. The raingauges provide a punctual measure of the observed "real" rainfall while the remote sensors (radar network or satellite constellation) supply rainfall estimation maps which give an idea of the correlation and structure of covariance of the observed field. In this work is studied an enhanced algorithm based on CM, called Modified Conditional Merging, which can be used in real-time to produce the optimal rainfall maps. The area of interest is Italy, where are both available a dense network of raingauge measurements (about 2000 stations) and a QPE estimated by the Italian Radar composite. The main innovation respect to classical CM is to estimate the structure of covariance and the length of spatial correlation λ, for every raingauge, directly from the cumulated radar rainfall fields. The advantages of this method is to estimate the local characteristic of the domain to obtain information at smaller scale, very useful for convective events. An operative use and a validation are presented and discussed.

  20. Validation of EGSIEM gravity field products with globally distributed in situ ocean bottom pressure observations

    NASA Astrophysics Data System (ADS)

    Poropat, Lea; Bergmann-Wolf, Inga; Flechtner, Frank; Dobslaw, Henryk

    2016-04-01

    Time variable global gravity field models that are processed by different research institutions all across Europe are currently compared and subsequently combined within the "European Gravity Field Service for Improved Emergency Management (EGSIEM)" project funded by the European Union. To objectively assess differences between the results from different groups, and also to evaluate the impact of changes in the data processing at an individual institution in preparation of a new data release, a validation of the final GRACE gravity fields against independent observations is required. 
For such a validation, we apply data from a set of globally distributed ocean bottom pressure sensors. The in situ observations have been thoroughly revised for outliers, instrumental drift and jumps, and were additionally reduced for tides. GRACE monthly mean solutions are then validated with the monthly resampled in situ observations. The validation typically concentrates on seasonal to interannual signals, but in case of GRACE-based series with daily sampling available from, e.g., Kalman Smoother Solutions, also sub-monthly signal variability can be assessed.

  1. The Influence of Dissolution on Bedrock Channel Evolution: Insights from Modelling and Field Observations

    NASA Astrophysics Data System (ADS)

    Thaler, E.; Myre, J. M.; Covington, M. D.

    2015-12-01

    Despite the large global distribution of soluble bedrock, fluvial geomorphological studies typically regard dissolution as a negligible erosion mechanism in bedrock channels when compared to rates of mechanical erosion. Limited prior field observations have suggested that at the transition from insoluble to soluble substrate bedrock channels become wider, less steep, or both. By extending the Fastscape landscape evolution model to include dissolution as an erosion mechanism, we repeatedly produce landscapes with trunk streams consistent with field observations. However, in small tributaries, channel steepening occurs at the contact of the insoluble and soluble lithologies. Furthermore, as the main channel in a basin encounters the soluble layer, the increased erosion due to dissolution acts produces a local increase in the rate of base level lowering, resulting in steepening of channels upstream of the lithologic contact. The increased erosion at the lithological contact in the main stem also causes hillsope steepening in the soluble reaches. Independent field observations in the Buffalo National River Basin agree with the model results. Knickpoints and slot canyons are common at the lithologic contact in small tributaries, and channel widening occurs in soluble reaches in the main stem.

  2. Sediment deposition from Tropical Storm Lee in the upper Chesapeake Bay: field observations and model predictions

    NASA Astrophysics Data System (ADS)

    Palinkas, C. M.; Halka, J. P.; Li, M.; Sanford, L. P.; Cheng, P.

    2012-12-01

    Episodic flood and storm events are important drivers of sediment dynamics in estuarine and marine environments. Event-driven sedimentation has been well-documented by field and modeling studies. Yet, few studies have integrated field observations and modeling results to overcome the limitations inherent in both techniques. A unique opportunity to integrate field observations and model results was provided in late August/early September 2011 with the passage of Hurricane Irene and the remnants of Tropical Storm Lee in the Chesapeake Bay region. These storms differed in their timing, track, and impact on the Bay region - Hurricane Irene was primarily a wind/resuspension event, whereas TS Lee was a hydrological/deposition event, with the second largest discharge of the Susquehanna River on record. Because these two storms occurred within a relatively short period of time, both are potentially represented in the sediment record obtained during rapid-response cruises in September and October 2011. The resulting sediment deposit was recognized in cores using classic flood-sediment signatures (fine grain size, uniform 7Be activity, physical stratification in x-radiographs) and was found to be <4 cm, thickest in the upper Bay. Model runs conducted for TS Lee generally agreed with these estimates. One exception with physical stratification but no 7Be activity appears to be due to extreme wave activity during Hurricane Irene. Integration of observations and modeling in this case greatly improved understanding of the transport and fate of flood sediments in the Chesapeake Bay.

  3. Constraining the Solar Coronal Magnetic Field Strength using Split-band Type II Radio Burst Observations

    NASA Astrophysics Data System (ADS)

    Kishore, P.; Ramesh, R.; Hariharan, K.; Kathiravan, C.; Gopalswamy, N.

    2016-11-01

    We report on low-frequency radio (85-35 MHz) spectral observations of four different type II radio bursts, which exhibited fundamental-harmonic emission and split-band structure. Each of the bursts was found to be closely associated with a whitelight coronal mass ejection (CME) close to the Sun. We estimated the coronal magnetic field strength from the split-band characteristics of the bursts, by assuming a model for the coronal electron density distribution. The choice of the model was constrained, based on the following criteria: (1) when the radio burst is observed simultaneously in the upper and lower bands of the fundamental component, the location of the plasma level corresponding to the frequency of the burst in the lower band should be consistent with the deprojected location of the leading edge (LE) of the associated CME; (2) the drift speed of the type II bursts derived from such a model should agree closely with the deprojected speed of the LE of the corresponding CMEs. With the above conditions, we find that: (1) the estimated field strengths are unique to each type II burst, and (2) the radial variation of the field strength in the different events indicate a pattern. It is steepest for the case where the heliocentric distance range over which the associated burst is observed is closest to the Sun, and vice versa.

  4. OBSERVATIONAL EVIDENCE OF CHANGING PHOTOSPHERIC VECTOR MAGNETIC FIELDS ASSOCIATED WITH SOLAR FLARES

    SciTech Connect

    Su, J. T.; Jing, J.; Wang, H. M.; Mao, X. J.; Wang, X. F.; Zhang, H. Q.; Deng, Y. Y.; Guo, J.; Wang, G. P.

    2011-06-01

    Recent observations have provided evidence that the solar photospheric magnetic fields could have rapid and permanent changes in both longitudinal and transverse components associated with major flares. As a result, the Lorentz force (LF) acting on the solar photosphere and solar interior could be perturbed, and the change of LF is always nearly in the downward direction. However, these rapid and permanent changes have not been systematically investigated, yet, using vector magnetograms. In this paper, we analyze photospheric vector magnetograms covering five flares to study the evolution of photospheric magnetic fields. In particular, we investigate two-dimensional spatial distributions of the changing LF. Around the major flaring polarity inversion line, the net change of the LF is directed downward in an area of {approx}10{sup 19} cm{sup 2} for X-class flares. For all events, the white-light observations show that sunspots darken in this location after flares, and magnetic fields become more inclined, which is consistent with the ideas put forward by Hudson et al. and Fisher et al., and observations.

  5. Reconstructing solar magnetic fields from historical observations. I. Renormalized Ca K spectroheliograms and pseudo-magnetograms

    NASA Astrophysics Data System (ADS)

    Pevtsov, Alexei A.; Virtanen, Ilpo; Mursula, Kalevi; Tlatov, Andrey; Bertello, Luca

    2016-01-01

    Aims: The present work is the first in a series of articles that develop a new proxy to represent the evolution of magnetic activity in past solar cycles by combining the information from historical Ca II K line spectroheliograms and sunspot magnetic field measurements. Methods: We use synoptic (Carrington) maps from 1915-1985 that were derived from daily Ca K line observations at Mount Wilson Observatory to identify the chromospheric plages and to create synoptic pseudo-magnetograms. We use historical observations of sunspot magnetic fields from 1917 to the present to assign polarity to pixels situated within plages. The original Ca K spectroheliograms are nonuniform in their brightness, and we develop a novel approach to re-normalize their intensities. Results: We show that a homogeneous long-term series of pseudo-magnetograms can be successfully constructed by combining sunspot field measurements and plages with renormalized intensities. In our tests, about 80% of pixels situated within plages showed the same magnetic polarity as the synoptic magnetograms taken with the Kitt Peak Vacuum Telescope. Finally, we discuss possible approaches to further improve the agreement between observed and pseudo-magnetograms.

  6. Observation of far-field Mach waves generated by the 2001 Kokoxili supershear earthquake

    NASA Astrophysics Data System (ADS)

    Vallée, M.; Dunham, Eric M.

    2012-03-01

    Regional surface wave observations offer a powerful tool for determining source properties of large earthquakes, especially rupture velocity. Supershear ruptures, being faster than surface wave phase velocities, create far-field surface wave Mach cones along which waves from all sections of the fault arrive simultaneously and, over a sufficiently narrow frequency band, in phase. We present the first observation of far-field Mach waves from the major Kokoxili earthquake (Tibet, 2001/11/14, Mw 7.9) and confirm that ground motion amplitudes are indeed enhanced on the Mach cone. Theory predicts that on the Mach cone, bandpassed surface wave seismograms from a large supershear rupture will be identical to those from much smaller events with similar focal mechanisms, with an amplitude ratio equal to the ratio of the seismic moments of the two events. Cross-correlation of 15-25 s Love waves from the Kokoxili event with those from a much smaller (Mw 5) foreshock indicates a high degree of similarity (correlation coefficients ranging from 0.8 to 0.95) in waveforms recorded at stations near the far-field Mach cone. This similarity vanishes away from the Mach cone. These observations provide further evidence for supershear propagation of the Kokoxili rupture, and demonstrate how this simple waveform correlation procedure can be used to identify supershear ruptures.

  7. Magnetospheric Multiscale Satellites Observations of Parallel Electric Fields Associated with Magnetic Reconnection.

    PubMed

    Ergun, R E; Goodrich, K A; Wilder, F D; Holmes, J C; Stawarz, J E; Eriksson, S; Sturner, A P; Malaspina, D M; Usanova, M E; Torbert, R B; Lindqvist, P-A; Khotyaintsev, Y; Burch, J L; Strangeway, R J; Russell, C T; Pollock, C J; Giles, B L; Hesse, M; Chen, L J; Lapenta, G; Goldman, M V; Newman, D L; Schwartz, S J; Eastwood, J P; Phan, T D; Mozer, F S; Drake, J; Shay, M A; Cassak, P A; Nakamura, R; Marklund, G

    2016-06-10

    We report observations from the Magnetospheric Multiscale satellites of parallel electric fields (E_{∥}) associated with magnetic reconnection in the subsolar region of the Earth's magnetopause. E_{∥} events near the electron diffusion region have amplitudes on the order of 100  mV/m, which are significantly larger than those predicted for an antiparallel reconnection electric field. This Letter addresses specific types of E_{∥} events, which appear as large-amplitude, near unipolar spikes that are associated with tangled, reconnected magnetic fields. These E_{∥} events are primarily in or near a current layer near the separatrix and are interpreted to be double layers that may be responsible for secondary reconnection in tangled magnetic fields or flux ropes. These results are telling of the three-dimensional nature of magnetopause reconnection and indicate that magnetopause reconnection may be often patchy and/or drive turbulence along the separatrix that results in flux ropes and/or tangled magnetic fields.

  8. Earthquake-related Electric Field Changes Observed in the Ionosphere and Ground

    NASA Astrophysics Data System (ADS)

    Fan, Yingying; Du, Xuebin; An, Zhanghui; Liu, Jun; Tan, Dacheng; Chen, Junying

    2015-06-01

    The changes of the ionospheric electric field before and after four huge earthquakes, which include the Ms 8.7 earthquake of 2004 and the Ms 8.5 earthquake of 2005 in Sumatra of Indonesia, the Ms 8.0 Wenchuan earthquake of 2008 in China, the Ms 8.8 earthquake of 2010 in Chile, and their strong aftershocks are studied in this paper. The significant results revealed that the power spectral density of low-frequency electric field below 20 Hz in the ionosphere, a kind of electromagnetic radiation phenomena, increased abnormally before and after the earthquakes and partially corresponded to the increased power spectral density of the low-frequency geoelectric field in time. This research preliminarily indicates that the low-frequency electromagnetic radiation during the imminent stages before such earthquakes could be detected by the observation of the ionospheric electric field. However, the spatial, temporal, and intensive complexities of the electric field anomalies in the ionosphere before earthquakes have come in sight also.

  9. Magnetospheric Multiscale Satellites Observations of Parallel Electric Fields Associated with Magnetic Reconnection

    NASA Technical Reports Server (NTRS)

    Ergun, R. E.; Goodrich, K. A.; Wilder, F. D.; Holmes, J. C.; Stawarz, J. E.; Eriksson, S.; Sturner, A. P.; Malaspina, D. M.; Usanova, M. E.; Torbert, R. B.; hide

    2016-01-01

    We report observations from the Magnetospheric Multiscale satellites of parallel electric fields (E (sub parallel)) associated with magnetic reconnection in the subsolar region of the Earth's magnetopause. E (sub parallel) events near the electron diffusion region have amplitudes on the order of 100 millivolts per meter, which are significantly larger than those predicted for an antiparallel reconnection electric field. This Letter addresses specific types of E (sub parallel) events, which appear as large-amplitude, near unipolar spikes that are associated with tangled, reconnected magnetic fields. These E (sub parallel) events are primarily in or near a current layer near the separatrix and are interpreted to be double layers that may be responsible for secondary reconnection in tangled magnetic fields or flux ropes. These results are telling of the three-dimensional nature of magnetopause reconnection and indicate that magnetopause reconnection may be often patchy and/or drive turbulence along the separatrix that results in flux ropes and/or tangled magnetic fields.

  10. Focus on the electrical field-induced strain of electroactive polymers and the observed saturation

    NASA Astrophysics Data System (ADS)

    Guyomar, D.; Yuse, K.; Cottinet, P.-J.; Kanda, M.; Lebrun, L.

    2010-12-01

    Thanks to their large electrical field-induced strains, electroactive polymers can be used in various applications; as electroactive materials for artificial muscles or as active materials of membranes, due to their flexibility. One drawback concerning their use involves the saturation of the electrical field-induced strain which occurs at around 20% for a polymer film with a thickness of 80 μm. Few studies have been devoted to the understanding of this saturation. To this end, the present paper describes mechanical measurements of the extensive strain versus stress and the determination of the current flowing through an electroactive polymer driven by an electrical field. These experiments have clearly demonstrated that the observed saturation of the electrical induced strain was not due to a mechanical saturation within the sample but to the saturation of the electrically induced polarization. By carrying out a suitable modeling of the polarization versus electrical field, it was possible to calculate the strain and current versus electrical field. These values were then compared to experimental data, and were found to show a very good agreement.

  11. Use of real-time tools to support field operations of NSF's Lower Atmosphere Observing Facilities

    NASA Astrophysics Data System (ADS)

    Daniels, M.; Stossmeister, G.; Johnson, E.; Martin, C.; Webster, C.; Dixon, M.; Maclean, G.

    2012-12-01

    NCAR's Earth Observing Laboratory (EOL) operates Lower Atmosphere Observing Facilities (LAOF) for the scientific community, under sponsorship of the National Science Foundation. In order to obtain the highest quality dataset during field campaigns, real-time decision-making critically depends on the availability of timely data and reliable communications between field operations staff and instrument operators. EOL incorporates the latest technologies to monitor the health of instrumentation, facilitate remote operations of instrumentation and keep project participants abreast of changing conditions in the field. As the availability of bandwidth on mobile communication networks and the capabilities of their associated devices (smart phone, tablets, etc.) improved, so has the ability of researchers to respond to rapidly changing conditions and coordinate ever more detailed measurements from multiple remote fixed, portable and airborne platforms. This presentation will describe several new tools that EOL is making available to project investigators and how these tools are being used in a mobile computing environment to support enhanced data collection during field campaigns. LAOF platforms such as radars, aircraft, sondes, balloons and surface stations all rely on displays of real-time data for their operations. Data from sondes are ingested into the Global Telecommunications System (GTS) for assimilation into regional forecasting models that help guide project operations. Since many of EOL's projects occur around the globe and at the same time instrument complexity has increased, automated monitoring of instrumentation platforms and systems has become essential. Tools are being developed to allow remote instrument control of our suite of observing systems where feasible. The Computing, Data and Software (CDS) Facility of EOL develops and supports a Field Catalog used in field campaigns for nearly two decades. Today, the Field Catalog serves as a hub for the

  12. Fitting a toroidal force-free field to multispacecraft observations of a magnetic cloud

    NASA Astrophysics Data System (ADS)

    Nakagawa, Tomoko; Matsuoka, Ayako

    2010-10-01

    A torus-type flux rope model with an arbitrary aspect ratio was applied to an interplanetary magnetic cloud observed by ACE and Nozomi on 16-18 April 1999, when Nozomi was 0.2 AU downstream of ACE in the solar wind within 3° of heliocentric longitude. The large and small radii of the torus, the direction of the symmetric axis, and the crossing points of the spacecraft were determined so that they would minimize the sum of the square of the difference between the model field and the hourly averages of the observed field. Self-similar expansion of the flux rope was assumed in proportion with the heliocentric distance. The best fit model had large and small radii of 0.16 and 0.09 AU, respectively. Both spacecraft passed through the northern part of the torus. Difference in the magnetic field observed by the two spacecraft was explained by the difference in their paths through the magnetic cloud. The model fit was consistent with the direction of the vector normal to the preceding planar magnetic structures. The chirality of the flux rope was positive (left handed), suggesting that the solar source was on the Northern Hemisphere. Assuming a probable association with the filament disappearance observed on 13 April 1999 at N16 E00, it is inferred that the filament had traveled in interplanetary space across the ecliptic plane. It was also found that nearly the same fitting result was obtained using a single-spacecraft observation in the case of a torus-shaped magnetic cloud with a small aspect ratio.

  13. A framework of field observations and spatial data for understanding dust emissions in the Mojave Desert

    NASA Astrophysics Data System (ADS)

    Ballantine, J.; Reynolds, R. L.; Chavez, P.; Bogle, R.; Clow, G.; Fulton, R.; Reheis, M.; Urban, F.; Wallace, C.; Yount, J.

    2007-12-01

    Modeling dust events at landscape to regional scales requires field observations of dust-source characteristics, mapping of source types by remote sensing, and wind fields representing the conditions that mobilize dust from the surface. A conceptual framework has been built for understanding dust-source types and their dynamics in the Mojave Desert. Observations of dust events in the Mojave indicate five general source types: 1) Sparsely vegetated surfaces that are vulnerable during periods of drought; 2) wet playas where a near-surface groundwater table generates "fluffy" (very soft sediment) conditions; 3) transitional playas where groundwater extraction has lowered the water table, and playa surface composition produces sediments that are vulnerable to erosion; 4) ephemeral flood deposits; and 5) anthropogenic sources where off-road vehicles, military training exercises, and dirt roads create a disturbed surface. Some sources are perennial and others are strongly influenced (sometimes in opposite ways) by precipitation cycles. A multi-year study of precipitation, vegetation, winds, and saltation at several plots in the Mojave National Preserve shows that blooms of annual vegetation in wet years can leave biomass that protects the surface for more than a year after the rains. Monitoring of the wet Franklin Lake Playa shows that a shallow ground-water table is associated with more vulnerable conditions for dust emission. Repeat photography of the relations between winds and dustiness at transitional Mesquite Lake Playa shows that dust is mobilized during the spring when winds are greater than about 5 m/s. Satellite images reveal dust emission from ephemeral fluvial systems, such as the Mojave River Sink, at the end of wet spring seasons. Satellite images also document dust emissions from areas of heavy military and off-road vehicle activity. Landsat imagery was used to map perennial vegetation cover for the Mojave Desert, calibrated to 250 field transects. The

  14. Intercomparison of surface heat transfer in the Arctic for multiple reanalyses, satellite data and field observations

    NASA Astrophysics Data System (ADS)

    Repina, Irina; Mazilkina, Alexandra; Ivanov, Vladimir

    2015-04-01

    This study evaluated surface heat fluxes from reanalyses (ERAInterim, NCEP/NCAR, ASR) in the Arctic Ocean during summer and fall. Several types of surface conditions are compared: very new ice cover during a period of low temperature, ice-free conditions, ice with leads and melt ponds, pack ice and marginal ice zone. Meteorological and micrometeorological observations were used to validate the temperature profiles and surface heat fluxes in the major reanalyses. We use data from Nansen and Amundsen basins observation system (NABOS) project to evaluate the performance of reanalyses forin the Arctic Ocean. The NABOS field experiment was carried out in the central part of the Arctic and in the eastern Arctic seas during summer and fall period of 2004-2009 and 2013. Compared data arrays are independent and sufficiently detailed to perform trustworthy evaluations. With the explicit treatment of the ice concentration, ERA-Interim generally reproduces the surface heat transfer, while NCEP/NCAR, based on a 55% concentration threshold, shows obvious disagreement with the observations in highly ice-covered and ice-free situations. The spatial and temporal patterns of the resulting flux fields are investigated and compared with those derived from satellite observations such as HOAPS, from blended data such as AOFLUX (in the open water cases). A computation of the sensible heat flux at the surface is formulated on the basis of spatial variations of the surface temperature estimated from satellite data. Based on the comparison of field experiments data, satellite-derived data and reanalysis the causes of underestimation of the values of turbulent heat fluxes in the Arctic modern reanalysis are investigated. Obtained differences are related to the temperature and structural inhomogeneity of the surface and the development of space-organized convection fields. Reanalyses data are sometimes used to calculate the surface heat budgets over polynyas to estimate ice production in

  15. Dust emissions of organic soils observed in the field and laboratory

    NASA Astrophysics Data System (ADS)

    Zobeck, T. M.; Baddock, M. C.; Guo, Z.; Van Pelt, R.; Acosta-Martinez, V.; Tatarko, J.

    2011-12-01

    . In the laboratory wind tunnel, samples with the same ratio of erodible to non-erodible aggregates as the field soils were abraded and dust emissions were observed with the same sampling system as used in the field wind tunnel. In the dust generator, 5 gm samples < 8 mm diameter of each organic soil were rotated in a 50 cm long tube and the dust generated was observed with the GRIMM during a 20 minute run. Comparisons of the field dust emission rates with the laboratory results will be presented.

  16. A comparison of laboratory and field observations of superelevation in debris flows

    NASA Astrophysics Data System (ADS)

    McArdell, Brian W.; Scheidl, Christian; Graf, Christoph; Rickenmann, Dieter

    2017-04-01

    Post-event estimation of debris-flow velocity is a central part of hazard analysis. Estimates of debris-flow velocity are useful for e.g. dimensioning mitigation measures, calibrating or testing debris-flow runout models, constructing intensity-based hazard maps, and designing warning systems. However independent field observations of velocity are rare and it is often necessary to indirectly estimate flow velocity. The difference in mud elevation on either side of a channel through a bend of a constant radius can be used to estimate the flow velocity using a vortex method developed for a Newtonian fluid. In 2015 we reported on the application of the vortex method to calculate the front velocity of debris flows in the laboratory (Scheidl et al., 2015). In the laboratory experiments, we found a statistically significant correction factor k for the application of the vortex equation to debris flows under supercritical flow conditions, with somewhat more scatter for subcritical flows. Nevertheless, it was possible to derive a forced-vortex equation, without a correction factor, after considering active and passive earth pressures within the flow. Herein, we compare the laboratory results with field data from the Illgraben and Schipfenbach torrents in Switzerland. Using video recordings and flow trajectory data for 17 debris flows at the Illgraben debris-flow observation station in Switzerland, we were able to independently test the application of the new forced vortex equation against field data. The general trend observed in the laboratory are confirmed using the field data: the correction factor k decreases with increasing Froude number of the flow. However the field data show a much larger degree of scatter in the vortex-equation correction factor in comparison with the laboratory data. The debris flows in the field differ from the laboratory channel in many ways. Although the observation section at the Illgraben was fairly uniform in terms of the surface width of

  17. A Cosmic Train Wreck: JVLA Radio Observations of the HST Frontier Fields Cluster Abell 2744

    NASA Astrophysics Data System (ADS)

    Pearce, Connor; Van Weeren, Reinout J.; Jones, Christine; Forman, William R.; Ogrean, Georgiana A.; Andrade-Santos, Felipe; Kraft, Ralph P.; Dawson, William; Brüggen, Marcus; Roediger, Elke; Bulbul, Esra; Mroczkowski, Tony

    2016-01-01

    The galaxy cluster mergers observed in the HST Frontier Fields represent some of the most energetic events in the Universe. Major cluster mergers leave distinct signatures in the ICM in the form of shocks, turbulence, and diffuse cluster radio sources. These diffuse radio sources, so-called radio relics and halos, provide evidence for the acceleration of relativistic particles and the presence of large scale magnetic fields in the ICM. Observations of these halos and relics allow us to (i) study the physics of particle acceleration and its relation with shocks and turbulence in the ICM and (ii) constrain the dynamical evolution of the merger eventsWe present Jansky Very Large Array 1-4 GHz observations of the Frontier cluster Abell 2744. We confirm the presence of the known giant radio halo and radio relic via our deep radio images. Owing to the much greater sensitivity of the JVLA compared to previous observations, we are able to detect a previously unobserved long Mpc-size filament of synchrotron emission to the south west of the cluster core. We also present a radio spectral index image of the diffuse cluster emission to test the origin of the radio relic and halo, related to the underlying particle acceleration mechanism. Finally, we carry out a search for radio emission from the 'jellyfish' galaxies in A2744 to estimate their star formation rate. These highly disturbed galaxies are likely influenced by the cluster merger event, although the precise origin of these galaxies is still being debated.

  18. THE INTERPLAY OF TURBULENCE AND MAGNETIC FIELDS IN STAR-FORMING REGIONS: SIMULATIONS AND OBSERVATIONS

    SciTech Connect

    Kirk, Helen; Johnstone, Doug; Basu, Shantanu

    2009-07-10

    We analyze a suite of thin-sheet magnetohydrodynamical simulations based on the formulation of Basu, Ciolek, Dapp, and Wurster. These simulations allow us to examine the observational consequences to a star-forming region of varying the input level of turbulence (between thermal and a Mach number of 4) and the initial magnetic field strength corresponding to a range of mass to flux ratios between subcritical ({mu}{sub 0} = 0.5) and supercritical ({mu}{sub 0} = 10). The input turbulence is allowed to decay over the duration of the simulation. We compare the measured observable quantities with those found from surveying the Perseus molecular cloud. We find that only the most turbulent of simulations (high Mach number and weak magnetic field) have sufficient large-scale velocity dispersion (at {approx}1 pc) to match that observed across extinction regions in Perseus. Generally, the simulated core ({approx}0.02 pc) and line-of-sight velocity dispersions provide a decent match to observations. The motion between the simulated core and its local environment, however, is far too large in simulations with high large-scale velocity dispersion.

  19. Estimation of Transpiration and Water Use Efficiency Using Satellite and Field Observations

    NASA Technical Reports Server (NTRS)

    Choudhury, Bhaskar J.; Quick, B. E.

    2003-01-01

    Structure and function of terrestrial plant communities bring about intimate relations between water, energy, and carbon exchange between land surface and atmosphere. Total evaporation, which is the sum of transpiration, soil evaporation and evaporation of intercepted water, couples water and energy balance equations. The rate of transpiration, which is the major fraction of total evaporation over most of the terrestrial land surface, is linked to the rate of carbon accumulation because functioning of stomata is optimized by both of these processes. Thus, quantifying the spatial and temporal variations of the transpiration efficiency (which is defined as the ratio of the rate of carbon accumulation and transpiration), and water use efficiency (defined as the ratio of the rate of carbon accumulation and total evaporation), and evaluation of modeling results against observations, are of significant importance in developing a better understanding of land surface processes. An approach has been developed for quantifying spatial and temporal variations of transpiration, and water-use efficiency based on biophysical process-based models, satellite and field observations. Calculations have been done using concurrent meteorological data derived from satellite observations and four dimensional data assimilation for four consecutive years (1987-1990) over an agricultural area in the Northern Great Plains of the US, and compared with field observations within and outside the study area. The paper provides substantive new information about interannual variation, particularly the effect of drought, on the efficiency values at a regional scale.

  20. Reliability of prediction of the magnetosheath BZ component from interplanetary magnetic field observations

    NASA Astrophysics Data System (ADS)

    Šafránková, J.; Hayosh, M.; Gutynska, O.; Němeček, Z.; Přech, L.

    2009-12-01

    In the present statistical study, we discuss a probability of simultaneous observations of the same sign of the magnetic field BZ component in the solar wind and magnetosheath. The analysis is based on 5 min data from four spacecraft (Interball-1, IMP 8, Cluster, and THEMIS) operating in different phases of the solar cycle in the magnetosheath. Their measurements are compared with Wind interplanetary magnetic field (IMF) observations, and other available upstream monitors (ACE, THEMIS B, and OMNI database) are tested for some sets. We can conclude that the probability of observations of the same BZ sign in the solar wind and in the magnetosheath is surprisingly very low from a general point of view. The probability changes through the solar cycle, being larger at the solar minimum. Regardless of the solar cycle phase, this probability is close to 0.5 (random coincidence) for IMF ∣BZ∣ < 1 nT, and it is a rising function of the BZ value. Distant solar wind monitors do not guarantee the same sign of the BZ component, even for values of IMF BZ exceeding ±9 nT, but such large values are observed about 3-5% of the time. A better probability profile is reached for a monitor located just upstream (less than 30 RE), as is demonstrated for the THEMIS project.

  1. Balloon observations of ultra-low-frequency waves in the electric field above the South Pole

    SciTech Connect

    Liao, B.; Benbrrook, J.R.; Bering E.A. III; Byrne, G.J.; Theall, J.R. )

    1988-01-01

    The physics of ultra-low-frequency waves in the magnetosphere, near the cusp and in the polar cap, is important because this region is one where ultra-low-frequency wave energy from the magnetopause can most easily enter the magnetosphere. During the 1985-1986 South Pole balloon campaign, eight stratospheric balloon payloads were launched from Amundsen-Scott Station, South Geographic Pole, Antarctica, to record data on ultra-low-frequency waves. The payloads were instrumented with three-axis double-probe electric field detectors and X-ray scintillation counters. This paper concentrates on the third flight of this series, which was launched at 2205 universal time on 21 December 1985. Good data were received from the payload until the transmitter failed at 0342 universal time on 22 December. During most of the four hours that the balloon was afloat, an intense ultra-low-frequency wave event was in progress. The electric-field data from this period have been examined in detail and compared with magnetic field data, obtained with ground-based fluxgate and induction magnetometers to determine the characteristics of the waves. After float was reached, the electric-field data in figure 1 show large-amplitude, quasi-periodic fluctuations suggesting the presence of intense ultra-low-frequency wave activity. In conclusion, the electric-field signature observed from flight 3 appears to have been essentially an electrostatic event or possibly a short-wavelength hydromagnetic wave with a varying and interesting polarization character. The authors are continuing the analysis of the data to determine the source of the observed ultra-low-frequency waves.

  2. Observed Enhancement of Reflectivity and Electric Field in Long-Lived Florida Anvils

    NASA Technical Reports Server (NTRS)

    Dye, James E.; Willett, John C.

    2007-01-01

    A study of two long-lived Florida anvils showed that reflectivity >20 dBZ increased in area, thickness and sometimes magnitude at mid-level well downstream of the convective cores. In these same regions electric fields maintained strengths >10 kV m1 for many tens of minutes and became quite uniform over tens of kilometers. Millimetric aggregates persisted at 9 to 10 km for extended times and distances. Aggregation of ice particles enhanced by strong electric fields might have contributed to reflectivity growth in the early anvil, but is unlikely to explain observations further out in the anvil. The enhanced reflectivity and existence of small, medium and large ice particles far out into the anvil suggest that an updraft was acting, perhaps in weak convective cells formed by instability generated from the evaporation and melting of falling ice particles. We conclude that charge separation must have occurred in these anvils, perhaps at the melting level but also at higher altitudes, in order to maintain fields >10 kV m 1 at 9 to 10 km for extended periods of time over large distances. We speculate that charge separation occurred as a result of ice-ice particle collisions (without supercooled water being present) via either a non-inductive or perhaps even an inductive mechanism, given the observed broad ice particle spectra, the strong pre-existing electric fields and the many tens of minutes available for particle interactions. The observations, particularly in the early anvil, show that the charge structure in these anvils was quite complex.

  3. An Evaluation of Tropical Cyclogenesis Theories through Intercomparison of Field Experiment Observations

    NASA Astrophysics Data System (ADS)

    Helms, C. N.; Hart, R. E.

    2011-12-01

    The process by which tropical cyclones evolve from loosely organized convective clusters into well organized systems is still poorly understood. A number of theories have been proposed to explain this evolution based on vortex dynamics, adiabatic processes, and diabatic processes. Due to the data sparse location in which many of these systems develop, many studies of tropical cyclogenesis theory are limited to either a few case studies or are forced to rely on simulations to critically evaluate the theories. The recent PREDICT and GRIP field experiments have provided a new opportunity to examine these theories using unusually dense observations. The present study aims at using this new data in conjunction with data from previous field experiments, such as NAMMA, GATE, and TOGA COARE, to evaluate three existing theories: top-down vortex merger (Ritchie and Holland, 1997; Simpson et al., 1997), top-down shower-head (Emanuel, 1993; Bister and Emanuel, 1997), and bottom-up vortex merger (Montgomery and Enagonio, 1998; Enagonio and Montgomery, 2001). Additionally, these observations are used to briefly examine the newer marsupial framework for tropical cyclogenesis in African easterly waves (Dunkerton et al. 2009). The processes associated with each of these theories create unique signatures in wind, vorticity, potential temperature, and humidity fields. Timelines of these fields, created from composited mean dropsonde soundings, are used to determine the system-wide evolution. Further, the temporal evolution of sub-system processes, which are minimized or removed as a result of the compositing process, are identified in isobaric surface plot series. While previous studies have shown that no theory completely explains tropical cyclogenesis, it is hoped that a thorough analysis of these data sets will highlight both consistencies and inconsistencies between theory and observation.

  4. Mars gravity field error analysis from simulated radio tracking of Mars Observer

    SciTech Connect

    Smith, D.E.; Lerch, F.J. ); Chan, J.C.; Chinn, D.S.; Iz, H.B.; Mallama, A.; Patel, G.B. )

    1990-08-30

    The Mars Observer (MO) Mission, in a near-polar orbit at 360-410 km altitude for nearly a 2-year observing period, will greatly improve our understanding of the geophysics of Mars, including its gravity field. To assess the expected improvement of the gravity field, the authors have conducted an error analysis based upon the mission plan for the Mars Observer radio tracking data from the Deep Space Network. Their results indicate that it should be possible to obtain a high-resolution model (spherical harmonics complete to degree and order 50 corresponding to a 200-km horizontal resolution) for the gravitational field of the planet. This model, in combination with topography from MO altimetry, should provide for an improved determination of the broad scale density structure and stress state of the Martian crust and upper mantle. The mathematical model for the error analysis is based on the representation of doppler tracking data as a function of the Martian gravity field in spherical harmonics, solar radiation pressure, atmospheric drag, angular momentum desaturation residual acceleration (AMDRA) effects, tracking station biases, and the MO orbit parameters. Two approaches are employed. In the first case, the error covariance matrix of the gravity model is estimated including the effects from all the nongravitational parameters (noise-only case). In the second case, the gravity recovery error is computed as above but includes unmodelled systematic effects from atmospheric drag, AMDRA, and solar radiation pressure (biased case). The error spectrum of gravity shows an order of magnitude of improvement over current knowledge based on doppler data precision from a single station of 0.3 mm s{sup {minus}1} noise for 1-min integration intervals during three 60-day periods.

  5. Observed chlorine concentrations during Jack Rabbit I and Lyme Bay field experiments

    NASA Astrophysics Data System (ADS)

    Hanna, Steven; Chang, Joseph; Huq, Pablo

    2016-01-01

    As part of planning for a series of field experiments where large quantities (up to 20 tons) of pressurized liquefied chlorine will be released, observations from previous chlorine field experiments are analyzed to estimate the ranges of chlorine concentrations expected at various downwind distances. In five field experiment days during the summer 2010 Jack Rabbit I (JR I) field trials, up to two tons of chlorine were released and concentrations were observed at distances, x, from 25 to 500 m. In the 1927 Lyme Bay (LB) experiments, there were four days of trials, where 3-10 tons of chlorine were released in about 15 min from the back of a ship. Concentrations were sampled at LB from four ships sailing across the cloud path at downwind distances in the range from about 350 to 3000 m. Thus, the distances from which JR I concentrations were available slightly overlapped the LB distances. One-minute arc-maximum chlorine concentrations, C (g/m3), were analyzed from four JR I trials and two LB trials. Normalized concentrations (Cu/Q) were plotted versus x (m), where u (m/s) is measured wind speed at heights of 2-10 m and Q (g/s) is continuous mass release rate. It is found that the JR I and LB Cu/Q observations smoothly merge with each other and fall along a line with approximate slope of -2 at distances beyond about 200 m (i.e., Cu/Q is proportional to x-2). At x < 200 m, where dense gas effects are more important, the slope is less (about -1.5). Most of the data points are within a factor of two of the "best-fit" line.

  6. An interplanetary magnetic field enhancement observed by five spacecraft: Deducing the magnetic structure, size and mass

    NASA Astrophysics Data System (ADS)

    Lai, H.; Russell, C. T.; Delzanno, G.; Angelopoulos, V.

    2012-12-01

    Interplanetary Field Enhancements (IFEs) were discovered almost 30 years ago in the PVO magnetic-field records and attributed to the interaction between solar wind and dust particles from comets or asteroids, but the physics of this interaction remained obscure. Our current understanding is that IFEs result from collisions of small interplanetary bodies that produce electrically charged nanometer-scale dust particles possibly enhanced by tribo-electric charging in the collision. These charged dust particles in turn interact with the magnetized solar wind. Momentum is transferred from the solar wind to the dust cloud via the collective effect of the formation of a magnetic barrier. This momentum transfer accelerates the particles to near the solar wind speed and moves the dust outward through the solar gravitational potential well. Multi-spacecraft observations can help us to determine the speed of the IFE and the orientation of the current sheet. They enable us to reconstruct the pressure profile of an IFE in three dimensions and estimate the mass contained in the IFE. We have done these reconstructions with an IFE observed on March 3, 2011 with Wind, ACE, ARTEMIS P1 and P2 and Geotail. We find that the magnetic field near the center of the IFE is highly twisted indicating a complicated magnetic topology as expected in a plasma-charged dust interaction. The magnetic field and plasma properties during this event distinguish it from a typical flux rope. Based on the statistical results obtained at 1 AU and the assumption that all the IFEs are self-similar, we find that this IFE has a radial scale length several times longer than the cross flow radius and contains a mass of about 108 kg. The rates of collisions expected for objects of this size are consistent with the observed rates of these disturbances.

  7. Voyager 1 observations of the interstellar magnetic field and the transition from the heliosheath

    SciTech Connect

    Burlaga, L. F.; Ness, N. F. E-mail: nfnudel@yahoo.com

    2014-04-01

    Voyager 1 (V1) has been observing interstellar magnetic fields for more than one year beginning ≈2012/209, when V1 crossed a current sheet, a 'CS0' having the structure of a tangential discontinuity. The inclination of this current sheet is consistent with an interstellar magnetic field B draped on a blunt heliopause. Two other current sheets (sector boundaries) were observed at ≈2012/167 and ≈2011/276 with high inclinations (99° ± 10° and 89° ± 10°, respectively). From 2013.0 to ≈2013.6, the difference between the azimuthal angle λ of B from the Parker spiral angle at the latitude 34.°6 of V1 was λ – λ{sub P} = 22° ± 3° and the corresponding difference of the elevation angle δ was δ – δ{sub P} = 23° ± 8°. During 2012, the deviation from the Parker spiral angle was somewhat smaller. The interstellar magnetic field has a 'west to east polarity,' opposite to the direction of planetary motions. The magnitude of B varied smoothly in the range 0.38-0.59 nT with an average B = 0.486 ± 0.045 after 2012/237.7. The transition from heliosheath to interstellar magnetic fields is related to a 'two-step' increase in the cosmic ray intensity observed by V1 from ≈2012.30 to ≈2012.65. The first step increase began near the end of an unusual 'away-polarity' sector, and it reached a plateau when V1 moved into a 'toward-polarity' sector that ended at CS0. The second step increase began slowly after V1 crossed CS0, and it ended abruptly at 2012/237.728.

  8. Discrepancies between Observational Data and Theoretical Forecast in Single Field Slow Roll Inflation

    NASA Astrophysics Data System (ADS)

    Amorós, Jaume; de Haro, Jaume

    2016-12-01

    The PLANCK collaboration has determined, or greatly constrained, values for the spectral parameters of the CMB radiation, namely the spectral index n s , its running α s , the running of the running β s , using a growing body of measurements of CMB anisotropies by the Planck satellite and other missions. These values do not follow the hierarchy of sizes predicted by single field, slow roll inflationary theory, and are thus difficult to fit for such inflation models. In this work we present first a study of 49 single field, slow roll inflationary potentials in which we assess the likelyhood of these models fitting the spectral parameters to their currently most accurate determination given by the PLANCK collaboration. We check numerically with a MATLAB program the spectral parameters that each model can yield for a very broad, comprehensive list of possible parameter and field values. The comparison of spectral parameter values supported by the models with their determinations by the PLANCK collaboration leads to the conclusion that the data provided by PLANCK2015 TT+lowP and PLANCK2015 TT,TE,EE+lowP taking into account the running of the running disfavours 40 of the 49 models with confidence level at least 92.8 %. Next, we discuss the reliability of the current computations of these spectral parameters. We identify a bias in the method of determination of the spectral parameters by least residue parameter fitting (using MCMC or any other scheme) currently used to reconstruct the power spectrum of scalar perturbations. This bias can explain the observed contradiction between theory and observations. Its removal is computationally costly, but necessary in order to compare the forecasts of single field, slow roll theories with observations.

  9. Observed Enhancement of Reflectivity and Electric Field in Long-Lived Florida Anvils

    NASA Technical Reports Server (NTRS)

    Dye, James E.; Willett, John C.

    2007-01-01

    A study of two long-lived Florida anvils showed that reflectivity greater than 20 dBZ increased in area, thickness and sometimes magnitude at mid-level well downstream of the convective cores. In these same regions electric fields maintained strengths greater than 10 kV m(sup -1) for many tens of minutes and became quite uniform over tens of kilometers. Millimetric aggregates persisted at 9 to 10 km for extended times and distances. Aggregation of ice particles enhanced by strong electric fields might have contributed to reflectivity growth in the early anvil, but is unlikely to explain observations further out in the anvil. The enhanced reflectivity and existence of small, medium and large ice particles far out into the anvil suggest that an updraft was acting, perhaps in weak convective cells formed by instability generated from the evaporation and melting of falling ice particles. We conclude that charge separation must have occurred in these anvils, perhaps at the melting level but also at higher altitudes, in order to maintain fields greater than 10 kV m(sup -1) at 9 to 10 km for extended periods of time over large distances. We speculate that charge separation occurred as a result of ice-ice particle collisions (without supercooled water being present) via either a noninductive or perhaps even an inductive mechanism, given the observed broad ice particle spectra, the strong pre-existing electric fields and the many tens of minutes available for particle interactions. The observations, particularly in the early anvil, show that the charge structure in these anvils was quite complex.

  10. A comparison of predicted and observed turbulent wind fields present in natural and internal wind park environments

    SciTech Connect

    Kelly, N D; Wright, A D

    1991-10-01

    This paper assesses the accuracy of simulated wind fields for both the natural flow and that within a wind park environment. The simulated fields are compared with the observed ones in both the time and frequency domains. Actual measurements of the wind fields and the derived kinematic scaling parameters upwind and downwind of a large San Gorgonio Pass wind park are used. The deviations in the modeled wind field from the observed are discussed. 10 refs., 6 figs., 2 tabs.

  11. Field Observations of Crustal Seismic Anisotropy: Implications for Mapping Tectonic Structure in Metamorphic Terranes

    NASA Astrophysics Data System (ADS)

    Christensen, N. I.; Okaya, D.; Meltzer, A.; Brocher, T.; Holbrook, W. S.

    2003-12-01

    The study of seismic anisotropy within continental tectonic provinces provides earth scientists with a powerful tool for measuring and quantifying deformation within the crust. Preferred mineral alignment observed in metamorphic terranes produced by recrystallization during metamorphism is associated with planar structures such as slaty cleavage, schistosity, and gneissic layering. These structures are often pervasive for tens to hundreds of kilometers and produce significant compressional wave seismic anisotropy as well as shear wave splitting. Observations of crustal anisotropy within (1) slates of the chlorite subzone of the Haast schist terrane of South Island, New Zealand, (2) lower greenschist facies phyllites and metagraywackes of the Valdez Group Chugach terrane in southern Alaska, (3) amphibolite facies mica schists within the Yukon-Tanana terrane in the eastern Alaska range and (4) amphibolite facies quartzofeldspathic gneisses, approaching granulite grade, within the Nanga Parbat-Haramosh massif demonstrate that crustal anisotropy is not limited to rocks of any particular metamorphic grade and thus can be present at all crustal levels. Two refraction lines at approximately right angles shown up to 10% compressional wave anisotropy in relatively low grade metapelites of the Haast schist terrane. Fast velocities parallel the strike of the upturned slaty cleavage. Measured field velocities in the Chugach terrane, obtained from observed first arrival travel times, demonstrate significant compressional wave anisotropy (~9%) with fastest directions oriented approximately east-west and parallel to foliations observed in outcrops. Within the Alaskan Yukon-Tanana terrane variations in seismic velocities of the first arrivals correlate with field observations of regional dips of foliated schists. A northward shallowing of foliation dips produces an observed northward increasing seismic velocity. The core of the Nanga-Parbat massif forms a large-scale antiformal

  12. In vivo observation of tree drought response with low-field NMR and neutron imaging

    DOE PAGES

    Malone, Michael W.; Yoder, Jacob; Hunter, James F.; ...

    2016-05-06

    Using a simple low-field NMR system, we monitored water content in a living tree in a greenhouse over 2 months. By continuously running the system, we observed changes in tree water content on a scale of half an hour. The data showed a diurnal change in water content consistent both with previous NMR and biological observations. Neutron imaging experiments show that our NMR signal is primarily due to water being rapidly transported through the plant, and not to other sources of hydrogen, such as water in cytoplasm, or water in cell walls. After accounting for the role of temperature inmore » the observed NMR signal, we demonstrate a change in the diurnal signal behavior due to simulated drought conditions for the tree. Lastly, these results illustrate the utility of our system to perform noninvasive measurements of tree water content outside of a temperature controlled environment.« less

  13. Radio observations of interplanetary magnetic field structures out of the ecliptic

    NASA Technical Reports Server (NTRS)

    Fitzenreiter, R. J.; Fainberg, J.; Weber, R. R.; Alvarez, H.; Haddock, F. T.; Potter, W. H.

    1976-01-01

    New observations of the out-of-the ecliptic trajectories of type 3 solar radio bursts have been obtained from simultaneous direction finding measurements on two independent satellite experiments, IMP-6 with spin plane in the ecliptic, and RAE-2 with spin plane normal to the ecliptic. Burst exciter trajectories were observed which originated at the active region and then crossed the ecliptic plane at about 0.8 AU. A considerable large scale north-south component of the interplanetary magnetic field is followed by the exciters. The apparent north-south and east-west angular source sizes observed by the two spacecraft are approximately equal, and range from 25 deg at 600 KHz to 110 deg at 80 KHz.

  14. In vivo Observation of Tree Drought Response with Low-Field NMR and Neutron Imaging

    PubMed Central

    Malone, Michael W.; Yoder, Jacob; Hunter, James F.; Espy, Michelle A.; Dickman, Lee T.; Nelson, Ron O.; Vogel, Sven C.; Sandin, Henrik J.; Sevanto, Sanna

    2016-01-01

    Using a simple low-field NMR system, we monitored water content in a living tree in a greenhouse over 2 months. By continuously running the system, we observed changes in tree water content on a scale of half an hour. The data showed a diurnal change in water content consistent both with previous NMR and biological observations. Neutron imaging experiments show that our NMR signal is primarily due to water being rapidly transported through the plant, and not to other sources of hydrogen, such as water in cytoplasm, or water in cell walls. After accounting for the role of temperature in the observed NMR signal, we demonstrate a change in the diurnal signal behavior due to simulated drought conditions for the tree. These results illustrate the utility of our system to perform noninvasive measurements of tree water content outside of a temperature controlled environment. PMID:27200037

  15. High-speed video and electric field observation of upward flashes in Brazil

    NASA Astrophysics Data System (ADS)

    Saba, Marcelo M. F.; Schumann, Carina; Ferro, Marco A. S.; Paiva, Amanda R.; Jaques, Robson; Warner, Tom A.

    2015-04-01

    Upward flashes from tall towers in Brazil have been observed since January 2012. They have been responsible for damages on equipment installed nearby tall structures that caused their initiation. Almost all upward flashes were observed with high-speed cameras and electric field sensors; a combination of measurements that provides a very accurate classification and characterization of their properties. Although present during all seasons, upward flashes are predominant during summer. They are almost always initiated by a preceding positive cloud-to-ground flash. This study is based on an up-to-date database of 86 upward flashes observed during the last three years. The main characteristics described in this work are: time interval between triggering event and the upward leader initiation, characteristics of the triggering +CG flashes, upward leader characteristics (polarity, presence of recoil leaders and branching), initial continuous current (duration, presence of pulses and recoil leaders), flash duration and presence of subsequence of return stroke.

  16. New Approach for Environmental Monitoring and Plant Observation Using a Light-Field Camera

    NASA Astrophysics Data System (ADS)

    Schima, Robert; Mollenhauer, Hannes; Grenzdörffer, Görres; Merbach, Ines; Lausch, Angela; Dietrich, Peter; Bumberger, Jan

    2015-04-01

    The aim of gaining a better understanding of ecosystems and the processes in nature accentuates the need for observing exactly these processes with a higher temporal and spatial resolution. In the field of environmental monitoring, an inexpensive and field applicable imaging technique to derive three-dimensional information about plants and vegetation would represent a decisive contribution to the understanding of the interactions and dynamics of ecosystems. This is particularly true for the monitoring of plant growth and the frequently mentioned lack of morphological information about the plants, e.g. plant height, vegetation canopy, leaf position or leaf arrangement. Therefore, an innovative and inexpensive light-field (plenoptic) camera, the Lytro LF, and a stereo vision system, based on two industrial cameras, were tested and evaluated as possible measurement tools for the given monitoring purpose. In this instance, the usage of a light field camera offers the promising opportunity of providing three-dimensional information without any additional requirements during the field measurements based on one single shot, which represents a substantial methodological improvement in the area of environmental research and monitoring. Since the Lytro LF was designed as a daily-life consumer camera, it does not support depth or distance estimation or rather an external triggering by default. Therefore, different technical modifications and a calibration routine had to be figured out during the preliminary study. As a result, the used light-field camera was proven suitable as a depth and distance measurement tool with a measuring range of approximately one meter. Consequently, this confirms the assumption that a light field camera holds the potential of being a promising measurement tool for environmental monitoring purposes, especially with regard to a low methodological effort in field. Within the framework of the Global Change Experimental Facility Project, founded by

  17. DC Electric Fields, Associated Plasma Drifts, and Irregularities Observed on the C/NOFS Satellite

    NASA Technical Reports Server (NTRS)

    Pfaff, R.; Freudenreich, H.; Klenzing, J.

    2011-01-01

    Results are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. The VEFI instrument includes a vector DC electric field detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux gate magnetometer, an optical lightning detector, and associated electronics including a burst memory. Compared to data obtained during more active solar conditions, the ambient DC electric fields and their associated E x B drifts are variable and somewhat weak, typically < 1 mV/m. Although average drift directions show similarities to those previously reported, eastward/outward during day and westward/downward at night, this pattern varies significantly with longitude and is not always present. Daytime vertical drifts near the magnetic equator are largest after sunrise, with smaller average velocities after noon. Little or no pre-reversal enhancement in the vertical drift near sunset is observed, attributable to the solar minimum conditions creating a much reduced neutral dynamo at the satellite altitude. The nighttime ionosphere is characterized by larger amplitude, structured electric fields, even where the plasma density appears nearly quiescent. Data from successive orbits reveal that the vertical drifts and plasma density are both clearly organized with longitude. The spread-F density depletions and corresponding electric fields that have been detected thus far have displayed a preponderance to appear between midnight and dawn. Associated with the narrow plasma depletions that are detected are broad spectra of electric field and plasma density irregularities for which a full vector set of measurements is available for detailed study. The VEFI data represents a new set of measurements that are germane to numerous fundamental aspects of the electrodynamics

  18. Observations of photospheric magnetic fields and shear flows in flaring active regions

    NASA Technical Reports Server (NTRS)

    Tarbell, T.; Ferguson, S.; Frank, Z.; Title, A.; Topka, K.

    1988-01-01

    Horizontal flows in the photosphere and subsurface convection zone move the footpoints of coronal magnetic field lines. Magnetic energy to power flares can be stored in the corona if the flows drive the fields far from the potential configuration. Videodisk movies were shown with 0.5 to 1 arcsecond resolution of the following simultaneous observations: green continuum, longitudinal magnetogram, Fe I 5576 A line center (mid-photosphere), H alpha wings, and H alpha line center. The movies show a 90 x 90 arcsecond field of view of an active region at S29, W11. When viewed at speeds of a few thousand times real-time, the photospheric movies clearly show the active region fields being distorted by a remarkable combination of systematic flows and small eruptions of new flux. Magnetic bipoles are emerging over a large area, and the polarities are systematically flowing apart. The horizontal flows were mapped in detail from the continuum movies, and these may be used to predict the future evolution of the region. The horizontal flows are not discernable in H alpha. The H alpha movies strongly suggest reconnection processes in the fibrils joining opposite polarities. When viewed in combination with the magnetic movies, the cause for this evolution is apparent: opposite polarity fields collide and partially cancel, and the fibrils reconnect above the surface. This type of reconnection, driven by subphotospheric flows, complicates the chromospheric and coronal fields, causing visible braiding and twisting of the fibrils. Some of the transient emission events in the fibrils and adjacent plage may also be related.

  19. High-Speed Electric Field Measurements and Lightning Mapping Observations at Langmuir Laboratory

    NASA Astrophysics Data System (ADS)

    Rison, W.; Edens, H. E.; Krehbiel, P. R.; Winn, W. P.; Aulich, G.; Hunyady, S. J.; Thomas, R. J.

    2007-12-01

    During the summer of 2007 we recorded broadband RF radiation waveforms, together with ground-based slow and fast electric field waveforms, from lightning in the vicinity of Langmuir Laboratory in central New Mexico. Three-dimensional observations of the lightning flashes from New Mexico Tech's Lightning Mapping Array (LMA) give context for interpreting the RF and electric field waveforms. In addition, high-speed in-situ vector electric field waveforms were recorded by a newly developed balloon-borne instrument. The broadband RF radiation was received using a Rhode & Schwarz model HE010 active rod antenna with a 100~MHz bandwidth, which was sampled at up to 400~MHz. Log-detected RF waveforms for two side-by-side LMA stations, one operating at 63 MHz (TV channel 3) and the other at 183 MHz (TV channel 9), and ground-based fast and slow electric field waveforms, were digitized at 25~MHz. All ground-based waveforms had a depth of 1~second, and were time-tagged with a GPS receiver. These comprehensive datasets are being used to study various processes associated with lightning flashes --- in particular, to detect high-frequency electrical activity at the onset of a flash. The ground based measurements, in conjunction with the in-situ vector field measurements, will be used to study the transfer of charge during a flash. Measurements of the log-detected RF (which is used by the LMA to map lightning flashes), in conjunction with the broadband RF and electric field waveforms, will help us better understand what types of events are detected and located by the LMA. In this paper we will present the results for a few interesting lightning flashes. ~

  20. Testing MHD models of prominences and flares with observations of solar plasma electric fields

    NASA Astrophysics Data System (ADS)

    Foukal, Peter V.; Behr, Bradford B.

    1995-02-01

    We present measurements of electric fields in quiescent prominences and in a small flare surge, obtained with CRI electrograph at the NSO/SP 40 cm coronagraph, in 1993 and 1994. Our results on the 9 brightest quiescent prominences enable us to place r.m.s. upper limits of Et less than 2 - 5 V/cm on the component of E transverse to the line of sight. We show that these upper limits may be difficult to reconcile with non-ideal MHD models of quiescent prominences formed in extended neutral sheets, whethere or not the tearing mode instability is present. They do, however, seem consistent with ideal MHD models of prominence support. We point out also that these upper limits are within a factor 4 of the minimum value of anistropic electric field that exists due to motional Stark effect in any thermal plasma permeated by a directed magnetic field. Our data on the flare surge suggest and electric field of intensity E approximately 35 V/cm, oriented approximately parallel to the inferred magnetic field. This detection of Eparallel needs to be verified in other flares. But we note that a detectable Eparallel would not be expected in the current interruption flare mechanism, if only a single double layer is present. We show further that the observed relatively narrow, approximately-Gaussian, and only slightly Doppler-shifted Paschen lines, seem inconsistent with the multiple double layers invoked in other models based on the current interruption mechanism. Our detection of Eparallel does seem consistent with reconnection (including tearing-mode) models of flares, provided the field-aligned electrical conductivity is anomalous over substantial volumes of the plasma circuit joining the reconnecting domain to the photosphere.

  1. Constraining the Magnetic Fields of Transiting Exoplanets through Ground-based Near-UV Observations

    NASA Astrophysics Data System (ADS)

    Turner, Jake; Smart, B.; Pearson, K.; Biddle, L. I.; Cates, I.; Berube, M.; Thompson, R.; Smith, C.; Teske, J. K.; Hardegree-Ullman, K.; Robertson, A.; Crawfod, B.; Zellem, R.; Nieberding, M. N.; Raphael, B. A.; Tombleson, R.; Cook, K.; Hoglund, S.; Hofmann, R.; Jones, C.; Towner, A. P.; Small, L.; Walker-LaFollette, A.; Sanford, B.; Sagan, T.

    2014-01-01

    We observed the primary transits of the exoplanets CoRoT-1b, HAT-P-1b, HAT-P-13b, HAT-P-22b, TrES-2b, TrES-4b, WASP-12b, WASP-33b, WASP-44b, WASP-48b, and WASP77A-b in the near-ultraviolet photometric band in an attempt to detect their magnetic fields and update their planetary parameters. Vidotto et al. (2011) suggest that the magnetic fields of these targets could be constrained if their near-UV light curves show an early ingress compared to their optical light curves, while their egress remain unaffected. We do not observe this effect in any of our targets, however, we have determined an upper limit on their magnetic field strengths. Our results are consistent with observations of TrES-3b and HAT-P-16b which both have had upper limits on their magnetic fields found using this method. We find abnormally low field strengths for all our targets. Due to this result we advocate for follow-up studies on the magnetic fields of all our targets using other detection methods (such as radio emission and magnetic star-planet interactions) and other telescopes capable of achieving a better near-UV cadence to verify our findings and the techniques of Vidotto et al. (2011). We find that the near-UV planetary radii of all our targets are consistent within error of their optical radii. Our data includes the only published near-UV light curves of CoRoT-1b, HAT-P-1b, HAT-P-13b, HAT-P-22b, TrES-2b, TrES-4b, WASP-33b, WASP-44b, WASP-48b, and WASP77A-b. We used an automated reduction pipeline, ExoDRPL, to perform aperture photometry on our data. In addition, we developed a modeling package called EXOMOP that utilizes the Levenberg-Marquardt minimization algorithm to find a least-squares best fit and a differential evolution Markov Chain Monte Carlo algorithm to find the best fit to the light curve. To constrain the red noise in both fitting models we used the residual permutation (rosary bead), time-averaging, and wavelet method.

  2. Constraining the Magnetic Fields of Transiting Exoplanets through Ground-based Near-UV Observations

    NASA Astrophysics Data System (ADS)

    Turner, Jake; Smart, B. M.; Pearson, K. A.; Biddle, L. I.; Cates, I. T.; Berube, M.; Thompson, R. M.; Smith, C. W.; Teske, J. K.; Hardegree-Ullman, K. K.; Robertson, A. N.; Crawfod, B. E.; Zellem, R.; Nieberding, M. N.; Raphael, B. A.; Tombleson, R.; Cook, K. L.; Hoglund, S.; Hofmann, R. A.; Jones, C.; Towner, A.; Small, L. C.; Walker-LaFollette, A. M.; Sanford, B.; Griffith, C. C.; Sagan, T.

    2013-10-01

    We observed the primary transits of the exoplanets CoRoT-1b, HAT-P-1b, HAT-P-13b, HAT-P-22b, TrES-2b, TrES-4b, WASP-12b, WASP-33b, WASP-44b, WASP-48b, and WASP77A-b in the near-ultraviolet photometric band in an attempt to detect their magnetic fields and update their planetary parameters. Vidotto et al. (2011) suggest that the magnetic fields of these targets could be constrained if their near-UV light curves show an early ingress compared to their optical light curves, while their egress remain unaffected. We do not observe this effect in any of our targets, however, we have determined an upper limit on their magnetic field strengths. Our results are consistent with observations of TrES-3b and HAT-P-16b which both have had upper limits on their magnetic fields found using this method. We find abnormally low field strengths for all our targets. Due to this result we advocate for follow-up studies on the magnetic fields of all our targets using other detection methods (such as radio emission and magnetic star-planet interactions) and other telescopes capable of achieving a better near-UV cadence to verify our findings and the techniques of Vidotto et al. (2011). We find that the near-UV planetary radii of all our targets are consistent within error of their optical radii. Our data includes the only published near-UV light curves of CoRoT-1b, HAT-P-1b, HAT-P-13b, HAT-P-22b, TrES-2b, TrES-4b, WASP-33b, WASP-44b, WASP-48b, and WASP77A-b. We used an automated reduction pipeline, ExoDRPL, to perform aperture photometry on our data. In addition, we developed a modeling package called EXOMOP that utilizes the Levenberg-Marquardt minimization algorithm to find a least-squares best fit and a differential evolution Markov Chain Monte Carlo algorithm to find the best fit to the light curve. To constrain the red noise in both fitting models we used the residual permutation (rosary bead), time-averaging, and wavelet method.

  3. The robustness of using near-UV observations to detect and study exoplanet magnetic fields

    NASA Astrophysics Data System (ADS)

    Turner, J.; Christie, D.; Arras, P.; Johnson, R.

    2015-10-01

    Studying the magnetic fields of exoplanets will allow for the investigation of their formation history, evolution, interior structure, rotation period, atmospheric dynamics, moons, and potential habitability. We previously observed the transits of 16 exoplanets as they crossed the face of their host-star in the near-UV in an attempt to detect their magnetic fields (Turner et al. 2013; Pearson et al. 2014; Turner et al. in press). It was postulated that the magnetic fields of all our targets could be constrained if their near-UV light curves start earlier than in their optical light curves (Vidotto et al. 2011). This effect can be explained by the presence of a bow shock in front of the planet formed by interactions between the stellar coronal material and the planet's magnetosphere. Furthermore, if the shocked material in the magnetosheath is optically thick, it will absorb starlight and cause an early ingress in the near- UV light curve. We do not observe an early ingress in any of our targets (See Figure 1 for an example light curve in our study), but determine upper limits on their magnetic field strengths. All our magnetic field upper limits are well below the predicted magnetic field strengths for hot Jupiters (Reiners & Christensen 2010; Sanchez-Lavega 2004). The upper limits we derived assume that there is an absorbing species in the near-UV. Therefore, our upper limits cannot be trusted if there is no species to cause the absorption. In this study we simulate the atomic physics, chemistry, radiation transport, and dynamics of the plasma characteristics in the vicinity of a hot Jupiter using the widely used radiative transfer code CLOUDY (Ferland et al. 2013). Using CLOUDY we have investigated whether there is an absorption species in the near-UV that can exist to cause an observable early ingress. The number density of hydrogen in the bow shock was varied from 104 - -108 cm-3 and the output spectrum was calculated (Figure 2) and compared to the input

  4. Sardinia Radio Telescope observations of Abell 194. The intra-cluster magnetic field power spectrum

    NASA Astrophysics Data System (ADS)

    Govoni, F.; Murgia, M.; Vacca, V.; Loi, F.; Girardi, M.; Gastaldello, F.; Giovannini, G.; Feretti, L.; Paladino, R.; Carretti, E.; Concu, R.; Melis, A.; Poppi, S.; Valente, G.; Bernardi, G.; Bonafede, A.; Boschin, W.; Brienza, M.; Clarke, T. E.; Colafrancesco, S.; de Gasperin, F.; Eckert, D.; Enßlin, T. A.; Ferrari, C.; Gregorini, L.; Johnston-Hollitt, M.; Junklewitz, H.; Orrù, E.; Parma, P.; Perley, R.; Rossetti, M.; B Taylor, G.; Vazza, F.

    2017-07-01

    Aims: We study the intra-cluster magnetic field in the poor galaxy cluster Abell 194 by complementing radio data, at different frequencies, with data in the optical and X-ray bands. Methods: We analyzed new total intensity and polarization observations of Abell 194 obtained with the Sardinia Radio Telescope (SRT). We used the SRT data in combination with archival Very Large Array observations to derive both the spectral aging and rotation measure (RM) images of the radio galaxies 3C 40A and 3C 40B embedded in Abell 194. To obtain new additional insights into the cluster structure, we investigated the redshifts of 1893 galaxies, resulting in a sample of 143 fiducial cluster members. We analyzed the available ROSAT and Chandra observations to measure the electron density profile of the galaxy cluster. Results: The optical analysis indicates that Abell 194 does not show a major and recent cluster merger, but rather agrees with a scenario of accretion of small groups, mainly along the NE-SW direction. Under the minimum energy assumption, the lifetimes of synchrotron electrons in 3C 40 B measured from the spectral break are found to be 157 ± 11 Myr. The break frequency image and the electron density profile inferred from the X-ray emission are used in combination with the RM data to constrain the intra-cluster magnetic field power spectrum. By assuming a Kolmogorov power-law power spectrum with a minimum scale of fluctuations of Λmin = 1 kpc, we find that the RM data in Abell 194 are well described by a magnetic field with a maximum scale of fluctuations of Λmax = (64 ± 24) kpc. We find a central magnetic field strength of ⟨ B0 ⟩ = (1.5 ± 0.2) μG, which is the lowest ever measured so far in galaxy clusters based on Faraday rotation analysis. Further out, the field decreases with the radius following the gas density to the power of η = 1.1 ± 0.2. Comparing Abell 194 with a small sample of galaxy clusters, there is a hint of a trend between central electron

  5. Using MERRA Gridded Innovations for Quantifying Uncertainties in Analysis Fields and Diagnosing Observing System Inhomogeneities

    NASA Technical Reports Server (NTRS)

    da Silva, Arlindo; Redder, Christopher

    2010-01-01

    MERRA is a NASA reanalysis for the satellite era using a major new version of the Goddard Earth Observing System Data Assimilation System Version 5 (GEOS-5). The project focuses on historical analyses of the hydrological cycle on a broad range of weather and climate time scales and places the NASA EOS suite of observations in a climate context. The characterization of uncertainty in reanalysis fields is a commonly requested feature by users of such data. While intercomparison with reference data sets is common practice for ascertaining the realism of the datasets, such studies typically are restricted to long term climatological statistics and seldom provide state dependent measures of the uncertainties involved. In principle, variational data assimilation algorithms have the ability of producing error estimates for the analysis variables (typically surface pressure, winds, temperature, moisture and ozone) consistent with the assumed background and observation error statistics. However, these "perceived error estimates" are expensive to obtain and are limited by the somewhat simplistic errors assumed in the algorithm. The observation minus forecast residuals (innovations) by-product of any assimilation system constitutes a powerful tool for estimating the systematic and random errors in the analysis fields. Unfortunately, such data is usually not readily available with reanalysis products, often requiring the tedious decoding of large datasets and not so-user friendly file formats. With MERRA we have introduced a gridded version of the observations/innovations used in the assimilation process, using the same grid and data formats as the regular datasets. Such dataset empowers the user with the ability of conveniently performing observing system related analysis and error estimates. The scope of this dataset will be briefly described. We will present a systematic analysis of MERRA innovation time series for the conventional observing system, including maximum

  6. Using MERRA Gridded Innovation for Quantifying Uncertainties in Analysis Fields and Diagnosing Observing System Inhomogeneities

    NASA Astrophysics Data System (ADS)

    da Silva, A.; Redder, C. R.

    2010-12-01

    MERRA is a NASA reanalysis for the satellite era using a major new version of the Goddard Earth Observing System Data Assimilation System Version 5 (GEOS-5). The Project focuses on historical analyses of the hydrological cycle on a broad range of weather and climate time scales and places the NASA EOS suite of observations in a climate context. The characterization of uncertainty in reanalysis fields is a commonly requested feature by users of such data. While intercomparison with reference data sets is common practice for ascertaining the realism of the datasets, such studies typically are restricted to long term climatological statistics and seldom provide state dependent measures of the uncertainties involved. In principle, variational data assimilation algorithms have the ability of producing error estimates for the analysis variables (typically surface pressure, winds, temperature, moisture and ozone) consistent with the assumed background and observation error statistics. However, these "perceived error estimates" are expensive to obtain and are limited by the somewhat simplistic errors assumed in the algorithm. The observation minus forecast residuals (innovations) by-product of any assimilation system constitutes a powerful tool for estimating the systematic and random errors in the analysis fields. Unfortunately, such data is usually not readily available with reanalysis products, often requiring the tedious decoding of large datasets and not so-user friendly file formats. With MERRA we have introduced a gridded version of the observations/innovations used in the assimilation process, using the same grid and data formats as the regular datasets. Such dataset empowers the user with the ability of conveniently performing observing system related analysis and error estimates. The scope of this dataset will be briefly described. We will present a systematic analysis of MERRA innovation time series for the conventional observing system, including maximum

  7. Mercury's Time-Averaged and Induced Magnetic Fields from MESSENGER Observations

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.; Winslow, R. M.; Anderson, B. J.; Purucker, M. E.; Korth, H.; Al Asad, M. M.; Slavin, J. A.; Baker, D. N.; Hauck, S. A.; Phillips, R. J.; Zuber, M. T.; Solomon, S. C.

    2012-12-01

    Observations from MESSENGER's Magnetometer (MAG) have allowed the construction of a baseline, time-averaged model for Mercury's magnetosphere. The model, constructed with the approximation that the magnetospheric shape can be represented as a paraboloid, includes two external (magnetopause and magnetotail) current systems and an internal (dipole) field. We take advantage of the geometry of the orbital MAG data to constrain all but one of the model parameters, and their ranges, directly from the observations. These parameters are then used as a priori constraints in the magnetospheric model, and the remaining parameter, the dipole moment, is estimated from a grid search. The model provides an excellent fit to the MAG observations, with a root-mean-square misfit of less than 20 nT globally. The mean distance from the planetary dipole origin to the magnetopause subsolar point, RSS, is 1.45 RM (where RM = 2440 km) and the mean planetary dipole moment is 190 nT- RM3. Temporal variations in the global-scale magnetic fields result from changes in solar wind ram pressure, Pram, at Mercury that arise from the planet's 88-day eccentric orbit around the Sun and from transient, rapid changes in solar wind conditions. For a constant planetary dipole moment, RSS varies as Pram-1/6. However, magnetopause crossings obtained from several Mercury years of MESSENGER observations indicate that RSS is proportional to Pram-1/a where a is greater than 6, suggesting induction in Mercury's highly conducting metallic interior. We obtain an effective dipole moment that varies by up to ˜15% about its mean value. We further investigate the periodic 88-day induction signature and use the paraboloid model to describe the spatial structure in the inducing magnetopause field, together with estimates for the outer radius of Mercury's liquid core and possible overlying solid iron sulfide layer, to calculate induced core fields. The baseline magnetospheric model is adapted to include the 88-day

  8. Observation of Novel Low-Field FMR modes in Permalloy Antidot Arrays

    NASA Astrophysics Data System (ADS)

    de Long, Lance; Bhat, Vinayak; Farmer, Barry; Woods, Justin; Hastings, Todd; Sklenar, Joseph; Ketterson, John

    2013-03-01

    Permalloy films of thickness 23 nm were patterned with square arrays of square antidots (AD) with feature size D = 120 nm, and lattice constants d = 200, 300, 500 and 700 nm (total sample area = 2 mm x 2mm), using electron beam lithography. Our broad-band (frequencies f = 10 MHz-15 GHz) and narrow-band (9.7 GHz) FMR measurements of even dilute (D/d <<1) AD lattices (ADL) reveal remarkably reproducible absorption spectra in the low-frequency, hysteretic regime in which disordered domain wall (DW) patterns and unsaturated magnetization textures are expected for unpatterned films, but in the present case are strongly affected by the periodic ADL. Other modes in the saturated regime exhibit strong dependence on the angle between the applied DC field H and the ADL axes, as confirmed by our micromagnetic simulations. Novel modes are observed at DC fields above that of the uniform mode, which simulations indicate are localized at AD edges. Other novel modes are observed for DC fields below that of the uniform mode, which simulated power and phase maps indicate are confined to ADL interstices oriented parallel to H. These results show even dilute AD concentrations can effect strong control of DW evolution. Research at Kentucky is supported by U.S. DoE Grant DE-FG02-97ER45653 and NSF Grant EPS-0814194.

  9. TSUBASA (MDS-1) observations of energetic electrons and magnetic field variations in outer radiation belt

    NASA Astrophysics Data System (ADS)

    Nakamura, M.; Matsuoka, H.; Liu, H.; Koshiishi, H.; Koga, K.; Matsumoto, H.; Goka, T.

    2002-12-01

    We have investigated variations of energetic electrons (> 0.4 MeV) and magnetic field in the radiation belt obtained from the Standard DOse Monitor (SDOM) and the MAgnetoMeter (MAM) of the Space Environment Data Acquisition equipment (SEDA) onboard TSUBASA (the Mission Demonstration Test Satellite (MDS)-1) launched on February 4, 2002. Since TSUBASA is operated in the geostationary transfer orbit, it has provided rare opportunities of directly observing near-equatorial radiation belt plasma particles and magnetic field, having already included several large magnetic storms. The energetic electrons in the outer radiation belt are contributors to the total radiation dose deposited in lightly shielded spacecraft electronics for high altitude orbits and are known to have a drastic variability associated with geomagnetic storm and high speed solar wind streams. The abrupt energetic electron flux decreases in the outside of outer radiation belt show characteristic variations of in situ magnetic field. These observations have implications for the possible mechanisms of the depletion and the following recovery and/or buildup of energetic electrons in the outer radiation belt.

  10. Field-aligned electron density irregularities near 500 km Equator to polar cap topside sounder observations

    SciTech Connect

    Benson, R.F.

    1985-06-01

    In addition to spread F, evidence for field-aligned electron density irregularities is commonly observed on Alouette 2 topside sounder ionograms recorded near perigee (500 km). This evidence is provided by distinctive signal returns from sounder-generated Z mode waves. At low latitudes these waves become guided in wave ducts caused by field-aligned electron density irregularities and give rise to strong long-duration echoes. At high latitudes, extending well into the polar cap, these Z mode waves (and stimulated electrostatic waves at the plasma frequency) produce a series of vertical bars on the ionogram display as the satellite traverses discrete field-aligned density structures. The radio frequency (RF) noise environment to be expected in the 400 to 500 km altitude region from low to high latitudes was examined by analyzing perigee Alouette 2 topside sounder data. All observed noise bands were scaled on nearly 200 topside sounder ionograms recorded near perigee at low, mid, and high latitude telemetry stations. The minimum and maximum frequencies of each noise band were entered into a data base or computer analysis. The signals of primary interest in the perigee study were found to be sounder-generated. 15 references.

  11. Neutral hydrogen and magnetic fields in M83 observed with the SKA Pathfinder KAT-7

    NASA Astrophysics Data System (ADS)

    Heald, G.; de Blok, W. J. G.; Lucero, D.; Carignan, C.; Jarrett, T.; Elson, E.; Oozeer, N.; Randriamampandry, T. H.; van Zee, L.

    2016-10-01

    We present new KAT-7 observations of the neutral hydrogen (H I) spectral line, and polarized radio continuum emission, in the grand-design spiral M83. These observations provide a sensitive probe of the outer-disc structure and kinematics, revealing a vast and massive neutral gas distribution that appears to be tightly coupled to the interaction of the galaxy with the environment. We present a new rotation curve extending out to a radius of 50 kpc. Based on our new H I data set and comparison with multiwavelength data from the literature, we consider the impact of mergers on the outer disc and discuss the evolution of M83. We also study the periphery of the H I distribution and reveal a sharp edge to the gaseous disc that is consistent with photoionization or ram pressure from the intergalactic medium. The radio continuum emission is not nearly as extended as the H I and is restricted to the main optical disc. Despite the relatively low angular resolution, we are able to draw broad conclusions about the large-scale magnetic field topology. We show that the magnetic field of M83 is similar in form to other nearby star-forming galaxies, and suggest that the disc-halo interface may host a large-scale regular magnetic field.

  12. Prediction and near-field observation of skull-guided acoustic waves

    NASA Astrophysics Data System (ADS)

    Estrada, Héctor; Rebling, Johannes; Razansky, Daniel

    2017-06-01

    Ultrasound waves propagating in water or soft biological tissue are strongly reflected when encountering the skull, which limits the use of ultrasound-based techniques in transcranial imaging and therapeutic applications. Current knowledge on the acoustic properties of the cranial bone is restricted to far-field observations, leaving its near-field unexplored. We report on the existence of skull-guided acoustic waves, which was herein confirmed by near-field measurements of optoacoustically-induced responses in ex-vivo murine skulls immersed in water. Dispersion of the guided waves was found to reasonably agree with the prediction of a multilayered flat plate model. We observed a skull-guided wave propagation over a lateral distance of at least 3 mm, with a half-decay length in the direction perpendicular to the skull ranging from 35 to 300 μm at 6 and 0.5 MHz, respectively. Propagation losses are mostly attributed to the heterogenous acoustic properties of the skull. It is generally anticipated that our findings may facilitate and broaden the application of ultrasound-mediated techniques in brain diagnostics and therapy.

  13. Prediction and near-field observation of skull-guided acoustic waves.

    PubMed

    Estrada, Hector; Rebling, Johannes; Razansky, Daniel

    2017-03-01

    Ultrasound waves propagating in water or soft biological tissue are strongly reflected when encountering the skull, which limits the use of ultrasound-based techniques in transcranial imaging and therapeutic applications. Current knowledge on the acoustic properties of the cranial bone is restricted to far-field observations, leaving its near-field unexplored. We report on the existence of skull-guided acoustic waves, which was herein confirmed by near-field measurements of optoacoustically-induced responses in ex-vivo murine skulls immersed in water. Dispersion of the guided waves was found to reasonably agree with the prediction of a multilayered flat plate model. We observed a skull-guided wave propagation over a lateral distance of at least 3 mm, with a half-decay length in the direction perpendicular to the skull ranging from 35 to 300 μm at 6 and 0.5 MHz, respectively. Propagation losses are mostly attributed to the heterogenous acoustic properties of the skull.. It is generally anticipated that our findings may facilitate and broaden the application of ultrasound-mediated techniques in brain diagnostics and therapy.

  14. Radar Observations of Density Gradients, Electric Fields, and Plasma Irregularities Near Polar Patches

    NASA Astrophysics Data System (ADS)

    Lamarche, L. J.; Makarevich, R. A.

    2016-12-01

    It is commonly accepted that large density structures in the polar F region ionosphere have more plasma structuring on their trailing edge than leading edge. This has been experimentally demonstrated and is traditionally interpreted in the context of linear gradient-drift instability (GDI) theory. The asymmetry around large scale density structures (polar patches) observed in one case event is investigated by examining the relationship between HF radar backscatter power observed with the Super Dual Auroral Radar Network (SuperDARN) radar at Rankin Inlet (RKN) and local plasma parameters measured by the Resolute Bay Incoherent Scatter Radar (RISR-N). The GDI growth rates are modeled based on a general theory with arbitrary density gradient and electric field vectors using RISR-N measurements. The model predictions are compared to irregularity characteristics measured by RKN, with a particular focus on the previously unexplored directional dependencies of the irregularity strengths/echo power on the density gradient and electric field. Relationships between irregularity strength, electron density, and gradient scale are also examined. It is demonstrated that echo occurrence peaks when density gradients are parallel to the drift velocity and RKN echo power is generally higher when electric field and/or gradient components increase. The presented experimental data indicate that both of these directional factors contribute to plasma irregularity growth through the GDI mechanism and must be considered in GDI modeling efforts.

  15. Salinity selection and preference of the grey snapper Lutjanus griseus: field and laboratory observations.

    PubMed

    Serrano, X; Grosell, M; Serafy, J E

    2010-05-01

    Field observations were supplemented with laboratory experiments to reveal patterns of salinity selection and preference for grey snapper Lutjanus griseus (c. 21 cm total length, L(T)), an ecologically and economically important species in the south-eastern U.S.A. Fish abundance data were examined from a long-term field survey conducted in the mangrove habitats of Biscayne Bay, Florida, where salinities ranged from <1 to 40. First, regression analyses indicated significant, positive linear relationships with salinity for both L. griseus frequency of occurrence and concentration (density when present). These patterns are inconsistent with physiological expectations of minimizing energetic osmoregulatory costs. Next, the salinity preference and swimming activity of 11 L. griseus (ranging from 18 to 23 cm L(T)) were investigated using a newly developed electronic shuttlebox system. In the laboratory, fish preferred intermediate salinities in the range of 9-23. Swimming activity (measured in terms of spontaneous swimming speed) followed a parabolic relationship with salinity, with reduced activity at salinity extremes perhaps reflecting compensation for higher osmoregulatory costs. It is suspected that the basis of the discrepancy between laboratory and field observations for size classes at or near maturity ultimately relates to the reproductive imperative to move towards offshore (high-salinity) coral-reef habitats, a necessity that probably overrides the strategy of minimizing osmoregulatory energetic costs.

  16. STAR FORMATION IN THE CHANDRA DEEP FIELD SOUTH: OBSERVATIONS CONFRONT SIMULATIONS

    SciTech Connect

    Damen, Maaike; Franx, Marijn; Foerster Schreiber, Natascha M.; Labbe, Ivo; Toft, Sune; Van Dokkum, Pieter G.; Wuyts, Stijn

    2009-11-01

    We investigate the star formation history of the universe using FIREWORKS, a multiwavelength survey of the Chandra Deep Field South. We study the evolution of the specific star formation rate (sSFR) with redshift in different mass bins from z = 0 to z approx 3. We find that the sSFR increases with redshift for all masses. The logarithmic increase of the sSFR with redshift is nearly independent of mass, but this cannot yet be verified at the lowest-mass bins at z>0.8, due to incompleteness. We convert the sSFRs to a dimensionless growth rate to facilitate a comparison with a semianalytic galaxy formation model that was implemented on the Millennium Simulation. The model predicts that the growth rates and sSFRs increase similarly with redshift for all masses, consistent with the observations. However, we find that for all masses, the inferred observed growth rates increase more rapidly with redshift than the mo