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1

The 2008 August 1 Eclipse Solar-Minimum Corona Unraveled  

NASA Astrophysics Data System (ADS)

We discuss the results stemming from observations of the white-light and [Fe XIV] emission corona during the total eclipse of the Sun of 2008 August 1, in Mongolia (Altaj region) and in Russia (Akademgorodok, Novosibirsk, Siberia). Corresponding to the current extreme solar minimum, the white-light corona, visible up to 20 solar radii, was of a transient type with well pronounced helmet streamers situated above a chain of prominences at position angles 48, 130, 241, and 322. A variety of coronal holes, filled with a number of thin polar plumes, were seen around the poles. Furthering an original method of image processing, stars up to 12 mag, a Kreutz-group comet (C/2008 O1) and a coronal mass ejection (CME) were also detected, with the smallest resolvable structures being of, and at some places even less than, 1 arcsec. Differences, presumably motions, in the corona and prominences are seen even with the 19 minutes time difference between our sites. In addition to the high-resolution coronal images, which show the continuum corona (K-corona) that results from electron scattering of photospheric light, images of the overlapping green-emission-line (530.3 nm, [Fe XIV]) corona were obtained with the help of two narrow-passband filters (centered on the line itself and for the continuum in the vicinity of 529.1 nm, respectively), each with an FWHM of 0.15 nm. Through solar observations, on whose scheduling and details we consulted, with the Solar and Heliospheric Observatory, Hinode's XRT and SOT, Transition Region and Coronal Explorer, and STEREO, as well as Wilcox Solar Observatory and Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms, we set our eclipse observations in the context of the current unusually low and prolonged solar minimum.

Pasachoff, J. M.; Ruin, V.; Druckmller, M.; Aniol, P.; Saniga, M.; Minarovjech, M.

2009-09-01

2

The Large-Scale Structure of the Solar Minimum Corona  

NASA Astrophysics Data System (ADS)

I will present the results of my Ph.D. thesis, the goal of which was to find a quantitative description of the large-scale structure of magnetic field and density in the solar minimum corona that was consistent with observations of both white light intensity and the magnetic field at the photosphere. We used white light images from NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High Altitude Observatory Mark III (MkIII) K-coronameter, along with photospheric field measurements from Stanford's Wilcox Solar Observatory (WSO), as constraints on the magnetostatic model of Bogdan and Low (B&L) [\\markcite{1986}]. We found a solution to the B&L model that reproduced observations of white light and photospheric flux to within quantifiable model and observational limits, and calculated the physical plasma properties of density, pressure, magnetic field, and temperature that corresponded to these parameters. Further, we extended the model to include current sheets at the equator and around the coronal helmet streamer, and showed that by doing so we improved the fit to white light data and to a lesser extent to the photospheric flux. Moreover, by including current sheets in the model, we produced a magnetic field line structure which better matched the underlying coronal white light structure, and which was more consistent with a solar wind accelerating along the open field lines. This work was partially funded by NASA GSRP grant number 50916.

Gibson, Sarah

1995-12-01

3

The Large-Scale Structure of the Solar Minimum Corona  

NASA Astrophysics Data System (ADS)

The goal of this thesis is to find a quantitative description of the large-scale structure of magnetic field and density in the solar minimum corona that is consistent with observations of both white light intensity and the magnetic field at the photosphere. We use white light images from NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High Altitude Observatory Mark III (MkIII) K-coronameter, along with photospheric field measurements from Stanford's Wilcox Solar Observatory (WSO), as constraints on the magnetostatic model of Bogdan and Low (B&L) (1986). We find a family of solutions to the B&L model that reproduce observations of white light quite well, each with a different magnetic field structure. We show that the observed photospheric field cannot be used as an exact boundary condition on the B&L model, but we can limit the white light solutions by matching the total observed photospheric magnetic flux. We find a set of seven model parameters that reproduces white light and photospheric field to within quantifiable model and observational limits, and calculate the physical plasma properties of density, pressure, magnetic field, and temperature that correspond to these parameters. We extend the model to include current sheets at the equator and around the coronal helmet streamer, and show that by doing so we improve the fit to white light data and to a lesser extent to the photospheric flux. Moreover, by including current sheets in the model, we produce a magnetic field line structure which better matches the underlying coronal white light structure, and which is more consistent with a solar wind accelerating along the open field lines. We use the magnetic field structure determined from our bulk current/current sheet model to calculate expansion factors, which can be used as essential inputs to solar wind models. Finally, we determine that the temperature structure predicted by our model is not in thermal equilibrium. We present a preliminary comparison of this temperature structure to independent emission line temperature diagnostics, and discuss how we hope in future to use such analyses to produce a more energetically consistent temperature distribution.

Gibson, Sarah Elizabeth

1995-01-01

4

THE SOLAR MINIMUM CORONA FROM DIFFERENTIAL EMISSION MEASURE TOMOGRAPHY  

SciTech Connect

We present results derived from a dual-spacecraft tomographic reconstruction of the solar corona's three-dimensional (3D) extreme ultraviolet (EUV) emissivity. We use simultaneously taken STEREO A and B spacecraft EUVI images from Carrington rotation 2077 (UT 2008 November 20 06:56 through UT December 17 14:34). During this period, the spacecraft view angles were separated by an average 85.{sup 0}4 which allowed for the reconstruction to be performed with data gathered in about 3/4 of a full solar rotational time. The EUV reconstructions provide the 3D emissivity in each of the three EUVI Fe bands, in the range of heights 1.00-1.25 R {sub s}. We use this information to perform local differential emission measure (LDEM) analysis. Taking moments of the so-derived LDEM distributions gives the 3D values of the electron density, temperature, and temperature spread. We determine relationships between the moments of the LDEM and the coronal magnetic field by making longitudinal averages of the moments, and relating them to the global-scale structures of a potential field source surface magnetic field model. In this way, we determine how the electron density, mean temperature, and temperature spread vary for different coronal structures. We draw conclusions about the relationship between the LDEM moments and the sources of the fast and slow solar winds, and the transition between the two regimes.

Vasquez, Alberto M. [Instituto de AstronomIa y Fisica del Espacio, CONICET-University of Buenos Aires, Ciudad de Buenos Aires, CC 67-Suc 28 (Argentina); Frazin, Richard A.; Manchester, Ward B., E-mail: albert@iafe.uba.a, E-mail: rfrazin@umich.ed [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States)

2010-06-01

5

Large-scale magnetic field and density distribution in the solar minimum corona  

NASA Astrophysics Data System (ADS)

We seek a quantitative description of the large-scale structure of magnetic field and density in the solar minimum corona that is consistent with observations of both white light intensity and the magnetic field at the photosphere. We use white light images from NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High-Altitude Observatory Mark III (MkIII) K-coronameter, along with photospheric field measurements from Stanford's Wilcox Solar Observatory (WSO), as constraints on the magnetostatic model of Bogdan and Low [1986] (B&L). We find a family of solutions to the B&L model that reproduce observations of white light quite well, each with a different magnetic field structure. We show that the observed photospheric field cannot be used as an exact boundary condition on the B&L model, but we can limit the white light solutions by matching the total observed photospheric magnetic flux. We find a set of model parameters that reproduces white light and photospheric field to within quantifiable model and observational limits and calculate the physical plasma properties corresponding to these parameters. We conclude that this fit represents a self-consistent description of the solar minimum coronal magnetic field and density.

Gibson, S. E.; Bagenal, F.

1995-10-01

6

Measurements of Faraday Rotation Through the Solar Corona During the 2009 Solar Minimum with the MESSENGER Spacecraft  

NASA Astrophysics Data System (ADS)

Measurements of Faraday rotation through the solar corona were collected using the radio beacon aboard the MESSENGER spacecraft during the longest solar minimum in a century. As MESSENGER entered superior conjunction, the plane of polarization of its radio signal was observed to rotate as it traversed the circularly birefringent plasma of the Sun's atmosphere. On time scales of less than three hours, these uncalibrated plane of polarization observations of Faraday rotation can be used to investigate the dynamic processes in the solar plasma, such as magnetohydrodynamic (MHD) waves and coronal mass ejections (CMEs). Here we describe the MESSENGER Faraday rotation experiment, the data processing conducted to obtain the plane of polarization, and the estimation of error.

Jensen, Elizabeth A.; Bisi, Mario M.; Breen, Andrew R.; Heiles, Carl; Minter, Toney; Vilas, Faith

2013-07-01

7

3D Differential Emission Measure of the 2008 Solar Minimum Corona with Dual-Spacecraft EUVI/STEREO Tomography  

NASA Astrophysics Data System (ADS)

We have recently developed solar rotational tomography (SRT) of EUV image time series for the empirical determination of the three-dimensional (3D) distribution of the differential emission measure (DEM) of the global corona. Using this technique, we present a 3D tomographic reconstruction of the local DEM (which also yields the electron density) of the global solar corona between 1.03 and 1.25 Rs for Carrington Rotation 2077 (starting 2008 November 20). The reconstructions were performed using simultaneous STEREO A and B spacecraft EUVI data in the 17.1, 19.5, 28.4 and 30.4 nm bands. At this time, the positions of the two spacecraft were separated by about 90, which allowed for the EUV reconstruction to be performed in about 3/4 of a solar rotational time instead of a full Carrington rotation, which improved the time resolution of the technique. We complement this reconstruction with a simultaneous potential field source-surface (PFSS) reconstruction of the magnetic field. During this period there were only two important active regions (ARs), and the corona was dominated by a large scale bipolar structure. We show both the full 3D results as well as the azimuthally averaged 2D results, excluding the ARs. The comparison of the 2D results among the tomographic local DEM and the PFSSM results, allows for the construction of a large scale quantitative semiempirical model of the geometry and thermodynamical properties of the equatorial streamer and subpolar regions of the solar minimum corona.

Vasquez, A. M.; Frazin, R. A.

2009-12-01

8

Space weather effectiveness during solar minimum  

NASA Astrophysics Data System (ADS)

Space weather effectiveness during solar minimum L. Trichtchenko Natural Resources Canada During the descending phase of a solar cycle and around solar minimum, recurrent coronal holes can persist for many solar rotations. Such recurrent solar activity manifests itself in in-terplanetary space as high speed solar wind streams. Though they do not cause severe magnetic storms, they can have significant effects on the technological infrastructure which is specifically sensitive to the long duration effects. Enhancements in high energy particles (electrons) are often associated with the recurrent solar features and thus would create a higher risk satellite environment for longer time than during solar transient events (that are more typical for solar maximum). On the ground the solar recurrent activity creates long-lasting (days) recurrent magnetic disturbances in the auroral zone. This would lead to increased cumulative effects on pipeline corrosion protection system, and can more effectively reduce pipeline lifetime than short-lived extreme geomagnetic storms. Estimations of cumulative times for elevated activi-ties produced by high speed streams during solar minimum and their projected effects on the infrastructure are presented. Their comparisons with cumulative times of geomagnetic storms for the last solar cycle are discussed in the presentation.

Trichtchenko, Larisa

9

Solar Wind Properties During the Current Solar Minimum: Ulysses Observations  

NASA Astrophysics Data System (ADS)

Using Ulysses solar wind composition data it is possible to compare observations in the current, unusual solar minimum with those obtained during the minimum in 1994-95. It has been re-ported earlier that, during the current minimum, there is a 15% reduction of the heliospheric magnetic field (Smith and Balogh, 2008), and 17% and 14% reduction in density and temperature, respectively (McComas et al., 2008), as compared to the previous minimum. But the polar coronal hole (PCH)-associated solar wind streams show long-term variability not only in dynamic, but also in compositional properties. The observed trends provide powerful tools to investigate the properties of the underlying corona during this time. From 1995 to 2008, the C and O freeze-in temperatures measured in high-latitude solar wind have steadily decreased by 15% and are now around 0.86 MK and 1.0 MK, respectively. Si and Fe ionization states also exhibit a substantial cooling with a reduction of 0.2 and 0.3 charge states, respectively. Thus it appears that all observed PCHs of cycle 23 are cooler overall than those of cycle 22. It is more difficult to assess whether there are significant changes of the elemental composition of the solar wind, as exhibited through the First Ionization Potential fractionation effect, which seems to have remained at f = 1.8 0.3 during all polar passages. These observations provide a unique test for theories of the solar wind and its composition. Furthermore, the comparative analysis of the corona with these data provides important insights about the physical processes that link the Sun and its heliosphere.

von Steiger, Rudolf; Zurbuchen, Thomas H.

10

The Evolution of Plasma Parameters on a Coronal Source Surface at 2.3 R ? during Solar Minimum  

NASA Astrophysics Data System (ADS)

We analyze data from the Solar and Heliospheric Observatory to produce global maps of coronal outflow velocities and densities in the regions where the solar wind is undergoing acceleration. The maps use UV and white light coronal data obtained from the Ultraviolet Coronagraph Spectrometer and the Large Angle Spectroscopic Coronagraph, respectively, and a Doppler dimming analysis to determine the mean outflow velocities. The outflow velocities are defined on a sphere at 2.3 R ? from Sun-center and are organized by Carrington Rotations during the solar minimum period at the start of solar cycle 23. We use the outflow velocity and density maps to show that while the solar minimum corona is relatively stable during its early stages, the shrinkage of the north polar hole in the later stages leads to changes in both the global areal expansion of the coronal hole and the derived internal flux tube expansion factors of the solar wind. The polar hole areal expansion factor and the flux tube expansion factors (between the coronal base and 2.3 R ?) start out as super-radial but then they become more nearly radial as the corona progresses away from solar minimum. The results also support the idea that the largest flux tube expansion factors are located near the coronal hole/streamer interface, at least during the deepest part of the solar minimum period.

Strachan, L.; Panasyuk, A. V.; Kohl, J. L.; Lamy, P.

2012-01-01

11

Are Sunspots Different During This Solar Minimum?  

NASA Astrophysics Data System (ADS)

For hundreds of years, humans have observed that the Sun has displayed activity where the number of sunspots increases and then decreases at approximately 11-year intervals. Sunspots are dark regions on the solar disk with magnetic field strengths greater than 1500 gauss (see Figure 1), and the 11-year sunspot cycle is actually a 22-year cycle in the solar magnetic field, with sunspots showing the same hemispheric magnetic polarity on alternate 11-year cycles. The last solar maximum occurred in 2001, and the magnetically active sunspots at that time produced powerful flares causing large geomagnetic disturbances and disrupting some space-based technology. But something is unusual about the current sunspot cycle. The current solar minimum has been unusually long, and with more than 670 days without sunspots through June 2009, the number of spotless days has not been equaled since 1933 (see http://users.telenet.be/j.janssens/Spotless//Spotless.html). The solar wind is reported to be in a uniquely low energy state since space measurements began nearly 40 years ago [Fisk and Zhao, 2009].

Livingston, W.; Penn, M.

2009-07-01

12

NEWLY DISCOVERED GLOBAL TEMPERATURE STRUCTURES IN THE QUIET SUN AT SOLAR MINIMUM  

SciTech Connect

Magnetic loops are building blocks of the closed-field corona. While active region loops are readily seen in images taken at EUV and X-ray wavelengths, quiet-Sun (QS) loops are seldom identifiable and are therefore difficult to study on an individual basis. The first analysis of solar minimum (Carrington Rotation 2077) QS coronal loops utilizing a novel technique called the Michigan Loop Diagnostic Technique (MLDT) is presented. This technique combines Differential Emission Measure Tomography and a potential field source surface (PFSS) model, and consists of tracing PFSS field lines through the tomographic grid on which the local differential emission measure is determined. As a result, the electron temperature T{sub e} and density N{sub e} at each point along each individual field line can be obtained. Using data from STEREO/EUVI and SOHO/MDI, the MLDT identifies two types of QS loops in the corona: so-called up loops in which the temperature increases with height and so-called down loops in which the temperature decreases with height. Up loops are expected, however, down loops are a surprise, and furthermore, they are ubiquitous in the low-latitude corona. Up loops dominate the QS at higher latitudes. The MLDT allows independent determination of the empirical pressure and density scale heights, and the differences between the two remain to be explained. The down loops appear to be a newly discovered property of the solar minimum corona that may shed light on the physics of coronal heating. The results are shown to be robust to the calibration uncertainties of the EUVI instrument.

Huang Zhenguang; Frazin, Richard A.; Landi, Enrico; Manchester, Ward B.; Gombosi, Tamas I. [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States); Vasquez, Alberto M. [Instituto de Astronomia y Fisica del Espacio, CONICET-University of Buenos Aires, Ciudad de Buenos Aires, CC 67-Suc 28 (Argentina)

2012-08-20

13

Viking solar corona experiment  

Microsoft Academic Search

The 1976 Mars solar conjunction resulted in complete occulations of the Viking spacecraft by the sun at solar minimum. During the conjunction period, coherent 3.5- and 13-cm wavelength radio waves from the orbiters passed through the solar corona and were received with the 64-m antennas of the NASA Deep Space Network. Data were obtained within at least 0.3 and 0.8

G. LEONARD Tyler; Joseph P. Brenkle; Thomas A. Komarek; Arthur I. Zygielbaum

1977-01-01

14

STEREO's in-situ perspective on the solar minimum solar wind structure  

NASA Astrophysics Data System (ADS)

STEREO multipoint measurements of the solar wind structure with the IMPACT and PLASTIC investigations, near Earth but off the Sun-Earth line, allow its sources and structure to be examined at solar minimum when such studies are particularly straightforward. With the aid of 3D models of the heliosphere available at the CCMC, we map the in-situ observations to their solar sources using a combination of the open field regions inferred from the SECCHI EUVI imagers and SOHO EIT, and the magnetogram-based models of the corona and solar wind. Our ultimate goal is the continuous tracking of solar wind source regions as the STEREO mission progresses, as well as the use of the mappings to deduce the distinctive properties of solar wind from different types of sources

Luhmann, J. G.; Larson, D.; Schroeder, P.; Lee, C. O.; Sauvaud, J.; Acuna, M. H.; Galvin, A. B.; Russell, C. T.; Jian, L.; Arge, C. N.; Odstrcil, D.; Riley, P.; Howard, R. A.; Aschwanden, M.; MacNeice, P.; Chulaki, A.

2007-05-01

15

THE EVOLUTION OF PLASMA PARAMETERS ON A CORONAL SOURCE SURFACE AT 2.3 R{sub Sun} DURING SOLAR MINIMUM  

SciTech Connect

We analyze data from the Solar and Heliospheric Observatory to produce global maps of coronal outflow velocities and densities in the regions where the solar wind is undergoing acceleration. The maps use UV and white light coronal data obtained from the Ultraviolet Coronagraph Spectrometer and the Large Angle Spectroscopic Coronagraph, respectively, and a Doppler dimming analysis to determine the mean outflow velocities. The outflow velocities are defined on a sphere at 2.3 R{sub Sun} from Sun-center and are organized by Carrington Rotations during the solar minimum period at the start of solar cycle 23. We use the outflow velocity and density maps to show that while the solar minimum corona is relatively stable during its early stages, the shrinkage of the north polar hole in the later stages leads to changes in both the global areal expansion of the coronal hole and the derived internal flux tube expansion factors of the solar wind. The polar hole areal expansion factor and the flux tube expansion factors (between the coronal base and 2.3 R{sub Sun }) start out as super-radial but then they become more nearly radial as the corona progresses away from solar minimum. The results also support the idea that the largest flux tube expansion factors are located near the coronal hole/streamer interface, at least during the deepest part of the solar minimum period.

Strachan, L.; Panasyuk, A. V.; Kohl, J. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Lamy, P., E-mail: lstrachan@cfa.harvard.edu [Laboratoire d'Astrophysique de Marseille, UMR6110 CNRS/Universite de Provence, 38 rue Frederic Joliot-Curie, 13388 Marseille Cedex 13 (France)

2012-01-20

16

Ion composition of the topside equatorial ionosphere during solar minimum  

Microsoft Academic Search

Observations from both the Bennett ion mass spectrometer and the retarding potential analyzer on board the Atmosphere Explorer E satellite were used to study the longitudinally averaged O(+), H(+), and He(+) concentrations from 150 to 1100 km in the equatorial ionosphere during the 1975-1976 solar minimum. The results suggest that the ion mass spectrometer measurements need to be increased by

S. A. Gonzalez; B. G. Fejer; R. A. Heels; W. B. Hanson

1992-01-01

17

Differential Emission Measure Analysis of a Polar Coronal Hole During the Recent Solar Minimum  

NASA Astrophysics Data System (ADS)

We have performed a differential emission measure (DEM) analysis for a polar coronal hole observed during the solar minimum in 2007. The analysis was performed for the above-limb portions of five observations from the EUV Imaging Spectrometer on Hinode. The slit pointings also included quiet Sun corona near the boundary with the coronal hole. Our DEM analysis showed that none of the positions were completely isothermal. Instead the emitting material appeared to have a significant high-temperature tail and was consistent with being composed of two plasmas at different temperatures, as measured in K, of log T = 5.95 and log T = 6.15. The lower temperature peak was dominant in the coronal hole and the higher temperature peak dominant in the quiet Sun corona. We used our DEM curves to model isothermal analyses and found that relatively small deviations from isothermality can distort the results inferred using an isothermal analysis method. Isothermal temperature analyses actually measure a DEM-weighted average and can infer artificial temperature gradients if the high and low temperature parts of the DEM curve do not change uniformly with position. The isothermal analyses also do not detect different structures along the line-of-sight, which can affect the interpretation of density diagnostic line ratios.

Hahn, Michael; Landi, E.; Savin, D. W.

2011-05-01

18

DIFFERENTIAL EMISSION MEASURE ANALYSIS OF A POLAR CORONAL HOLE DURING THE SOLAR MINIMUM IN 2007  

SciTech Connect

We have performed a differential emission measure (DEM) analysis for a polar coronal hole observed during solar minimum in 2007. Five observations are analyzed spanning the coronal hole from the central meridian to the boundary with the quiet-Sun corona. The observed heights ranged from 1.05 to 1.20 R{sub sun}. The analysis shows that the plasma is not strictly isothermal anywhere, but rather has a high-temperature component that extends up to log T(K) = 6.2-6.3. The size and importance of this component depend on location, and its evolving magnitude with height marks the boundary between the coronal hole and the quiet corona, where it becomes dominant. The DEM of the coronal hole plasma below log T(K) = 6.0 decreases faster with height than that of the high-temperature component. We discuss the possible nature of the high-temperature component. Our results highlight the potential limitations of isothermal analyses. Such methods actually measure a DEM-weighted average temperature and as a result can infer artificial temperature gradients. Assuming the gas is isothermal along the line of sight can also yield incorrect electron densities. By revealing structures along the line of sight, a DEM analysis can also be used to more reliably interpret electron temperature and density measurements.

Hahn, M.; Savin, D. W. [Columbia Astrophysics Laboratory, Columbia University, MC 5247, 550 West 120th Street, New York, NY 10027 (United States); Landi, E. [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI 48109 (United States)

2011-08-01

19

Ground-Level Neutron Rates during the Recent Solar Minimum  

NASA Astrophysics Data System (ADS)

Neutron monitors have recorded by proxy the flux of Galactic cosmic rays since the 1950s. This work evaluates cosmic ray fluxes during the recent extraordinary solar minimum in a longer-term context. Bartol neutron monitors are supported by the University of Delaware Department of Physics and Astronomy and Bartol Research Institute, by NSF grants ANT-0739620 and ANT-0838839, and by NASA EPSCoR.

Bieber, J. W.; Oh, S.; Evenson, P. A.; Clem, J. M.; Yi, Y.

2010-12-01

20

Observations of Lower Thermospheric Nitric Oxide During the Current Solar Minimum: Comparison with HALOE and the Previous Solar Minimum  

NASA Astrophysics Data System (ADS)

Nitric oxide (NO) is a key minor constituent in the lower thermosphere. Of particular im-portance is its role in the energy balance in that altitude region. NO is produced through the reaction of excited atomic nitrogen with molecular oxygen. Thus its production is very sensitive to those energy sources able to break the strong molecular nitrogen bond. These include solar soft X-rays and precipitating energetic particles. Nitric oxide emits efficiently in the infrared and is an important cooling mechanism in the lower thermosphere. The abundance of NO is thus both a direct response to recent energy deposition as well as a key mechanism by which the upper atmosphere releases that energy. The Solar Occultation for Ice Experiment (SOFIE) instrument was launched on-board the Aeronomy of Ice in the Mesosphere (AIM) satellite on April 25, 2007. SOFIE is a 16 channel differential absorption radiometer using the solar occultation technique to measure ice and environmental properties at a range of altitudes, and in particular the mesopause region. One of the constituents measured by SOFIE is NO in the mesosphere and lower thermosphere to about 130 km. The AIM orbit and the solar occultation technique confine observations to latitudes of 65 to 85 degrees in each hemisphere and varying with season. In this talk we overview the SOFIE observations of NO in the southern hemisphere lower thermosphere and provide a preliminary description of its behavior during the extended solar minimum. Because the measurements are similar to observations by the Halogen Occultation Experiment (HALOE) which observed NO during the previous solar minimum, the two data sets allow for a comparison of how NO, and by extension solar energy deposition, was different between the two solar minima. Preliminary results show the solar minimum observations from both experiments are similar to within the uncertainties of the measurements.

Bailey, Scott; Thirukovelori, Padma; Hervig, Mark; Gordley, Larry; Deaver, Lance; Russell, J. M., III

21

Modulation of Galactic Cosmic Rays at Solar Minimum  

NASA Astrophysics Data System (ADS)

Cosmic ray particles respond to the heliospheric magnetic field in the expanding solar wind and its turbulence and therefore provide a unique probe for conditions in the changing heliosphere. During the last four years, concentrated around the solar minimum period of solar cycle 22, the exploration of the solar polar regions by the joint ESA/NASA mission Ulysses revealed the three-dimensional behavior of cosmic rays in the inner and middle heliosphere. Also during the last decades, the Pioneer and Voyager missions have greatly expanded our understanding of the structure and extent of the outer heliosphere. Simultaneously, numerical models describing the propagation of galactic cosmic rays are becoming sophisticated tools for interpreting and understanding these observations. We give an introduction to the subject of the modulation of galactic cosmic rays in the heliosphere during solar minimum. The modulation effects on cosmic rays of corotating interaction regions and their successors in the outer heliosphere are discussed in more detail by Gazis, McDonald et al. (1999) and McKibben, Jokipii et al. (1999) in this volume. Cosmic-ray observations from the Ulysses spacecraft at high heliographic latitudes are also described extensively in this volume by Kunow, Lee et al. (1999).

Heber, B.; Burger, R. A.

1999-07-01

22

SphinX MEASUREMENTS OF THE 2009 SOLAR MINIMUM X-RAY EMISSION  

SciTech Connect

The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured soft X-ray emission in the 1-15 keV energy range during the deep solar minimum of 2009 with a sensitivity much greater than GOES. Several intervals are identified when the X-ray flux was exceptionally low, and the flux and solar X-ray luminosity are estimated. Spectral fits to the emission at these times give temperatures of 1.7-1.9 MK and emission measures between 4 Multiplication-Sign 10{sup 47} cm{sup -3} and 1.1 Multiplication-Sign 10{sup 48} cm{sup -3}. Comparing SphinX emission with that from the Hinode X-ray Telescope, we deduce that most of the emission is from general coronal structures rather than confined features like bright points. For one of 27 intervals of exceptionally low activity identified in the SphinX data, the Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT (0.1-2.4 keV) was less than most nearby K and M dwarfs.

Sylwester, J.; Kowalinski, M.; Gburek, S.; Siarkowski, M.; Bakala, J.; Gryciuk, M.; Podgorski, P.; Sylwester, B. [Space Research Centre, Polish Academy of Sciences, 51-622, Kopernika 11, Wroclaw (Poland); Kuzin, S. [P. N. Lebedev Physical Institute (FIAN), Russian Academy of Sciences, Leninsky Prospect 53, Moscow 119991 (Russian Federation); Farnik, F. [Astronomical Institute, Ondrejov Observatory (Czech Republic); Reale, F. [Dipartimento di Fisica, Universita di Palermo, Palermo, Italy, and INAF, Osservatorio Astronomico di Palermo, Palermo (Italy); Phillips, K. J. H., E-mail: js@cbk.pan.wroc.pl [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom)

2012-06-01

23

MULTI-FLUID MODEL OF A STREAMER AT SOLAR MINIMUM AND COMPARISON WITH OBSERVATIONS  

SciTech Connect

We present the results of a time-dependent 2.5-dimensional three-fluid magnetohydrodynamic model of the coronal streamer belt, which is compared with the slow solar wind plasma parameters obtained in the extended corona by the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) on board SOHO during the past minimum of solar activity (Carrington Rotation 1913). Our previous three-fluid streamer model has been improved by considering the solar magnetic field configuration relevant for solar minimum conditions, and preferential heating for O{sup 5+} ions. The model was run until a fully self-consistent streamer solution was obtained in the quasi-steady state. The plasma parameters from the multi-fluid model were used to compute the expected UV observables from H I Ly{alpha} 1216 A and O VI 1032 A spectral lines, and the results were compared in detail with the UVCS measurements. A good agreement between the model and the data was found. The results of the study provide insight into the acceleration and heating of the multi-ion slow solar wind.

Ofman, Leon [Department of Physics, Catholic University of America, and NASA Goddard Space Flight Center, Code 671, Greenbelt, MD 20771 (United States); Abbo, Lucia; Giordano, Silvio, E-mail: Leon.Ofman@nasa.gov [INAF Astronomical Observatory of Turin (Italy)

2011-06-10

24

SphinX Measurements of the 2009 Solar Minimum X-Ray Emission  

NASA Astrophysics Data System (ADS)

The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured soft X-ray emission in the 1-15 keV energy range during the deep solar minimum of 2009 with a sensitivity much greater than GOES. Several intervals are identified when the X-ray flux was exceptionally low, and the flux and solar X-ray luminosity are estimated. Spectral fits to the emission at these times give temperatures of 1.7-1.9 MK and emission measures between 4 1047 cm-3 and 1.1 1048 cm-3. Comparing SphinX emission with that from the Hinode X-ray Telescope, we deduce that most of the emission is from general coronal structures rather than confined features like bright points. For one of 27 intervals of exceptionally low activity identified in the SphinX data, the Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT (0.1-2.4 keV) was less than most nearby K and M dwarfs.

Sylwester, J.; Kowalinski, M.; Gburek, S.; Siarkowski, M.; Kuzin, S.; Farnik, F.; Reale, F.; Phillips, K. J. H.; Baka?a, J.; Gryciuk, M.; Podgorski, P.; Sylwester, B.

2012-06-01

25

Observations of upper atmospheric weather during solar minimum winter  

NASA Astrophysics Data System (ADS)

The paper reports on a wide variety of thermospheric and ionospheric observations from three consecutive January World Day campaign periods. Despite remarkably similar geophysical conditions characterizing the in situ forcing of the upper atmosphere during these solar minimum campaigns, significant variability is found in the observations of the ionosphere and thermosphere, particularly at low latitudes in the American sector. Further observational evidence is presented of the unexpected exospheric temperature suppression at low latitudes initially reported by Hagan and Salah (1988). The paper discusses the lower and upper atmospheric coupling mechanisms of plausible importance to the interpretation of the observed thermospheric weather patterns. Evidence is reported that lower thermospheric nitric oxide number density and upward propagating atmospheric tides affected the thermospheric energy and momentum budgets during the campaign periods.

Hagan, M. E.; Barth, C. A.; Tobiska, W. K.; Manson, A. H.; Vincent, R. A.; Bounsanto, M. J.; Burnside, R. G.; Wickwar, V. B.

1992-04-01

26

Observations of upper atmospheric weather during solar minimum winter  

SciTech Connect

The authors report on a wide variety of thermospheric and ionospheric observations from three consecutive January World Day campaign periods. Despite remarkably similar geophysical conditions characterizing the in situ forcing of the upper atmosphere during these solar minimum campaigns, they find significant variability in the observations of the ionosphere and thermosphere particularly at low latitudes in the American sector. In addition, they present further observational evidence of the unexpected exospheric temperature suppression at low latitudes initially reported by Hagran and Salah (1988). They discuss the lower and upper atmospheric coupling mechanisms of plausible importance to the interpretation of the observed thermospheric weather patterns. They report evidence that lower thermospheric (NO) (nitric oxide number density) and upward propagating atmospheric tides affected the thermospheric energy and momentum budgets during the campaign periods.

Hagan, M.E. (Massachusetts Inst. of Tech., Westford (United States) National Center for Atmospheric Research, Boulder, CO (United States)); Barth, C.A. (Univ. of Colorado, Boulder (United States)); Tobiska, W.K. (Univ. of California, Berkeley (United States)); Manson, A.H. (Univ. of Saskatchewan, Saskatoon (Canada)); Vincent, R.A. (Univ. of Adelaide (Australia)); Buonsanto, M.J. (Massachusetts Inst. of Tech., Westford (United States)); Burnside, R.G. (Cornell Univ., Arecibo (Puerto Rico)); Wickwar, V.B. (Utah State Univ., Logan (United States))

1992-04-01

27

Modeling the large-scale structure of the solar corona  

NASA Astrophysics Data System (ADS)

The aim of this study is to find a quantitative description of both the magnetic field and the distribution of plasma in the lower corona that matches the white light images of the K-corona. The magnetostatic model of Bogdan and Low (1986) and data obtained by the High Altitude Observatory Mark III K-Coronameter stationed at Mauna Loa, Hawaii is used. To start with, the simplest, solar minimum case when the corona is approximately longitudinally symmetric is taken. By varying parameters in the Bogdan and Low model it is possible to quantitatively match the general characteristics of the lower corona at solar minimum: power law radial profiles of coronal brightness; enhanced brightness at the equator; uniform density depletion at the pole.

Bagenal, F.; Gibson, S.

1991-10-01

28

Modeling the large-scale structure of the solar corona  

NASA Astrophysics Data System (ADS)

The aim of this study is to find a quantitative description of both the magnetic field and the distribution of plasma in the lower corona that matches the white light images of the K-corona. We use the magnetostatic model of Bogdan and Low (1986) and data obtained by the High Altitude Observatory Mark III K-Coronameter stationed at Mauna Loa, Hawaii. To start with, we take the simplest, solar minimum case when the corona is approximately longitudinally symmetric. By varying parameters in the Bogdan and Low model we are able to quantitatively match the general characteristics of the lower corona at solar minimum: power law radial profiles of coronal brightness; enhanced brightness at the equator; uniform density depletion at the pole.

Bagenal, F.; Gibson, S.

29

Anomalously low solar extreme-ultraviolet irradiance and thermospheric density during solar minimum  

Microsoft Academic Search

Solar activity during 20072009 was very low, and during this protracted solar minimum period, the terrestrial thermosphere was cooler and lower in density than expected. Measurements from instruments on the SOHO and TIMED spacecraft, and by suborbital rocket flights, indicate that solar extreme-ultraviolet irradiance levels were lower than they were during the previous solar minimum. Analysis of atmospheric drag on

Stanley C. Solomon; Thomas N. Woods; Leonid V. Didkovsky; John T. Emmert; Liying Qian

2010-01-01

30

Ion-neutral coupling during deep solar minimum  

NASA Astrophysics Data System (ADS)

The equatorial ionosphere under conditions of deep solar minimum exhibits structuring due to tidal forces. Data from instruments carried by the Communication/Navigation Outage Forecasting System (C/NOFS) which was launched in April 2008 have been analyzed for the first 2 years following launch. The Planar Langmuir Probe (PLP), Ion Velocity Meter (IVM) and Vector Electric Field Investigation (VEFI) all detect periodic structures during the 2008-2010 period which appear to be tides. However when the tidal features detected by these instruments are compared, there are distinctive and significant differences between the observations. Tides in neutral densities measured by the Gravity Recovery and Climate Experiment (GRACE) satellite were also observed during June 2008. In addition, Broad Plasma Decreases (BPDs) appear as a deep absolute minimum in the plasma and neutral density tidal pattern. These are co-located with regions of large downward-directed ion meridional velocities and minima in the zonal drifts, all on the nightside. The region in which BPDs occur coincides with a peak in occurrence rate of dawn depletions in plasma density observed on the Defense Meterological Satellite Program (DMSP) spacecraft, as well as a minimum in radiance detected by UV imagers on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) and IMAGE satellites.

Huang, Cheryl Y.; Roddy, Patrick A.; Sutton, Eric K.; Stoneback, Russell; Pfaff, Robert F.; Gentile, Louise C.; Delay, Susan H.

2013-10-01

31

Estimates of galactic cosmic ray shielding requirements during solar minimum  

NASA Astrophysics Data System (ADS)

Estimates of radiation risk from galactic cosmic rays are presented for manned interplanetary missions. The calculations use the Naval Research Laboratory cosmic ray spectrum model as input into the Langley Research Center galactic cosmic ray transport code. This transport code, which transports both heavy ions and nucleons, can be used with any number of layers of target material, consisting of up to five different arbitrary constituents per layer. Calculated galactic cosmic ray fluxes, dose and dose equivalents behind various thicknesses of aluminum, water and liquid hydrogen shielding are presented for the solar minimum period. Estimates of risk to the skin and the blood-forming organs (BFO) are made using 0-cm and 5-cm depth dose/dose equivalent values, respectively, for water. These results indicate that at least 3.5 g/sq cm (3.5 cm) of water, or 6.5 g/sq cm (2.4 cm) of aluminum, or 1.0 g/sq cm (14 cm) of liquid hydrogen shielding is required to reduce the annual exposure below the currently recommended BFO limit of 0.5 Sv. Because of large uncertainties in fragmentation parameters and the input cosmic ray spectrum, these exposure estimates may be uncertain by as much as a factor of 2 or more. The effects of these potential exposure uncertainties or shield thickness requirements are analyzed.

Townsend, Lawrence W.; Nealy, John E.; Wilson, John W.; Simonsen, Lisa C.

1990-02-01

32

STEREO ICMEs and their Solar Source Regions Near Solar Minimum  

NASA Astrophysics Data System (ADS)

Although the quiet activity period surrounding the current solar minimum has prevailed since the launch of STEREO in October 2006, there have been at least 9 clear in-situ detections of ICMEs (Interplanetary Coronal Mass Ejections) by one or more spacecraft during the time the imagers were also operating. These observations provide unusually complete data sets for evaluating helio-longitude extent of the ICMEs and for identifying the probable solar cause(s) of the events. In this poster we present information on these ICMEs from the IMPACT and PLASTIC and ACE in-situ investigations, together with solar images from STEREO and SOHO that seem to capture the causative activity at the Sun. We find that even though the Sun was very quiet in '07-'08, with few active regions visible in GONG and SOHO magnetograms, there were numerous CME candidates that erupted through the near-equatorial helmet streamers. Most events could be identified with EUV disk activity as well as a coronagraph CME, even if the associated active region was very small or weak. Old cycle active regions, new and decayed, continued to maintain a warp in the large-scale helmet streamer belt that was a frequent site of the eruptions. However, the warp in the streamer belt may simply indicate that the active region(s) present is(are) sufficiently strong to affect the large scale quiet coronal field structure. Overall we see no gross differences between the solar activity and ICME causes during this and the previous solar activity minimum, when the Streamer belt was less warped due to the existence of stronger solar polar fields.

Toy, V.; Li, Y.; Luhmann, J. G.; Schroeder, P.; Vourlidas, A.; Jian, L. K.; Russell, C. T.; Galvin, A. B.; Simunac, K.; Acuna, M.; Sauvaud, J. A.; Skoug, R.; Petrie, G.

2008-12-01

33

Solar Wind Properties During the Current Solar Minimum: Ulysses Observations  

NASA Astrophysics Data System (ADS)

During its nearly 19 year mission, Ulysses pioneered novel measurements of the three-dimensional heliosphere and particularly first in situ observations of solar wind from polar coronal holes (PCHs). It is thus possible to compare observations in the current, peculiar solar minimum with those obtained in 1994-95. It has been reported earlier that, during the current minimum, there is a ~ 15% reduction of the heliospheric magnetic field (Smith and Balogh, 2008), and ~ 17% and ~ 14% reduction in density and temperature, respectively (McComas et al., 2008), as compared to the previous minimum. But the PCH-associated solar wind streams show long-term variability not only in dynamic, but also in compositional signatures. From 1995 to 2008, the C and O freeze-in temperatures measured in high-latitude solar wind have decreased by ~ 15% and are now around 0.86 MK and 1.0 MK, respectively. Si and Fe ionization states also exhibit a substantial cooling with a reduction of 0.2 and 0.3 charge states, respectively. Thus it appears that the PCH of cycle 23 are cooler overall than those of cycle 22. It is more difficult to assess whether there are significant changes of the elemental composition of the solar wind, as exhibited through the First Ionization Potential fractionation effect, which seems to have remained at f = 1.8 0.3 during both sets of polar passages, i.e., enhanced to the photospheric composition (f = 1). If this can be confirmed the streams from PCH would truly be the 'ground state' of the solar wind. These observations provide a unique test for theories of the solar wind and its composition. We will present results from this data analysis and also provide a discussion of their scientific implications.

von Steiger, Rudolf; Zurbuchen, Thomas H.

2010-05-01

34

Meridional Surface Flows and the Recent Extended Solar Minimum  

NASA Astrophysics Data System (ADS)

Nandy, Munoz, & Martens, have published a kinematic dynamo model that successfully reproduces the main characteristics of the recent extended solar minimum (Nature 2011, 471, 80). The model depends on the solar meridional flow and its return flow along the tachocline determining the period and character of the cycle. In particular Nandy et al. found that a meridional flow that is fast in the first half of the cycle and then slows down around solar maximum, can lead to an extended minimum with the characteristics of the recent minimum: an extended period without sunspots and weak polar fields. It has been pointed out that the observed surface meridional flows over the last cycle do not fit the pattern assumed by Nandy et al. Hathaway & Rightmire (Science 2010, 327-1350) find that the meridional speed of small magnetic surface elements observed by SoHO/MDI decreased around solar maximum and has not yet recovered. Basu & Antia (ApJ 2010, 717, 488) find surface plasma meridional flow speeds that are lower at solar maximum 23 than at the surrounding minima, which is different from both Hathaway and Nandy. While there is no physical reason that solar surface flows -- both differential rotation and meridional flow -- would vary in lockstep with flows at greater depth, as the large radial gradients near the surface clearly indicate, and while Nandy et al. have demonstrated that the deeper flows dominate the net meridional mass flow, we find that there is in effect a very satisfying agreement between the observational results of Hathaway & Rightmire, Basu & Antia, and the model assumptions of Nandy, Munoz, & Martens. We present an analytical model that reconciles the first two, followed by a hydrodynamical model that demonstrates the consistency of these observational results with the model assumptions of Nandy et al.

Martens, Petrus C.; Nandy, D.; Munoz-Jaramillo, A.

2011-05-01

35

Quality of IRI predictions during extreme solar minimum conditions  

NASA Astrophysics Data System (ADS)

The complexity of the deep, long and flat Solar Cycle minimum 23-24, and the IRI performance for these conditions are discussed. The solar control over the ionospheric behavior is not linear, and the ionospheric consequences of the prolonged, low and complicated Solar Cycle 23-24 minimum shows a consequentially complex picture. The ionospheric vTEC parameters present a consistent decrease of the mean day values for minimum 23-24, respect to minimum 22-23. The variability of this parameter generally decreases for the latest minimum. NmF2, on the other hand, shows an inconsistent and complex behavior, with cases in which the average values were lower, and other cases where the values were similar and even higher for the 23-24 minimum. The IRI output generally shows good agreement for both parameters for night time conditions, but its performance worsened for day time conditions. The hmF2 results, on the other hand, show that IRI hmF2 values are in reasonable agreement with the observations for the earlier minimum in 1996. The exceptions are October and December in the SH, where IRI hmF2 tends to high, particularly on the dayside, and also July for which the daytime measured values tend to be larger than the IRI ones. For the recent minimum in 2008, IRI tends to over-estimate the hmF2 in most of the observations. The results support the general assertion that thermospheric temperatures were cooler during the last solar minimum as a consequence of an unusually low, and extended, minimum in solar extreme-ultraviolet flux, and in response to continually increasing long-term trend in anthropogenic carbon dioxide. The cooler temperatures not only decrease density at a fixed height, but also make the corresponding contraction of the atmosphere lower the height of the F-region peak.

Araujo-Pradere, Eduardo; Bilitza, Dieter; Fuller-Rowell, Tim; Fuller-Rowell, Dominic

2012-07-01

36

TEC fluctuations during recent Solar Minimum: technique and analysis.  

NASA Astrophysics Data System (ADS)

The increasing number of permanent GNSS stations including regions near the North Geomagnetic Pole allows us to use the GPS-derived total electron content (TEC) observations to detect the ionospheric disturbances with high spatial and temporal resolution. The most intensive phase fluctuations are observed at the high latitude, equatorial and strong disturbed mid-latitude ionosphere. In the space weather service developed at GRL/UWM, the data from the Arctic stations belonging to IGS/EPN/POLENET networks were used in order to study TEC fluctuations and scintillations. The present research study is based on 30sec precise phase GPS measurements provided by permanent IGS network for period 2008-2011. Effects of the ionosphere irregularities were evaluated via rate of TEC variations. [1]. By use of these data the 2-hour maps of the TEC variability and daily map of the ionospheric fluctuations as a function of geomagnetic local time are created. Based on numerous TEC measurements (more than 200 permanent GNSS stations) it was obtained the statistical data about occurrence of TEC fluctuations at high and midlatitudes during the extended solar minimum period. The diurnal, seasonal, and storm-time variations of TEC fluctuation activity were estimated. The most intensive TEC fluctuations at considered period were observed during several weak and moderate geomagnetic disturbances at November 2008, July 2009 and May 2010. It was revealed that TEC fluctuations can be observed on quiet days at midlatitudes and midlatitudinal TEC fluctuations are regular phenomena which demonstrate day-to-day variability. The low frequency fluctuations can be caused directly due to electron density changes along transionospheric radio ray path or the TEC temporal changes. This type of TEC fluctuations was associated with wave-like processes in the ionosphere. It was carried out the statistical analysis of fluctuation intensity and TEC fluctuations maps. We propose that GNSS-derived monthly TEC medians and rate of TEC maps can be useful for IRI community in order to update the IRI model, in particular at high latitudes. Since the beginning of 2011, a near real-time service presenting the conditions in the ionosphere has being operational at GRL/UWM www site. This report presents the architecture, algorithms, performance and future developments of the space weather services at GRL/UWM. 1. Shagimuratov I.I., Krankowski A., Ephishov I., Zakharenkova I., Tepenitsyna N., 2009, Occurrence of GPS Phase Fluctuations in Northen and Southern Hemisphere, Proceedings of 20th International Symposium on Electromagnetic Compatibility. Zurich, Switzerland, 12-16 January 2009, pp. 305-308.

Cherniak, Iurii; Krankowski, Andrzej; Zakharenkova, Irina; Shagimuratov, Irk; Sieradzki, Rafal

2012-07-01

37

Particle Flux Variations at Solar Minimum: Comparisons of ACE/CRIS Data with Model Calculations  

NASA Astrophysics Data System (ADS)

During the current solar minimum condition, galactic cosmic ray (GCR) flux of several particle species reached peak values, as expected. Model calculations for the current solar minimum condition (2009-2010) are compared with the measurements from the ACE/CRIS instrument. During the first half of 2010, oxygen particle flux decreases as anticipated and closely follows the predicted model calculations. However, nitrogen flux variation did not show the expected trends. Implications of these particle flux variations will be presented and discussed in the context of dose estimations for intended human explorations.

Erickson, G. M.; Saganti, P. B.; Cudnik, B.; Scott-Turner, A.

2010-12-01

38

THE UPPER THERMOSPHERE AT NORTHERN HIGH LATITUDES DURING THE CURRENT SOLAR MINIMUM  

NASA Astrophysics Data System (ADS)

At high latitudes, the thermodynamics of the upper thermosphere have undergone long-term synoptic sampling by ground-based Fabry Perot Interferometers, including the last three minimum phases of the solar cycle. These observations provide neutral winds and temperatures from feeble OI (6300A) airglow emission during Arctic nights that last as long as 24 hours/day. At present during the current solar minimum, the altitude of the peak of this airglow layer is approximately 220 km, based on TIDI spacecraft OI (6300A) airglow observations. Monthly (January) averages of geophysical parameters provide insight into changes in the thermosphere that are directly related to solar conditions (F10.7 solar flux) during the evolution of a solar minimum. The current extended solar minimum has provided an opportunity to observe the thermosphere during a progressively quieter sun: January 2006 to January 2009. At Sondre Stromfjord Greenland, the monthly averaged neutral temperature has dropped from ~1100K to ~800K in January during these years. The magnitude of the average equatorial meridional wind has also decreased during this period. Finally, the monthly averaged brightness of OI (6300A) airglow has decreased by ~50% from 2006 to 2009. This paper will place the current solar minimum observations at Sondre Stromfjord into context with previous solar minima measurements. At midnight, this site is typically within the polar cap though it often lies beneath the auroral oval at dusk and dawn. Comparisons with observations in Alaska and Scandinavia will provide a context against other northern geomagnetic locations.

Niciejewski, R.; Meriwether, J. W.; Aruliah, A. L.; Wu, Q.; Wang, W.

2009-12-01

39

Behavior of the Ionosphere and Thermosphere at Solar Minimum: Data and Model Comparisons and Analysis  

Microsoft Academic Search

UV remote sensing is the single most powerful technique for making space-based global observations of the ionosphere and thermosphere. During the descending phase of the last solar cycle and the current solar minimum we have had the opportunity to make unique observations of the behavior of the upper atmosphere. Comparisons with models are particularly important because they inform our understanding

L. J. Paxton; Y. Zhang; H. Kil; R. K. Schaefer; J. Comberiate; A. B. Christensen

2009-01-01

40

Solar Wind and Global Electron Hemispheric Power in Solar Minimum Intervals  

NASA Astrophysics Data System (ADS)

We assess the periodicities of the hourly and daily solar wind velocity (Vsw) and average global electron auroral hemispheric power (Hpeg) with Lomb-Scargle (L-S) and Fast Fourier Transforms (FFTs) using three Carrington Rotations (CRs) to a year or more of data in two different solar minimum periods. The first Whole Sun Month (WSM) interval (96223-96252) was during the last solar minimum where the solar magnetic field relaxed into a dipole. A strong 'semiannual' periodicity in Vsw maximizing in equinoxes was found, which enhanced the equinoctial maxima found in Hpeg (and Kp) due to the preferred solar wind and magnetospheric reconnection during equinoxes. In the present solar minimum, the solar magnetic field has considerable quadrupole components during the Whole Heliospheric Interval (WHI, 08080-08107). Hpeg exhibits solar rotational periodicities similar to those for Vsw using both L-S and FFT analyses, where the 9- day periodicity is particularly strong in the present solar minimum period. The 9-day periodicity in the WHI CR was caused by three periods of slow-speed solar wind from near the ecliptic plane as seen in the sign of IMF Bx. Periodicities are examined in Vsw since 1972, and in Hpeg since 1978 to assess solar cycle variations. Periodicities longer than 100 days are not as strong or as well correlated between Vsw and Hpeg compared to the shorter solar rotational periodicities.

Emery, B. A.; Richardson, I. G.; Evans, D. S.; Rich, F. J.; Wilson, G.

2008-12-01

41

If the Sun is so quiet, why is the Earth ringing? A comparison of two solar minimum intervals  

Microsoft Academic Search

Observations from the recent Whole Heliosphere Interval (WHI) solar minimum campaign are compared to last cycle's Whole Sun Month (WSM) to demonstrate that sunspot numbers, while providing a good measure of solar activity, do not provide sufficient information to gauge solar and heliospheric magnetic complexity and its effect at the Earth. The present solar minimum is exceptionally quiet, with sunspot

S. E. Gibson; J. U. Kozyra; G. de Toma; B. A. Emery; T. Onsager; B. J. Thompson

2009-01-01

42

The long-term stability of the visible F corona at heights of 3-6 R_?  

NASA Astrophysics Data System (ADS)

Context: CMEs can effect the distribution of dust grains in the corona. The brightness of the visible F corona is expected therefore to change as the frequency of CMEs varies with solar cycle. Aims: We search for a variation in the F corona by comparing LASCO C2 observations from solar minimum and maximum. Methods: An established inversion method is used to calculate the visible F corona brightness from LASCO C2 solar minimum observations made during 1996/10. Good agreement is found with the F corona brightness calculated from Skylab observations during 1973/05-1974/02 for heights of 3-6 R_?. The unpolarized brightness, which is dominated by the unpolarized F corona brightness at these heights, is obtained by subtracting many pairs of polarized brightness images from total brightness images and averaging over a solar rotation. We calculate the unpolarized brightness for both solar activity minimum and maximum. Results: The unpolarized brightness, and therefore the F corona, remain virtually unchanged between solar minimum and maximum at heights above 2.6 R_?, despite the large change in the shape and activity of the corona. Using a simple density model, it is shown that the small variation in unpolarized brightness seen below 2.6 R_? can arise from differences in the distribution of electron density, and therefore cannot be attributed to a variation in the F corona. Conclusions: Despite the large rise in frequency of CMEs from solar minimum to maximum, the F coronal brightness, at heights of 3-6 R_? in the visible, remains very stable.

Morgan, H.; Habbal, S. R.

2007-08-01

43

Modelling the Large Scale Structure of the Solar Corona  

NASA Astrophysics Data System (ADS)

We report on recent attempts to find a quantitative description of both the magnetic field and the distribution of plasma in the lower corona that matches the white light images of the K-corona. We use the magnetostatic model of Bogdan and Low and data obtained by the High Altitude Observatory K-Coronameter (1.2 - 2.3 Rsun) and the Solar Maximum Mission Coronameter/Polarimeter (1.5 - 4 Rsun). By varying parameters in the Bogdan and Low model we are able to quantitatively match the general characteristics of the lower corona at solar minimum: power law radial profiles of coronal brightness: enhanced brightness at the equator; uniform density depletion at the pole. Further, we use the best fit model to determine a temperature distribution in the corona and investigate the implications this has for solar wind theory.

Gibson, S.; Bagenal, F.

1992-05-01

44

Solar wind ion trends and signatures: STEREO PLASTIC observations approaching solar minimum  

NASA Astrophysics Data System (ADS)

STEREO has now completed the first two years of its mission, moving from close proximity to Earth in 2006/2007 to more than 50 degrees longitudinal separation from Earth in 2009. During this time, several large-scale structures have been observed in situ. Given the prevailing solar minimum conditions, these structures have been predominantly coronal hole-associated solar wind, slow solar wind, their interfaces, and the occasional transient event. In this paper, we extend earlier solar wind composition studies into the current solar minimum using high-resolution (1-h) sampling times for the charge state analysis. We examine 2-year trends for iron charge states and solar wind proton speeds, and present a case study of Carrington Rotation 2064 (December 2007) which includes minor ion (He, Fe, O) kinetic and Fe composition parameters in comparison with proton and magnetic field signatures at large-scale structures observed during this interval.

Galvin, A. B.; Popecki, M. A.; Simunac, K. D. C.; Kistler, L. M.; Ellis, L.; Barry, J.; Berger, L.; Blush, L. M.; Bochsler, P.; Farrugia, C. J.; Jian, L. K.; Kilpua, E. K. J.; Klecker, B.; Lee, M.; Liu, Y. C.-M.; Luhmann, J. L.; Moebius, E.; Opitz, A.; Russell, C. T.; Thompson, B.; Wimmer-Schweingruber, R. F.; Wurz, P.

2009-10-01

45

STEREO's in-situ perspective on the solar minimum solar wind structure  

Microsoft Academic Search

STEREO multipoint measurements of the solar wind structure with the IMPACT and PLASTIC investigations, near Earth but off the Sun-Earth line, allow its sources and structure to be examined at solar minimum when such studies are particularly straightforward. With the aid of 3D models of the heliosphere available at the CCMC, we map the in-situ observations to their solar sources

J. G. Luhmann; D. Larson; P. Schroeder; C. O. Lee; J. Sauvaud; M. H. Acuna; A. B. Galvin; C. T. Russell; L. Jian; C. N. Arge; D. Odstrcil; P. Riley; R. A. Howard; M. Aschwanden; P. MacNeice; A. Chulaki

2007-01-01

46

Anomalous behavior of the thermosphere during solar minimum observed by CHAMP and GRACE  

Microsoft Academic Search

High-resolution density observations inferred from accelerometer measurements on the Challenging Mini-Satellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites for the period 1117 December 2008 during the solar minimum are analyzed and compared to reference model predictions. The density distribution as a function of altitude can be studied because the satellites were in the same 8.4\\/20.4 hour (0824\\/2024)

Sean L. Bruinsma; Jeffrey M. Forbes

2010-01-01

47

Equatorial F region irregularity morphology during an equinoctial month at solar minimum  

Microsoft Academic Search

A large number of instruments was used in October 1996 to record activities in the equatorial ionosphere above South America.\\u000a In a month at solar minimum, data were obtained at various levels of magnetic activity and various levels of ionospheric irregularity\\u000a development. With this multi-instrumented study, it was possible to utilize optical data, radar, GPS transmissions, and ionosondes\\u000a at various

J. Aarons; M. Mendillo; B. Lin; M. Colerico; T. Beach; P. Kintner; J. Scali; B. Reinisch; G. Sales; E. Kudeki

1999-01-01

48

Galactic Cosmic-Ray Energy Spectra and Composition during the 2009-2010 Solar Minimum Period  

NASA Astrophysics Data System (ADS)

We report new measurements of the elemental energy spectra and composition of galactic cosmic rays during the 2009-2010 solar minimum period using observations from the Cosmic Ray Isotope Spectrometer (CRIS) onboard the Advanced Composition Explorer. This period of time exhibited record-setting cosmic-ray intensities and very low levels of solar activity. Results are given for particles with nuclear charge 5 <= Z <= 28 in the energy range ~50-550 MeV nucleon-1. Several recent improvements have been made to the earlier CRIS data analysis, and therefore updates of our previous observations for the 1997-1998 solar minimum and 2001-2003 solar maximum are also given here. For most species, the reported intensities changed by less than ~7%, and the relative abundances changed by less than ~4%. Compared with the 1997-1998 solar minimum relative abundances, the 2009-2010 abundances differ by less than 2?, with a trend of fewer secondary species observed in the more recent time period. The new 2009-2010 data are also compared with results of a simple "leaky-box" galactic transport model combined with a spherically symmetric solar modulation model. We demonstrate that this model is able to give reasonable fits to the energy spectra and the secondary-to-primary ratios B/C and (Sc+Ti+V)/Fe. These results are also shown to be comparable to a GALPROP numerical model that includes the effects of diffusive reacceleration in the interstellar medium.

Lave, K. A.; Wiedenbeck, M. E.; Binns, W. R.; Christian, E. R.; Cummings, A. C.; Davis, A. J.; de Nolfo, G. A.; Israel, M. H.; Leske, R. A.; Mewaldt, R. A.; Stone, E. C.; von Rosenvinge, T. T.

2013-06-01

49

The TWINS exospheric neutral H-density distribution under solar minimum conditions  

NASA Astrophysics Data System (ADS)

Terrestrial exospheric atomic hydrogen (H) resonantly scatters solar Lyman-? (121.567 nm) radiation, observed as the glow of the H-geocorona. The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) satellites are equiped with two Lyman-? line-of-sight Detectors (LADs) each. Since during the past solar minimum conditions the relevant solar control parameters practically did not vary, we are using LAD data between June and September 2008 to create a time averaged hydrogen geocorona model representative for these solar minimum conditions. In this averaged model we assume that the H-geocorona is longitudinally symmetric with respect to the earth-sun line. We find a 3-dimensional H-density distribution in the range from 3 to 8 earth radii which with some caution can also be extrapolated to larger distances. For lower geocentric distances than 3 earth radii a best fitting r-dependent Chamberlain (1963)-like model is adapted. Main findings are larger than conventionally expected H-densities at heights above 5 RE and a pronounced day-to-night side H-density asymmetry. The H-geocorona presented here should serve as a reference H-atmosphere for the earth during solar minimum conditions.

Zoennchen, J. H.; Bailey, J. J.; Nass, U.; Gruntman, M.; Fahr, H. J.; Goldstein, J.

2011-12-01

50

Comparison between IRI-2007 model predictions and ionospheric observations at European region during extended solar minimum  

NASA Astrophysics Data System (ADS)

The solar minimum began around March 2006 and many predictions of the start and size of Solar Cycle 24 were given since then. In 2007 the Solar Cycle 24 Prediction Panel anticipates the solar minimum marking the onset of Cycle 24 will occur in March 2008 (6 months). Then this date was shifted to the August 2008, after that -to the December 2008. At least solar minimum is extended to the end of 2009. This unusually deep and extended solar minimum makes corrections to the predicted values of solar cycle progression. With every update the predicted values of sunspot number is decreased. It leads to the significant discrepancies in IRI model results in depend on the predicted indices. To calculate the ionospheric parameters the IRI model uses indices file with ionospheric index IG12 and solar sunspot number (12-months running median) Rz12. This IRI file is regularly updated with the newest available indices and predictions. It was considered the IRI model results obtained with use of different predicted and observed IG and Rz indices during 2007-2009 years. For the given study it was done the comparison of the IRI-2007 predicted values of F2 layer critical frequency (foF2) with those observed at several mid-latitude ionospheric stations in European region. Values of foF2 have been scaled manually from ionograms to avoid the evident risks related with using of the autoscaled data that have ionosonde-related errors and uncertainties. It was the ionograms and foF2 values provided by European Digital Upper Atmosphere Server (DIAS). The DIAS bases on real-time and historical data provided by most operating ionospheric stations in Europe. This server collects information from stations located in Rome, Pruhonice, Juliusruh, Athens, Chilton, Ebre and El Arenosillo. For each station it was calculated monthly median of foF2 variation on the base of full month data analysis. We have considered observations taken in the months of January, April, July and October for 2007-2009 years. We present results of the analysis of diurnal variations for the different seasons of the observed and IRI-2007 predicted (using different IG and Rz indices) foF2 values. We acknowledge the IRI Working group for providing and evaluating of the IRI model FORTRAN code. We are grateful to European Digital Upper Atmosphere Server (DIAS) for providing the ionosondes' products.

Zakharenkova, Irina; Krankowski, Andrzej; Bilitza, Dieter; Cherniak, Iurii; Shagimuratov, Irk; Krypiak-Gregorczyk, Anna

51

Fast Solar Wind Streams From the Sun to 1 AU During the Recent Solar Minimum  

NASA Astrophysics Data System (ADS)

The origin and evolution of the solar wind from coronal holes is studied by characterizing the physical properties of the solar wind plasma (temperature, density, outflow velocity, and composition) with multi-spacecraft and ground-based observations. PFSS modeling is also used to confirm interpretation of the source regions and in wind-stream boundary mapping. We discuss the results for the fast solar wind from polar and low-latitude coronal-hole wind streams. We also compare the characteristics of these wind streams with results from the previous solar minimum.

Miralles, M. P.; Simunac, K. D.; Strachan, L.; Galvin, A. B.; Landi, E.; Lee, C. O.; Luhmann, J. G.; McIntosh, P. S.

2010-12-01

52

Characteristics of low-latitude ionospheric depletions and enhancements during solar minimum  

NASA Astrophysics Data System (ADS)

Under the waning solar minimum conditions during 2009 and 2010, the Ion Velocity Meter, part of the Coupled Ion Neutral Dynamics Investigation aboard the Communication/Navigation Outage Forecasting System satellite, is used to measure in situ nighttime ion densities and drifts at altitudes between 400 and 550 km during the hours 21:00-03:00 solar local time. A new approach to detecting and classifying well-formed ionospheric plasma depletions and enhancements (bubbles and blobs) with scale sizes between 50 and 500 km is used to develop geophysical statistics for the summer, winter, and equinox seasons during the quiet solar conditions. Some diurnal and seasonal geomagnetic distribution characteristics confirm previous work on equatorial irregularities and scintillations, while other elements reveal new behaviors that will require further investigation before they may be fully understood. Events identified in the study reveal very different and often opposite behaviors of bubbles and blobs during solar minimum. In particular, more bubbles demonstrating deeper density fluctuations and faster perturbation plasma drifts typically occur earlier near the magnetic equator, while blobs of similar magnitude occur more often far away from the geomagnetic equator closer to midnight.

Haaser, R. A.; Earle, G. D.; Heelis, R. A.; Klenzing, J.; Stoneback, R.; Coley, W. R.; Burrell, A. G.

2012-10-01

53

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval  

NASA Astrophysics Data System (ADS)

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar-heliospheric-planetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March - 16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earths mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.

Thompson, Barbara J.; Gibson, Sarah E.; Schroeder, Peter C.; Webb, David F.; Arge, Charles N.; Bisi, Mario M.; de Toma, Giuliana; Emery, Barbara A.; Galvin, Antoinette B.; Haber, Deborah A.; Jackson, Bernard V.; Jensen, Elizabeth A.; Leamon, Robert J.; Lei, Jiuhou; Manoharan, Periasamy K.; Mays, M. Leila; McIntosh, Patrick S.; Petrie, Gordon J. D.; Plunkett, Simon P.; Qian, Liying; Riley, Peter; Suess, Steven T.; Tokumaru, Munetoshi; Welsch, Brian T.; Woods, Thomas N.

2011-12-01

54

Longitudinal and Seasonal variation of ion density, temperature and composition during solar minimum  

NASA Astrophysics Data System (ADS)

Plasma temperature, composition and density observed below 500 km altitude during solar minimum by the ~13 degrees inclination C/NOFS satellite are studied. Based on the C/NOFS satellite observations from 2008 and 2009, the averaged longitudinal and seasonal distributions of the ion temperature (Ti), total ion density (Ni) and ion composition is studied in terms of local time, season, latitude, magnetic declination and solar flux intensity. The longitudinal variations of both Ti and Ni exhibit obvious seasonal dependence in different magnetic declinations in the morning and evening local hours. The electron temperature shows a steep rise in the early morning (well known as "morning overshoot"), a decrease after that and again an increase at ~18 hours (well known as "evening overshoot"). The extended solar minimum prevailing during the C/NOFS mission allows us to establish a baseline model of the quiescent seasonal variations of the topside equatorial ionosphere. The IRI measurements at ~500km altitude of the total ion density and temperature are compared with the C/NOFS measured parameters at the same altitude.

Mohapatra, S.

2011-12-01

55

The Association of Solar Flares with Coronal Mass Ejections During the Extended Solar Minimum  

NASA Astrophysics Data System (ADS)

We study the association of solar flares with coronal mass ejections (CMEs) during the deep, extended solar minimum of 2007 - 2009, using extreme-ultraviolet (EUV) and white-light (coronagraph) images from the Solar Terrestrial Relations Observatory (STEREO). Although all of the fast (v>900 km s-1), wide (?>100?) CMEs are associated with a flare that is at least identified in GOES soft X-ray light curves, a majority of flares with relatively high X-ray intensity for the deep solar minimum (e.g. ?110-6 W m-2 or C1) are not associated with CMEs. Intense flares tend to occur in active regions with a strong and complex photospheric magnetic field, but the active regions that produce CME-associated flares tend to be small, including those that have no sunspots and therefore no NOAA active-region numbers. Other factors on scales similar to and larger than active regions seem to exist that contribute to the association of flares with CMEs. We find the possible low coronal signatures of CMEs, namely eruptions, dimmings, EUV waves, and Type III bursts, in 91 %, 74 %, 57 %, and 74 %, respectively, of the 35 flares that we associate with CMEs. None of these observables can fully replace direct observations of CMEs by coronagraphs.

Nitta, N. V.; Aschwanden, M. J.; Freeland, S. L.; Lemen, J. R.; Wlser, J.-P.; Zarro, D. M.

2013-09-01

56

IRI-2007 model overestimates electron density during the 23/24 solar minimum  

NASA Astrophysics Data System (ADS)

We compare electron density predictions of the International Reference Ionosphere (IRI-2007) model with in-situ measurements of the satellites CHAMP and GRACE for the years 2000-2009. Orbital-averages of the electron density are considered. During the first half of the period (2000-2004) measurements and collocated model predictions track each other reasonably well at both sampling heights. From 2005 onward the overestimation of the electron density by the model is progressively increasing. Annual averages show that IRI-2007 values are too high by 50% for 2008 and by more than 60% by 2009. An inspection of the latitudinal and local time distributions reveals that the too high predictions primarily occur at low latitudes during daytime hours. From comparison with observations it becomes obvious that IRI-2007 is strongly overestimating the equatorial ion fountain effect during the last deep solar minimum.

Lhr, H.; Xiong, C.

2010-12-01

57

Pamela Measurements of Galactic and Solar Cosmic Rays in the 23rd Solar Minimum (Invited)  

NASA Astrophysics Data System (ADS)

We will discuss the measurements of protons and helium of galactic, solar and trapped origin taken with PAMELA detector in the period 2006-2010. PAMELA was launched in 2006 and is currently orbiting the Earth in a 350*600 km, 70 degree inclination polar orbit in a pressurized container located on one side of the Russian Resurs-DK1 satellite. Data were acquired at solar minimum, but show the effect of solar modulation on p and he low energy spectra (about 100 MeV/n - 1 GeV/n). Galactic protons and helium particles are measured up to 1 TV. Trapped and secondary proton component will be compared with existing models; the spectra of solar particle events of 13 and 14 December 2006 will also be discussed.

Casolino, M.; PAMELA Collaboration

2010-12-01

58

Solar energetic proton events and coronal mass ejections near solar minimum  

SciTech Connect

The association of coronal mass ejections (CMEs) with solar energetic (9-23 MeV) proton (SEP) events are examined during the 1983-1985 approach to solar minimum. Twenty-two of 25 SEP events were associated with CMEs, a result comparable to that previously found for the period 1979-1982 around solar maximum. Peak SEP fluxes were correlated with CME speeds but not with CME angular sizes. In addition, many associated CMEs lay well out of the ecliptic plane. In a reverse study using all west hemisphere CMEs lay CMEs of speeds exceeding 800 km/s and covering the period 1979-1985, 29 of 31 events originating on the solar disk or limb were associated with observed SEPs. However, in contrast to the previous study, no cases of SEP events were found associated with magnetically well connected flares of short duration that lacked CMEs.

Kahler, S.W.; Cliver, E.W.; Cane, H.V.; McGuire, R.E.; Reames, D.V.

1987-08-15

59

Solar minimum Lyman alpha sky background observations from Pioneer Venus orbiter ultraviolet spectrometer - Solar wind latitude variation  

Microsoft Academic Search

Measurements of interplanetary H I Lyman alpha over a large portion of the celestial sphere were made at the recent solar minimum by the Pioneer Venus orbiter ultraviolet spectrometer. These measurements were performed during a series of spacecraft maneuvers conducted to observe Halley's comet in early 1986. Analysis of these data using a model of the passage of interstellar wind

J. M. Ajello

1990-01-01

60

Key features of intense geospace stormsA comparative study of a solar maximum and a solar minimum storm  

Microsoft Academic Search

This paper addresses the question of particular causes and dynamical characteristics of intense geospace storms through the comparative study of two specific examples: a solar maximum storm (46 June 1991) and a solar minimum storm (2426 September 1998). We concentrate on issues pertaining to the origin, development, dynamical evolution and recovery of intense storms. The comparative study addresses the solar

I. A. Daglis; B. T. Tsurutani; W. D. Gonzalez; J. U. Kozyra; S. Orsini; J. Cladis; Y. Kamide; M. G. Henderson; D. Vassiliadis

2007-01-01

61

Comparative study of foF2 measurements with IRI-2007 model predictions during extended solar minimum  

NASA Astrophysics Data System (ADS)

The unusually deep and extended solar minimum of cycle 23/24 made it very difficult to predict the solar indices 1 or 2 years into the future. Most of the predictions were proven wrong by the actual observed indices. IRI gets its solar, magnetic, and ionospheric indices from an indices file that is updated twice a year. In recent years, due to the unusual solar minimum, predictions had to be corrected downward with every new indices update. In this paper we analyse how much the uncertainties in the predictability of solar activity indices affect the IRI outcome and how the IRI values calculated with predicted and observed indices compared to the actual measurements. Monthly median values of F2 layer critical frequency (foF2) derived from the ionosonde measurements at the mid-latitude ionospheric station Juliusruh were compared with the International Reference Ionosphere (IRI-2007) model predictions. The analysis found that IRI provides reliable results that compare well with actual measurements, when the definite (observed and adjusted) indices of solar activity are used, while IRI values based on earlier predictions of these indices noticeably overestimated the measurements during the solar minimum. One of the principal objectives of this paper is to direct attention of IRI users to update their solar activity indices files regularly. Use of an older index file can lead to serious IRI overestimations of F-region electron density during the recent extended solar minimum.

Zakharenkova, I. E.; Krankowski, A.; Bilitza, D.; Cherniak, Iu. V.; Shagimuratov, I. I.; Sieradzki, R.

2013-02-01

62

A statistical comparison of solar wind sources of moderate and intense geomagnetic storms at solar minimum and maximum  

Microsoft Academic Search

Superposed epoch analyses of 549 storms are performed to make a comparison of solar wind features of geomagnetic storm events at solar minimum (July 1974 to June 1977; July 1984 to June 1987; July 1994 to June 1997) and solar maximum (January 1979 to December 1981; January 1989 to December 1991; July 1999 to June 2002). In this study, geomagnetic

Jichun Zhang; Michael W. Liemohn; Janet U. Kozyra; Michelle F. Thomsen; Heather A. Elliott; James M. Weygand

2006-01-01

63

Anomalous Cosmic Rays in the Outer Heliosphere During the Present Solar Minimum (Invited)  

NASA Astrophysics Data System (ADS)

The Voyager 1 (V1) spacecraft crossed the termination shock of the solar wind on 16 December 2004, just as energetic particles in the outer heliosphere had started to recover from solar maximum conditions. By the time Voyager 2 (V2) crossed the termination shock in late August of 2007, the intensities of anomalous cosmic rays (ACRs) were entering a stabler period of solar minimum conditions in the outer heliosphere, with slower intensity increases of low-energy ACRs. Both spacecraft are still in the heliosheath and neither has found the source region of ACRs, as the ACR intensities at the lowest energies measured continue to increase at V1. At the highest ACR energies, the V1/V2 gradient is ~0, suggesting we are observing the source intensity at these energies and that the mean-free path of these particles is very long, since the separation distance of the two spacecraft is ~130 AU. In addition, there is a strong solar-cycle polarity dependence of these high-energy ACRs, with the intensity at present being similar to that in the last A<0 period in 1987 but approximately a factor of 3.5 times greater than that in the intervening A>0 period in 1998. During their time in the heliosheath, the Voyagers have experienced periods when the modulation changes appear to have been beyond the location of V1, as well as times when both spacecraft appeared to be flying through a fixed radial gradient. Near the end of 2009, the solar minimum conditions near Earth appeared to be ending, as evidenced by, e.g., a sharp increase in the tilt angle of the heliospheric current sheet that was accompanied by decreases in intensities of ACRs and galactic cosmic rays. These conditions may take several years to reach the Voyager spacecraft, which are deep in the heliosheath where the radial solar wind velocity is low. This work was supported by NASA under contract NAS7-03001 and grant NNX10AE45G.

Cummings, A. C.; Stone, E. C.; McDonald, F. B.; Heikkila, B.; Lal, N.; Webber, W. R.

2010-12-01

64

Estimation of the Ionosphere and Plasmasphere Contribution to the GPS TEC under Solar Minimum Conditions  

NASA Astrophysics Data System (ADS)

The plasmaspheric electron content (PEC) was estimated by comparison GPS observations and FORMOSAT-3/COSMIC radio occultation (RO) measurements at the extended solar minimum of cycle 23/24. GPS observations provide information about values of vertical total electron content (TEC) up to the metricconverterProductID20,200 km20,200 km. FORMOSAT-3/COSMIC now provides unprecedented global coverage of GPS RO measurements. Depending on the state of the constellation, COSMIC has been producing 1,500 -- 2,500 good soundings of the ionosphere and atmosphere per day, uniformly distributed around the globe. This number of RO is much higher than even before. In this study, COSMIC RO data for different seasons corresponded to equinoxes and solstices of 2007-2009 (March, June, September and December) were analyzed. All selected COSMIC RO electron density profiles were integrated up to the height of metricconverterProductID700 km700 km (altitude of COSMIC satellites), in that way the estimates of ionospheric electron content (IEC) were retrieved on a global scale. The final IGS combined global ionospheric maps (GIMs) were used to calculate the global maps of monthly medians of TEC values. As a result there were analyzed global distributions of GPS TEC and IEC estimates corresponded to the monthly median values for different seasons of 2007-2009. We consider the quantitative differences PEC = TEC -- IEC as a measure of the contribution of the PEC to GPS TEC. In order to analyze seasonal behaviour of PEC contribution to GPS TEC at the different regions we selected several specific points with coordinates, corresponded to the approximate positions of different, mid-latitude and low-latitude, ionospheric sounding stations. Such points were selected at Northern America, European and Asian regions, Southern America, Southern Africa and country-regionplaceAustralia. For each specific points GPS TEC, COSMIC IEC and PEC estimates were analyzed. Results of our comparative study revealed that for mid-latitude stations PEC estimates varied weakly with the time of a day and reached the value of several TECU (3-5 TECU) for the condition of solar minimum. Percentage contribution of PEC to GPS TEC indicates the clear dependence from the time and varies from a minimum of about 25-30% during day-time to the value of more than 60% at night-time. The presented results are compared with TEC, PEC and IEC estimates retrieved by Standard Plasmasphere-Ionosphere Model (SPIM, http://ftp.izmiran.ru/pub/izmiran/SPIM/).

Zakharenkova, Irina; Cherniak, Iurii; Krankowski, Andrzej; Shagimuratov, Irk; Sieradzki, Rafal

2012-07-01

65

The Solar Oblateness at Solar Minimum as Observed by RHESSI/SAS  

NASA Astrophysics Data System (ADS)

The RHESSI solar aspect sensor (SAS) has provided oblateness measurements of the optical solar disk with unprecedented precision. SAS measures the optical solar profile at 670 nm in the red continuum. SAS consists of three spacially uniformly distributed linear CCDs mounted on a rotating spacecraft; a crucial ingredient in access of calibration parameters. From the SAS data, differential radius measurements can be derived at about 100 Hz including about 1000 full CCD readouts per day for calibration purposes. For a three month period during the active phase of the solar cycle in 2004, the shape of the solar disk has been measured discovering an apparent excess oblateness which we attributed to the enhanced network. In order to avoid confusion between magnetic activity and a correlated brightness enhancement in the SAS signal at 670 nm, the SAS data has been masked using the SOHO/EIT284A data. The measured oblateness as function of the masking level is then extrapolated for a value of the underlaying, presumably non-magnetic sun. Here, we present the analysis of the RHESSI/SAS data during the solar minimum with the inferred interpretation for the oblateness signal.

Fivian, M. D.; Hudson, H. S.; Lin, R. P.

2010-12-01

66

GPS TEC, scintillation and cycle slips observed at high latitudes during solar minimum  

NASA Astrophysics Data System (ADS)

High-latitude irregularities can impair the operation of GPS-based devices by causing fluctuations of GPS signal amplitude and phase, also known as scintillation. Severe scintillation events lead to losses of phase lock, which result in cycle slips. We have used data from the Canadian High Arctic Ionospheric Network (CHAIN) to measure amplitude and phase scintillation from L1 GPS signals and total electron content (TEC) from L1 and L2 GPS signals to study the relative role that various high-latitude irregularity generation mechanisms have in producing scintillation. In the first year of operation during the current solar minimum the amplitude scintillation has remained very low but events of strong phase scintillation have been observed. We have found, as expected, that auroral arc and substorm intensifications as well as cusp region dynamics are strong sources of phase scintillation and potential cycle slips. In addition, we have found clear seasonal and universal time dependencies of TEC and phase scintillation over the polar cap region. A comparison with radio instruments from the Canadian GeoSpace Monitoring (CGSM) network strongly suggests that the polar cap scintillation and TEC variations are associated with polar cap patches which we therefore infer to be main contributors to scintillation-causing irregularities in the polar cap.

Prikryl, P.; Jayachandran, P. T.; Mushini, S. C.; Pokhotelov, D.; MacDougall, J. W.; Donovan, E.; Spanswick, E.; St.-Maurice, J.-P.

2010-06-01

67

Physics of the weird solar minimum: New observations of the Sun  

NASA Astrophysics Data System (ADS)

While solar physicists expected more sunspots, flares, and coronal mass ejections by now, the Sun has defied most predictions by persisting in a relatively quiet state for an unusually long time. Can we tell whether this solar minimum is likely to ease in the next decade, or if it may become a Maunder-type minimum? What evidence is there for mechanisms that might explain the observed delayed and low-amplitude magnetic activity? What effects could decreased solar activity have on Earth's climate? Evergreen undergraduates study the Sun with colleagues who built the new Solar Dynamics Observatory (SDO). Students analyzed flow velocities with respect to magnetic field tilts; analyzed waves of UV light in active regions; developed a software suite to enable the public to engage with solar dynamics; and cataloged movies of solar events for public release. We use data from the high-resolution HINODE satellite and from the new full-disk SDO. Zita studied the solar dynamo, and found that resistivity gradients can drive magnetic advection. We summarize our work and the light it may shed on questions such as those above.

Zita, E.; Smith, C.; Ballou, C.; Friedman, B.; Showalter, C.; Rex, R.; Hurlburt, N.

2010-10-01

68

Impact of a potential 21st century "grand solar minimum" on surface temperatures and stratospheric ozone  

NASA Astrophysics Data System (ADS)

We investigate the effects of a recently proposed 21st century Dalton minimum like decline of solar activity on the evolution of Earth's climate and ozone layer. Three sets of two member ensemble simulations, radiatively forced by a midlevel emission scenario (Intergovernmental Panel on Climate Change RCP4.5), are performed with the atmosphere-ocean chemistry-climate model AOCCM SOCOL3-MPIOM, one with constant solar activity, the other two with reduced solar activity and different strength of the solar irradiance forcing. A future grand solar minimum will reduce the global mean surface warming of 2 K between 1986-2005 and 2081-2100 by 0.2 to 0.3 K. Furthermore, the decrease in solar UV radiation leads to a significant delay of stratospheric ozone recovery by 10 years and longer. Therefore, the effects of a solar activity minimum, should it occur, may interfere with international efforts for the protection of global climate and the ozone layer.

Anet, J. G.; Rozanov, E. V.; Muthers, S.; Peter, T.; BrNnimann, S.; Arfeuille, F.; Beer, J.; Shapiro, A. I.; Raible, C. C.; Steinhilber, F.; Schmutz, W. K.

2013-08-01

69

Modulation of Galactic cosmic rays during the unusual solar minimum of cycle 24  

NASA Astrophysics Data System (ADS)

Intensity of Galactic cosmic rays (GCR) measured during the recent solar minimum was the highest ever recorded since space age, while the magnitude of solar and interplanetary magnetic field and the speed of the solar wind in heliosphere was very low, but the tilt of heliospheric current sheet was not at the lowest level. This indicates that the modulation of cosmic ray is not dominated by the mechanism of particle drift through the current sheet during this A<0 cycle as we normally think. Possible reasons for the record cosmic ray flux include increase of particle diffusion and regular drift due to the weaker magnetic field, reduction of particle energy loss due to the slower solar wind speed, or closer termination shock radial distance due to smaller solar wind pressure. In this paper, We use a model of GCR transport in the three-dimensional heliosphere based on a simulation of Markov stochastic process to study the effect of these parameters. We will show which is the proper reason for the abnormally high observed GCR flux. Implication or relationship of this study to the understanding of the modulation of cosmic rays during historical deep solar minima will be discussed.

Lingling, Z.; Qin, G.; Zhang, M.

2010-12-01

70

On Equatorial Spread F During the Solstices Under Solar Minimum Conditions  

NASA Astrophysics Data System (ADS)

There is mounting evidence that large-scale wave structure (LSWS), seeded by atmospheric gravity waves (AGWs) from the troposphere, is playing an important role in the development of plasma structure, generically referred to as equatorial spread F (ESF) [Tsunoda, 2010a,b,c]. The process involves neutral-ion coupling via polarization of the spatially-divergent Pedersen current, which is associated with zonally propagating AGWs, but only by AGWs excited along the magnetic dip equator. Hence, ESF via seeding of LSWS by AGWs is strongest, when the intertropical convergence zone (ITCZ) becomes aligned with the magnetic dip equator [Tsunoda, 2010a]. In this presentation, we show that the validity of what we have referred to as the GWBA (gravity wave-B alignment) hypothesis, where B is the geomagnetic field, becomes most evident during the solstices under solar minimum conditions. We focus here on the interpretation of enhanced ESF activity, which occurs in the Brazilian sector during the June solstice. We show that this feature, which dominated the dawn ESF climatology during 2008, appears to involve seeding, as described above, but must involve other drivers, such as an effective neutral wind in the thermosphere and coupled polarization behavior, which occurs in the presence of a sporadic-E layer [e.g., Tsunoda, 2009]. The dawn ESF climatology used in this presentation is from the DMSP satellite.

Tsunoda, R. T.; Gentile, L. C.; Burke, W. J.

2010-12-01

71

An Empirical Model of a Polar Coronal Hole at Solar Minimum  

Microsoft Academic Search

We present a comprehensive and self-consistent empirical model for several plasma parameters in the extended solar corona above a polar coronal hole. The model is derived from observations with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS\\/SOHO) during the period between 1996 November and 1997 April. We compare observations of H I Lyalpha and O VI lambdalambda1032, 1037 emission lines with detailed

S. R. Cranmer; J. L. Kohl; G. Noci; E. Antonucci; G. Tondello; M. C. E. Huber; L. Strachan; A. V. Panasyuk; L. D. Gardner; M. Romoli; S. Fineschi; D. Dobrzycka; J. C. Raymond; P. Nicolosi; O. H. W. Siegmund; D. Spadaro; C. Benna; A. Ciaravella; S. Giordano; S. R. Habbal; M. Karovska; X. Li; R. Martin; J. G. Michels; A. Modigliani; G. Naletto; R. H. O'Neal; C. Pernechele; G. Poletto; P. L. Smith; R. M. Suleiman

1999-01-01

72

Modulation of Galactic Protons in the Heliosphere During the Unusual Solar Minimum of 2006 to 2009  

NASA Astrophysics Data System (ADS)

The last solar minimum activity period, and the consequent minimum modulation conditions for cosmic rays, was unusual. The highest levels of galactic protons were recorded at Earth in late 2009 in contrast to expectations. Proton spectra observed for 2006 to 2009 from the PAMELA cosmic ray detector on-board the Resurs-DK1 satellite are presented together with the solutions of a comprehensive numerical model for the solar modulation of cosmic rays. The model is used to determine what mechanisms were mainly responsible for the modulation of protons during this period, and why the observed spectrum for 2009 was the highest ever recorded. From mid-2006 until December 2009 we find that the spectra became significantly softer because increasingly more low energy protons had reached Earth. To simulate this effect, the rigidity dependence of the diffusion coefficients had to decrease significantly below 3 GeV. The modulation minimum period of 2009 can thus be described as relatively more `diffusion dominated' than previous solar minima. However, we illustrate that drifts still had played a significant role but that the observable modulation effects were not as well correlated with the waviness of the heliospheric current sheet as before. Protons still experienced global gradient and curvature drifts as the heliospheric magnetic field had decreased significantly until the end of 2009, in contrast to the moderate decreases observed during previous minimum periods. We conclude that all modulation processes contributed to the observed increases in the proton spectra for this period, exhibiting an intriguing interplay of these major mechanisms.

Potgieter, M. S.; Vos, E. E.; Boezio, M.; De Simone, N.; Di Felice, V.; Formato, V.

2013-06-01

73

COSMIC/FORMOSAT-3 Observations of Equatorial Ionospheric Irregularities during Solar Minimum  

NASA Astrophysics Data System (ADS)

The data of ionospheric electron density and S4 scintillation index from the COSMIC/FORMOSAT-3 GPS occultation observations during 2007-2008 are used to study the morphology of equatorial F-region irregularity (EFI). The six LEO constellating satellites of COSMIC provide daily global measurements of the ionosphere at altitudes below ~800 km. The large volume of radio sensing data enables the correlative study of electron density depletion and strong amplitude scintillation, thus allows the global and altitudinal irregularity distributions to be examined. Under solar minimum and geomagnetic quiet conditions, post sunset EFI/scintillation events are found to concentrate in the South Atlantic magnetic Anomaly (SAA) longitude sector during the northern winter months (D-months), but absent from the same longitude sector during the opposite season (J-months). The D-months average pattern of EFI in the SAA longitude sector reveals that most of irregularities occurred in the bottom side F-region (200~350 km altitudes) and at the low magnetic latitudes adjacent to the locations of the maximum post-sunset Nmax and Hmax. The association of EFI with high values of Nmax and Hmax is consistent with the observations that early post sunset irregularities are generated in the region where plasma upward drifts have been greatly enhanced. During the December solstice, the E-region sunset terminator in the SAA longitude sector is nearly parallel to the magnetic field direction (westward declination) at equatorial latitudes, where density depletion and strong scintillation were observed. These observations confirm the published reports that the sunset equatorial electrodynamics plays a key role in controlling the seasonal and longitudinal occurrence of the quiet time equatorial F-region irregularities.

Yeh, H.; Ko, C.

2009-12-01

74

Statistics of counter-streaming solar wind suprathermal electrons at solar minimum: STEREO observations  

NASA Astrophysics Data System (ADS)

Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counter-streaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counter-streaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period March-December 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90 pitch angle. The occurrence rate of CSE is found to be about 15-20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate >35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunward-directed fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs.

Lavraud, B.; Opitz, A.; Gosling, J. T.; Rouillard, A. P.; Meziane, K.; Sauvaud, J.-A.; Fedorov, A.; Dandouras, I.; Gnot, V.; Jacquey, C.; Louarn, P.; Mazelle, C.; Penou, E.; Larson, D. E.; Luhmann, J. G.; Schroeder, P.; Jian, L.; Russell, C. T.; Foullon, C.; Skoug, R. M.; Steinberg, J. T.; Simunac, K. D.; Galvin, A. B.

2010-01-01

75

Analysis of electron content variations over Japan during solar minimum: Observations and modeling  

NASA Astrophysics Data System (ADS)

Comparative analysis of GPS TEC data and FORMOSAT-3/COSMIC radio occultation measurements was carried out for Japan region during period of the extremely prolonged solar minimum of cycle 23/24. COSMIC data for different seasons corresponded to equinox and solstices of the years 20072009 were analyzed. All selected electron density profiles were integrated up to the height of 700 km (altitude of COSMIC satellites), the monthly median estimates of Ionospheric Electron Content (IEC) were retrieved with use of spherical harmonics expansion. Monthly medians of TEC values were calculated from diurnal variations of GPS TEC estimates during considered month. Joint analysis of GPS TEC and COSMIC data allows us to extract and estimate electron content corresponded to the ionosphere (its bottom and topside parts) and the plasmasphere (h > 700 km) for different seasons of 20072009. Percentage contribution of ECpl to GPS TEC indicates the clear dependence from the time and varies from a minimum of about 2550% during day-time to the value of 5075% at night-time. Contribution of both bottom-side and topside IEC has minimal values during winter season in compare with summer season (for both day- and night-time). On average bottom-side IEC contributes about 510% of GPS TEC during night and about 2027% during day-time. Topside IEC contributes about 1520% of GPS TEC during night and about 3540% during day-time. The obtained results were compared with TEC, IEC and ECpl estimates retrieved by Standard PlasmasphereIonosphere Model that has the plasmasphere extension up to 20,000 km (GPS orbit).

Zakharenkova, I. E.; Cherniak, Iu. V.; Krankowski, A.; Shagimuratov, I. I.

2013-11-01

76

Gyro-resonant scattering of radiation belt electrons during the solar minimum by fast magnetosonic waves  

NASA Astrophysics Data System (ADS)

In the current study, we perform statistical analysis of the magnetosonic (MS) waves (also often referred to as extremely low frequency (ELF) equatorial noise) in the range between the ion cyclotron frequency and the lower hybrid resonance frequency within 10 of the magnetic equator. Observations were made between 2 and 9 RE using THEMIS Filter Bank (FBK) data. ELF waves with spectral power exceeding 10-6 nT2/Hz are registered in ~3% of all samples in the inner magnetosphere. The survey has shown that, during the solar minimum, the average amplitude of equatorial ELF waves is less than 0.025 nT. Interpreting ELF events as MS waves, we have evaluated the corresponding wave-induced resonant scattering coefficients of radiation belt energetic electrons. We also study the effect of heavy ions on the scattering rates. The analysis reveals that the scattering by magnetosonic waves for various plasma compositions during geomagnetically quiet times is by up to two orders of magnitude slower than was previously reported and cannot significantly contribute to the long-term dynamics of the radiation belts. Computed electron scattering rates by magnetosonic waves extends to higher ?eq when the fraction of H+ in the plasma decreases, while the range of pitch angles for which resonance occurs remains relatively insensitive to the plasma composition. While inclusion of multi-ion species into the wave dispersion relation produces noticeable changes in bounce-averaged scattering rates, the average rates are still significantly below typical scattering rates of chorus or hiss waves.

Shprits, Yuri Y.; Runov, Andrei; Ni, Binbin

2013-02-01

77

Measurement of the cosmic-ray antiproton spectrum at solar minimum with a long-duration balloon flight over Antarctica  

Microsoft Academic Search

The energy spectrum of cosmic-ray antiprotons from 0.17 to 3.5 GeV has been measured using 7886 antiprotons detected by BESS-Polar II during a long-duration flight over Antarctica near solar minimum in December 2007 and January 2008. This shows good consistency with secondary antiproton calculations. Cosmologically primary antiprotons have been investigated by comparing measured and calculated antiproton spectra. BESS-Polar II data

K. Abe; H. Fuke; S. Haino; T. Hams; M. Hasegawa; A. Horikoshi; K. C. Kim; A. Kusumoto; M. H. Lee; Y. Makida; S. Matsuda; Y. Matsukawa; J. W. Mitchell; J. Nishimura; M. Nozaki; R. Orito; J. F. Ormes; K. Sakai; M. Sasaki; E. S. Seo; R. Shinoda; R. E. Streitmatter; J. Suzuki; K. Tanaka; N. Thakur; T. Yamagami; A. Yamamoto; T. Yoshida; K. Yoshimura

2011-01-01

78

The Humanities, Unraveled  

ERIC Educational Resources Information Center

|Graduate education in the humanities is in crisis. Every aspect, from the most specific details of the curriculum to the broadest questions about its purpose, is in crisis. It is a seamless garment of crisis: If one pulls on any one thread, the entire thing unravels. It is therefore exceptionally difficult to discuss any one aspect of graduate

Berube, Michael

2013-01-01

79

Unraveling hemophilic arthropathy.  

PubMed

In this issue of Blood, Acharya and colleagues provide evidence for the role of angiogenesis in the pathophysiology of hemophilic joint disease. Is this the linchpin that unravels this important clinical condition or merely a cog in a not so stepwise process? PMID:21350060

Abshire, Thomas

2011-02-24

80

The Solar Corona  

NSDL National Science Digital Library

This site describes the corona of the sun from three different points of view. In the first case, the white-light corona is the sight that is visible during total eclipses of the sun as a pearly white crown surrounding the sun and displays a variety of features including streamers, plumes, and loops. The emission line corona is explained on the basis of the extreme heat of the corona and the X-ray corona is described in terms of past and present research projects designed to study it. The site also contains an image for each of the three parts.

Hathaway, David

81

Corona physics and diagnostics  

SciTech Connect

The criterions for oscillations in DC-fed coronas are discussed, both for the well-understood negative Trichel pulse coronas and for the unexplained positive glow pulse coronas. Trichel-like pulses occur also in non-electron-attaching gases, due to the external circuit impedance, and this lowers the sensitivity of Trichel coronas as detectors for electronegative gas traces. Pulse excitation of positive glow coronas in argon with added trace gases show that the corona stability and resonance frequency strongly depend on the trace gas type and concentration, but the physics involved is unknown. Finally, it is shown that the low-current U(I) curve of relaxation-pulsed coronas always must have a negative slope, equal to the negative of the series resistance. {copyright} {ital 1996 American Institute of Physics.}

Sigmond, R.S. [The Electron and Ion Physics Research Group, Physics Department, The Norwegian Institute of Technology, N-7034 Trondheim (Norway)

1996-03-01

82

Variations in equatorial F2-layer parameters and comparison with IRI-2007 during a deep solar minimum  

NASA Astrophysics Data System (ADS)

During the deep solar minimum between 23rd and 24th solar cycles, we study the variations in F2-layer peak electron density (NmF2), its height (hmF2), and the F2-layer thickness parameter (B0) at Jicamarca, and compare the observation with IRI-2007 predication. The observation results show that the hmF2, NmF2, and B0 are greater and smaller during daytime and nighttime, respectively. The sunrise peaks in hmF2 and B0 appear in all months. However, the post-sunset peaks do not occur in hmF2 and B0, except hmF2 in the equinox months. Seasonal variations show that the daytime hmF2 and NmF2 are greater in the equinox and summer months, while the daytime B0 are slightly greater in the equinox and winter months. For the comparison of observation with IRI-2007, the observed hmF2 is close to the predicted one during 19:00-23:00 LT. The NmF2 of URSI map and observation are close to each other during 00:00-13:00 LT, while the CCIR map modeled value generally agrees with the observed ones. Regarding the B0 comparison, the evident discrepancy between observation and Gulyaeva option is the locations of annual maxima. For the other option, the daily B0 peak is much broader in the IRI-B0-table option than observation. The CCIR map and Gulyaeva option produce a slightly better predication of NmF2 and B0, respectively. In contrast to the comparison results in preceding solar minimum, IRI-2007 provides a worse predication in the deep solar minimum.

Lee, C. C.; Reinisch, B. W.

2012-01-01

83

Measurement of the Cosmic-Ray Antiproton Spectrum at Solar Minimum with a Long-Duration Balloon Flight over Antarctica  

NASA Astrophysics Data System (ADS)

The energy spectrum of cosmic-ray antiprotons (ps) from 0.17 to 3.5 GeV has been measured using 7886 ps detected by BESS-Polar II during a long-duration flight over Antarctica near solar minimum in December 2007 and January 2008. This shows good consistency with secondary p calculations. Cosmologically primary ps have been investigated by comparing measured and calculated p spectra. BESS-Polar II data show no evidence of primary ps from the evaporation of primordial black holes.

Abe, K.; Fuke, H.; Haino, S.; Hams, T.; Hasegawa, M.; Horikoshi, A.; Kim, K. C.; Kusumoto, A.; Lee, M. H.; Makida, Y.; Matsuda, S.; Matsukawa, Y.; Mitchell, J. W.; Nishimura, J.; Nozaki, M.; Orito, R.; Ormes, J. F.; Sakai, K.; Sasaki, M.; Seo, E. S.; Shinoda, R.; Streitmatter, R. E.; Suzuki, J.; Tanaka, K.; Thakur, N.; Yamagami, T.; Yamamoto, A.; Yoshida, T.; Yoshimura, K.

2012-02-01

84

Measurement of the cosmic-ray antiproton spectrum at solar minimum with a long-duration balloon flight over antarctica.  

PubMed

The energy spectrum of cosmic-ray antiprotons (p's) from 0.17 to 3.5 GeV has been measured using 7886 p's detected by BESS-Polar II during a long-duration flight over Antarctica near solar minimum in December 2007 and January 2008. This shows good consistency with secondary p calculations. Cosmologically primary p's have been investigated by comparing measured and calculated p spectra. BESS-Polar II data show no evidence of primary p's from the evaporation of primordial black holes. PMID:22400920

Abe, K; Fuke, H; Haino, S; Hams, T; Hasegawa, M; Horikoshi, A; Kim, K C; Kusumoto, A; Lee, M H; Makida, Y; Matsuda, S; Matsukawa, Y; Mitchell, J W; Nishimura, J; Nozaki, M; Orito, R; Ormes, J F; Sakai, K; Sasaki, M; Seo, E S; Shinoda, R; Streitmatter, R E; Suzuki, J; Tanaka, K; Thakur, N; Yamagami, T; Yamamoto, A; Yoshida, T; Yoshimura, K

2012-01-31

85

STRUCTURE AND DYNAMICS OF THE 2009 JULY 22 ECLIPSE WHITE-LIGHT CORONA  

SciTech Connect

The white-light corona (WLC) during the total solar eclipse of 2009 July 22 was observed by several teams in the Moon's shadow stretching from India and China across the Pacific Ocean with its many isolated islands. We present a comparison of the WLC as observed by eclipse teams located in China (Shanghai region) and on the Enewetak Atoll in the Marshall Islands, with observations taken 112 minutes apart, combined with near-simultaneous space observations. The eclipse was observed at the beginning of solar cycle 24, during a deep solar minimum (officially estimated as 2008 December according to the smoothed sunspot number, but very extended). The solar corona shows several different types of features (coronal holes, polar rays, helmet streamers, faint loops, voids, etc.), though it was extremely sparse in streamers as shown from Large-Angle Spectroscopic Coronagraph data. No large-scale dynamical phenomena were seen when comparing the observations from the two sites, confirming that the corona was quiescent. We measure a Ludendorff flattening coefficient of 0.238, typical of solar minimum.

Pasachoff, J. M.; Babcock, B. A. [Williams College-Hopkins Observatory, Williamstown, MA 01267 (United States); Rusin, V.; Saniga, M. [Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranska Lomnica (Slovakia); Druckmuellerova, H., E-mail: eclipse@williams.edu, E-mail: bryce.a.babcock@williams.edu, E-mail: vrusin@ta3.sk, E-mail: msaniga@ta3.sk, E-mail: hanadruck@seznam.cz [Faculty of Mechanical Engineering, Brno University of Technology, Technicka 2, 616 69 Brno (Czech Republic)

2011-11-20

86

Observations of the Solar Minimum Thermosphere Above Poker Flat, Alaska, with an All-Sky Imaging Fabry-Perot Spectrometer  

NASA Astrophysics Data System (ADS)

The recent deep solar minimum conditions have provided an ideal opportunity to resolve how various external drivers perturb the state of Earth's thermosphere. Here, we present observations of thermospheric wind and temperature fields above Poker Flat, Alaska, during the 2007/08 and 2008/09 northern winters. These data were taken with an all-sky imaging Fabry-Perot spectrometer, that was recently upgraded to improve sensitivity and to allow interleaved observations of both the 6300A (red) and 5577A (green) emission in a single night. The multi-wavelength capability provides vertical resolution, whereas the observing cadence of 2-5 minutes allows determination of the ion-neutral coupling time constant. All-sky wind mapping resolves these responses horizontally, on scales down to 100 km or less. Even at solar minimum we often observed signatures of strong localized ion-neutral coupling; horizontal divergence and shear with magnitudes up to 0.0005 inverse seconds were not uncommon, even in the E-region. The quiescent conditions also allowed us to observe an approximately 3-week long cooling period in the F-region, following the stratospheric warming event of January/February 2009. The magnitude of this cooling was around 100K.

Conde, M. G.; Anderson, C.; Andersen, C. S.

2009-12-01

87

On the Origin, 3D Structure and Dynamic Evolution of CMEs Near Solar Minimum  

NASA Astrophysics Data System (ADS)

We have conducted a statistical study 27 coronal mass ejections (CMEs) from January 2007 - June 2008, using the stereoscopic views of STEREO SECCHI A and B combined with SOHO LASCO observations. A flux-rope model, in conjunction with 3D triangulations, has been used to reconstruct the 3D structures and determine the actual speeds of CMEs. The origin and the dynamic evolution of the CMEs are investigated using COR1, COR2 and EUVI images. We have identified four types of solar surface activities associated with CMEs: i) total eruptive prominence (totEP), ii) partially eruptive prominence (PEP), iii) X-ray flare, and iv) X-type magnetic structure (X-line). Among the 27 CMEs, 18.5% (5 of 27) are associated with totEPs, 29.6% (8 of 27) are associated with PEPs, 26% (7 of 27) are flare related, and 26% (7 of 27) are associated with X-line structures, and 43% (3 of 7) are associated with both X-line structures and PEPs. Three (11%) could not be associated with any detectable activity. The mean actual speeds for totEP-CMEs, PEP-CMEs, flare-CMEs, and X-line-CMEs are 404 km s-1,247 km s-1,909 km s-1, and 276 km s-1, respectively; the average mean values of edge-on and broadside widths for the 27 CMEs are 52 and 85 degrees, respectively. We found that slow CMEs ( V?400 km s-1) tend to deflect towards and propagate along the streamer belts due to the deflections by the strong polar magnetic fields of corona holes, while some faster CMEs show opposite deflections away from the streamer belts.

Xie, H.; St. Cyr, O. C.; Gopalswamy, N.; Yashiro, S.; Krall, J.; Kramar, M.; Davila, J.

2009-10-01

88

Corona discharge processes  

Microsoft Academic Search

Applications of corona discharge induced plasmas and unipolar ions are reviewed. Corona process applications emphasize one of two aspects of the discharge: the ions produced or the energetic electrons producing the plasma. The ion identities depend on the polarity of the discharge and the characteristics of the gas mixture, specifically on the electron attaching species. The electron energies depend on

J.-S. Chang; P. A. Lawless; T. Yamamoto

1991-01-01

89

The inner heliosphere from solar minimum to solar maximum Short- and long-term variations in the energetic particle population  

NASA Astrophysics Data System (ADS)

Between 1975 and 1983 Helios 1 scanned the interplanetary medium between 0.3 and 1 AU 31 times. The observed variations in the differential and integral flux of protons and helium nuclei in the energy range from 4 to over 50 MeV/n are characterized by large temporal changes in the intensities, moderate changes in the energy spectrum, and changes in the gradient below the detection level (60 percent). During solar minimum conditions, recurrent disturbances are caused mainly by corotating interaction regions. The onset of solar activity near the end of 1977, characterized by a large number of solar events, is accompanied by a monotonous decrease of galactic cosmic radiation. The successive reduction of the cosmic ray intensity to the level of solar maximum is discussed in view of the role of large transient disturbances, as compared to such processes as diffusion, convection, adiabatic energy losses, and drifts.

Mueller-Mellin, R.; Wibberenz, G.

90

Asymmetry in the periodicities of solar photospheric fields: A probe to the unusual solar minimum prior to cycle 24  

NASA Astrophysics Data System (ADS)

Employing wavelet and Fourier methods, we investigate temporal variations of periodicities in the photospheric fields obtained from synoptic magnetograms of the National Solar Observatory at Kitt Peak (NSO/KP) spanning the years 1975-2009. A north-south asymmetry is noticed in the periodicities of photospheric fields in the latitude range, 45-78, when the data is grouped into fields prior to and after 1996. This asymmetry when coupled with the fact that both solar fields in the latitude range, 45-78, and the micro-turbulence levels in the inner heliosphere began declining ~ 1995-1996 suggests that active changes occurred in the underlying basic solar processes which eventually initiated, at the end of solar cycle 23, the build-up of the deepest solar minimum, in the past 100 years.

Bisoi, Susanta Kumar; Janardhan, P.

2013-07-01

91

Exospheric hydrogen density distributions for equinox and summer solstice observed with TWINS1/2 during solar minimum  

NASA Astrophysics Data System (ADS)

The Lyman-? Detectors (LAD) on board the two TWINS 1/2-satellites allow for the simultaneous stereo imaging of the resonant emission glow of the H-geocorona from very different orbital positions. Terrestrial exospheric atomic hydrogen (H) resonantly scatters solar Lyman-? (121.567 nm) radiation. During the past solar minimum, relevant solar parameters that influence these emissions were quite stable. Here, we use simultaneous LAD1/2-observations from TWINS1 and TWINS2 between June 2008 and June 2010 to study seasonal variations in the H-geocorona. Data are combined to produce two datasets containing (summer) solstice and (combined spring and fall) equinox emissions. In the range from 3 to 10 Earth radii (RE), a three-dimensional (3-D) mathematical model is used that allows for density asymmetries in longitude and latitude. At lower geocentric distances (< 3 RE), a best fitting r-dependent (Chamberlain, 1963)-like model is adapted to enable extrapolation of our information to lower heights. We find that dawn and dusk H-geocoronal densities differ by up to a factor of 1.3 with higher densities on the dawn side. Also, noon densities are greater by up to a factor of 2 compared to the dawn and dusk densities. The density profiles are aligned well with the Earth-Sun line and there are clear density depletions over both poles that show additional seasonal effects. These solstice and equinox empirical fits can be used to determine H-geocoronal densities for any day of the year for solar minimum conditions.

Zoennchen, J. H.; Nass, U.; Fahr, H. J.

2013-03-01

92

Modeling and observations of the north-south ionospheric asymmetry at low latitudes at long deep solar minimum  

NASA Astrophysics Data System (ADS)

Using the physics based model SUPIM and FORMOSAT-3/COSMIC electron density data measured at the long deep solar minimum (2008-2010) we investigate the longitude variations of the north-south asymmetry of the ionosphere at low latitudes (30 magnetic). The data at around diurnal maximum (12:30-13:30 LT) for magnetically quiet (Ap ? 15) equinoctial conditions (March-April and September-October) are presented for three longitude sectors (a) 60E-120E, (b) 60W-120W and (c) 15W-75W. The sectors (a) and (b) have large displacements of the geomagnetic equator from geographic equator but in opposite hemispheres with small magnetic declination angles; and sector (c) has large declination angle with small displacement of the equators; vertical E B drift velocities also have differences in the three longitude sectors. SUPIM investigates the importance of the displacement of the equators, magnetic declination angle, and E B drift on the north-south asymmetry. The data and model qualitatively agree; and indicate that depending on longitudes both the displacement of the equators and declination angle are important in producing the north-south asymmetry though the displacement of the equators seems most effective. This seems to be because it is the displacement of the equators more than the declination angle that produces large north-south difference in the effective magnetic meridional neutral wind velocity, which is the main cause of the ionospheric asymmetry. For the strong control of the neutral wind, east-west electric field has only a small effect on the longitude variation of the ionospheric asymmetry. Though the study is for the long deep solar minimum the conclusions seem valid for all levels of solar activity since the displacement of the equators and declination angle are independent of solar activity.

Balan, N.; Rajesh, P. K.; Sripathi, S.; Tulasiram, S.; Liu, J. Y.; Bailey, G. J.

2013-08-01

93

The impact of helium on thermosphere mass density response to geomagnetic activity during the recent solar minimum  

NASA Astrophysics Data System (ADS)

High-resolution mass density observations inferred from accelerometer measurements on the CHAMP and GRACE satellites are employed to investigate the thermosphere mass density response with latitude and altitude to geomagnetic activity during the recent solar minimum. Coplanar orbital periods in February 2007 and December 2008 revealed the altitude and latitude response in thermosphere mass density for their respective winter hemispheres was influenced by the relative amount of helium and oxygen present. The CHAMP-to-GRACE (C/G) mass density ratio depends on two terms; the first proportional to the ratio of the mean molecular weight to temperature and the second proportional to the vertical gradient of the logarithmic mean molecular weight. For the relative levels of helium and oxygen in February 2007, the winter hemisphere C/G mass density response to geomagnetic activity, although similar to the summer hemisphere, was caused predominantly by changes in the vertical gradient of the logarithmic mean molecular weight. In December 2008, the significant presence of helium caused the mean molecular weight changes to exceed temperature changes in the winter hemisphere leading to an increase in the C/G ratio with increasing geomagnetic activity, in opposition to the decrease observed in the summer hemisphere that was caused primarily by temperature changes. The observed behavior is indicative of composition effects influencing the mass density response and the dynamic action of the oxygen to helium transition region in both latitude and altitude will lead to complex behaviors in the mass density at GRACE altitudes throughout the extended solar minimum from 2007 to 2010.

Thayer, J. P.; Liu, X.; Lei, J.; Pilinski, M.; Burns, A. G.

2012-07-01

94

Characteristics of a corona discharge with a hot corona electrode  

SciTech Connect

The effect of the temperature of the corona electrode on the electrical characteristics of a corona discharge was studied experimentally. A modified Townsend formula for the current-voltage characteristic of a one-dimensional corona is proposed. Gasdynamic and thermal characteristics of a positive corona discharge in a coaxial electrode system are calculated. The calculated results are compared with the experimental data.

Kulumbaev, E. B.; Lelevkin, V. M.; Niyazaliev, I. A.; Tokarev, A. V. [Kyrgyz-Russian Slavic University (Kyrgyzstan)

2011-08-15

95

The distribution of solar wind speeds during solar minimum: Calibration for numerical solar wind modeling constraints on the source of the slow solar wind  

Microsoft Academic Search

It took the solar polar passage of Ulysses in the early 1990s to establish the global structure of the solar wind speed during solar minimum. However, it remains unclear if the solar wind is composed of two distinct populations of solar wind from different sources (e.g., closed loops which open up to produce the slow solar wind) or if the

S. L. McGregor; W. J. Hughes; C. N. Arge; M. J. Owens; D. Odstrcil

2011-01-01

96

Distribution of Solar Wind Speeds During Solar Minimum: Calibration for Numerical Solar Wind Modeling Constraints on the Source of the Slow Solar Wind (Postprint).  

National Technical Information Service (NTIS)

It took the solar polar passage of Ulysses in the early 1990s to establish the global structure of the solar wind speed during solar minimum. However, it remains unclear if the solar wind is composed of two distinct populations of solar wind from differen...

C. N. Arge D. Odstreil M. J. Owens S. L. McGregor W. J. Hughes

2012-01-01

97

Differential Rotation of the Ultraviolet Corona at Solar Maximum  

NASA Astrophysics Data System (ADS)

Synoptic observations of the O VI 1032 spectral line from the UltraViolet Coronagraph Spectrometer (UVCS) telescope on board the Solar and Heliospheric Observatory (SOHO) have been analyzed in order to establish the rotational characteristics of the solar corona in the time interval from 1999 March 18 to 2002 December 31, corresponding to the maximum phase of solar cycle 23. By using autocorrelation analysis techniques, we determined the latitude and time dependence of the coronal rotation rate at a heliocentric distance of 1.6 R sun from the solar equator up to about 15 from the poles. Although the equatorial rotation rate is initially consistent with the coronal synodic rotation period (~27.5 days) inferred in a previous study by Giordano & Mancuso around solar minimum, a systematic and substantial acceleration is observed to occur during the second part of the year 2000, with the equatorial coronal synodic rotation period settling to an average value of 25.7 days in the time interval extending from 2001 August to 2002 April, corresponding to a ~7% increase in coronal rotation rate. It is shown that the coronal magnetic structures rotate much faster at all latitudes, and less differentially, than the underlying small-scale magnetic structures linked to the photospheric plasma. The rotation rate of sunspots is however compatible, at least within ~20 from the solar equator, with the one estimated in the middle corona.

Mancuso, Salvatore; Giordano, Silvio

2011-03-01

98

Temporal Evolution of the Solar Wind Bulk Velocity at Solar Minimum by Correlating the STEREO A and B PLASTIC Measurements  

NASA Astrophysics Data System (ADS)

The two STEREO spacecraft with nearly identical instrumentation were launched near solar activity minimum and they separate by about 45 per year, providing a unique tool to study the temporal evolution of the solar wind. We analyze the solar wind bulk velocity measured by the two PLASTIC plasma instruments onboard the two STEREO spacecraft. During the first half year of our measurements (March - August 2007) we find the typical alternating slow and fast solar wind stream pattern expected at solar minimum. To evaluate the temporal evolution of the solar wind bulk velocity we exclude the spatial variations and calculate the correlation between the solar wind bulk velocity measured by the two spacecraft. We account for the different spacecraft positions in radial distance and longitude by calculating the corresponding time lag. After adjusting for this time lag we compare the solar wind bulk velocity measurements at the two spacecraft and calculate the correlation between the two time-shifted datasets. We show how this correlation decreases as the time difference between two corresponding measurements increases. As a result, the characteristic temporal changes in the solar wind bulk velocity can be inferred. The obtained correlation is 0.95 for a time lag of 0.5 days and 0.85 for 2 days.

Opitz, A.; Karrer, R.; Wurz, P.; Galvin, A. B.; Bochsler, P.; Blush, L. M.; Daoudi, H.; Ellis, L.; Farrugia, C. J.; Giammanco, C.; Kistler, L. M.; Klecker, B.; Kucharek, H.; Lee, M. A.; Mbius, E.; Popecki, M.; Sigrist, M.; Simunac, K.; Singer, K.; Thompson, B.; Wimmer-Schweingruber, R. F.

2009-05-01

99

Stagnated Outflow of O+5 Ions in the Source Region of the Slow Solar Wind at Solar Minimum  

NASA Astrophysics Data System (ADS)

Using recent coordinated UVCS and LASCO measurements by Strachan and coworkers to constrain the heating parameters of a one-dimensional single-fluid minor ion model, we calculate the outflow velocity profile of O+5 ions in the flow tube overlying the helmet streamer, which has been supposed to be the source region of the slow solar wind at least during solar minimum. The background solar wind parameters and the flow tube geometry are taken from a recent two-dimensional magnetohydrodynamic solar wind model. We show that in this slow-wind source region the O+5 outflow speed varies nonmonotonically with increasing heliocentric distance. There is a local minimum of the outflow speed near the streamer cusp point (about 3 Rsolar), which is below the current observational sensitivity. This type of ion outflow in the slow solar wind is termed ``stagnated outflow'' in this paper. We also show that the observed effective temperature in the perpendicular direction (to the magnetic field) and the outflow speed of the O+5 ions can be used to put limits on their parallel thermal temperature.

Chen, Y.; Esser, R.; Strachan, L.; Hu, Y.

2004-02-01

100

Empirically Determined Anisotropic Velocity Distributions and Outflows of O5+ Ions in a Coronal Streamer at Solar Minimum  

NASA Astrophysics Data System (ADS)

Empirical constraints on the O5+ velocity distributions and outflow speeds in a solar minimum equatorial streamer between 2.6 and 5.1 Rsolar are determined using a spectral synthesis code that includes O VI Doppler dimming. These constraints follow directly from UV spectra taken on 1996 October 12 with the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) satellite and three-dimensional electron densities derived from tomography applied to a time series of polarized white-light images taken with the Large Angle and Spectrometric Coronagraph (LASCO) also on SOHO. Four conclusions result from this work: (1) our analysis shows O5+ velocity distribution anisotropy in the streamer legs and stalk and gives strong evidence that the microscopic velocity distribution (which excludes wave motions that equally affect all charged particles) is anisotropic, where the most probable speed perpendicular to the magnetic field direction exceeds that in the parallel direction; (2) there is preferential heating of the O5+ ions over the protons in the streamer stalk and legs; (3) there is no evidence for preferential O5+ heating in the core; and (4) the outflow velocity of the O5+ ions is determined at heights above 4.6 Rsolar. All results have a confidence level of at least 70%.

Frazin, R. A.; Cranmer, S. R.; Kohl, J. L.

2003-11-01

101

The zonal EB plasma drift effects on the low latitude ionosphere electron density at solar minimum near equinox  

NASA Astrophysics Data System (ADS)

The F2-layer peak density, NmF2, and peak altitude, hmF2, which were observed by 12 ionospheric sounders during the 20 September 1964 geomagnetically quiet time period at solar minimum are compared with those calculated by the three-dimensional time-dependent theoretical model of the Earth's low and middle latitude ionosphere and plasmasphere. The modeled NmF2 are also compared with those measured during the geomagnetically quiet time periods of 12-15, 18-21, and 26 September 1964 to take into account observed day-to-day ionospheric variability. Major features of the data are reproduced by the model if the corrected HWM90 neutral wind is used. The changes in NmF2 due to the zonal EB plasma drift are found to be less than 20% in the daytime low latitude ionosphere. The model, which does not take into account the zonal EB plasma drift, underestimates night-time NmF2 up to the maximum factor of 2 at low geomagnetic latitudes. The night-time increase of NmF2 caused by the zonal EB plasma drift is less pronounced at -20 and 20 geomagnetic latitudes in comparison with that between -10 and 10 geomagnetic latitude. The longitude dependence of the calculated night-time low latitude influence of the zonal EB plasma drift on NmF2 is explained in terms of the longitudinal asymmetry in B (the eccentric magnetic dipole is displaced from the Earth's center and the Earth's eccentric tilted magnetic dipole moment is inclined with respect to the Earth's rotational axis), and the variations of the wind induced plasma drift and the meridional EB plasma drift in geomagnetic longitude. The difference between the hmF2 values calculated by including the effect of zonal EB drift and that obtained when it is excluded does not exceed 19 km in the low latitude ionosphere. Over the geomagnetic equator the zonal EB plasma drift produces the maximum increase in the electron density by a factor of 1.06-1.48 and 1.05-1.30 at 700 and 1000 km altitude, respectively, and this increase is not significant above about 1500 km. Changes in the vertical electron content, VEC, caused by the zonal EB plasma do not exceed 16% during the day, while the value of the night-time VEC is increased up to a factor of 1.4 due to this drift. The maximum effects of the zonal EB plasma drift on the night-time electron density derived from the model results corresponding to solar minimum and maximum are quite comparable.

Pavlov, A. V.; Pavlova, N. M.

2008-08-01

102

Solar wind control of ionization enhancements in D Region during solar minimum as seen by the EISCAT Svalbard Radar  

NASA Astrophysics Data System (ADS)

EISCAT Svalbard Radar was operated in a continuous mode during the International Polar Year (IPY), with experiment start on 1 March 2007 and end on 29 February 2008. This period occured during the prolonged solar minimum time and was on the average geophysically very quiet. The incoherent scatter radar experiment was designed to cover the entire altitude range of the ionosphere, from D and lower E regions to the ionospheric F peak, reaching into the topside ionosphere. The low altitude IPY electron density data from backscattered power measurements, with 3 km range resolution and 2.25 km steps, start from the altitude of 45 km. The lowest altitude data is subject to variable sea and/or tropospheric clutter, but normally data is usable for altitudes higher than 70 km. This unique set of electron density data from a high-latitude station reveals repeated occurence of short lasting low-altitude ionisation enhancements and thus high-energy electron precipitation events, in spite of the generally geomagnetically quiet conditions. We compare the occurence of the high energy precipitation to sudden variations in the solar wind parameters, and specially with occurence of high-speed solar wind. By selecting a threshold for the occurence of the high-speed streams we make a superimposed epoch analysis of simultaneus electron density measured by the radar. This analysis suggests that the low altitude ionization enhancements are directly driven by the high-speed streams. Comparison between riometer data from Svalbard and mainland stations shows that precipitation is generally very localized and restricted to higher latitudes.

Turunen, E.; Kavanagh, A.; Hggstrm, I.

2012-04-01

103

Relationship between vertical ExB drift and F2-layer characteristics in the equatorial ionosphere at solar minimum conditions  

NASA Astrophysics Data System (ADS)

Equatorial and low-latitude electrodynamics plays a dominant role in determining the structure and dynamics of the equatorial and low-latitude ionospheric F-region. Thus, they constitute essential input parameters for quantitative global and regional modeling studies. In this work, hourly median value of ionosonde measurements namely, peak height F2-layer (hmF2), F2-layer critical frequency (foF2) and propagation factor M(3000)F2 made at near equatorial dip latitude, Ouagadougou, Burkina Faso (12oN, 1.5oW; dip: 1.5oN) and relevant F2-layer parameters such as thickness parameter (Bo), electron temperature (Te), ion temperature (Ti), total electron content (TEC) and electron density (Ne, at the fixed altitude of 300 km) provided by the International Reference Ionosphere (IRI) model for the longitude of Ouagadougou are contrasted with the IRI vertical drift model to explore in detail the monthly climatological behavior of equatorial ionosphere and the effects of equatorial vertical plasma drift velocities on the diurnal structure of F2-layer parameters. The analysis period covers four months representative of solstitial and equinoctial seasonal periods during solar minimum year of 1987 for geomagnetically quiet-day. We show that month-by-month morphological patterns between vertical EB drifts and F2-layer parameters range from worst to reasonably good and are largely seasonally dependent. A cross-correlation analysis conducted between equatorial drift and F2-layer characteristics yield statistically significant correlations for equatorial vertical drift and IRI-Bo, IRI-Te and IRI-TEC, whereas little or no acceptable correlation is obtained with observational evidence. Assessment of the association between measured foF2, hmF2 and M(3000)F2 illustrates consistent much more smaller correlation coefficients with no systematic linkage. In general, our research indicates strong departure from simple electrodynamically controlled behavior.

Oyekola, Oyedemi S.

2012-07-01

104

High-speed stream impacts on the equatorial ionization anomaly region during the deep solar minimum year 2008  

NASA Astrophysics Data System (ADS)

To demonstrate high-speed stream effects during the recent deep solar minimum year 2008, we have analyzed manually scaled foF2 and hmF2 at Jicamarca and total electron content (TEC) in the equatorial ionization anomaly (EIA) region over the America longitudinal sector. Our results reveal that a prominent 9 day oscillation appears in the hmF2 and foF2 at the dip equator. The 9 day oscillation amplitudes of foF2 are not always positively correlated with TEC in the equatorial ionosphere, and they show nonlinear dependence on the intensity of geomagnetic disturbances. With the outputs of Fejer and Scherliess's (1997) empirical model, we found that this periodicity is also present in equatorial vertical drifts caused by disturbance dynamoelectric field (DDEF) but absent in the drifts due to prompt penetration electric field (PPEF). DDEF effects on the equatorial periodic variations alone are not sufficient to explain the observed phenomena; other mechanisms, such as thermal expansion/contraction and neutral composition changes, are also the plausible causes of the periodic oscillation in the equatorial ionosphere. Further, the complicated patterns appear in the 9 day band-pass-filtered TEC perturbations in the EIA region, and they are quite different from the patterns of global coherent thermospheric oscillations triggered by high-speed streams. We also found that the latitudinal variations of band-passed-filtered TEC present different behaviors involving tilt latitudinal configuration, antiphased correlation between the crests and trough, and south-north asymmetry, which vary as a function of season, local time, or even from event to event.

Liu, Jing; Liu, Libo; Zhao, Biqiang; Wei, Yong; Hu, Lianhuan; Xiong, B.

2012-10-01

105

Corona Characteristics of Simulated Rain  

Microsoft Academic Search

Influence of rain upon electromagnetic characteristics of corona was studied in an experimental setup consisting of a single corona point located in cylindrical geometry. Distilled water flowing to the corona point through a plastic tube simulated the rain. Wave shape of current pulses, their repetition rate and the frequency spectrum were observed for the ac as well as dc excitations

W. Janischewskyj; A. Arainy

1981-01-01

106

Coronae of Parga Chasma, Venus  

Microsoft Academic Search

Parga Chasma is a 10,000 km long fracture and trough system in the southern hemisphere of Venus. In this study, we analyze coronae in the Parga region, addressing the relationship between corona and rift formation, the relationship of volcanism to rifting and coronae, and the overall evolution of the rift system. Our observations are compared with various models, with the

P. Martin; E. R. Stofan; L. S. Glaze; S. Smrekar

2007-01-01

107

The EUV Unresolved Corona  

NASA Astrophysics Data System (ADS)

The unresolved corona for three active regions (ARs) above the solar limb is investigated. Intensities measured for ions formed above 1 MK are presented as a function of height above the solar surface. The observed decrease in intensity with altitude is found to be best fit by an exponential. Furthermore, this exponential decrease is approximately the decrease in emission expected for a hydrostatic planar geometry atmosphere, where the scale height temperature is dependent on the dynamics of the AR. For two of the ARs analyzed, we have found that the best-fit temperature derived from the exponential fits is consistent with an isothermal hydrostatic unresolved corona.

Cirtain, Jonathan; Martens, P. C. H.; Acton, L. W.; Weber, Mark

2006-05-01

108

Evolution of equatorial ionospheric plasma bubbles and formation of broad plasma depletions measured by the C\\/NOFS satellite during deep solar minimum  

Microsoft Academic Search

An unexpected feature revealed by the measurements of the Communication\\/Navigation Outage Forecasting System (C\\/NOFS) satellite is the presence of broad plasma depletions in the midnightdawn sector during deep solar minimum. It has not been well understood what causes the broad plasma depletions and how equatorial plasma bubbles are related to the broad depletions. In this paper we present the C\\/NOFS

Chao-Song Huang; O. de La Beaujardiere; P. A. Roddy; D. E. Hunton; R. F. Pfaff; C. E. Valladares; J. O. Ballenthin

2011-01-01

109

Evolution of equatorial ionospheric plasma bubbles and formation of broad plasma depletions measured by the C\\/NOFS satellite during deep solar minimum  

Microsoft Academic Search

An unexpected feature revealed by the measurements of the Communication\\/Navigation Outage Forecasting System (C\\/NOFS) satellite is the presence of broad plasma depletions in the midnight-dawn sector during deep solar minimum. It has not been well understood what causes the broad plasma depletions and how equatorial plasma bubbles are related to the broad depletions. In this paper we present the C\\/NOFS

Chao-Song Huang; O. de La Beaujardiere; P. A. Roddy; D. E. Hunton; R. F. Pfaff; C. E. Valladares; J. O. Ballenthin

2011-01-01

110

CORONA STABILIZER TUBE  

Microsoft Academic Search

garian) Various types of corona stabilizing tubes were prepared in the ; Nuclear Research Institute on the basis of previously published data resulting in ; a broad experience in the fields of application of the tube. Of the types used ; the 1-cm diameter cathode and 1-mm dismeter anode tubes were found to be the most ; satisfactory ones. The

Csongor

1961-01-01

111

Climatology of GPS phase scintillation and HF radar backscatter for the high-latitude ionosphere under solar minimum conditions  

NASA Astrophysics Data System (ADS)

Maps of GPS phase scintillation at high latitudes have been constructed after the first two years of operation of the Canadian High Arctic Ionospheric Network (CHAIN) during the 2008-2009 solar minimum. CHAIN consists of ten dual-frequency receivers, configured to measure amplitude and phase scintillation from L1 GPS signals and ionospheric total electron content (TEC) from L1 and L2 GPS signals. Those ionospheric data have been mapped as a function of magnetic local time and geomagnetic latitude assuming ionospheric pierce points (IPPs) at 350 km. The mean TEC depletions are identified with the statistical high-latitude and mid-latitude troughs. Phase scintillation occurs predominantly in the nightside auroral oval and the ionospheric footprint of the cusp. The strongest phase scintillation is associated with auroral arc brightening and substorms or with perturbed cusp ionosphere. Auroral phase scintillation tends to be intermittent, localized and of short duration, while the dayside scintillation observed for individual satellites can stay continuously above a given threshold for several minutes and such scintillation patches persist over a large area of the cusp/cleft region sampled by different satellites for several hours. The seasonal variation of the phase scintillation occurrence also differs between the nightside auroral oval and the cusp. The auroral phase scintillation shows an expected semiannual oscillation with equinoctial maxima known to be associated with aurorae, while the cusp scintillation is dominated by an annual cycle maximizing in autumn-winter. These differences point to different irregularity production mechanisms: energetic electron precipitation into dynamic auroral arcs versus cusp ionospheric convection dynamics. Observations suggest anisotropy of scintillation-causing irregularities with stronger L-shell alignment of irregularities in the cusp while a significant component of field-aligned irregularities is found in the nightside auroral oval. Scintillation-causing irregularities can coexist with small-scale field-aligned irregularities resulting in HF radar backscatter. The statistical cusp and auroral oval are characterized by the occurrence of HF radar ionospheric backscatter and mean ground magnetic perturbations due to ionospheric currents.

Prikryl, P.; Jayachandran, P. T.; Mushini, S. C.; Chadwick, R.

2011-02-01

112

Global S4 index variations observed using FORMOSAT-3/COSMIC GPS RO technique during a solar minimum year  

NASA Astrophysics Data System (ADS)

In this paper, presented for the first time the three-dimensional global morphology and seasonal variations of scintillation index (S4 index) measured from the signal-to-noise ratio (SNR) intensity fluctuations of L1 channel of GPS radio occultation (RO) signals using FORMOSAT-3/COSMIC (in short, F3/C) satellites for a low solar activity year 2008. The S4 index, which confined around 30 magnetic latitudes, is found to start around post-sunset hours (1900 MLT, magnetic local time) and often persists till post-midnight hours (0300 MLT) between 150 and 350 km altitudes during equinox and northern winter seasons while no activity is observed during southern winter season. However, high latitudes are characterized with no scintillation activity beyond 150 km during any season, which implying that in the solar minimum period the drives of instabilities in the auroral, cusp and polar cap regions, namely the gradient drift and velocity shear, are absent. The S4 index at F region altitudes during magnetically quiet times is more intense and extends to higher latitudes than that observed during disturbed time consistent with earlier studies. The equatorial S4 index appears below the peak of F2 layer (hmF2) during most of the seasons although the associated intensities and the time of maximum occurrences are relatively higher and earlier during vernal equinox followed by autumn equinox. This equinoctial asymmetry could be primarily attributed to the asymmetries in eastward drift velocities, thermospheric meridional winds and plasma densities. Further, the global maps of S4 index at E region altitudes (between 75 and 125 km) show strong seasonal variations with highest activity during northern and southern summer solstice in the middle latitudes while it appears on both sides of magnetic equator with less or no activity at and around the equator during equinox seasons. The absence of S4 index along the equator can be understood in terms of the vanishing vertical component of the magnetic field lines that can inhibit the vertical movement and layered deposition of ionized particles of thin irregular electron density layers such as Es-layers. Keeping in view the importance of these valuable database, we would like to emphasize that the F3/C GPS RO technique can be used to study the ionospheric irregularities at GHz frequency globally directly from the high-rate L1 data, which reiterating its importance as a powerful tool to explore the terrestrial ionosphere on a global scale.

Brahmanandam, P. S.; Uma, G.; Liu, J. Y.; Chu, Y. H.; Latha Devi, N. S. M. P.; Kakinami, Y.

2012-09-01

113

Biophysical chemistry: Unravelling capsid transformations  

NASA Astrophysics Data System (ADS)

The interactions between a virus capsid and its cargo are essential for viral infection as well as in the design of synthetic virus-like particles. Now a combination of analytical techniques has unravelled key steps in the transformation of a model virus and the release of its RNA cargo.

Uchida, Masaki; Douglas, Trevor

2013-06-01

114

A METHOD FOR SEPARATING CORONAL MASS EJECTIONS FROM THE QUIESCENT CORONA  

SciTech Connect

A method for separating coronal mass ejections (CMEs) from the quiescent corona in white-light coronagraph images is presented. Such a separation allows the study of CME structure, as well as enabling a study of the quiescent coronal structure, without contamination by the CME. The fact that the large-scale quiescent corona is very close to radial, whilst CMEs are highly non-radial, enables the separation of the two components. The method is applied to Large Angle Spectrometric Coronagraph/Solar and Heliospheric Observatory C2 and C3 observations, and is successful in revealing CME signal, faint CMEs and blobs, and dark rarefactions within a CME. The success of the separation is tested at solar minimum, a time when streamers are in general most non-radial. The technique is also compared to other commonly used methods. The separation method enables (1) the study of extremely faint CME structure, down to almost the noise level of the coronagraphs, (2) paves the way for automated categorization of CME internal structure, and (3) provides a cleaner basis for tomography of the quiescent corona, without contamination from CMEs.

Morgan, Huw; Habbal, Shadia, E-mail: hmorgan@ifa.hawaii.ed [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

2010-03-10

115

Magnetic Clouds at/near the 2007 - 2009 Solar Minimum: Frequency of Occurrence and Some Unusual Properties  

NASA Astrophysics Data System (ADS)

Magnetic clouds (MCs) have been identified for the period 2007 - 2009 (at/near the recent solar minimum) from Wind data, then confirmed through MC parameter fitting using a force-free model. A dramatic increase in the frequency of occurrence of these events took place from the two early years of 2007 (with five MCs) and 2008 (one MC) compared to 2009 (12 MCs). This pattern approximately mirrors the occurrence-frequency profile that was observed over a three-year interval 12 years earlier, with eight events in 1995, four in 1996, and 17 in 1997, but decreased overall by a factor of 0.62 in number. However, the average estimated axial field strength [<| B O|>] taken over all of the 18 events of 2007 - 2009 (called the recent period here) was only 11.0 nT, whereas <| B O|> for the 29 events of 1995 - 1997 (called the earlier period) was 16.5 nT. This 33% average drop in <| B O|> is more or less consistent with the decreased three-year average interplanetary magnetic field intensity between these two periods, which shows a 23% drop. In the earlier period, the MCs were clearly of mixed types but predominantly of the South-to-North type, whereas those in the recent period are almost exclusively the North-to-South type; this change is consistent with global solar field changes predicted by Bothmer and Rust ( Geophys. Monogr. Ser. 99, 139, 1997). As we have argued in earlier work (Lepping and Wu, J. Geophys. Res. 112, A10103, 2007), this change should make it possible to carry out (accurate short-term) magnetic storm forecasting by predicting the latter part of an MC from the earlier part, using a good MC parameter-fitting model with real-time data from a spacecraft at L1, for example. The recent sets average duration is 15.2 hours, which is a 27% decrease compared to that of the earlier set, which had an average duration of 20.9 hours. In fact, all physical aspects of the recent MC set are shown to drop with respect to the earlier set; e.g., as well as the average internal magnetic field drop, the recent set had a somewhat low average speed of 379 km s-1 (5% drop), and the average diameter had a 24% drop. Hence, compared to the earlier set, the recent set consists of events that are smaller, slightly slower, and weaker in every respect (and fewer in number), but in a relative sense the two three-year sets have similar frequency-of-occurrence profiles. It is also interesting that the two sets have almost the same average axial inclinations, i.e., axial latitude ?31 (in GSE). These MC characteristics are compared to relevant solar features and their changes. A preliminary assessment of the statistics on possible shocks and pressure pulses upstream of these recent MCs yields the following: About 28% of the MCs, at most, had shocks, and 33% had shocks and/or pressure pulses. These are low values, since typically the percentage of cases with shocks is about 50%, and the percentage with shocks and/or pressure pulses is usually about 75%.

Lepping, R. P.; Wu, C.-C.; Berdichevsky, D. B.; Szabo, A.

2011-12-01

116

Corona chemistry in Titan.  

PubMed

The atmosphere of Titan is constantly bombarded by galactic cosmic rays and Saturnian magnetospheric electrons causing the formation of free electrons and primary ions, which are then stabilized by ion cluster formation and charging of aerosols. These charged particles accumulate in drops in cloud regions of the troposphere. Their abundance can substantially increase by friction, fragmentation or collisions during convective activity. Charge separation occurs with help of convection and gravitational settling leading to development of electric fields within the cloud and between the cloud and the ground. Neutralization of these charged particles leads to corona discharges which are characterized by low current densities. We have therefore, experimentally studied the corona discharge of a simulated Titan's atmosphere (10% methane and 2% argon in nitrogen) at 500 Torr and 298 K by GC-FTIR-MS techniques. The main products have been identified as hydrocarbons (ethane, ethyne, ethene, propane, propene+propyne, cyclopropane, butane, 2-methylpropane, 2-methylpropene, n-butane, 2-butene, 2,2-dimethylpropane, 2-methylbutane, 2-methylbutene, n-pentane, 2,2-dimethylbutane, 2-methylpentane, 3-methylpentane, n-hexane, 2,2-dimethylhexane, 2,2-dimethylpentane, 2,2,3-trimethylbutane, 2,3-dimethylpentane and n-heptane), nitriles (hydrogen cyanide, cyanogen, ethanenitrile, propanenitrile, 2-methylpropanenitrile and butanenitrile) and a highly branched hydrocarbon deposit. We present the trends of hydrocarbons and nitriles formation as a function of discharge time in an ample interval and have derived their initial yields of formation. The results clearly demonstrate that a complex organic chemistry can be initiated by corona processes in the lower atmosphere. Although photochemistry and charged particle chemistry occurring in the stratosphere can account for many of the observed hydrocarbon species in Titan, the predicted abundance of ethene is too low by a factor of 10 to 40. While some ethene will be produced by charged-particle chemistry, the production of ethene by corona processes and its subsequent diffusion into the stratosphere appears to be an adequate source. Because little UV penetrates to the lower atmosphere to destroy the molecules formed there, the corona-produced species may be long-lived and contribute significantly to the composition of the lower atmosphere and surface. PMID:11541887

Navarro-Gonzalez, R; Ramirez, S I; Matrajt, G; Basiuk, V; Basiuk, E

1998-06-01

117

Influence of meteorological and wave processes on the lower ionosphere during solar minimum conditions according to the data on midlatitude VLF-LF propagation  

NASA Astrophysics Data System (ADS)

The statistical characteristics of the intensity of VLF-LF radio signals transmitted from the midlatitude radio stations and recorded by the receiver at the Mikhnevo geophysical observatory (54.94N, 37.73E; Institute of Geosphere Dynamics, Russian Academy of Sciences) in 2007-2010 are analyzed. The experiments revealed strong variations in the intensity of radio signals during the deep solar minimum conditions, when the medium does not experience impacts from above associated with solar and geomagnetic activity. We relate the observed variations to the disturbances from below, which are caused by the meteorological and wave processes occurring in the lower atmosphere.

Egoshin, A. A.; Ermak, V. M.; Zetzer, Yu. I.; Kozlov, S. I.; Kudryavtsev, V. P.; Lyakhov, A. N.; Poklad, Yu. V.; Yakimenko, E. N.

2012-03-01

118

Evolucin de la Estructura Trmica Global de la Corona alrededor del ltimo Mnimo de Actividad Solar  

NASA Astrophysics Data System (ADS)

We study the solar corona temperature structure during several Carrington rotations (CR) around the last minimum of solar activity (CR 2077). The combination of Differential Emission Measure Tomography (DEMT) with magnetic models allows determination of the electron density and electron temperature along individual magnetic field lines. Two types of quiet Sun (QS) coronal loops were identified: "up" loops in which the temperature increases with height, and "down" loops in which the temperature decreases with height. We find that the population of up loops dominates the intermediate latitudes, while down loops are always located in the low-latitude region. We also find that the population of down loops was maximum at solar minimum. FULL TEXT IN SPANISH

Nuevo, F. A.; Vsquez, A. M.; Huang, Z.; Frazin, R. A.

119

PULSE ENERGIZATION IN THE TUFT CORONA REGIME OF NEGATIVE CORONA  

EPA Science Inventory

The paper discusses pulse energization in the tuft corona regime of negative corona. Fabric filtration, with integral particle charging and collection in a combined electric and flow field, is sensitive to maldistribution of current among bags energized by one power source, espec...

120

Towards Unraveling Multiscale Solar, Terrestrial, and Heliospheric Drivers of Global Change  

NASA Astrophysics Data System (ADS)

The Sun is emerging from a deep protracted solar minimum when Galactic Cosmic Rays (GCRs) achieved the highest levels observed in the space age, and the power, pressure, flux and magnetic flux of the solar wind were at their lowest levels. Even observations of the global heliosphere show remarkably rapid changes caused by dropping solar wind pressure. Does the recent anomalous deep solar minimum hint at larger changes in store and how anomalous was it both in terms of occurrence and severity? As these solar drivers, heliospheric conditions, and GCR fluxes change, we are forced to ask fundamental questions about their effects on our atmosphere, and even their implications for life on the planet. The Earth System is remarkably complex, driven both by internal variability and by these multiscale external drivers. The interplay between internal and external processes is further complicated in that elements of the same underlying variation may have multiple manifestations. Furthermore, these various manifestations affect the system in different ways and with magnitudes that are not typically well quantified. Consequently, unraveling the pathways of global change remain elusive, yet are also incredibly important to society. In this presentation, we outline early efforts of a group of broadly interdisciplinary scientists who are collectively exploring aspects of this grand challenge. We review potential agents of global change, including but not limited to: solar variability, ranging on time scales from billions of years down to fractions of a day; external variations of GCR imposed both by the heliosphere's passage through the local interstellar medium and by solar variability; and also internal processes such as geomagnetic field reversals. We review the evidence for such past changes by appealing to a variety of approaches and techniques, including: historic sunspot records; astronomical observations and models of Milky Way structures; chemical and isotopic tracers preserved in ice and ocean sediment cores; and even possible global change indicators in biodiversity records. Our goal is to identify such potential drivers as a first step towards establishing their relative importance.

Spence, H. E.; Schwadron, N. A.

2011-12-01

121

Observations of DC electric fields in the low-latitude ionosphere and their variations with local time, longitude, and plasma density during extreme solar minimum  

NASA Astrophysics Data System (ADS)

DC electric fields and associated E B plasma drifts detected with the double-probe experiment on the C/NOFS satellite during extreme solar minimum conditions near the June 2008 solstice are shown to be highly variable, with weak to moderate ambient amplitudes of 1-2 mV/m (25-50 m/s). Average field or drift patterns show similarities to those reported for more active solar conditions, i.e., eastward and outward during day and westward and inward at night. However, these patterns vary significantly with longitude and are not always present. Daytime vertical drifts near the magnetic equator are largest in the prenoon sector. Observations of weak to nonexistent prereversal enhancements in the vertical drifts near sunset are attributable to reduced dynamo activity during solar minimum as well as seasonal effects. Enhanced meridional drifts are observed near sunrise in certain longitude regions, precisely where the enhanced eastward flow that persisted from earlier local times terminates. The nightside ionosphere is characterized by larger-amplitude, structured electric fields dominated by horizontal scales of 500-1500 km even where local plasma densities appear relatively undisturbed. Data acquired during successive orbits indicate that plasma drifts and densities are persistently organized by longitude. The high duty cycle of the C/NOFS observations and its unique orbit promise to expose new physics of the low-latitude ionosphere.

Pfaff, R.; Rowland, D.; Freudenreich, H.; Bromund, K.; Le, G.; AcuA, M.; Klenzing, J.; Liebrecht, C.; Martin, S.; Burke, W. J.; Maynard, N. C.; Hunton, D. E.; Roddy, P. A.; Ballenthin, J. O.; Wilson, G. R.

2010-12-01

122

Instabilities in the solar corona  

Microsoft Academic Search

It is shown that both observations and theoretical evidence exists for the presence of high levels of low-frequency plasma turbulence in the solar corona. A rough survey of relevant plasma instabilities is given with emphasis on their applicability to circumstances in the solar corona. It is found that mainly low-frequency waves with frequency up to the electron cyclotron frequency can

J. Rosenberg

1973-01-01

123

Heating of the Solar Corona  

Microsoft Academic Search

This article reviews recent results about physical mechanisms that contribute to heat the solar corona as well as their impact on the energetic balance of the coronal plasma. A general description of the solar corona is given, mainly based on X-ray images and complemented with data from other spectral ranges. The presence of a magnetic field is found to be

D. O. Gomez

1990-01-01

124

Solar Corona Seismology  

NASA Astrophysics Data System (ADS)

The presence of oscillations in solar coronal structures has been known for more than seventy years. Observational reports about the presence of oscillatory motions in solar filaments go back to 1930 while in the case of other coronal structures (loops, plumes, etc) direct evidence has been recently obtained thanks to the detailed observations made by SoHO and TRACE. Due to these satellites, as well as to ground-based observations, evidence of magnetohydrodynamic (MHD) waves in the solar corona has risen dramatically. MHD coronal seismology provides with an indirect path to determine the physical conditions and parameters of the solar corona [coronal magnetic field, transport coefficients (viscosity, resistivity, thermal conductivity, etc.), heating function, filling factors] which are difficult to measure accurately. In essence, it is similar to the acoustic diagnostic of the solar interior (Helioseismology) and to MHD spectroscopy used to determine physical helioseismology parameters of laboratory plasmas. In spite that there are many solar coronal structures in which oscillations have been detected (prominences, loops, plumes, coronal holes, etc.), in the following we will concentrate in prominences and coronal loops trying to summarize part of our current knowledge about their oscillations as well as about the theoretical models developed to explain those oscillations in terms of MHD waves.

Ballester, J. L.

2006-12-01

125

Post-midnight low-latitude ionospheric irregularities during solar minimum observed simultaneously with probes on the C/NOFS satellite and the Equatorial Atmosphere Radar  

NASA Astrophysics Data System (ADS)

Since the launch of Communication/Navigation Outage Forecasting System (C/NOFS) satellite, post-midnight plasma density irregularities have frequently been detected in the low-latitude region during the present solar minimum period. Using the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36oS dip latitude), it is shown that the post-midnight irregularities observed with the EAR are different from standard irregularities typically observed near the magnetic equator but instead, are quite similar to those observed with the MU radar in midlatitude (29.3oN dip latitude). Utilizing rapid beam-steering capability of the EAR, it is found that their tilted spatial structures are the same as medium-scale traveling ionospheric disturbances (MSTIDs) which are frequently observed in midlatitude, and they usually propagate westward as opposed to typical plasma depletions that propagate eastward observed in the post-sunset period, for example during solar maximum. The zonal and meridional E B drift velocities measured by C/NOFS are consistent with the westward propagation of backscatter echoes and the line-of-sight Doppler velocities observed with the EAR, respectively. The density structures and EAR echo intensity do not show a clear correlation, but some echoes are observed at the edge of density depletions, which may be a manifestation of a secondary E B instability to produce 3-m scale irregularities. During solar minimum, the nighttime zonal drift could be reversed from eastward to westward with increasing altitude because of very low Pedersen conductivity in the F region, which could explain the high occurrence of midlatitude-type irregularities in the low-latitude region which is connected with the topside equatorial ionosphere.

Yokoyama, T.; Pfaff, R. F.; Roddy, P. A.; Yamamoto, M.; Otsuka, Y.

2010-12-01

126

Radiation Measured with Different Dosimeters for ISS-Expedition 18-19/ULF2 on Board International Space Station during Solar Minimum  

NASA Astrophysics Data System (ADS)

Radiation field of particles in low Earth orbit (LEO) is mainly composed of galactic cosmic rays (GCR), solar energetic particles and particles in SAA (South Atlantic Anomaly). GCR are modulated by solar activity, at the period of solar minimum activity, GCR intensity is at maximum and the main contributor for space radiation is GCR. At present for space radiation measurements conducted by JSC (Johnson Space Center) -SRAG (Space Radiation Analysis Group), the preferred active dosimeter sensitive to all LET (Linear Energy Transfer) is the tissue equivalent proportional counter (TEPC); the preferred passive dosimeters are thermoluminescence dosimeters (TLDs) and optically stimulated luminescence dosimeters (OSLDs) sensitive to low LET as well as CR-39 plastic nuclear track detectors (PNTDs) sensitive to high LET. For the method using passive dosimeters, radiation quantities for all LET can be obtained by combining radiation results measured with TLDs/OSLDs and CR-39 PNTDs. TEPC, TLDs/OSLDs and CR-39 detectors were used to measure the radiation field for the ISS (International Space Station) -Expedition 18-19/ULF2 space mission which was conducted from 15 November 2008 to 31 July 2009 -near the period of the recent solar minimum activity. LET spectra (differential and integral fluence, absorbed dose and dose equivalent) and radiation quantities were measured for positions TEPC, TESS (Temporary Sleeping Station, inside the polyethylene lined sleep station), SM-P 327 and 442 (Service Module -Panel 327 and 442). This paper presents radiation LET spectra measured with TEPC and CR-39 PNTDs and radiation dose measured with TLDs/OSLDs as well as the radiation quantities combined from results measured with passive dosimeters.

Zhou, Dazhuang

127

The effects of Corotating interaction region/High speed stream storms on the thermosphere and ionosphere during the last solar minimum  

NASA Astrophysics Data System (ADS)

Geomagnetic storms at solar minimum are driven by the interaction between high speed streams and low speed streams (Corotating Interactions regions/High Speed StreamsCIR/HSSs- this includes both the CIR part of the storm and the HSS part as both has effects on the thermosphere and ionosphere), rather than by Coronal Mass Ejections (CMEs). Solar minimum storms are generally of smaller amplitude, but they also have other characteristics that affect the response of the thermosphere/ionosphere (TI) system to them. We explore both the background upper atmosphere and the characteristics of these CIR/HSS events in 2008 using both models and data. The model data comparisons were good, showing mid-latitude positive storm effects on NmF2 on the day of the storm and long, extended periods of storm induced changes on the following days. Generally, the version of the NCAR-TIEGCM (National Center for Atmospheric Research-Thermosphere Ionosphere Electrodynamics Model) run with the Heelis convection pattern was in better agreement with the data than the version run with the Weimer convection pattern. We attribute this difference in the response of the two versions of the NCAR-TIEGCM to the fact that the precipitation we associate with the Heelis model has been tuned to better represent observed precipitation over many years, whereas such tuning has just begun for the version of the NCAR-TIEGCM that uses the Weimer model. Physically, the most important conclusion that we draw is the CIR/HSS events can have significant effects on the ionosphere and thermosphere for several days after the CIR has ended. While CIR/HSS events are normally weaker than CME events, the effects of the latter normally disappear in a day or two. Thus the effects of CIR/HSS events may be comparable to those of CME events for some fields, notably neutral density changes.

Burns, A. G.; Solomon, S. C.; Qian, L.; Wang, W.; Emery, B. A.; Wiltberger, M.; Weimer, D. R.

2012-07-01

128

Corona Discharge Influence on Moulds  

NASA Astrophysics Data System (ADS)

It is known that the electric discharge has bacteriocid effect. We are interesting on influence of corona discharge on moulds and searching for it's fungicide effect. In this work we study the mould penicillium digitatum by using an easy apparatus, where may be situated two measured samples. One in the burning corona discharge and one in the area with ozone generated by this corona only. We expose the spores of penicillium digitatum on a metal plate and on a cultivating medium on cca 0.01mA, 5kV corona discharge and on generated ozone only for time cca two days. It is the time needed for sprouting of spores and growing of they to a visible size. The pilot results show, that the ozone generated by the corona discharge has none or very low influence on the sprouting and growing of the spores. Direct corona discharge inhibit the sprouting only, but does not kill the spores. In next experiments we will try to find some minimum inhibit and killing concentration of ozone and try to expose the sprout inhibition.

Scholtz, Vladimir

2004-09-01

129

MESSENGER Observations of Magnetohydrodynamic Waves in the Solar Corona from Faraday Rotation  

NASA Astrophysics Data System (ADS)

During the declining phase of the longest solar minimum in a century, the arrival of the MESSENGER spacecraft at superior conjunction allowed the measurement of magnetohydrodynamic (MHD) waves in the solar corona with its 8 GHz radio frequency signal. MHD waves crossing the line of sight were measured via Faraday rotation fluctuations (FRFs) in the plane of polarization (PP) of MESSENGER's signal. FRFs in previous observations of the solar corona (at greater offset distances) consisted of a turbulent spectrum that decreased in power with increasing frequency and distance from the Sun. Occasionally a spectral line, a distinct peak in the power spectral density spectrum around 4 to 8 mHz, was also observed in these early data sets at offset distances of about 5 to 10 solar radii. The MESSENGER FRF data set shows a spectral line at an offset distance between 1.55 to 1.85 solar radii with a frequency of 0.60.2 mHz. Other possible spectral lines may be at 1.2, 1.7, and 4.5 mHz; MHD waves with these same frequencies have been observed in X-ray data traveling along closed coronal loops at lower offset distances. An initial analysis of the MESSENGER spectral line(s) shows behavior similar to turbulent spectra: decreasing power with increasing frequency and distance from the Sun. Here we detail the steps taken to process the MESSENGER change in PP data set for the MHD wave investigation.

Jensen, E. A.; Nolan, M.; Bisi, M. M.; Chashei, I.; Vilas, F.

2013-07-01

130

STRUCTURE AND DYNAMICS OF THE 2010 JULY 11 ECLIPSE WHITE-LIGHT CORONA  

SciTech Connect

The white-light corona (WLC) during the total solar eclipse on 2010 July 11 was observed by several teams in the Moon's shadow stretching across the Pacific Ocean and a number of isolated islands. We present a comparison of the WLC as observed by eclipse teams located on the Tatakoto Atoll in French Polynesia and on Easter Island, 83 minutes later, combined with near-simultaneous space observations. The eclipse was observed at the beginning of the solar cycle, not long after solar minimum. Nevertheless, the solar corona shows a plethora of different features (coronal holes, helmet streamers, polar rays, very faint loops and radial-oriented thin streamers, a coronal mass ejection, and a puzzling 'curtain-like' object above the north pole). Comparing the observations from the two sites enables us to detect some dynamic phenomena. The eclipse observations are further compared with a hairy-ball model of the magnetic field and near-simultaneous images from the Atmospheric Imaging Assembly on NASA's Solar Dynamics Observatory, the Extreme Ultraviolet Imager on NASA's Solar Terrestrial Relations Observatory, the Sun Watcher, using Active Pixel System Detector and Image Processing on ESA's PRoject for Onboard Autonomy, and the Naval Research Laboratory's Large Angle and Spectrometric Coronagraph on ESA's Solar and Heliospheric Observatory. The Ludendorff flattening coefficient is 0.156, matching the expected ellipticity of coronal isophotes at 2 Rs{sub un}, for this rising phase of the solar-activity cycle.

Pasachoff, J. M. [Williams College-Hopkins Observatory, Williamstown, MA 01267-2565 (United States); Rusin, V.; Saniga, M. [Astronomical Institute, Slovak Academy of Sciences, 059 60 Tatranska Lomnica (Slovakia)

2011-06-20

131

Structure and Dynamics of the 2010 July 11 Eclipse White-light Corona  

NASA Astrophysics Data System (ADS)

The white-light corona (WLC) during the total solar eclipse on 2010 July 11 was observed by several teams in the Moon's shadow stretching across the Pacific Ocean and a number of isolated islands. We present a comparison of the WLC as observed by eclipse teams located on the Tatakoto Atoll in French Polynesia and on Easter Island, 83 minutes later, combined with near-simultaneous space observations. The eclipse was observed at the beginning of the solar cycle, not long after solar minimum. Nevertheless, the solar corona shows a plethora of different features (coronal holes, helmet streamers, polar rays, very faint loops and radial-oriented thin streamers, a coronal mass ejection, and a puzzling "curtain-like" object above the north pole). Comparing the observations from the two sites enables us to detect some dynamic phenomena. The eclipse observations are further compared with a hairy-ball model of the magnetic field and near-simultaneous images from the Atmospheric Imaging Assembly on NASA's Solar Dynamics Observatory, the Extreme Ultraviolet Imager on NASA's Solar Terrestrial Relations Observatory, the Sun Watcher, using Active Pixel System Detector and Image Processing on ESA's PRoject for Onboard Autonomy, and the Naval Research Laboratory's Large Angle and Spectrometric Coronagraph on ESA's Solar and Heliospheric Observatory. The Ludendorff flattening coefficient is 0.156, matching the expected ellipticity of coronal isophotes at 2 R sun, for this rising phase of the solar-activity cycle.

Pasachoff, J. M.; Ruin, V.; Druckmllerov, H.; Saniga, M.; Lu, M.; Malamut, C.; Seaton, D. B.; Golub, L.; Engell, A. J.; Hill, S. W.; Lucas, R.

2011-06-01

132

Cosmic radiation in the heliosphere at successive solar minima 5. Modulation of anomalous cosmic ray helium during the three consecutive solar minimum periods of 1977\\/1978, 1987, and 1997  

Microsoft Academic Search

A renewed attempt is made to model anomalous cosmic ray He+ spectra observed during the solar minimum periods of 1977\\/1978, 1987, and 1997, from 1 to 66 AU in the heliosphere. This model improves on the one in our paper 3 in this series [Reinecke et al., 1996], because it now contains the new 1997 observations, and because a physically

J. P. L. Reinecke; F. B. McDonald; H. Moraal

2000-01-01

133

Enhancement of Heat Transfer by Corona Wind.  

National Technical Information Service (NTIS)

The mechanism of heat transfer enhancement across solid gaseous interfaces by corona wind directed towards the heat transfer surface is investigated. Corona wind may adequately be described by the Navier-Stokes equations of motion. The Coulomb ion drag fo...

H. Kadete

1987-01-01

134

Generation and evolution of equatorial ionospheric plasma bubbles and broad plasma depletions measured by the C/NOFS satellite during deep solar minimum  

NASA Astrophysics Data System (ADS)

A spectacular phenomenon in the equatorial ionosphere is the occurrence of broad plasma depletions in which the plasma density is reduced by 1-3 orders of magnitude over thousands of kilometers in longitude near dawn. This phenomenon is observed repeatedly by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during deep solar minimum. Our purpose is to study where the postmidnight plasma bubbles start to occur, how long they exist, what the maximum size of individual bubbles is, how plasma bubbles are related to broad depletions, and how broad plasma depletions form. The orbit of C/NOFS can be approximately parallel to the geomagnetic equator over a large local time range. If a plasma bubble exists long enough, it may be detected by C/NOFS over successive orbits. The C/NOFS measurements can be used to trace the growth and development of plasma bubbles. In several cases we analyzed, a series of plasma bubbles was first detected by C/NOFS over a longitudinal range of up to 3800 km around midnight. Each of the individual bubbles has a typical width of ~100 km in longitude, and the upward ion drift velocity inside the bubbles is 200-400 m/s. The plasma bubbles rotate to the dawn sector and become broad plasma depletions. The strong upward plasma flow inside the bubbles exist for more than 7 hours, and the bubbles do not become dead/fossil bubbles over the entire night time. The observations clearly show the evolution from multiple plasma bubbles into broad depletions. We propose that the broad plasma depletions with strong upward plasma flow are the result of merging of multiple equatorial plasma bubbles. We will also present the numerical simulations of bubble merging with the physics-based low-latitude ionospheric model (PBMOD). It is found that two separate plasma bubbles join together and form a new single bubble. The simulations demonstrate for the first time that the merging process of plasma bubbles can indeed occur in incompressible ionospheric plasma. The C/NOFS measurements reveal significant new characteristics of equatorial plasma bubbles and broad depletions during deep solar minimum.

Huang, Chaosong; De La Beaujardiere, Odile; Retterer, John; Pfaff, Robert; Roddy, Patrick; Hunton, Donald; Ballenthin, John

2012-07-01

135

Topological Structure of the Magnetic Solar Corona  

NASA Astrophysics Data System (ADS)

The solar corona is a highly complex and active plasma environment, containing many exotic phenomena such as solar flares, coronal mass ejections, prominences, coronal loops, and bright points. The fundamental element giving coherence to all this apparent diversity is the strong coronal magnetic field, the dominant force shaping the plasma there. In this thesis, I model the 3D magnetic fields of various coronal features using the techniques of magnetic charge topology (MCT) in a potential field. Often the real coronal field has departures from its potential state, but these are so small that the potential field method is accurate enough to pick out the essential information about the structure and evolution of the magnetic field. First I perform a topological analysis of the magnetic breakout model for an eruptive solar flare. Breakout is represented by a topological bifurcation that allows initially enclosed flux from the newly emerging region in my MCT model of a delta sunspot to reconnect out to large distances. I produce bifurcation diagrams showing how this behaviour can be caused by changing the strength or position of the emerging flux source, or the force-free parameter ?. I also apply MCT techniques to observational data of a coronal bright point, and compare the results to 3D numerical MHD simulations of the effects of rotating the sources that underlie the bright point. The separatrix surfaces that surround each rotating source are found to correspond to locations of high parallel electric field in the simulations, which is a signature of magnetic reconnection. The large-scale topological structure of the magnetic field is robust to changes in the method of deriving point magnetic sources from the magnetogram. Next, I use a Green's function expression for the magnetic field to relax the standard topological assumption of a flat photosphere and extend the concept of MCT into a spherical geometry, enabling it to be applied to the entire global coronal magnetic field. I perform a comprehensive study of quadrupolar topologies in this new geometry, producing several detailed bifurcation diagrams. These results are compared to the equivalent study for a flat photosphere. A new topological state is found on the sphere which has no flat photosphere analogue; it is named the dual intersecting state because of its twin separators joining a pair of magnetic null points. The new spherical techniques are then applied to develop a simple six-source topological model of global magnetic field reversal during the solar cycle. The evolution of the large-scale global magnetic field is modelled through one complete eleven-year cycle, beginning at solar minimum. Several distinct topological stages are exhibited: active region flux connecting across the equator to produce transequatorial loops; the dominance of first the leading and then the following polarities of the active regions; the magnetic isolation of the poles; the reversal of the polar field; the new polar field connecting back to the active regions; the polar flux regaining its dominance; and the disappearance of the transequatorial loops.

Maclean, R. C.

2007-12-01

136

Corona aging studies on silicone rubber nanocomposites  

Microsoft Academic Search

In EHV and UHV power transmission lines, corona could occur even on well designed transmission line hardware and insulators especially under wet conditions. Corona if allowed to occur continuously can significantly damage the polymeric insulators used in such lines in the long run. This paper presents the experimental results of corona aging studies conducted on unfilled silicone rubber as well

B. Venkatesulu; M. Joy Thomas

2010-01-01

137

Estimation of Galactic Cosmic Ray exposure inside and outside the Earth's magnetosphere during the recent solar minimum between solar cycles 23 and 24  

NASA Astrophysics Data System (ADS)

The evidently low solar activity observed between solar cycles 23 and 24 during the years 2008-2010 led to a substantial increase in the Galactic Cosmic Ray (GCR) intensity in comparison with preceding solar minima. As the GCRs consist of highly-ionizing charged particles having the potential to cause biological damage, they are a subject of concern for manned missions to space. With the enhanced particle fluxes observed between 2008 and 2010, it is reasonable to assume that the radiation exposure from GCR must have also increased to unusually high levels. In this paper, the GCR exposure outside and inside the Earth's magnetosphere is numerically calculated for time periods starting from 1970 to the end of 2011 in order to investigate the increase in dose levels during the years 2008-2010 in comparison with the last three solar minima. The dose rates were calculated in a water sphere, used as a surrogate for the human body, either unshielded or surrounded by aluminium shielding of 0.3, 10 or 40 g/cm2. By performing such a long-term analysis, it was estimated that the GCR exposure during the recent solar minimum was indeed the largest in comparison with previous minima and that the increase was more pronounced for locations outside the magnetosphere.

Mrigakshi, Alankrita Isha; Matthi, Daniel; Berger, Thomas; Reitz, Gnther; Wimmer-Schweingruber, Robert F.

2013-09-01

138

On postmidnight low-latitude ionospheric irregularities during solar minimum: 1. Equatorial Atmosphere Radar and GPS-TEC observations in Indonesia  

NASA Astrophysics Data System (ADS)

Using the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36S dip latitude), it is shown that postmidnight irregularities during solar minimum are morphologically different from those detected during solar maximum and are quite similar to those observed with the middle and upper atmosphere (MU) radar in midlatitudes (29.3N dip latitude). Utilizing the rapid beam-steering capability of the EAR, the spatial structure of the postmidnight irregularities is clearly presented for the first time. It is found that they usually propagate westward and can be categorized into two types. One shows sharp upwelling plumes near local midnight, which should not be a mere passage of fossil plasma bubbles. The other has successive tilted structures which have the same orientation as medium-scale traveling ionospheric disturbances typically observed at midlatitudes. We suggest that the convergence of the equatorward thermospheric wind which is believed to be responsible for the midnight temperature maximum may be an important factor to produce a preferable condition for the upwelling plumes in the postmidnight sector. The displacement between geographic and magnetic equators may also be important for seasonal/longitudinal variation of the postmidnight irregularities.

Yokoyama, T.; Yamamoto, M.; Otsuka, Y.; Nishioka, M.; Tsugawa, T.; Watanabe, S.; Pfaff, R. F.

2011-11-01

139

On postmidnight low-latitude ionospheric irregularities during solar minimum: 2. C/NOFS observations and comparisons with the Equatorial Atmosphere Radar  

NASA Astrophysics Data System (ADS)

A detailed comparison between the observations of the Communication/Navigation Outage Forecasting System (C/NOFS) satellite and the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36S dip latitude) on the postmidnight irregularities is presented. The zonal and meridional E B drift velocities measured by the vector electric field instrument on the C/NOFS are consistent with the westward propagation of backscatter echoes and the line-of-sight Doppler velocities observed with the EAR, respectively. The plasma density depletions are observed in the postmidnight sector for several consecutive orbits, which suggests the depletions grow slowly during the premidnight period and reach the spacecraft altitude around local midnight. The convergence of the equatorward wind which could be responsible for the midnight temperature maximum may produce a preferable condition for the growth of the Rayleigh-Taylor instability around midnight. Electric field fluctuations of medium-scale traveling ionospheric disturbances may play an important role in seeding the instability. Both equatorial and midlatitude-type plasma instabilities could be operational at the EAR latitude sector, which together would foster a high occurrence of postmidnight irregularities during solar minimum.

Yokoyama, T.; Pfaff, R. F.; Roddy, P. A.; Yamamoto, M.; Otsuka, Y.

2011-11-01

140

Study of maximum electron density N mF 2 at Karachi and Islamabad during solar minimum (1996) and solar maximum (2000) and its comparison with IRI  

NASA Astrophysics Data System (ADS)

The monthly hourly medians of maximum electron density, N mF 2, at two Pakistani ionospheric stations, Karachi and Islamabad, have been determined for solar minimum (1996) and solar maximum (2000) and compared with IRI predictions using the URSI coefficients. At night and pre-noon period the N mF 2 values at both stations are almost equal during the 2 years. However, at post-noon the values at Karachi are considerably larger than those at Islamabad due to the equatorial or geomagnetic anomaly. Karachi (geomag. coord. 16.44N, 139.08E) lies near the region of the equatorial anomaly (+20 and -20 geomagnetic latitude), so most of the N mF 2 values at Karachi are larger than those at Islamabad (geomag. coord. 24.46N, 145.67E). The maximum monthly values of N mF 2 show a semi-annual variation at Karachi and Islamabad both during 1996 and 2000 as predicted by IRI.

Ayub, M.; Iqbal, S.; Ameen, M. A.; Reinisch, B. W.

2009-06-01

141

Temporal Evolution of the Solar-Wind Electron Core Density at Solar Minimum by Correlating SWEA Measurements from STEREO A and B  

NASA Astrophysics Data System (ADS)

The twin STEREO spacecraft provide a unique tool to study the temporal evolution of the solar-wind properties in the ecliptic since their longitudinal separation increases with time. We derive the characteristic temporal variations at 1 AU between two different plasma parcels ejected from the same solar source by excluding the spatial variations from our datasets. As part of the onboard IMPACT instrument suite, the SWEA electron experiment provides the solar-wind electron core density at two different heliospheric vantage points. We analyze these density datasets between March and August 2007 and find typical solar minimum conditions. After adjusting for the theoretical time lag between the two spacecraft, we compare the two density datasets. We find that their correlation decreases as the time difference increases between two ejections. The correlation coefficient is about 0.80 for a time lag of a half day and 0.65 for two days. These correlation coefficients from the electron core density are somewhat lower than the ones from the proton bulk velocity obtained in an earlier study, though they are still high enough to consider the solar wind as persistent after two days. These quantitative results reflect the variability of the solar-wind properties in space and time, and they might serve as input for solar-wind models.

Opitz, A.; Sauvaud, J.-A.; Fedorov, A.; Wurz, P.; Luhmann, J. G.; Lavraud, B.; Russell, C. T.; Kellogg, P.; Briand, C.; Henri, P.; Malaspina, D. M.; Louarn, P.; Curtis, D. W.; Penou, E.; Karrer, R.; Galvin, A. B.; Larson, D. E.; Dandouras, I.; Schroeder, P.

2010-10-01

142

Coronae of Mnemosyne Regio - Morphology and origin  

NASA Astrophysics Data System (ADS)

The Mnemosine Regio area of Venus contains seven of the circular-to-elliptical structures, characterized by an annulus of concentric ridges, that are known as 'coronae'. Several corona-origin models are presently considered, and it is found that the processes associated with diapirism or hot-spots, and the gravitational relaxation of high topography, are most consistent with the topography and morphology of these coronae. The sequence of the formation and evolution of the coronae proceeds from regional volcanic and tectonic activity, through localized uplift and volcanism, to annulus and trough formation related to gravitational relaxation, and finally local volcanic flooding of the corona, annulus, and trough.

Stofan, E. R.; Head, J. W.

1990-01-01

143

Manganese Star Iota Coronae Borealis.  

National Technical Information Service (NTIS)

An abundance analysis of the manganese star Iota Coronae Borealis is carried out in detail by making use of a model atmosphere with theta sub e = 0.458, log g = 3.7, N(He)/N(H) = 0.12. The energy distribution and H gamma profile are reproduced by this mod...

J. E. Ross L. H. Aller

1969-01-01

144

Turbulence in the solar corona  

Microsoft Academic Search

The solar corona has been revealed in the past decade to be a highly dynamic nonequilibrium plasma environment. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be strongly turbulent, but direct observational evidence for a cascade of fluctuation energy from large to small scales is lacking. In this paper I will review

Steven R. Cranmer

2007-01-01

145

Waves in the Solar Corona  

Microsoft Academic Search

Waves at all scales ranging in wavelength from the size of a loop (fraction of a solar radius) down to the gyroradii (a few meters) of coronal ions are believed to play a key role in the transport of mechanical energy from the chromosphere to the Sun's corona and wind and through the dissipation of wave energy in the heating

E. Marsch

2004-01-01

146

Interferometry of the e corona.  

PubMed

Descriptions are given of Fabry-Perot spectrometer systems used in the total eclipses of 1965, 1966, and 1970 to observe the emission lines 5303 A, Fe XIV and 6374 A, Fe x at different points in the solar corona. Some results of coronal temperature measurements for the 12 November 1966 eclipse are presented. PMID:20094331

Henderson, G

1970-12-01

147

Interplanetary fast shocks and associated drivers observed through the 23rd solar minimum by Wind over its first 2.5 years  

NASA Astrophysics Data System (ADS)

A list of the interplanetary shocks observed by Wind from its launch (in Nov 1994) to May 1997 is presented. The magnetohydrodynamic nature of the shocks is investigated, and the associated shock parameters and their uncertainties are accurately computed using two techniques. These are: 1) a combination of the ``preaveraged'' magnetic-coplanarity, velocity-coplanarity, and the Abraham-Schrauner-mixed methods, and 2) the Vias and Scudder [1986] technique for solving the nonlinear least squares Rankine-Hugoniot equations. Within acceptable limits these two techniques generally gave the same results, with some exceptions. The reasons for the exceptions are discussed. The mean strength and rate of occurrence of the shocks appear to correlate with the solar cycle. Both showed a decrease in 1996 coincident with the time of the lowest ultraviolet solar radiance, indicative of solar minimum and the beginning of solar cycle 23. Eighteen shocks appeared to be associated with corotating interaction regions (CIRs). The shock normal distribution showed a mean direction peaking in the ecliptic plane and with a longitude of ~200 (GSE coordinates). Another 16 shocks were determined to be driven by solar transients, including magnetic clouds. These had a broader distribution of normal directions than those of the CIR cases with a mean direction close to the Sun-Earth line. Eight shocks of unknown origin had normal orientations far off the ecliptic plane. No shock propagated with longitude ?n>=220+/-10, i.e. against the average Parker spiral direction. Examination of the obliquity angle ?Bn (i.e., between the shock normal and the upstream interplanetary magnetic field) for the full set of shocks revealed that about 58% were quasi-perpendicular, and about 32% of the shocks oblique, and the rest quasi-parallel. Small uncertainty in the estimated angle ?Bn was obtained for about 10 shocks with magnetosonic Mach numbers between 1 and 2.

Berdichevsky, Daniel B.; Szabo, Adam; Lepping, Ronald P.; Vias, Adolfo F.; Mariani, Franco

2000-12-01

148

Periodic solar wind forcing due to recurrent coronal holes during 1996-2009 and its impact on Earth's geomagnetic and ionospheric properties during the extreme solar minimum  

NASA Astrophysics Data System (ADS)

Periodicities in the area of coronal hole (CH) regions on the solar disk and solar wind (SW) high-speed streams (HSSs) have been studied, for the first time, during complete solar cycle 23 (SC 23) from 1996 to 2009 using solar EUV image data from the Solar and Heliospheric Observatory and STEREO satellites and ACE solar wind-magnetic data. Both the SW velocity and the area of CH regions consistently exhibit large values during the declining phase and the minimum of SC23 (2003-2009) due to equatorward extended holes and/or low-latitude isolated holes. Further, the SW velocity and CH area exhibit a greater tendency for subharmonic (13.5 and 9 day) periodicities during the declining phase and solar minimum. The response of Earths' geomagnetic and ionospheric properties to these periodicities associated with corotating interaction regions in SW HSSs is studied, with a focus on the extremely low-solar-activity period of 2008. Subharmonic oscillations in both day- and nightside ionospheric electron density are found to correlate well with oscillations in SW and Kp during 2008. The topside ionospheric response (above 350 km) appears to be dominated by changes in the plasma temperature and/or scale height and exhibits concurrent enhancements with the oscillations in geomagnetic activity during both day- and nighttime. However, the electron density response at altitudes between 200 and 350 km is dominated by changes in the neutral composition and exhibits significant latitudinal, local time, and seasonal variations. The results are discussed in light of equatorward wind perturbations during enhanced geomagnetic activity and summer-to-winter transequatorial neutral wind patterns.

Tulasi Ram, S.; Liu, C. H.; Su, S.-Y.

2010-12-01

149

Corona tests of prototype connector  

NASA Astrophysics Data System (ADS)

Seven prototype connector boards were tested at Wright Laboratory in the Aerospace Power Division High Power Lab. Each connector board incorporates two types of connectors: (1) ac/dc hybrid connector with six power feedthroughs, i.e. two for dc power and four for ac power, and (2) dc connector with two power feedthroughs. The 270 volt dc rated power feedthroughs were tested with 500 volts dc. The three phase, 208 volt ac (line-to-line) power feedthroughs were tested with 354 volts ac rms. The boards were tested at ground level and at simulated altitudes of 50,000 and 100,000 feet. Corona data acquisition was accomplished in accordance with ASTM 1868-81, using a multichannel analyzer for discharge magnitude characterization. The boards performed well with only insignificant corona activity above five picocoulombs.

Rhoads, Gregory L.; Horwath, John; Schweickart, Daniel

1994-12-01

150

Negative corona triggering in air  

NASA Astrophysics Data System (ADS)

The role of positive ions and field emission in the negative corona triggering is discussed, in room air, at atmospheric pressure. First, an artificial positive space charge is created in a point-to-plane gap by focusing a pulsed ultraviolet laser beam at a determined distance from the point. The triggered corona current pulse is compared with the natural one. Numerical simulations which are presented take into account the insulating layers charging by positive ions on the cathode surface. The theory of electron emission is based upon a conduction mechanism in the bulk of insulating layers. Second, the role of field emission is enhanced by covering the point with a graphite coating. Field emission is modeled by introducing a field enhancement factor and current instabilities are attributed to the switch-off of emission sites on the cathode surface.

Bessires, D.; Paillol, J.; Soulem, N.

2004-04-01

151

Turbulence in the Solar Corona  

Microsoft Academic Search

The solar corona has been revealed in the past decade to be a highly dynamic\\u000anonequilibrium plasma environment. Both the loop-filled coronal base and the\\u000aextended acceleration region of the solar wind appear to be strongly turbulent,\\u000abut direct observational evidence for a cascade of fluctuation energy from\\u000alarge to small scales is lacking. In this paper I will review

Steven R. Cranmer

2007-01-01

152

Pulse corona dishcarge in water  

Microsoft Academic Search

The discharge in water creates chemical species such as OH radicals, ozone and hydrogen peroxide (H2O2) as well as UV and shock waves. It is promising for degradation of organic compounds and for sterilization. This article presents a corona-in-water pulse discharging system. A wire-cylinder reactor was used. The anode is a 12 cm long hollow brass tube with thin pins.

Z. Liu; A. J. M. Pemen; G. J. J. Winands; E. J. M. Van Heesch; Keping Yan

2008-01-01

153

Toward Unraveling the Photochemistry of TATB.  

National Technical Information Service (NTIS)

A combined theoretical and experimental chemical analysis has been conducted to unravel the mechanism underlying the color change of yellow TATB (1,3,5, triamino- trinitro-benzene) to green upon UV irradiation. There is strong evidence to conclude that th...

M. R. Manaa R. Schmidt G. Overturf B. Watkins L. Fried

1999-01-01

154

Temperature structure of the corona  

NASA Astrophysics Data System (ADS)

New aspects in the temperature structure of solar corona are briefly discussed mainly based on the observations obtained by Yohkoh. The dynamic behavior of the solar corona is recognizable in the temperature structures. Yohkoh has two instruments which are capable of diagnosing coronal plasmas in 'non-flaring states,' namely Soft X-Ray Telescope (SXT) and Brogg Crystal Spectrometer (BCS) sulfur channel (SXV). The major characteristic of these two instruments is that they put more emphasis on looking at high-temperature components in the corona than the instruments flown in the Skylab era. Numerous tiny loop brightenings in active regions can be observed in the BCS sulfur channel as well as SXT and this flare-like activity (microflares) is responsible for producing the high-temperature part of the differential emission measure distribution in active regions. High temperature loops seen in SXT/BCS and the coronal yellow line are spatially different from those seen in Normal Incident X-Ray Telescope (NIXT) or the green/red lines and evolve differently. This also suggests that the high-temperture component comes from non-stationary activity. Coronal holes have plamsas having temperatures comparable to the quiet-sun, though the emission measure is very low.

Watanabe, T.

155

Turbulence in the solar corona  

NASA Astrophysics Data System (ADS)

The solar corona has been revealed in the past decade to be a highly dynamic nonequilibrium plasma environment. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be strongly turbulent, but direct observational evidence for a cascade of fluctuation energy from large to small scales is lacking. In this paper I will review the observations of wavelike motions in the corona over a wide range of scales, as well as the macroscopic effects of wave-particle interactions such as preferential ion heating. I will also present a summary of recent theoretical modeling efforts that seem to explain the time-steady properties of the corona (and the fast and slow solar wind) in terms of an anisotropic MHD cascade driven by the partial reflection of low-frequency Alfvn waves propagating along the superradially expanding solar magnetic field. Complete theoretical models are difficult to construct, though, because many of the proposed physical processes act on a multiplicity of spatial scales (from centimeters to solar radii) with feedback effects not yet well understood. This paper is thus a progress report on various attempts to couple these disparate scales.

Cranmer, Steven R.

2007-08-01

156

Waves in the Solar Corona  

NASA Astrophysics Data System (ADS)

Waves at all scales ranging in wavelength from the size of a loop (fraction of a solar radius) down to the gyroradii (a few meters) of coronal ions are believed to play a key role in the transport of mechanical energy from the chromosphere to the Sun's corona and wind and through the dissipation of wave energy in the heating and sustaining of the solar corona. A concise review of new observations and theories of waves in the magnetically confined (loops) as well as open (holes) corona is given with emphasis on energetics and dynamics. Recent remote-sensing solar observations have revealed loop oscillations as expected from MHD theory. These low-frequency oscillations are excited in connection with flares and appear to be strongly damped. Recent analysis of in-situ measurements of ions in fast solar wind and related theory have indicated the importance of pitch-angle scattering of ions in the wave frame as predicted from kinetic plasma theory a microprocess that may hold the key to understand plasma acceleration and heating by damping of high-frequency waves. Evidence obtained from spectroscopy of coronal ions points to cyclotron resonance absorption as a possible cause of the observed emission-line broadenings.

Marsch, E.

2004-01-01

157

Gravity over coronae and chasmata on Venus  

NASA Astrophysics Data System (ADS)

The global spherical harmonic model of Venus' gravity field MGNP60FSAAP, with horizontal resolution of about 600 km, shows that most coronae have little or no signature in the gravity field. Nevertheless, some coronae and some segments of chasmata are associated with distinct positive gravity anomalies. No corona has been found to have a negative gravity anomaly. The spatial coincidence of the gravity highs over four closely spaced 300- to 400-km-diameter coronae in Eastern Eistla Regio with the structures themselves is remarkable and argues for a near-surface or lithospheric origin of the gravity signals over such relatively small features. Apparent depths of compensation (ADCs) of the prominent gravity anomalies at Artemis, Latona, and Heng-o Coronae are about 150 to 200 km. The geoid/topography ratios (GTRs) at Artemis, Latona, and Heng-o Coronae lie in the range 32 to 35 m/km. The large ADCs and GTRs of Artemis, Latona, and Heng-o Coronae are consistent with topographically related gravity and a thick Venus lithosphere or shallowly compensated topography and deep positive mass anomalies due to subduction of underthrusting at these coronae. At arcuate segments of Hecate and Parga Chasmata ADCs are about 125 to 150 km, while those at Fauta Corona, four coronae in Eastern Eistla Regio, and an arcuate segment of Wester Parga Chasmata are about 75 km. The GTRs at Fauta Corona, the four coronae in eastern Eistla Regio, and the accurate segments of Hecate, Parga, and Western Parga Chasmata are about 12 to 21 m/km. By analogy with gravity anomalies of similar horizontal scale (600 km-several thousand kilometers) on the concave sides of terrestrial subduction zone arcs, which are due in large part to subducted lithosphere, it is inferred that the gravity anomalies on Venus are consistent with retrograde subduction at Artemis Chasma, along the northern and southern margins of Latona Coronam, and elsewhere along Parga and Hecate Chasmata.

Schubert, Gerald; Moore, William B.; Sandwell, David T.

1994-11-01

158

Research on Method to Get Corona Inception Electric-Field Intensity Based on Small Corona Cage  

Microsoft Academic Search

Corona is an important aspect which influences the design of transmission lines and electric equipments. With the increase of altitude and voltage grade, the corona performance of equipments becomes more complex. First, this paper explains electric field distribution around the overhead multiple conductors is consistent to one of multiple conductors in the corona cage; then according to the test data

Ren Lei-Jian; Liu Yun-Peng; Lu Jie; Yu Tao

2009-01-01

159

The temperature and density structure in the closed field regions of the solar corona  

NASA Astrophysics Data System (ADS)

In this paper we study the temperature and density structure in the closed field region of the solar corona using a dipole plus current sheet model to simulate the global solar magnetic field and a heating function of the same type used in models of the fast wind. The heat equation, describing the redistributing effects of heat conduction on the heat input in the presence of radiative losses, is solved simultaneously with hydrostatic pressure balance. At the base we prescribe the temperature and assume that the heat flux is zero there. We also insist that the heat flux is zero at the equator. This ensures that whatever heat has been added is radiated away. From the mathematical viewpoint this additional requirement sets up an eigenvalue problem which implies that the density at the base must be chosen in just the right way to fulfill the condition of zero heat flux at the equator. Thus our model not only provides the temperature and density structure in the closed regions of a global solar magnetic field appropriate to solar minimum but also predicts the latitudinal variation of the base density whose characteristic value is determined by the ratio of the amplitudes of the heating to the cooling. However it should be stressed that this last prediction represents, at best, an approximation to the real stale of affairs which is more complex and involves the connection of the coronal field lines to the magnetic funnels of the chromospheric network.

McKenzie, J. F.; Sukhorukova, G. V.; Axford, W. I.

1999-10-01

160

Tomography and the distribution of streamers in the extended solar corona: some implications for large-scale MHD models  

NASA Astrophysics Data System (ADS)

cycle. Streamers are most often shaped as extended, often very narrow, plasma sheets. At most times outside the height of solar maximum, there are two separate stable large helmet streamer belts extending from mid-latitudes (in both North and South). At solar minimum, the streamers converge and join near the equator, giving the impression of a single large helmet streamer. Outside of solar minimum, the two streamers do not join, forming separate high-density sheets in the extended corona (one in the North, another in the South). At solar maximum, streamers rise radially from their source regions, whilst during the ascending and descending activity phases, streamers are skewed towards the equator. For most of the activity cycle, streamers share the same latitudinal extent as filaments on the disk, showing that large-scale stable streamers are closely linked to the same large-scale photospheric magnetic configuration which give rise to large filaments. The polewards footpoints of the streamers are often above crown polar filaments and the equatorial footpoints are above filaments or active regions (or above the photospheric neutral lines which underlie these structures). The high-density structures arising from the equatorial active regions either rise and form the equatorial footpoints of mid-latitude quiescent streamers, or form unstable streamers at the equator, not connected to the quiescent streamer structure at higher latitude (so there are often three streamer sheets sharing the same extended longitudinal region). Comparison between the tomography results and a potential field source surface model shows that streamers are not necessarily associated with a magnetic polarity reversal, but rather are regions containing field lines arising from widely-separated sources at the Sun. We call these convergence sheets (sometimes called 'pseudostreamers'). Large-scale coronal MHD models could improve their agreement with observation by incorporating the results of tomography.

Morgan, H.; Habbal, S. R.

2010-12-01

161

Coronal Heating in the Quiet Corona  

Microsoft Academic Search

The radial variation of temperature in the inner corona is examined using long exposure Yohkoh images for two regions of diffuse (quiet) corona. The results indicate a steady radial increase of temperature for both regions, out to 0.7 and 0.9 solar radii above the limb, respectively. We find that the filter ratio data for the two regions is well fitted

M. Wheatland; P. Sturrock

1996-01-01

162

Magnetic fields and the solar corona  

Microsoft Academic Search

Coronal magnetic fields calculated by the methods developed in Paper I (Altschuler and Newkirk, 1969) and the empirical description of the solar corona of November 1966 derived in Paper II (Newkirket al., 1970) are combined in order to investigate what connection exists between the magnetic fields and the density structure of the corona.

Gordon Newkirk; Martin D. Altschuler

1970-01-01

163

Magnetohydrodynamic modeling of the global solar corona  

Microsoft Academic Search

A three-dimensional magnetohydrodynamic model of the global solar corona is described. The model uses observed photospheric magnetic fields as a boundary condition. A version of the model with a polytropic energy equation is used to interpret solar observations, including eclipse images of the corona, Ulysses spacecraft measurements of the interplanetary magnetic field, and coronal hole boundaries from Kitt Peak He

Zoran Mikic; Jon A. Linker; Dalton D. Schnack; Roberto Lionello; Alfonso Tarditi

1999-01-01

164

Superplastic Forming & Diffusion Bonding of CORONA 5.  

National Technical Information Service (NTIS)

The processing of CORONA 5 (Ti-4.5 Al-5 Mo-1.5 Cr) to cold-rolled sheet and the subsequent evaluation of this sheet for superplastic formability, diffusion bondability and post-forming heat treatment response is discussed. Two heats of CORONA 5, one of 's...

J. Chesnutt C. H. Hamilton C. F. Yolton

1981-01-01

165

Sulfur Dioxide Conversion under Corona Discharge Catalysis.  

National Technical Information Service (NTIS)

Synthetic flue gas was exposed to ultraviolet radiation and to a corona discharge in laboratory type reactors and the efficiency of SO2 oxidation to SO3 for each of these methods was compared. For the conditions studied, corona treatment appeared to be su...

W. R. Browne E. E. Stone

1965-01-01

166

Nanoflare heating of solar and stellar coronae  

Microsoft Academic Search

A combination of observational and theoretical evidence suggests that much, and perhaps most, of the Sun's corona is heated by small unresolved bursts of energy called nanoflares. It seems likely that stellar coronae are heated in a similar fashion. Nanoflares are here taken to mean any impulsive heating that occurs within a magnetic flux strand. Many mechanisms have this property,

James Klimchuk

2010-01-01

167

Heating the solar corona by plasma loops  

Microsoft Academic Search

We investigate the heating of the corona via plasma loops. It is shown that it may be possible to maintain the high corona temperatures using plasma loops as conduits. Under certain conditions heat can flow across magnetic fields up temperature gradients, a mechanism that has been previously applied to the heating of plasma loops. A typical conduit loop is hotter

J. M. A. Ashbourn; L. C. Woods

2006-01-01

168

Pulsed positive corona streamer propagation and branching  

Microsoft Academic Search

The propagation and branching of pulsed positive corona streamers in a short gap is observed with high resolution in space and time. The appearance of the pre-breakdown phenomena can be controlled by the electrode configuration, the gas composition and the impedance of the pulsed power circuit. In a point-wire gap the positive corona shows much more branching than in the

E M van Veldhuizen; W R Rutgers

2002-01-01

169

Social Neuroscience: Complexities to Be Unravelled  

Microsoft Academic Search

The use of hormone actions to help unravel brain mechanisms for behavior has led to several striking successes in analyzing\\u000a neural circuits and cellular mechanisms for social behaviors. This success has prompted us to look forward and speculate about\\u000a the essential nature of the most complex social behaviors. We propose that there are several aspects that distinguish social\\u000a neuroscience fromneuroscience

Donald W. Pfaff; Ralph Adolphs

170

The fibrillar substructure of keratin filaments unraveled  

PubMed Central

We show that intermediate-sized filaments reconstituted from human epidermal keratins appear unraveled in the presence of phosphate ions. In such unraveling filaments, up to four "4.5-nm protofibrils" can be distinguished, which are helically twisted around each other in a right- handed sense. Lowering the pH of phosphate-containing preparations causes the unraveling filaments to further dissociate into "2-nm protofilaments." In addition, we find that reconstitution of keratin extracts in the presence of small amounts of trypsin yields paracrystalline arrays of 4.5-nm protofibrils with a prominent 5.4-nm axial repeat. Limited proteolysis of intact filaments immobilized on an electron microscope grid also unveils the presence of 4.5-nm protofibrils within the filament with the same 5.4-nm axial repeat. These results, together with other published data, are consistent with a 10-nm filament model based on three distinct levels of helical organization: (a) the 2-nm protofilament, consisting of multi-chain extended alpha-helical segments coiled around each other; (b) the 4.5- nm protofibril, being a multi-stranded helix of protofilaments; and (c) the 10-nm filament, being a four-stranded helix of protofibrils.

1983-01-01

171

The influence of contaminations on HVDC conductor corona characteristics  

Microsoft Academic Search

The contaminations adhering to the surface of HVDC overhead transmission line affect the conductor corona characteristics, such as radio interference, audible noise and corona loss, remarkably. The measurement of corona characteristics in a laboratory corona cage is introduced in this paper, and some experiment results are presented. The artificial pollution experiments of DC transmission line were carried out in the

Minhua Ma; Yuming Zhao; Zhicheng Guan; Liming Wang

2007-01-01

172

Dynamic Temperature Structure of the Corona  

NASA Astrophysics Data System (ADS)

The solar corona is heated to million degrees and information about the temperature structure is a key to understand the heating mechanisms. Although it is not easy to measure, the temperature looks to be remarkably steady in the solar corona and in active regions outside of transient events, like flares. On the other hand, there is strong evidence of multi-thermal structures, out of equilibrium for most of the time. Is there a way to obtain a coherent scenario? The secret might be in the fine structuring of the corona, and SDO is providing new and important information on this issue.

Reale, Fabio

2012-07-01

173

The spatial distribution of coronae on Venus  

NASA Astrophysics Data System (ADS)

Coronae on Venus are large, generally circular surface features that have distinctive tectonic, volcanic, and topographic expressions. They range in diameter from less than 200 km to at least 1000 km. Data from the Magellan spacecraft have now allowed complete global mapping of the spatial distribution of coronae on the planet. Unlike impact craters, which show a random (i.e., Poisson) spatial distribution, the distribution of coronae appears to be nonrandom. We investigate the distribution here in detail, and explore its implications in terms of mantle convection and surface modification processes.

Squyres, S. W.; Schubert, G.; Bindschadler, D. L.; Janes, D. M.; Moersch, J. E.; Moore, W.; Olson, P.; Ratcliff, J. T.; Stofan, E. R.; Turcotte, D. L.

1992-12-01

174

Tectonic patterns and regional stresses near Venusian coronae  

NASA Astrophysics Data System (ADS)

A stress analysis of tectonic patterns near Venusian coronae is reported. Combined local corona stresses and uniform regional stresses are used to predict patterns of surface tectonic features. The patterns are compared to those of coronae on Magellan images to determine the regional stress and elastic lithospheric thickness about the coronae. Regional stresses of 0.1-0.6 kbar and elastic lithospheric thicknesses of 10 +/- 5 km are estimated for three specific coronae.

Cyr, K. E.; Melosh, H. J.

1993-04-01

175

Dynamics of the Transition Corona  

NASA Astrophysics Data System (ADS)

Magnetic reconnection between open and closed magnetic field in the corona is believed to play a crucial role in the corona / heliosphere coupling. At large scale, the exchange of open /closed connectivity is expected to occur in pseudo-streamer structures. However, there is neither clear observational evidence of how such coupling occurs in pseudo-streamers, nor evidence for how the magnetic reconnection evolves. Using a newly-developed technique, we enhance the off-limb magnetic fine structures observed with AIA and identify a pseudo-streamer-like feature located close to the northern coronal hole. We first identify that the magnetic topology associated with the observation is a pseudo-streamer, null-point-related topology bounded by open field. We then compare the evolution of the observed pseudo- streamer fine structure in the location of strong currents, i.e. in the region of energy dissipation, with the dynamics of the magnetic field resulting from the interchange reconnection obtained in a fully 3D MHD simulation. The morphological and dynamical similarities between the pseudo-streamer observations and the results from the simulation strongly suggest that the evolution of the pseudo-streamer is caused by interchange reconnection in a null-point topology that is embedded in Quasi-Separatrix layers. Besides identifying the mechanism at work in the large-scale coupling between open and closed field, our results highlight that interchange reconnection in pseudo-streamers is a gradual physical process that differs from the impulsive reconnection of the solar-jet model.

Masson, Sophie; McCauley, P.; Golub, L.; Reeves, K.; DeLuca, E. E.

2013-07-01

176

Effect of Rain Drops on Corona Discharge in Alternating Current Transmission Lines with a Corona Cage  

NASA Astrophysics Data System (ADS)

The dielectric distributed around the surface of electrodes has a significant effect on the corona discharge. Corona discharge in power transmission lines in fine weather is different from that in rainy days as the surface condition is greatly changed. The surface of conductors is filled with the drops of rainwater; hence, the electric field around the conductors will be distorted. The use of a corona cage is an effective and economical means for duplicating corona progress in power transmission lines with lower voltage on the conductor in the cage. The practical conductor was utilized in this experiment under both fine and rainy conditions. The process of corona discharge was recorded and investigated. It was found that the corona discharge turned to be much more intense when rain drops were enlarged and more compressed around the conductor. The corona inception voltage, which is an important parameter of corona discharge, was also gained using an ultraviolet imager (UV imager). The corona inception voltage under the rainy condition was about 25% lower than that under the fine condition. The results of the comparison of audible noise and radio interference were analyzed.

Chen, Lan; Bian, Xingming; Wang, Lingming; Guan, Zhicheng

2012-09-01

177

Science Nation: Unraveling the Mysteries of Tornadoes  

NSDL National Science Digital Library

To better understand tornadoes, scientists, with the help of the National Science Foundation, are embarking on a quest to unravel the mysteries of tornadoes. The project is called VORTEX2, but it could also be called the amazing chase. For five weeks in the spring of 2009, and again in spring 2010, 100 researchers and scientists from 16 universities will deploy about 40 vehicles armed with high tech equipment to measure and probe tornadoes and tornado development. The researchers will span across the Midwest in search of tornadoes--all to better understand how, when and why they form.

178

Laboratory Analysis of Back-Corona Discharge.  

National Technical Information Service (NTIS)

The paper discusses an experimental research program to characterize back-corona generation and behavior in a range of environments and geometries common to electrostatic precipitators (ESPs). A wire-parallel plate device was used to monitor the intensity...

T. R. Snyder P. Vann Bush D. H. Pontius

1987-01-01

179

Construction of a Pulsed Streamer Corona Reactor.  

National Technical Information Service (NTIS)

The objective of this effort was to construct a pulsed corona discharge capability for conducting investigations into the destruction of noxious combustion products from jet engines and ground support equipment. As the first step in the investigations, a ...

B. R. Locke W. C. Finney

1995-01-01

180

A Preliminary Investigation of Corona Discharge Phenomena.  

National Technical Information Service (NTIS)

A preliminary study of corona breakdown between highly charged moving aerosols and grounded objects was conducted. The experimental facility was improved to the extent that the current carried by the aerosol, before and after a grounded needle, can be acc...

E. Barreto K. Martinot

1965-01-01

181

Degradation of organic dyes by corona discharge.  

National Technical Information Service (NTIS)

Several dyes in water were individually exposed to corona discharge. Light absorbance decreased for all organic dyes with time. Absorbance losses with methylene blue, malachite green, and new coccine were studied. The loss of color was followed using an i...

S. C. Goheen M. McCulloch D. E. Durham W. O. Heath

1992-01-01

182

Pulsed corona for gas and water treatment  

Microsoft Academic Search

The successful introduction of pulsed corona for industrial processes very much depends on the reliability of high-voltage and pulsed power technology and on the efficiency of energy transfer. In addition, it is crucial that adequate electromagnetic compatibility (EMC) is achieved between the high-voltage pulse source and surrounding equipment. Pulsed corona (1.5 kW) is generated in a pilot unit that produces

E. J. M. van Heesch; H. W. M. Smulders; S. V. B. van Paasen; P. P. M. Blom; F. M. van Gompel; A. J. P. M. Staring; K. J. Ptasinski

1997-01-01

183

Effect of Electrode Configuration and Corona Polarity on NO Removal by Pulse Corona Plasma  

Microsoft Academic Search

NOx emission (mainly NO) from industrial boilers and other sources can cause harm to public health and ecosystem. In recent years, non-thermal plasma processes including pulse corona for gaseous pollutants control have received many attentions. For pulse corona discharge, electrode configuration and pulse polarity may have influence on NOx removal through their effect on the generation of active de-NOx species.

Kefeng Shang; Yan Wu

2010-01-01

184

Method of and Apparatus for Reducing Back Corona Effects.  

National Technical Information Service (NTIS)

The invention relates to a method of, and apparatus for, reducing back corona effects in the process of charging particulate material in an electrostatic precipitator. An apparatus for reducing back corona effects while charging high resistivity dust or t...

Pontius Smith

1978-01-01

185

TRIANGLE-SHAPED DC CORONA DISCHARGE DEVICE FOR MOLECULAR DECOMPOSITION  

EPA Science Inventory

The paper discusses the evaluation of electrostatic DC corona discharge devices for the application of molecular decomposition. A point-to-plane geometry corona device with a rectangular cross section demonstrated low decomposition efficiencies in earlier experimental work. The n...

186

Particle-in-cell simulation of bipolar dc corona  

Microsoft Academic Search

Most of the existing methods for calculating dc ionized fields of monopolar and bipolar corona have ignored the ionization regions and excluded the transient phenomena of corona discharges. In this paper, bipolar dc corona was studied with a two-dimensional particle-in-cell simulation, which allowed us to model time-dependent, nonlinear, microscopic phenomena involved in the corona discharge. The technique followed simulation particles

Bai-Lin Qin; Patrick D. Pedrow

1994-01-01

187

On Rotation of the Solar Corona  

NASA Astrophysics Data System (ADS)

We have studied the rotation of the solar corona using the images taken at a 9.4 nm wavelength by the AIA 094 instrument on board the Solar Dynamics Observatory (SDO) satellite. Our analysis implies that the solar corona rotates differentially. It appears that ?, the angular rotation velocity of the solar corona, does not only depend on heliographic latitude but is also a function of time, while the nature of the latter dependence remains unclear. Besides measurement errors, deviations ? ? from the mean rotational speed are also caused by proper motion of the observed point source (the tracer) with respect to its surroundings. The spread in ? values at a particular heliographic latitude is a real effect, not caused by measurement errors. Most of the observations carry relative error less than 1 % in ?.

Lorenc, M.; Rybansk, M.; Dorotovi?, I.

2012-12-01

188

Validation Techniques for the MAS Corona Model  

NASA Astrophysics Data System (ADS)

In the interest of making competent predictions about the structure of the solar corona, we have developed the tools necessary to quantitatively compare the Magnetohydrodynamics Around a Sphere (MAS) numerical model to the observed corona. The SAIC coronal modeling group has written an algorithm that creates a two dimensional polarization brightness image of the corona from the model density output by computing the line of sight integral for scattered white light. Using the tools we developed for the CISM Data Explorer, the white light intensity is extracted from the image around the full disk of the Sun at a given radial height. A series of these images, spanning a Carrington rotation, are processed through this method into a Carrington Map, which we use for direct comparison against LASCO C2 polarization brightness data. Our validation will begin with a chi-squared comparison of model to observations of the latitude of the streamer belt brightness maximum during the Whole Sun Month.

Schmit, D.; Gibson, S.; Detoma, G.; Wiltberger, M.

2006-05-01

189

System for increasing corona inception voltage of insulating oils  

DOEpatents

The Corona Inception Voltage of insulating oils is increased by repetitive cycles of prestressing the oil with a voltage greater than the corona inception voltage, and either simultaneously or serially removing byproducts of corona by evacuation and heating the oil. 5 figs.

Rohwein, G.J.

1998-05-19

190

On the sizes of stellar X-ray coronae  

Microsoft Academic Search

Spatial information from stellar X-ray coronae cannot be assessed directly, but scaling laws from the solar corona make it possible to estimate sizes of stellar coronae from the physical parameters temperature and density. While coronal plasma temperatures have long been available, we concentrate on the newly available density measurements from line fluxes of X-ray lines measured for a large sample

J.-U. Ness; M. Gdel; J. H. M. M. Schmitt; M. Audard; A. Telleschi

2004-01-01

191

Transport of cosmic rays in the solar corona  

Microsoft Academic Search

A model is proposed to explain the transport of energetic protons in the solar corona. The particles are assumed to undergo an enhanced gradient-B drift along thin current sheets separating discontinuous field structures in the corona. These discontinuities may represent the extension into the corona of photospheric granular and supergranular cell boundaries. We have made a quantitative analysis of this

L. A. Fisk; K. H. Schatten

1972-01-01

192

Electric Current Equilibrium in the Corona  

NASA Astrophysics Data System (ADS)

A hyperbolic flux-tube configuration containing a null point below the flux rope is considered as a pre-eruptive state of coronal mass ejections that start simultaneously with flares. We demonstrate that this configuration is unstable and cannot exist for a long time in the solar corona. The inference follows from general equilibrium conditions and from analyzing simple models of the flux-rope equilibrium. A direct consequence of the stable flux-rope equilibrium in the corona are separatrices in the horizontal-field distribution in the chromosphere. They can be recognized as specific "herring-bone structures" in a chromospheric fibril pattern.

Filippov, Boris

2013-04-01

193

Corona-generated space charge effects on electric field distribution for an indoor corona cage and a monopolar test line  

Microsoft Academic Search

The effects of corona-generated space charge on the resultant electric field near a conductor were determined both for a simulated test line and a corona cage, since both are used in predicting the corona behavior of EHV and UHV transmission lines. Programs were developed for the calculation of the potential, the electric field and the space charge distributions for a

Xingming Bian; Deming Yu; Xiaobo Meng; Mark Macalpine; Liming Wang; Zhicheng Guan; Wenjun Yao; Shuzhen Zhao

2011-01-01

194

Unraveling the complex metabolic nature of astrocytes  

PubMed Central

Since the initial description of astrocytes by neuroanatomists of the nineteenth century, a critical metabolic role for these cells has been suggested in the central nervous system. Nonetheless, it took several technological and conceptual advances over many years before we could start to understand how they fulfill such a role. One of the important and early recognized metabolic function of astrocytes concerns the reuptake and recycling of the neurotransmitter glutamate. But the description of this initial property will be followed by several others including an implication in the supply of energetic substrates to neurons. Indeed, despite the fact that like most eukaryotic non-proliferative cells, astrocytes rely on oxidative metabolism for energy production, they exhibit a prominent aerobic glycolysis capacity. Moreover, this unusual metabolic feature was found to be modulated by glutamatergic activity constituting the initial step of the neurometabolic coupling mechanism. Several approaches, including biochemical measurements in cultured cells, genetic screening, dynamic cell imaging, nuclear magnetic resonance spectroscopy and mathematical modeling, have provided further insights into the intrinsic characteristics giving rise to these key features of astrocytes. This review will provide an account of the different results obtained over several decades that contributed to unravel the complex metabolic nature of astrocytes that make this cell type unique.

Bouzier-Sore, Anne-Karine; Pellerin, Luc

2013-01-01

195

Black hole accretion disks with coronae  

Microsoft Academic Search

Observations suggest the existence of both hot and cold dark matter in the centers of active galactic nuclei. Recent spectral models require a major fraction of power to be dissipated in the hot matter. We study the case when the hot matter forms a corona around a standard cold alpha-disk. In particular, we investigate the case when a major fraction,

Roland Svensson; Andrzej A. Zdziarski

1994-01-01

196

Impulse corona simulation for flue gas treatment  

Microsoft Academic Search

The lack of experimental results on transport coefficients in flue gases makes the macroscopic discharge models not applicable to the simulation of impulse corona for flue gas treatment. In the present paper the microscopic formulation, based on Boltzmann and Poisson's equations, is analyzed and a simplified model is derived. This has been numerically implemented in two sections: in the first

Ivo Gallimberti

1988-01-01

197

Differential rotation of the solar electron corona  

Microsoft Academic Search

Autocorrelation analyses of K-coronameter observations made at Haleakala and Mauna Loa, Hawaii, during 19641967 have established average yearly rotation rates of coronal features as a function of latitude and height above the limb. At low latitudes the corona was found to rotate at the same rate as sunspots but at higher latitudes was consistently faster than the underlying photosphere. There

Richard T. Hansen; Shirley F. Hansen; Harold G. Loomis

1969-01-01

198

Locating Current Sheets in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection. Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even topological properties of a force-free coronal magnetic field. First, there are separatrices related to magnetic nulls. Through separatrices the magnetic connectivity changes discontinuously. Coronal magnetic nulls are, however, very rare. Second, inspired by the concept of generalized magnetic reconnection without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the magnetic connectivity changes continuously, though strongly. The strength of the connectivity change can be quantified by measuring the squashing of the flux tubes which connect the magnetically conjugated photospheres. We verify the QSL and separatrix concepts by comparing the sites of magnetic nulls and enhanced squashing with the location of current concentrations in the corona. Due to the known difficulties of their direct observation, we simulated coronal current sheets by numerically calculating the response of the corona to energy input from the photosphere, heating a simultaneously observed Extreme Ultraviolet Bright Point. We did not find coronal current sheets at separatrices but at several QSL locations. The reason is that, although the geometrical properties of force-free extrapolated magnetic fields can indeed hint at possible current concentrations, a necessary condition for current sheet formation is the local energy input into the corona.

Bchner, J.

2006-02-01

199

Pulsating radio emissions from the solar corona  

Microsoft Academic Search

Three solar outbursts which show pulsating radio emissions at metric waves (239 MHz) are examined. The behaviour of the single frequency, high-time resolution records and the spectral diagrams seem to indicate that such phenomena are peculiar phases of type IV radiation, perhaps connected with absorptions in the solar corona. The spectral analysis of the low-frequency modulation of the emissions show

A. Abrami

1970-01-01

200

The heating of the solar corona  

Microsoft Academic Search

The heating of the solar corona has been a fundamental astrophysical issue for over sixty years. Over the last decade in particular, space-based solar observatories (Yohkoh, SOHO and TRACE) have revealed the complex and often subtle magnetic-field and plasma interactions throughout the solar atmosphere in unprecedented detail. It is now established that any energy release mechanism is magnetic in origin

R. W. Walsh; J. Ireland

2003-01-01

201

Wave heating of the solar corona  

Microsoft Academic Search

The possible role of waves in the heating of the solar corona has been investigated. A dispersion relation has been derived for waves propagating in a homogeneous plasma subject to dissipation by viscosity and thermal conduction. The dissipation mechanisms have been incorporated self-consistently into the equations, and no assumptions about the strength of the damping have been made. Solutions of

Lisa Janice Porter

1994-01-01

202

MHD Shock Heating in Solar Corona Holes  

Microsoft Academic Search

Summary form only given. We report on a one dimensional simulation of plane polarized, large amplitude, Alfven waves traveling upwards through a gravitationally stratified solar corona hole. In the low plasma beta region the waves develop into fast magnetic shocks that reach great heights with little heat dissipation, where they excite large amplitude slow hydrodynamic shocks that deposit sufficient energy

M. A. Huerta; J. A. Orta; G. C. Boynton; J. Lee

2007-01-01

203

A mechanism for heating the solar corona  

Microsoft Academic Search

The high temperatures measured in the solar corona are explained in terms of heating which results from the work done on the plasma by expanding magnetic flux. This theory, which invokes no wave deposition or ohmic heating processes, is consistent with the strongly magnetized, highly variable nature of the solar atmosphere.

1980-01-01

204

Heating the Solar Corona by Magnetic Reconnection  

Microsoft Academic Search

Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging flux motions as the key for

E. R. Priest

1999-01-01

205

Heating the Solar Corona by Magnetic Reconnection  

Microsoft Academic Search

Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging flux motions as the key for

E. R. Priest

1998-01-01

206

The theory of positive glow corona  

Microsoft Academic Search

A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions, negative ions and metastable oxygen molecules, coupled

R. Morrow

1997-01-01

207

Solar corona caused by juniper pollen in Texas.  

PubMed

Coronas are colorful, concentric rings centered on a bright light such as the Sun, the Moon, or even a streetlamp. Coronas are most commonly caused by water droplets or ice particles of relatively uniform size. Observers in Finland have reported spectacular clear-sky coronas caused by pollen grains. A clear-sky corona in central Texas occurred during the peak of the juniper pollinating season. The aerosol optical thickness at each of three wavelengths was highest when the corona was most prominent. Photographic measurements of the corona infer a particle diameter of ~32.4 mum. Because juniper pollen grains have a diameter of from 22 to 30 mum, they are the aerosol most likely to have caused the corona. PMID:18268739

Mims, F M

1998-03-20

208

Radio seismology of the outer solar corona  

NASA Astrophysics Data System (ADS)

Context. Observed oscillations of coronal loops in extreme ultraviolet (EUV) lines have been successfully used to estimate plasma parameters in the inner corona (<0.2 R0, where R0 is the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because of rapid decrease in line intensity. Aims: We aim to use radio observations to estimate the plasma parameters of the outer solar corona (>0.2 R0). Methods: We used the large Ukrainian radio telescope URAN-2 to observe type IV radio bursts at the frequency range of 8-32 MHz during the time interval of 09:50-12:30 UT on April 14, 2011. The burst was connected to C2.3 flare, which occurred in AR 11190 during 09:38-09:49 UT. The dynamic spectrum of radio emission shows clear quasi-periodic variations in the emission intensity at almost all frequencies. Results: Wavelet analysis at four different frequencies (29 MHz, 25 MHz, 22 MHz, and 14 MHz) shows the quasi-periodic variation of emission intensity with periods of ~34 min and ~23 min. The periodic variations can be explained by the first and second harmonics of vertical kink oscillation of transequatorial coronal loops, which were excited by the same flare. The apex of transequatorial loops may reach up to 1.2 R0 altitude. We derive and solve the dispersion relation of trapped magnetohydrodynamic oscillations in a longitudinally inhomogeneous magnetic slab. The analysis shows that a thin (with width to length ratio of 0.1), dense (with the ratio of internal and external densities of ?20) magnetic slab with weak longitudinal inhomogeneity of the Alfvn speed may trap the observed oscillations. Seismologically estimated Alfvn speed inside the loop at the height of ~1 R0 is ~1000 km s-1. The magnetic field strength at this height is estimated as ~0.9 G. Extrapolation of magnetic field strength to the inner corona gives ~10 G at the height of 0.1 R0. Conclusions: Radio observations can be successfully used for the sounding of the outer solar corona, where EUV observations of coronal loops fail. Therefore, radio seismology of the outer solar corona is complementary to EUV seismology of the inner corona.

Zaqarashvili, T. V.; Melnik, V. N.; Brazhenko, A. I.; Panchenko, M.; Konovalenko, A. A.; Franzuzenko, A. V.; Dorovskyy, V. V.; Rucker, H. O.

2013-07-01

209

Are Coronae Restricted to Venus?: Corona-Like Tectonovolcanic Structures on Earth  

NASA Astrophysics Data System (ADS)

Coronae may not be tectonovolcanic features unique to Venus because both the processes that lead to corona formation, and their final tectonovolcanic output (formation of domes, plateaus, extensional rings, etc.), are also found on Earth. Large-scale corona formation processes on Earth may be restricted (because of plate motion) but not absent. The same applies to resurfacing processes. We here suggest that at least, the early stages of corona formation can be recognized in intraplate tectonic settings on Earth. The African plate displays many Cenozoic examples of plume-related domal uplifts and volcanism (e.g., Hoggar, Tibesti, Darfur, Ethiopia). Furthermore, the east African rift system (EARS) around lake Victoria displays many striking features that resemble those of the Venus coronae associated with extensional belts. Among these are the following: (1) an overall elliptical shape; (2) the existence of a mantle plume (Kenya plume) centered beneath lake Victoria; (3) a central plateau (east African plateau); (4) an external extensional belt (the EARS east and west branches); (5) doming processes (Kenya dome); and last but not least (6) volcanism.

Lopez, Ivan; Marquez, Alvaro; Oyarzun, Roberto

1997-04-01

210

Corona and Motor Voltage Interim Report  

SciTech Connect

It has been suggested that to meet the FreedomCAR objectives for cost, size, weight, efficiency, and reliability higher buss voltages be utilized in HEV and FC automotive applications. The reasoning is that since electric power is equal to the product of voltage and current for a given power a higher voltage and lower current would result in smaller cable and inverter switching components. Consequently, the system can be lighter and smaller. On the other hand, higher voltages are known to require better and thicker electrical insulation that reduce the available slot area for motor windings. One cause of slow insulation breakdown is corona that gradually erodes the insulation and shortens the life expectancy of the motor. This study reports on the results of a study on corona initiating voltages for mush-wound and bobbin-wound stators. A unique testing method is illustrated.

Hsu, J.S.

2005-05-06

211

Helium corona-assisted air discharge  

SciTech Connect

Operation of atmospheric discharge of electronegative gases including air at low voltages yet without consuming any inert gas will enormously promote the application of non-thermal plasmas. By taking advantage of the low onset voltage for helium corona, air discharge was successfully launched at much reduced voltages with a needle-plate system partly contained in a helium-filled glass bulb--for a needle-plate distance of 12 mm, 1.0 kV suffices. Ultraviolet emission from helium corona facilitates the discharging of air, and the discharge current manifests distinct features such as relatively broad Trichel pulses in both half periods. This design allows safe and economic implementation of atmospheric discharge of electronegative gases, which will find a broad palette of applications in surface modification, plasma medicine and gas treatment, etc.

Jiang Nan; Gao Lei; Ji Ailing; Cao Zexian [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2011-10-15

212

Helium corona-assisted air discharge  

NASA Astrophysics Data System (ADS)

Operation of atmospheric discharge of electronegative gases including air at low voltages yet without consuming any inert gas will enormously promote the application of non-thermal plasmas. By taking advantage of the low onset voltage for helium corona, air discharge was successfully launched at much reduced voltages with a needle-plate system partly contained in a helium-filled glass bulb--for a needle-plate distance of 12 mm, 1.0 kV suffices. Ultraviolet emission from helium corona facilitates the discharging of air, and the discharge current manifests distinct features such as relatively broad Trichel pulses in both half periods. This design allows safe and economic implementation of atmospheric discharge of electronegative gases, which will find a broad palette of applications in surface modification, plasma medicine and gas treatment, etc.

Jiang, Nan; Gao, Lei; Ji, Ailing; Cao, Zexian

2011-10-01

213

Nanoflare heating of solar and stellar coronae  

NASA Astrophysics Data System (ADS)

A combination of observational and theoretical evidence suggests that much, and perhaps most, of the Sun's corona is heated by small unresolved bursts of energy called nanoflares. It seems likely that stellar coronae are heated in a similar fashion. Nanoflares are here taken to mean any impulsive heating that occurs within a magnetic flux strand. Many mechanisms have this property, including waves, but we prefer Parker's picture of tangled magnetic fields. The tangling is caused by turbulent convection at the stellar surface, and magnetic energy is released when the stresses reach a critical level. We suggest that the mechanism of energy release is the "secondary instability" of electric current sheets that are present at the boundaries between misaligned strands. I will discuss the collective evidence for solar and stellar nanoflares and hopefully present new results from the Solar Dynamics Observatory that was just launched.

Klimchuk, James

214

Solar Corona on 10.21.2010  

NASA Video Gallery

The solar corona on 2010/10/21, observed by SDOs AIA. The false colors represent images taken with different filters that are sensitive to distinct coronal temperatures: blue for one million degrees, green -1.5 million, and red - 2 million. The movie shows three simultaneous eruptions: one near the center of the disk, and two at opposite sides of the Sun, together spanning over a million miles.

Holly Zell

2010-12-13

215

Modeling of the electrostatic corona discharge reactor  

Microsoft Academic Search

A model is presented for the electrostatic corona discharge reactor (ECDR) in a pin-plate configuration. The main objective is to describe the fundamental chemistry and physics governing the discharge behavior and to predict the ECDR performance under various operating conditions. The electric field strength is estimated assuming a space-charge-free field. A two-term spherical harmonic expansion is used to solve the

S. Mukkavilli; C. K. Lee; K. Varghese; L. L. Tavlarides

1988-01-01

216

Theory of negative corona in oxygen  

Microsoft Academic Search

Theoretical predictions are given of the development of the current and the distributions of charge and electric field in negative corona, or Trichel current pulses [G. W. Trichel, Phys. Rev. 54, 1078 (1938)], in oxygen at a pressure of 6.67 kPa (50 Torr). For a 10-mm-diam negative sphere located 20 mm from a positive plane, the calculated current pulse has

R. Morrow

1985-01-01

217

Corona discharge: A doping method for polyaniline  

Microsoft Academic Search

Corona discharge has been successfully employed to dope thin films of polyaniline coated on poly (ethylene terephthalate) films. Similarly to the conventional doping with aqueous HCl, the process is accompanied by a color change from blue to green and the conductivity can be tuned in the range from 10-10 up to 0.3 S cm-1. This doping method presents several advantages

Aldo E. Job; Jos A. Giacometti; Luiz H. C. Mattoso

1998-01-01

218

Corona discharge: A doping method for polyaniline  

Microsoft Academic Search

Corona discharge has been successfully employed to dope thin films of polyaniline coated on poly (ethylene terephthalate) films. Similarly to the conventional doping with aqueous HCl, the process is accompanied by a color change from blue to green and the conductivity can be tuned in the range from 10?10 up to 0.3 S cm?1. This doping method presents several advantages

Aldo E. Job; Jose A. Giacometti; Luiz H. C. Mattoso

1998-01-01

219

Locating Current Sheets in the Solar Corona  

Microsoft Academic Search

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection.\\u000a Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an\\u000a unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even\\u000a topological properties of a force-free coronal magnetic field.

J. Bchner

2006-01-01

220

Locating current sheets in the solar corona  

Microsoft Academic Search

Current sheets are essential for energy dissipation in the solar corona, in\\u000aparticular by enabling magnetic reconnection. Unfortunately, sufficiently thin\\u000acurrent sheets cannot be resolved observationally and the theory of their\\u000aformation is an unresolved issue as well. We consider two predictors of coronal\\u000acurrent concentrations, both based on geometrical or even topological\\u000aproperties of a force free coronal magnetic

Joerg Buechner

2007-01-01

221

Nonlinear Plasma Physics of the Solar Corona  

NASA Astrophysics Data System (ADS)

As a tribute to Dennis Papadopoulos, we present a review of some recent ideas in solar coronal plasma physics. In particular we discuss some models of coronal heating, notably the coronal tectonics model, as well as some ideas on the nature of reconnection in three dimensions. In addition, we summarise a model for the time-dependent response of the corona to the sudden dissipation of a current sheet.

Priest, Eric R.

2011-01-01

222

HEATING THE SOLAR X-RAY CORONA  

Microsoft Academic Search

The X-ray corona of the Sun consists of the diffuse X-ray background and the bright X-ray loops (107 erg\\/cm2sec) confined in the strong (100 Gauss) bipolar fields of mag- netic active regions. The bipolar fields are rooted in the solar granules which continually intermix the photo- spheric footpoints of the bipolar fields and progressively interlace the field lines. The intermixing

E. N. Parker

223

Heating the Solar Corona by Magnetic Reconnection  

Microsoft Academic Search

Here I review briefly the theory of magnetohydrodynamic reconnection and ask what observational evidence is there that it\\u000a is heating the corona. In particular, the new directions in which three-dimensional theory for reconnection is heading are\\u000a outlined. Part of the coronal heating problem has been solved with the identification of reconnection driven by converging\\u000a flux motions as the key for

E. R. Priest

1998-01-01

224

Decay of electric charge on corona charged polyethylene  

NASA Astrophysics Data System (ADS)

This paper describes a study on the surface potential decay of corona charged low density polyethylene (LDPE) films. A conventional corona charging process is used to deposit charge on the surface of film and surface potential is measured by a compact JCI 140 static monitor. The results from corona charged multilayer sample reveal that the bulk process dominates charge decay. In addition, the pulsed-electro-acoustic (PEA) technique has been employed to monitor charge profiles in corona charged LDPE films. By using the PEA technique, we are able to monitor charge migration through the bulk. Charge profiles in corona charged multilayer sample are consistent with surface potential results. Of further significance, the charge profiles clearly demonstrate that double injection has taken place in corona charged LDPE films.

Xu, Zhiqiang; Zhang, Linwen; Chen, George

2007-11-01

225

Deep solar minimum and global climate changes  

NASA Astrophysics Data System (ADS)

This paper examines the deep minimum of solar cycle 23 and its potential impact on climate change. In addition, a source region of the solar winds at solar activity minimum, especially in the solar cycle 23, the deepest during the last 500 years, has been studied. Solar activities have had notable effect on palaeoclimatic changes. Contemporary solar activity are so weak and hence expected to cause global cooling. Prevalent global warming, caused by building-up of green-house gases in the troposphere, seems to exceed this solar effect. This paper discusses this issue.

Hady, Ahmed A.

2013-05-01

226

Are Sunspots Different During This Solar Minimum?  

Microsoft Academic Search

For hundreds of years, humans have observed that the Sun has displayed activity where the number of sunspots increases and then decreases at approximately 11-year intervals. Sunspots are dark regions on the solar disk with magnetic field strengths greater than 1500 gauss (see Figure 1), and the 11-year sunspot cycle is actually a 22-year cycle in the solar magnetic field,

W. Livingston; M. Penn

2009-01-01

227

Coronae are more abundant than previously recognized: Results of a new survey of coronae and arachnoids on Venus  

NASA Astrophysics Data System (ADS)

We performed a new survey of coronae on the surface of Venus. We compared three previously published catalogues of coronae and related structures on Venus [1-3] and compiled a new catalogue of coronae and arachnoids by including features from all three lists that met the criteria for coronae or arachnoids [4]. In addition 38 new structures were recognized from Magellan radar data as a byproduct of the survey of multiple coronae of Venus [5]. We classified all structures into Type 1 and Type 2 based on the completeness of their fracture annulus [1]. Our list currently includes 716 coronae and arachnoids: 586 coronae and 130 arachnoids. Of these 519 are Type 1 and 197 Type 2. (Compare to e.g. 513 coronae in [1], and 209 coronae and 265 arachnoids in [2].) These numbers may still change in the course of our further investigations. We note that there are most likely even more coronae (and related structures) on the surface of Venus. These may not be easily recognizable, because of their small size, lack of clear structural annulus and/or relatively poor spatial resolution of the Magellan altimetry data, which is often needed for identification of Type 2 coronae. We will present new distribution maps, new data and preliminary results on corona dimensions and topographic characteristics as well as comparisons between our data and earlier published results. References: [1] Stofan E.R. et al. (2001) GRL, 28, 4267-427. [2] Crumpler L.S. & Aubele J.C. (2000) in Encyclopedia of Volcanoes, eds. Sigurdsson H. et al., Academic Press, [3] Kostama V.-P, & Aittola M., (2001) Catalogue of Venusian Volcano-tectonic Features, http://cc.oulu.fi/tati/JR/Venus/volcanotectonics/catalogue.html, [4] Kostama P. & Trmnen T., (2006), this volume, [5] Trmnen T. et al. (2005) LPS XXXVI, #1640.

Tormanen, T.; Kostama, P.; Hyvarinen, M.; Raitala, J.

228

Large-scale volcanism associated with coronae on Venus  

NASA Astrophysics Data System (ADS)

The formation and evolution of coronae on Venus are thought to be the result of mantle upwellings against the crust and lithosphere and subsequent gravitational relaxation. A variety of other features on Venus have been linked to processes associated with mantle upwelling, including shield volcanoes on large regional rises such as Beta, Atla and Western Eistla Regiones and extensive flow fields such as Mylitta and Kaiwan Fluctus near the Lada Terra/Lavinia Planitia boundary. Of these features, coronae appear to possess the smallest amounts of associated volcanism, although volcanism associated with coronae has only been qualitatively examined. An initial survey of coronae based on recent Magellan data indicated that only 9 percent of all coronae are associated with substantial amounts of volcanism, including interior calderas or edifices greater than 50 km in diameter and extensive, exterior radial flow fields. Sixty-eight percent of all coronae were found to have lesser amounts of volcanism, including interior flooding and associated volcanic domes and small shields; the remaining coronae were considered deficient in associated volcanism. It is possible that coronae are related to mantle plumes or diapirs that are lower in volume or in partial melt than those associated with the large shields or flow fields. Regional tectonics or variations in local crustal and thermal structure may also be significant in determining the amount of volcanism produced from an upwelling. It is also possible that flow fields associated with some coronae are sheet-like in nature and may not be readily identified. If coronae are associated with volcanic flow fields, then they may be a significant contributor to plains formation on Venus, as they number over 300 and are widely distributed across the planet. As a continuation of our analysis of large-scale volcanism on Venus, we have reexamined the known population of coronae and assessed quantitatively the scale of volcanism associated with them. In particular, we have examined the percentage of coronae associated with volcanic flow fields (i.e., a collection of digitate or sheet-like lava flows extending from the corona interior or annulus); the range in scale of these flow fields; the variations in diameter, structure and stratigraphy of coronae with flow fields; and the global distribution of coronae associated with flow fields.

Roberts, K. Magee; Head, James W.

1993-03-01

229

Dyspraxia or developmental coordination disorder? Unravelling the enigma  

Microsoft Academic Search

Dyspraxia is an enigma to many people, both professional and lay alikewhat is it, how does it relate to developmental coordination disorder and associated conditions, how common is it, how is it recognised and diagnosed and how should it be managed? This article attempts to unravel this enigma by: dealing with the terminology of coordination difficulties from the clumsy child

John Gibbs; Jeanette Appleton; Richard Appleton

2007-01-01

230

Unraveling "Braid": Puzzle Games and Storytelling in the Imperative Mood  

ERIC Educational Resources Information Center

|"Unraveling Braid" analyzes how unconventional, non-linear narrative fiction can help explain the ways in which video games signify. Specifically, this essay looks at the links between the semiotic features of Jonathan Blow's 2008 puzzle-platform video game Braid and similar elements in Georges Perec's 1978 novel "Life A User's Manual," as well

Arnott, Luke

2012-01-01

231

Model of the Negative DC Corona Plasma: Comparison to the Positive DC Corona Plasma  

Microsoft Academic Search

A numerical model of the negative DC corona plasma along a thin wire in dry air is presented. The electron number density and electric field are determined from solution of the one-dimensional coupled continuity equations of charge carriers and Maxwell's equation. The electron kinetic energy distribution is determined from the spatially homogeneous Boltzmann equation. A parametric study is conducted to

Junhong Chen; Jane H. Davidson

2003-01-01

232

Relationship Between Corona and Radio Noise on Transmission Lines II. Conductor and Insulator Corona  

Microsoft Academic Search

The basic goal of our past studies and our future plans is to strive for a means for predicting the RI level of any proposed EHV transmission line by corona measurements of its components. Our general experimental program directed toward this end is outlined as follows: 1. Find a correlation between radio noise and pulses of known characteristics with simple

T. W. Liao; J. J. Laforest

1959-01-01

233

Reconnection Processes in the Chromosphere and Corona  

NASA Astrophysics Data System (ADS)

Magnetic reconnection is a fundamental key physical process in magnetized plasmas. Recent space solar observations revealed that magnetic reconnection is ubiquitous in the solar chromospheres and corona. Especially recent Hinode observations has found various types of tiny chromospheric jets, such as chromospheric anemone jets (Shibata et al. 2007), penumbral microjets (Katsukawa et al. 2007), light bridge jets from sunspot umbra (Shimizu et al. 2009), etc. It was also found that the corona is full of tiny X-ray jets (Cirtain et al. 2007). Often they are seen as helical spinning jets (Shimojo et al. 2007, Patsourakos et al. 2008, Pariat et al. 2009, Filippov et al. 2009, Kamio et al. 2010) with Alfvenic waves (Nishizuka et al. 2008, Liu et al. 2009) and there are increasing evidence of magnetic reconnection in these tiny jets. We can now say that as spatial resolution of observations become better and better, smaller and smaller flares and jets have been discovered, which implies that the magnetized solar atmosphere consist of fractal structure and dynamics, i.e., fractal reconnection. Bursty radio and hard X-ray emissions from flares also suggest the fractal reconnection and associated particle acceleration. Since magnetohydrodynamics (MHD) does not contain any characteristic length and time scale, it is natural that MHD structure, dynamics, and reconnection, tend to become fractal in ideal MHD plasmas with large magnetic Reynolds number such as in the solar atmosphere. We would discuss recent observations and theories related to fractal reconnection in the chromospheres and corona, and discuss possible implication to chromospheric and coronal heating.

Shibata, Kazunari

2012-07-01

234

A magmatic loading model for coronae on Venus  

Microsoft Academic Search

Models for the formation of coronae, quasi-circular, volcanotectonic features on Venus, must explain four critical characteristics: coronae display (1) a wide range of diameters, (2) complex, varied topography, (3) fracture annuli, and (4) sometimes extensive volcanism. Previous models have difficulty simultaneously satisfying all four constraints. On the basis of observations and interpretations of features on Venus and Earth and experiments

Andrew J. Dombard; Catherine L. Johnson; Mark A. Richards; Sean C. Solomon

2007-01-01

235

A new pelobiont protist Pelomyxa corona sp. n. (Peloflagellatea, Pelobiontida)  

Microsoft Academic Search

Summary A new species of multinucleate pelobionts, Pelomyxa corona, is described. Morphology of the amoebae has been studied with the use of the light and the transmission electron microscope. The cells of P. corona are rounded. The cytoplasm is clearly differentiated into the marginal hyaloplasm and the endoplasm. Numerous hyaline pseudopodia of approximately equal length make the amoeba look like

Alexander O. Frolov; Ludmila V. Chystjakova; Andrew V. Goodkov

236

Solar corona expansion and heliospheric current sheet creation  

Microsoft Academic Search

Heliospheric current sheet (CS) creation has been investigated by numerical solution of 3D MHD equations, using the PERESVET code to the problem of solar corona expansion. The dipole magnetic field corresponds to the solar activity minimum, and typical corona parameters are used as initial conditions. Plasma compression, dissipation, thermal conductivity, and gravitation are taken into account. The normal magnetic field

I. M. Podgorny; A. I. Podgorny

2008-01-01

237

Radio Observations of the Solar Corona During an Eclipse  

NASA Astrophysics Data System (ADS)

We carried out radio observations of the solar corona at 170 MHz during the eclipse of 2008 August 1, from the Gauribidanur observatory located about 100 km north of Bangalore in India. The results indicate the presence of a discrete radio source of very small angular dimension (?15'') in the corona from where the observed radiation originated.

Kathiravan, C.; Ramesh, R.; Barve, Indrajit V.; Rajalingam, M.

2011-04-01

238

Extension of lightning corona sheath model during return stroke  

Microsoft Academic Search

A generalized lightning traveling current source return stroke model has been used to examine the characteristics of the lightning channel corona sheath. A model of lightning channel consisting of a charged corona sheath and a narrow, high conducting central core is assumed. The return stroke process is modeled with the positive charge coming from the channel core discharging the negative

Jovan Cvetic; Predrag Osmokrovic; Fridolin Heidler; Zoran Trifkovic

2011-01-01

239

Mass and energy flow in the solar chromosphere and corona  

Microsoft Academic Search

Some results of investigations into the mass and energy flow in the solar chromosphere and corona are reviewed. The objective of these investigations is the development of a physical model that will not only account for the physical conditions in the outer atmosphere of the sun but also can be applied to the study of the chromospheres and coronae of

G. L. Withbroe; R. W. Noyes

1977-01-01

240

Magnetic reconnection in the corona and the loop prominence phenomenon  

Microsoft Academic Search

Many classes of transient solar phenomena, such as flares, flare sprays, and eruptive prominences, cause major disruptions in the magnetic geometry of the overlying corona. Typically, the results from Skylab indicate that pre-existing closed magnetic loops in the corona are torn open by the force of the disruption. We examine here some of the theoretical consequences to be expected during

R. A. Kopp; G. W. Pneuman

1976-01-01

241

Hydrophobicity recovery of polydimethylsiloxane after exposure to corona discharges  

Microsoft Academic Search

A high-temperature-vulcanized polydimethylsiloxane (PDMS) elastomer has been subjected to corona discharges for different periods of time in dry air. The loss and recovery of hydrophobicity of the surface have been characterized by contact angle measurements. Immediately after exposure to corona discharges, samples showed a low surface hydrophobicity and, on storage in dry air, a continuous increase in hydrophobicity finally approaching

H. Hillborg; U. W. Gedde

1998-01-01

242

Inorganic fillers for corona endurance enhancement of selected polymers  

Microsoft Academic Search

In high voltage applications, polymer insulation can be exposed to very high electrical field stress, resulting in long term exposure to corona. The electrical field stress may be much below dielectric breakdown threshold. Eventually the exposure to corona can lead to failure of the high voltage component. Nanometer sized inorganic fillers are increasingly used as reinforcing materials for mechanical or

J. Horwath; D. Schweickart

2002-01-01

243

Collisional damping of surface waves in the solar corona  

Microsoft Academic Search

It has been suggested that surface waves may be able to heat the solar corona. These waves can propagate into the corona and supply the required energies, and because they are linearly compressive they can be dissipated by ion viscosity and electron heat conduction. In this paper the authors evaluate the damping of surface waves by viscosity and heat conduction.

B. E. Gordon; J. V. Hollweg

1983-01-01

244

A study of the composition of the lower solar corona  

Microsoft Academic Search

Some trends in the composition of the lower solar corona due to mixing and diffusion have been examined. Mixing has been treated through plausible inference from the thermal gradient and through analogy with the neutral atmosphere of the earth. These indicate that diffusion may be important in the lower corona. Changes in composition due to pressure and thermal gradients have

M. P. Nakada

1969-01-01

245

The structure of the external corona in solar activity minimum.  

NASA Astrophysics Data System (ADS)

The external corona was observed using the photography method during the total solar eclipse at Mohe on March 9, 1997. The observational data was disposed using the astronomical Video Image Collecting Processing System. The shape and structure of the external corona in solar activity minimum are analysed.

Luo, Baorong; Wang, Feng

246

Joule heating and anomalous resistivity in the solar corona  

Microsoft Academic Search

Recent radioastronomical observations of Faraday rotation in the solar corona can be interpreted as evidence for coronal currents, with values as large as 2.5109 Amperes (Spangler, 2007). These estimates of currents are used to develop a model for Joule heating in the corona. It is assumed that the currents are concentrated in thin current sheets, as suggested by theories of

S. R. Spangler

2009-01-01

247

Nanoflares and the Heating of the Solar Corona  

Microsoft Academic Search

There is a simmering dispute on the heating of the solar corona. Waves or flares that is the question. New observational signatures of the heating process(es) have been revealed by observations of SoHO TRACE Yohkoh and RHESSI. The evidence for heating in the quiet corona active region loops and the solar wind are different and must be distinguished. Prime indications

A. O. Benz

2004-01-01

248

HEATING OF THE SOLAR CORONA BY GRAVITY WAVES  

Microsoft Academic Search

ABS>A new type of hydrodynamic-wave heating is proposed for the solar ; corona. It is shown that internal gravity waves are preferentially generated by ; the convection zone and are easily transmitted to the corona. Acoustic waves ; with frequency characteristic of the photospheric granules cannot be transmitted ; through the reversing layer. The gravity waves are shown to dissipate

William A. Whitaker

1963-01-01

249

Scintillation Effects on Radio Wave Propagation Through Solar Corona  

Microsoft Academic Search

When RF waves pass through the solar corona and solar wind regions close to the Sun, strong scintillation effects appear at their amplitude, frequency and phase, especially in the regions very close to the Sun (less than 4 solar radius). After analyzing recent solar corona conjunction experimental data at S, X and Ka bands, we have developed a group of

C. M. Ho; M. K. Sue; A. Bedrossian; R. W. Sniffin

250

Corona Losses at 230 Kv With One Conductor Grounded  

Microsoft Academic Search

Tests have been made to determine the increase in corona losses on a high voltage transmission line, due to the grounding of one of the conductors. The corona losses under this condition of operation, which may occur on a transmission system not having the neutral solidly grounded, are shown to be considerably increased over the more usual operation with all

Joseph S. Carroll; Donald M. Simmons

1935-01-01

251

Structure and Dynamics of the Solar Corona  

NASA Astrophysics Data System (ADS)

We briefly review several aspects of the quasi-stationary structure of the corona in relation with the helio-sheet and, also, of the more confined by the magnetic field structures, including streamers, loops, jets, plumes and narrow linear rays. Both the temperature and the density structures are tentatively considered. Flows deduced from proper motions analysis are discussed. We did not include CMEs and flares in this presentation but other more radial and possibly highly impulsive beams with flows are discussed. We stress the importance of the variations of the coronal magnetic field and inferred currents in explaining the observed structures.

Koutchmy, S.

252

Rapid formation of plasma protein corona critically affects nanoparticle pathophysiology  

NASA Astrophysics Data System (ADS)

In biological fluids, proteins bind to the surface of nanoparticles to form a coating known as the protein corona, which can critically affect the interaction of the nanoparticles with living systems. As physiological systems are highly dynamic, it is important to obtain a time-resolved knowledge of protein-corona formation, development and biological relevancy. Here we show that label-free snapshot proteomics can be used to obtain quantitative time-resolved profiles of human plasma coronas formed on silica and polystyrene nanoparticles of various size and surface functionalization. Complex time- and nanoparticle-specific coronas, which comprise almost 300 different proteins, were found to form rapidly (<0.5 minutes) and, over time, to change significantly in terms of the amount of bound protein, but not in composition. Rapid corona formation is found to affect haemolysis, thrombocyte activation, nanoparticle uptake and endothelial cell death at an early exposure time.

Tenzer, Stefan; Docter, Dominic; Kuharev, Jrg; Musyanovych, Anna; Fetz, Verena; Hecht, Rouven; Schlenk, Florian; Fischer, Dagmar; Kiouptsi, Klytaimnistra; Reinhardt, Christoph; Landfester, Katharina; Schild, Hansjrg; Maskos, Michael; Knauer, Shirley K.; Stauber, Roland H.

2013-10-01

253

Rapid formation of plasma protein corona critically affects nanoparticle pathophysiology.  

PubMed

In biological fluids, proteins bind to the surface of nanoparticles to form a coating known as the protein corona, which can critically affect the interaction of the nanoparticles with living systems. As physiological systems are highly dynamic, it is important to obtain a time-resolved knowledge of protein-corona formation, development and biological relevancy. Here we show that label-free snapshot proteomics can be used to obtain quantitative time-resolved profiles of human plasma coronas formed on silica and polystyrene nanoparticles of various size and surface functionalization. Complex time- and nanoparticle-specific coronas, which comprise almost 300 different proteins, were found to form rapidly (<0.5 minutes) and, over time, to change significantly in terms of the amount of bound protein, but not in composition. Rapid corona formation is found to affect haemolysis, thrombocyte activation, nanoparticle uptake and endothelial cell death at an early exposure time. PMID:24056901

Tenzer, Stefan; Docter, Dominic; Kuharev, Jrg; Musyanovych, Anna; Fetz, Verena; Hecht, Rouven; Schlenk, Florian; Fischer, Dagmar; Kiouptsi, Klytaimnistra; Reinhardt, Christoph; Landfester, Katharina; Schild, Hansjrg; Maskos, Michael; Knauer, Shirley K; Stauber, Roland H

2013-09-22

254

Electron Density and Energy Distributions in the Positive DC Corona: Interpretation for Corona-Enhanced Chemical Reactions  

Microsoft Academic Search

Electrons produced in atmospheric pressure corona discharges are used for a variety of beneficial purposes including the destruction of gaseous contaminants, and surface treatment. In other applications, such as electrostatic precipitators and photocopiers, unintended reactions such as ozone production and deposition of silicon dioxide are detrimental. In both situations, a kinetic description of the electron distribution in the corona plasma

Junhong Chen; Jane H. Davidson

2002-01-01

255

Heating of Solar Corona and Acceleration of a Low-Speed Wind by Acoustic Waves Generated in the Corona  

Microsoft Academic Search

We investigate possibilities of solar coronal heating by acoustic waves generated not at the photosphere but in the corona, aiming at heating in the mid- to low-latitude corona where the low-speed wind is expected to come from. Acoustic waves of period tau 100 s are triggered by chromospheric reconnection, which is one model of small scale magnetic reconnection events recently

Takeru Ken Suzuki

2002-01-01

256

RADIATIVE HEATING OF THE SOLAR CORONA  

SciTech Connect

We investigate the effect of solar visible and infrared radiation on electrons in the Sun's atmosphere using a Monte Carlo simulation of the wave-particle interaction and conclude that sunlight provides at least 40% and possibly all of the power required to heat the corona, with the exception of dense magnetic flux loops. The simulation uses a radiation waveform comprising 100 frequency components spanning the solar blackbody spectrum. Coronal electrons are heated in a stochastic manner by low coherence solar electromagnetic radiation. The wave 'coherence time' and 'coherence volume' for each component is determined from optical theory. The low coherence of solar radiation allows moving electrons to gain energy from the chaotic wave field which imparts multiple random velocity 'kicks' to these particles causing their velocity distribution to broaden or heat. Monte Carlo simulations of broadband solar radiative heating on ensembles of 1000 electrons show heating at per particle levels of 4.0 x 10{sup -21} to 4.0 x 10{sup -20} W, as compared with non-loop radiative loss rates of {approx}1 x 10{sup -20} W per electron. Since radiative losses comprise nearly all of the power losses in the corona, sunlight alone can explain the elevated temperatures in this region. The volume electron heating rate is proportional to density, and protons are assumed to be heated either by plasma waves or through collisions with electrons.

Moran, Thomas G., E-mail: moran@grace.nascom.nasa.gov [Physics Department, Catholic University of America, 200 Hannan Hall, Washington, DC 20064 (United States) and NASA/GSFC, Code 671, Greenbelt, MD 20771 (United States)

2011-10-20

257

Radiative Heating of the Solar Corona  

NASA Astrophysics Data System (ADS)

We investigate the effect of solar visible and infrared radiation on electrons in the Sun's atmosphere using a Monte Carlo simulation of the wave-particle interaction and conclude that sunlight provides at least 40% and possibly all of the power required to heat the corona, with the exception of dense magnetic flux loops. The simulation uses a radiation waveform comprising 100 frequency components spanning the solar blackbody spectrum. Coronal electrons are heated in a stochastic manner by low coherence solar electromagnetic radiation. The wave "coherence time" and "coherence volume" for each component is determined from optical theory. The low coherence of solar radiation allows moving electrons to gain energy from the chaotic wave field which imparts multiple random velocity "kicks" to these particles causing their velocity distribution to broaden or heat. Monte Carlo simulations of broadband solar radiative heating on ensembles of 1000 electrons show heating at per particle levels of 4.0 10-21 to 4.0 10-20 W, as compared with non-loop radiative loss rates of ?1 10-20 W per electron. Since radiative losses comprise nearly all of the power losses in the corona, sunlight alone can explain the elevated temperatures in this region. The volume electron heating rate is proportional to density, and protons are assumed to be heated either by plasma waves or through collisions with electrons.

Moran, Thomas G.

2011-10-01

258

A gravity survey of Type 2 coronae on Venus  

NASA Astrophysics Data System (ADS)

Coronae are roughly circular tectonic features believed to form as a result of small-scale mantle upwellings. We examine the admittance signature for all the 32 Type 2 coronae (defined as having less than 50% complete fracture annuli) that are both well resolved in the gravity data and have fairly well constrained lithospheric parameters. We use top and bottom loading models to derive values of elastic thickness and crustal thickness or apparent depth of compensation. Both Cartesian and spatiospectral methods are used to calculate admittance. Overall we find reasonable agreement between the two methods. The shape of the filter used in the spatiospectral method [Simons et al., 1997] provides a means of isolating the signature of coronae that occur in close proximity to other geologic features. The narrow filters used in the Cartesian approach are useful for identifying transitions between different types of compensation, as well as for estimating error. We obtain a wide range of elastic thicknesses, from 25 to 80 km. Larger values are derived from bottom loading models, which have not been used in most prior studies of Venus. Fifteen of the coronae have elastic thickness values between 0 and 20 km and are probably isostatically compensated. Estimates of crustal and elastic thicknesses and apparent depth of compensation obtained for Type 2 coronae span the range obtained for Venus globally. Neither the thickness of the elastic lithosphere nor the crust appear to control whether Type 1 coronae, Type 2 coronae, or volcanoes form over small-scale mantle upwellings.

Smrekar, Suzanne E.; Comstock, Robert; Anderson, F. Scott

2003-08-01

259

Contact angle analysis of corona treated polypropylene films  

NASA Astrophysics Data System (ADS)

In this work, the effect of the surface modification of polypropylene films via corona treatment was investigated. Polypropylene films were treated with negative and positive corona discharge, at atmospheric pressure, for 5 minutes, at two different temperatures - 25 C and 90 C. The changes in the surface free energy were investigated by means of contact angle measurements. The Bickerman's method was applied to determine the polar and dispersion components of the polymer surface free energy, on the basis of the theory of Owens, Wendt, Kaelble and Uy. Atomic force microscopy was used to analyze the polymer surface morphology changes of the films with temperature. According to the findings, in all cases the corona treatment increases the surface free energy of polypropylene films and its polar part, in comparison with the untreated samples. The effects of negative and positive corona polarities display some specific features which could be associated with different charged group introduced onto the film surface during the corona treatment. The total final effect depends on the simultaneous action of the two competing factors - temperature and corona polarity. The most pronounced effect was observed for high temperature negative corona treatment.

Vlaeva, I.; Yovcheva, T.; Viraneva, A.; Kitova, S.; Exner, G.; Guzhova, A.; Galikhanov, M.

2012-12-01

260

R Coronae Australis: A Cosmic Watercolour  

NASA Astrophysics Data System (ADS)

This magnificent view of the region around the star R Coronae Australis was created from images taken with the Wide Field Imager (WFI) at ESO's La Silla Observatory in Chile. R Coronae Australis lies at the heart of a nearby star-forming region and is surrounded by a delicate bluish reflection nebula embedded in a huge dust cloud. The image reveals surprising new details in this dramatic area of sky. The star R Coronae Australis lies in one of the nearest and most spectacular star-forming regions. This portrait was taken by the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. The image is a combination of twelve separate pictures taken through red, green and blue filters. This image shows a section of sky that spans roughly the width of the full Moon. This is equivalent to about four light-years at the distance of the nebula, which is located some 420 light-years away in the small constellation of Corona Australis (the Southern Crown). The complex is named after the star R Coronae Australis, which lies at the centre of the image. It is one of several stars in this region that belong to the class of very young stars that vary in brightness and are still surrounded by the clouds of gas and dust from which they formed. The intense radiation given off by these hot young stars interacts with the gas surrounding them and is either reflected or re-emitted at a different wavelength. These complex processes, determined by the physics of the interstellar medium and the properties of the stars, are responsible for the magnificent colours of nebulae. The light blue nebulosity seen in this picture is mostly due to the reflection of starlight off small dust particles. The young stars in the R Coronae Australis complex are similar in mass to the Sun and do not emit enough ultraviolet light to ionise a substantial fraction of the surrounding hydrogen. This means that the cloud does not glow with the characteristic red colour seen in many star-forming regions. The huge dust cloud in which the reflection nebula is embedded is here shown in impressively fine detail. The subtle colours and varied textures of the dust clouds make this image resemble an impressionist painting. A prominent dark lane crosses the image from the centre to the bottom left. Here the visible light emitted by the stars that are forming inside the cloud is completely absorbed by the dust. These objects could only be detected by observing at longer wavelengths, by using a camera that can detect infrared radiation. R Coronae Australis itself is not visible to the unaided eye, but the tiny, tiara-shaped constellation in which it lies is easily spotted from dark sites due to its proximity on the sky to the larger constellation of Sagittarius and the rich star clouds towards the centre of our own galaxy, the Milky Way. More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

2010-06-01

261

Coronae as a result of giant magma intrusions in the lithosphere of Venus: insights from laboratory experiments  

NASA Astrophysics Data System (ADS)

Coronae on the surface of Venus are unique volcano-tectonic structures in the solar systems. Their circular morphology is associated with various topographic signatures, from bell-shape domes, flat-topped plateaus, to uplifted rings surrounding a subsided centre similar to caldera. Their extensive size and associated lava flows erupting from their periphery, indicate that they result from deep processes in the Venus mantle. Understanding their origin is thus essential for unraveling the dynamics of Venus through time. There are several scenarios explaining the formation of coronae, the most popular being the interaction between an upwelling mantle plume and the lithosphere, creating dynamic topography. In this contribution, we propose that coronae can result from the emplacement of giant magma intrusions below the Venus' lithosphere, on the basis of laboratory experiments. The experimental apparatus consists of a square box filled with compacted fine-grained silica flour (model crust), in which a low viscosity vegetable oil (model magma) is injected at constant flow rate. The initial conditions are such that magma initially flows horizontally, forming a sill-like body, to simulate magmatic underplating. During the experiments, oil injection triggers deformation of the model surface, which is monitored periodically using a moir projection device, producing time series topographic maps of the model surface. Our results show that the surface evolution of the models follows three stages: (1) initial bell-shaped doming occurs above the injection inlet, producing radial open fractures at the model surfaces; (2) the bell-shape dome evolves to a flat-topped plateau, at the rim of which the oil erupts; (3) after the injection stops, the centre of the plateau subsides, and a positive topographic ring surrounding a depression, like a caldera, remains. The collapse of the plateau also generates concentric extensional fractures at the rims of the caldera. After the dynamic experiment, the oil solidifies and we extracted the intrusion, which exhibits a sill-shape, feeding outward circular inclined sheets at its external edges (i.e. a saucer-shaped sill). From a series of experiments in which the depth of injection h was varied, we show that the diameter of the intrusion and its associated topographic structure correlates linearly with h. The three evolutionary stages simulated in the experiments reproduce remarkably well (1) the three main corona morphologies observed on Venus, and (2) their established succession through time. In addition, the relationships between the structures and the oil flow in our experiments are also similar to those observed on Venus. Therefore, our experimental results suggest that corona structures are the result of giant magma intrusions in the lithosphere of Venus. In addition, our experiments suggest that the diameters of coronae are related to the depth of emplacement of the underlying intrusions, which might be controlled by the rheological architecture of the Venus' lithosphere. Therefore, the analysis of the dimensions and morphologies of coronae are likely to provide crucial information of the structure of the lithosphere of Venus.

Galland, Olivier; Polteau, Stephane; Werner, Stephanie C.

2013-04-01

262

Ultraviolet spectroscopy of the extended solar corona  

NASA Astrophysics Data System (ADS)

The first observations of ultraviolet spectral line profiles and intensities from the extended solar corona (i.e., more than 1.5 solar radii from Sun-center) were obtained on 13 April 1979 when a rocket-borne ultraviolet coronagraph spectrometer of the Harvard-Smithsonian Center for Astrophysics made direct measurements of proton kinetic temperatures, and obtained upper limits on outflow velocities in a quiet coronal region and a polar coronal hole. Following those observations, ultraviolet coronagraphic spectroscopy has expanded to include observations of over 60 spectral lines in coronal holes, streamers, coronal jets, and solar flare/coronal mass ejection (CME) events. Spectroscopic diagnostic techniques have been developed to determine proton, electron and ion kinetic temperatures and velocity distributions, proton and ion bulk flow speeds and chemical abundances. The observations have been made during three sounding rocket flights, four Shuttle deployed and retrieved Spartan 201 flights, and the Solar and Heliospheric Observatory (SOHO) mission. Ultraviolet spectroscopy of the extended solar corona has led to fundamentally new views of the acceleration regions of the solar wind and CMEs. Observations with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO revealed surprisingly large temperatures, outflow speeds, and velocity distribution anisotropies in coronal holes, especially for minor ions. Those measurements have guided theorists to discard some candidate physical processes of solar wind acceleration and to increase and expand investigations of ion cyclotron resonance and related processes. Analyses of UVCS observations of CME plasma properties and the evolution of CMEs have provided the following: temperatures, inflow velocities and derived values of resistivity and reconnection rates in CME current sheets, compression ratios and extremely high ion temperatures behind CME shocks, and three dimensional flow velocities and magnetic field chirality in CMEs. Ultraviolet spectroscopy has been used to determine the thermal energy content of CMEs allowing the total energy budget to be known for the first time. Such spectroscopic observations are capable of providing detailed empirical descriptions of solar energetic particle (SEP) source regions that allow theoretical models of SEP acceleration to be tailored to specific events, thereby enabling in situ measurements of freshly emitted SEPs to be used for testing and guiding the evolution of SEP acceleration theory. Here we review the history of ultraviolet coronagraph spectroscopy, summarize the physics of spectral line formation in the extended corona, describe the spectroscopic diagnostic techniques, review the advances in our understanding of solar wind source regions and flare/CME events provided by ultraviolet spectroscopy and discuss the scientific potential of next generation ultraviolet coronagraph spectrometers.

Kohl, John L.; Noci, Giancarlo; Cranmer, Steven R.; Raymond, John C.

2006-04-01

263

Exploring dynamic events in the solar corona  

NASA Astrophysics Data System (ADS)

With the advent of modern computational technology it is now becoming the norm to employ detailed 3D computer models as empirical tools that directly account for the inhomogeneous nature of the Sun-Heliosphere environment. The key advantage of this approach lies in the ability to compare model results directly to observational data and to use a successful comparison (or lack thereof) to glean information on the underlying physical processes. Using extreme ultraviolet waves (EUV waves) as the overarching scientific driver, we apply this observation modeling approach to study the complex dynamics of the magnetic and thermodynamic structures that are observed in the low solar corona. Representing a highly non-trivial effort, this work includes three main scientific thrusts: an initial modeling effort and two EUV wave case-studies. First we document the development of the new Low Corona (LC) model, a 3D time-dependent thermodynamic magnetohydrodynamic (MHD) model implemented within the Space Weather Modeling Framework (SWMF). Observation synthesis methods are integrated within the LC model, which provides the ability to compare model results directly to EUV imaging observations taken by spacecraft. The new model is then used to explore the dynamic interplay between magnetic structures and thermodynamic energy balance in the corona that is caused by coronal heating mechanisms. With the model development complete, we investigate the nature of EUV waves in detail through two case-studies. Starting with the 2008 March 25 event, we conduct a series of numerical simulations that independently vary fundamental parameters thought to govern the physical mechanisms behind EUV waves. Through the subsequent analysis of the 3D data and comparison to observations we find evidence for both wave and non-wave mechanisms contributing to the EUV wave signal. We conclude with a comprehensive observation and modeling analysis of the 2010 June 13 EUV wave event, which was observed by the recently launched Solar Dynamics Observatory. We use a high resolution simulation of the transient to unambiguously characterize the globally propagating front of EUV wave as a fast-mode magnetosonic wave, and use the rich set of observations to place the many other facets of the EUV transient within a unified scenario involving wave and non-wave components.

Downs, Cooper James

264

Formation models of the multiple coronae of Venus  

NASA Astrophysics Data System (ADS)

We have analyzed the topographic and morphologic characteristics of the 62 multiple coronae [1,2,3] on the surface of Venus in order to assess their possible formation models.We have evaluated the following models: 1) Movement of the lithosphere over a stationary mantle plume [4, 5]. 2) Migration of a mantle plume or diapir under the lithosphere [4], perhaps by lithospheric channeling of the diapir [5]. 3) Emplacement of several spacially close interacting diapirs [6] either more or less synchronously or in succession [4,6]. 4) A secondary diapir arising from a larger diapir [6]. This may require a thicker lithosphere and/or more pronounced rheological layering of the lithosphere (with perhaps higher heat flow) or crust. Cybele Corona (8S, 21E; Class D [1]) may be an example of model 4 multiple corona. 5) Emplacement of an elongated diapir where diapir shape may have been influenced by the crustal/ lithospheric structure, e.g. a zone of weakness (e.g. a rift or a fracture zone) and/or stress field. Model 1 can be ruled out because Venus appears to be a one-plate planet (at least for the past 500-1000 m.yr.) where surface horizontal movements have been small. For many multiple coronae, and especially for many coronae in morphological Classes A, B, E and F [1], model 3 appears to be most simple and plausible formation mechanism. This applies especially to those multiple coronae where component structures have different topographic morphologies [2]. However, there are multiple coronae where lithospheric channeling [5] could have played a role (Oanuava Corona (32.5S, 255.5E) [5]; Class E1 [1]), and perhaps also Sandzimari Corona (11S, 339.5E; Class D [1]). In model 4, the secondary diapir could also be a magmatic diapir rising from the zone of melting on top of the main diapir. This magmatic diapir could then lead to volcanism and deformation of the crust or formation of a large magma chamber and eventually to downsagging and formation of a caldera-like secondary corona part. This could explain characteristics of some Class D multiple coronae (e.g. Ereshkigal Corona (21N, 84.5E)). Lithospheric channeling may also explain shapes and some topographic characteristics of Class D [1] multiple coronae. A few multiple coronae of Class C (e.g. Erkir Corona (16.3S, 233.7E)) may be explained by model 5, but formation by multiple diapirs cannot always be ruled out. Multiple corona morphological and topographic classes thus do not always directly imply a single formation mechanism and formation of the multiple coronae has to be evaluated case by case from geological and geophysical characteristics and interpretations. References: [1

Trmnen, T.; Aittola, M.; Kostama, V.-P.; Raitala, J.

2007-08-01

265

SZ effect from Corona Borealis supercluster  

NASA Astrophysics Data System (ADS)

The Corona Borealis supercluster has been observed with the millimeter and infrared testa grigia observatory (MITO). Here we present the results of the observations together with a comparison with observations performed at 33 GHz with the very small array (VSA) interferometer. We have observed in the direction of the supercluster toward a cosmic microwave background (CMB) cold spot previously detected in a VSA temperature map. We claim a weak detection of a faint signal compatible with a SZ effect characterized at most by a comptonization parameter y=(7.8-4.4+5.3)10 68% CL. The low level of confidence in the presence of a SZ signal invites us to study this sky region with higher sensitivity and angular resolution experiments such as already planned upgraded versions of VSA and MITO. This is the first millimetric evidence of unknown cluster/diffuse intra-supercluster gas (possibly warm hot intergalactic medium (WHIM)) interacting, via inverse Compton, scattering with the CMB.

Battistelli, E. S.; de Petris, M.; Lamagna, L.; Watson, R. A.; Rebolo, R.; Gnova-Santos, R.; Luzzi, G.; de Gregori, S.; Rubio-Martin, J. A.

2007-03-01

266

The Solar Corona: Why It Is Interesting for Us  

NASA Astrophysics Data System (ADS)

Strong magnetic fields are of vital importance to the physics of the solar corona. They easily move a rarefied coronal plasma. Physical origin of the main structural element of the corona, the so-called coronal streamers, is discussed. It is shown that the reconnecting current layers inside streamers determine their large-scale structure and evolution, including creation, disruption and recovery. Small-scale (fine) magnetic fields in the photosphere experience random motion. Their reconnection appears to be an important source of energy flux for quiet-corona heating. For active-corona heating, the peculiarities of entropy and magnetoacoustic waves, related to radiative cooling, are significant and should be taken into account in the coronal heating theory.

Somov, B. V.

2013-02-01

267

Numerical simulation of three-dimensional tuft corona and electrohydrodynamics  

SciTech Connect

The numerical simulation of three-dimensional tuft corona and electrohydrodynamics (EHD) is discussed. The importance of high-voltage and low-current operation in the wire-duct precipitator has focused attention on collecting high-resistivity dust. The local current density of individual tufts is considerably higher even at a low average current level and, therefore, could contribute to both the formation of back corona in the collected-dust layer and the generation of the secondary flow. Numerical simulation for three-dimensional tuft corona is successfully solved. The electrical characteristics of tuft corona are investigated, and the structure and role of the three-dimensional secondary flow and EHD in relation to transport of the fine particles are described.

Yamamoto, T.; Sparks, L.E.

1986-01-01

268

Static and Dynamic Calibration of a Corona Discharge Anemometer.  

National Technical Information Service (NTIS)

A Corona Discharge Anemometer (CDA) which is to be used in some balloon experiments designed to measure clear air turbulence, was tested. First a modified version of the anemometer commercially was tested statically to determine its sensitivity, its abili...

F. H. Durgin J. P. Fanucci

1976-01-01

269

Magmatic versus metamorphic origin of olivine-plagioclase coronas  

NASA Astrophysics Data System (ADS)

An SEM, REE, and mineral Sm-Nd isotope study on olivine-plagioclase coronas in the Vestre Dale gabbro, Norway, was carried out in order to solve the temporal relationships within these coronas. It is demonstrated that in contrast to common models, corona formation is a multistage, late-magmatic process, starting with the formation of orthopyroxene by (partial) dissolution of olivine, followed by the nucleation and rapid outward growth of orthopyroxene+spinel symplectites at its outer margin, and concluded by replacement of this precursory outer shell by calcic amphibole. Isotopic equilibrium between inner shell orthopyroxene and the magmatic assemblage, and the REE contents of orthopyroxene and outer shell amphibole also provide strong arguments for a magmatic origin, with the local availability of fractionated magma acting as a limiting factor. The absence of replacement of intercumulus clinopyroxene by amphibole also favours a late stage magmatic rather than a metamorphic origin for corona amphibole.

de Haas, Geert-Jan; Nijland, Timo; Valbracht, Peter; Maijer, Cees; Verschure, Rob; Andersen, Tom

2002-05-01

270

Large-Scale Volcanism Associated with Coronae on Venus.  

National Technical Information Service (NTIS)

The formation and evolution of coronae on Venus are thought to be the result of mantle upwellings against the crust and lithosphere and subsequent gravitational relaxation. A variety of other features on Venus have been linked to processes associated with...

K. M. Roberts J. W. Head

1993-01-01

271

High-tension corona controlled ozone generator for environment protection  

NASA Astrophysics Data System (ADS)

Engineering details of a high voltage driven corona-plasma ozone generator are described. The plasma diode of generator has coaxial cylindrical geometry with cathode located inside anode. Cathode is made of a large number of radial gas nozzles arranged on central tubular mast which admits oxygen gas. The sharp endings of the nozzles along with a set of corona rings create the high electric field at the cathode required for formation of dense corona plume responsible for O3 evolution. A model of coronal plasma generation and ozone production is presented. The plasma formation is strongly dependent on the electric field and temperature in side diode where a high electron density in a low temperature negative corona is suited for high ozone yields. These are established by suitable regulation of A-K gap, voltage, oxygen pressure, and cathode-nozzle population.

Vijayan, T.; Patil, Jagadish G.

2010-02-01

272

Negative corona discharge: application to nanoparticle detection in rf reactors  

NASA Astrophysics Data System (ADS)

Negative corona discharges have been studied for their possible use to detect nanoparticles in capacitively coupled plasma (CCP) reactors. Silicon nanoparticles (below 20 nm in diameter) were produced in a pulsed CCP discharge in a silane-argon-hydrogen mixture. An emissive probe with a tungsten filament biased to a sufficient negative potential (in the range 350-450 V) was used to create a negative corona in the postplasma regime when the rf power was switched off. Due to surface contamination, the probe was operated in the regime of weak electron emission to allow stable operation. Nevertheless, the filament temperature was high enough for nanoparticle deceleration/acceleration by induced thermophoretic force. It appears that positively charged nanoparticles decelerated near the filament can switch the negative corona from a pulsed (subnormal) discharge mode into a normal glow discharge mode. Hence the negative corona may have potential for detecting nanoparticles in CCP reactors operating in silane-containing mixtures.

Abolmasov, S. N.; Kroely, L.; Cabarrocas, P. Roca i.

2009-02-01

273

Nanoparticles formation and deposition in the trichel pulse corona  

NASA Astrophysics Data System (ADS)

Cathode erosion in the negative corona discharge has been studied in the point-to-plane electrode configuration with Cu cathodes in the Trichel pulse regime. Redeposition of erosion products has been found on the cathode surface in form of agglomerates of 10-nm nanoparticles. Nanocraters and nanoparticles formation in the negative corona discharge has been considered in frames of electro-explosive mechanism of cathode erosion. According to this mechanism the cathode erosion is performed as a consequence of elementary erosion events each of which is caused by a Trichel pulse. A 1-dimentional model of corona-produced nanoparticles dynamics in the gap was elaborated. According to results of the simulation, the redeposition is explained by charging of the nanoparticles due to positive ions adsorption and thermionic emission. The size, temperature and initial velocity of the aerosol nanoparticles have the decisive action on redeposition in the negative corona discharge.

Amirov, R. H.; Petrov, A. A.; Samoylov, I. S.

2013-03-01

274

A Data-Driven Evolution Model for the Global Corona  

NASA Astrophysics Data System (ADS)

In this work we have developed a new time-dependent global corona model for the study of dynamic evolution of the global corona that can respond continuously to the changing of the photospheric magnetogram. A surface flux transport (SFT) model is employed to produce the time-varying and self-consistent magnetogram with synoptic map as input. The global corona model is established with our newly-developed numerical code AMR-CESE-MHD on an overset grid of Yin-Yang overlapping structure. The SFT model and the three-dimensional global corona model is coupled through the boundary condition of projected-characteristic method. Numerical study of the coronal evolution from Carrington rotation 1913 to 1915 presents results comparable with multi-observed coronal images.

Feng, X. S.; Jiang, C.; Xiang, C. Q.; Wu, S.

2011-12-01

275

Heating of the solar corona plasma by fast electron streams  

SciTech Connect

The heating of the solar corona above active regions due to the dissipation of plasma turbulence, which is excited by energetic electron streams, is discussed. The efficiency of energy transfer from electron beams to the main plasma is estimated. It is shown that a layer of nonisothermal plasma is formed in the corona above an active region during developed type III noise storms. The role of heat conduction in the process of formation of such a layer is discussed.

Levin, B.N.

1979-11-01

276

Waste Water Cleanup by Aerosol Pulsed Corona Reactor  

Microsoft Academic Search

Summary form only given. This paper presents a study of waste water treatment by multielectrode corona reactor. A mixture of gas and polluted water aerosol flows through the 1.2-m length reactor. The flow rate is 200 l\\/h. A nanosecond solid state power supply (45 kV, 60 ns, up to 1 kHz) was used as a driver for the corona discharge.

Y. Yankelevich; M. Wolf; S. Wald; A. Pokryvailo; P. Kempenaers; L. Grabowski; E. van Veldhuizen; W. Rutgers

2007-01-01

277

Admittance survey of type 1 coronae on Venus  

NASA Astrophysics Data System (ADS)

In this study, we analyze Magellan gravity and topography data for Type 1 coronae on Venus to estimate crustal thickness (Zc), elastic thickness (Te), and apparent depth of compensation (ZL). We examine the free-air admittance for all 103 Type 1 coronae (defined as having greater than 50% complete fracture annuli) that are resolved in the gravity data. A spatio-spectral method is used to calculate a localized admittance signature of each corona from a global admittance map. This method extracts spectral information from a region in space whose area is varied as a function of degree to make it large enough to yield robust results at every individual wavelength. Elastic flexure models with either bottom- or top-loading compensation are used to fit the data. The estimated lithospheric flexural parameters span the range obtained for other topographic features on Venus, suggesting that the lithosphere on which coronae form is variable. We find no significant difference in lithospheric properties between Type 1 and 2 coronae. Fifty-four percent of all coronae are consistent with local isostasy, which may indicate that they are no longer active. Very few coronae with dome or plateau morphologies have a bottom-loading signature or the small Te and large ZL expected if a mantle plume were present. Approximately 71% have ZL estimates less than 70 km, indicating that compensation probably occurs within the crustal layer. We find no systematic relationship between Te or Zc and corona diameter, as would be expected for the spreading-drop model of formation.

Hoogenboom, Trudi; Smrekar, Suzanne E.; Anderson, F. Scott; Houseman, Greg

2004-03-01

278

Dielectric barrier discharge using corona-modified silicone rubber  

NASA Astrophysics Data System (ADS)

Results from scanning electron microscopy, Fourier transform infrared spectroscopy and the measurement of thermally stimulated current show that a high density of the physical defects and the chemical defects are introduced into the surface of the silicone rubber plates after they are treated by corona discharge plasma. These defects behave electrically as shallow electron traps, leading to the formation of a uniform discharge in air at higher pressure when the corona-modified silicone rubber is used in dielectric barrier discharge.

Li, Chengrong; Wang, Xinxin; Li, Ming; Zhan, Huamao; Xu, Jinbao; Liang, Ying; Liang, Xidong

2008-10-01

279

Magnetic fields and the structure of the solar corona  

Microsoft Academic Search

During the eclipse of 12 November 1966, the solar corona was photographed at an effective wavelength of 6500 with an f\\/16, 11.1 cm aperture camera. Reduction of the observations yields coronal radiances and polarizations from 1.4 to 3.5 solar radii. Standard techniques are used for the separation of F and K-coronas, determination of coronal electron densities and temperatures, and

Gordon Newkirk; Robert G. Dupree; Edward J. Schmhl

1970-01-01

280

Joule heating and anomalous resistivity in the solar corona  

Microsoft Academic Search

Recent radioastronomical observations of Faraday rotation in the solar corona\\u000acan be interpreted as evidence for coronal currents, with values as large as\\u000a$2.5 \\\\times 10^9$ Amperes (Spangler 2007). These estimates of currents are used\\u000ato develop a model for Joule heating in the corona. It is assumed that the\\u000acurrents are concentrated in thin current sheets, as suggested by

Steven R. Spangler

2009-01-01

281

The Temperature and Density Structure of the Quiet Solar Corona  

NASA Astrophysics Data System (ADS)

The temperature and density structure of the quiet solar corona remains unclear. In this poster, we will present a preliminary analysis of a quiet solar coronal loop structure observed with SOHO and TRACE. After determining the magnetic field structure from potential field extrapolation, we attempt to model this loop using RTV scaling laws with various heating functions. This work is in preparation for a full-scale statistical study of SOHO/TRACE data to determine the structure of the quiet solar corona.

Winebarger, A. R.; Warren, H. P.

2001-05-01

282

Positive DC Coronas with Arbitrary Outer-Conductor Geometries  

Microsoft Academic Search

The two-dimensional Poisson's equation for a positive dc corona in air with arbitrarily-shaped boundaries-is solved using numerical methods. Solutions to the problem give the potential, electric field, space charge density, ion trajectories, and current density for all points in the field of interest, and the corona current flowing to any boundary. Good agreement is obtained between the theory and experimental

Albert W. Baird

1979-01-01

283

Nanoflares and the Heating of the Solar Corona  

NASA Astrophysics Data System (ADS)

There is a simmering dispute on the heating of the solar corona. Waves or flares that is the question. New observational signatures of the heating process(es) have been revealed by observations of SoHO TRACE Yohkoh and RHESSI. The evidence for heating in the quiet corona active region loops and the solar wind are different and must be distinguished. Prime indications come from the distribution of temperature and radiation loss in relation to height the correlation of magnetic flux and brightness nanoflares and other fluctuations line broadening and waves. The reported microevents in the quiet regions are about 3 orders of magnitude smaller than microevents reported in active regions. The effects from localized energy release regardless of the energy source must be considered. In particular the reaction of the chromosphere on energy release by evaporation has an important effect on the corona. A further requirement for the heating process is to deposit most of the heat in the low corona but heat the upper corona to even higher temperature. Finally the heating process(es) must be able to account for the coronae of more active stars showing coronal emissions at levels of more than 3 orders of magnitude higher than the Sun

Benz, A. O.

2004-01-01

284

Staubbildung in den Huellen von Kohlenstoffsternen: R Coronae Borealis (Dust Production in the Envelopes of Carbon Stars: R Coronae Borealis).  

National Technical Information Service (NTIS)

A quantitative, analytic model of darkening events of R Coronae Borealis, based on phenomenological models of light decline by soot formation, with focus on causal relation between the pulsating atmosphere and episodic condensation processes, is presented...

A. Goeres

1992-01-01

285

Direct observation of a single nanoparticle-ubiquitin corona formation  

NASA Astrophysics Data System (ADS)

The advancement of nanomedicine and the increasing applications of nanoparticles in consumer products have led to administered biological exposure and unintentional environmental accumulation of nanoparticles, causing concerns over the biocompatibility and sustainability of nanotechnology. Upon entering physiological environments, nanoparticles readily assume the form of a nanoparticle-protein corona that dictates their biological identity. Consequently, understanding the structure and dynamics of a nanoparticle-protein corona is essential for predicting the fate, transport, and toxicity of nanomaterials in living systems and for enabling the vast applications of nanomedicine. Here we combined multiscale molecular dynamics simulations and complementary experiments to characterize the silver nanoparticle-ubiquitin corona formation. Notably, ubiquitins competed with citrates for the nanoparticle surface, governed by specific electrostatic interactions. Under a high protein/nanoparticle stoichiometry, ubiquitins formed a multi-layer corona on the particle surface. The binding exhibited an unusual stretched-exponential behavior, suggesting a rich binding kinetics. Furthermore, the binding destabilized the ?-helices while increasing the ?-sheet content of the proteins. This study revealed the atomic and molecular details of the structural and dynamic characteristics of nanoparticle-protein corona formation.The advancement of nanomedicine and the increasing applications of nanoparticles in consumer products have led to administered biological exposure and unintentional environmental accumulation of nanoparticles, causing concerns over the biocompatibility and sustainability of nanotechnology. Upon entering physiological environments, nanoparticles readily assume the form of a nanoparticle-protein corona that dictates their biological identity. Consequently, understanding the structure and dynamics of a nanoparticle-protein corona is essential for predicting the fate, transport, and toxicity of nanomaterials in living systems and for enabling the vast applications of nanomedicine. Here we combined multiscale molecular dynamics simulations and complementary experiments to characterize the silver nanoparticle-ubiquitin corona formation. Notably, ubiquitins competed with citrates for the nanoparticle surface, governed by specific electrostatic interactions. Under a high protein/nanoparticle stoichiometry, ubiquitins formed a multi-layer corona on the particle surface. The binding exhibited an unusual stretched-exponential behavior, suggesting a rich binding kinetics. Furthermore, the binding destabilized the ?-helices while increasing the ?-sheet content of the proteins. This study revealed the atomic and molecular details of the structural and dynamic characteristics of nanoparticle-protein corona formation. Electronic supplementary information (ESI) available: Experimental and computational methods as well as supporting figures. See DOI: 10.1039/c3nr02147e

Ding, Feng; Radic, Slaven; Chen, Ran; Chen, Pengyu; Geitner, Nicholas K.; Brown, Jared M.; Ke, Pu Chun

2013-09-01

286

The theory of positive glow corona  

NASA Astrophysics Data System (ADS)

A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions, negative ions and metastable oxygen molecules, coupled with Poisson's equation. A series of `saw-toothed' current pulses of period about 0022-3727/30/22/008/img1 is predicted with a DC current level. Accompanying the current peaks are discrete pulses of light 30 ns wide. Successive `shells' of positive ions, from successive current pulses, carry 96% of the mean current. The mean current - voltage relationship has the classic square-law form. The seed electrons required for successive pulses are detached from negative ions by metastable oxygen molecules. Photo-ionization is crucial for the discharge at the anode and for the formation of negative ions throughout the gap. The pulse frequency varies with applied voltage and is found to be approximately proportional to the positive-ion mobility. The surface electric field at the central electrode remains close to Peek's onset field. The origin of onset streamers is explained and sub-microsecond voltage pulses are found to produce streamers. The results for concentric-cylinder electrodes are described briefly.

Morrow, R.

1997-11-01

287

What Are the R Coronae Borealis Stars?  

NASA Astrophysics Data System (ADS)

The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich, supergiants, best known for their spectacular declines in brightness at irregular intervals. Efforts to discover more RCB stars have more than doubled the number known in the last few years and they appear to be members of an old, bulge population. Two evolutionary scenarios have been suggested for producing an RCB star, a double degenerate merger of two white dwarfs, or a final helium shell flash in a planetary nebula central star. The evidence pointing toward one or the other is somewhat contradictory, but the discovery that RCB stars have large amounts of 18O has tilted the scales towards the merger scenario. If the RCB stars are the product of white dwarf mergers, this would be a very exciting result since RCB stars would then be low-mass analogs of type Ia supernovae. The predicted number of RCB stars in the Galaxy is consistent with the predicted number of He/CO WD mergers. But, so far, only about sixty-five of the predicted 5,000 RCB stars in the Galaxy have been discovered. The mystery has yet to be solved.

Clayton, G. C.

2012-06-01

288

Towards a Comprehensive Model of Coronae Formation on Venus  

NASA Astrophysics Data System (ADS)

Coronae are roughly circular volcano-tectonic features that are interpreted as a manifestation of small-scale upwelling and are unique to Venus. The topographic expression of coronae is highly variable, ranging from domes to plateaus, with or without moats or single or multiple outer rises. Two outstanding questions in the study of coronae are how the full range of topographic profiles are produced and the relationship between topography and the annulus of fractures that characterize coronae. Domes, plateaus, and outer rises can be formed by thermal relaxation of a topographic high due to a rising and cooling of a hot upwelling, but interior depressions, isolated rims, and inner highs with rims, troughs and outer rises, can not. Relaxation can produce fracture annuli, but observed annuli frequently do not occur on the outer rise, as predicted by relaxation models. A new model of upwelling is presented that can produce nearly the full range of observed topographic morphologies and commonly observed off-set between tectonic fracture annuli and the outer topographic rise. The cold lithosphere at the edge of the plume head is sucked downward until the thermal anomaly dissipates, explaining the limited subduction qualities of some coronae. This model differs from past approaches to corona formation in the use of temperature-dependent rheology and the prediction of pressure-release melting. Other aspects that may be key to the development of certain coronae topographic features are the presence of a low-density depleted mantle layer beneath the high viscosity thermal lithosphere and the cooling of the thermal lithosphere during upwelling. This approach could provide constraints on thermal history.

Smrekar, S. E.; Stofan, E. R.

1996-03-01

289

MAGNETIC STRUCTURE OF RAPIDLY ROTATING FK COMAE-TYPE CORONAE  

SciTech Connect

We present a three-dimensional simulation of the corona of an FK Com-type rapidly rotating G giant using a magnetohydrodynamic model that was originally developed for the solar corona in order to capture the more realistic, non-potential coronal structure. We drive the simulation with surface maps for the radial magnetic field obtained from a stellar dynamo model of the FK Com system. This enables us to obtain the coronal structure for different field topologies representing different periods of time. We find that the corona of such an FK Com-like star, including the large-scale coronal loops, is dominated by a strong toroidal component of the magnetic field. This is a result of part of the field being dragged by the radial outflow, while the other part remains attached to the rapidly rotating stellar surface. This tangling of the magnetic field, in addition to a reduction in the radial flow component, leads to a flattening of the gas density profile with distance in the inner part of the corona. The three-dimensional simulation provides a global view of the coronal structure. Some aspects of the results, such as the toroidal wrapping of the magnetic field, should also be applicable to coronae on fast rotators in general, which our study shows can be considerably different from the well-studied and well-observed solar corona. Studying the global structure of such coronae should also lead to a better understanding of their related stellar processes, such as flares and coronal mass ejections, and in particular should lead to an improved understanding of mass and angular momentum loss from such systems.

Cohen, O.; Drake, J. J.; Kashyap, V. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Korhonen, H. [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany); Elstner, D. [Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Gombosi, T. I. [Center for Space Environment Modeling, University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109 (United States)

2010-08-10

290

Protein corona formation for nanomaterials and proteins of a similar size: hard or soft corona?  

PubMed

Nanoparticles (NPs) entering a biological fluid undergo surface modification due to dynamic, physicochemical interactions with biological components, especially proteins. In this work we used complementary bio-physico-chemical approaches to characterize the effects of interactions between CeO(2) NPs, immunoglobulins (IgGs) and bovine serum albumin (BSA) of a similar size on protein structural evolution as well as formation of (hetero-) aggregates. Using circular dichroism we showed that IgGs and BSA underwent significant structural changes after interaction with NPs. The NPs and protein-NPs were observed after size exclusion chromatography, highlighting the fact that few aggregates were stable enough to pass this mild separation step. X-ray absorption spectroscopy suggested that the surface chemistry of NPs was not affected by these proteins, also implying weak interactions. Competitive experiments revealed that, while the serum was more concentrated for BSA, IgG-NP aggregates were more stable. Altogether, our results indicate that, under our experimental conditions, the formation of a "protein corona" is an unstable and reversible mechanism. This indicates that, when NPs and proteins are similar in size, the adsorption concept (i.e. protein corona concept) cannot be applied to model the NP-protein interaction, and a heteroaggregation model is more appropriate. PMID:23334428

Liu, Wei; Rose, Jrme; Plantevin, Sophie; Auffan, Mlanie; Bottero, Jean-Yves; Vidaud, Claude

2013-02-21

291

Evidence for wave heating in the solar corona.  

PubMed

The temperature of the Sun increases over a short distance from a few thousand degrees in the photosphere to over a million degrees in the corona. To understand coronal heating is one of the major problems in astrophysics. There is general agreement that the energy source is convective motion in and below the photosphere. It remains to determine how this mechanical energy is transported outward into the corona and then deposited as heat. Two classes of models have been proposed, namely those that rely on magnetic reconnection and those that rely on waves, particularly Alfvn waves. There is increasing evidence that waves are ubiquitous in the corona. However, a difficulty for wave-driven models has been that most theories predict Alfvn waves to be undamped in the corona, and therefore they cannot dissipate their energy into heat. Our research has shown unambiguous observational evidence that the waves do damp at sufficiently low heights in the corona to be important for coronal heating. PMID:23676178

Hahn, Michael

2013-05-15

292

Reconnection-Driven Alfven (RDA) Waves in the Solar Corona  

NASA Astrophysics Data System (ADS)

The mechanisms for heating the corona and accelerating the solar wind remain active areas of solar and heliospheric research. Currently, two relatively distinct paradigms confront these problems: a waves/turbulence paradigm, and a magnetic reconnection/dissipation paradigm. The fact that magnetic reconnection generates Alfvn waves suggests that the heating of the low-beta corona and the acceleration of the wind are likely the result of both paradigms operating simultaneously. This research aims to unify the two competing viewpoints. We present 3D MHD simulations of magnetic reconnection/dissipation processes in the solar corona that provide a self-consistent mechanism for producing the energy injection spectrum required by the waves/turbulence paradigm. We analyze the simulations to quantify the amount of magnetic energy released in the reconnection process and the material and energy fluxes carried by large-amplitude, nonlinear, reconnection-driven Alfvn (RDA) waves. In addition to isolating the RDA waves, characterizing their physical properties, and investigating their evolution in a low-beta, gravitationally stratified model corona, we examine their time-dependent material and energy outflows and discuss their observable consequences in the corona and inner heliosphere.

Edmondson, J. K.; Lynch, B. J.; DeVore, C. R.; Velli, M.

2011-12-01

293

Direct observation of a single nanoparticle-ubiquitin corona formation.  

PubMed

The advancement of nanomedicine and the increasing applications of nanoparticles in consumer products have led to administered biological exposure and unintentional environmental accumulation of nanoparticles, causing concerns over the biocompatibility and sustainability of nanotechnology. Upon entering physiological environments, nanoparticles readily assume the form of a nanoparticle-protein corona that dictates their biological identity. Consequently, understanding the structure and dynamics of a nanoparticle-protein corona is essential for predicting the fate, transport, and toxicity of nanomaterials in living systems and for enabling the vast applications of nanomedicine. Here we combined multiscale molecular dynamics simulations and complementary experiments to characterize the silver nanoparticle-ubiquitin corona formation. Notably, ubiquitins competed with citrates for the nanoparticle surface, governed by specific electrostatic interactions. Under a high protein/nanoparticle stoichiometry, ubiquitins formed a multi-layer corona on the particle surface. The binding exhibited an unusual stretched-exponential behavior, suggesting a rich binding kinetics. Furthermore, the binding destabilized the ?-helices while increasing the ?-sheet content of the proteins. This study revealed the atomic and molecular details of the structural and dynamic characteristics of nanoparticle-protein corona formation. PMID:23921560

Ding, Feng; Radic, Slaven; Chen, Ran; Chen, Pengyu; Geitner, Nicholas K; Brown, Jared M; Ke, Pu Chun

2013-08-07

294

Effect of Surface Charge Control on DC Corona Onset Voltages  

NASA Astrophysics Data System (ADS)

A dielectric disc with a thickness of 0.1 cm placed on the plane electrode in a rod to plane room air gap of 2 cm long is charged by DC corona discharges with the positive and negative polarities. The dielectric discs made of acryl PMMA have six kinds of radii from 2 to 16 cm. The surface potentials induced from the accumulated surface charges are measured by a vibrating capaciting voltage meter which can be controlled in the direction of X and Y, and the effect of surface potential on the corona onset voltage is also investigated from both the laser-induced measurement of electric field and the theoretical calculation of surface potential and electric field. In order to make clear the effect of surface charge on the corona onset voltage under the same gap condition, we measure the onset voltage by using the applied voltage of same or inversed polarity to the polarity of surface charge just after the charge deposition was achieved on the dielectric disc. In the case of same polarity, the corona onset voltages increase with increasing the amount of surface charge. However, in the case of inverse polarity the corona onset voltages remarkably decrease in increase of the amount of the charge and are much lower than those without the surface charge. Also, it is surprising that in spite of short gap length 2 cm, the charging area spreads more than that with a radius of 16 cm around the disc center.

Nishijima, Kiyoto; Furuie, Shigemasa; Izawa, Yasuji

295

UVCS\\/[ITAL]SOHO[\\/ITAL] Empirical Determinations of Anisotropic Velocity Distributions in the Solar Corona  

Microsoft Academic Search

We present a self-consistent empirical model for several plasma parameters of a polar coronal hole near solar minimum, derived from observations with the Solar and Heliospheric ObservatoryUltraviolet Coronagraph Spectrometer. The model describes the radial distribution of density for electrons, H , and O and the outflow 05 1

J. L. Kohl; G. Noci; E. Antonucci; G. Tondello; M. C. E. Huber; S. R. Cranmer; L. Strachan; A. V Panasyuk; L. D. Gardner; M. Romoli; S. Fineschi; D. Dobrzycka; J. C. Raymond; P. Nicolosi; O. H. W. Siegmund; D. Spadaro; C. Benna; A. Ciaravella; S. Giordano; S. R. Habbal; M. Karovska; X. Li; R. Martin; J. G. Michels; A. Modigliani; G. Naletto; R. H. O'Neal; C. Pernechele; G. Poletto; P. L. Smith; R. M. Suleiman

1998-01-01

296

RF Multicoupler Design Techniques to Minimize Problems of Corona, Multipaction, and Stability.  

National Technical Information Service (NTIS)

A mathematical expression was derived describing multipacting and corona effects in a coaxial cavity. Both mechanical and electrical design techniques were investigated to minimize the susceptibility of coaxial cavity to corona and multipacting-type break...

D. J. Kozakoff H. S. Hurley

1971-01-01

297

Analysis of the Frequency Characteristics of Corona Discharge at Low Pressure.  

National Technical Information Service (NTIS)

Corona discharge is becoming more of a concern now that the space program is looking at higher power and voltage requirements for future missions. Improved detection methods for studying corona discharge will increase the knowledge base of how this phenom...

G. G. Karady M. D. Sirkis T. G. Lewis

1991-01-01

298

Interchange Reconnection in a Turbulent Corona  

NASA Astrophysics Data System (ADS)

Magnetic reconnection at the interface between coronal holes and loops, the so-called interchange reconnection, can release the hotter, denser plasma from magnetically confined regions into the heliosphere, contributing to the formation of the highly variable slow solar wind. The interchange process is often thought to develop at the apex of streamers or pseudo-streamers, near Y- and X-type neutral points, but slow streams with loop composition have been recently observed along fanlike open field lines adjacent to closed regions, far from the apex. However, coronal heating models, with magnetic field lines shuffled by convective motions, show that reconnection can occur continuously in unipolar magnetic field regions with no neutral points: photospheric motions induce a magnetohydrodynamic turbulent cascade in the coronal field that creates the necessary small scales, where a sheared magnetic field component orthogonal to the strong axial field is created locally and can reconnect. We propose that a similar mechanism operates near and around boundaries between open and closed regions inducing a continual stochastic rearrangement of connectivity. We examine a reduced magnetohydrodynamic model of a simplified interface region between open and closed corona threaded by a strong unipolar magnetic field. This boundary is not stationary, becomes fractal, and field lines change connectivity continuously, becoming alternatively open and closed. This model suggests that slow wind may originate everywhere along loop-coronal-hole boundary regions and can account naturally and simply for outflows at and adjacent to such boundaries and for the observed diffusion of slow wind around the heliospheric current sheet.

Rappazzo, A. F.; Matthaeus, W. H.; Ruffolo, D.; Servidio, S.; Velli, M.

2012-10-01

299

Theory of negative corona in oxygen  

NASA Astrophysics Data System (ADS)

Theoretical predictions are given of the development of the current and the distributions of charge and electric field in negative corona, or Trichel current pulses [G. W. Trichel, Phys. Rev. 54, 1078 (1938)], in oxygen at a pressure of 6.67 kPa (50 Torr). For a 10-mm-diam negative sphere located 20 mm from a positive plane, the calculated current pulse has a rise time of 11 ns, a pulse width of 50 ns, and a peak amplitude of 13 mA. These results agree satisfactorily with experimental values. The predicted velocity of the cathode-directed light pulse also agrees well with observations. The theory is based on the accurate numerical solution of Poisson's equation in conjunction with the continuity equations for electrons, positive ions, and negative ions. The effects of ionization, attachment, recombination, electron diffusion, and photoemission and ion secondary-electron emission from the cathode are all included. The initial steep rise of the current pulse is largely due to rapid ionization and electron motion in the high Laplacian field near the cathode. As the discharge develops, a dense plasma forms near the cathode, leading to strong space-charge distortion of the field. A prominent cathode fall region is formed immediately adjacent to the cathode, an almost zero field is formed within the plasma and the field is enhanced over the region to the anode. The current pulse is quenched because the low electric field in the plasma immobilizes the majority of the electrons which then undergo three-body attachment; furthermore, the cathode fall region becomes reduced to such a short distance that insignificant current is produced from this region. Because of the low mobility of the negative ions, the current remains low and the structure of the space-charge fields changes only slowly with time between pulses.

Morrow, R.

1985-09-01

300

Experimental Investigation of the Induced Airflow of Corona Discharge  

NASA Astrophysics Data System (ADS)

In order to improve the acceleration effect of corona discharge acting on air, we present an experimental study on the induced airflow produced by corona discharge between two parallel electrodes. The parameters investigated are the type of electrodes, actuation voltage and the distance in the absence of free airflow. The induced flow velocity is measured directly in the accelerated region using the particle image velocimetry technology. The results show that if corona discharge is not developed into arc discharge, the induced airflow velocity increases nearly linearly with the applied voltage and the maximum induced airflow velocity near the needle electrode reaches 36 m/s. It is expected that in the future, the result can be referred to in the research about effect of active flow control to reach much higher induced airflow speed.

Huang, Yong; Zhang, Xin; Wang, Xun-Nian; Wang, Wan-Bo; Huang, Zong-Bo; Li, Hua-Xing

2013-09-01

301

Biomolecular coronas provide the biological identity of nanosized materials.  

PubMed

The search for understanding the interactions of nanosized materials with living organisms is leading to the rapid development of key applications, including improved drug delivery by targeting nanoparticles, and resolution of the potential threat of nanotechnological devices to organisms and the environment. Unless they are specifically designed to avoid it, nanoparticles in contact with biological fluids are rapidly covered by a selected group of biomolecules to form a corona that interacts with biological systems. Here we review the basic concept of the nanoparticle corona and its structure and composition, and highlight how the properties of the corona may be linked to its biological impacts. We conclude with a critical assessment of the key problems that need to be resolved in the near future. PMID:23212421

Monopoli, Marco P; Aberg, Christoffer; Salvati, Anna; Dawson, Kenneth A

2012-12-01

302

A Laboratory Study of the Effects of Wind on DC Corona  

Microsoft Academic Search

The effects of wind on corona discharges from HV dc transmission lines were studied using two laboratory models. One model was used for studying the corona vs. wind characteristics of discrete metal projections from smooth conductors, while the other dealt with corona on stranded conductors. The investigation encompassed both 2-conductor and conductor-to-plane configurations at wind speeds up to 50 miles

M. M. Khalifa; R. M. Morris

1967-01-01

303

Characteristics of Corona Discharge in an Icicle\\/Iced-plate Electrode System under Negative DC Voltage  

Microsoft Academic Search

This paper presents the results of a series of experiments on the corona discharges occurring at icicle tips under negative DC voltage, using an icicle-iced-plate electrode system. The corona discharge development processes and the responding discharge current pulses were recorded. The influences of the gap distance, the icicle surface state and the freezing water conductivity on the corona inception voltage

M. Farzanehl; J. Zhang; D. Yu; C. Sun; W. Sima; L. Shu

2006-01-01

304

Ozone Production in the Positive DC Corona Discharge: Model and Comparison to Experiments  

Microsoft Academic Search

A numerical model of ozone generation in clean, dry air by positive DC corona discharges from a thin wire is presented. The model combines the physical processes in the corona discharge with the chemistry of ozone formation and destruction in the air stream. The distributions of ozone and nitrogen oxides are obtained in the neighborhood of the corona discharge wire.

Junhong Chen; Jane H. Davidson

2002-01-01

305

On the observation of scattered radio emission from sources in the solar corona  

Microsoft Academic Search

The effects of scattering and refraction on radio waves in the solar corona are considered for several different coronal models. By considering a source near the plasma level in a spherically symmetric corona and in a streamer enhancement superimposed on a spherically symmetric corona we obtain results relating to bursts of types I, II and III.

A. C. Riddle

1974-01-01

306

Pulse corona induced plasma chemical process: a horizon of new plasma chemical technologies  

Microsoft Academic Search

A very intense corona discharge can be produced by applying a sharp rising, narrow pulse high voltage bet- ween corona and counter electrodes of a corona system. Because of an extremely increased spark voltage electrons are highly accelerated even under ordinary gas pressure, while ions with much larger mass are not effectively accele- rated as a resuLt of too short

Senichi Masuda

1988-01-01

307

EHD study of the corona wind between wire and plate electrodes  

Microsoft Academic Search

The corona wind, with a velocity of several meters per second, is caused by applying high electric tension to bring about corona discharge in gases. In this paper the corona wind is experimentally and theoretically analyzed from an electrohydrodynamical (EHD) standpoint. Experiments have been performed mainly in nitrogen by a two-dimensional electrode arrangement of a fine wire anode and a

A. Yabe; Y. Mori; K. Hijikata

1978-01-01

308

Small Corona Cage for Wideband HVac Radio Noise Studies: Rationale and Critical Design  

Microsoft Academic Search

Corona cages are used in overhead power line studies to investigate physical mechanisms involved in corona discharge and to predict radio noise generation. In this paper, we design a small laboratory corona cage to investigate wideband radio noise generation on practical HVac conductor bundles. We introduce and describe cage design criteria including the insulation of the cage mesh. Our measurement

Rodney G. Urban; Howard C. Reader; Jacobus P. Holtzhausen

2008-01-01

309

Hot coronas of galaxies: The effects of a dark halo, the intergalactic medium, and heat conduction  

Microsoft Academic Search

The dynamics of hot coronas of galaxies is studied by numerical solution of the nonlinear equations of gas dynamics for a series of corresponding models. It is shown that the observed coronas may represent relics of a hot protogalaxy that have hardly changed in approx.10⁹ yr after the initial phase of rapid evolution. A quasisteady state and retention of coronas

A. A. Suchkov; V. G. Berman

1988-01-01

310

Extensional tilt blocks on Miranda: Evidence for an upwelling origin of Arden Corona  

Microsoft Academic Search

Subparallel ridges and troughs in the outer belt of Arden Corona, on the Uranian satellite Miranda, are interpreted as tilt blocks formed by extension and normal faulting. Fault scarps generally face outward from the corona, exposing dark material in the subsurface. Reconstruction of faults along a deep rift zone bounding the corona suggests initial dips of-50 . Local extension reaches

Robert T. Pappalardo; Stephen J. Reynolds; Ronald Greeley

1997-01-01

311

Mars solar wind interaction: Formation of the Martian corona and atmospheric loss to space  

Microsoft Academic Search

A three-dimensional (3-D) atomic oxygen corona of Mars is computed for periods of low and high solar activities. The thermal atomic oxygen corona is derived from a collisionless Chamberlain approach, whereas the nonthermal atomic oxygen corona is derived from Monte Carlo simulations. The two main sources of hot exospheric oxygen atoms at Mars are the dissociative recombination of O2+ between

J. Y. Chaufray; R. Modolo; F. Leblanc; G. Chanteur; R. E. Johnson; J. G. Luhmann

2007-01-01

312

Charging of particulates in the corona field of roll-type electroseparators  

Microsoft Academic Search

The physics of corona charging phenomena is of paramount importance for the development of such electrotechnologies as precipitation of dust, spraying of powders and selective sorting of particulate mixtures. This study focused on the use of corona discharge in electroseparation processes. Crude theoretical evaluations pointed out that the required corona current density and high-voltage level in this application depend on

L. Dascalescu; R. Morar; A. Iuga; A. Samuila; V. Neamtu; I. Suarasan

1994-01-01

313

The Structure and Dynamics of the CoronaHeliosphere Connection  

NASA Astrophysics Data System (ADS)

Determining how the heliospheric magnetic field and plasma connect to the Sun's corona and photosphere is, perhaps, the central problem in solar and heliospheric physics. For much of the heliosphere, this connection appears to be well understood. It is now generally accepted that so-called coronal holes, which appear dark in X-rays and are predominantly unipolar at the photosphere, are the sources of quasi-steady wind that is generally fast, >500 km/s, but can sometimes be slow. However, the connection to the Sun of the slow, non-steady wind is far from understood and remains a major mystery. We review the existing theories for the sources of the non-steady wind and demonstrate that they have difficulty accounting for both the observed composition of the wind and its large angular extent. A new theory is described in which this wind originates from the continuous opening and closing of narrow open field corridors in the corona, which give rise to a web of separatrices (the S-Web) in the heliosphere. Note that in this theory the coronaheliosphere connection is intrinsically dynamic, at least for this type of wind. Support for the S-Web model is derived from MHD solutions for the corona and wind during the time of the August 1, 2008 eclipse. Additionally, we perform fully dynamic numerical simulations of the corona and heliosphere in order to test the S-Web model as well as the interchange model proposed by Fisk and co-workers. We discuss the implications of our simulations for the competing theories and for understanding the coronaheliosphere connection, in general.

Antiochos, Spiro K.; Linker, Jon A.; Lionello, Roberto; Miki?, Zoran; Titov, Viacheslav; Zurbuchen, Thomas H.

2012-11-01

314

Mapping the Structure of the Corona Using Fourier Backprojection Tomography  

NASA Astrophysics Data System (ADS)

Estimating the structure, or density distribution, of the solar corona from a set of two-dimensional white-light images made by coronagraphs is a critical challenge in coronal physics. This work describes new data-analysis procedures which are used to create global maps of the coronal structure at heights where the corona becomes approximately radial (>= 3 R sun). The technique, which is named Qualitative Solar Rotational Tomography (QSRT), uses total brightness white light observations, processed with a suitable background subtraction and a Normalizing Radial Graded Filter (NRGF). These observations are made with high frequency by the Large Angle and Spectrometric Coronagraph Experiment (LASCO) C2 coronagraph, which allows a standard Fourier-transform-based tomographical reconstruction. In this paper, we first test the technique using a model corona. QSRT is then applied to a set of observations made during Carrington Rotation (CR) 2000-2001 (2003 March 16 to 2003 March 31). Since the maps are constructed from data which are normalized using the NRGF process, QSRT cannot give electron density directly. Nevertheless, the tests using the model corona demonstrate the technique's ability to give a good qualitative reconstruction of the coronal structure at high latitude, with decreasing but acceptable accuracy at the equator. These tests also demonstrate QSRT's insensitivity to noise. For the LASCO C2 observations, good agreement is found between synthetic images calculated from the reconstructed corona and the original observations, and good agreement is found between the distribution of density in a QSRT reconstruction and that found using a global MHD model. Despite their lack of quantitative information on absolute electron density, the resulting maps (which are constructed directly from high-resolution coronal data observed at the appropriate height), contain useful information on the distribution of density in the corona.

Morgan, Huw; Habbal, Shadia Rifai; Lugaz, No

2009-01-01

315

Dyspraxia or developmental coordination disorder? Unravelling the enigma  

PubMed Central

Dyspraxia is an enigma to many people, both professional and lay alikewhat is it, how does it relate to developmental coordination disorder and associated conditions, how common is it, how is it recognised and diagnosed and how should it be managed? This article attempts to unravel this enigma by: dealing with the terminology of coordination difficulties from the clumsy child syndrome through dyspraxia to developmental coordination disorder (DCD); briefly examining the debate as to whether dyspraxia or DCD should be regarded as a medical or social disorder; discussing the differential diagnosis of dyspraxia or DCD; considering the assessment of children with dyspraxia or DCD; reviewing the range of current treatment approaches in the UK.

Gibbs, John; Appleton, Jeanette; Appleton, Richard

2007-01-01

316

Is nanotechnology the key to unravel and engineer biological processes?  

PubMed

Regenerative medicine is an emerging field aiming to the development of new reparative strategies to treat degenerative diseases, injury, and trauma through developmental pathways in order to rebuild the architecture of the original injured organ and take over its functionality. Most of the processes and interactions involved in the regenerative process take place at subcellular scale. Nanotechnology provides the tools and technology not only to detect, to measure, or to image the interactions between the different biomolecules and biological entities, but also to control and guide the regenerative process. The relevance of nanotechnology for the development of regenerative medicine as well as an overview of the different tools that contribute to unravel and engineer biological systems are presented in this chapter. In addition, general data about the social impact and global investment in nanotechnology are provided. PMID:22042669

Navarro, Melba; Planell, Josep A

2012-01-01

317

Structural-flow trajectories for unravelling 3D tubular bundles.  

PubMed

We cast segmentation of 3D tubular structures in a bundle as partitioning of structural-flow trajectories. Traditional 3D segmentation algorithms aggregate local pixel correlations incrementally along a 3D stack. In contrast, structural-flow trajectories establish long range pixel correspondences and their affinities propagate grouping cues across the entire volume simultaneously, from informative to non-informative places. Segmentation by trajectory clustring recovers from persistent ambiguities caused by faint boundaries or low contrast, common in medical images. Trajectories are computed by linking successive registration fields, each one registering pairs of consecutive slices of the 3D stack. We show our method effectively unravels densely packed tubular structures, without any supervision or 3D shape priors, outperforming previous 2D and 3D segmentation algorithms. PMID:23286184

Fragkiadaki, Katerina; Zhang, Weiyu; Shi, Jianbo; Bernardis, Elena

2012-01-01

318

Unraveling the Atomic Structure of Ultrafine Iron Clusters  

PubMed Central

Unraveling the atomic structures of ultrafine iron clusters is critical to understanding their size-dependent catalytic effects and electronic properties. Here, we describe the stable close-packed structure of ultrafine Fe clusters for the first time, thanks to the superior properties of graphene, including the monolayer thickness, chemical inertness, mechanical strength, electrical and thermal conductivity. These clusters prefer to take regular planar shapes with morphology changes by local atomic shuffling, as suggested by the early hypothesis of solid-solid transformation. Our observations differ from observations from earlier experimental study and theoretical model, such as icosahedron, decahedron or cuboctahedron. No interaction was observed between Fe atoms or clusters and pristine graphene. However, preferential carving, as observed by other research groups, can be realized only when Fe clusters are embedded in graphene. The techniques introduced here will be of use in investigations of other clusters or even single atoms or molecules.

Wang, Hongtao; Li, Kun; Yao, Yingbang; Wang, Qingxiao; Cheng, Yingchun; Schwingenschlogl, Udo; Zhang, Xi Xiang; Yang, Wei

2012-01-01

319

Propagation of Radio Waves in the Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

The solar corona and solar wind are plasmas characterized by large scale MHD structures, waves, and turbulence. These introduce both systematic and random variations in the refractive index which affect the propagation of radio waves. A variety of propagation phenomena occur -- regular refraction; angular, temporal, and spectral broadening; scintillations in amplitude and phase -- widely referred to as scattering phenomena. In this tutorial I review the physical basis of these phenomena and describe a variety of techniques designed to exploit observations of scattering phenomena to deduce properties of the corona and solar wind plasma.

Bastian, T. S.

320

Protein corona formation for nanomaterials and proteins of a similar size: hard or soft corona?  

NASA Astrophysics Data System (ADS)

Nanoparticles (NPs) entering a biological fluid undergo surface modification due to dynamic, physicochemical interactions with biological components, especially proteins. In this work we used complementary bio-physico-chemical approaches to characterize the effects of interactions between CeO2 NPs, immunoglobulins (IgGs) and bovine serum albumin (BSA) of a similar size on protein structural evolution as well as formation of (hetero-) aggregates. Using circular dichroism we showed that IgGs and BSA underwent significant structural changes after interaction with NPs. The NPs and protein-NPs were observed after size exclusion chromatography, highlighting the fact that few aggregates were stable enough to pass this mild separation step. X-ray absorption spectroscopy suggested that the surface chemistry of NPs was not affected by these proteins, also implying weak interactions. Competitive experiments revealed that, while the serum was more concentrated for BSA, IgG-NP aggregates were more stable. Altogether, our results indicate that, under our experimental conditions, the formation of a ``protein corona'' is an unstable and reversible mechanism. This indicates that, when NPs and proteins are similar in size, the adsorption concept (i.e. protein corona concept) cannot be applied to model the NP-protein interaction, and a heteroaggregation model is more appropriate.Nanoparticles (NPs) entering a biological fluid undergo surface modification due to dynamic, physicochemical interactions with biological components, especially proteins. In this work we used complementary bio-physico-chemical approaches to characterize the effects of interactions between CeO2 NPs, immunoglobulins (IgGs) and bovine serum albumin (BSA) of a similar size on protein structural evolution as well as formation of (hetero-) aggregates. Using circular dichroism we showed that IgGs and BSA underwent significant structural changes after interaction with NPs. The NPs and protein-NPs were observed after size exclusion chromatography, highlighting the fact that few aggregates were stable enough to pass this mild separation step. X-ray absorption spectroscopy suggested that the surface chemistry of NPs was not affected by these proteins, also implying weak interactions. Competitive experiments revealed that, while the serum was more concentrated for BSA, IgG-NP aggregates were more stable. Altogether, our results indicate that, under our experimental conditions, the formation of a ``protein corona'' is an unstable and reversible mechanism. This indicates that, when NPs and proteins are similar in size, the adsorption concept (i.e. protein corona concept) cannot be applied to model the NP-protein interaction, and a heteroaggregation model is more appropriate. Electronic supplementary information (ESI) available: Details of control of sterile CeO2 NP suspension preparation by DLS; the fluorescence measurement data from fractional analysis of chromatographic elution; EXAFS spectra analysis of the structure of CeO2 in contact with BSA and IgG; the zeta potential measurement of NPs in different experimental media. See DOI: 10.1039/c2nr33611a

Liu, Wei; Rose, Jrme; Plantevin, Sophie; Auffan, Mlanie; Bottero, Jean-Yves; Vidaud, Claude

2013-01-01

321

High-resolution spectroscopy of the R Coronae Borealis star V Coronae Australis  

NASA Astrophysics Data System (ADS)

Optical high-resolution spectra of the R Coronae Borealis star V CrA at light maximum and during minimum light are discussed. Abundance analysis confirms previous results showing that V CrA has the composition of the small subclass of R Coronae Borealis (RCB) stars know as `minority' RCBs, i.e. the Si/Fe and S/Fe ratios are 100 times their solar values. A notable novel result for RCBs is the detection of the 1-0 Swan system 12C13C bandhead indicating that 13C is abundant: spectrum synthesis shows that 12C/13C is about 3-4. Absorption-line profiles are variable at maximum light with some lines showing evidence of splitting by about 10 kms-1. A spectrum obtained as the star was recovering from a deep minimum shows the presence of cool C2 molecules with a rotational temperature of about 1200K, a temperature suggestive of gas in which carbon is condensing into soot. The presence of rapidly outflowing gas is shown by blueshifted absorption components of the NaI D and KI 7698 resonance lines. Based on observations obtained with (1) The Blanco 4-m Telescope at the Cerro Tololo Inter-American Observatory, which is operated by AURA, Inc., under contract to the National Science Foundation of USA and (2) The Harlan J. Smith Telescope of the W. J. McDonald Observatory of the University of Texas at Austin. E-mail: nkrao@iiap.res.in

Rao, N. Kameswara; Lambert, David L.

2008-02-01

322

Joint Soviet--French investigations of the solar corona. 2. Photometry of solar corona of June 30, 1973  

SciTech Connect

The results are presented on a study of eclipse negative obtained on June 30, 1973, in Africa in the program of the Soviet--French experiment ''Dynamics of the White Corona'' by expeditions of Kiev University (Atar, Mauritania) and the Paris Astropysical Institute (Moussoro, Chad). The distributions of the total brightness of the corona out to rapprox. =4.5 R/sub sun/ and of its K and F components for the E and N directions are found with high accuracy on the basis of a new method of photometry and colorimetry using the images of stars down to 8.5/sup m/ as photometric standards. Neither reddening nor flattening of the dusty F component were detected at r<2.5 R/sub sun/. The integral brightness of the corona in the standard zone (1.03--6.0 R/sub sun/) is 0.64 x 10/sup -6/ E/sub sun/.

Vsekhsvyatskii, S.; Dzyubenko, N.; Ivanchuk, V.; Popov, O.; Rubo, G.; Koutchmy, S.; Koutchmy, O.; Stellmacher, G.

1981-03-01

323

Polymer micelles with hydrophobic core and ionic amphiphilic corona. 1. Statistical distribution of charged and nonpolar units in corona.  

PubMed

Polymer micelles with hydrophobic polystyrene (PS) core and ionic amphiphilic corona from charged N-ethyl-4-vinylpyridinium bromide (EVP) and uncharged 4-vinylpyridine (4VP) units spontaneously self-assembled from PS-block-poly(4VP-stat-EVP) macromolecules in mixed dimethylformamide/methanol/water solvent. The fraction of statistically distributed EVP units in corona-forming block is ? = [EVP]/([EVP]+[4VP]) = 0.3-1. Micelles were transferred into water via dialysis technique, and pH was adjusted to 9, where 4VP is insoluble. Structural characteristics of micelles were investigated both experimentally and theoretically as a function of corona composition ?. Methods of dynamic and static light scattering, electrophoretic mobility measurements, sedimentation velocity, transmission electron microscopy, and UV spectrophotometry were applied. All micelles possessed spherical morphology. The aggregation number, structure, and electrophoretic mobility of micelles changed in a jumplike manner near ? ~ 0.6-0.75. Below and above this region, micelle characteristics were constant or insignificantly changed upon ?. Theoretical dependencies for micelle aggregation number, corona dimensions, and fraction of small counterions outside corona versus ? were derived via minimization the micelle free energy, taking into account surface, volume, electrostatic, and elastic contributions of chain units and translational entropy of mobile counterions. Theoretical estimations also point onto a sharp structural transition at a certain corona composition. The abrupt reorganization of micelle structure at ? ~ 0.6-0.75 entails dramatic changes in micelle dispersion stability in the presence of NaCl or in the presence of oppositely charged polymeric (sodium polymethacrylate) or amphiphilic (sodium dodecyl sulfate) complexing agents. PMID:23137284

Lysenko, Evgeny A; Kulebyakina, Alevtina I; Chelushkin, Pavel S; Rumyantsev, Artem M; Kramarenko, Elena Yu; Zezin, Alexander B

2012-11-29

324

Polymer micelles with hydrophobic core and ionic amphiphilic corona. 2. Starlike distribution of charged and nonpolar blocks in corona.  

PubMed

Mixed polymer micelles with hydrophobic polystyrene (PS) core and ionic amphiphilic poly(4-vinylpyridine)/poly(N-ethyl-4-vinylpyridinium bromide) corona (P4VP/PEVP) spontaneously self-assembled from mixtures of PS-b-PEVP and PS-b-P4VP macromolecules in dimethylformamide/methanol/water selective solvent. The fraction of PEVP units in corona was ? = [PEVP]/([PEVP] + [P4VP]) = 0.05-1.0. Micelles were transferred into pure water via dialysis technique and pH was adjusted to 9, where P4VP blocks are insoluble. Structural characteristics of micelles as a function of corona composition ? were investigated. Methods of dynamic and static light scattering, electrophoretic mobility measurements, sedimentation velocity, transmission electron microscopy, and UV spectrophotometry were applied. Spherical morphology with core (PS)-shell (P4VP)-corona (PEVP) organization was postulated. Micelles demonstrated a remarkable inflection in structural characteristics near ? ~ 0.5-0.7. Above this region, aggregation number (m), core and corona radii of mixed micelles coincided with those of individual PS-b-PEVP micelles. When ? decreased below 0.5, dramatic growth of aggregation number was observed, accompanied by growth in micelle size and stretching PEVP chains. At ? below 0.2, dispersions of mixed micelles were unstable and easily precipitated upon addition of NaCl. Scaling relationships between micelle characteristics and ? were obtained via minimization the micelle free energy, taking into account electrostatic, osmotic, volume, and surface contributions. Theoretical estimations predicted dramatic influence of ? on aggregation number, m ~ ?(-3). This result is in general agreement with experimental data and confirms the correctness of the core-shell-corona model. The inflection in micelle characteristics entails drastic changes in micelle dispersion stability in the presence of oppositely charged polymeric (sodium polymethacrylate) or amphiphilic (sodium dodecyl sulfate) complexing agents. PMID:22846072

Lysenko, Evgeny A; Kulebyakina, Alevtina I; Chelushkin, Pavel S; Rumyantsev, Artem M; Kramarenko, Elena Yu; Zezin, Alexander B

2012-08-17

325

Patchy reconnection in the solar corona  

NASA Astrophysics Data System (ADS)

Magnetic reconnection in plasmas, a process characterized by a change in connectivity of field lines that are broken and connected to other ones with different topology, owes its usefulness to its ability to unify a wide range of phenomena within a single universal principle. There are newly observed phenomena in the solar corona that cannot be reconciled with two-dimensional or steady-state standard models of magnetic reconnection. Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs) descending from reconnection regions toward solar post-flare arcades seem to be two different observational signatures of retracting, isolated reconnected flux tubes with irreducible three-dimensional geometries. This dissertation describes work in refining and improving a novel model of patchy reconnection, where only a small bundle of field lines is reconnected across a current sheet (magnetic discontinuity) and forms a reconnected thin flux tube. Traditional models have not been able to explain why some of the observed SADs appear to be hot and relatively devoid of plasma. The present work shows that plasma depletion naturally occurs in flux tubes that are reconnected across nonuniform current sheets and slide trough regions of decreasing magnetic field magnitude. Moreover, through a detailed theoretical analysis of generalized thin flux tube equations, we show that the addition to the model of pressure-driven parallel dynamics, as well as temperature-dependent, anisotropic viscosity and thermal conductivity is essential for self-consistently producing gas-dynamic shocks inside reconnected tubes that heat and compress plasma to observed temperatures and densities. The shock thickness can be as long as the entire tube and heat can be conducted along tube's legs, possibly driving chromospheric evaporation. We developed a computer program that solves numerically the thin flux tube equations that govern the retraction of reconnected tubes. Simulations carried out with this program corroborate our theoretical predictions. A comparison of these simulations with fully three-dimensional magnetohydrodynamic simulations is presented to assess the validity of the thin flux tube model. We also present an observational method based on total emission measure and mean temperature to determine where in the current sheet a tube was reconnected.

Guidoni, Silvina Esther

2011-05-01

326

Simultaneous Observation of High Temperature Plasma of Solar Corona By TESIS CORONAS-PHOTON and XRT Hinode.  

NASA Astrophysics Data System (ADS)

The Mg XII spectroheliograph is a part of instrumentation complex TESIS (satellite CORONAS-PHOTON). This instrument builds monochromatic images of hot plasma of the solar corona (? = 8.42 , T>5 MK). The Mg XII spectroheliograph observed hot plasma in the non-flaring active-region NOAA 11019 during nine days. We reconstructed DEM of this active region with the help of genetic algorithm (we used data of the Mg XII spectroheliograph, XRT and EIT). Emission measure of the hot component amounts 1 % of the emission measure of the cool component.

Reva, A.; Kuzin, S.; Bogachev, S.; Shestov, S.

2012-05-01

327

The effect of ring electrodes attachment to a corona gun on control of free ion concentration and back corona for improving powder paint appearance  

Microsoft Academic Search

In a powder coating process using corona guns, only a small fraction (6%-10%) of the total ions generated during the corona discharge contribute to powder charging. Most of the remaining free ions deposit on the powder layer and on the grounded workpiece, increasing the charge-to-mass ratio (Q\\/M) of the powder layer, which contributes to the early onset of back corona.

Alexandru S. Biris; Malay K. Mazumder; Robert A. Sims; Caner U. Yurteri; Steve Farmer; Justin Snodgrass

2003-01-01

328

Radio evidence on shock wave formation in the solar corona  

Microsoft Academic Search

In order to investigate the formation of radio emitting shock waves above flaring active regions, we combine spectral and imaging observations of type II radio events with X-ray imaging and full-Sun observations and, in one case, with the extrapolated magnetic field configuration in the corona. We confirm and extend earlier findings that type II bursts are emitted above active region

A. Klassen; H. Aurass; K.-L. Klein; A. Hofmann; G. Mann

1999-01-01

329

Theoretical investigation of ozone production in negative corona discharge  

Microsoft Academic Search

The purpose of this work is to highlight the chemical kinetics in plasma of pure oxygen. A comprehensive model of ozone generation in wire-to-cylinder negative corona discharge is presented. The model combines the physical processes in the discharge with the chemistry of ozone formation. It is based on an extensive reaction scheme including the major electronic and ionic processes. The

B. Mennad; Z. Harrache; D. Amir Aid; A. Belasri

2010-01-01

330

Physicochemical modeling of positive corona discharge in carbon dioxide  

Microsoft Academic Search

Positive wire-to-cylinder corona discharge in pure CO2 has been simulated using a model that includes elementary plasma processes (ionization, electron attachment and detachment, ion recombination, etc.) and chemical reactions between neutral species. The plasma chemistry model is included in the continuity equations of species, which are coupled with Poissons equation for the electric field and the energy conservation equation for

K. Yanallah; F. Pontiga; H. Moreno; A. Castellanos

2010-01-01

331

Next-Generation Model of the Corona and Solar Wind.  

National Technical Information Service (NTIS)

A central goal of solar and space physics is to understand the influence of the sun and its activity on the heliosphere, particularly the space environment near the Earth. A quantitative description of the ambient solar corona and solar wind is key to und...

J. A. Linker

2011-01-01

332

Magnetic Dissipation in the Photosphere and Heating of the Corona  

Microsoft Academic Search

Spatio-temporal dynamics of magnetic flux tubes in the photosphere of the Sun is thought to be a driving mechanism for energy built-up and energy release phenomena in the solar atmosphere. Turbulent flows in the photosphere braid and intertwine magnetic flux tubes creating a complex topology of the magnetic field in the corona which might result in the coronal heating. Intensity

Valentyna Abramenko; A. Pevtsov

2007-01-01

333

Occultation of a Radio Star by the Solar Corona  

Microsoft Academic Search

IT has been suggested1 that the radiation from a radio star might be cut off by refraction in the solar corona, even when the angular separation of the sun and the star is several times the angular radius of the visible disk (Rsolar). The existing data on the coronal electron density have been used for predicting the effective radius of

K. E. Machin; F. G. Smith

1952-01-01

334

NUMERICAL SIMULATION OF THREE-DIMENSIONAL TUFT CORONA AND ELECTROHYDRODYNAMICS  

EPA Science Inventory

The numerical simulation of three-dimensional tuft corona and electrohydrodynamics (EHD) is discussed. The importance of high-voltage and low-current operation in the wire-duct precipitator has focused attention on collecting high-resistivity dust. The local current density of in...

335

Simulations of Jet Production in Magnetized Accretion Disk Coronae  

Microsoft Academic Search

We describe the results of over 40 MHD simulations, per- formed on Caltech\\/JPL parallel supercomputers, of the coronae of mag- netized accretion disks around compact objects. All produce some type of outflow from the disk. Our parameter study investigated the character of the outflow as a function of the strength of the initial poloidal mag- netic field and its angle

David L. Meier; Samantha Edgington; Patrick Godon; David G. Payne; Kevin R. Lind

336

OH generation in steam-air pulsed corona  

Microsoft Academic Search

The measurement of OH concentration in a pulsed corona discharge through a steam-air mixture is compared with a chemical kinetics model. The original motivation was to develop a technological hydroxilizer for oxidizing gas pollutants to acids. Time dependent measurements of the 3,064 emission of OH indicate a production of nearly 4 ppm within a spark. This measurement was accomplished

M. Garcia; B. Chang

1995-01-01

337

Energy balance of stellar coronae. II. Effect of coronal heating  

Microsoft Academic Search

Models of magnetically open regions in hot stellar coronae are computed; and their dependence on the total amount and the location of coronal heating is investigated in terms of the following characteristic quantities: the pressure at the base of the transition region; the maximum coronal temperature and the temperature at the critical point; the heights of the temperature maximum and

1982-01-01

338

37. VIEW OF SIX GAP ROTARY RECTIFIER FOR MAINTAINING CORONA ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

37. VIEW OF SIX GAP ROTARY RECTIFIER FOR MAINTAINING CORONA DISCHARGE IN THE COTTRELL ELECTROSTATIC GENERATORS. THE SYSTEM WAS CAPABLE OF PROVIDING 88,000 VOLTS TO THE ELECTRODES WITHIN THE PRECIPITATOR CHAMBER THE UNIT WAS LOCATED TO THE REAR OF BOILER 904 IN AN ENCLOSED ROOM. - New York, New Haven & Hartford Railroad, Cos Cob Power Plant, Sound Shore Drive, Greenwich, Fairfield County, CT

339

Voltage Endurance Tests of Insulating Materials Under Corona Conditions  

Microsoft Academic Search

A systematic study shows how the failure times of insulating materials exposed to corona discharges are influenced by various factors, including conductor edge surface discharge conditions, test frequency, void depth, humidity, temperature, material thickness, and average electric stress. Accelerated higher frequency tests permit testing at low-voltage stresses used continuously in applications. These yield results equivalent to 60-cps (cycles per second)

G. W. Hewitt; T. W. Dakin

1963-01-01

340

Measurement of the polarization of the solar corona  

NASA Astrophysics Data System (ADS)

The position of the polarization plane in the solar corona during the total eclipse of July 11, 1991 was measured with a rotating polaroid with the axis oriented to the radius at an angle of +/- 45 deg. The polarization plane was everywhere tangential to the solar surface with an accuracy of up to 1 percent.

Kuchmi, S.; Molodenskij, M. M.; Nikol'Skij, G. M.; Filippov, B. P.

1993-06-01

341

The cooling of flare produced plasmas in the solar corona  

Microsoft Academic Search

Solar flare X-rays, at energies less than 10 keV, are emitted by hot plasmas located in the corona. Three plasma cooling models are examined in detail. The cooling of the electrons by Coulomb collisions with ions at a lower temperature would require the observed material to occupy very large volumes. Cooling could take place by conduction or by radiation and

J. L. Culhane; J. F. Vesecky; K. J. H. Phillips

1970-01-01

342

Energy Distribution of Heating Processes in the Quiet Solar Corona  

Microsoft Academic Search

We have determined the variations in the emission measure of the solar corona using EUV Imaging Telescope\\/Solar and Heliospheric Observatory observations of iron lines in a quiet region of the Sun. The emission measure is found to vary significantly in at least 85% of all the pixels within 42 minutes. The variations are interpreted as heating events that bring chromospheric

Saem Krucker; Arnold O. Benz

1998-01-01

343

THE LOWER SOLAR CORONA: INTERPRETATION OF THE ULTRAVIOLET SPECTRUM  

Microsoft Academic Search

An analysis of the resonance lines of nine elements (27 ions) formed in ; the chromosphere and corona of the sun yields the following results: the chemical ; composition of this region of the sun can be determined, without any knowledge of ; the detailed temperature-density structure in this region; a further clue ; concerning the detailed structure of this

Stuart R. Pottasch

1963-01-01

344

Development of a complex of activity in the solar corona  

Microsoft Academic Search

Skylab observations of the Sun in soft X-rays gave us the first possibility to study the development of a complex of activity in the solar corona during its whole lifetime of seven solar rotations. The basic components of the activity complex were permanently interconnected (including across the equator) through sets of magnetic field lines, which suggests similar connections also below

Robert Howard; Zden?k vestka

1977-01-01

345

Diffusion of heavy ions in the solar corona  

Microsoft Academic Search

The steady-state diffusive motion of ionized atoms (more massive than hydrogen) in the solar corona has been investigated theoretically, with special emphasis on relating the flow velocity and density of these ions to the flow properties of the ionized hydrogen background. The basic approach taken in this study was to regard the ions as 'test particles' interacting with the background

Y. Alloucherie

1970-01-01

346

A simulation of the corona discharge by FCT method  

Microsoft Academic Search

The characteristics of corona discharge in needle to plane electrodes have been simulated by a two-dimensional fluid method. It was assumed that the transport coefficients of nitrogen gas were only the function of reduced electric field. In this discharge mechanism, Townsend first ionization and a secondary electron emission were considered. The spatio-temporal distributions of electron and ion densities at three

Seung-Kil Choi; Jae-Hak Shim; Kwang-Cheol Ko; Cheon Lee; Hyung-Boo Kang

2001-01-01

347

AC Corona in Foul Weather I-Above Freezing Point  

Microsoft Academic Search

After a brief survey of water appearance in the close-to-ground layer of atmosphere, behavior of water drops in the electric field is analyzed and the mechanism of streamer formations shown. Water influence, causing corona increase, has two components: (1) discharges between conductor and passing drops and (2) streamers produced by water presence on the conductor. Results of some attempts to

L. Boulet; B. J. Jakubczyk

1964-01-01

348

Electric winds driven by time oscillating corona discharges  

NASA Astrophysics Data System (ADS)

We investigate the formation of steady gas flows--so-called electric winds--created by point-plane corona discharges driven by time oscillating (ac) electric fields. By varying the magnitude and frequency of the applied field, we identify two distinct scaling regimes: (i) a low frequency (dc) regime and (ii) a high frequency (ac) regime. These experimental observations are reproduced and explained by a theoretical model describing the transport and recombination of ions surrounding the discharge and their contribution to the measured wind velocity. The two regimes differ in the spatial distribution of ions and in the process by which ions are consumed. Interestingly, we find that ac corona discharges generate strong electric forces localized near the tip of the point electrode, while dc corona discharges generate weaker forces distributed throughout the interelectrode region. Consequently, the velocity of the electric winds (>1 m/s) generated by ac discharges is largely independent of the position of the counter electrode. The unified theoretical description of dc and ac electric winds presented here reconciles previous observations of winds driven by dc corona and ac dielectric barrier discharges; insights from the model should also prove useful in the design of other plasma actuators.

Drews, Aaron M.; Cademartiri, Ludovico; Whitesides, George M.; Bishop, Kyle J. M.

2013-10-01

349

Fine particle counting with aerodynamic particle focusing and corona charging  

Microsoft Academic Search

The conceptual design and evaluation of a fine particle sizing and counting instrument are introduced in this paper. A corresponding laboratory prototype was developed by coupling aerodynamic particle focusing with corona charging techniques that could detect particle sizes down to 25nm in diameter. Comparison between the prototype and a condensation particle counter (CPC) using identical monodisperse particles showed that the

Z. C. Tan; A. S. Wexler

2007-01-01

350

Particle Charging in Combined Corona-Electrostatic Fields  

Microsoft Academic Search

The association of several ionizing and nonionizing electrodes generates combined corona-electrostatic fields, characterized by space charge zones of well-defined extensions. In a previous paper, the authors presented an effective numerical method for the computation of such fields. The aim of this present work is to show how these results can be employed for estimating the charge acquired by insulating and

Laurentiu Marius Dumitran; Octavian Blejan; Petru V. Notingher; Adrian Samuila; Lucian Dascalescu

2008-01-01

351

Modular ion mobility spectrometer for explosives detection using corona ionization.  

PubMed

Ion mobility spectrometry (IMS) has become the most widely used technology for trace explosives detection. A key task in designing IMS systems is to balance the explosives detection performance with size, weight, cost, and safety of the instrument. Commercial instruments are, by and large, equipped with radioactive (63)Ni ionization sources which pose inherent problems for transportation, safety, and waste disposal regulation. An alternative to a radioactive source is a corona discharge ionization source, which offers the benefits of simplicity, stability, and sensitivity without the regulatory problems. An IMS system was designed and built based on modeling and simulation with the goal to achieve a lightweight modular design that offered high performance for the detection of trace explosives using a corona ionization source. Modeling and simulations were used to investigate design alternatives and optimize parameters. Simulated spectra were obtained for 2,4,6-trinitrotoluene (TNT) and cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) and showed good agreement with experimentally measured spectra using a corona ionization source. The reduced mobilities for TNT and RDX obtained with corona ionization were 1.53 and 1.46 cm(2)/(V s), respectively, and this agreed well with literature values. PMID:21682306

Roscioli, Kristyn M; Davis, Eric; Siems, William F; Mariano, Adrian; Su, Wansheng; Guharay, Samar K; Hill, Herbert H

2011-07-08

352

Gas-magnetic field interactions in the solar corona  

Microsoft Academic Search

It is evident from eclipse photographs that gas-magnetic field interactions are important in determining the structure and dynamical properties of the solar corona and interplanetary medium. Close to the Sun in regions of strong field, the coronal gas can be contained within closed loop structures. However, since the field in these regions decreases outward rapidly, the pressure and inertial forces

G. W. Pneuman; Roger A. Kopp

1971-01-01

353

Ion Heating in the Solar Corona and Solar Wind  

Microsoft Academic Search

The solar corona is the hot, ionized outer atmosphere of the Sun that expands into interplanetary space as a supersonic solar wind. This tenuous medium is a unique laboratory for the study of magnetohydrodynamics (MHD) and plasma physics with ranges of parameters that are inaccessible on Earth. The last decade has seen significant progress toward identifying and characterizing the processes

Steven Cranmer

2009-01-01

354

Ion Cyclotron Damping in the Solar Corona and Solar Wind  

Microsoft Academic Search

The solar corona is the hot, ionized outer atmosphere of the Sun. Coronal plasma expands into interplanetary space as a supersonic bulk outflow known as the solar wind. This tenuous and unbounded medium is a unique laboratory for the study of kinetic theory in a nearly collisionless plasma, as well as magnetohydrodynamic waves, shocks, and jets. Particle velocity distributions in

Steven R. Cranmer

355

Mass and energy flow in the solar chromosphere and corona  

Microsoft Academic Search

The work reviews some investigations into the mass and energy flow in the solar chromosphere and corona; the objective of these investigations is the development of a physical model that will not only account for the physical conditions in the outer atmosphere of the sun, but can also be applied to the study of the outer atmospheres of other stars.

G. L. Withbroe; R. W. Noyes

1977-01-01

356

Possible Role of mhd Waves in Heating the Solar Corona  

Microsoft Academic Search

Heating of the solar corona by MHD waves has been investigated. Taking account of dissipation mechanisms self-consistently, a new general dispersion relation has been derived for waves propagating in a homogeneous plasma. Solution of this sixth-order dispersion relation provides information on how the damping of both slow and fast mode waves depends upon the plasma density, temperature, field strength, and

B. N. Dwivedi; V. S. Pandey

2003-01-01

357

Ion cyclotron damping in the solar corona and solar wind  

Microsoft Academic Search

The solar corona is the hot, ionized outer atmosphere of the Sun. Coronal plasma expands into interplanetary space as a supersonic bulk outflow known as the solar wind. This tenuous and unbounded medium is a unique laboratory for the study of kinetic theory in a nearly collisionless plasma, as well as magnetohydrodynamic waves, shocks, and jets. Particle velocity distributions in

Steven R. Cranmer

2001-01-01

358

Nano?ares and the Heating of the Solar Corona  

Microsoft Academic Search

New observational signatures of the heating process(es) have been revealed by space missions including SoHO, TRACE, Yohkoh, and RHESSI. Evidences for heating in the quiet corona, active region loops, and the solar wind are difierent and must be distinguished. Prime indi- cations come from line broadening and waves, the distribution of temper- ature and radiation loss in relation to height,

Arnold O. Benz

359

Catastrophic cooling and cessation of heating in the solar corona  

NASA Astrophysics Data System (ADS)

Context. Condensations in the more than 106 K hot corona of the Sun are commonly observed in the extreme ultraviolet (EUV). While their contribution to the total solar EUV radiation is still a matter of debate, these condensations certainly provide a valuable tool for studying the dynamic response of the corona to the heating processes. Aims: We investigate different distributions of energy input in time and space to investigate which process is most relevant for understanding these coronal condensations. Methods: For a comparison to observations we synthesize EUV emission from a time-dependent, one-dimensional model for coronal loops, where we employ two heating scenarios: simply shutting down the heating and a model where the heating is very concentrated at the loop footpoints, while keeping the total heat input constant. Results: The heating off/on model does not lead to significant EUV count rates that one observes with SDO/AIA. In contrast, the concentration of the heating near the footpoints leads to thermal non-equilibrium near the loop top resulting in the well-known catastrophic cooling. This process gives a good match to observations of coronal condensations. Conclusions: This shows that the corona needs a steady supply of energy to support the coronal plasma, even during coronal condensations. Otherwise the corona would drain very fast, too fast to even form a condensation. Movies are available in electronic form at http://www.aanda.org

Peter, H.; Bingert, S.; Kamio, S.

2012-01-01

360

Coronae Formation on Venus by Rayleigh-Taylor Instability  

NASA Astrophysics Data System (ADS)

In this study we explore the idea that coronae have formed on Venus as a result of gravitational (Rayleigh-Taylor) instability of the mantle lithosphere. The lithosphere is represented by a system of stratified homogeneous viscous layers (low-density crust over high-density mantle, over a lower density layer beneath the lithosphere). A small harmonic perturbation imposed on the base of the lithosphere is observed to result in gravitational instability under the constraint of assumed axisymmetry. Numerical solutions are obtained for viscous strain on the order of 200 percent or more. Topography develops with time under the influence of dynamic stress associated with downwelling or upwelling, and spatially variable crustal thickening or thinning. Axisymmetric Rayleigh-Taylor instability can produce the scale of uplift and most of the topographic forms displayed by coronae. A central upwelling mechanism is inferred for some coronae (e.g. group 3a, rim surrounding elevated central region coronae), whereas central downwelling is required for others (e.g. Group 8, depressions). Observed average coronae radii are consistent with a lithospheric thickness of only 60 km. The sign of topography is not diagnostic of central upwelling or downwelling because crustal thickness variations induced by the deformation may cause a topographic high above a downwelling or a low above an upwelling when the opposite would be observed in the absence of a crustal layer. The model calculations show, however, that the gravity anomaly is always negative above a downwelling, although its amplitude may be diminished by deformation of the crust. Using the ratio of peak gravity to peak topography anomaly removes uncertainty associated with lithospheric thickness and the density contrast between the crust and mantle. This measure depends primarily on the ratios of crust to lithospheric thickness and strength. The variation of observed gravity to topography ratios suggests spatial variability in the relative strength and thickness of the crust. Average values are consistent however with a low-density crustal layer only 10 to 20 km thick.

Hoogenboom, T.; Houseman, G. A.

2004-12-01

361

Relationship Between Corona and Radio Influence on Transmission Lines, Laboratory Studies I-Point and Conductor Corona  

Microsoft Academic Search

1. When a quasipeak-type RN meter is used for the measurement of a corona noise, it is advisable to calibrate the meter with a pulse generator. 2. A procedure of calibration and a calibration chart are given. Consistent readings have been obtained for all the meters so calibrated. 3. Within the range of measurements the RN meter readings are linearly

T. W. Liao; W. A. Keen; D. R. Powell

1957-01-01

362

Unraveling shock-induced chemistry using ultrafast lasers  

SciTech Connect

The exquisite time synchronicity between shock and diagnostics needed to unravel chemical events occurring in picoseconds has been achieved using a shaped ultrafast laser pulse to both drive the shocks and interrogate the sample via a multiplicity of optical diagnostics. The shaped laser drive pulse can produce well-controlled shock states of sub-ns duration with sub-10 ps risetimes, sufficient for investigation offast reactions or phase transformations in a thin layer with picosecond time resolution. The shock state is characterized using ultrafast dynamic ellipsometry (UDE) in either planar or Gaussian spatial geometries, the latter allowing measurements of the equation of state of materials at a range of stresses in a single laser pulse. Time-resolved processes in materials are being interrogated using UDE, ultrafast infrared absorption, ultrafast UV/visible absorption, and femtosecond stimulated Raman spectroscopy. Using these tools we showed that chemistry in an energetic thin film starts only after an induction time of a few tens of ps, an observation that allows differentiation between proposed shock-induced reaction mechanisms. These tools are presently being applied to a variety of energetic and reactive sample systems, from nitromethane and carbon disulfide, to microengineered interfaces in tunable energetic mixtures. Recent results will be presented, and future trends outlined.

Moore, David Steven [Los Alamos National Laboratory

2010-12-06

363

Unraveling condition specific gene transcriptional regulatory networks in Saccharomyces cerevisiae  

PubMed Central

Background Gene expression and transcription factor (TF) binding data have been used to reveal gene transcriptional regulatory networks. Existing knowledge of gene regulation can be presented using gene connectivity networks. However, these composite connectivity networks do not specify the range of biological conditions of the activity of each link in the network. Results We present a novel method that utilizes the expression and binding patterns of the neighboring nodes of each link in existing experimentally-based, literature-derived gene transcriptional regulatory networks and extend them in silico using TF-gene binding motifs and a compendium of large expression data from Saccharomyces cerevisiae. Using this method, we predict several hundreds of new transcriptional regulatory TF-gene links, along with experimental conditions in which known and predicted links become active. This approach unravels new links in the yeast gene transcriptional regulatory network by utilizing the known transcriptional regulatory interactions, and is particularly useful for breaking down the composite transcriptional regulatory network to condition specific networks. Conclusion Our methods can facilitate future binding experiments, as they can considerably help focus on the TFs that must be surveyed to understand gene regulation. (Supplemental material and the latest version of the MATLAB implementation of the United Signature Algorithm is available online at [1] or [see Additional files 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

Kim, Hyunsoo; Hu, William; Kluger, Yuval

2006-01-01

364

Unraveling shock-induced chemistry using ultrafast lasers  

SciTech Connect

The exquisite time synchronicity between shock and diagnostics needed to unravel chemical events occurring in picoseconds has been achieved using a shaped ultrafast laser pulse to both drive the shocks and interrogate the sample via a multiplicity of optical diagnostics. The shaped laser drive pulse can produce well-controlled shock states of sub-ns duration with sub-10 ps risetimes, sufficient for investigation of fast reactions or phase transformations in a thin layer with picosecond time resolution. The shock state is characterized using ultrafast dynamic ellipsometry (UDE) in either planar or Gaussian spatial geometries, the latter allowing measurements of the equation of state of materials at a range of stresses in a single laser pulse. Time-resolved processes in materials are being interrogated using UDE, ultrafast infrared absorption, ultrafast UV/visible absorption, and femtosecond stimulated Raman spectroscopy. Using these tools we showed that chemistry in an energetic thin film starts only after an induction time of a few tens of ps, an observation that allows differentiation between proposed shock-induced reaction mechanisms. These tools are presently being applied to a variety of energetic and reactive sample systems, from nitromethane and carbon disulfide, to micro-engineered interfaces in tunable energetic mixtures.

Moore, David S [Los Alamos National Laboratory

2009-01-01

365

Topographic characteristics of the multiple coronae on Venus: Preliminary results from measurements  

NASA Astrophysics Data System (ADS)

We have analyzed the topographic characteristics of the 63 multiple coronae [1,2] on the surface of Venus. We have defined the topographic classification for all component parts of the multiple coronae [2]. We also measured main topographic characteristics of the multiple coronae, such as basal altitude, maximum elevation, minimum depth and rim height. Multiple coronae have maximum heights (as measured relative to the basal altitude of the corona i.e. the mean altitude of the surrounding plain near the base of the corona) that range from -0.4 km to 2 km (in some multiple coronae one of the component parts may actually lie completely below the basal level of the whole corona). The arithmetic mean of maximum elevations is 0.70 km, st.dev. = 0.43 km and median = 0.66 km. The maximum relative rim heights range from 0.15 km to 1.77 km with a lognormal distribution. Geometric mean of rim height is 0.67 km with a 95% confidence interval of 0.61 km - 0.73 km. There is no statistically significant difference between mean maximum elevations, rim heights or basal elevations of Type 1 and Type 2 multiple coronae. Also, the mean rim heights of the multiple coronae parts of different topographic groups (3a, 3b, 4 and 7) do not appear to be statistically different. Initial results of the analysis of this data, including other statistical comparisons between characteristics of different topographic groups, will be reported. We are also compiling data on the larger population of coronae and arachnoids on Venus [3], and we will present some preliminary comparisons of the topographic measurements of the multiple coronae and coronae-arachnoid population as a whole. References: [1

Tormanen, T.; Aittola, M.; Kostama, P.; Raitala, J.

366

Characterization of a solid state air corona charging device  

NASA Astrophysics Data System (ADS)

Two new solid state devices which produced an atmospheric air corona discharge for generating and depositing a layer of static charge for Xerographic imaging have been fabricated and characterized. One type had a parallel plate capacitive structure and the other had an interdigitated capacitive structure. It was determined that the interdigitated capacitive structure performed better than the parallel plate capacitive structure in terms of reduced power consumption, charging current stability and device reliability. Several metal electrode material alternatives were investigated and gold electrodes performed the best. The air corona's light emission peaks were measured to be in the 350 nm to 400 nm range. Ozone gas by-product generation to ~ 13 ppm was detected for an active surface area of 5 cm^2. Charge deposition on to an imaging drum surface with a significant charging current density of 1.6E-4 A/cm^2 has been successfully demonstrated.

Young, Michael; Xu, Baomin; Buhler, Steve; Littau, Karl

2013-02-01

367

Solar corona expansion and heliospheric current sheet creation  

NASA Astrophysics Data System (ADS)

Heliospheric current sheet (CS) creation has been investigated by numerical solution of 3D MHD equations, using the PERESVET code to the problem of solar corona expansion. The dipole magnetic field corresponds to the solar activity minimum, and typical corona parameters are used as initial conditions. Plasma compression, dissipation, thermal conductivity, and gravitation are taken into account. The normal magnetic field component is an important feature of the heliospheric CS. The sheet cannot be a neutral one. Current generation is similar to action of a short closed MHD generator. The solar wind temperature is determined by plasma cooling because of plasma expansion and heat conduction from the Sun. In the process of expansion the solar wind is accelerated and achieves the supersonic velocity at a distance of about 3 solar radii. The CS is surrounded by a thick plasma sheet. Plasma velocity is decreased inside the sheet as demonstrated by previous workers.

Podgorny, I. M.; Podgorny, A. I.

2008-02-01

368

Spectral parameters of quiescent state coronae of RS CVn binaries  

NASA Astrophysics Data System (ADS)

We present analyses of quiescent state coronae of RS CVn-type binaries observed with XMM-Newton observatory. The quiescent state X-ray luminosities in the energy band of 0.3-10.0 keV of these star were found to be 10^{30-32} erg s^{-1}. Most of the stars were found to have three temperatures coronal plasma. The median value of hottest coronal temperature of these stars was found to be 2.92 keV. However, the coolest temperatures were near the 0.38 keV and 0.99 keV, respectively. The median value of global abundances of quiescent state coronae of these stars were found to be 0.14 times solar photospheric value.

Pandey, J. C.; Pant, Vaibhav

369

Nanoflares and the solar X-ray corona  

SciTech Connect

Observations of the sun with high time and spatial resolution in UV and X-rays show that the emission from small isolated magnetic bipoles is intermittent and impulsive, while the steadier emission from larger bipoles appears as the sum of many individual impulses. We refer to the basic unit of impulsive energy release as a nanoflare. The observations suggest, then, that the active X-ray corona of the sun is to be understood as a swarm of nanoflares. This interpretation suggests that the X-ray corona is created by the dissipation at the many tangential discontinuities arising spontaneously in the bipolar fields of the active regions of the sun as a consequence of random continuous motion of the footpoints of the field in the photospheric convection. The quantitative characteristics of the process are inferred from the observed coronal heat input. 105 references.

Parker, E.N.

1988-07-01

370

THE CONNECTION OF TYPE II SPICULES TO THE CORONA  

SciTech Connect

We examine the hypothesis that plasma associated with 'Type II' spicules is heated to coronal temperatures, and that the upward moving hot plasma constitutes a significant mass supply to the solar corona. One-dimensional hydrodynamical models including time-dependent ionization are brought to bear on the problem. These calculations indicate that heating of field-aligned spicule flows should produce significant differential Doppler shifts between emission lines formed in the chromosphere, transition region, and corona. At present, observational evidence for the computed 60-90 km s{sup -1} differential shifts is weak, but the data are limited by difficulties in comparing the proper motion of Type II spicules with spectral and kinematic properties of an associated transition region and coronal emission lines. Future observations with the upcoming infrared interferometer spectrometer instrument should clarify if Doppler shifts are consistent with the dynamics modeled here.

Judge, Philip G.; McIntosh, Scott W. [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000 (United States); De Pontieu, Bart [Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Building 252, Palo Alto, CA 94304 (United States); Olluri, Kosovare [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo (Norway)

2012-02-20

371

Remote sensing measurements of the corona with the Solar Probe  

NASA Astrophysics Data System (ADS)

Remote sensing measurements of the solar corona are indispensable for the exploration of the source and acceleration regions of the solar wind which are inaccessible to in situ plasma, particles and fields experiments. Furthermore, imaging the solar disk and corona from the unique vantage point of the trajectory and the proximity of the Solar Probe spacecraft, will provide the first ever opportunity to explore the small scale structures within coronal holes and streamers from viewing angles and with spatial resolutions never attained before. Imaging will also provide the essential context for the in situ measurements. The scientific advantages of different proposed imagers are summarized here. Both disk and limb observations are recommended. Given the power, weight and telemetry limitations of the Solar Probe, the optimal choice of imagers could not be provided at the time of the workshop. Further concentrated studies were highly recommended.

Rifai Habbal, Shadia; Woo, Richard

1997-01-01

372

Charging and corona modifications to the ORNL 25URC accelerator  

SciTech Connect

A chain-charge monitoring system was first installed in the 25URC accelerator in October 1982, and has provided valuable information about the charging system. Additions to the system during the past year have significantly increased the amount of information provided by the monitor. Cables connecting pickoff wheels and inductors in the terminal were improved to provide higher reliability of the charging system. The tube corona points supplied with the 25URC accelerator had a point-to-plane spacing of 0.175 inches. Our operating experience indicated that the corona currents for the normal gas pressure and voltage range of the accelerator were lower than optimum. Current-voltage characteristics of a three-needle point set were measured at several spacings and gas pressures to provide criteria for ordering new points.

Ziegler, N.F.; McPherson, R.L.

1986-11-01

373

Aspects of nonlinear magnetohydrodynamics in the solar corona  

NASA Astrophysics Data System (ADS)

The solar corona is structured by the dynamics of plasmas and magnetic fields, which, at the global scales of coronal loops, prominences and helmet streamers may be described by magnetohydrodynamics. Here we will discuss the importance and role of nonlinear interactions both in the heating of the solar corona, which relies on the transfer, storage and dissipation of the mechanical energy present in photospheric motion, and in the acceleration of the slow solar wind above helmet streamers. In the first example, nonlinear interactions including the coupling of coronal magnetic fields to the velocity field and emerging flux through the photosphere determine both the rate of heating and the resulting coronal topology. In the second example, linear resistive instabilities in develop nonlinearly to accelerate plasmoids into the slow wind. Once plasmoids are generated, the melon-seed force due to the overall magnetic field radial gradients is followed using an Expanding Box Model.

Einaudi, G.; Rappazzo, A. F.; Velli, M.; Dahlburg, R. B.

2004-04-01

374

A new mechanism for heating the solar corona  

NASA Astrophysics Data System (ADS)

The heating of the solar corona to temperatures of the order of 106 K and more is one of the outstanding problems of solar physics. Beside the high temperatures, Soho/UVCS observations have shown that heavy ions in polar corona, like O5+ and Mg9+, are heated more than protons, and that heavy ion heating is more than mass proportional; further, the perpendicular temperatures T? are much larger than parallel temperatures Tparallel . Here we show that the heating of heavy ions can be explained by ion reflection off supercritical quasi-perpendicular collisionless shocks and the subsequent acceleration by the motional electric field E = - (1/c) V B. The energization due to E is perpendicular to the magnetic field, and is more than mass proportional with respect to protons, because the heavy ion orbit is mostly upstream of the quasi-perpendicular shock foot.

Zimbardo, Gaetano

375

The degradation of organic dyes by corona discharge  

SciTech Connect

Several dyes in water were individually exposed to corona discharge. Light absorbance decreased for all organic dyes with time. Absorbance losses with methylene blue, malachite green, and new coccine were studied. The loss of color was followed using an in situ colorimeter and the effects of varying the current, voltage, gas phase, stirring rates, salinity, and electrode spacing were investigated. The highest reaction rates were observed using the highest current, highest voltage (up to 10kV), highest stirring rate, lowest salinity, smallest electrode spacing, and an environment containing enhanced levels of oxygen. Current was higher in the presence of nitrogen than in the presence of oxygen (for the same voltage), but the reaction of methylene blue did not proceed unless oxygen was present. These results help identify conditions using corona discharge in which dyes, and potentially other organics, can be destroyed. 22 refs., 5 figs.

Goheen, S.C.; McCulloch, M.; Durham, D.E.; Heath, W.O.

1992-02-01

376

Propagation Of P-modes Into The Solar Corona  

NASA Astrophysics Data System (ADS)

Magneto-hydrodynamic (MHD) wave modes are observed to propagate from the photosphere into the corona. These have the potential to be exploited as an observational tool in an analogous way to the use of acoustic waves in helio/terrestrial seismology. In regions of strong magnetic field p-modes are thought to undergo mode conversion to slow magneto-acoustic waves. New observations are presented of the propagation of these slow magneto-acoustic p-modes into the solar corona along the loops emerging from active regions. The prospects for new observations with STEREO and Solar-B are also discussed. This work is supported through the NASA post doctoral program.

Marsh, Michael

2006-06-01

377

Confirmed assignments of isomeric dimethylbenzyl radicals generated by corona discharge.  

PubMed

The controversial vibronic assignments of isomeric dimethylbenzyl radicals were clearly resolved by using different precursors. By employing corresponding dimethylbenzyl chlorides as precursors, we identified the origins of the vibronic bands of the dimethylbenzyl radicals generated by corona discharge of 1,2,4-trimethylbenzene. From the analysis of the spectra observed from the dimethylbenzyl chlorides in a corona excited supersonic expansion, we revised previous assignments of the 3,4-, 2,4-, and 2,5-dimethylbenzyl radicals. Spectroscopic data of electronic transition and vibrational mode frequencies in the ground electronic state of each isomer were accurately determined by comparing them with those obtained by an ab initio calculation and with the known vibrational data of 1,2,4-trimethylbenzene. PMID:22149790

Yoon, Young Wook; Lee, Sang Kuk

2011-12-01

378

Modelling the large scale structure of the solar corona  

NASA Astrophysics Data System (ADS)

A quantitative description of the large scale structure of magnetic field and density distribution in the coronal plasma is found. The magnetostatic model of Bogdan and Low and white light images from both NASA's Solar Maximum Mission (SMM) Coronagraph/Polarimeter and the High Altitude Observatory Mark 3 (MK3) K coronameter are used. This is an extension of previous work which used only the Mk3 data. The SMM data were considerably less noisy than the Mk3 data for radii higher than about 1.5 solar radii, particularly at mid-to-high latitude. By combining the SMM and Mk3 datasets, a density distribution that matched the white light images of the corona was more accuratly obtained. The model then allows calculation of the magnetic field and plasma characteristics (such as the coronal temperature structure) which are essential for understanding the mechanisms that heat the corona and drive the solar wind.

Gibson, Sarah; Bagenal, F.

1992-11-01

379

The Connection of Type II Spicules to the Corona  

NASA Astrophysics Data System (ADS)

We examine the hypothesis that plasma associated with "Type II" spicules is heated to coronal temperatures, and that the upward moving hot plasma constitutes a significant mass supply to the solar corona. One-dimensional hydrodynamical models including time-dependent ionization are brought to bear on the problem. These calculations indicate that heating of field-aligned spicule flows should produce significant differential Doppler shifts between emission lines formed in the chromosphere, transition region, and corona. At present, observational evidence for the computed 60-90 km s-1 differential shifts is weak, but the data are limited by difficulties in comparing the proper motion of Type II spicules with spectral and kinematic properties of an associated transition region and coronal emission lines. Future observations with the upcoming infrared interferometer spectrometer instrument should clarify if Doppler shifts are consistent with the dynamics modeled here.

Judge, Philip G.; de Pontieu, Bart; McIntosh, Scott W.; Olluri, Kosovare

2012-02-01

380

Magnetic fields and the structure of the solar corona  

Microsoft Academic Search

Several different mathematical methods are described which use the observed line-of-sight component of the photospheric magnetic field to determine the magnetic field of the solar corona in the current-free (or potential-field) approximation. Discussed are (1) a monopole method, (2) a Legendre polynomial expansion assuming knowledge of the radial photospheric magnetic field, (3) a Legendre polynomial expansion obtained from the line-of-sight

Martin D. Altschuler; Gordon Newkirk

1969-01-01

381

Ultraviolet radiation from the pulsed corona discharge in water  

Microsoft Academic Search

Quantitative analysis of ultraviolet radiation from the pulsed corona discharge in water with needle-plate electrode geometry (~1-3 J pulse-1) was performed using the potassium ferrioxalate actinometry. Photon flux J190-280 and radiant energy Q190-280 of the UV light emitted from the discharge at spectral region 190-280 nm was determined in dependence on the applied voltage (17-29 kV, positive polarity) and the

Petr Lukes; Martin Clupek; Vaclav Babicky; Pavel Sunka

2008-01-01

382

Catalytic oxidation of benzene using DBD corona discharges  

Microsoft Academic Search

Plasma oxidation of benzene (C6H6) in oxygen and nitrogen was investigated using a dielectric barrier discharge (DBD) reactor with or without MnO2 or TiO2 at atmospheric pressure and without external heating except plasma heating. An alternative current power supply was used to generate corona discharges for the plasma oxidation. The energy density was controlled under 200J\\/L to keep an increase

B. Lu; X. Zhang; X. Yu; T. Feng; S. Yao

2006-01-01

383

Peptide fragmentation by corona discharge induced electrochemical ionization  

Microsoft Academic Search

Fundamental studies have greatly improved our understanding of electrospray, including the underlying electrochemical reactions.\\u000a Generally regarded as disadvantageous, we have recently shown that corona discharge (CD) can be used as an effective method\\u000a to create a radical cation species [M]+., thus optimizing the electrochemical reactions that occur on the surface of the stainless steel (SS) electrospray capillary\\u000a tip. This technique

John R. Lloyd; Sonja Hessb

2010-01-01

384

Abatement of NOx with Propene Activated by Corona Plasmas  

Microsoft Academic Search

This paper presents an improved wire-to-plate type plasma reactor for remediation of flue gas containing NOx\\/SO2, in which a nozzle electrode for injection of de-NOx additive was installed in the front of wire electrodes to enhance the production of de-NOx radicals. The experimental results indicate that additive activated by corona plasmas could effectively increase NOx removal in a wire-plate type

Kefeng Shang; Yan Wu

2009-01-01

385

Rigid and differential rotation of the solar corona  

Microsoft Academic Search

The rotation of the solar corona has been studied using recurrence properties of the green coronal line (5303 ) for the interval 19471970. Short-lived coronal activity is found to show the same differential rotation as short-lived photospheric magnetic field features. Long-lived recurrences show rigid rotation in the latitude interval 57.5. It is proposed that at least part of the variability

Ester Antonucci; Leif Svalgaard

1974-01-01

386

DIRECT MEASUREMENTS OF MAGNETIC TWIST IN THE SOLAR CORONA  

SciTech Connect

In the present work, we study the evolution of magnetic helicity in the solar corona. We compare the rate of change of a quantity related to the magnetic helicity in the corona to the flux of magnetic helicity through the photosphere and find that the two rates are similar. This gives observational evidence that helicity flux across the photosphere is indeed what drives helicity changes in the solar corona during emergence. For the purposes of estimating coronal helicity, we neither assume a strictly linear force-free field nor attempt to construct a nonlinear force-free field. For each coronal loop evident in extreme ultraviolet, we find a best-matching line of a linear force-free field and allow the twist parameter {alpha} to be different for each line. This method was introduced and its applicability discussed in Malanushenko et al. The object of this study is emerging and rapidly rotating AR 9004 over about 80 hr. As a proxy for coronal helicity, we use the quantity ({alpha}{sub i} L{sub i} /2) averaged over many reconstructed lines of magnetic field. We argue that it is approximately proportional to the 'flux-normalized' helicity H/{Phi}{sup 2}, where H is the helicity and {Phi} is the total enclosed magnetic flux of the active region. The time rate of change of such a quantity in the corona is found to be about 0.021 rad hr{sup -1}, which is comparable with the estimates for the same region obtained using other methods, which estimated the flux of normalized helicity to be about 0.016 rad hr{sup -1}.

Malanushenko, A.; Longcope, D. W. [Department of Physics, Montana State University, Bozeman, MT 59717 (United States); Yusuf, M. H. [Berea College, Berea, KY 40404 (United States)

2011-08-01

387

Numerical Simulation of Three-Dimensional Tuft Corona and Electrohydrodynamics  

Microsoft Academic Search

The importance of high-voltage and low-current operation in the wire-duct precipitator has focused attention on collecting high-resistivity dust. The local current density of individual tufts is considerably higher even at a low average current level and therefore could contribute to both the formation of back corona in the collected-dust layer and the generation of the secondary flow. Numerical simulation for

Toshiaki Yamamoto; Leslie E. Sparks

1986-01-01

388

Effects of HV Conductor Aging Surface Elements, on Corona Characteristics  

Microsoft Academic Search

\\u000a For power lines with operating voltages in excess of 400 kV, the key environmental factors of the design are generally imposed\\u000a measures taken to limit radio and audible noise generated by corona. In this study a chemical analysis of the long term formatted\\u000a black coating on the surface of differently treated single stranded aluminium conductors, was carried out. The effect

Nick. A. Tsoligkas

389

ESTIMATING THE ''DARK'' ENERGY CONTENT OF THE SOLAR CORONA  

SciTech Connect

The discovery of ubiquitous low-frequency (3-5 mHz) Alfvenic waves in the solar chromosphere (with Hinode/Solar Optical Telescope) and corona (with CoMP and SDO) has provided some insight into the non-thermal energy content of the outer solar atmosphere. However, many questions remain about the true magnitude of the energy flux carried by these waves. Here we explore the apparent discrepancy in the resolved coronal Alfvenic wave amplitude ({approx}0.5 km s{sup -1}) measured by the Coronal Multi-channel Polarimeter (CoMP) compared to those of the Hinode and the Solar Dynamics Observatory (SDO) near the limb ({approx}20 km s{sup -1}). We use a blend of observational data and a simple forward model of Alfvenic wave propagation to resolve this discrepancy and determine the Alfvenic wave energy content of the corona. Our results indicate that enormous line-of-sight superposition within the coarse spatio-temporal sampling of CoMP hides the strong wave flux observed by Hinode and SDO and leads to the large non-thermal line broadening observed. While this scenario has been assumed in the past, our observations with CoMP of a strong correlation between the non-thermal line broadening with the low-amplitude, low-frequency Alfvenic waves observed in the corona provide the first direct evidence of a wave-related non-thermal line broadening. By reconciling the diverse measurements of Alfvenic waves, we establish large coronal non-thermal line widths as direct signatures of the hidden, or ''dark'', energy content in the corona and provide preliminary constraints on the energy content of the wave motions observed.

McIntosh, Scott W. [High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 (United States); De Pontieu, Bart, E-mail: mscott@ucar.edu [Lockheed Martin Solar and Astrophysics Lab, 3251 Hanover St., Org. A021S, Bldg. 252, Palo Alto, CA 94304 (United States)

2012-12-20

390

Experimental studies with HCI by CORONA group at TMU  

NASA Astrophysics Data System (ADS)

The aim of the CORONA project was to study targets after collisions with highly charged ions (HCI) as a part of a research project `Atomic Physics of Multi-Charged Ions'. Experimental results were obtained in four areas: (1) differential cross section measurements of electron-ion collisions, (2) snap shots of highly charged molecular ions produced by electron capture reactions of HCI, (3) polarization spectroscopy of charge transfer reactions, and (4) sputtering and deformation of solid surfaces by slow HCI.

Kobayashi, Nobuo

2004-01-01

391

X-ray coronae in simulations of disc galaxy formation  

NASA Astrophysics Data System (ADS)

The existence of X-ray luminous gaseous coronae around massive disc galaxies is a long-standing prediction of galaxy formation theory in the cold dark matter cosmogony. This prediction has garnered little observational support, with non-detections commonplace and detections for only a relatively small number of galaxies which are much less luminous than expected. We investigate the coronal properties of a large sample of bright, disc-dominated galaxies extracted from the GIMIC suite of cosmological hydrodynamic simulations recently presented by Crain et al. Remarkably, the simulations reproduce the observed scalings of X-ray luminosity with K-band luminosity and star formation rate (SFR) and, when account is taken of the density structure of the halo, with disc rotation velocity as well. Most of the star formation in the simulated galaxies (which have realistic stellar mass fractions) is fuelled by gas cooling from a quasi-hydrostatic hot corona. However, these coronae are more diffuse, and of a lower luminosity, than predicted by the analytic models of White & Frenk because of a substantial increase in entropy at z ~ 1-3. Both the removal of low entropy gas by star formation and energy injection from supernovae contribute to this increase in entropy, but the latter is dominant for halo masses M200 <~ 1012.5Msolar. Only a small fraction of the mass of the hot gas is outflowing as a wind but, because of its high density and metallicity, it contributes disproportionally to the X-ray emission. The bulk of the X-ray emission, however, comes from the diffuse quasi-hydrostatic corona which supplies the fuel for ongoing star formation in discs today. Future deep X-ray observations with high spectral resolution (e.g. with NeXT/ASTRO-H or IXO) should be able to map the velocity structure of the hot gas and test this fundamental prediction of current galaxy formation theory.

Crain, Robert A.; McCarthy, Ian G.; Frenk, Carlos S.; Theuns, Tom; Schaye, Joop

2010-09-01

392

Hetero-coagulation of polymeric core-corona microspheres  

Microsoft Academic Search

Hetero-coagulation between polystyrene core-poly(vinylamine) (PVAmMS) and poly(methacrylic acid) corona microspheres in an aqueous phase was studied by quantitative analysis of precipitated microspheres, absorbance change of mixed dispersions using UV-Vis spectroscopy, transmittance electron microscopy (TEM) observation, hydrodynamic particle size measurement, and ?-potential analysis. It was found that a 12-h incubation was enough for the formation of hetero-coagulation. The microspheres were electrostatically

Takeshi Serizawa; Kouta Taniguchi; Mitsuru Akashi

2000-01-01

393

Long term storage of relativistic particles in the solar corona  

Microsoft Academic Search

A model is presented which shows that large numbers of energetic electrons (0.3-> 10 MeV) and protons (130 MeV) can be stored in the solar corona at altitudes around 3 105 km for periods in excess of 5 days. Specific reference is made to the time period July 616 1968 as an excellent example of energetic solar particle storage.

George M. Simnett; Stephen S. Holt

1971-01-01

394

Possible Role of mhd Waves in Heating the Solar Corona  

Microsoft Academic Search

Heating of the solar corona by MHD waves has been investigated. Taking account of dissipation mechanisms self-consistently,\\u000a a new general dispersion relation has been derived for waves propagating in a homogeneous plasma. Solution of this sixth-order\\u000a dispersion relation provides information on how the damping of both slow and fast mode waves depends upon the plasma density,\\u000a temperature, field strength, and

B. N. Dwivedi; V. S. Pandey

2003-01-01

395

Formation and Investigation of Corona Charged Films from Polylactic Acid  

Microsoft Academic Search

The aim of the present work is the development of technology for formation of corona charged electret films from polylactic acid and investigation of their structural, optical and electret properties. Polylactide films with different degree of crystalinity were prepared by casting of poly-L-lactide and poly-DL lactide blended solutions. Then glass transition, crystallization and melting temperatures, as well as the crystalinity

E. A. Gencheva; T. A. Yovcheva; M. G. Marudova; A. P. Viraneva; I. P. Bodurov; G. A. Mekishev; S. H. Sainov

2010-01-01

396

Unraveling hidden regulatory sites in structurally homologous metalloproteases.  

PubMed

Monitoring enzymatic activity in vivo of individual homologous enzymes such as the matrix metalloproteinases (MMPs) by antagonist molecules is highly desired for defining physiological and pathophysiological pathways. However, the rational design of antagonists targeting enzyme catalytic moieties specific to one of the homologous enzymes often appears to be an extremely difficult task. This is mainly due to the high structural homology at the enzyme active sites shared by members of the protein family. Accordingly, controlling enzymatic activity via alternative allosteric sites has become an attractive proposition for drug design targeting individual homologous enzymes. Yet, the challenge remains to identify such regulatory alternative sites that are often hidden and scattered over different locations on the protein's surface. We have designed branched amphiphilic molecules exhibiting specific inhibitory activity towards individual members of the MMP family. These amphiphilic isomers share the same chemical nature, providing versatile nonspecific binding reactivity that allows to probe hidden regulatory residues on a given protein surface. Using the advantage provided by amphiphilic ligands, here we explore a new approach for determining hidden regulatory sites. This approach includes diverse experimental analysis, such as structural spectroscopic analyses, NMR, and protein crystallography combined with computational prediction of effector binding sites. We demonstrate how our approach works by analyzing members of the MMP family that possess a unique set of such sites. Our work provides a proof of principle for using ligand effectors to unravel hidden regulatory sites specific to members of the structurally homologous MMP family. This approach may be exploited for the design of novel molecular effectors and therapeutic agents affecting protein catalytic function via interactions with structure-specific regulatory sites. PMID:23583775

Udi, Yael; Fragai, Marco; Grossman, Moran; Mitternacht, Simon; Arad-Yellin, Rina; Calderone, Vito; Melikian, Maxime; Toccafondi, Mirco; Berezovsky, Igor N; Luchinat, Claudio; Sagi, Irit

2013-04-11

397

Enhanced Neon in the Coronae of HR 1099  

NASA Astrophysics Data System (ADS)

Chandra HETG spectra of the tidally interacting RS CVn-type binary HR 1099 (V711 Tau) have been analysed in order to investigate the abundances of elements in the coronae of the system. Analogous to the results of previous studies based on EUVE and ASCA observations, the high resolution X-ray spectrum is characterised by a general paucity of metals relative to the solar photosphere, but perhaps simply reflects the underlying stellar photospheric metallicity. The most striking feature of the spectrum, however, is the very strong Ly-? feature in H-like Ne. The only plausible explanation for the strength of the Ne lines is that the abundance of Ne in the coronae of HR 1099 is strongly enhanced relative to that of Fe, as compared to the solar (photospheric) mixture. We discuss the implications of this result in the context of stellar coronae and coronal abundances anomalies, draw attention to possible solar coronal analogies to the phenomena, and suggest possible reasons for the Ne enhancement. JJD, NSB, VK, BW and RS were supported by Chandra X-ray Center NASA contract NAS8-39073.

Drake, J. J.; Brickhouse, N. S.; Kashyap, V.; Smith, R.; Wargelin, B.; Laming, J. M.; Huenemoerder, D. P.

2000-10-01

398

Large-scale structure of the solar corona magnetic field  

NASA Astrophysics Data System (ADS)

The configuration of the solar corona magnetic field has been studied. Data on the position of the K-corona emission polarization plane during the solar eclipses of September 21, 1941; February 25, 1952; and August 1, 2008, were used as an indicator of the magnetic field line orientation. Based on an analysis of these data, a conclusion has been made that the studied configuration has a large-scale organization in the form of a cellular structure with an alternating field reversal. The estimated cell size was 61 6 (or 36 2) in longitude with a latitudinal extension of 40-50 in the range of visible distances 1.3-2.0 R Sun . A comparison of the detected cellular structure of the coronal magnetic field with synoptic {ie908-1} maps indicated that the structure latitudinal boundaries vary insignificantly within 1.1-2.0 R Sun . The possible causes of the formation of the magnetic field large-scale cellular configuration in the corona and the conditions for the transformation of this configuration into a two-sector structure are discussed.

Merzlyakov, V. L.; Starkova, L. I.

2012-12-01

399

Formation and Investigation of Corona Charged Films from Polylactic Acid  

NASA Astrophysics Data System (ADS)

The aim of the present work is the development of technology for formation of corona charged electret films from polylactic acid and investigation of their structural, optical and electret properties. Polylactide films with different degree of crystalinity were prepared by casting of poly-L-lactide and poly-DL lactide blended solutions. Then glass transition, crystallization and melting temperatures, as well as the crystalinity degree were determined by a differential scanning calorimetry. The charging of the samples in a corona discharge was carried out by means of a conventional corona triode system. Sample surface potential was measured by the method of the vibrating electrode with compensation. The time dependences of the sample surface potential under room conditions were studied for 50 days. The effect of lower pressure on the surface potential of charged samples was investigated. It was established that the reduced pressure leaded to the surface potential decay of the PLA electrets. The same effect was earlier observed for other polymer films. The optical characteristics-surface refractive index and optical dispersion, were determined by the method of the disappearing diffraction pattern using a laser refractometer.

Gencheva, E. A.; Yovcheva, T. A.; Marudova, M. G.; Viraneva, A. P.; Bodurov, I. P.; Mekishev, G. A.; Sainov, S. H.

2010-01-01

400

Ion Heating in the Solar Corona and Solar Wind  

NASA Astrophysics Data System (ADS)

The solar corona is the hot, ionized outer atmosphere of the Sun that expands into interplanetary space as a supersonic solar wind. This tenuous medium is a unique laboratory for the study of magnetohydrodynamics (MHD) and plasma physics with ranges of parameters that are inaccessible on Earth. The last decade has seen significant progress toward identifying and characterizing the processes that heat the corona and accelerate the solar wind, but the basic physics is still unclear. Some key clues about the mechanisms responsible for energizing the plasma have come from UV spectroscopy of the extended corona (i.e., using a combination of an occulting coronagraph and a spectrometer). There is evidence for preferential acceleration of heavy ions in the fast solar wind, ion temperatures exceeding 100 million K, and marked departures from Maxwellian velocity distributions. These collisionless departures from thermal equilibrium point to specific types of kinetic processes. This presentation reviews the measurements (both telescopic and from `in situ' probes) that constrain theoretical explanations and provides a current survey of the landscape of proposed ideas for ion energization. Many of the suggested processes are related to the dissipation of MHD waves (e.g., ion cyclotron waves), and many involve multiple steps of energy conversion between waves, turbulence, current sheets, and other nonlinear plasma features. A discussion of future measurements that could help to test, refine, and possibly winnow down the list of competing models will also be presented.

Cranmer, Steven

2009-05-01

401

Joule heating and anomalous resistivity in the solar corona  

NASA Astrophysics Data System (ADS)

Recent radioastronomical observations of Faraday rotation in the solar corona can be interpreted as evidence for coronal currents, with values as large as 2.5109 Amperes (Spangler, 2007). These estimates of currents are used to develop a model for Joule heating in the corona. It is assumed that the currents are concentrated in thin current sheets, as suggested by theories of two dimensional magnetohydrodynamic turbulence. The Spitzer result for the resistivity is adopted as a lower limit to the true resistivity. The calculated volumetric heating rate is compared with an independent theoretical estimate by Cranmer et al. (2007). This latter estimate accounts for the dynamic and thermodynamic properties of the corona at a heliocentric distance of several solar radii. Our calculated Joule heating rate is less than the Cranmer et al estimate by at least a factor of 3105. The currents inferred from the observations of Spangler (2007) are not relevant to coronal heating unless the true resistivity is enormously increased relative to the Spitzer value. However, the same model for turbulent current sheets used to calculate the heating rate also gives an electron drift speed which can be comparable to the electron thermal speed, and larger than the ion acoustic speed. It is therefore possible that the coronal current sheets are unstable to current-driven instabilities which produce high levels of waves, enhance the resistivity and thus the heating rate.

Spangler, S. R.

2009-06-01

402

Further Results on the Rotation of the Solar Corona  

NASA Astrophysics Data System (ADS)

Synoptic photoelectric observations of the coronal Fe XIV and Fe X emission lines at 530.3 nm and 637.4 nm, respectively, are analyzed to study the rotational behavior of the solar corona as a function of latitude, height and time. The data used are measurements made with the Sacramento Peak 40-cm coronagraph and Emission-Line Coronal Photometer of the intensity of these lines observed at 1.15 to 1.45 solar radii (Ro) between 1973 (1984 for Fe X) and 2000. An earlier similar temporal-correlation analysis of the Fe XIV data at 1.15 Ro over only one 11-year solar activity cycle (Sime, Fisher and Altrock 1989, Astrophys. J. 336, 454) found suggestions of solar-cycle variations in the differential-rotation and latitude-averaged-rotation patterns that combined the effects of large-scale patterns seen in the white-light corona and smaller-scale patterns seen in chromospheric and photospheric rotation. These results will be tested over the longer epoch now available. In addition, the new 1.15 Ro Fe XIV results will be compared with those at greater heights and with results from the Fe X line and radio frequencies (Vats et al. 2001, Astrophys. J., 548, L87) to form a global picture of solar rotation throughout the corona and over more than two solar cycles.

Altrock, R. C.

2001-12-01

403

Direct Impact Corona Ionization of Bacteria for Rapid, Reproducible Identification via Spectral Pattern Recognition  

Microsoft Academic Search

A novel atmospheric pressure ionization process, Direct Impact Corona Ionization (DICI), is described here. In this process, a corona impinges onto the flat surface of a stainless steel pin carrying a thin film of dried bacterial suspension, the analyte. Two electrodes--a corona electrode and the sample pin--are immersed in hot inert He gas flux, flowing past them towards a 0.4

Pierre Alusta; Dan Buzatu; Olga Tarasenko; Jon Wilkes; Jerry Darsey

2011-01-01

404

The effect of corona discharge on dust mite and cat allergens  

Microsoft Academic Search

Corona discharge has previously been reported to destroy the house dust mite allergen Der p1. This present paper describes the efficacy of corona discharge to destroy three more clinically important allergens and investigates the factors that affect this process. Using Der p1, Der p2, Der f1 and Fel d1 the allergen reducing efficacies of both negative and positive corona, of

Neil Goodman; John F Hughes

2004-01-01

405

Aerosol Charge Neutralization by a Mixing-Type Bipolar Charger using Corona Discharge at High Pressure  

Microsoft Academic Search

An aerosol neutralizer called the Mixing-type Bipolar Charger using Corona-Discharge at High Pressure (MBCCHP) was developed. In the MBCCHP, a corona discharge (High-Pressure Corona Ionizer; HPC Ionizer) induced by high frequency voltage (>100 Hz) at high pressure (>0.2 MPa) is used to generate bipolar ions at high concentration (13 10 ions\\/cm) that are then mixed with aerosol particles flowing

S. Kimoto; K. Mizota; M. Kanamaru; H. Okuda; D. Okuda; M. Adachi

2009-01-01

406

Energy Release in a Magnetized Resistive Corona Driven by Continuous Footpoint Motions  

Microsoft Academic Search

The solar corona is a highly conducting plasma (Lundquist number S 10^10-13). As such, Ohmic dissipation is negligible except within thin current filaments. In his corona heating model, Parker suggests that thin current filaments can be induced in a magnetized corona via the shuffling of the field lines driven by continuous footpoint motions. We study this model with a three-dimensional

Yi-Min Huang; Dalton Schnack; Ellen G. Zweibel; Zoran Mikic

2006-01-01

407

SemiEmpirical 2-D MHD Model of the Solar corona and Solar Wind: Energy Flow in the Corona  

Microsoft Academic Search

We have developed a semi-empirical 2-D MHD model of the solar corona and solar wind for which the major data inputs are white\\u000a light coronagraph data and plasma and magnetic field data from the Ulysses spacecraft. With regard to the white light coronagraph data we have used data from Spartan 201-05 to construct our empirical\\u000a models of the electron density

Ed Sittler; Madhullika Guhathakurta; Ruth Skoug

2001-01-01

408

Correlation between UV radiation intensity and current strength during corona discharge  

NASA Astrophysics Data System (ADS)

The ratio of optical pulse numbers to corona current (ROPC) is proposed to study the correlation between UV radiation intensity and current strength during AC corona discharge. It's found that the ROPC curves rose rapidly before a critical voltage and then the curves flatten with the supplied voltage rising, even if the voltage is increased approximately 1 fold higher than the critical voltage. Finally, according to ROPC curves, a new method of determining the voltage for corona inception is introduced, and a novel quantitative analysis method is put forward to judge the level of corona discharge by the means of optical measurement.

Wu, Ligang; Yuan, Yonggang; Yan, Haojun; Liang, Shuaiwei; Wang, Lun; Cheng, Peihong; Wang, Hongtao; Hu, Jinsong

2012-10-01

409

Old and young coronae on Venus - Combining regional and global studies to constrain thermal evolution models  

NASA Astrophysics Data System (ADS)

Coronae on Venus have been studied extensively: globally they have been characterized according to morphology, tectonics and associated volcanism, and are generally inferred to be the result of mantle upwelling. Previous studies based on impact crater densities at coronae and geological syntheses suggest a global stratigraphy for Venus in which coronae are relatively young features. However, recent mapping indicates that regionally a significant fraction of coronae have formation onset ages comparable to the ages of regional plains, and that more detailed models are required to explain the long and complex evolution of individual coronae. The question of the duration of corona formation on Venus since the last global resurfacing event (GRE) has an important bearing on thermal evolution models and the style of mantle convection. We attempt to reconcile these apparently conflicting global and local perspectives by combining a regional geological study of coronae at E. Eistla Regio and results from other recent mapping with a revised global study of impact crater densities at coronae. We integrate our results with estimates of lithospheric thickness from topographic flexure at coronae and gravity/topography admittance to develop firmer constraints on thermal evolution models.

Johnson, Catherine L.; Hargrave, Eric V.; Simons, Mark; Solomon, Sean C.

1997-03-01

410

Surface roughness effects on the corona discharge intensity of long-term operating conductors  

NASA Astrophysics Data System (ADS)

An investigation into the effect of surface roughness on corona discharge intensity of long-term operating conductors is presented. The electric field distortion level was found to increase linearly with surface average roughness Ra. At the corona inception voltages, the ionization intensity ? in the ionization zone was calculated, it would increase exponentially with the raise of Ra. As a result, the corona discharge intensity of long-term operating conductors was stronger, and the corona inception voltages were lower than those of the new conductors. The deviation of radio noise and audible noise was found to increase linearly with the raise of Ra.

Bian, X. M.; Chen, L.; Yu, D. M.; Wang, L. M.; Guan, Z. C.

2012-10-01

411

Dynamics of Nanoparticle-Protein Corona Complex Formation: Analytical Results from Population Balance Equations  

PubMed Central

Background Nanoparticle-protein corona complex formation involves absorption of protein molecules onto nanoparticle surfaces in a physiological environment. Understanding the corona formation process is crucial in predicting nanoparticle behavior in biological systems, including applications of nanotoxicology and development of nano drug delivery platforms. Method This paper extends the modeling work in to derive a mathematical model describing the dynamics of nanoparticle corona complex formation from population balance equations. We apply nonlinear dynamics techniques to derive analytical results for the composition of nanoparticle-protein corona complex, and validate our results through numerical simulations. Results The model presented in this paper exhibits two phases of corona complex dynamics. In the first phase, proteins rapidly bind to the free surface of nanoparticles, leading to a metastable composition. During the second phase, continuous association and dissociation of protein molecules with nanoparticles slowly changes the composition of the corona complex. Given sufficient time, composition of the corona complex reaches an equilibrium state of stable composition. We find analytical approximate formulae for metastable and stable compositions of corona complex. Our formulae are very well-structured to clearly identify important parameters determining corona composition. Conclusion The dynamics of biocorona formation constitute vital aspect of interactions between nanoparticles and living organisms. Our results further understanding of these dynamics through quantitation of experimental conditions, modeling results for in vitro systems to better predict behavior for in vivo systems. One potential application would involve a single cell culture medium related to a complex protein medium, such as blood or tissue fluid.

Darabi Sahneh, Faryad; Scoglio, Caterina; Riviere, Jim

2013-01-01

412

Pulsed corona discharge at atmospheric and supercritical conditions  

NASA Astrophysics Data System (ADS)

Pulsed corona discharge is one of the non-equilibrium plasma techniques, by which electrical power is mainly utilized to generate high-energy electrons. These react further with the background gas to produce radicals, which can be further employed in chemically selective reactions. Study of the initiation of pulsed corona discharge in carbon dioxide and air was conducted. Furthermore due to its high removal efficiency, energy yields and good economy, the pulsed corona discharge was employed for removal of methanol and dimethyl sulfide. These compounds are part of the volatile organic compounds (VOC) air pollutants, which are subject of severe environmental regulations due to their toxicity, environmental persistence and intensity of smell. The study provides experimental data for the destruction of methanol and dimethyl sulfide from dry and humid air streams. The effects of the process parameters, including applied voltage, pulse repetition rate, initial concentration of pollutants, temperature and humidity on the destruction and removal efficiency and energy cost are analyzed. Specific consideration is given to the formation of unwanted byproducts. The study on plasma application for pollution control showed that small amounts of dispersed liquid droplets increase the efficiency of the chemical utilization of the high-energy electrons and reduce the required power. So media that could facilitate homogeneous and heterogeneous chemistry at the same time would enhance the efficiency of the removal process. Such medium that has properties intermediate between the gas and liquid phase is the supercritical fluid. Generation of plasma in supercritical fluids is an unexplored area in plasma science. The generation of plasma at elevated pressures usually requires high voltages or small interelectrode distances. The supercritical phase is characterized by extensive cluster formation in the vicinity of the critical point. Typically the clusters have lower ionization potentials, which in turn reduce the required breakdown voltages. This study provides an experimental database for pulsed streamer breakdown in supercritical conditions over a wide range of supercritical conditions.

Lock, Evgeniya Hristova

413

New Constraints on Plasma Turbulence in the Solar Corona  

NASA Astrophysics Data System (ADS)

One suggestion for coronal heating invokes the dissipation of high frequency, Alfvn-ion cyclotron waves which are generated in the photosphere and chromosphere and propagate into the corona. As we have previously noted (Spangler and Mancuso 2000, ApJ 530, 491) the properties of such waves can be constrained by radioastronomical observations. The observational effect is Faraday screen depolarization, in which stochastic Faraday rotation randomizes the polarization position angle on scales smaller than the telescope beam. We present observations made with the NRAO Very Large Array on August 16 and 18, 2003, when the radio galaxy 3C228 was viewed through the corona at heliocentric distances of 6.7 and 5.2 R?, respectively. The depolarization parameter D ? (m)/(m0) was measured, where m is the fractional linear polarization measured through the corona, and m0 is the intrinsic degree of polarization. Measurements were available for both hot spots of 3C228, and on both days of observation. The measurements are consistent with D=1 for both components on both days. These results are in agreement with, but superior to, previous reports of no coronal screen depolarization. Equations from Spangler and Mancuso (2000) are used to constrain the dimensionless amplitude and outer scale of the coronal turbulence. Turbulence with a dimensionless amplitude of 50 % or greater, and outer scale larger than 1000-2000 km, would have produced depolarization close to, or in excess of our limits. Turbulence with smaller dimensionless amplitude and outer scale would not have been detected with these measurements. This research was supported by grant ATM-0354782 from the National Science Foundation.

Spangler, S. R.; Spitler, L. G.

2005-12-01

414

Hot Carbon Corona in Mars Upper Thermosphere and Exosphere  

NASA Astrophysics Data System (ADS)

The production of energetic particles results in the formation of the hot corona, where the most of the escape of neutral atoms occur, in the Martian upper atmosphere. In order to investigate the dynamics of these energetic neutral atoms, we have carried out a study that provides a self-consistent global description of the hot corona in the upper thermosphere and exosphere by employing a self-consistent global kinetic model coupled with a thermosphere/ionosphere model. In this work, we evaluate the carbon atom inventory by studying the production and distribution of energetic carbon atoms. The most important source reactions for hot atomic carbon are expected to be photodissociation of CO and dissociative recombination of CO+, which are highly sensitive to solar activity and occur mostly deep in the dayside of the thermosphere. The latest available branching ratios is adopted, and appropriate choices of the rate coefficient and the photodissociation frequencies are made. In this study, we simulate the variations of the hot carbon corona over the solar cycle and seasons. The spatial distributions and profiles of density and temperature, atmospheric loss rates are discussed for the cases considered. The total global escape of hot carbon from all dominant photochemical processes is computed and compared with those from other previous models. To describe self-consistently the upper thermosphere and exosphere, a combination of our 3D Direct Simulation Monte Carlo (DSMC) model [Valeille, A., Combi, M., Bougher, S., Tenishev, V., Nagy, A., 2009. J. Geophys. Res. 114, E11006. doi:10.1029/2009JE003389] and the 3D Mars Thermosphere General Circulation Model (MTGCM) [Bougher, S. W., Bell, J. M., Murphy, J. R., Lopez-Valverde, M. A., Withers, P. G., 2006. Geophys. Res. Lett. 32, doi: 10.1029/2005GL024059. L02203] is used. Finally, our computed global total escape rate of hot carbon ranges ~ (5.2 - 57.1) 1023 s-1 for the aphelion solar low to perihelion solar high case.

Lee, Yuni; Combi, M.; Tenishev, V.; Bougher, S.

2013-10-01

415

Desorption corona beam ionization source for mass spectrometry.  

PubMed

A novel Desorption Corona Beam Ionization (DCBI) source for direct analysis of samples from surface in mass spectrometry is reported. The DCBI source can work under ambient conditions without time-consuming sample pretreatments. The source shares some common features with another ionization source - Direct Analysis in Real Time (DART), developed earlier. For example, helium was used as the discharge gas (although only corona discharge is involved in the present source), and heating of the discharge gas is required for sample desorption. However, the difference between the two sources is substantial. In the present source, a visible thin corona beam extending out around 1 cm can be formed by using a hollow needle/ring electrode structure. This feature would greatly facilitate localizing sampling areas and performing imaging/profiling experiments. The DCBI source is also capable of performing progressive temperature scans between room temperature and 450 degrees C in order to sequentially desorb samples from the surface and, therefore, to achieve a rough separation of the individual components in a complex mixture, resulting in less congestion in the mass spectrum acquired. Mass spectra for a broad range of compounds (pesticides, veterinary additives, OTC drugs, explosive materials) have been acquired using the DCBI source. For most of the compounds tested, the heater temperature required for efficient desorption is at least 150 degrees C. The molecular weight of the sample that can be desorbed/ionized is normally below 600 dalton even at the highest heater temperature, which is mainly limited by the volatility of the sample. PMID:20349536

Wang, Hua; Sun, Wenjian; Zhang, Junsheng; Yang, Xiaohui; Lin, Tao; Ding, Li

2010-04-01

416

Vortex focusing of ions produced in corona discharge.  

PubMed

Completeness of the ion transportation into an analytical path defines the efficiency of ionization analysis techniques. This is of particular importance for atmospheric pressure ionization sources like corona discharge, electrospray, ionization with radioactive ((3)H, (63)Ni) isotopes that produce nonuniform spatial distribution of sample ions. The available methods of sample ion focusing are either efficient at reduced pressure (~1Torr) or feature high sample losses. This paper deals with experimental research into atmospheric pressure focusing of unipolar (positive) ions using a highly swirled air stream with a well-defined vortex core. Effects of electrical fields from corona needle and inlet capillary of mass spectrometer on collection efficiency is considered. We used a corona discharge to produce an ionized unipolar sample. It is shown experimentally that with an electrical field barrier efficient transportation and focusing of an ionized sample are possible only when a metal plate restricting the stream and provided with an opening covered with a grid is used. This gives a five-fold increase of the transportation efficiency. It is shown that the electric field barrier in the vortex sampling region reduces the efficiency of remote ionized sample transportation two times. The difference in the efficiency of light ion focusing observed may be explained by a high mobility and a significant effect of the electric field barrier upon them. It is possible to conclude based on the experimental data that the presence of the field barrier narrows considerably (more than by one and half) the region of the vortex sample ion focusing. PMID:23618173

Kolomiets, Yuri N; Pervukhin, Viktor V

2013-02-14

417

Constant cross section of loops in the solar corona  

NASA Astrophysics Data System (ADS)

Context. The corona of the Sun is dominated by emission from loop-like structures. When observed in X-ray or extreme ultraviolet emission, these million K hot coronal loops show a more or less constant cross section. Aims: In this study we show how the interplay of heating, radiative cooling, and heat conduction in an expanding magnetic structure can explain the observed constant cross section. Methods: We employ a three-dimensional magnetohydrodynamics (3D MHD) model of the corona. The heating of the coronal plasma is the result of braiding of the magnetic field lines through footpoint motions and subsequent dissipation of the induced currents. From the model we synthesize the coronal emission, which is directly comparable to observations from, e.g., the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO). Results: We find that the synthesized observation of a coronal loop seen in the 3D data cube does match actually observed loops in count rate and that the cross section is roughly constant, as observed. The magnetic field in the loop is expanding and the plasma density is concentrated in this expanding loop; however, the temperature is not constant perpendicular to the plasma loop. The higher temperature in the upper outer parts of the loop is so high that this part of the loop is outside the contribution function of the respective emission line(s). In effect, the upper part of the plasma loop is not bright and thus the loop actually seen in coronal emission appears to have a constant width. Conclusions: From this we can conclude that the underlying field-line-braiding heating mechanism provides the proper spatial and temporal distribution of the energy input into the corona - at least on the observable scales. Movies associated to Figs. 1 and 2 are available in electronic form at http://www.aanda.org

Peter, H.; Bingert, S.

2012-12-01

418

Evaporation of stars from clusters, with the development of coronas and moving clusters  

SciTech Connect

Because of the irregular forces of the star field surrounding it, a star cluster can develop a corona. This process will operate efficiently for open clusters but not for globular clusters. As the central structure of an open cluster decays, some of its stars will escape into the general field while others will enter the corona of the cluster.

Agekyan, T.A.; Belozerova, M.A.

1979-01-01

419

A method to detect the deterioration of HTV silicone rubber under corona discharge  

Microsoft Academic Search

This paper has investigated the thermally stimulated current (TSC) characteristics of the deteriorated HTV silicone rubber under varied corona discharge duration, the hydrophobicity, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) of the corresponding test samples have also been measured. The experimental results show that the TSC characteristics of HTV silicone rubber gradually varied with the corona deterioration process,

Ying Liang; Lijian Ding; C. R. Li; Kun Yang; Youping Tu

2006-01-01

420

Heavy ion reflection and heating by collisionless shocks in polar solar corona  

Microsoft Academic Search

We propose a new model for explaining the observations of preferential heating of heavy ions in the polar solar corona. We consider that a large number of small scale shock waves can be present in the solar corona, as suggested by recent observations of polar coronal jets by the Hinode and STEREO spacecraft. The heavy ion energization mechanism is, essentially,

Gaetano Zimbardo

2011-01-01

421

Heating the polar corona by collisionless shocks: an example of cross-fertilization in space physics  

Microsoft Academic Search

We propose a new model for explaining the observations of preferential heating of heavy ions in the polar solar corona. We consider that a large number of small scale shock waves can be present in the solar corona, as suggested by recent observations of polar coronal jets. The heavy ion energization mechanism is, essentially, the ion reflection off supercritical quasi-perpendicular

Gaetano Zimbardo; Giuseppe Nistico

2010-01-01

422

Silver discharge electrode for suppression of ozone generation in positive dc corona  

Microsoft Academic Search

The aim of this paper is to suppress the ozone production in dc corona discharges, and is to report the effect of material of the discharge electrode on the ozone production. In this study, corona discharges were generated in a coaxial wire-cylinder reactor stressed by positive or negative dc voltage. A set of high purity wires made of different metals,

A. Yehia; A. Mizuno

2005-01-01

423

Corona emission and ozone production by carbonized and oxidized high-voltage wires  

Microsoft Academic Search

High-voltage wires exhibit corona discharges that cause emission of ozone. Precipitation, dirt, and wire imperfections have been shown in earlier works to increase both processes by a factor of up to 50. Here, a small coaxial cylinder setup is used to quantify the effects of volatile organic atmospheres and wire oxidation on corona and ozone production. With both positive and

Mara E. M. Horwitz; S. Gray Horwitz; Chris M. Horwitz

2006-01-01

424

Experimental study of a multipoint cathode corona in an argon flow  

SciTech Connect

Results are presented from experimental studies of a multipoint negative corona in an atmospheric-pressure argon flow. It is shown that a decrease in the interpoint distance, gas circulation through the discharge gap, and the adjustment of ballast resistances in the corona supply circuit allow one to stabilize the discharge and enlarge the operating range of discharge currents.

Baldanov, B. B. [Russian Academy of Sciences, Department of Physical Problems, Buryat Science Center, Siberian Branch (Russian Federation)

2009-07-15

425

Analysis of Corona Losses on DC Transmission Lines Part II - Bipolar Lines  

Microsoft Academic Search

As in the case of unipolar corona, theoretical calculation of corona losses for bipolar dc transmission line configurations involves the analysis of the nonlinear ionized field in the interelectrode region. However, the complexity of the analysis is increased considerably because of the presence of ions of both polarities in the region.

Maruvada Sarma; Wasyl Janischewskyj

1969-01-01

426

The solar wind and the temperature-density structure of the solar corona  

Microsoft Academic Search

The influence of the solar wind on large-scale temperature and density distributions in the lower corona is studied. This influence is most profoundly felt through its effect upon the geometry of coronal magnetic fields since the presence of expansion divides the corona into magnetically open and closed regions. Each of these regions is governed by entirely different energy transport processes.

G. W. Pneuman

1973-01-01

427

A Study of Corona Discharge Rate and Energy Loss in Spark Gaps  

Microsoft Academic Search

A study was carried out on the corona discharge rate and energy loss occurring within artificial cavities. An air gap with metallic electrodes was utilized to simulate the ionization sources within a cable. The corona discharge rates, obtained with varying gap spacings under different vapor pressures, showed marked deviations from the idealized behavior. thhe calculated tangent values, in terms

R. Bartnikas; G. L. d'Ombrain

1965-01-01

428

Satellite imagery and archaeology: the example of CORONA in the Altai Mountains  

Microsoft Academic Search

Satellite imagery, and specifically CORONA, is now of common use in archaeology. CORONA, as it produces two images of the same spot (afterward and forward), allows for stereoscopic view and is a perfect tool for the production of maps, especially in remote areas, where maps are not reliable of even absent.However, in all cases until now, often, it appears that

Rudi Goossens; Alain De Wulf; Jean Bourgeois; Wouter Gheyle; Tom Willems

2006-01-01

429

Corona noise on the 400 kV overhead power line - measurements and computer modeling  

Microsoft Academic Search

The paper presents an experimental research in the corona noise performed on a 400 kV overhead power line with a horizontal disposition of conductors. The high-voltage (HV) power line in its role of a communication channel is a source of different noises characterizing an important feature of this communication media. The main objective was measuring and modeling the corona noise.

A. MUJ?I?; N. SULJANOVI?; M. ZAJC; J. F. TASI?

430

Optical Micro-current Transducer for the Measurement of Corona Discharge Current Under High Voltage Environment  

Microsoft Academic Search

Measuring corona discharge current directly on the high voltage side is essential for the discharge mechanism research of test object. The corona discharge is so weak that the amplitude of the current is in the level of muA and its frequency ranges from DC to MHz. An optical micro-current transducer used for the measurement of this current is described in

Peng Wang; Guixin Zhang; Jun Zhou; Chen Gu

2007-01-01

431

Surface Modification of Low Density Polyethylene (LDPE) Film Using Corona Discharge Plasma for Technological Applications  

Microsoft Academic Search

Surface modification by corona discharge plasma is one of the most interesting industrial applications for surface modification compared with other techniques which require vacuum conditions. In this work, we have used the corona discharge plasma technique to modify the wettability properties of low density polyethylene (LDPE) film. The effects of this treatment on the surface of LDPE film have been

M. Pascual; R. Sanchis; L. Snchez; D. Garca; R. Balart

2008-01-01

432

The effect of support media on corona treated paper sorption properties  

Microsoft Academic Search

The absorbency properties of certain paper products are great important. The basic methods to improve absorbency is the addition of chemical. This method is expensive and cause to loose some absorbent materials due to high shear. In recent years corona discharge treatment were utilized in different application to change surface properties of the materials. In general, corona discharge treatment is

Birol Uner

433

Positive corona inception in HVDC configurations under variable air density and humidity conditions  

Microsoft Academic Search

The stable corona discharge has found use in a large number of electrostatic applications and one of their important properties is the inception voltage which can be easily and accurately measured. The empirical Peek's law which yields the corona inception field is previously made in standard air for wire-to-cylinder geometry and used for many years. However, the generalisation of this

Y. Zebboudj; R. Ikene

2000-01-01

434

A study of the composition of the solar corona and solar wind  

Microsoft Academic Search

Effects of diffusion on the composition of the solar corona and solar wind have been examined. Multi-component diffusion equations have been solved simultaneously in attempts to account for the flux of He and heavier elements in the solar wind. Large enhancements of these elements at the base of the assumed isothermal corona appear to be required to give observed fluxes.

M. P. Nakada

1970-01-01

435

A Comparison of Galileo and Ground-Based Observations of Io's Sodium Corona  

Microsoft Academic Search

Between Io's atmosphere and extended neutral clouds exists a corona or exosphere composed of neutral atoms and molecules bound by Io's gravity. Although sodium is probably only a minor constituent of the corona, the fact that it is has a high cross section for resonant scattering makes it very easy to detect. However, close to Io's surface, sodium abundance can

M. H. Burger; N. M. Schneider; I. de Pater; M. Brown; A. Bouchez; T. Mallama

1998-01-01

436

Magneto-gravity waves and the heating of the solar corona  

Microsoft Academic Search

It is generally believed that the heating of the solar corona is caused by waves originating in the photosphere and propagating into the corona where their energy is dissipated. The medium through which these waves propagate is in general permeated by magnetic fields complicating the behaviour of this propagation considerably. We have therefore analysed the wave motions in a plasma

Alden McLellan IV; F. Winterberg

1968-01-01

437

Heating of the solar corona by the resonant absorption of Alfven waves  

Microsoft Academic Search

An improved method for calculating the resonance absorption heating rate is discussed and the results are compared with observations in the solar corona. To accomplish this, the wave equation for a dissipative, compressible plasma is derived from the linearized magnetohydrodynamic equations for a plasma with transverse Alfven speed gradients. For parameters representative of the solar corona, it is found that

Joseph M. Davila

1987-01-01

438

The influence of water on corona discharge in the flue gas  

Microsoft Academic Search

In this paper a novel type of a water film corona discharge experiment model is designed. The reactor is composed of needle-plate electrodes that are placed in a glass container filled with the flue gas, (the plate electrode is immersed in the water). The mechanism of the formation of corona discharge in the pollution flue gas containing sulfur dioxide (SO2)

Peiping Wei; Limin Dong; Shuyu Han; Xiaochun Chi; Jiaxiang Yang

2002-01-01

439

Nanoparticle size and surface properties determine the protein corona with possible implications for biological impacts  

Microsoft Academic Search

Nanoparticles in a biological fluid (plasma, or otherwise) associate with a range of biopolymers, especially proteins, organized into the ``protein corona'' that is associated with the nanoparticle and continuously exchanging with the proteins in the environment. Methodologies to determine the corona and to understand its dependence on nanomaterial properties are likely to become important in bionanoscience. Here, we study the

Martin Lundqvist; Johannes Stigler; Giuliano Elia; Iseult Lynch; Tommy Cedervall; Kenneth A. Dawson

2008-01-01

440

Guide for Calibration of Test Equipment and Circuits for Measurement of Corona Pulses  

Microsoft Academic Search

Corona pulses originating in an insulation system under an applied test voltage may be observed on a cathode-ray oscilloscope coupled into the test circuit. The relation between a corona pulse at the system terminals and the height of the resulting oscilloscope deflection is influenced by the arrangement of the test circuit and is generally determined by a calibration procedure. The

1967-01-01

441

CORONA DESTRUCTION: AN INNOVATIVE CONTROL TECHNOLOGY FOR VOCS AND AIR TOXICS  

EPA Science Inventory

This paper discusses the work and results to date leading to the demonstration of the corona destruction process at pilot scale. The research effort in corona destruction of volatile organic compounds (VOCs) and air toxics has shown significant promise for providing a valuable co...

442

Study on physical and chemical structure changes of polyimide caused by corona ageing  

Microsoft Academic Search

Modified isothermal discharge current method (MIDC) was introduced to investigate the trap level distribution in Kapton 100HN and 100CR (nanodielectrics) PI films before and after corona ageing. The physical and chemical changes were studied by AFM and FT-IR respectively. Experiments showed that the quantity of traps was increased evidently after corona ageing and lots of deeper traps were produced in

Fuqiang Tian; Wenbin Bu; Chun Yang; Lijuan He; Yi Wang; Xuan Wang; Qingquan Lei

2009-01-01

443