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1

A study of the background corona near solar minimum  

Microsoft Academic Search

The white light coronagraph data from Skylab is used to investigate the equatorial and polarK andF coronal components during the declining phase of the solar cycle near solar minimum. Measurements of coronal brightness and polarization brightness product between 2.5 and 5.5R? during the period of observation (May 1973 to February 1974) lead to the conclusions that: (1) the equatorial corona

Kuniji Saito; Arthur I. Poland; Richard H. Munro

1977-01-01

2

Slow wind and magnetic topology in the solar minimum corona in 1996-1997  

Microsoft Academic Search

This study examines the physical conditions of the outer solar corona in order to identify the regions where the slow solar wind is accelerated and to investigate the latitudinal transition from slow to fast wind during the minimum of the solar cycle. The analysis is based on observations of six streamers obtained during the years of solar minimum, 1996 and

E. Antonucci; L. Abbo; M. A. Dodero

2005-01-01

3

The heliospheric structure during the recent solar minimum: shocks in the lower corona and the magnetic field structure in the heliosheath  

NASA Astrophysics Data System (ADS)

In this talk we review the recent heliospheric structure as affected by the recent solar minimum. We will focus especially on two frontiers areas: a) evolution of shocks in the lower corona and b) the heliosheath. In particular, we will focus on how the recent extended minimum allowed us to separate spatial and temporal effects in the outer heliosphere. We will describe new phenomena that we were able to explore, the reconnection of the sectored magnetic field in the heliosheath. Very little is known on how shocks thought to be driven by CMEs, form and evolve in the lower corona. This is a crucial area since its has been shown by observations that they form low in the corona (1-4Rs) and coincide with the acceleration to GeV energies. We will describe our recent attempts (e.g., Evans et al. 2011; Das et al.; 2011) to uncover the evolution of CMEs at these locations. All the current global models of the heliosphere are based on the assumption that the magnetic field in the heliosheath, in the region close to the heliopause is laminar and connect back to the Sun. We argue recently, based on Voyager observations that in that region the heliospheric magnetic field is not laminar but instead consists of magnetic bubbles, or magnetic structures disconnected from the Sun (Opher et al. 2011). The consequence is that the heliopause might be a porous membrane instead of a shield. As the sun increased its activity, it will be more complicated to disentangle temporal from spatial and global structure. We will comment on how the increased solar activity might affect the sector structure in the heliosheath as well as the implication for our understanding of how galactic cosmic rays enter the heliosphere. Due to the slow flows in the heliosheath, the heliosheath has a long time memory of solar activity. Moreover, Corotating Interaction Regions and Global Merged Interacting Regions are known to disturb the termination shock and heliopause as well as the heliosheath flows and fields. For example it is still poorly understood how temporal effects propagate in the heliosheath and affect the level of turbulence. We will present some of our recent work trying to understand how temporal effects, such as CIRs propagates from the sun into the outer heliosphere.

Opher, M.; Drake, J. F.; Evans, R.; Provornikova, E.; Swisdak, M. M.; Schoeffler, K. M.; van der Holst, B.; Toth, G.

2011-12-01

4

The Thermosphere at Solar Minimum  

NASA Astrophysics Data System (ADS)

The sustained decrease in solar extreme ultraviolet radiation during the current minimum is greater than any in recent history. This gives us the opportunity to study neutral density conditions that are outside the domain of the available empirical models of the thermosphere. While there are currently no experiments measuring in-situ composition of the thermosphere, the accelerometers aboard the CHAMP and GRACE satellites provide a monitor of total atmospheric density, spanning most of solar cycle 23 through the current minimum (2001-2008). Using these data, complemented by ground-based measurements of satellite drag (1996-2008), it appears that agreement between data and empirical models is strongly dependent on satellite altitude during solar minimum, implying an error in our empirical knowledge of the atmospheric scale height. Knowledge of species-dependent behavior with respect to local-time and latitude gives us a crude method of separating the observed scale heights into the competing effects of composition and temperature changes.

Sutton, E. K.; Marcos, F. A.; Lin, C. S.

2009-12-01

5

Coronal electron temperature in the protracted solar minimum, the cycle 24 mini maximum, and over centuries  

NASA Astrophysics Data System (ADS)

Recent in situ observations of the solar wind show that charge states (e.g., the O7+/O6+and C6+/C5+abundance ratios) evolved through the extended, deep solar minimum between solar cycles 23 and 24 (i.e., from 2006 to 2009) reflecting cooler electron temperatures in the corona. We extend previous analyses to study the evolution of the coronal electron temperature through the protracted solar minimum and observe not only the reduction in coronal temperature in the cycles 23-24 solar minimum but also a small increase in coronal temperature associated with increasing activity during the "mini maximum" in cycle 24. We use a new model of the interplanetary magnetic flux since 1749 to estimate coronal electron temperatures over more than two centuries. The reduction in coronal electron temperature in the cycles 23-24 protracted solar minimum is similar to reductions observed at the beginning of the Dalton Minimum (˜1805-1840). If these trends continue to reflect the evolution of the Dalton Minimum, we will observe further reductions in coronal temperature in the cycles 24-25 solar minimum. Preliminary indications in 2013 do suggest a further post cycle 23 decline in solar activity. Thus, we extend our understanding of coronal electron temperature using the solar wind scaling law and compare recent reductions in coronal electron temperature in the protracted solar minimum to conditions that prevailed in the Dalton Minimum.

Schwadron, N. A.; Goelzer, M. L.; Smith, C. W.; Kasper, J. C.; Korreck, K.; Leamon, R. J.; Lepri, S. T.; Maruca, B. A.; McComas, D.; Steven, M. L.

2014-03-01

6

Space climate and the recent unusual solar minimum  

NASA Astrophysics Data System (ADS)

Solar minima represent times of low magnetic activity and simple heliospheres. They are thus excellent targets for interdisciplinary, system-wide studies of the origins of solar variability and consequent impacts on planetary systems. The recent solar minimum extended longer and was "quieter" than any we have observed in the Space Age, inspiring both scientific and public interest. It was the lowest and longest minimum in about a century, having weak polar magnetic fields, a complex corona and heliosphere, and recurrent high-speed streams impacting the Earth's space environment. I will review scientific results from Sun to Earth pertaining to the recent minimum, and place these results in a broad context encompassing historical solar and stellar minima, theoretical models of generative dynamo mechanisms, and implications of solar and stellar cyclic behavior for the space climate around planets.

Gibson, Sarah

2012-07-01

7

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.

8

The solar drivers of geomagnetic disturbances during solar minimum  

Microsoft Academic Search

Recurrent high speed solar wind from coronal holes still existed around the solar minimum. Their effect on geomagnetic disturbances seems to be weak during this period. High speed solar wind sometimes overlapped with disturbances in association with coronal mass ejections (CMEs). However, a large number of geomagnetic disturbances (Dst<=-50nT) were associated with CMEs even around the solar minimum of the

Shinichi Watari; Takashi Watanabe

1998-01-01

9

Newly Discovered Global Temperature Structures in the Quiet Sun at Solar Minimum  

NASA Astrophysics Data System (ADS)

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 Te and density Ne 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.; Vásquez, Alberto M.; Gombosi, Tamas I.

2012-08-01

10

Geo-effective Stream Interactions and CMEs in Solar Minimum  

NASA Astrophysics Data System (ADS)

A statistical study of stream interactions and CME events from January 2007 to December 2010 which result in storm and substorm activity is presented. During this solar minimum the decrease in solar activity has resulted in less geomagnetic activity. The observed activity has been from stream interaction regions (SIRs), shocks, and some interplanetary coronal mass ejections (ICMEs). Geomagnetic activity is characterized by indices derived from ground based magnetometers and a minimum Dst threshold of -30 nT is used. For each geoeffective event, we identified CMEs in the STEREO/SECCHI coronagraphs, and SIRs in the STEREO/SECCHI Heliospheric Imagers and associated lower coronal signatures in STEREO/EUVI and SDO/AIA. Subsequent CME and/or SIR signatures were identified in ACE, WIND, THEMIS, and other in-situ data when available. CME evolution in the lower corona and properties such as acceleration, speed and width were determined along with the in-situ plasma data for ICMEs. The propagation of these structures were tracked in the STEREO Heliospheric Imagers and subsequently in-situ. Geoeffectiveness, the strength and duration of geomagnetic activity, is compared with upstream solar wind conditions. In 2007 and 2008, SIRs produce most of the storms (~75% and ~78% respectively), however the strongest storms are produced by ICME and SIR interactions in 2007 and SIRs in 2008. The number of SIR driven storms drops to just below half (~46%) in 2009, and the remaining storms result from an ICME followed by an SIR (~39% and strongest storm), and ICMEs (~16%). In 2010 the number ICME driven storms markedly increase (~50%) and produce 57% of the strongest storms, while SIR driven storms continue to decrease (36%). So far in 2011, and around half of the storms are SIR driven, but ~66% of the strongest storms are driven by ICMEs. Overall, the percentage of geoeffective SIRs (observed in-situ) from 2007-2009 was 36%, 30%, and 14%, respectively, and ICMEs were geoeffective 60%, 33%, and 42% of the time.

Mays, M. L.; St Cyr, O. C.; Xie, H.; Sibeck, D. G.

2011-12-01

11

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

12

Mars ionopause during solar minimum: A lesson from Venus  

SciTech Connect

The ion densities measured by the Viking landers (Hanson et al., 1977) do not show an abrupt falloff with height, giving the false impression that Mars has no ionopause. On the basis of knowledge gained from the solar wind interaction at Venus during solar minimum, they demonstrate that the observed O{sub 2}{sup +} profile above about 160 km on Mars is a distributed photodynamical ionosphere and can produce an ionopause at around 325 km, similar to that observed on Venus during solar minimum. They conclude that the solar wind interacts directly with the Mars ionosphere, suggesting that the planet does not have an intrinsic magnetic field of any consequence.

Mahajan, K.K.; Mayr, H.G. (NASA Goddard Space Flight Center, Greenbelt, MD (USA))

1990-06-01

13

The transterminator ion flow at Venus at solar minimum  

NASA Astrophysics Data System (ADS)

The transterminator ion flow in the Venusian ionosphere is observed at solar minimum for the first time. Such a flow, which transports ions from the day to the nightside, has been observed previously around solar maximum. At solar minimum this transport process is severely inhibited by the lower altitude of the ionopause. The observations presented were those made of the Venusian ionospheric plasma by the ASPERA-4 experiment onboard the Venus Express spacecraft, and which constitute the first extensive in-situ measurements of the plasma near solar minimum. Observations near the terminator of the energies of ions of ionospheric origin showed asymmetry between the noon and midnight sectors, which indicated an antisunward ion flow with a velocity of (2.5±1.5) km s-1. It is suggested that this ion flow contributes to maintaining the nightside ionosphere near the terminator region at solar minimum. The interpretation of the result was reinforced by observed asymmetries in the ion number counts. The observed dawn-dusk asymmetry was consistent with a nightward transport of ions while the noon-midnight observations indicated that the flow was highly variable but could contribute to the maintenance of the nightside ionosphere.

Wood, A. G.; Pryse, S. E.; Grande, M.; Whittaker, I. C.; Coates, A. J.; Husband, K.; Baumjohann, W.; Zhang, T. L.; Mazelle, C.; Kallio, E.; Fränz, M.; McKenna-Lawlor, S.; Wurz, P.

2012-12-01

14

The solar drivers of geomagnetic disturbances during solar minimum  

Microsoft Academic Search

Recurrent high speed solar wind from coronal holes still existed around the solar minimum. Their effect on geomagnetic disturbances seems to be weak during this period. High speed solar wind sometimes overlapped with disturbances in association with coronal mass ejections (CMEs). However, a large number of geomagnetic disturbances (Dst ? ?50 nT) were associated with CMEs even around the solar

Shinichi Watari; Takashi Watanabe

1998-01-01

15

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

16

External ionospheric and thermospheric forcing during solar minimum  

Microsoft Academic Search

In this study we focus on dynamics of the ionosphere-thermosphere (I-T) system during a solar minimum interval. We compare and contrast the state of the I-T system during weakly disturbed high speed stream (HSS) intervals (Dst ~ -50 nT) with ``quiet'' days. Using GPS TEC measurements and infrared radiative power of NO and CO2 derived from SABER\\/TIMED measurements we study

O. P. Verkhoglyadova; B. Tsurutani; A. J. Mannucci; A. Komjathy; M. G. Mlynczak; L. A. Hunt

2010-01-01

17

Recent Studies of the Behavior of the Sun's White-Light Corona Over Time  

NASA Technical Reports Server (NTRS)

Predictions of upcoming solar cycles are often related to the nature and dynamics of the Sun's polar magnetic field and its influence on the corona. For the past 30 years we have a more-or-less continuous record of the Sun's white-light corona from groundbased and spacebased coronagraphs. Over that interval, the large scale features of the corona have varied in what we now consider a 'predictable' fashion--complex, showing multiple streamers at all latitudes during solar activity maximum; and a simple dipolar shape aligned with the rotational pole during solar minimum. Over the past three decades the white-light corona appears to be a better indicator of 'true' solar minimum than sunspot number since sunspots disappear for months (even years) at solar minimum. Since almost all predictions of the timing of the next solar maximum depend on the timing of solar minimum, the white-light corona is a potentially important observational discriminator for future predictors. In this contribution we describe recent work quantifying the large-scale appearance of the Sun's corona to correlate it with the sunspot record, especially around solar minimum. These three decades can be expanded with the HAO archive of eclipse photographs which, although sparse compared to the coronagraphic coverage, extends back to 1869. A more extensive understanding of this proxy would give researchers confidence in using the white-light corona as an indicator of solar minimum conditions.

SaintCyr, O. C.; Young, D. E.; Pesnell, W. D.; Lecinski, A.; Eddy, J.

2008-01-01

18

A NOTE ON THE TORSIONAL OSCILLATION AT SOLAR MINIMUM  

SciTech Connect

We examine the evolution of the zonal flow pattern in the upper solar convection zone during the current extended solar minimum, and compare it with that during the previous minimum. The results suggest that a configuration matching that at the previous minimum was reached during 2008, but that the flow band corresponding to the new cycle has been moving more slowly toward the equator than was observed in the previous cycle, resulting in a gradual increase in the apparent length of the cycle during the 2007-2008 period. The current position of the lower-latitude fast-rotating belt corresponds to that seen around the onset of activity in the previous cycle.

Howe, R.; Hill, F.; Komm, R. [National Solar Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States); Christensen-Dalsgaard, J. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Schou, J. [HEPL Solar Physics, 452 Lomita Mall, Stanford University, Stanford, CA 94305-4085 (United States); Thompson, M. J. [School of Mathematics and Statistics, University of Sheffield, Hounsfield Road, Sheffield S3 7RH (United Kingdom)], E-mail: rhowe@noao.edu

2009-08-20

19

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

20

Ion-neutral Coupling During Deep Solar Minimum  

NASA Technical Reports Server (NTRS)

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 (CNOFS) 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 20082010 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.

2013-01-01

21

Radiation Environment on Mir Orbital Station During Solar Minimum  

NASA Technical Reports Server (NTRS)

Space radiation poses a significant risk for the stay and rotation cycle of astronauts on the International Space Station (ISS). The ISS is in the same orbit as the Mir orbital station and as such, data acquired onboard the Mir station is of direct applicability to the ISS astronaut. During the seven NASA-Mir missions, data were acquired with a variety of both passive and active detectors, including measurements of astronaut doses. This paper describes these measurements and comparisons with measurements carried out by other groups. It is shown that trapped protons absorbed can be very well described by quadratic equation in In(p), where p is the atmospheric density. Similarly, the galactic cosmic ray absorbed dose is nearly exponentially related to the deceleration potential. The average radiation quality factor with the ICRP-60 definition is about 2.44. Using the measured quality factor, absorbed crew doses, and estimates of neutron dose equivalent, leads to crew stay times as short as 9 months during a deep solar minimum. The data are compared with in vivo dose estimates using chromosome aberrations (simple translocations and total exchange) on same astronauts.

Badhwar, Gautam D.; McKay, Gordon A. (Technical Monitor)

1999-01-01

22

Estimates of galactic cosmic ray shielding requirements during solar minimum  

NASA Technical Reports Server (NTRS)

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.

1990-01-01

23

External ionospheric and thermospheric forcing during solar minimum  

NASA Astrophysics Data System (ADS)

In this study we focus on dynamics of the ionosphere-thermosphere (I-T) system during a solar minimum interval. We compare and contrast the state of the I-T system during weakly disturbed high speed stream (HSS) intervals (Dst ~ -50 nT) with “quiet” days. Using GPS TEC measurements and infrared radiative power of NO and CO2 derived from SABER/TIMED measurements we study 4 HSSs that occurred during the time interval from March 20th to April 25th 2008. The study shows distinct response in the I-T system to external forcing. We attempt to trace the energy transfer and coupling from the heliosphere through the magnetosphere and into the I-T system. The GIM/JPL model is used to construct Global Ionospheric Maps using ~100 ground GPS sites. Difference global maps show local disturbances in VTEC from the “quiet” values throughout HSS intervals. Dynamics of VTEC variations in different latitude zones and LT ranges will be illustrated. Physical mechanisms for magnetosphere-ionosphere-thermosphere coupling will be discussed. The results suggest that intense Alfven waves in the HSS streams and related weak magnetic storms are causing I-T response.

Verkhoglyadova, O. P.; Tsurutani, B.; Mannucci, A. J.; Komjathy, A.; Mlynczak, M. G.; Hunt, L. A.

2010-12-01

24

Cosmic ray particles behavior during last solar minimum  

NASA Astrophysics Data System (ADS)

The work presents the Heliosphere characterization during the minimum solar activity. It is possible to identify phenomena caused by the Corrotating Interaction Regions - CIRs, during this solar activity phase. CIRs can be visualized in satellite data for each 27 days, approximately, and it is frequently accompanied by the Earth crossing through the Heliospheric Current Sheath - HCS. These crossing occur in a period of time lower than a day, and it is possible to study the behavior of cosmic rays particles in two different regions with opposite magnetic field polarities. The last solar minimum was special because their long duration and it was the first that the Global Muon Detector Network - GMDN operated in its full capacity. This cosmic ray detectors network is composed by muon scintillators installed in Nagoya - Japan, Hobart - Australia, São Martinho da Serra - Brazil and Kuwait City - Kuwait. Analyzing the GMDN data together with data from SOHO and/or ACE satellites it is possible to study the behavior of the cosmic ray particles and presents a Heliosphere characterization during the minimum solar activity, giving a better understanding of the cosmic ray particles modulation.

Rockenbach, Marlos; Dal Lago, Alisson; Munakata, Kazuoki; Kato, Chihiro; Kuwabara, Takao; Bieber, John; Schuch, Nelson; Duldig, Marc; Humble, John; Jassar, Hala Al; Sharma, Madan; Sabbah, Ismail

2013-04-01

25

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

26

Coronal Rotation at Solar Minimum from UV Observations  

NASA Technical Reports Server (NTRS)

UVCS/SOHO observations have been analyzed to reconstruct intensity time series of the O VI 1032 A and H 11216 A spectral lines at different coronal heliolatitudes from 1.5 to 3.0 solar radii from Sun center. Evidence was found for coronal differential rotation that differs significantly from that of the photospheric plasma. The study of the latitudinal variation shows that the UV corona decelerates toward the photospheric rates from the equator up to the poleward boundary 2 of the midlatitude streamers, reaching a peak of 28.16+/-0.20 days around +30 from the equator at 1.5 solar radii, while a less evident peak is observed in the northern hemisphere. This result suggests a real north-south rotational asymmetry as a consequence of different activity and weak coupling between the magnetic fields of the two hemispheres. The study of the radial rotation profiles shows that the corona is rotating almost rigidly with height.

Mancuso, S.

2008-01-01

27

3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum  

NASA Astrophysics Data System (ADS)

Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington Rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 R? using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron-density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 Å band obtained by tomography for the same CR. A global 3D MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic-field structures. We show that the density-maximum locations can serve as an indicator of current-sheet position, while the locations of the density-gradient maximum can be a reliable indicator of coronal-hole boundaries. We find that the magnetic-field configuration during CR 2066 has a tendency to become radially open at heliocentric distances greater than 2.5 R?. We also find that the potential-field model with a fixed source surface is inconsistent with the boundaries between the regions with open and closed magnetic-field structures. This indicates that the assumption of the potential nature of the coronal global magnetic field is not satisfied even during the deep solar minimum. Results of our 3D density reconstruction will help to constrain solar coronal-field models and test the accuracy of the magnetic-field approximations for coronal modeling.

Kramar, M.; Airapetian, V.; Miki?, Z.; Davila, J.

2014-04-01

28

3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum  

NASA Astrophysics Data System (ADS)

Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington Rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 R? using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron-density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 Å band obtained by tomography for the same CR. A global 3D MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic-field structures. We show that the density-maximum locations can serve as an indicator of current-sheet position, while the locations of the density-gradient maximum can be a reliable indicator of coronal-hole boundaries. We find that the magnetic-field configuration during CR 2066 has a tendency to become radially open at heliocentric distances greater than 2.5 R?. We also find that the potential-field model with a fixed source surface is inconsistent with the boundaries between the regions with open and closed magnetic-field structures. This indicates that the assumption of the potential nature of the coronal global magnetic field is not satisfied even during the deep solar minimum. Results of our 3D density reconstruction will help to constrain solar coronal-field models and test the accuracy of the magnetic-field approximations for coronal modeling.

Kramar, M.; Airapetian, V.; Miki?, Z.; Davila, J.

2014-08-01

29

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

30

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

31

Characteristics of the Global Ionosphere During the Solar Minimum of Cycle 23/24  

NASA Astrophysics Data System (ADS)

The last solar minimum period was anomalously low and lasted long compared with previous solar minima. The resulting solar irradiance received in the Earth's upper atmosphere was extremely low and therefore it can readily be expected that the upper atmosphere should be greatly affected by this low solar activity. It has been well reported that the thermospheric temperature was cooler and the density was lower during the last solar minimum than the previous solar minimum periods. The low solar irradiance should also affect the ionosphere, not only via the lower ion-electron production but also through the interactions with the thermosphere that was greatly influenced by the low solar irradiance. In this study, we utilized the measurements of total electron content (TEC) from the TOPEX and JASON-1 satellites for the precious solar minimum and the last solar minimum, respectively, in order to investigate the differences between the ionospheric TECs during the two minimum periods. For this investigation, we first made a comparison between TOPEX and JASON TECs to confirm that they produced identical TECs during the overlap period of the two satellite missions and can be considered as a single TEC observation. Next, the global ionospheric TEC maps are produced during the last two solar minimums for different seasons and the results of the comparison will be discussed, in particular, in relation to the thermospheric changes during the same periods.

Jee, G.; Lee, H.; Solomon, S. C.

2013-12-01

32

Global ionospheric total electron contents (TECs) during the last two solar minimum periods  

NASA Astrophysics Data System (ADS)

last solar minimum period was anomalously extended and low in EUV irradiance compared with previous solar minima. It can readily be expected that the thermosphere and the ionosphere must be correspondingly affected by this low solar activity. While there have been unanimous reports on the thermospheric changes, being cooler and lower in its density as expected, the ionospheric responses to low solar activity in previous studies were not consistent with each other, probably due to the limited ionospheric observations used for them. In this study, we utilized the measurements of total electron content (TEC) from TOPEX and JASON-1 satellites during the periods of 1992 to 2010, which includes both the last two solar minimum periods, in order to investigate how the ionosphere responded to the extremely low solar activity during the last solar minimum compared with previous solar minimum. Although the global daily mean TECs show negligible differences between the two solar minimum periods, the global TEC maps reveal that there are significant systematic differences ranging from about -30% to +50% depending on local time, latitude, and season. The systematic variations of the ionospheric responses seem to mainly result from the relative effects of reduced solar EUV production and reduced recombination rate due to thermospheric changes during the last solar minimum period.

Jee, Geonhwa; Lee, Han-Byul; Solomon, Stanley C.

2014-03-01

33

The 3D solar minimum with differential emission measure tomography  

NASA Astrophysics Data System (ADS)

Differential emission measure tomography (DEMT) makes use of extreme ultraviolet (EUV) image series to deliver two products: a) the three-dimensional (3D) reconstruction of the coronal emissivity in the instrumental bands, and b) the 3D distribution of the local differential emission measure (LDEM). The LDEM allows, in turn, construction of 3D maps of the electron density and temperature distribution. DEMT is being currently applied to the space-based EUV imagers, allowing reconstruction of the inner corona in the height range 1.00 to 1.25 R?. In this work we applied DEMT to different Carrington Rotations corresponding to the last two solar Cycle minima. To reconstruct the 2008 minimum we used data taken by the Extreme UltraViolet Imager (EUVI), on board the Solar TErrestrial RElations Observatory (STEREO) spacecraft, and to reconstruct the 1996 minimum we used data taken by the Extreme ultraviolet Imaging Telescope (EIT), on board the Solar and Heliospheric Observatory (SOHO). We show here comparative results, discussing the observed 3D density and temperature distributions in the context of global potential magnetic field extrapolations. We also compare the DEMT results with other observational and modeling efforts of the same periods.

Vásquez, Alberto M.; Frazin, Richard A.; Huang, Zhenguang; Manchester, Ward B.; Shearer, Paul

2012-07-01

34

Could a future "Grand Solar Minimum" like the Maunder Minimum stop global warming?  

NASA Astrophysics Data System (ADS)

A future Maunder Minimum type grand solar minimum, with total solar irradiance reduced by 0.25% over a 50 year period from 2020 to 2070, is imposed in a future climate change scenario experiment (RCP4.5) using, for the first time, a global coupled climate model that includes ozone chemistry and resolved stratospheric dynamics (Whole Atmosphere Community Climate Model). This model has been shown to simulate two amplifying mechanisms that produce regional signals of decadal climate variability comparable to observations, and thus is considered a credible tool to simulate the Sun's effects on Earth's climate. After the initial decrease of solar radiation in 2020, globally averaged surface air temperature cools relative to the reference simulation by up to several tenths of a degree Centigrade. By the end of the grand solar minimum in 2070, the warming nearly catches up to the reference simulation. Thus, a future grand solar minimum could slow down but not stop global warming.

Meehl, Gerald A.; Arblaster, Julie M.; Marsh, Daniel R.

2013-05-01

35

Field-aligned currents during the extreme solar minimum between the solar cycles 23 and 24  

NASA Astrophysics Data System (ADS)

solar minimum between solar cycles 23 and 24 was unusually long and deep. The upward region-1 (R1) field-aligned current (FAC) response to this extreme solar minimum was investigated using Defense Meteorological Satellite Program observations. The solar cycle responses on the dayside are different than those on the nightside. The field-aligned current density (J//) on the dayside, at 12-17 magnetic local time (MLT), peaks in the declining phase of the solar cycle, in 2003, when the solar wind speed also peaks, whereas J// on the nightside, at 18-23 MLT, appears insensitive to the solar cycle. In 1995-2010, J// at 15-17 MLT reaches the lowest value during the extreme solar minimum in 2009, when the solar wind speed also reaches the lowest value. At 12-17 MLT, R1 is located mostly on open field lines or at the boundary layer, where the current is driven mostly by the velocity shear at the magnetopause boundary. However, on the nightside, R1 is located mostly on the closed field lines where J// is not driven directly and immediately by the solar wind. The nightside current width (?) exhibits a solar cycle effect such that ? is smaller at the solar minimum and smallest in 2009. However, the dayside ? exhibits little solar cycle effect. As a result, the FAC intensity (latitudinally integrated J//) exhibits a solar cycle variation at all local times and the FAC intensity is lower during the extreme solar minimum than that of the previous solar minimum.

Wing, Simon; Ohtani, Shinichi; Johnson, Jay; Wilson, Gordon R.; Higuchi, Tomoyuki

2014-04-01

36

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

37

Observations of the Van Allen Radiation Belt, Solar Wind and Corotating Interaction Regions during Solar Minimum  

NASA Astrophysics Data System (ADS)

Fast moving streams from coronal holes can interact with slower downstream solar wind (SW) to form co-rotating interaction regions (CIRs). The CIRs can be very effective in producing variations in the outer zone of the Van Allen radiation belt (RB). This effect is particularly noticeable during solar minimum when there is little other solar activity. In this study, we use a combination of THEMIS and GOES radiation belt observations, STEREO images and SW data from 2008 and 2009 to analyze the relationships among individual features on the Sun, SW parameters, and variations in outer zone RB relativistic electrons. Variations in the RB outer zone relativistic fluxes are often observed during times of persistent trans-equatorial coronal holes during solar minimum. During solar minimum, the likelihood of CIRs forming by 1 AU increases if the interacting regions appear at low solar latitudes. We will discuss the solar wind conditions that correlate with changes in outer zone RB fluxes during solar minimum and how these conditions relate to trans-equatorial coronal holes and active regions.

Loto'Aniu, P. T.; Li, J.; Angelopoulos, V.; Singer, H. J.

2009-12-01

38

Magnetohydrodynamic modeling of the solar corona during Whole Sun Month  

Microsoft Academic Search

The Whole Sun Month campaign (August 10 to September 8, 1996) brought together a wide range of space-based and ground-based observations of the Sun and the interplanetary medium during solar minimum. The wealth of data collected provides a unique opportunity for testing coronal models. We develop a three-dimensional magnetohydrodynamic (MHD) model of the solar corona (from 1 to 30 solar

J. A. Linker; Z. Mikic; D. A. Biesecker; R. J. Forsyth; S. E. Gibson; A. J. Lazarus; A. Lecinski; P. Riley; A. Szabo; B. J. Thompson

1999-01-01

39

Wind in the Solar Corona: Dynamics and Composition  

Microsoft Academic Search

The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on\\u000a SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed\\u000a by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close\\u000a to

Ester Antonucci

40

Wind in the Solar Corona: Dynamics and Composition  

Microsoft Academic Search

The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on\\u000a SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed\\u000a by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close\\u000a to

Ester Antonucci

2006-01-01

41

Solar Minimum  

NASA Astrophysics Data System (ADS)

Calcium K plage, H alpha plage and sunspot area have been monitored daily on the INTERNET since November of 1992. The plage and sunspot area have been measured by image processing. The purpose of the project is to investigate the degree of correlation between plage area and solar irradiance. The plage variation shows the expected variation produced by solar rotation and the longer secular changes produced by the solar cycle. The H alpha and sunspot plage area reached a minimum in about late 1994 or early 1995. This is in agreement with the K2 spectral index obtained daily from Sacramento Peak Observatory. The Calcium K plage area minimum seems delayed with respect to the others mentioned above. The minimum of the K line plage area is projected to come within the last few months of 1995.

Lopresto, James C.; Mathews, John; Manross, Kevin

1995-12-01

42

Neutron monitor latitude survey of cosmic ray intensity during the 1986/1987 solar minimum  

SciTech Connect

A latitude survey of the cosmic ray intensity at sea level was conducted during the 1986/1987 solar minimum period on commercial vessels of the South African Marine Corporation (SAFMARINE). The results show that the differential response function for the 1986/1987 solar minimum agrees well with that measured in 1965. Both these response functions are significantly lower than those for 1976 and 1954. This result supports the 22-year modulation cycle as predicted, for example, by models including drift effects of the charged cosmic ray particles in the large-scale interplanetary magnetic field. A crossover of the spectra at rigidities of about 7 GV was also observed. Such a crossover is necessary to explain both the stationary neutron monitor counting rates and the lower-energy balloon and space observations in consecutive solar cycles. copyright American Geophysical Union 1989

Moraal, H.; Potgieter, M.S.; Stoker, P.H.; van der Walt, A.J.

1989-02-01

43

Little or no solar wind enters Venus' atmosphere at solar minimum.  

PubMed

Venus has no significant internal magnetic field, which allows the solar wind to interact directly with its atmosphere. A field is induced in this interaction, which partially shields the atmosphere, but we have no knowledge of how effective that shield is at solar minimum. (Our current knowledge of the solar wind interaction with Venus is derived from measurements at solar maximum.) The bow shock is close to the planet, meaning that it is possible that some solar wind could be absorbed by the atmosphere and contribute to the evolution of the atmosphere. Here we report magnetic field measurements from the Venus Express spacecraft in the plasma environment surrounding Venus. The bow shock under low solar activity conditions seems to be in the position that would be expected from a complete deflection by a magnetized ionosphere. Therefore little solar wind enters the Venus ionosphere even at solar minimum. PMID:18046399

Zhang, T L; Delva, M; Baumjohann, W; Auster, H-U; Carr, C; Russell, C T; Barabash, S; Balikhin, M; Kudela, K; Berghofer, G; Biernat, H K; Lammer, H; Lichtenegger, H; Magnes, W; Nakamura, R; Schwingenschuh, K; Volwerk, M; Vörös, Z; Zambelli, W; Fornacon, K-H; Glassmeier, K-H; Richter, I; Balogh, A; Schwarzl, H; Pope, S A; Shi, J K; Wang, C; Motschmann, U; Lebreton, J-P

2007-11-29

44

THE TURBULENT CASCADE AND PROTON HEATING IN THE SOLAR WIND DURING SOLAR MINIMUM  

SciTech Connect

The recently protracted solar minimum provided years of interplanetary data that were largely absent in any association with observed large-scale transient behavior on the Sun. With large-scale shear at 1 AU generally isolated to corotating interaction regions, it is reasonable to ask whether the solar wind is significantly turbulent at this time. We perform a series of third-moment analyses using data from the Advanced Composition Explorer. We show that the solar wind at 1 AU is just as turbulent as at any other time in the solar cycle. Specifically, the turbulent cascade of energy scales in the same manner proportional to the product of wind speed and temperature. Energy cascade rates during solar minimum average a factor of 2-4 higher than during solar maximum, but we contend that this is likely the result of having a different admixture of high-latitude sources.

Coburn, Jesse T.; Smith, Charles W.; Vasquez, Bernard J. [Physics Department and Space Science Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH (United States); Stawarz, Joshua E. [Department of Astrophysical and Planetary Sciences, University of Colorado at Boulder, Boulder, CA (United States); Forman, Miriam A., E-mail: jtu46@wildcats.unh.edu, E-mail: Charles.Smith@unh.edu, E-mail: Bernie.Vasquez@unh.edu, E-mail: Joshua.Stawarz@Colorado.edu, E-mail: Miriam.Forman@sunysb.edu [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, NY (United States)

2012-08-01

45

The Radial Distribution of Galactic Cosmic Rays in the Heliosphere at Solar Minimum and Solar Maximum  

NASA Astrophysics Data System (ADS)

The radial intensity gradients, gr , for the qA>0 solar minimum periods of cycle 20 and 22 for 265 MeV/n galactic cosmic ray (GCR) He and 175 MeV GCR H are very small (<0.2%/AU) between 15 and 72 AU, suggesting that most of the GCR modulation at this time is occurring near the termination shock (T.S.) or in the heliosheath. The GCR latitudinal gradients (g? ) at this time are also small (<0.0 ± 0.2%/° ). For the qA<0 (1987), gr shows a much stronger radial dependence. The increased modulation from solar minimum to solar maximum is found to occur mainly inside the T.S.. In the inner heliosphere (r<15 AU) there does not appear to be a significant change in the particle transport parameters over the last 3 cycles.

McDonald, F. B.; Fujii, Z.; Heikkila, B.; Lal, N.; McGuire, R.E.

2003-07-01

46

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

47

A search for hard X-ray microflares near solar minimum  

Microsoft Academic Search

Near solar maximum, hard X-ray microflares with peak 20 keV fluxes of greater than about 0.01\\/sq cm s keV, more than ten times smaller than for typical flares and subflares, can occur at the rate of about once every five minutes. A search for hard X-ray microflares made on a long duration balloon flight in February 1987 near solar minimum,

R. P. Lin; K. C. Hurley; D. M. Smith; R. M. Pelling

1991-01-01

48

Solar minimum streamer densities and temperatures using Whole Sun Month coordinated data sets  

Microsoft Academic Search

We model electron densities of the simplest, most symmetric solar minimum streamer structure observed during the Whole Sun Month (WSM) campaign, using coronal observations of both visible white light and extreme ultraviolet (EUV) emission. Using white light data from the SOHO\\/LASCO\\/C2 and HAO\\/Mauna Loa Mark 3 coronagraphs, we determine electron densities by way of a Van de Hulst inversion. We

S. E. Gibson; A. Fludra; F. Bagenal; D. Biesecker; G. del Zanna; B. Bromage

1999-01-01

49

Modulation of galactic cosmic rays during the unusual solar minimum between cycles 23 and 24  

NASA Astrophysics Data System (ADS)

During the recent solar minimum between cycles 23 and 24 (solar minimum P23/24), the intensity of galactic cosmic rays (GCR) measured at the Earth was the highest ever recorded since space age. It is the purpose of this paper to resolve the most plausible mechanism for this unusually high intensity. A GCR transport model in three-dimensional heliosphere based on a simulation of Markov stochastic process is used to find the relation of cosmic ray modulation to various transport parameters, including solar wind (SW) speed, distance of heliospheric boundary, magnitude of interplanetary magnetic field (IMF) at the Earth, tilt angle of heliospheric current sheet, and values of parallel and perpendicular diffusion coefficients. We calculate GCR proton energy spectra at the Earth for the last three solar minima P21/22, P22/23, and P23/24, with the transport parameters obtained from observations. Besides weak IMF magnitude and slow SW speed, we find that a possible low magnetic turbulence, which increases the parallel diffusion and reduces the perpendicular diffusion in the polar direction, might be an additional possible mechanism for the high GCR intensity in the solar minimum P23/24.

Zhao, L.-L.; Qin, G.; Zhang, M.; Heber, B.

2014-03-01

50

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

51

Geomagnetic activity effect on the global ionosphere during the 2007-2009 deep solar minimum  

NASA Astrophysics Data System (ADS)

this paper the significant effect of weaker geomagnetic activity during the 2007-2009 deep solar minimum on ionospheric variability on the shorter-term time scales of several days was highlighted via investigating the response of daily mean global electron content (GEC, the global area integral of total electron content derived from ground-based GPS measurements) to geomagnetic activity index Ap. Based on a case during the deep solar minimum, the effect of the recurrent weaker geomagnetic disturbances on the ionosphere was evident. Statistical analyses indicate that the effect of weaker geomagnetic activity on GEC variations on shorter-term time scales was significant during 2007-2009 even under relatively quiet geomagnetic activity condition; daily mean GEC was positively correlated with geomagnetic activity. However, GEC variations on shorter-term time scales were poorly correlated with geomagnetic activity during the solar cycle descending phase of 2003-2005 except under strong geomagnetic disturbance condition. Statistically, the effects of solar EUV irradiance, geomagnetic activity, and other factors (e.g., meteorological sources) on GEC variations on shorter-term time scales were basically equivalent during the 2007-2009 solar minimum.

Chen, Yiding; Liu, Libo; Le, Huijun; Wan, Weixing

2014-05-01

52

The Viking solar corona experiment  

NASA Technical Reports Server (NTRS)

The 1976 Mars solar conjunction resulted in complete occultations 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 R sub s of the photosphere at the 3.5- and 13-cm wavelengths, respectively. The data can be used to determine the plasma density integrated along the radio path, the velocity of density irregularities in the coronal plasma, and the spectrum of the density fluctuations in the plasma. Observations of integrated plasma density near the south pole of the sun generally agree with a model of the corona which has an 8:1 decrease in plasma density from the equator to the pole. Power spectra of the 3.5- and 13-cm signals at a heliocentric radial distance of about 2 R sub s have a 1/2 power width of several hundred hertz and vary sharply with proximate geometric miss distance. Spectral broadening indicates a marked progressive increase in plasma irregularities with decreasing ray altitude at scales between about 1 and 100 km.

Tyler, G. L.; Brenkle, J. P.; Komarek, T. A.; Zygielbaum, A. I.

1977-01-01

53

Low Energy Charged Particles in the High Latitude Heliosphere: Comparing Solar Maximum to Solar Minimum  

NASA Astrophysics Data System (ADS)

The structure of the inner heliosphere that was delineated by the energetic charged particle populations (electrons and ions) during the recent Ulysses fast latitude scan during solar maximum conditions is found to be very different from that measured during a similar latitudinal transit in solar minimum conditions. Measurements made by the Heliosphere Instrument for Spectra, Composition and Anisoptropy at Low Energies (HI-SCALE; electrons ~50-1000 keV and ions ~50 keV-10000 keV/nucl) during solar maximum show that the inner heliosphere was populated at all latitudes, and with varying spatial scales, by particles largely originating from active solar regions. During solar minimum the major particle populations were confined to the near equatorial solar current sheet. The relative energetic ion (Z>2) abundances throughout the inner heliosphere were also substantially different, a result of the dominance in the inner heliosphere of solar-produced particles during solar maximum and the dominance of anomalous cosmic ray ions (especially O) and interplanetary accelerated particles during solar minimum. The H/He abundance ratios are nearly a factor of ten larger during solar maximum conditions at all heliolatitudes, showing the importance of a dominant solar source during this epoch. The ratios of the HI-SCALE ion abundances in the fast latitude scan during solar maximum are compared to measurements of ions made during the same time interval with a similar instrument (EPAM) on the ACE spacecraft in the ecliptic plane near 1 AU and show significant variations with time and spatial location. However, there are several intervals of time following solar maximum activity, including at latitudes as high as 80 degrees, during which the ion abundances and the electron fluxes at both locations are nearly identical. These intervals demonstrate that at times particle reservoirs (which are found to persist for nearly a solar rotation), can be established in the inner heliosphere and have volumes ranging from ~40 to ~ 150AU3.

Maclennan, C. G.; Lanzerotti, L. J.; Gold, R. E.; Hawkins, S. E.; Lario, D.

2002-05-01

54

GALACTIC COSMIC-RAY ENERGY SPECTRA AND COMPOSITION DURING THE 2009-2010 SOLAR MINIMUM PERIOD  

SciTech Connect

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 {approx}50-550 MeV nucleon{sup -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 {approx}7%, and the relative abundances changed by less than {approx}4%. Compared with the 1997-1998 solar minimum relative abundances, the 2009-2010 abundances differ by less than 2{sigma}, 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.; Binns, W. R.; Israel, M. H. [Department of Physics and the McDonnell Center for the Space Sciences, Washington University, St. Louis, MO 63130 (United States); Wiedenbeck, M. E. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Christian, E. R.; De Nolfo, G. A.; Von Rosenvinge, T. T. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Cummings, A. C.; Davis, A. J.; Leske, R. A.; Mewaldt, R. A.; Stone, E. C. [California Institute of Technology, Pasadena, CA 91125 (United States)

2013-06-20

55

The radial distribution of cosmic rays in the heliosphere at solar minimum and solar maximum  

NASA Astrophysics Data System (ADS)

The cosmic -ray intensity at solar minimum and maximum are an excellent metric for the quantitative comparison of their modulation over various 11 year solar activity cycles. The cosmic ray data from the Pioneer 10/11, Voyager 1/2 and IMP 8 missions span the period from the solar minimu m of cycle 20 through the solar maximum of cycle 23 to a heliocentric distance of 84 AU. As Pioneer and Voyager spacecraft move radially outward they explore a different part of the heliosphere over each successive cycle. At 1 AU, IMP 8 detailed H and He spectra and the counting rate of the climax neutron monitor are essentially the same over the cycle 20 and 22 solar minima--suggesting that the modulation state of the heliosphere was very similar for these periods. This allows the Pioneer and Voyager intensities for these periods to be combined. In addition, the Pioneer and Voyager missions were launched during the extended solar minimum of cycle 20, permitting a much more detailed examination of the radial intensity gradients, gr , in the inner heliosphere. Combining these 2 analysis techniques provides a detailed mapping of the cosmic ray distribution at solar minimum in a qA > 0 epoch (when positive ions drift inward over the solar poles). At this time gr for 265 MeV/n He is relatively steep (~ 12/r % / AU) inside 12 AU and becomes very small between ~ 12 and 70 AU. In cycle 21 (1987, qA<0), gr in the outer heliosphere is quite different. For solar maximum periods, a straightforward analysis technique has been developed that permits normalizing the GCR cosmic-ray data over all 3 solar maxima (21-23).

McDonald, F.; Fujii, Z.; Heikkila, B.; Lal, N.

56

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

NASA Technical Reports Server (NTRS)

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 Earth's 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

2011-01-01

57

Automated identification and tracking of polar-cap plasma patches at solar minimum  

NASA Astrophysics Data System (ADS)

A method of automatically identifying and tracking polar-cap plasma patches, utilising data inversion and feature-tracking methods, is presented. A well-established and widely used 4-D ionospheric imaging algorithm, the Multi-Instrument Data Assimilation System (MIDAS), inverts slant total electron content (TEC) data from ground-based Global Navigation Satellite System (GNSS) receivers to produce images of the free electron distribution in the polar-cap ionosphere. These are integrated to form vertical TEC maps. A flexible feature-tracking algorithm, TRACK, previously used extensively in meteorological storm-tracking studies is used to identify and track maxima in the resulting 2-D data fields. Various criteria are used to discriminate between genuine patches and "false-positive" maxima such as the continuously moving day-side maximum, which results from the Earth's rotation rather than plasma motion. Results for a 12-month period at solar minimum, when extensive validation data are available, are presented. The method identifies 71 separate structures consistent with patch motion during this time. The limitations of solar minimum and the consequent small number of patches make climatological inferences difficult, but the feasibility of the method for patches larger than approximately 500 km in scale is demonstrated and a larger study incorporating other parts of the solar cycle is warranted. Possible further optimisation of discrimination criteria, particularly regarding the definition of a patch in terms of its plasma concentration enhancement over the surrounding background, may improve results.

Burston, R.; Hodges, K.; Astin, I.; Jayachandran, P. T.

2014-03-01

58

Measurement of cosmic-ray proton and helium spectra during the 1987 solar minimum  

NASA Technical Reports Server (NTRS)

The differential cosmic-ray proton and helium spectra have been measured during the 1987 solar minimum using a balloon-borne superconducting magnetic spectrometer launched from Prince Albert, Canada. The changing geomagnetic cutoff along the balloon trajectory was observed in the low-energy proton data to be about 25 percent below the nominal calculated values. The absolute particle fluxes were approximately equal to the highest fluxes observed at the previous solar minimum in 1977. Above 10 GV the observed spectra are represented by a power law in rigidity with spectral indices of 2.74 + or - 0.02 for protons and 2.68 + or - 0.03 for helium. The measurements above 200 MeV per nucleon are consistent with rigidity power-law interstellar spectra modulated with the solar modulation parameter phi = 500 MV. The energy dependence of the proton-to-helium ratio is consistent with rigidity power-law injection spectra and rigidity-dependent propagation without reacceleration.

Seo, E. S.; Ormes, J. F.; Streitmatter, R. E.; Stochaj, S. J.; Jones, W. V.; Stephens, S. A.; Bowen, T.

1991-01-01

59

Topside Equatorial Ionospheric Density and Composition During and After Extreme Solar Minimum  

NASA Technical Reports Server (NTRS)

During the recent solar minimum, solar activity reached the lowest levels observed during the space age. This extremely low solar activity has accompanied a number of unexpected observations in the Earth s ionosphere-thermosphere system when compared to previous solar minima. Among these are the fact that the ionosphere is significantly contracted beyond expectations based on empirical models. Altitude profiles of ion density and composition measurements near the magnetic dip equator are constructed from the Communication/Navigation Outage Forecast System (C/NOFS) satellite to characterize the shape of the topside ionosphere during the recent solar minimum and into the new solar cycle. The variation of the profiles with respect to local time, season, and solar activity are compared to the IRI-2007 model. Building on initial results reported by Heelis et al. (2009), here we describe the extent of the contracted ionosphere, which is found to persist throughout 2009. The shape of the ionosphere during 2010 is found to be consistent with observations from previous solar minima.

Klenzing, J.; Simoes, F.; Ivanov, S.; Heelis, R. A.; Bilitza, D.; Pfaff, R.; Rowland, D.

2011-01-01

60

A Topside Equatorial Ionospheric Density and Composition Climatology During and After Extreme Solar Minimum  

NASA Technical Reports Server (NTRS)

During the recent solar minimum, solar activity reached the lowest levels observed during the space age. This extremely low solar activity has accompanied a number of unexpected observations in the Earth's ionosphere and thermosphere when compared to previous solar minima. Among these are the fact that the ionosphere is significantly contracted beyond expectations based on empirical models. Climatological altitude profiles of ion density and composition measurements near the magnetic dip equator are constructed from the C/NOFS satellite to characterize the shape of the top side ionosphere during the recent solar minimum and into the new solar cycle. The variation of the profiles with respect to local time, season, and solar activity are compared to the IRI-2007 model. Building on initial results reported by Heelis et al. [2009], here we describe the extent of the contracted ionosphere, which is found to persist throughout 2009. The shape of the ionosphere during 2010 is found to be consistent with observations from previous solar minima.

Klenzing, J. H.; Simoes, F.; Ivanov, S.; Heelis, R. A.; Bilitza, D.; Pfaff, R. F.; Rowland, D. E.

2011-01-01

61

Measurements of the radiation quality factor Q at aviation altitudes during solar minimum (2006-2008)  

NASA Astrophysics Data System (ADS)

In radiation protection, the Q-factor has been defined to describe the biological effectiveness of the energy deposition or absorbed dose to humans in the mixed radiation fields at aviation altitudes. This particular radiation field is generated by the interactions of primary cosmic particles with the atoms of the constituents of the Earth’s atmosphere. Thus the intensity, characterized by the ambient dose equivalent rate H?(10), depends on the flight altitude and the energy spectra of the particles, mainly protons and alpha particles, impinging on the atmosphere. These charged cosmic projectiles are deflected both by the interplanetary and the Earth’s magnetic field such that the corresponding energy spectra are modulated by these fields. The solar minimum is a time period of particular interest since the interplanetary magnetic field is weakest within the 11-year solar cycle and the dose rates at aviation altitudes reach their maximum due to the reduced shielding of galactic cosmic radiation. For this reason, the German Aerospace Center (DLR) performed repeated dosimetric on-board measurements in cooperation with several German airlines during the past solar minimum from March 2006 to August 2008. The Q-factors measured with a TEPC range from 1.98 at the equator to 2.60 in the polar region.

Meier, Matthias M.; Hubiak, Melina

2010-05-01

62

Galactic and Anomalous Cosmic Rays at 1 AU During the Recent Unusual Solar Minimum (Invited)  

NASA Astrophysics Data System (ADS)

Anomalous cosmic ray (ACR) intensities at 1 AU at solar minimum have generally tracked galactic cosmic ray (GCR) intensities such as those measured by neutron monitors, albeit with differences between solar polarity cycles. Throughout the present A<0 cycle ACR intensities have been consistently a factor of 3-4 lower than expected from scaling neutron monitor rates during the last A>0 cycle, similar to what was observed during the last A<0 period in the mid-1980's. Although the present solar minimum was deep and long-lasting with very low sunspot numbers and no major solar particle events, peak ACR intensities just barely reached their last A<0 levels. Meanwhile, GCR intensities (neutron monitor rates) were at the highest levels recorded during the last 50 years, indicating that these particles had easier access to the inner heliosphere than ACRs. During A<0 cycles particles preferentially drift inward along the heliospheric current sheet (HCS), and the HCS tilt angle dropped much more slowly this cycle than it did during the previous two cycles. Using neutron monitor data along with ACR and GCR measurements from the Advanced Composition Explorer spacecraft, we find that for a given HCS tilt angle both ACR and GCR intensities were actually much higher this cycle than they were during the last A<0 cycle. Evidently there was less overall modulation, but ACRs were more sensitive to the larger tilt of the HCS than GCRs, perhaps because of the latitudinal distribution of ACRs at their source. The HCS tilt angle increased abruptly in late 2009, and by early 2010 both ACR and GCR intensities showed dramatic decreases, apparently marking the end of solar minimum modulation conditions for this cycle. We present measurements of ACR and GCR intensities at 1 AU throughout the solar cycle and discuss possible explanations for the different behavior between the present A<0 epoch and the previous one. This work was supported by NASA grants NNX08AI11G and NNX10AE45G.

Leske, R. A.; Cummings, A. C.; Mewaldt, R. A.; Stone, E. C.

2010-12-01

63

Average photospheric poloidal and toroidal magnetic field components near solar minimum  

NASA Technical Reports Server (NTRS)

Average (over longitude and time) photospheric magnetic field components are derived from 3-min Stanford magnetograms made near the solar minimum of cycle 21. The average magnetograph signal is found to behave as the projection of a vector for measurements made across the disk. The poloidal field exhibits the familiar dipolar structure near the poles, with a measured signal in the line Fe I 5250 A of about 1 G. At low latitudes the poloidal field has the polarity of the poles, but is of reduced magnitude (about 0.1 G). A net photospheric toroidal field with a broad latitudinal extent is found. The polarity of the toroidal field is opposite in the northern and southern hemispheres and has the same sense as subsurface flux tubes giving rise to active regions of solar cycle 21. These observations are used to discuss large-scale electric currents crossing the photosphere and angular momentum loss to the solar wind.

Duvall, T. L., Jr.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M.

1979-01-01

64

Solar energetic proton events and coronal mass ejections near solar minimum  

NASA Technical Reports Server (NTRS)

We have examined the association of coronal mass ejections (CME's) with solar energetic (9-23 MeV) proton (SEP) events during the 1983-1985 approach to solar minimum. Twenty-two of 25 SEP events were associated with CME's, 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 CME's lay well out of the ecliptic plane. In a reverse study using all west hemisphere CME's of speeds exceeding 800 km/s and covering the period 1979-1985, we found that 29 of 31 events originating on the solar disk or limb were associated with observed SEP's. However, in contrast to the previous study, we found no cases of SEP events associated with magnetically well connected flares of short duration that lacked CME's.

Kahler, S. W.; Cliver, E. W.; Cane, H. V.; Mcguire, R. E.; Reames, D. V.; Sheeley, N. R., Jr.; Howard, R. A.

1987-01-01

65

The turbulent cascade and proton heating in the solar wind during solar minimum  

SciTech Connect

Solar wind measurements at 1 AU during the recent solar minimum and previous studies of solar maximum provide an opportunity to study the effects of the changing solar cycle on in situ heating. Our interest is to compare the levels of activity associated with turbulence and proton heating. Large-scale shears in the flow caused by transient activity are a source that drives turbulence that heats the solar wind, but as the solar cycle progresses the dynamics that drive the turbulence and heat the medium are likely to change. The application of third-moment theory to Advanced Composition Explorer (ACE) data gives the turbulent energy cascade rate which is not seen to vary with the solar cycle. Likewise, an empirical heating rate shows no significan changes in proton heating over the cycle.

Coburn, Jesse T.; Smith, Charles W.; Vasquez, Bernard J. [Physics Department and Space Science Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire (United States); Stawarz, Joshua E. [Department of Astrophysical and Planetary Sciences, University of Colorado at Boulder, Boulder, Colorado (United States); Forman, Miriam A. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York (United States)

2013-06-13

66

Comparison of Magnesium II Core-to-Wing Ratio Measurements During Solar Minimum 23/24  

NASA Astrophysics Data System (ADS)

Solar extreme ultraviolet (EUV) radiation is the primary energy source to the Earth's upper atmosphere; it heats the thermosphere, creates the ionosphere, and drives photochemistry. A useful proxy for EUV irradiance is the Magnesium II Core-to-Wing Ratio (Mg II index) which is calculated from solar irradiance measurements near 280 nm. This poster compares different satellite measurements of the Mg II index made during the recent solar minimum. We also contrast the indices calculated from high spectral resolution data with indices derived with the classic calculation and 1.1 nm resolution data. These results will be combined with prior Mg II composite time series to create a composite that best represents solar activity over the spacecraft era - 35 years and counting.

Machol, J. L.; Snow, M. A.; Viereck, R. A.; Weber, M.; Richard, E. C.; Puga, L. C.

2013-12-01

67

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

NASA Astrophysics Data System (ADS)

The Solar Aspect System (SAS) of the RHESSI satellite measures the optical solar limb in the red continuum with a cadence typically set at 32 samples/s in each of three linear CCD sensors. RHESSI has observed the Sun continuously now for more than 10 years, and we have acquired a unique data set ranging almost over a full solar cycle and consisting of about 25x10^9 single data points. For a three month period during the active phase of the last 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. These measurements have led to the most accurate oblateness measurement to date, 8.01+-0.14 milli arcsec (Fivian et al., 2008), a value consistent with models predicting an oblateness from surface rotation. In order to avoid confusion between magnetic activity and a correlated brightness enhancement in the SAS signal, the SAS data has been masked using the SOHO/EIT284A data, and SDO/AIA for more recent data. The measured oblateness as function of the masking level is then extrapolated for a value of the underlaying, presumably non-magnetic sun. A recent and significantly improved calibration of the SAS data have allowed a new access to a measurement of the solar oblateness during the last, extended solar minimum. 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.

2012-12-01

68

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

NASA Astrophysics Data System (ADS)

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 11-17 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) local solar time plane, CHAMP at a mean altitude of 332 km and GRACE 144 km higher. The mean observed and model density profiles at 476 km reveal considerable differences, which, except for a 25% bias, is not the case at an altitude of 332 km. These differences result from the fact that during this solar minimum the transition from predominantly O to He occurs at a much lower altitude in connection with the winter helium bulge than is predicted by the model. When averaged over the 1 week period, striking wave-3 structures are revealed with respect to longitude that are remarkably consistent between CHAMP and GRACE. We interpret these as the manifestations of nonmigrating tides propagating upward from the lower atmosphere. Comparisons are made with similar data from August 2008, which reveal a wave-4 structure. However, whereas previous results and conventional wisdom would suggest that these features are produced by the eastward propagating diurnal tides with zonal wave numbers s = -2 (DE2) and s = -3 (DE3), respectively, the asymmetries and day-night phase differences that are present suggest the predominance of semidiurnal tides SE1 and SE2, respectively, along with the aforementioned diurnal tides as well as tides SW5 and SW6.

Bruinsma, Sean L.; Forbes, Jeffrey M.

2010-11-01

69

Plasmaspheric electron content derived from GPS TEC and FORMOSAT-3/COSMIC measurements: Solar minimum condition  

NASA Astrophysics Data System (ADS)

The plasmaspheric electron content (PEC) was estimated by comparison of GPS TEC observations and FORMOSAT-3/COSMIC radio occultation measurements at the extended solar minimum of cycle 23/24. Results are retrieved for different seasons (equinoxes and solstices) of the year 2009. COSMIC-derived electron density profiles were integrated up to the height of 700 km in order to retrieve estimates of ionospheric electron content (IEC). Global maps of monthly median values of COSMIC IEC were constructed by use of spherical harmonics expansion. The comparison between two independent measurements was performed by analysis of the global distribution of electron content estimates, as well as by selection specific points corresponded to mid-latitudes of Northern America, Europe, Asia and the Southern Hemisphere. The analysis found that both kinds of observations show rather similar diurnal behavior during all seasons, certainly with GPS TEC estimates larger than corresponded COSMIC IEC values. It was shown that during daytime both GPS TEC and COSMIC IEC values were generally lower at winter than in summer solstice practically over all specific points. The estimates of PEC (h > 700 km) were obtained as a difference between GPS TEC and COSMIC IEC values. Results of comparative study revealed that for mid-latitudinal points PEC estimates varied weakly with the time of a day and reached the value of several TECU for the condition of solar minimum. Percentage contribution of PEC to GPS TEC indicated the clear dependence from the time with maximal values (more than 50-60%) during night-time and lesser values (25-45%) during day-time.

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

2012-08-01

70

Altitude variations in the thermosphere mass density response to geomagnetic activity during the recent solar minimum  

NASA Astrophysics Data System (ADS)

data from coplanar orbits of Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites were used to study the complex altitude and latitude variations of the thermosphere mass density response to geomagnetic activity during 1-10 December 2008 near 09 LT. Helium number densities near 500 km altitude were extracted from the CHAMP and GRACE measurements and clearly show the presence of a winter hemisphere helium bulge. This recent extreme solar minimum indicates that wintertime helium concentrations exceed NRLMSISE-00 model estimates by 30%-70% during quiet geomagnetic activity after adjusting F10.7 input into MSIS. The perturbation in mass density from quiet to active conditions is found to be less enhanced in the winter hemisphere at the higher GRACE altitudes (25%) than at the lower CHAMP altitudes (60%) and is attributed to dynamic behavior in the helium/oxygen transition. The investigation revealed the maximum storm time density perturbation to occur near the He/O transition region with a much weaker maximum near the O/N2 transition region. The altitude of maximum density perturbation occurs where the perturbation in the weighted pressure scale height is equal and opposite to the perturbation in the weighted mean molecular weight scale height. The altitude structure of density scale height perturbation is significantly influenced by the changes in the molecular weight scale height and can account for 50% of the change in mass density scale height in a region correspondingly close to the He/O transition during the 2008 solar minimum period.

Liu, X.; Thayer, J. P.; Burns, A.; Wang, W.; Sutton, E.

2014-03-01

71

The spatial distribution of galactic and anomalous cosmic rays in the heliosphere at solar minimum  

NASA Astrophysics Data System (ADS)

As they move out at an average rate of 3 AU/year, the Pioneer and Voyager spacecraft sample a different region of space over each phase of the 11-year solar activity and 22 year heliomagnetic cycle. To separate temporal and spatial variations and to obtain a more detailed description of the radial variation it would be highly desirable to combine the data from different solar cycle. For the cycle 20 and 22 solar minima it was found that the 1 AU IMP 8 detailed H and He spectra and the counting rate of the Climax neutron monitor were essentially the same, suggesting that the modulation state of the heliosphere was very similar for these periods (McDonald et al., 2001). This allowed the Pioneer and Voyager intensities for these times to be combined. In addition, P-10 was launched near the beginning of the extended solar minimum of cycle 20, which made possible a more detailed examination of the radial intensity gradients, g_r, in the inner heliosphere. The combined GCR He and H spectra for cycle 20 and 22 (qA>0) and for cycle 21 (qA<0) have been published. In this paper we present the combined cycle 20 and 22, and cycle 21 ACR intensities for 4-10 MeV/n, 10-21 MeV/n and 30-56 MeV/n ACR He and 8-18 MeV/n ACR O. A strong rigidity dependence in the ACR radial distribution is observed at the lower rigidities, a very different result from that reported for GCR H and He at solar minimum.

Fujii, Z.; McDonald, F. B.

72

Cosmic Rays in the Heliosphere over the Solar Minimum of Cycle 22  

NASA Astrophysics Data System (ADS)

The combination of Voyager 1 and 2 in the distant heliosphere and IMP 8 and Ulysses in the inner heliosphere provide cosmic ray observations over the solar minimum period of cycle 22 that extend beyond 70 AU. The cosmic ray intensity at 1 AU over the 1996-1997 time period exhibits the quasi-plateau like characteristic predicted for qA>0 epochs and the energy spectra of 20-450 MeV/n He and 20-220 MeV H are essentially identical to those observed for 1976-1977 over a similar phase of the heliomagnetic cycle, suggesting that modulation conditions at both times are very similar throughout the heliosphere. This similarity makes it possible to combine the Pioneer 10 data from 1977 with that of Voyager 1 and 2 from 1997 to obtain a more detailed measure of the distribution of cosmic rays in the heliosphere from 1 to > 70 AU near the ecliptic plane (?<35?). It is found that beyond ~12 AU the radial intensity gradients are very small; less than 0.33% AU for 265 MeV/n He. Such a small intensity gradient indicates that the intensity levels observed at V-1 for 7-18 MeV/n ACR 0+ and 265 MeV/n He are close to those expected at the termination shock at the V-1 heliolatitude of 34ºN. Furthermore the measured 1997 intensities of the GCR He and ACR 0+ at 70 AU are significantly less (x 5 smaller for ACR 0+ ) than those observed at the 1987 solar minimum at 42 AU. For the ACR component such changes appear to be qualitatively consistent with Jokipii's diffusive shock drift acceleration model. For GCR He the difference may be further evidence for modulation in the region of the heliosheath combined with gradient and curvature drift effects over the two different phases of the heliomagnetic cyle.

McDonald, F.; Cummings, A.; Lal, N.; McGuire, R.; Stone, E.

2001-08-01

73

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

SciTech Connect

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 hydrogen through the solar wind system shows that the rate of charge exchange with solar wind protons is 30% less over the solar poles than in the ecliptic. This result is in agreement with a similar experiment performed with Mariner 10 at the previous solar minimum.

Ajello, J.M. (California Inst. of Tech., Pasadena (USA))

1990-09-01

74

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Technical Reports Server (NTRS)

Under this contract, we have continued our investigations of the large scale structure of the solar corona and inner heliosphere using global magnetohydrodynamic (MHD) simulations. These computations have also formed the basis for studies of coronal mass ejections (CMES) using realistic coronal configurations. We have developed a technique for computing realistic magnetohydrodynamic (MHD) computations of the solar corona and inner heliosphere. To perform computations that can be compared with specific observations, it is necessary to incorporate solar observations into the boundary conditions. We have used the Wilcox Solar Observatory synoptic maps (collected during a solar rotation by daily measurements of the line-of-sight magnetic field at central meridian) to specify the radial magnetic field (B,) at the photosphere. For the initial condition, we use a potential magnetic field consistent with the specified distribution of B, at the lower boundary, and a wind solution consistent with the specified plasma density and temperature at the solar surface. Together this initial condition forms a (non-equilibrium) approximation of the state of the solar corona for the time-dependent MHD computation. The MHD equations are then integrated in time to steady state. Here we describe solutions relevant to a recent solar eclipse, as well as Ulysses observations. We have also developed a model configuration of solar minimum, useful for studying CME initiation and propagation.

Linker, Jon A.

1997-01-01

75

Comparative Study of foF2 Measurements with IRI-2007 Model Predictions During Extended Solar Minimum  

NASA Technical Reports Server (NTRS)

The unusually deep and extended solar minimum of cycle 2324 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 IRIprovides reliable results that compare well with actual measurements, when the definite (observed and adjusted) indices of solar activityare 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.

2013-01-01

76

Comparison of the effect of the correlation length on modulation during solar minimum and solar maximum conditions  

Microsoft Academic Search

Ab initio approaches to study the solar modulation of cosmic rays during solar minimum conditions have shown that we do not yet have a full understanding of, e.g., the diffusion tensor. In this paper we show that during periods near solar maximum conditions the constraints on turbulence quantities which enter into the diffusion tensor become even more severe than during

R. Burger; S. Parhi; J. Minnie; J. Bieber; W. Matthaeus

2002-01-01

77

Comprehensive Ionospheric Polar and Auroral Observations for Solar Minimum of Cycle 23/24  

NASA Astrophysics Data System (ADS)

Only the incoherent scatter radar (ISR) is able to simultaneously measure full profiles of elec-tron density, ion temperature, and electron temperatures through the E-and F-layers of the terrestrial ionosphere. Historically ISR's have been operated for periods much less than a month. Hence, their measurements do not constitute a continuous sequence from which quiet, disturbed, and storm periods can reliably be discerned. This is particularly true in the auroral and polar regions. During the International Polar Year (IPY) two ISRs achieved close to 24/7 continuous observations. This presentation describes their data sets and specifically how they can provide the IRI with a fiduciary E-and F-region ionosphere descriptions for solar minimum conditions at auroral and polar cap locations. The ionospheric description being electron den-sity, ion temperature, electron temperature, and even molecular ion composition profiles from as low as 90 km extending several scale heights above the F-layer peak. The auroral location is Poker Flat in Alaska at 65.4° N, 147.5° W where the NSF's new Poker Flat Incoherent Scatter Radar (PFISR) is located. During solar minimum conditions this location is in the auroral region for most of the day and is at mid-latitudes, equatorward of the cusp, for about 4 to 8 hours per day dependent upon geomagnetic activity. In contrast the polar location is Svalbard, at 78° N, 16° E where the EISCAT Svalbard Radar (ESR) is located. For most of the day the ESR is in the Northern Polar Cap often with a noon sector passage through the dayside cusp. Of unique relevance to IRI is that these extended observations have enabled the ionospheric morphology to be demarked between quiet and disturbed. During the IPY year, 1 March 2007 to 29 February 2008, a total of 50 solar wind corotating interaction regions (CIRs) impacted geospace. Each CIR has a one-to-three day geomagnetic disturbance that is observed in the ISR auroral and polar observations. Hence, this data set enables the quiet-background ionosphere to be established as a function of season and local time. This quiet-background ionosphere has the unique attribute that it has self-consistent altitude profiles of the density and the temper-ature. This we believe is a true fiduciary reference for the IRI in a high latitude region, that is otherwise particularly difficult to quantify.

Sojka, Jan J.; Nicolls, Michael; van Eyken, Anthony; Heinselman, Craig

78

24/7 Solar Minimum Polar Cap and Auroral Ion Temperature Observations  

NASA Technical Reports Server (NTRS)

During the International Polar Year (IPY) two Incoherent Scatter Radars (ISRs) achieved close to 24/7 continuous observations. This presentation describes their data sets and specifically how they can provide the International Reference Ionosphere (IRI) a fiduciary E- and F-region ionosphere description for solar minimum conditions in both the auroral and polar cap regions. The ionospheric description being electron density, ion temperature and electron temperature profiles from as low as 90 km extending to several scale heights above the F-layer peak. The auroral location is Poker Flat in Alaska at 65.1 N latitude, 212.5 E longitude where the NSF s new Poker Flat Incoherent Scatter Radar (PFISR) is located. This location during solar minimum conditions is in the auroral region for most of the day but is at midlatitudes, equator ward of the cusp, for about 4-8 h per day dependent upon geomagnetic activity. In contrast the polar location is Svalbard, at 78.2 N latitude, 16.0 E longitude where the EISCAT Svalbard Radar (ESR) is located. For most of the day the ESR is in the Northern Polar Cap with a noon sector passage often through the dayside cusp. Of unique relevance to IRI is that these extended observations have enabled the ionospheric morphology to be distinguished between quiet and disturbed geomagnetic conditions. During the IPY year, 1 March 2007 - 29 February 2008, about 50 solar wind Corotating Interaction Regions (CIRs) impacted geospace. Each CIR has a two to five day geomagnetic disturbance that is observed in the ESR and PFISR observations. Hence, this data set also enables the quiet-background ionospheric climatology to be established as a function of season and local time. These two separate climatologies for the ion temperature at an altitude of 300 km are presented and compared with IRI ion temperatures. The IRI ion temperatures are about 200-300 K hotter than the observed values. However, the MSIS neutral temperature at 300 km compares favorably with the quiet-background in temperature, both in magnitude and climatology.

Sojka, Jan J.; Nicolls, Michael; van Eyken, Anthony; Heinselman, Craig; Bilitza, Dieter

2011-01-01

79

24/7 Solar minimum polar cap and auroral ion temperature observations  

NASA Astrophysics Data System (ADS)

During the International Polar Year (IPY) two Incoherent Scatter Radars (ISRs) achieved close to 24/7 continuous observations. This presentation describes their data sets and specifically how they can provide the International Reference Ionosphere (IRI) a fiduciary E- and F-region ionosphere description for solar minimum conditions in both the auroral and polar cap regions. The ionospheric description being electron density, ion temperature and electron temperature profiles from as low as 90 km extending to several scale heights above the F-layer peak. The auroral location is Poker Flat in Alaska at 65.1 °N latitude, 212.5 °E longitude where the NSF's new Poker Flat Incoherent Scatter Radar (PFISR) is located. This location during solar minimum conditions is in the auroral region for most of the day but is at mid-latitudes, equator ward of the cusp, for about 4-8 h per day dependent upon geomagnetic activity. In contrast the polar location is Svalbard, at 78.2 °N latitude, 16.0 °E longitude where the EISCAT Svalbard Radar (ESR) is located. For most of the day the ESR is in the Northern Polar Cap with a noon sector passage often through the dayside cusp. Of unique relevance to IRI is that these extended observations have enabled the ionospheric morphology to be distinguished between quiet and disturbed geomagnetic conditions. During the IPY year, 1 March 2007 - 29 February 2008, about 50 solar wind Corotating Interaction Regions (CIRs) impacted geospace. Each CIR has a two to five day geomagnetic disturbance that is observed in the ESR and PFISR observations. Hence, this data set also enables the quiet-background ionospheric climatology to be established as a function of season and local time. These two separate climatologies for the ion temperature at an altitude of 300 km are presented and compared with IRI ion temperatures. The IRI ion temperatures are about 200-300 K hotter than the observed values. However, the MSIS neutral temperature at 300 km compares favorably with the quiet-background in temperature, both in magnitude and climatology.

Sojka, Jan J.; Nicolls, Michael; van Eyken, Anthony; Heinselman, Craig; Bilitza, Dieter

2011-07-01

80

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

81

The galactic and anomalous cosmic-ray intensiity during the extended 2009 solar minimum  

NASA Astrophysics Data System (ADS)

The solar minimum of 2009 was characterized by a prolonged increase towards the maximum galactic cosmic-ray intensity, which was higher than it was during the maxima of 22 and 44 years ago. Solar activity parameters were significantly different from previous solar minima, in particular the heliospheric magnetic field which was almost 40% weaker. In the previous two so-called qA<0 (solar dipole moment facing South) magnetic cycles, these increases were more sharply peaked than in 2009. Neutron monitor observations are used to investigate this behavior in terms of propagation conditions due to solar activity, the heliospheric magnetic field, and the profile of the wavy current sheet in the field. Anomalous cosmic rays did not observe this large increase, and from this difference between the two species we demonstrate how the magnitude of the heliospheric magnetic field controls this modulation. This result can be used to infer the strength of the solar and interplanetary magnetic field in the distant past (before the instrumental era).

Moraal, H.

2013-05-01

82

Response of Venusian bow shock to solar wind under long-lasting solar minimum  

NASA Astrophysics Data System (ADS)

The period of low solar activity between solar cycles 23 and 24 that occurred from 2006 through 2010 was as long and as quiet as any on record since the beginning of space flight, and likely in over a century. From May 2006 the Venus Express (VEX) spacecraft continuously operated at Venus and crossed its bow shock twice per orbit (24 hour). Since the location and shape of the bow shock are highly sensitive to solar EUV, Here the long-lasting solar minimum provides such an opportunity to extract the influence of interplanetary magnetic field (IMF) on the bow shock from the observations. We use VEX data during 2006/06-2010/07 to determine the locations of bow shock, and then investigate the variations of these boundary positions as response to the orientation and magnitude of IMF. Our analysis of the large database shows that the magnitude of perpendicular component of IMF can affect the size of bow shock and there are some magnetic pole-equator asymmetries of bow shock location near the subsolar point and in tail region.

Chai, Lihui; Wei, Yong; Fraenz, Markus; Wan, Weixing; Zhang, Tielong

2014-05-01

83

The impact of radiation belts region on top side ionosphere condition during last solar minimum.  

NASA Astrophysics Data System (ADS)

The wave particle interactions in radiation belts region are one of the key parameters in understanding the global physical processes which govern the near Earth environment. The populations of outer radiation belts electrons increasing in response to changes in the solar wind and the interplanetary magnetic field, and decreasing as a result of scattering into the loss cone and subsequent absorption by the atmosphere. The most important question in relation to understanding the physical processes in radiation belts region relates to estimate the ratio between acceleration and loss processes. This can be also very useful for construct adequate models adopted in Space Weather program. Moreover the wave particle interaction in inner radiation zone and in outer radiation zone have significant influence on the space plasma property at ionospheric altitude. The aim of this presentation is to show the manifestation of radiation belts region at the top side ionosphere during the last long solar minimum. The presentation of longitude and seasonal changes of plasma parameters affected by process occurred in radiation belts region has been performed on the base of the DEMETER and COSMIC 3 satellite registration. This research is partly supported by grant O N517 418440

Rothkaehl, Hanna; Przepiórka, Dororta; Matyjasiak, Barbara

2014-05-01

84

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

85

The Mapping of high-latitude TEC fluctuations during the last extended solar minimum  

NASA Astrophysics Data System (ADS)

During the last few years the number of the GPS permanent stations have been increasing systematically. Currently it is possible to use phase GPS observations for detecting of the ionospheric disturbances with high spatial and temporal resolution. In this study 30 second GPS measurements were used to investigate the occureance of the TEC fluctuations at high and mid latitudes during the extended solar minimum period (2008-2011). Based on observations from more than 100 permanent stations the 2-hour maps of the TEC variability and daily map of the ionospheric fluctuations as a function geomagnetic local time were created. In order to determine the variability of the ionosphere ROT (Rate of TEC) and ROTI (Rate of TEC index) were used. 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. The statistical characteristics of fluctuation intensity and TEC fluctuations maps as well as data processing technique are presented.

Sieradzki, R.; Cherniak, I.

2012-04-01

86

Comparison of Transport Codes, HZETRN, HETC and FLUKA, Using 1977 GCR Solar Minimum Spectra  

NASA Technical Reports Server (NTRS)

The HZETRN deterministic radiation transport code is one of several tools developed to analyze the effects of harmful galactic cosmic rays (GCR) and solar particle events (SPE) on mission planning, astronaut shielding and instrumentation. This paper is a comparison study involving the two Monte Carlo transport codes, HETC-HEDS and FLUKA, and the deterministic transport code, HZETRN. Each code is used to transport ions from the 1977 solar minimum GCR spectrum impinging upon a 20 g/cm2 Aluminum slab followed by a 30 g/cm2 water slab. This research is part of a systematic effort of verification and validation to quantify the accuracy of HZETRN and determine areas where it can be improved. Comparisons of dose and dose equivalent values at various depths in the water slab are presented in this report. This is followed by a comparison of the proton fluxes, and the forward, backward and total neutron fluxes at various depths in the water slab. Comparisons of the secondary light ion 2H, 3H, 3He and 4He fluxes are also examined.

Heinbockel, John H.; Slaba, Tony C.; Tripathi, Ram K.; Blattnig, Steve R.; Norbury, John W.; Badavi, Francis F.; Townsend, Lawrence W.; Handler, Thomas; Gabriel, Tony A.; Pinsky, Lawrence S.; Reddell, Brandon; Aumann, Aric R.

2009-01-01

87

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.; BröNnimann, S.; Arfeuille, F.; Beer, J.; Shapiro, A. I.; Raible, C. C.; Steinhilber, F.; Schmutz, W. K.

2013-08-01

88

High-cadence observations of CME initiation and plasma dynamics in the corona with TESIS on board CORONAS-Photon  

NASA Astrophysics Data System (ADS)

The TESIS is an ensemble of space instruments designed in Lebedev Institute of Russian Academy of Sciences for spectroscopic and imaging investigation of the Sun in EUV and soft X-ray spectral range with high spatial, temporal and spectral resolution. From 2009 January, when TESIS was launched onboard the Coronas-Photon satellite, it provided about 200 000 new images and spectra of the Sun, obtained during one of the deepest solar minimum in last century. Because of the wide field of view (4 solar radii) and high sensitivity, TESIS provided high-quality data on the origin and dynamics of eruptive prominences and CMEs in the low and intermediate solar corona. TESIS is also the first EUV instrument which provided high-cadence observations of coronal bright points and solar spicules with temporal resolution of a few seconds. We present first results of TESIS observations and discuss them from a scientific point of view.

Bogachev, Sergey; Kuzin, Sergey; Zhitnik, I. A.; Bugaenko, O. I.; Goncharov, A. L.; Ignatyev, A. P.; Krutov, V. V.; Lomkova, V. M.; Mitrofanov, A. V.; Nasonkina, T. P.; Oparin, S. N.; Petzov, A. A.; Shestov, S. V.; Slemzin, V. A.; Soloviev, V. A.; Suhodrev, N. K.; Shergina, T. A.

89

Polar cap convection/precipitation states during Earth passage of two ICMEs at solar minimum  

NASA Astrophysics Data System (ADS)

We report important new aspects of polar cap convection and precipitation (dawn-dusk and inter-hemisphere asymmetries) associated with the different levels of forcing of the magnetosphere by two interplanetary (IP) magnetic clouds on 20 November 2007 and 17 December 2008 during solar minimum. Focus is placed on two intervals of southward magnetic cloud field with large negative By components (Bx=-5 versus 0 nT) and with high and low plasma densities, respectively, as detected by spacecraft Wind. The convection/precipitation states are documented by DMSP spacecraft (Southern Hemisphere) and SuperDARN radars (Northern Hemisphere). The (negative) By component of the cloud field is accompanied by a newly-discovered flow channel (called here FC 2) threaded by old open field lines (in polar rain precipitation) at the dusk and dawn sides of the polar cap in the Northern and Southern Hemispheres, respectively, and a corresponding Svalgaard-Mansurov (S-M) effect in ground magnetic deflections. On 20 November 2007 the latter S-M effect in the Northern winter Hemisphere appears in the form of a sequence of six 5-10 min long magnetic deflection events in the 71-74° MLAT/14:30-16:00 MLT sector. The X-deflections are consistent with the flow direction in FC 2 (i.e. caused by Hall currents) in both IP cloud cases. The presence of a lobe cell and associated polar arcs in the Southern (summer) Hemisphere in the low density (1-2 cm-3) and Bx=0 ICME case is accompanied by the dropout of polar rain precipitation in the dusk-side regime of sunward polar cap convection and inward-directed Birkeland current. The low-altitude observations are discussed in terms of momentum transfer via dynamo processes in the high- and low-latitude boundary layers and Birkeland currents located poleward of the traditional R1-R2 system.

Sandholt, P. E.; Andalsvik, Y.; Farrugia, C. J.

2010-04-01

90

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 2007-2009 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 2007-2009. Percentage contribution of ECpl to GPS TEC indicates the clear dependence from the time and varies from a minimum of about 25-50% during day-time to the value of 50-75% 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 5-10% of GPS TEC during night and about 20-27% during day-time. Topside IEC contributes about 15-20% of GPS TEC during night and about 35-40% during day-time. The obtained results were compared with TEC, IEC and ECpl estimates retrieved by Standard Plasmasphere-Ionosphere 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

91

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

92

Solar minimum spectra of galactic cosmic rays and their implications for models of the near-earth radiation environment  

NASA Astrophysics Data System (ADS)

The radiation dose from galactic cosmic rays during a manned mission to Mars is expected to be comparable to the allowable limit for space shuttle astronauts. Most of this dose would be due to galactic cosmic rays with energies <1 GeV nucleon-1, with important contributions from heavy nuclei in spite of their low abundance relative to H and He. Using instruments on NASA's Advanced Composition Explorer (ACE) spacecraft, we have made the most statistically precise measurements to date of the solar minimum energy spectra of cosmic ray nuclei with charge Z=4-28 in the energy range ~40-500 MeV nucleon-1. We compare these measurements obtained during the 1997-1998 solar minimum period with measurements from previous solar minima and with models of the near-Earth radiation environment currently used to perform shielding and dose calculations. We find that the cosmic ray heavy-element spectra measured by ACE are as much as 20% higher than previously published solar minimum measurements. We also find significant differences between the ACE measurements and the predictions of available models of the near-Earth radiation environment, suggesting that these models need revision. We describe a cosmic ray interstellar propagation and solar modulation model that provides an improved fit to the ACE measurements compared to radiation environment models currently in use.

Davis, A. J.; Mewaldt, R. A.; Cohen, C. M. S.; Cummings, A. C.; George, J. S.; Leske, R. A.; Stone, E. C.; Wiedenbeck, M. E.; Yanasak, N. E.; Christian, E. R.; von Rosenvinge, T. T.; Binns, W. R.; Hink, P. L.

2001-12-01

93

Coronal Rotation Between 1.5 and 3.5 Solar Radii at Solar Minimum  

NASA Astrophysics Data System (ADS)

Here we report on coronal rotation measurements using STEREO COR1. Multiple studies have confirmed that rotation rates in the outer corona differ markedly from those of the photosphere, where a steady decline in rotation rate with latitude is observed. Emission line observations of low-lying coronal magnetic features typically correspond well with photospheric rotation rates, while white-light measurements in the upper corona indicate very rigid rotation. Some studies have reported a sudden jump in the rotation rate in the 2.3-2.5 R_sun range, indicating a transition from differentially rotating features to rigidly rotating ones. It has been suggested that the rotation rates measured in a given study may be related to the lifetimes of features observed, which should make the simultaneous observation of features rotating at different rates difficult. Using autocorrelation measurements of COR1 data we have studied rotation rates between 1.5 and 3.5 solar radii for features with lifetimes longer than one full rotation. We observe latitudinally and radially rigid rotation during 2007 and 2008, and no transition from differentially rotating to rigidly rotating features. This is consistent with the idea that longer-lived features rotate more rigidly, or with a transition from differential to rigid rotation below 1.5 R_sun.

Jones, S. I.; Davila, J. M.

2009-12-01

94

Atmospheric effect of repeated high-energy electron precipitation at high latitude during solar minimum time  

NASA Astrophysics Data System (ADS)

Today it is a well established concept how high-energy auroral electrons and solar protons, when precipitating into the atmosphere, may cause significant variations of minor neutral gas concentrations. The excess ionization events initiate production of odd hydrogen and odd nitrogen, the latter even being long-lived in the absence of sunlight, so that the chemistry effects which finally may affect even the upper atmospheric ozone concentration, are transported even to lower altitudes and latitudes. Whereas the solar proton events, including experimental verification of the effects, are well studied in recent literature, very few experimental findings are published about the actual contribution of the high-energy electron precipitation events. After reviewing shortly the recent advance in understanding the effects of excess ionisation events on neutral atmospheric composition, we present an analysis of a unique data set of electron precipitation effects at high latitudes during solar minimum time: The one year long IPY data set of incoherent scatter radar measurements in Longyearbyen by the EISCAT Svalbard Radar (ESR). ESR was operated in a continuous mode from 1 March 2007 to 29 February 2008, and backscattered power measurements, with 3 km range resolution and 2.25 km range steps, start from the altitude of 45 km. Data is subject to sea and/or tropospheric clutter, which is variable with season/day up to 65 km. However, 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 perform analysis of the atmospheric effects of these ionisation events by using the detailed Sodankyla Ion Chemistry model of D region throughout the 1-year long IPY period, and point out possibilities to observe these variations in other sets of data, as well as the significance of improving continuous monitoring of D region ionisation by the existing and proposed new incohorent scatter facilities, such as the EISCAT 3D volumetric imaging incoherent scatter radar in Northern Scandinavia.

Turunen, Esa; Haggstrom, Ingemar; Enell, Carl-Fredrik

2012-07-01

95

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

96

The Peculiar Solar Minimum 23/24 Revealed by the Microwave Butterfly Diagram  

NASA Technical Reports Server (NTRS)

The diminished polar magnetic field strength during the minimum between cycles 23 and 24 is also reflected in the thermal radio emission originating from the polar chromosphere. During solar minima, the polar corona has extended coronal holes containing intense unipolar flux. In microwave images, the coronal holes appear bright, with a brightness enhancement of 500 to 2000 K with respect to the quiet Sun. The brightness enhancement corresponds to the upper chromosphere, where the plasma temperature is approx.10000 K. We constructed a microwave butterfly diagram using the synoptic images obtained by the Nobeyama radioheliograph (NoRH) showing the evolution of the polar and low latitude brightness temperature. While the polar brightness reveals the chromospheric conditions, the low latitude brightness is attributed to active regions in the corona. When we compared the microwave butterfly diagram with the magnetic butterfly diagram, we found a good correlation between the microwave brightness enhancement and the polar field strength. The microwave butterfly diagram covers part of solar cycle 22, whole of cycle 23, and part of cycle 24, thus enabling comparison between the cycle 23/24 and cycle 22/23 minima. The microwave brightness during the cycle 23/24 minimum was found to be lower than that during the cycle 22/23 minimum by approx.250 K. The reduced brightness temperature is consistent with the reduced polar field strength during the cycle 23/24 minimum seen in the magnetic butterfly diagram. We suggest that the microwave brightness at the solar poles is a good indicator of the speed of the solar wind sampled by Ulysses at high latitudes..

Gopalswamy, Natchimuthuk; Yashiro, Seiji; Makela, Pertti; Shibasaki, Kiyoto; Hathaway, David

2010-01-01

97

Ionospheric VTEC and thermospheric infrared emission dynamics during corotating interaction region and high-speed stream intervals at solar minimum: 25 March to 26 April 2008  

Microsoft Academic Search

Thermospheric infrared emission shows strong response to HSS drivingVTEC data show fast, continuous, and global response to external forcing by HSSsHeliospheric-magnetospheric-ionospheric-thermospheric coupling at solar minimum

O. P. Verkhoglyadova; B. T. Tsurutani; A. J. Mannucci; M. G. Mlynczak; L. A. Hunt; A. Komjathy; T. Runge

2011-01-01

98

Ultrasonic corona sensor study  

NASA Technical Reports Server (NTRS)

The overall objective of this program is to determine the feasibility of using ultrasonic (above 20 kHz) corona detection techniques to detect low order (non-arcing) coronas in varying degrees of vacuum within large high vacuum test chambers, and to design, fabricate, and deliver a prototype ultrasonic corona sensor.

Harrold, R. T.

1976-01-01

99

CHANDRA OBSERVATIONS OF COMETS 8P/TUTTLE AND 17P/HOLMES DURING SOLAR MINIMUM  

SciTech Connect

We present results for Chandra X-ray Observatory observations of two comets made during the minimum of solar cycle 24. The two comets, 17P/Holmes (17P) and 8P/Tuttle (8P), were very different in their activity and geometry. 17P was observed, for 30 ks right after its major outburst, on 2007 October 31 (10:07 UT), and comet 8P/Tuttle was observed in 2008 January for 47 ks. During the two Chandra observations, 17P was producing at least 100 times more water than 8P but was 2.2 times further away from the Sun. Also, 17P was at a relatively high solar latitude (+19.{sup 0}1) while 8P was observed at a lower solar latitude (3.{sup 0}4). The X-ray spectrum of 17P is unusually soft with little significant emission at energies above 500 eV. Depending on our choice of background, we derive a 300-1000 eV flux of 0.5-4.5 x 10{sup -13} erg cm{sup -2} s{sup -1}, with over 90% of the emission in the 300-400 eV range. This corresponds to an X-ray luminosity between 0.4 and 3.3 x 10{sup 15} erg s{sup -1}. However, we cannot distinguish between this significant excess emission and possible instrumental effects, such as incomplete charge transfer across the CCD. 17P is the first comet observed at high latitude during solar minimum. Its lack of X-rays in the 400-1000 eV range, in a simple picture, may be attributed to the polar solar wind, which is depleted in highly charged ions. 8P/Tuttle was much brighter, with an average count rate of 0.20 counts s{sup -1} in the 300-1000 eV range. We derive an average X-ray flux in this range of 9.4 x 10{sup -13} erg cm{sup -2} s{sup -1} and an X-ray luminosity for the comet of 1.7 x 10{sup 14} erg s{sup -1}. The light curve showed a dramatic decrease in flux of over 60% between observations on January 1 and 4. When comparing outer regions of the coma to inner regions, its spectra showed a decrease in ratios of C VI/C V, O VIII/O VII, as predicted by recent solar wind charge exchange (SWCX) emission models. There are remarkable differences between the X-ray emission from these two comets, further demonstrating the qualities of cometary X-ray observations, and SWCX emission in general as a means of remote diagnostics of the interaction of astrophysical plasmas.

Christian, D. J. [Eureka Scientific, 2420 Delmer Ave, Suite 100, Oakland, CA, 94602 (United States); Bodewits, D. [NASA Goddard Space Flight Center, Solar System Exploration Division, Mailstop 690.3, Greenbelt, MD 20771 (United States); Lisse, C. M. [Planetary Exploration Group, Space Department, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD 20723 (United States); Dennerl, K. [Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1603, 85740 Garching (Germany); Wolk, S. J. [Chandra X-Ray Center, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hsieh, H. [Department of Physics and Astronomy, Queen's University Belfast, Astronomy Research Centre, Belfast (United Kingdom); Zurbuchen, T. H.; Zhao, L. [Department of Atmospheric Oceanic and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143 (United States)], E-mail: damian.christ@gmail.com, E-mail: damian.christian@csun.edu, E-mail: Dennis.Bodewits@nasa.gov, E-mail: carey.lisse@jhuapl.edu, E-mail: kod@mpe.mpg.de, E-mail: swolk@cfa.harvard.edu, E-mail: h.hseih@qub.c.uk, E-mail: thomasz@umich.edu, E-mail: lzh@umich.edu

2010-04-01

100

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

NASA Technical Reports Server (NTRS)

The energy spectrum of cosmic-ray antiprotons (p-bar's) from 0.17 to 3.5 GeV has been measured using 7886 p-bar'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-bar calculations. Cosmologically primary p-bar's have been investigated by comparing measured and calculated p-bar spectra. BESS-Polar II data.show no evidence of primary p-bar's 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.

2012-01-01

101

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

NASA Technical Reports Server (NTRS)

The energy spectrum of cosmic-ray antiprotons (p(raised bar)'s) collected by the BESS-Polar II instrument during a long-duration flight over Antarctica in the solar minimum period of December 2007 through January 2008. The p(raised bar) spectrum measured by BESS-Polar II shows good consistency with secondary p(raised bar) calculations. Cosmologically primary p(raised bar)'s have been searched for by comparing the observed and calculated p(raised bar) spectra. The BESSPolar II result shows no evidence of primary p(raised bar)'s originating from the evaporation of PBH.

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.

2011-01-01

102

Validation of IRI-2012 TEC model over Ethiopia during solar minimum (2009) and solar maximum (2013) phases  

NASA Astrophysics Data System (ADS)

This paper investigates the capacity of the latest version of the International Reference Ionosphere (IRI-2012) model in predicting the vertical Total Electron Content (vTEC) over Ethiopian regions during solar minimum (2009) and solar maximum (2013) phases. This has been carried out by comparing the IRI-2012 modeled and experimental vTEC inferred from eight ground based dual frequency GPS (Global Positioning System) receivers installed recently at different regions of the country. In this work, the diurnal, monthly and seasonal variation in the measured vTEC have been analyzed and compared with the IRI-2012 modeled vTEC. During the solar minimum phase, the lowest and highest diurnal peak of the experimental vTEC are observed in July and October, respectively. In general, the diurnal variability of vTEC has shown minimum values around 0300 UT (0600 LT) and maximum values between around 1000 and 1300 UT (1300 and 1600 LT) during both solar activity phases. Moreover, the maximum and minimum monthly and seasonal mean hourly vTEC values are observed in October and July and in the March equinox and June solstice, respectively. It is also shown that the IRI-2012-model better predicts the diurnal vTEC in the time interval of about 0000-0300 UT (0300-0600 LT) during the solar minimum phase. However, the model generally overestimates the diurnal vTEC except in the time interval of about 0900-1500 UT (1200-1800 LT) during the solar maximum phase. The overall result of this work shows that the diurnal vTEC prediction performance of the model is generally better during the solar minimum phase than during solar maximum phase. Regarding the monthly and seasonal prediction capacity of the model, there is a good agreement between the modeled and measured monthly and seasonal mean hourly vTEC values in January and December solstice, respectively. Another result of the work depicts that unlike the GPS-TEC the IRI-2012 TEC does not respond to the effect resulted from geomagnetic storms.

Asmare, Yekoye; Kassa, Tsegaye; Nigussie, Melessew

2014-06-01

103

Performance of the IRI-2007 Model for Topside Ion Density and Composition Profiles During the 23/24 Solar Minimum  

NASA Technical Reports Server (NTRS)

The recent solar minimum between cycles 23 and 24 was unusually extended and deep, resulting in an ionosphere that is significantly different from that expected based on previous solar minima. The ion density and composition estimates from the Communication/Navigation Outage Forecast System (C/NOFS) satellite are used to evaluate the performance of the IRI-2007 model between 400 and 850 kIn altitude in equatorial regions. The current model is shown to typically overestimate the expected topside density of 0+ and underestimate the density of H+ during 2008 and 2009. The overestimation of ion density by IRI-2007 is found to vary with local time and longitude.

Klenzing, J. H.; Simoes, F.; Ivanov, S.; Pfaff, R. F.; Rowland, D. E.; Bilitza, D.; Heelis, R. A.

2011-01-01

104

The Sun's X-ray Emission During the Recent Solar Minimum  

NASA Astrophysics Data System (ADS)

The Sun recently underwent a period of a remarkable lack of major activity such as large flares and sunspots, without equal since the advent of the space age a half century ago. A widely used measure of solar activity is the amount of solar soft X-ray emission, but until recently this has been below the threshold of the X-ray-monitoring Geostationary Operational Environmental Satellites (GOES). There is thus an urgent need for more sensitive instrumentation to record solar X-ray emission in this range. Anticipating this need, a highly sensitive spectrophotometer called Solar Photometer in X-rays (SphinX) was included in the solar telescope/spectrometer TESIS instrument package on the third spacecraft in Russia's Complex Orbital Observations Near-Earth of Activity of the Sun (CORONAS-PHOTON) program, launched 30 January 2009 into a near-polar orbit. SphinX measures X-rays in a band similar to the GOES longer-wavelength channel.

Sylwester, Janusz; Kowalinski, Mirek; Gburek, Szymon; Siarkowski, Marek; Kuzin, Sergey; Farnik, Frantisek; Reale, Fabio; Phillips, Kenneth J. H.

2010-02-01

105

Chromospheric Signatures of the Subdued Cycle 23/24 Solar Minimum in Microwaves  

NASA Technical Reports Server (NTRS)

Coronal holes appear brighter than the quiet Sun in microwave images, with a brightness enhancement of 500 to 2000 K. The brightness enhancement corresponds to the upper chromosphere, where the plasma temperature is about 10000 K. We constructed a microwave butterfly diagram using the synoptic images obtained by the Nobeyama radio-heliograph (NoRH) showing the evolution of the polar and low latitude brightness temperature. While the polar brightness reveals the chromospheric conditions, the low latitude brightness is attributed to active regions in the corona. When we compared the microwave butterfly diagram with the magnetic butterfly diagram, we found a good correlation between the microwave brightness enhancement and the polar field strength. The microwave butterfly diagram covers part of solar cycle 22, whole of cycle 23, and part of cycle 24, thus enabling comparison between the cycle 23/24 and cycle 22/23 minima. The microwave brightness during the cycle 23/24 minimum was found to be lower than that during the cycle 22/23 minimum by approx.250 K. The reduced brightness temperature is consistent with the reduced polar field strength during the cycle 23/24 minimum seen in the magnetic butterfly diagram. We suggest that the microwave brightness at the solar poles is a good indicator of the speed of the solar wind sampled by Ulysses at high latitudes.

Yashiro, S.; Makela, P.; Shibasaki, K.; Hathaway, D.

2011-01-01

106

Polar Chromospheric Signatures of the Subdued Cycle 23/24 Solar Minimum  

NASA Technical Reports Server (NTRS)

Coronal holes appear brighter than the quiet Sun in microwave images, with a brightness enhancement of 500 to 2000 K. The brightness enhancement corresponds to the upper chromosphere, where the plasma temperature is about 10000 K. We constructed a microwave butterfly diagram using the synoptic images obtained by the Nobeyama radioheliograph (NoRH) showing the evolution of the polar and low latitude brightness temperature. While the polar brightness reveals the chromospheric conditions, the low latitude brightness is attributed to active regions in the corona. When we compared the microwave butterfly diagram with the magnetic butterfly diagram, we found a good correlation between the microwave brightness enhancement and the polar field strength. The microwave butterfly diagram covers part of solar cycle 22, whole of cycle 23, and part of cycle 24, thus enabling comparison between the cycle 23/24 and cycle 22/23 minima. The microwave brightness during the cycle 23/24 minimum was found to be lower than that during the cycle 22/23 minimum by approximately 250 K. The reduced brightness temperature is consistent with the reduced polar field strength during the cycle 23/24 minimum seen in the magnetic butterfly diagram. We suggest that the microwave brightness at the solar poles is a good indicator of the speed of the solar wind sampled by Ulysses at high latitudes.

Gopalswamy, N.; Yashiro, S.; Makela, P.; Shibasaki, K.; Hathaway, D.

2010-01-01

107

Solar Wind Influence on the Oxygen Content of Ion Outflow in the High Altitude Polar Cap During Solar Minimum Conditions  

NASA Technical Reports Server (NTRS)

We correlate solar wind and IMF properties with the properties of O(+) and H(+) in the polar cap in early 1996 during solar minimum conditions at altitudes between 5.5 and 8.9 Re geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the POLAR satellite. Throughout the high altitude polar cap, we observe H(+) to be more abundant than O(+). H(+) is a significant fraction of both the ionosphere and the solar wind, and O(+) is not a significant species in the solar wind. O(+) is the major species in the ionosphere so the faction of O(+) present in the magnetosphere is commonly used as a measure of the ionospheric contribution to the magnetosphere. For these reasons, 0+ is of primary interest in this study. We observe O(+) to be most abundant at lower latitudes when the solar wind speed is low (and low Kp), and at higher solar wind speeds (and high Kp) O(+) is observed across most of the polar cap. We also find that O(+) density and parallel flux are well organized by solar wind dynamic pressure; they both increase with solar wind dynamic pressure. H(+) is not as highly correlated with solar wind and IMF parameters, but H(+) density and parallel flux have some negative correlation with IMF By, and some positive correlation with VswBIMF. In this solar minimum data set, H(+) is dominant so that contributions of this plasma to the plasma sheet would have a very low O(+) to H(+) ratio.

Elliott, Heather A.; Comfort, Richard H.; Craven, Paul D.; Chandler, Michael O.; Moore, Thomas E.

2000-01-01

108

Climatology of the equatorial and low latitude ionosphere over Brazil during solar minimum of solar cycle 23/24  

NASA Astrophysics Data System (ADS)

We present a study of the Brazilian equatorial and low latitude ionosphere during the solar minimum of the solar cycle 23 and the initial phase of solar cycle 24. We analyzed data from ground-based sounding with digisondes at two equatorial sites, São Luís (44.2° W, 2.33° S, dip angle: -6.9°) and Fortaleza (38.45°W, 3.9° S, dip angle: -16°) and at a low latitude site Cachoeira Paulista (22.4° S, 45° W, dip angle: -37°). The plasma densities and the F-layer heights presented values lower than the previous solar minimum of solar cycle 22/23. The spread-F occurrence was investigated and revealed some distinct features such as the occurrence of abnormal spread-F signatures in ionograms associated with post-midnight irregularities. In the equatorial region, it was observed significant decreases in the plasma densities during nighttime hours lasting for several hours with no-echoes in ionograms. We present a statistic study of the plasma irregularities occurrence as well as some examples of unusual signatures of spread-F/plasma irregularities observed in ionograms.

Nicoli Candido, C. M.; Batista, I. S.; Santos, A.

2012-12-01

109

SuperDARN observations of an unusually contracted ionospheric convection pattern during the recent deep solar minimum  

NASA Astrophysics Data System (ADS)

We present a long term study, from 1995 - 2011, of the latitude of the Heppner-Maynard Boundary (HMB) determined using the northern hemisphere SuperDARN radars. The HMB represents the equatorward extent of ionospheric convection. We find that the average latitude of the HMB at midnight is 61° magnetic latitude during the solar maximum of 2003, but it moves significantly poleward during solar minimum, averaging 64° latitude during 1996, and 68° during 2010. This poleward motion is observed despite the increasing number of low latitude radars built in recent years as part of the StormDARN network, and so is not an artefact of data coverage. We believe that the recent extreme solar minimum lead to an average HMB location that was further poleward than previous solar cycles. We also calculated the open-closed field line boundary (OCB) from auroral images during the years 2000-2002 and find that on average the HMB is located equatorward of the OCB by ~6°. We suggest that the HMB may be a useful proxy for the OCB when global auroral images are not available.

Imber, S. M.; Milan, S. E.; Lester, M.

2012-04-01

110

Changing anomalous cosmic ray oxygen radial intensity gradients between 1 AU and Voyager with the return to solar minimum  

NASA Astrophysics Data System (ADS)

Using the Solar Isotope Spectrometer (SIS) on NASA's ACE spacecraft, we have measured the composition and energy spectra of anomalous cosmic rays (ACRs) near 1 AU down to energies of ~10 MeV/nucleon since August 1997. Recently these measurements have been augmented by data from the Low Energy Telescope (LET) on the STEREO spacecraft, which allows us to extend the energy spectra down to ~3 MeV/nucleon. As solar minimum modulation conditions return, ACR intensities at 1 AU are recovering, although they are still a factor of ~5 lower than in 1997. Also, their intensities during the present A<0 magnetic polarity cycle are significantly lower relative to galactic cosmic rays (GCRs) than they were during the last A>0 cycle. We present updated measurements of the variation of the ACR oxygen intensity at 1 AU throughout the solar cycle. Combined with observations from Voyager 1 and 2 in the outer heliosphere, we estimate the large-scale intensity gradients of ACR oxygen and GCR carbon at solar maximum, solar minimum, and during the ongoing recovery, and we investigate the role of drifts and convective processes in ACR modulation. This work was supported by NASA under grants NAG5-12929, NAS5-03131, and contract NAS7-03001.

Leske, R. A.; Cummings, A. C.; Cohen, C. M. S.; et al.

111

Diagnostics of the Solar Corona from Comparison between Faraday Rotation Measurements and Magnetohydrodynamic Simulations  

NASA Astrophysics Data System (ADS)

Polarized natural radio sources passing behind the Sun experience Faraday rotation as a consequence of the electron density and magnetic field strength in coronal plasma. Since Faraday rotation is proportional to the product of the density and the component of the magnetic field along the line of sight of the observer, a model is required to interpret the observations and infer coronal structures. Faraday rotation observations have been compared with relatively ad hoc models of the corona. Here for the first time we compare these observations with magnetohydrodynamic (MHD) models of the solar corona driven by measurements of the photospheric magnetic field. We use observations made with the NRAO Very Large Array of 34 polarized radio sources occulted by the solar corona between 5 and 14 solar radii. The measurements were made during 1997 May, and 2005 March and April. We compare the observed Faraday rotation values with values extracted from MHD steady-state simulations of the solar corona. We find that (1) using a synoptic map of the solar magnetic field just one Carrington rotation off produces poorer agreements, meaning that the outer corona changes in the course of one month, even in solar minimum; (2) global MHD models of the solar corona driven by photospheric magnetic field measurements are generally able to reproduce Faraday rotation observations; and (3) some sources show significant disagreement between the model and the observations, which appears to be a function of the proximity of the line of sight to the large-scale heliospheric current sheet.

Le Chat, G.; Kasper, J. C.; Cohen, O.; Spangler, S. R.

2014-07-01

112

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

NASA Astrophysics Data System (ADS)

A system-oriented analysis of new observations from the recent international Whole Heliosphere Interval (WHI) campaign in comparison with the equivalent Whole Sun Month (WSM) campaign from last cycle’s minimum yields new insight into solar quiet intervals and the solar minimum Sun-Earth system. We use a side-by-side comparison of these two intervals 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 numbers the lowest in 75 years, solar wind density and IMF strength at the lowest values ever observed, and geomagnetic indices and solar EUV fluxes the lowest in three solar cycles. Despite, or perhaps because of this global weakness in the heliospheric magnetic field, large near-equatorial coronal holes lingered even as the sunspots disappeared, indicating significant open magnetic flux at low latitudes. Consequently, for the months surrounding the WHI campaign, strong, long, and recurring high-speed streams in the solar wind intercepted the Earth in contrast to the weaker and more sporadic streams that occurred around the time of the WSM campaign. Since the speed, duration and southward magnetic field component in wind streams determine the severity of space weather effects, the geospace environment responded quite differently to the two solar minimum heliospheric morphologies. We illustrate this point with the behavior of relativistic electrons in the Earth’s outer radiation belt, which were more than three times stronger during WHI than in WSM. The cause is clear: it is well-known that high-speed streams drive radiation belt population, and indeed, for the months surrounding WHI, geospace and upper atmospheric parameters were ringing with the periodicities of the solar wind in a manner that was absent last cycle minimum. Such behavior could not have been predicted using sunspot numbers alone, indicating the importance of considering variation within and between solar minima in analyzing and predicting space weather responses at the Earth during solar quiet intervals, as well as in interpreting the Sun’s past behavior as preserved in geological and historical records.

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

2009-12-01

113

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) 60°E-120°E, (b) 60°W-120°W and (c) 15°W-75°W. 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

114

Changes in Quasi-periodic Variations of Solar Photospheric Fields: Precursor to the Deep Solar Minimum in Cycle 23?  

NASA Astrophysics Data System (ADS)

Possible precursor signatures in the quasi-periodic variations of solar photospheric fields were investigated in the build-up to one of the deepest solar minima experienced in the past 100 years. This unusual and deep solar minimum occurred between Solar Cycles 23 and 24. We used both wavelet and Fourier analysis to study the changes in the quasi-periodic variations of solar photospheric fields. Photospheric fields were derived using ground-based synoptic magnetograms spanning the period 1975.14 to 2009.86 and covering Solar Cycles 21, 22, and 23. A hemispheric asymmetry in the periodicities of the photospheric fields was seen only at latitudes above ± 45? when the data were divided into two parts based on a wavelet analysis: one prior to 1996 and the other after 1996. Furthermore, the hemispheric asymmetry was observed to be confined to the latitude range of 45? to 60?. This can be attributed to the variations in polar surges that primarily depend on both the emergence of surface magnetic flux and varying solar-surface flows. The observed asymmetry along with the fact that both solar fields above ± 45? and micro-turbulence levels in the inner-heliosphere have been decreasing since the early- to mid-nineties (Janardhan et al. in Geophys. Res. Lett. 382, 20108, 2011) suggest that around this time active changes occurred in the solar dynamo that governs the underlying basic processes in the Sun. These changes in turn probably initiated the build-up to the very deep solar minimum at the end of Cycle 23. The decline in fields above ± 45?, for well over a solar cycle, would imply that weak polar fields have been generated in the past two successive solar cycles, viz. Cycles 22 and 23. A continuation of this declining trend beyond 22 years, if it occurs, will have serious implications for our current understanding of the solar dynamo.

Bisoi, Susanta Kumar; Janardhan, P.; Chakrabarty, D.; Ananthakrishnan, S.; Divekar, Ankur

2014-01-01

115

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

116

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

117

Physics of Stellar Coronae  

Microsoft Academic Search

For the plasma physicist, the solar corona offers an outstanding example of a space plasma, and surely one that deserves a lifetime of study. Not only can we observe the solar corona on scales of a few hundred kilometers and monitor its changes in the course of seconds to minutes, we also have a wide range of detailed diagnostics at

Manuel Gudel

118

The Code Unravelled  

NSDL National Science Digital Library

This excellent Web site is a winner of the 2001 ThinkQuest Internet Challenge. Developed by a team of students, The Code Unravelled is a creative way to learn about DNA and its influence on all living things. The best way to view the site is with the Flash plug-in, but much of the information is accessible in text-only format. With interactive trait inheritance games and virtual lab demonstrations, the Games section is a highlight of the site. The Articles section, however, is the heart of the site, detailing the science of DNA in words and pictures. To access the site, you will need to click on the appropriate link on the ThinkQuest site.

1995-01-01

119

Alzheimer's Disease: Unraveling the Mystery  

MedlinePLUS

... Referral Center Alzheimer's Disease Education and Referral Center Alzheimer's Disease Education and Referral Center Home About Alzheimer’s ... Plan National Alzheimer's Project Act (NAPA) About ADEAR Alzheimer's Disease: Unraveling the Mystery Preface Over the past ...

120

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

121

Cosmic ray survey to Antarctica and coupling functions for neutron component near solar minimum (1996-1997), 3. Geomagnetic effects and coupling functions  

NASA Astrophysics Data System (ADS)

We present the sea-level latitude effect of two components of cosmic ray radiation obtained by a survey conducted by ship from Italy to Antarctica and back during 1996-1997 solar minimum. High energy atmospheric neutrons were detected by a 3NM-64; thermalized atmospheric neutrons by 2 bare BF3 counters. The internal consistency of data and stability of detectors, the investigation of meteorological effects and data correction are presented in two parallel papers, together with the computation of updated vertical cut-off rigidities corrected for penumbra effect (Rcp). In the present paper the effect on survey data of North-South asymmetry of cosmic ray flux in near-Earth space is evaluated and data correction is ap applied; apparent cut-off rigidities ( Rcp ), which take into account the contribution of inclined particles to the counting rate, are estimated. A small Forward-Backward effect is found and explained by the influence of an asymmetric shielding structure around the monitor. The latitude dependencies (i.e. neutron intensities vs. cut-off rigidity) and associated coupling functions are computed for both monitors and compared. The NM latitude dependence obtained for this solar minimum is found to be almost identical to that obtained by other authors in the previous solar minimum. The absence of the so-called "crossover" effect, when comparing coupling functions of subsequent solar minimums, is discussed on the light of cosmic ray intensity changes observed by neutron monitor stations.

Dorman, L. I.

122

DMSP F8 observations of the mid-latitude and low-latitude topside ionosphere near solar minimum  

SciTech Connect

The retarding potential analyzer on the DMSP F8 satellite measured ion density, composition, temperature, and ram flow velocity at 840-km altitude near the dawn and dusk meridians close to solar minimum. Nine days of data were selected for study to represent the summer and winter solstices and the autumnal equinox under quiet, moderately active, and disturbed geomagnetic conditions. The observations revealed extensive regions of light-ion dominance along both the dawn and dusk legs of the DMSP F8 orbit. These regions showed seasonal, longitudinal, and geomagnetic control, with light ions commonly predominating in places where the subsatellite ionosphere was relatively cold. Field-aligned plasma flows also were detected. In the morning, ions flowed toward the equator from both sides. In the evening, DMSP F8 detected flows that either diverged away from the equator or were directed toward the northern hemisphere. The effects of diurnal variations in plasma pressure gradients in the ionosphere and plasmasphere, momentum coupling between neutral winds and ions at the feet of field lines, and E {times} B drifts qualitatively explain most features of these composition and velocity measurements. 23 refs., 5 figs., 2 tabs.

Greenspan, M.E.; Hughes, W.J. [Boston Univ., MA (United States)] [Boston Univ., MA (United States); [Univ. of Maryland, College Park, MD (United States); Burke, W.J.; Rich, F.J. [Hanscom Air Force Base, Bedford, MA (United States)] [Hanscom Air Force Base, Bedford, MA (United States); Heelis, R.A. [Univ. of Texas, Dallas, TX (United States)] [Univ. of Texas, Dallas, TX (United States)

1994-03-01

123

Polar cap ionosphere and thermosphere during the solar minimum period: EISCAT Svalbard radar observations and GCM simulations  

NASA Astrophysics Data System (ADS)

The IPY long-run data were obtained from the European Incoherent Scatter Svalbard radar (ESR) observations during March 2007 and February 2008. Since the solar and geomagnetic activities were quite low during the period, this data set is extremely helpful for describing the basic states (ground states) of the thermosphere and ionosphere in the polar cap region. The monthly-averaged ion temperatures for 12 months show similar local time (or UT) variations to each other. The ion temperatures also show significant seasonal variations. The amplitudes of the local time and seasonal variations observed are much larger than the ones predicted by the IRI-2007 model. In addition, we performed numerical simulations with a general circulation model (GCM), which covers all the atmospheric regions, to investigate variations of the neutrals in the polar thermosphere. The GCM simulations show significant variations of the neutral temperature in the polar region in comparison with the NRLMSISE-00 empirical model. These results indicate that both the ions and neutrals would show larger variations than those described by the empirical models, suggesting significant heat sources in the polar cap region even under solar minimum and geomagnetically quiet conditions.

Fujiwara, H.; Nozawa, S.; Maeda, S.; Ogawa, Y.; Miyoshi, Y.; Jin, H.; Shinagawa, H.; Terada, K.

2012-06-01

124

Parga Chasma: Coronae and Rifting on Venus.  

National Technical Information Service (NTIS)

The majority of coronae (quasicircular volcano-tectonic features) are found along rifts or fracture belts, and the majority of rifts have coronae. However, the relationship between coronae and rifts remains unclear. There is evidence that coronae can form...

S. E. Smrekar E. R. Stofan W. R. Buck P. Martin

2005-01-01

125

Pulse Energization in the Tuft Corona Regime of Negative Corona.  

National Technical Information Service (NTIS)

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 b...

N. Plaks

1988-01-01

126

Current Sheets in the Corona and the Complexity of Slow Wind  

NASA Technical Reports Server (NTRS)

The origin of the slow solar wind has long been one of the most important problems in solar/heliospheric physics. Two observational constraints make this problem especially challenging. First, the slow wind has the composition of the closed-field corona, unlike the fast wind that originates on open field lines. Second, the slow wind has substantial angular extent, of order 30 degrees, which is much larger than the widths observed for streamer stalks or the widths expected theoretically for a dynamic heliospheric current sheet. We propose that the slow wind originates from an intricate network of narrow (possibly singular) open-field corridors that emanate from the polar coronal hole regions. Using topological arguments, we show that these corridors must be ubiquitous in the solar corona. The total solar eclipse in August 2008, near the lowest point of cycle 23 affords an ideal opportunity to test this theory by using the ultra-high resolution Predictive Science's (PSI) eclipse model for the corona and wind. Analysis of the PSI eclipse model demonstrates that the extent and scales of the open-field corridors can account for both the angular width of the slow wind and its closed-field composition. We discuss the implications of our slow wind theory for the structure of the corona and heliosphere at solar minimum and describe further observational and theoretical tests.

Antiochos, Spiro

2010-01-01

127

Latitudinal Variation of Solar Wind Speed and Mass Flux in the Acceleration Region of the Solar Wind during Solar Minimum Inferred from Spectral Broadening measurements  

NASA Technical Reports Server (NTRS)

In this paper, we use an aggregate of S-band 2.3 GHz (13 cm) spectral broadening observations conducted during solar minimum conditions by the Mariner 4, Pioneer 10, Mariner 10, Helios 1 & 2 and Viking spacecraft to infer the first measurements of the latitudinal variation of solar wind speed and mass flux in the acceleration region of the solar wind at 3-8 R(sub o).

Woo, R.; Goldstein, R.

1993-01-01

128

Cosmic ray survey to Antarctica and coupling functions for neutron component near solar minimum (1996-1997) 3. Geomagnetic effects and coupling functions  

NASA Astrophysics Data System (ADS)

We present the results of a ship survey conducted from Italy to Antarctica and back during the 1996-1997 solar minimum measuring the latitude variation in the neutron component of cosmic radiation at sea level. High-energy atmospheric neutrons were detected by a 3NM-64 and thermalized atmospheric neutrons were detected by two bare BF3 counters. Discussions of the internal consistency of the data and the stability of the detectors, investigations of meteorological effects, and data corrections are presented in two companion papers. In this paper we compute updated vertical cutoff rigidities corrected for the penumbra effect, and we estimate apparent cutoff rigidities, which take into account the contribution of nonvertically incident particles to the counting rate. When comparing cosmic ray intensities observed in the same place, a small forward-backward effect is found and explained as the effect of an asymmetric shielding structure around the monitor. Latitude dependencies (i.e., neutron intensities versus cutoff rigidity) and associated coupling functions are computed for both monitors and compared. The NM latitude dependence obtained for the 1996-1997 solar minimum is found to be almost identical to that obtained by other authors in the previous solar minimum. The absence of the so-called ``crossover'' effect when comparing coupling functions of subsequent solar minima is discussed also on the basis of cosmic ray intensity changes observed by neutron monitor stations.

Dorman, L. I.; Villoresi, G.; Iucci, N.; Parisi, M.; Tyasto, M. I.; Danilova, O. A.; Ptitsyna, N. G.

129

Corotating interaction regions and the 27 day variation of galactic cosmic rays intensity at 1 AU during the cycle 23/24 solar minimum  

NASA Astrophysics Data System (ADS)

We investigate the formation and evolution of corotating interaction regions (CIRs) in the solar wind and their effects on galactic cosmic rays (GCR) during the recent solar cycle 23/24 solar minimum. The output from a three-dimensional MHD model serves as background for kinetic time-dependent simulations of GCR transport based on the Parker equation. The results show that the CIR forward/reverse shock pairs or compression/rarefaction regions play important roles in the transport of GCR particles and directly control the observed 27 day periodic intensity variations. We find that stream interfaces (SIs) in CIRs and the heliospheric current sheet (HCS) are both closely associated with the GCR depression onset, in agreement with the observations at 1 AU. The HCS is more important when its tilt angle becomes small during the declining phase of the solar minimum, while the passages of SIs control the onset of GCR depressions for larger HCS tilt angles. The mechanism of GCR intensity variation near 1 AU can be explained through an interplay between the effects of particle drift and diffusion. The simulated plasma background and GCR intensity are compared with the observations from spacecraft and a neutron monitor on the ground, to find good qualitative agreement. Evidently, CIRs had a substantial modulational effect on GCR during the recent solar minimum.

Guo, X.; Florinski, V.

2014-04-01

130

Variation of the Schwabe Cycle Length During the Grand Solar Minimum in the 4th Century BC Deduced from Radiocarbon Content in Tree Rings  

NASA Astrophysics Data System (ADS)

Solar activity alternates between active and quiet phases with an average period of 11 years, and this is known as the Schwabe cycle. Additionally, solar activity occasionally falls into a prolonged quiet phase (grand solar minimum), as represented by the Maunder Minimum in the 17th century, when sunspots were almost absent for 70 years and the length of the Schwabe cycle increased to 14 years. To examine the consistency of the cycle length characteristics during the grand solar minima, the carbon-14 contents in single-year tree rings were measured using an accelerator mass spectrometer as an index of the solar variability during the grand solar minimum of the 4th century BC. The signal of the Schwabe cycle was detected with a statistical confidence level of higher than 95 % by wavelet analysis. This is the oldest evidence for the Schwabe cycle at the present time, and the cycle length is considered to have increased to approximately 16 years during the grand solar minimum of the 4th century BC. This result confirms the association between the increase of the Schwabe cycle length and the weakening of solar activity, and indicates the possible prolonged absence of sunspots in the 4th century BC as during the Maunder Minimum. Theoretical implications from solar dynamo theory are discussed in order to identify the trigger of prolonged sunspot absence. A possible association between the long-term solar variation around the 4th century BC and terrestrial cooling in this period is also discussed.

Nagaya, K.; Kitazawa, K.; Miyake, F.; Masuda, K.; Muraki, Y.; Nakamura, T.; Miyahara, H.; Matsuzaki, H.

2012-09-01

131

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

132

The structure of Io's corona  

NASA Astrophysics Data System (ADS)

A spatial profile of the distribution of sodium in Io's corona has been constructed using measurements obtained during satellite mutual eclipses. The data reveal a fairly symmetric corona whose density falls steeply from the surface out to 6 r(Io) and more slowly outside. An upper limit of 700 km is placed on the exobase altitude, but the observations do not constrain the surface density. Several theoretical models adequately match some traits of the corona, but none satisfies all the observations. No strong upstream/downstream asymmetry of the corona is observed, so it is unlikely that the corona is primarily generated by the impact of corotating ions into the trailing hemisphere.

Schneider, N. M.; Hunten, D. M.; Wells, W. K.; Schultz, A. B.; Fink, U.

1991-02-01

133

The New Solar Corona  

NASA Technical Reports Server (NTRS)

We focus on new observational capabilities (Yohkoh, SoHO, TRACE) observations, modeling, approaches, and insights into physical processes of the solar corona. The most impressive new results and problems discussed in this article can be appreciated from the movies and available on the Annual Reviews web site.

Aschwanden, Markus J.; Poland, Arthur I.; Rabin, Douglas M.; Fisher, Richard R. (Technical Monitor)

2001-01-01

134

Thermally peeling the Corona  

Microsoft Academic Search

The outer atmospheres of most low-mass stars, including the Sun, are composed of very hot plasma (1-50 MK) which is organized in spatially and thermally complex structures. A proper determination of these structures is necessary to decide the energetics of coronae, to establish their compositions, and to distinguish between different physical processes that may operate on them. The challenge of

V. L. Kashyap

2007-01-01

135

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

NASA Technical Reports Server (NTRS)

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 taken over all of the 18 events of 2007 - 2009 (called the "recent period" here) was only 11.0 nT, whereas |BO| for the 29 events of 1995 - 1997 (called the "earlier period" ) was 16.5 nT. This 33% average drop in |BO| 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 set s 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 (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 approx. = 31deg (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.

2011-01-01

136

The New Solar Corona  

NASA Astrophysics Data System (ADS)

We focus on new observational capabilities (Yohkoh, SoHO, TRACE), observations, modeling approaches, and insights into physical processes of the solar corona. The most impressive new results and problems discussed in this article can be appreciated from the movies available on the Annual Reviews website and at http://www.lmsal.com/pub/araa/araa.html. "The Sun is new each day." Heraclites (ca 530-475 BC) "Everything flows." Heraclites (ca 530-475 BC)

Aschwanden, Markus J.; Poland, Arthur I.; Rabin, Douglas M.

137

Interplanetary Shocks in the Inner Solar System: Observations with STEREO and MESSENGER During the Deep Solar Minimum of 2008  

NASA Astrophysics Data System (ADS)

The two major sources of collisionless shocks in the solar wind are interplanetary coronal mass ejections (ICMEs) and stream interactions (SIRs). ICMEs are ejected by magnetic forces in the lower corona and accelerate outwards often forming shocks quite close to the Sun. The strength of these ICMEs and their frequency of occurrence both peak at solar maximum. Stream inter-actions in contrast are present throughout the solar cycle with very little change in occurrence rate or strength. We have previously examined the rate of occurrence of interplanetary shocks with the Helios data and its variation with heliocentric distance. Herein we examine this gradi-ent with MESSENGER and STEREO magnetic records during the deep minimum of 2008. In contrast to solar cycle 21 studied with Helios in which ICME-driven shocks dominated the inner heliosphere, there were no ICME-driven shocks at MESSENGER or STEREO in 2008. Rather, the SIR-driven shocks began to form about 0.5 AU and increased in number until they reached a rate of about 18 per year at 1 AU in the STEREO data. This observation is consistent with the paucity of solar energetic particle events at this time.

Lai, Hairong; Russell, C. T.; Jian, Lan; Anderson, Brian J.; Luhmann, Janet G.; Wennmacher, A.

138

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

139

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...

140

Evolución de la Estructura Térmica Global de la Corona alrededor del Último Mínimo 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.; Vásquez, A. M.; Huang, Z.; Frazin, R. A.

141

Solar Wind Influence on the Oxygen Content of Ion Outflow in the High-Altitude Polar Cap During Solar Minimum Conditions  

NASA Technical Reports Server (NTRS)

We correlate solar wind and interplanetary magnetic field (IMF) properties with the properties of O(+) and H(+) during early 1996 (solar minimum) at altitudes between 5.5 and 8.9 R(sub E) geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the Polar satellite. Throughout the high-altitude polar cap we observe H(+) to be more abundant than O(+). O(+) is found to be more abundant at lower latitudes when the solar wind speed is low (and Kp is low), while at higher solar wind speeds (and high Kp), O(+) is observed across most of the polar cap. The O(+) density and parallel flux are well organized by solar wind dynamic pressure, both increasing with solar wind dynamic pressure. Both the O(+) density and parallel flux have positive correlations with both V(sub SW)B(sub IMF) and E(sub SW). No correlation is found between O(+) density and IMF Bz, although a nonlinear relationship with IMF By is observed, possibly due to a strong linear correlation with the dynamic pressure. H(+) is not as highly correlated with solar wind and IMF parameters, although H(+) density and parallel flux are negatively correlated with IMF By and positively correlated with both V(sub SW)B(sub IMF) and E(sub SW). In this solar minimum data set, H(+) is dominant, so that contributions of this plasma to the plasma sheet would have very low O(+) to H(+) ratios.

Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Chandler, M. O.; Moore, T. E.

2001-01-01

142

Understanding the Behavior of the Heliospheric Magnetic Field and the Solar Wind During the Unusual Solar Minimum Between Cycles 23 and 24  

NASA Astrophysics Data System (ADS)

The properties of the heliospheric magnetic field and the solar wind were substantially different in the unusual solar minimum between Cycles 23 and 24: the magnetic-field strength was substantially reduced, as were the flow properties of the solar wind, such as the mass flux. Explanations for these changes are offered that do not require any substantial reconsideration of the general understandings of the behavior of the heliospheric magnetic field and the solar wind that were developed in the minimum of Cycle 22 - 23. Solar-wind composition data are used to demonstrate that there are two distinct regions of solar wind: solar wind likely to originate from the stalk of the streamer belt (the highly elongated loops that underlie the heliospheric current sheet), and solar wind from outside this region. The region outside the streamer-stalk region is noticeably larger in the minimum of Cycle 23 - 24; however, the increased area can account for the reduction in the heliospheric magnetic-field strength in this minimum. Thus, the total magnetic flux contained in this region is the same in the two minima. Various correlations among the solar-wind mass flux and coronal electron temperature inferred from solar-wind charge states were developed for the Cycle 22 - 23 solar minimum. The data for the minimum of Cycle 23 - 24 suggest that the correlations still hold, and thus the basic acceleration mechanism is unchanged in this minimum.

Zhao, L.; Fisk, L.

2011-12-01

143

Ionospheric total electron content, thermospheric emission and and stratospheric temperature dynamics during the SC23 deep solar minimum: 2008-2009  

NASA Astrophysics Data System (ADS)

We will study external driving of the ionosphere-thermosphere and stratosphere systems during the deep solar minimum: the WHI 2008 interval as well as 2009. We report evidence of prompt penetrating interplanetary electric fields (PPEFs) into the ionosphere during CIR/HSS intervals for both 2008 and 2009. Daily averages of vertical daytime total electron content (VTEC) derived from GPS measurements from the JPL database are studied. VTEC data show the well-known semi-annual anomalies especially prominent in the low latitude ionosphere. Low- to middle-latitude VTEC variability is shown to coincide with PPEF events. Somewhat decreased variability is found around the solstices. CIR/HSS intervals are typically characterized by high energy deposition into the auroral regions through increased Joule heating and particle precipitation. Elevated nitric oxide densities and temperatures in the thermosphere lead to variations in corresponding infrared emission. We present measurements from SABER/TIMED of NO and CO2 emissions during 2008-2009 to illustrate efficient thermospheric response to moderate external driving and I-T dynamics throughout the time interval. We will discuss solar and geomagnetic activity influences on climate by analyzing lower stratospheric temperatures using GPS radio occultation measurements from CHAMP. Results for the deep solar minimum will be compared with the declining phase and solar maximum conditions.

Verkhoglyadova, O. P.; Tsurutani, B.; Mannucci, A. J.; Mlynczak, M. G.; Hunt, L. A.; Ao, C. O.; Runge, T.

2011-12-01

144

A Comparison of C/NOFS Neutral Wind Meter Thermospheric Measurements near 400 km under Solar Minimum Conditions and Those Approaching Solar Maximum  

NASA Astrophysics Data System (ADS)

Since the beginning of 2011, solar activity has increased leading to a recovery from the unusual thermospheric conditions of the recent solar minimum of 2008 and 2009. Examples of those unusual conditions were an unusually low neutral density and the periodic dominance of neutral helium at topside F-region altitudes measured by CINDI instruments aboard the Communication/ Navigation Outage Forecast System (C/NOFS). The CINDI Neutral Wind Meter (NWM) aboard C/NOFS contains two instruments, the Ram Wind Sensor (RWS) and Cross Track Sensor (CTS) which can obtain velocity, temperature, composition and relative pressure information about neutral particles within the limits of the C/NOFS orbit altitudes, currently 395km - 760km. Due to increased thermospheric densities and more monatomic oxygen present at orbit altitudes the instruments are no longer always working at the edge of their pressure tolerances. We will show current thermospheric conditions at these altitudes, as measured by the instruments, compared to the previous measurements during the deep solar minimum.

Haaser, R. A.

2012-12-01

145

White light solar corona: an atlas of 1985 K- coronameter synoptic charts, December 1984-December 1985. Technical note  

SciTech Connect

The synoptic observing program of the Mauna Loa Solar Observatory (MLSO) has as its goal the specification of the time-dependent structure of the solar corona. The growth of the low intensity polar regions and ordering of the brighter corona into a band near the equator seen in the second, third, and fourth years of observations (1981-1983) continued through 1984. In 1985, the corona remains in the same general form, with the brightest regions concentrated in a band around the equator, similar to the situation noted near the last solar minimum. The apparent excursions of the darkest regions (polar holes) towards the equator seen at the start of the year become less pronounced with time. However, the area embraced by the highest brightness contours tends to increase throughout the year, perhaps indicating that the corona has gone through its minimum configuration. The material presented here is in a format providing a convenient access to investigators intending to make correlation studies or an intercomparison of standard synoptic data sets.

Sime, D.G.; Garcia, C.; Yasukawa, E.; Lundin, E.; Rock, K.

1986-10-01

146

Topological Dissipation & The Solar Corona  

NASA Astrophysics Data System (ADS)

Reconnection in the solar corona has to take place, as was convincingly shown by tet{Parker72}, the question remains if it is sufficient to heat the corona. One of the major problems in coronal physics, is modeling reconnection. Reconnection is the basis of most heating models, in spite the fact that we really don't know how reconnection works. Simulating reconnection with realistic parameters is highly problematic and the solar corona has a parameter space not well explored. Here I try to give a hint of what conclusions one can reach about reconnection from large scale simulations of the solar corona. A model of the solar corona with a numerical diffusion reproduces a number of observables, and seem to reproduce the corona well, only using minimal assumptions. The overall well reproduced corona, means that it is highly likely that reconnection does not differ much from the diffusion scheme of the numerical code. That means that reconnection in the solar corona transfers most of the liberated magnetic energy into heat locally and mechanisms such as waves and high energy particles can not carry the a significant part of the energy released in reconnection.

Gudiksen, B. V.

2007-10-01

147

Accretion disk coronae  

NASA Technical Reports Server (NTRS)

Recent observations of partial X-ray eclipses from 4U1822-37 have shown that the central X-ray source in this system is diffused by a large Compton-thick accretion disk corona (ADC). Another binary, 4U2129-47, also displays a partial eclipse and contains an ADC. The possible origin of an ADC is discussed and a simple hydrostatic evaporated ADC model is developed which, when applied to 4U1822-37, 4U2129+47 and Cyg X-3, can explain their temporal and spectral properties. The quasi-sinusoidal modulation of all three sources can be reconciled with the partial occultation of the ADC by a bulge at the edge of the accretion disk which is caused by the inflowing material. The height of this bulge is an order of magnitude larger than the hydrostatic disk height and is the result of turbulence in the outer region of the disk. The spectral properties of all three sources can be understood in terms of Compton scattering of the original source spectrum by the ADC. Spectral variations with epoch in Cyg X-3 are probably caused by changes in the optical depth of the corona. A consequence of our model is that any accreting neutron star X-ray source in a semi-detached binary system which is close to its Eddington limit most likely contains an optically thick ADC.

White, N. E.; Holt, S. S.

1981-01-01

148

Climatological study of the daytime occurrence of the 3-meter EEJ plasma irregularities over Jicamarca close to the solar minimum (2007 and 2008)  

NASA Astrophysics Data System (ADS)

We have developed algorithms for conducting a seasonal statistical study of the occurrence of plasma irregularities in the Peruvian sector as a function of height and local time, covering two years of data (2007 and 2008) close to the solar minimum. This study was performed based on radar measurements carried out at the Jicamarca Radio Observatory (JRO), which is located in Lima-Peru (11.57°S, 76.52°W, dip: 2°N), under the magnetic equator. The statistical analysis runs over daily Range Time Intensity (RTI) maps obtained with the radar operating in the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere (JULIA) mode. Our results revealed relevant features of the diurnal variation of the plasma irregularities embedded in the equatorial electrojet, such as: a more often occurring presence of the 3-m irregularities during equinox, and a descent of the scattering profile in the morning hours, followed by its ascent in the afternoon.

Guizelli, L. M.; Denardini, C. M.; Moro, J.; Resende, L. C. A.

2013-01-01

149

Changes in radial gradients of low-energy cosmic rays between solar minimum and maximum: Observations from 1 to 31 AU  

SciTech Connect

Observations of the fluxes and radial gradients of protons and helium (10solar minimum values (5%-10% per AU for galactic protons and helium) to values of 2%--4% per AU or less. For these low-energy cosmic rays we find (..cap alpha..) that the variation in modulation with the phase of the solar cycle is much stronger at radii of 20--30 AU than at 1 AU, and (b) that at solar maximum, more than 99% of the total modulation takes place beyond 31 AU.

McKibben, R.B.; Pyle, K.R.; Simpson, J.A.

1985-02-15

150

Ultraviolet corona detection sensor study  

NASA Technical Reports Server (NTRS)

The feasibility of detecting electrical corona discharge phenomena in a space simulation chamber via emission of ultraviolet light was evaluated. A corona simulator, with a hemispherically capped point to plane electrode geometry, was used to generate corona glows over a wide range of pressure, voltage, current, electrode gap length and electrode point radius. Several ultraviolet detectors, including a copper cathode gas discharge tube and a UV enhanced silicon photodiode detector, were evaluated in the course of the spectral intensity measurements. The performance of both silicon target vidicons and silicon intensified target vidicons was evaluated analytically using the data generated by the spectroradiometer scans and the performance data supplied by the manufacturers.

Schmitt, R. J.; MATHERN

1976-01-01

151

Properties of accretion disk coronae  

NASA Technical Reports Server (NTRS)

The properties of accretion disk corona in a parameter regime suitable for Galactic black hole candidates are considered and the results of an analysis of these properties using a self-consistent Monte Carlo code are presented. Examples of the coronal temperature structure, the shape and angular dependency of the spectrum and the maximum temperature allowed for each optical depth of the corona are presented. It is shown that the observed spectrum of the Galactic black hole candidate Cygnus X-1 cannot be explained by accreting disk corona models with a slab geometry, where the accretion disk is sandwiched by the comptonizing medium.

Wilms, J.; Dove, J.; Staubert, R.; Begelman, M. C.

1997-01-01

152

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

153

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

NASA Technical Reports Server (NTRS)

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; Gaza, R.; Roed, Y.; Semones, E.; Lee, K.; Steenburgh, R.; Johnson, S.; Flanders, J.; Zapp, N.

2010-01-01

154

Constraining Corona Formation on Venus  

NASA Astrophysics Data System (ADS)

We model the formation of off-rift coronae at Parga Chasma in order to understand how Venus loses its heat. We find the data required to make proper comparisons between models and observations is lacking.

Piskorz, D.; Elkins-Tanton, L. T.; Smrekar, S. E.

2014-05-01

155

Corona: America's First Satellite Program.  

National Technical Information Service (NTIS)

Since the CORONA satellite made its first successful flight in August 1960, the Intelligence Community overhead reconnaissance programs have been among the nation's most closely guarded secrets. The CIA History Staff is publishing this collection of newly...

1995-01-01

156

Genetic unraveling of colorectal cancer.  

PubMed

Colorectal cancer is a common disease in both men and women (being the third most common cancer in men and the second most common among women) and thus represents an important and serious public health issue, especially in the western world. Although it is a well-established fact that cancers of the large intestine produce symptoms relatively earlier at a stage that can be easily cured by resection, a large number of people lose their lives to this deadly disease each year. Recent times have seen an important change in the incidence of colorectal cancer in different parts of the world. The etiology of colorectal cancer is multifactorial and is likely to involve the actions of genes at multiple levels along the multistage carcinogenesis process. Exhaustive efforts have been made out in the direction of unraveling the role of various environmental factors, gene mutations, and polymorphisms worldwide (as well as in Kashmir-"a valley of gastrointestinal cancers") that have got a role to play in the development of this disease so that antitumor drugs could be developed against this cancer, first, and, finally, the responsiveness or resistance to these agents could be understood for combating this global issue. PMID:24573608

Rasool, Sabha; Rasool, Vamiq; Naqvi, Tahira; Ganai, Bashir A; Shah, Bhahwal Ali

2014-06-01

157

Signatures of Two Distinct Initiation Mechanisms while CMEs Evolve in the Lower Corona  

NASA Astrophysics Data System (ADS)

We present a comparison of a three-dimensional (3D) simulation of coronal mass ejections (CMEs) formed with two different initiation mechanisms: Gibson & Low (1998) (as GL98 from now on) and Titov & Démoulin (1999) (as TD99 from now on). Mainly we aim to compare how the CME magnetic configuration changes during their propagation in the lower corona, until 6RS. The simulations are performed using the Space Weather Modeling Framework (SWMF) during the solar minimum (CR1922). We found that both CME-driven shocks are quasi-parallel at the nose and that GL98 presents a higher shock acceleration (~150 m/ s2versus ~100 m/ s2) and a higher Mach number, suggesting it would accelerate particles more efficiently. Both initiation mechanisms also presented a post-shock compression for R>3RS, being slightly larger in TD99. They presented also a similar sheath width that increases while propagating away from the Sun (larger in GL98 case). We also found that in GL98 case the CME is driven by a combination of magnetic and thermal pressure, while in TD99 case the thermal pressure dominates its evolution. GL98 presents a sheath mass 20% larger than TD99, a possible explanation for the presence of higher force values for GL98. This paper intends to serve as a prototype for future comparisons of CME evolution, in the lower corona.

Alves, M. V.; de Souza Costa, C. L.; Opher, M.; Liu, Y. C.; Manchester, W. B.; Gombosi, T. I.

2009-04-01

158

Rainbows, Coronas and Glories  

NASA Astrophysics Data System (ADS)

Rainbows, coronas and glories are examples of atmospheric optical phenomena caused by the scattering of sunlight from spherical drops of water. It is surprising that the apparently simple process of scattering of light by spherical drops of water can result in this wide range of colourful effects. However, the scattering mechanisms are very complicated. Eminent scientists (such as Descartes, Newton, Young, Airy and many others) offered various explanations for the formation of rainbows—thus making major contributions to our understanding of the nature of light. The basic features of rainbows can be explained by geometrical optics but, in the early 1800s, supernumerary arcs on rainbows provided crucial supporting evidence for the wave theory of light. In 1908, Mie provided a rigorous (but very complicated) solution to the problem of scattering of light by spherical particles. More than 100 years later, Mie's solution can now be used to produce excellent full-colour simulations. Examples of such simulations show how the appearance of these phenomena vary with the size of the water drops, as well as describing the scattering mechanisms that are responsible for their formation.

Laven, Philip

159

Spectroscopic investigation of protein corona  

NASA Astrophysics Data System (ADS)

Nanotechnology has revolutionalized the landscape of modern science and technology, including materials, electronics, therapeutics, bioimaging, sensing, and the environment. Research in the past decade has examined the fate of nanomaterials in vitro and in vivo, as well as the interactions between nanoparticles and biological and ecosystems using primarily toxicological and ecotoxicological approaches. However, due to the versatility in the physical and physicochemical properties of nanoparticles, and due to the vast complexity of their hosting systems, the solubility, transformation, and biocompatibility of nanomaterials are still poorly understood. Nanotechnology has been undergoing tremendous development in recent decades, driven by realized perceived applications of nanomaterials in electronics, therapeutics, imaging, sensing, environmental remediation, and consumer products. Nanoparticles on entering the blood stream undergo an identity change, they become coated with proteins. There are different kind of proteins present in blood. Proteins compete for getting coated over the surface of nanoparticle and this whole entity of proteins coated over nanoparticle surface is called Protein Corona. Proteins tightly bound to the surface of nanoparticle form hard corona and the ones loosely bound on the outer surface form soft corona. This dissertation is aimed at spectroscopic investigation of Protein Corona. Chapter I of this dissertation offers a comprehensive review of the literature based on nanomaterials with the focus on carbon based nanomaterilas and introduction to Protein Corona. Chapter II is based different methods used for Graphene Synthesis,different types of defects and doping. In Chapter III influence of defects on Graphene Protein Corona was investigated. Chapter IV is based on the study of Apoptosis induced cell death by Gold and silver nanoparticles. In vitro study of effect of Protein Corona on toxicity of cells was done.

Choudhary, Poonam

160

Survey of the spectral properties of turbulence in the solar wind, the magnetospheres of Venus and Earth, at solar minimum and maximum  

NASA Astrophysics Data System (ADS)

In the framework of the European FP7 project STORM ("Solar system plasma Turbulence: Observations, inteRmittency and Multifractals") we analyze the properties of turbulence in various regions of the solar system, for the minimum and respectively maximum of the solar activity. The main scientific objective of STORM is to advance the understanding of the turbulent energy transfer, intermittency and multifractals in space plasmas. Specific analysis methods are applied on magnetic field and plasma data provided by Ulysses, Venus Express and Cluster, as well as other solar system missions (e.g. Giotto, Cassini). In this paper we provide an overview of the spectral properties of turbulence derived from Power Spectral Densities (PSD) computed in the solar wind (from Ulysses, Cluster, Venus Express) and at the interface of planetary magnetospheres with the solar wind (from Venus Express, Cluster). Ulysses provides data in the solar wind between 1992 and 2008, out of the ecliptic, at radial distances ranging between 1.3 and 5.4 AU. We selected only those Ulysses data that satisfy a consolidated set of selection criteria able to identify "pure" fast and slow wind. We analyzed Venus Express data close to the orbital apogee, in the solar wind, at 0.72 AU, and in the Venus magnetosheath. We investigated Cluster data in the solar wind (for time intervals not affected by planetary ions effects), the magnetosheath and few crossings of other key magnetospheric regions (cusp, plasma sheet). We organize our PSD results in three solar wind data bases (one for the solar maximum, 1999-2001, two for the solar minimum, 1997-1998 and respectively, 2007-2008), and two planetary databases (one for the solar maximum, 2000-2001, that includes PSD obtained in the terrestrial magnetosphere, and one for the solar minimum, 2007-2008, that includes PSD obtained in the terrestrial and Venus magnetospheres and magnetosheaths). In addition to investigating the properties of turbulence for the minimum and maximum of the solar cycle we also analyze the spectral similarities and differences between fast and slow wind turbulence. We emphasize the importance of our data survey and analysis in the context of understanding the solar wind turbulence, the exploitation of data bases and as a first step towards developing a (virtual) laboratory for studying solar system plasma turbulence. Research supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no 313038/STORM, and a grant of the Romanian Ministry of National Education, CNCS - UEFISCDI, project number PN-II-ID-PCE-2012-4-0418.

Echim, Marius M.

2014-05-01

161

Insights into Corona Formation Through Statistical Analyses  

NASA Technical Reports Server (NTRS)

Statistical analysis of an expanded database of coronae on Venus indicates that the populations of Type 1 (with fracture annuli) and 2 (without fracture annuli) corona diameters are statistically indistinguishable, and therefore we have no basis for assuming different formation mechanisms. Analysis of the topography and diameters of coronae shows that coronae that are depressions, rimmed depressions, and domes tend to be significantly smaller than those that are plateaus, rimmed plateaus, or domes with surrounding rims. This is consistent with the model of Smrekar and Stofan and inconsistent with predictions of the spreading drop model of Koch and Munga. The diameter range for domes, the initial stage of corona formation, provides a broad constraint on the buoyancy of corona-forming plumes. Coronae are only slightly more likely to be topographically raised than depressions, with Type 1 coronae most frequently occurring as rimmed depressions and Type 2 coronae most frequently occurring with flat interiors and raised rims. Most Type 1 coronae are located along chasmata systems or fracture belts, while Type 2 coronae are found predominantly as isolated features in the plains. Coronae at hot spot rises tend to be significantly lager than coronae in other settings, consistent with a hotter upper mantle at hot spot rises and their active state.

Glaze, L. S.; Stofan, E. R.; Smrekar, S. E.; Baloga, S. M.

2002-01-01

162

Insights into Corona Formation through Statistical Analyses  

NASA Technical Reports Server (NTRS)

Statistical analysis of an expanded database of coronae on Venus indicates that the populations of Type 1 (with fracture annuli) and 2 (without fracture annuli) corona diameters are statistically indistinguishable, and therefore we have no basis for assuming different formation mechanisms. Analysis of the topography and diameters of coronae shows that coronae that are depressions, rimmed depressions, and domes tend to be significantly smaller than those that are plateaus, rimmed plateaus, or domes with surrounding rims. This is consistent with the model of Smrekar and Stofan and inconsistent with predictions of the spreading drop model of Koch and Manga. The diameter range for domes, the initial stage of corona formation, provides a broad constraint on the buoyancy of corona-forming plumes. Coronae are only slightly more likely to be topographically raised than depressions, with Type 1 coronae most frequently occurring as rimmed depressions and Type 2 coronae most frequently occuring with flat interiors and raised rims. Most Type 1 coronae are located along chasmata systems or fracture belts, while Type 2 coronas are found predominantly as isolated features in the plains. Coronae at hotspot rises tend to be significantly larger than coronae in other settings, consistent with a hotter upper mantle at hotspot rises and their active state.

Glaze, L. S.; Stofan, E. R.; Smrekar, S. E.; Baloga, S. M.

2002-01-01

163

Corona processing of insulating oil  

SciTech Connect

It is well known that sustained corona discharge in insulating oil lowers its dielectric strength and simultaneously reduces its corona resistance. Therefore, for operating stresses in the corona regime, activity typically increases with time and, if allowed to continue, eventually leads to breakdown of the oil and failure of the component or system. It is, therefore, common practice to periodically replace oil in devices such as large power transformers and switch gear before breakdown occurs. Sealed components such as capacitors are typically replaced. Recent experiments have demonstrated that the dielectric properties of corona weakened oil can not only be restored, but actually improved by a simple regeneration process. These experiments were carried out on high voltage pulse transformer windings which were operated at high rep rates until partial discharges formed. Reprocessing the oil after each operating cycle resulted in successively longer operational periods before partial discharges appeared. In a separate experiment, a process was developed to precondition transformer oil to raise its corona inception voltage before using it to insulate a high voltage component, thus giving it a longer initial service life for a given operating stress or permitting higher stress operation for limited operating times.

Rohwein, G.J.

1996-07-01

164

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

165

The Day the Sun Stood Still: Using global Thermodynamic MHD Simulations to Infer the Structure of the Solar Corona and Inner Heliosphere during the Maunder Minimum  

NASA Astrophysics Data System (ADS)

Observations of the Sun's corona during the space era have led to a picture of relatively constant, but modulating solar output and structure. Longer-term, more indirect measurements, such as from Beryllium-10, coupled by other albeit less reliable contemporaneous reports, however, suggest periods of significant departure from this standard, which, in turn, may have produced terrestrial weather effects. The Maunder Minimum, was one such epoch where: (1) Sunspots effectively disappeared for long intervals during a 70-year period; (2) Eclipse `observations' suggested the distinct lack of a visible K-corona but possible appearance of the F-corona; (3) Reports of aurora were notably reduced; and (4) Cosmic ray intensities at Earth were substantially higher. Using a global thermodynamic MHD model, we constructed a broad range of possible coronal configurations for the Maunder Minimum period and compared their predictions with these limited observational constraints. We conclude that the most likely state of the corona during the Maunder Minimum was not merely that of the 2008/2009 solar minimum, as has been suggested in several recent studies. Instead, we argue that the Sun's photospheric magnetic field was substantially reduced (by up to an order of magnitude) and this led to, and is consistent with the observations associated with this period. We discuss the implications of this work in terms of future long-term space weather forecasting.

Riley, P.; Lionello, R.

2012-12-01

166

Prediction of galactic cosmic ray proton intensities from simultaneous proton and electron measurements during an A smaller than zero solar minimum  

NASA Astrophysics Data System (ADS)

Galactic cosmic rays (GCRs) are high energy charged particles, mainly protons and doubly ionized helium, originating in the galaxy and striking the Earth from all directions. There are three lines of defends which protect humans on Earth against this radiation. While the inner two shields, the atmosphere and magnetosphere, protect us against cosmic rays from several hundreds of MeV/nuc to about 15 GeV/nuc depending on geomagnetic latitude, the outer shield, the heliosphere, is reducing the intensities of particles with energies up to a few tens of GeV. This reduction depends on the solar activity and can vary by a few ten percent at 5 GeV to several orders of magnitude at a few tenth of MeV. Nevertheless, on a long journey to Mars galactic cosmic rays will pose a risk to astronauts of receiving a harmful dose of radiation. An often used tool to describe this modulation is the force-field solution. This approximation can not take into account the differences between positive and negative solar magnetic epochs or the difference in the modulation of electrons and protons. The current solar minimum is the lowest observed since the space area. The intensity of GCR electrons measured by the Kiel Electron Telescope aboard Ulysses exceed that of protons by more than 30

Heber, Bernd; Gieseler, Jan; Herbst, Klaudia; Kopp, Andreas; Müller-Mellin, Reinhold; Fichtner, Horst; Scherer, Klaus; Steinhilber, Friedhelm; Potgieter, Marius; Ferreira, Stefan

167

VHF Scintillation Measurements from Cape Verde and Ascension Island During the Current Deep Solar Minimum Including Impact of a Geomagnetic Storm in August 2010 from Space and Ground  

NASA Astrophysics Data System (ADS)

Scintillation measurements at 250 MHZ were performed starting September 2009 to the present at Cape Verde (dip latitude 11°N) and Ascension Island (dip latitude 15°S), both in the African longitude sector. The Cape Verde measurements are similar to the earlier established longitude variation for this sector based on scintillation observations at Ascension Island during solar cycle 23. This pattern consists of equinoctial maxima, a June solstice minimum and a reduced secondary maximum in the December solstice. However, the differing dip latitude of the two stations provided a very interesting asymmetry in the occurrence of scintillations, with a much larger occurrence observed at Cape Verde. It seems that during this low solar minimum period the pre-reversal upward drift is not large enough for the irregularity layer to embrace the Ascension Island location at 15°S. The recent magnetic storm on 3-4 August, 2010, provided a very large impact on VHF scintillations at both Cape Verde and Ascension Island. The storm effect was prominent because it occurred during a time of very low normal scintillation activity. The same storm was also studied from space using perigee orbits at dusk of the C/NOFS satellite which provided electron density perturbations over the African sector.

Basu, S.; MacKenzie, E.; Roddy, P. A.; Groves, K. M.

2010-12-01

168

Variations of the Levels of the Vlf/lf Radio Signals on the Middle-Latitude Traces during the Deep Solar Minimum  

NASA Astrophysics Data System (ADS)

Statistical characteristics of the levels of the VLF/LF radio signals from the different European radio stations are presented. The regular observations were been carried out by the test receiver Rohde & Shwarz ESH-3 on the geophysical observatory of IDG RAS Michnevo (54.94°N, 37.73°E) during the period of the deep solar minimum (2007-2009). The radio signals from the radio stations Le Blanc (France, 18.3 kHz), GBZ (Great Britain, 19.6 kHz), HBG (Switzerland, 75 kHz), DCF-77 (Germany, 77.5 kHz) and RBU (Russia, 66.6 kHz) have been chosen for the analysis. In the amplitudes of observable signals the diurnal variations, the seasonal and secular trends were observed. In spite of the absence of the external drivers from above the variations of the radio signal amplitude can obtain 5 - 20 dB and have duration of 2-3 hours. The obtained data can testify that processes from below can make independent strong impact on the ionosphere condition.

Zetzer, J. I.; Lyakhov, A.

2010-12-01

169

Nonlocal Unified Type-I and Type-II Model of the Low-Latitude E-region Irregularities at Solar Minimum and Solar Maximum  

NASA Astrophysics Data System (ADS)

The onset of the small-scale irregularities at the E-region are due to both Farley-Buneman and gradient-drift instabilities. Those instabilities were detected at Jicamarca Radar Observatory at 50-MHz and differentiated according their Doppler-Shifts and called Type-I and Type-II, respectively. We developed a nonlocal unified model to study the characteristics of these two instabilities in the linear a nonlinear regimes. The simulation results are based on data of the charged-carrier densities from IRI2012, neutral densities from NMSIS00, electric potential from TIEGCM-1.94, and magnetic field from IGRF-like model. In this model, which based on quasi-neutrality and isothermal approximations, we study the perturbations in the electron carrier density, the electric potential, and ion velocity to show how the instabilities are evolving due to the mode-interactions among these three fields. We compare the simulation results of this model under the conditions of solar minimum and solar maximum. W.H. is supported by NSF Grant 0964692 to the University of Texas at Austin. W.H. and A. S. are partially supported by Aix-Marseille/CNRS and the International Space Science Institute in Bern, Switzerland through the Grant on on "Vortices and zonal winds in planetary atmospheres/ionospheres."

Hassan, E.; Horton, W.; Smolyakov, A.; Litt, S.; Hatch, D.

2013-12-01

170

Solar tides in the equatorial upper thermosphere: A comparison between AE-E data and the TIGCM for solstice, solar minimum conditions  

SciTech Connect

Equatorial thermospheric tidal temperatures and densities inferred from Atmosphere Explorer E (AE-E) mass spectrometer data are compared with theoretical predictions from the National Center for Atmospheric Research Thermosphere/Ionisphere General Circulation Model (TIGCM) for solar minimum, solstice conditions. The thermospheric diurnal and semidiurnal tides are excited in situ by solar heating and by ion-neutral momentum coupling. Semidiurnal tides are also generated by upward propagating waves excited by heating in the lower atmosphere. The model calculations include all of these sources. The TIGCM reproduces the gross tidal features observed by the satellite, including the midnight temperature anomaly, and the diurnal phases are in good agreement for the densities of atomic oxygen and molecular nitrogen. However, for the neutral temperature, the predicted phases are 1-2 hours earlier than observed. In addition, the diurnal temperature and density amplitudes predicted by the model are considerably weaker than indicated by the AE-E measurements. The semidiurnal variations found in the observations agree well with the model for December solstice but not for June. The present results indicate that upward propagating tides from the lower atmosphere are responsible for at least half of the amplitude of the semidiurnal tide in the upper thermosphere.

Burrage, M.D.; Storz, M.F.; Abreu, V.J. (Univ. of Michigan, Ann Arbor (USA)); Fesen, C.G. (Dartmouth College, Hanover,NH (USA)); Roble, R.G. (National Center for Atmospheric Research, Boulder, CO (USA))

1991-01-01

171

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

172

Gravity over coronae and chasmata on Venus  

Microsoft Academic Search

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

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

1994-01-01

173

Energy release in the solar corona from spatially resolved magnetic braids  

NASA Astrophysics Data System (ADS)

It is now apparent that there are at least two heating mechanisms in the Sun's outer atmosphere, or corona. Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000K (refs 1, 2, 3). The active corona needs additional heating to reach 2,000,000-4,000,000K this heat has been theoretically proposed to come from the reconnection and unravelling of magnetic `braids'. Evidence favouring that process has been inferred, but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought to have an angular width of about 0.2arc seconds have not been resolved. Fine-scale braiding has been seen in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating.

Cirtain, J. W.; Golub, L.; Winebarger, A. R.; de Pontieu, B.; Kobayashi, K.; Moore, R. L.; Walsh, R. W.; Korreck, K. E.; Weber, M.; McCauley, P.; Title, A.; Kuzin, S.; Deforest, C. E.

2013-01-01

174

MODELING THE LINE-OF-SIGHT INTEGRATED EMISSION IN THE CORONA: IMPLICATIONS FOR CORONAL HEATING  

SciTech Connect

One of the outstanding problems in all of space science is uncovering how the solar corona is heated to temperatures greater than 1 MK. Though studied for decades, one of the major difficulties in solving this problem has been unraveling the line-of-sight (LOS) effects in the observations. The corona is optically thin, so a single pixel measures counts from an indeterminate number (perhaps tens of thousands) of independently heated flux tubes, all along that pixel's LOS. In this paper we model the emission in individual pixels imaging the active region corona in the extreme ultraviolet. If LOS effects are not properly taken into account, erroneous conclusions regarding both coronal heating and coronal dynamics may be reached. We model the corona as an LOS integration of many thousands of completely independently heated flux tubes. We demonstrate that despite the superposition of randomly heated flux tubes, nanoflares leave distinct signatures in light curves observed with multi-wavelength and high time cadence data, such as those data taken with the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. These signatures are readily detected with the time-lag analysis technique of Viall and Klimchuk in 2012. Steady coronal heating leaves a different and equally distinct signature that is also revealed by the technique.

Viall, Nicholeen M.; Klimchuk, James A. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2013-07-10

175

Unraveling the riddle of syringomyelia.  

PubMed

The pathophysiology of syringomyelia development is not fully understood. Current prevailing theories suggest that increased pulse pressure in the subarachnoid space forces cerebrospinal fluid (CSF) through the spinal cord into the syrinx. It is generally accepted that the syrinx consists of CSF. The here-proposed intramedullary pulse pressure theory instead suggests that syringomyelia is caused by increased pulse pressure in the spinal cord and that the syrinx consists of extracellular fluid. A new principle is introduced implying that the distending force in the production of syringomyelia is a relative increase in pulse pressure in the spinal cord compared to that in the nearby subarachnoid space. The formation of a syrinx then occurs by the accumulation of extracellular fluid in the distended cord. A previously unrecognized mechanism for syrinx formation, the Bernoulli theorem, is also described. The Bernoulli theorem or the Venturi effect states that the regional increase in fluid velocity in a narrowed flow channel decreases fluid pressure. In Chiari I malformations, the systolic CSF pulse pressure and downward motion of the cerebellar tonsils are significantly increased. This leads to increased spinal CSF velocities and, as a consequence of the Bernoulli theorem, decreased fluid pressure in narrow regions of the spinal CSF pathways. The resulting relatively low CSF pressure in the narrowed CSF pathway causes a suction effect on the spinal cord that distends the cord during each systole. Syringomyelia develops by the accumulation of extracellular fluid in the distended cord. In posttraumatic syringomyelia, the downwards directed systolic CSF pulse pressure is transmitted and reflected into the spinal cord below and above the traumatic subarachnoid blockage, respectively. The ensuing increase in intramedullary pulse pressure distends the spinal cord and causes syringomyelia on both sides of the blockage. The here-proposed concept has the potential to unravel the riddle of syringomyelia and affords explanations to previously unanswered clinical and theoretical problems with syringomyelia. It also explains why syringomyelia associated with Chiari I malformations may develop in any part of the spinal cord including the medullary conus. Syringomyelia thus preferentially develops where the systolic CSF flow causes a suction effect on the spinal cord, i.e., at or immediately caudal to physiological or pathological encroachments of the spinal subarachnoid space. PMID:16752160

Greitz, Dan

2006-10-01

176

Impact of tropospheric tides on the nitric oxide 5.3 ?m infrared cooling of the low-latitude thermosphere during solar minimum conditions  

NASA Astrophysics Data System (ADS)

This paper explores the impact of diurnal tides that begin near the surface as heat is released by evaporation and condensation on Earth's upper atmosphere natural thermostat: the nitric oxide (NO) infrared cooling of the thermosphere at 5.3 ?m. Equatorial NO volume emission rate measurements from 100 to 180 km made by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on TIMED during the solar minimum year 2008 are analyzed on two important nonmigrating tides, the DE2 and DE3 components. DE3 (DE2) amplitudes maximize around 125 km altitude and, depending on season, are on the order of 0.18 (0.16) nW/m3. This represents a substantial modulation of the mean NO emission that maximizes in the same altitude range with a value of about 0.8 nW/m3. Tropospheric tides are therefore important not only for the dynamics and electrodynamics of the ionosphere-thermosphere system but also for modulating the thermospheric energy budget. Supporting photochemical tidal modeling indicates that the main tidal coupling mechanism is the temperature dependence of the collisional excitation of the NO (?=1) vibrational state. However, the response to vertical tidal advection is also important. It is in-phase with the response to temperature and contributes as much as 50% to the NO tides at and above the emission maximum. Neutral density tidal variations contribute about 25% but with a 9 h phase offset resulting in a net damping. These results imply that NO 5.3 ?m emissions are a suitable proxy for studying tidal dynamics in the thermosphere where no global temperature measurements are available.

Oberheide, J.; Mlynczak, M. G.; Mosso, C. N.; Schroeder, B. M.; Funke, B.; Maute, A.

2013-11-01

177

Equatorial vertical plasma drifts and the measured and IRI model-predicted F2-layer parameters above Ouagadougou during solar minimum  

NASA Astrophysics Data System (ADS)

In this paper, hourly median value of ionosonde measurements: peak height F2-layer (hmF2), F2-layer critical frequency (foF2) and propagation factor M3000F2made at near-equatorial dip latitude, Ouagadougou, Burkina Faso (12°N, 1.5°W; dip: 1.5°N) and relevant F2-layer parameters: 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 electrodynamicson 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. It is demonstrated that the month-by-month morphological patterns between vertical E × B 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. Examination of the association between measured foF2, hmF2 and M3000F2illustrates consistent much more smaller correlation coefficients with no systematic linkage.

Oyekola, O. S.

2012-06-01

178

Comparison of the extended solar minimum of 2006-2009 with the Spoerer, Maunder, and Dalton Grand Minima in solar activity in the past  

NASA Astrophysics Data System (ADS)

use cosmic radiation records (neutron monitor and the cosmogenic radionuclides, 10Be and 14C) as a proxy to compare the solar activity during the extended solar minimum 2006-2009, with that during the Grand Solar Minima and Maxima that occurred between 1391 and 2010. The inferred cosmic ray intensities during the Spoerer, Maunder, and Dalton Grand Minima were significantly greater than those during 2006-2009. The onset phases of the three Grand Minima extended over between two and five Schwabe (sunspot) cycles, the cosmic ray intensity at the Schwabe minima increasing from a value approximating that of 2006-2009, to substantially higher values later in the Grand Minimum. The minimum estimated strengths of the heliospheric magnetic field near Earth during the Grand Minima were 2.4 nT (Spoerer), <2.0 nT (Maunder), and 2.6 nT (Dalton), compared to 3.9 nT in 2009. We conclude that the periods of highest solar activity during the Maunder Minimum approximated those near the sunspot minima between 1954 and 1996. The average ratio of the maximum to minimum estimated HMF in the six Schwabe cycles in the Maunder Minimum is 1.54 (range 1.30-1.85) compared to 1.52 (1.31-1.63) for the modern epoch suggesting similar operation of the solar dynamo in both intervals. The onset phase of the Maunder Minimum extending over five Schwabe cycles, and the large increase in cosmic ray flux (and decrease in estimated heliospheric magnetic field), leads us to speculate that the magnetohydrodynamic amplification in the solar dynamo exhibits a relaxation time well in excess of the 11 year period of the Schwabe cycle.

McCracken, K. G.; Beer, J.

2014-04-01

179

The morphology of streamer coronas  

SciTech Connect

Streamer coronas are of interest due to their application to pollution control devices. A streamer coronal discharge produces energetic electrons which, through dissociation and ionization processes, generate active radicals that in turn react with toxic molecules. The morphology of streamer coronas determines the energy distribution of the electrons produced. Streamers propagate due to a highly non-linear space charge driven ionization wave. Because of the complexity of the equations describing streamer dynamics, most of the numerical simulations have been restricted to one (longitudinal) spatial dimension. Some low resolution 2-D simulations have been previously performed, but so far have been restricted to plane-parallel electrode configurations. The authors have developed multi-dimensional streamer models that can be applied to arbitrarily shaped electrode structures. Their models have generated the first multi-dimensional fully resolved streamers which form self-consistent radial structure. They have applied these codes to study some of the issues related to finding the optimum working conditions for streamer corona reactors. Their results show that the radial components of the electron flow and the space charge field are very important in providing an accurate picture of the streamer morphology, especially near the highly stressed electrode.

Vitello, P.A.; Penetrante, B.M.; Bardsley, J.N. [Lawrence Livermore National Lab., CA (United States)

1992-12-01

180

Remote Sensing of Low and Mid-Latitude Ionospheric Disturbances During Solar Minimum Using CITRIS and CERTO Measurements of TEC and Radio Scintillation  

NASA Astrophysics Data System (ADS)

Unique data on ionospheric plasma disturbances from the Naval Research Laboratory CITRIS (Scintillation and TEC Receiver in Space) instrument will be presented. CITRIS is a multi-band receiver that recorded TEC (Total Electron Content) and radio scintillations from Low-Earth Orbit (LEO) on STPSat1. The 555+/5 km altitude 35° inclination orbit covers low and mid-latitudes. The measurements require propagation from a transmitter to a receiver through the F-region plasma. CITRIS used both 1) satellite beacons in LEO, such as the NRL CERTO (Coherent Electromagnetic Radio TOmography) three-frequency beacons transmitting at 150/400/1067 MHz and 2) the French global network of ground-based DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) beacons transmitting at 401.25 and 2036.25 MHz. CITRIS was operated in a complementary fashion with the C/NOFS satellite during most of its first year of operations; C/NOFS carries CERTO beacon along with in-situ diagnostics. CITRIS and ground receivers can simultaneously measure TEC and scintillations on different paths using CERTO on C/NOFS. When C/NOFS is not in view, CITRIS makes measurements from DORIS beacons and other LEO satellites. Because of the orbits CITRIS will always make measurements at the same longitude within 48 min of C/NOFS. The ability to look at multiple paths is unique and useful for studying the spatial extent and time duration of disturbances. The combination of TEC and scintillation measurements provides information on a range of scale-sizes from >1 km to about 100 m. The joint data set on plasma structures at low-latitudes is a focus of our presentation, with the addition of comparisons to CITRIS data taken at mid-latitude. Several types of irregularities have been studied including Spread-F and the newly discovered dawn-side depletions. The data covers large portions of the Earth (including the Pacific, African and South American sectors) during an unusually quite portion of the most recent solar minimum.

Siefring, C. L.; Bernhardt, P. A.

2010-12-01

181

Ionosphere/Thermosphere Climatology at Low and Mid-Latitude During Solar Minimum Obtained From the GAIM-Physics-Based Data Assimilation Model (GAIM-FP)  

NASA Astrophysics Data System (ADS)

Our ability to specify and forecast ionospheric dynamics and weather at low and mid latitudes is strongly limited by our current understanding of the coupling processes in the ionosphere-thermosphere system and the coupling between the high and low latitude regions. Furthermore only a limited number of observations are available for a specification of ionospheric dynamics and weather at these latitudes. As shown by meteorologists and oceanographers, the best specification and weather models are physics-based data assimilation models that combine the observational data with our understanding of the physics of the environment. Therefore, we have developed and continue to develop four data assimilation models; two for the ionosphere, one for the high-latitude ionosphere dynamics, and one for the thermosphere. One of these models is the Global Assimilation of Ionospheric Measurements Full-Physics model (GAIM-FP). The model is based on an Ensemble Kalman filter technique and a physics-based model of the ionosphere/plasmasphere (IPM), which covers the altitude range from 90 to 20,000 km, includes six ion species, is based on the International Geomagnetic Reference Field (IGRF), and allows for inter-hemisphere flow. The model can assimilate bottom-side Ne profiles from ionosondes, slant TEC from ground-based GPS stations, in situ Ne from the DMSP satellites, occultation data from several satellites, and line-of-sight UV emissions measured by satellites. As an output the assimilation model provides the 3-dimensional density distribution throughout the ionosphere and information about the physical drivers, including the neutral winds, composition and electric fields. In the current application of the model we have assimilated COSMIC occultation data over several 4-month long periods During the last solar minimum to specify the low- and mid-latitude ionosphere/thermosphere climatology. The model was used to determine the average ionospheric morphology and the various driving forces. We will present examples of the ionosphere climatology and driver specifications obtained from our model runs with an emphasis on a comparison with independent data.

Scherliess, L.; Lomidze, L.; Schunk, R. W.

2011-12-01

182

Tectonics of Neyterkob corona on Venus  

NASA Technical Reports Server (NTRS)

Neyterkob double corona (50 deg N 202 deg) presents an area of corona-related interfering tectonic patterns which are formed in different phases of evolution of the corona and modified by regional stresses. Analyzing the patterns can reveal something about the coronal formation. Tectonic features form distinct units on topographic depressions, slopes, and volcanic flows extending over one radius of the corona. A remarkable amount of compressional features were found near the rim and related to interaction between adjacent coronae. Radial extension was mainly observed on a peculiar NE-SW trending high crossing the corona. Concentric fractures were found to the east partly connected to the lithospheric flexure. Tectonic features indicate movements of volcanic activity and modification of the area by more regional stresses.

Kauhanen, K.

1993-01-01

183

Corona Discharge Influences Ozone Concentrations Near Rats  

SciTech Connect

Ozone is produced by corona discharge in air. Its production is enhanced near grounded water. Whether grounded animals behave like grounded water, producing more ozone was investigated. Rats were exposed to corona discharge in a plastic cage. The concentration of ozone in the gas phase was monitored. The ozone concentration exceeded ambient levels only in the presence of corona discharge and either rats or water. When water or rats were exposed to corona discharge, ozone levels were more than 10 times higher than controls. Ozone levels increased rapidly with applied voltage. There was also a correlation between the distance of the corona needle to the rats and the amount of ozone produced. As the distance increased, ozone production decreased. These results are discussed in relation to the potential exposure of mammals to ozone in the vicinity of corona discharge and electric fields.

Goheen, Steven C.; Gaither, Kari A.; Anantatmula, Shantha M.; Mong, Gary M.; Sasser, Lyle B.; Lessor, Delbert L.

2004-02-26

184

Gravity over coronae and chasmata on Venus  

NASA Technical Reports Server (NTRS)

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.

1994-01-01

185

EVOLUTION OF THE GLOBAL TEMPERATURE STRUCTURE OF THE SOLAR CORONA DURING THE MINIMUM BETWEEN SOLAR CYCLES 23 AND 24  

SciTech Connect

The combination of differential emission measure tomography with extrapolation of the photospheric magnetic field allows determination of the electron density and electron temperature along individual magnetic field lines. This is especially useful in quiet-Sun (QS) plasmas where individual loops cannot otherwise be identified. In Paper I, this approach was applied to study QS plasmas during Carrington rotation (CR) 2077 at the minimum between solar cycles (SCs) 23 and 24. In that work, two types of QS coronal loops were identified: ''up'' loops in which the temperature increases with height, and ''down'' loops in which the temperature decreases with height. While the first ones were expected, the latter ones were a surprise and, furthermore, were found to be ubiquitous in the low-latitude corona. In the present work, we extend the analysis to 11 CRs around the last solar minimum. We found that the ''down'' population, always located at low latitudes, was maximum at the time when the sunspot number was minimum, and the number of down loops systematically increased during the declining phase of SC-23 and diminished during the rising phase of SC-24. ''Down'' loops are found to have systematically larger values of {beta} than do ''up'' loops. These discoveries are interpreted in terms of excitation of Alfven waves in the photosphere, and mode conversion and damping in the low corona.

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

2013-08-10

186

Corona discharge of Titan's troposphere.  

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 charge particles leads to corona discharges which are characterized by low current densities. These electric discharges could induce a number of chemical reactions in the troposphere and hence it is of interest to explore such effects. 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-butene, 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 an uncharacterized film deposit. We present their trends of formation as a function of discharge time in an ample interval and have derived their initial yields of formation. These 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 to low by a factor of 10 to 40. While some ethene will be produced by charged-particle chemistry, its production by corona processes and 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:11541341

Navarro-Gonzalez, R; Ramirez, S I

1997-01-01

187

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.

Rohwein, Gerald J. (Albuquerque, NM)

1998-01-01

188

Inverted Temperature Loops in The Quiet Corona: Properties and Physical Origin  

NASA Astrophysics Data System (ADS)

Huang et al. 2012 revealed the existence of inverted temperature ("down") loops, in which temperature decreases with height, as well as the usual ("up") loops, in which the temperature increases with height, in the quiet solar Corona. It was shown that the "down" loops are mostly located at low latitudes and "up" loops most often appear in high latitudes. A recent study by Nuevo et al. 2013 confirmed this discovery and further showed that the "down" loop population is greatest at solar minimum; and strongly decreases with solar activity. Moreover, the "down" loops were found to be associated with values of the plasma beta greater than about unity, while the "up" loops were associated with much smaller values of beta. Here, we review the properties of "up" and "down" loops, and employ a state-of-the-art global MHD model to understand the physics of these loops as well as to investigate their thermodynamic stability. The 3D MHD model uses a phenomenological wave dissipation model based on wave reflection (proportional to the Alfvén speed gradients) and turbulent dissipation.

Huang, Z.; van der Holst, B.; Frazin, R. A.; Nuevo, F.; Vásquez, A. M.; Manchester, W.; Sokolov, I.; Gombosi, T. I.

2013-12-01

189

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

190

Interplanetary Fast Shocks and Associated Drivers Observed through the Twenty-Third Solar Minimum by WIND Over its First 2.5 Years  

NASA Technical Reports Server (NTRS)

A list of the interplanetary (IP) shocks observed by WIND from its launch (in November 1994) to May 1997 is presented. Forty two shocks were identified. The magnetohydrodynamic nature of the shocks is investigated, and the associated shock parameters and their uncertainties are accurately computed using a practical scheme which combines two techniques. These techniques are a combination of the "pre-averaged" magnetic-coplanarity, velocity-coplanarity, and the Abraham-Schrauner-mixed methods, on the one hand, and the Vinas and Scudder [1986] technique for solving the non-linear least-squares Rankine-Hugoniot shock equations, on the other. Within acceptable limits these two techniques generally gave the same results, with some exceptions. The reasons for the exceptions are discussed. It is found that the mean strength and rate of occurrence of the shocks appears to correlated 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 start of solar cycle 23, which began around June 1996. Eighteen shocks appeared to be associated with corotating interaction regions (CIRs). The distribution of their shock normals showed a mean direction peaking in the ecliptic plane and with a longitude (phi(sub n)) in that plane between perpendicular to the Parker spiral and radial from the Sun. When grouped according to the sense of the direction of propagation of the shocks the mean azimuthal (longitude) angle in GSE coordinates was approximately 194 deg for the fast-forward and approximately 20 deg for the fast-reverse shocks. Another 16 shocks were determined to be driven by solar transients, including magnetic clouds. These shocks 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 orientation well off the ecliptic plane. No shock propagated with longitude phi(sub n) >= 220 +/- 10 deg, this would suggest strong hindrance to the propagation of shocks contra a rather tightly winding Parker spiral. Examination of the obliquity angle theta(sub Bn) (that between the shock normal and the upstream interplanetary magnetic field) for the full set of shocks revealed that about 58% was quasi-perpendicular, and some were very nearly perpendicular. About 32% of the shocks were oblique, and the rest (only 10%) were quasi-parallel, with one on Dec. 9, 1996 that showed field pulsations. Small uncertainty in the estimated angle theta(sub Bn) was obtained for about 10 shocks with magnetosonic Mach numbers between 1 and 2, hopefully significantly contributing to studies researching particle acceleration mechanisms at IP shocks, and to investigations where accurate values of theta(sub Bn) are crucial.

Mariani, F.; Berdichevsky, D.; Szabo, A.; Lepping, R. P.; Vinas, A. F.

1999-01-01

191

Parga Chasma: Coronae and Rifting on Venus  

NASA Technical Reports Server (NTRS)

The majority of coronae (quasicircular volcano-tectonic features) are found along rifts or fracture belts, and the majority of rifts have coronae [e.g. 1,2]. However, the relationship between coronae and rifts remains unclear [3-6]. There is evidence that coronae can form before, after, or synchronously with rifts [3,4]. The extensional fractures in the rift zones have been proposed to be a result of broad scale upwelling and traction on the lower lithosphere [7]. However, not all rift systems have a significant positive geoid anomaly, as would be expected for an upwelling site [8]. This could be explained if the rifts lacking anomalies are no longer active. Coronae are generally accepted to be sites of local upwelling [e.g. 1], but the observed rifting is frequently not radial to the coronae and extends well beyond the coronae into the surrounding plains. Thus the question remains as to whether the rifts represent regional extension, perhaps driven by mantle tractions, or if the coronae themselves create local thinning and extension of the lithosphere. In the first case, a regional extension model should be consistent with the observed characteristics of the rifts. In the latter case, a model of lithospheric loading and fracturing would be more appropriate. A good analogy may be the propagation of oceanic intraplate volcanoes [9].

Smrekar, S. E.; Stofan, E. R.; Buck, W. R.; Martin, P.

2005-01-01

192

Extraatmospheric observations of the outer solar corona  

Microsoft Academic Search

The paper describes a small, externally occulted Lyot coronagraph intended for the spaceborne photography of the solar corona; the instrument can be modified to perform observations of the corona from stratospheric balloons. The basic characteristics of the coronagraph are considered, and results obtained with the instrument on a rocket flight on December 19, 1976 are briefly discussed.

O. I. Babich; Y. B. Kolesnik; Y. A. Krayev; A. V. Lensky; A. T. Nesmyanovich; V. V. Polezhayev; B. B. Ponomaryov; O. S. Popov

1981-01-01

193

Io's Corona: Asymmetries and AO Observations  

Microsoft Academic Search

Io's corona is the critical link between Io's atmosphere and the plasma torus. This region, from the exobase to the Hill sphere at about 6 RIo, has now been studied in enough detail to search for temporal variations, spatial asymmetries, and differences between atomic species. Our mutual eclipse observations reveal a relatively stable sodium corona with a significant asymmetry: Io's

N. M. Schneider; M. H. Burger; S. E. Sutton; M. A. Dubson

2003-01-01

194

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

195

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

196

Dynamics of the quiescent solar corona  

Microsoft Academic Search

A model for the quiescent, inhomogeneous solar corona is developed, based upon the concept of loop structures as the basic structural element of the corona. The results, which are compared with observations obtained by the S-054 Skylab X-ray telescope, show that (a) hydrostatic solutions are stable only if the temperature maximum is located at the top of loop structures, and

R. Rosner; W. H. Tucker; G. S. Vaiana

1978-01-01

197

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

198

Improved Method for Calculating DC Corona Losses  

Microsoft Academic Search

Existing methods for calculating corona losses on monopolar and bipolar dc transmission lines have resorted to the assumption that the space charge of corona does not affect the direction of the electrostatic field. This assumption was aimed at making the calculations possible. In this report corena loss calculations are made in which this assumption and others are replaced by correlating

Mohammed Khalifa; Mazen Abdel-Salam

1974-01-01

199

System reliability analysis through corona testing  

NASA Technical Reports Server (NTRS)

In the Reliability and Quality Engineering Test Laboratory at the NASA Lewis Research Center a nondestructive, corona-vacuum test facility for testing power system components was developed using commercially available hardware. The test facility was developed to simulate operating temperature and vacuum while monitoring corona discharges with residual gases. This facility is being used to test various high voltage power system components.

Lalli, V. R.; Mueller, L. A.; Koutnik, E. A.

1975-01-01

200

System reliability analysis through corona testing  

NASA Technical Reports Server (NTRS)

A corona vacuum test facility for nondestructive testing of power system components was built in the Reliability and Quality Engineering Test Laboratories at the NASA Lewis Research Center. The facility was developed to simulate operating temperature and vacuum while monitoring corona discharges with residual gases. The facility is being used to test various high-voltage power system components.

Lalli, V. R.; Mueller, L. A.; Koutnik, E. A.

1975-01-01

201

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Technical Reports Server (NTRS)

The solar corona, the hot, tenuous outer atmosphere of the Sun, exhibits many fascinating phenomena on a wide range of scales. One of the ways that the Sun can affect us here at Earth is through the large-scale structure of the corona and the dynamical phenomena associated with it, as it is the corona that extends outward as the solar wind and encounters the Earth's magnetosphere. The goal of our research sponsored by NASA's Supporting Research and Technology Program in Solar Physics is to develop increasingly realistic models of the large-scale solar corona, so that we can understand the underlying properties of the coronal magnetic field that lead to the observed structure and evolution of the corona. We describe the work performed under this contract.

Linker, Jon A.; Wagner, William (Technical Monitor)

2001-01-01

202

The helium shells of HeI and HeII at solar minimum: New results from eclipse flash spectra of 2008- 2010  

NASA Astrophysics Data System (ADS)

Flash spectra taken at high frame rate during the total solar eclipse of August 1st 2008 in Siberia and during the July 11th 2010 in French Polynesia are compared in the context of the quiet Sun near the minimum of activity. They both reveal the weak Paschen ? 468.6 nm ionized helium line, seen as a helium shell in layers up to the 8 Mm heights. The preliminary evaluated effective height of the He I 4713 shell is 1.8 Mm and it is approximately 2.0 Mm for the He II 4686 emissions outside polar regions. These lines can be measured only in eclipse conditions, when the parasitic scattered light is negligible for very low solar fluxes corresponding to the coronal levels. Many faint lines are also seen in emission such as Ba +, Ti +, Fe +, but with a much lower radial extension. They were observed to be superposed to F-lines when defining the solar limb using the continuum background. A cartoon is proposed to describe the structuration of these low layers and to illustrate the contribution of the magnetic field. These observations are important new insights for understanding (i) the magnetic field inference in the very low layers of the solar transition region and (ii) the ionisation mechanisms producing the big jump of the temperature towards the corona, including the source of heating.

Bazin, C.; Koutchmy, S.; Lamy, P.

2011-12-01

203

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.

204

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

205

Vertical elliptical coronas caused by pollen.  

PubMed

Near-forward scattering by cloud droplets is known to give rise to colored rings, centered on the Sun or the Moon, which are called the corona. Because of the spherical shape of the droplets, the corona can be circular. A Finnish amateur astronomers' network has found a corona, in a seemingly cloudless sky, with a regular vertically elliptical shape. The aspect ratio of these ellipses changes with the altitude of the Sun or the Moon. Some brightening in the coronas has also been reported. Because of observations of high pollen concentrations at the time of occurrence of these coronas, we propose that some coronas can be explained as a result of scatteringbybirch pollen grains, which are more or less spheroidal. To explain other observed coronas, pollen grains with more complicated shapes, such as pine and spruce pollen grains, must be invoked. Our analysis is limited to spheroidal grains, for which the Fraunhofer theory gives analytical expressions of simple form. The more complicated shapes require numerical simulations or laboratory experiments, which we have not done. PMID:20935822

Parviainen, P; Bohren, C F; Mäkelä, V

1994-07-20

206

Corona discharge in electroporation of cell membranes  

NASA Astrophysics Data System (ADS)

The objective of the present work is to demonstrate that electrical corona discharge is very efficient in cellular membrane electroporation due to current pulses with sharp front (2-5 ns) and to the fact that corona discharge is associated with UV radiation and micro particles emission. A comparison between DC and AC at 800 Hz and a special waveform to corona application is presented. The comparison is analyzed by means of applying all these in the maceration process (electroplasmolysis) of red wine production and in the processes of different types of the microbes.

Cramariuc, R.; Tudorache, A.; Popa, M. E.; Branduse, E.; Nisiparu, L.; Mitelut, A.; Turtoi, M. O.; Fotescu, L.

2008-12-01

207

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

208

Dynamics of the Transition Corona  

NASA Astrophysics Data System (ADS)

Magnetic reconnection between the open and closed magnetic fields 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 (PS) structures. However, there is neither clear observational evidence of how such coupling occurs in PSs, nor evidence for how the magnetic reconnection evolves. Using a newly developed technique, we enhance the off-limb magnetic fine structures observed with the Atmospheric Imaging Assembly and identify a PS-like feature located close to the northern coronal hole. We first identify that the magnetic topology associated with the observation is a PS, null-point (NP) related topology bounded by the open field. By comparing the magnetic field configuration with the EUV emission regions, we determined that most of the magnetic flux associated with plasma emission are small loops below the PS basic NP and open field bounding the PS topology. In order to interpret the evolution of the PS, we referred to a three-dimensional MHD interchange reconnection modeling the exchange of connectivity between small closed loops and the open field. The observed PS fine structures follow the dynamics of the magnetic field before and after reconnecting at the NP obtained by the interchange model. Moreover, the pattern of the EUV plasma emission is the same as the shape of the expected plasma emission location derived from the simulation. These morphological and dynamical similarities between the PS observations and the results from the simulation strongly suggest that the evolution of the PS, and in particular the opening/closing of the field, occurs via interchange/slipping reconnection at the basic NP of the PS. Besides identifying the mechanism at work in the large-scale coupling between the open and closed fields, our results highlight that interchange reconnection in PSs is a gradual physical process that differs from the impulsive reconnection of the solar-jet model.

Masson, Sophie; McCauley, Patrick; Golub, Leon; Reeves, Katharine K.; DeLuca, Edward E.

2014-06-01

209

Unraveling the Origins of Nearby Young Stars  

NASA Astrophysics Data System (ADS)

A systematic search for close conjunctions and clusterings in the past of nearby stars younger than the Pleiades is undertaken, which may reveal the time, location, and mechanism of formation of these often isolated, disconnected from clusters and star-forming regions, objects. The sample under investigation includes 101 T Tauri, post-TT, and main-sequence stars and stellar systems with signs of youth, culled from the literature. Their Galactic orbits are traced back in time and near approaches are evaluated in time, distance, and relative velocity. Numerous clustering events are detected, providing clues to the origin of very young, isolated stars. Each star's orbit is also matched with those of nearby young open clusters, OB and TT associations and star-forming molecular clouds, including the Ophiuchus, Lupus, Corona Australis, and Chamaeleon regions. Ejection of young stars from open clusters is ruled out for nearly all investigated objects, but the nearest OB associations in Scorpius-Centaurus, and especially, the dense clouds in Ophiuchus and Corona Australis have likely played a major role in the generation of the local streams (TWA, Beta Pic, and Tucana-Horologium) that happen to be close to the Sun today. The core of the Tucana-Horologium association probably originated from the vicinity of the Upper Scorpius association 28 Myr ago. A few proposed members of the AB Dor moving group were in conjunction with the coeval Cepheus OB6 association 38 Myr ago.

Makarov, Valeri V.

2007-03-01

210

Alfven waves in the solar corona.  

PubMed

Alfvén waves, transverse incompressible magnetic oscillations, have been proposed as a possible mechanism to heat the Sun's corona to millions of degrees by transporting convective energy from the photosphere into the diffuse corona. We report the detection of Alfvén waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico. Ubiquitous upward propagating waves were seen, with phase speeds of 1 to 4 megameters per second and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. An estimate of the energy carried by the waves that we spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfvén waves may carry sufficient energy. PMID:17761876

Tomczyk, S; McIntosh, S W; Keil, S L; Judge, P G; Schad, T; Seeley, D H; Edmondson, J

2007-08-31

211

Global MHD Models of the Solar Corona  

NASA Technical Reports Server (NTRS)

Global magnetohydrodynamic (MHD) models of the solar corona are computationally intensive, numerically complex simulations that have produced important new results over the past few years. After a brief overview of how these models usually work, I will address three topics: (1) How these models are now routinely used to predict the morphology of the corona and analyze Earth and space-based remote observations of the Sun; (2) The direct application of these models to the analysis of physical processes in the corona and chromosphere and to the interpretation of in situ solar wind observations; and (3) The use of results from global models to validate the approximations used to make detailed studies of physical processes in the corona that are not otherwise possible using the global models themselves.

Suess, S. T.; Rose, Franklin (Technical Monitor)

2001-01-01

212

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

213

Coronas from the Thessaloniki gabbros (North Greece)  

Microsoft Academic Search

Coronas which have been developed between olivine and plagioclase in Precambrian gabbroic rocks from Thessaloniki, Greece, have been studied. These consist commonly of (olivine), clinopyroxene, amphibole (plagioclase) and rarely of (olivine) orthopyroxene, clinopyroxene amphibole (plagioclase) assemblages.

Elias S. Sapountzis

1975-01-01

214

Olivines and olivine coronas in mesosiderites  

NASA Technical Reports Server (NTRS)

The paper presents a study of olivines and their surrounding coronas in mesosiderites texturally and compositionally using optical and microprobe methods. Olivine composition ranges from Fo(58-92) and shows no consistent pattern of distribution within and between mesosiderites; olivine occurs as large single crystals or as partially recrystallized mineral clasts, except for two lithic clasts. These are Emery and Vaca Muerta, and both are shock-modified olivine orthopyroxenites. Fine-grained coronas surround olivine, except for those in impact-melt group mesosiderites and those without tridymite in their matrices. Coronas consist largely of orthopyroxene, plagioclase, clinopyroxene, chromite, merillite, and ilmenite, and are similar to the matrix, but lack metal and tridymite. Texturally the innermost parts of the corona can be divided into three stages of development: (1) radiating acicular, (2) intermediate, and (3) granular.

Nehru, C. E.; Zucker, S. M.; Harlow, G. E.; Prinz, M.

1980-01-01

215

Computed conditions of corona emission from raindrops  

NASA Astrophysics Data System (ADS)

The altitude of corona emission from charged raindrops located in a vertical ambient electric field is calculated by coupling the corona experimental results obtained by Dawson (1969) with the raindrop model of Coquillat and Chauzy (1993). This model provides the drop shape and electric surface field necessary to calculate the corona occurrence altitude from a fitting of Dawson's data. The original results are presented in the form of vertical profiles of the critical field, which is the ambient field that causes disruption or a corona. These results are directly comparable with in situ measurements of electric field, raindrop size, and net charge. If we make the assumption that positive streamer propagation is of prime importance for lightning initiation, the critical field profiles allow us to determine the minimum net charge of a drop which could initiate a discharge in a given ambient field.

Coquillat, Sylvain; Chauzy, Serge

1994-08-01

216

Olivines and olivine coronas in mesosiderites  

NASA Astrophysics Data System (ADS)

The paper presents a study of olivines and their surrounding coronas in mesosiderites texturally and compositionally using optical and microprobe methods. Olivine composition ranges from Fo(58-92) and shows no consistent pattern of distribution within and between mesosiderites; olivine occurs as large single crystals or as partially recrystallized mineral clasts, except for two lithic clasts. These are Emery and Vaca Muerta, and both are shock-modified olivine orthopyroxenites. Fine-grained coronas surround olivine, except for those in impact-melt group mesosiderites and those without tridymite in their matrices. Coronas consist largely of orthopyroxene, plagioclase, clinopyroxene, chromite, merillite, and ilmenite, and are similar to the matrix, but lack metal and tridymite. Texturally the innermost parts of the corona can be divided into three stages of development: (1) radiating acicular, (2) intermediate, and (3) granular.

Nehru, C. E.; Zucker, S.; Harlow, G. E.; Prinz, M.

1980-08-01

217

Global Magnetohydrodynamic Modeling of the Solar Corona  

NASA Technical Reports Server (NTRS)

The coronal magnetic field defines the structure of the solar corona, the position of the heliospheric current sheet, the regions of fast and slow solar wind, and the most likely sites of coronal mass ejections. There are few measurements of the magnetic fields in the corona, but the line-of-sight component of the global magnetic fields in the photosphere have been routinely measured for many years (for example, at Stanford's Wilcox Solar Observatory, and at the National Solar Observatory at Kitt Peak). The SOI/MDI instrument is now providing high-resolution full-disk magnetograms several times a day. Understanding the large-scale structure of the solar corona and inner heliosphere requires accurately mapping the measured photospheric magnetic field into the corona and outward. Ideally, a model should not only extrapolate the magnetic field, but should self-consistently reconstruct both the plasma and magnetic fields in the corona and solar wind. Support from our NASA SR&T contract has allowed us to develop three-dimensional magnetohydrodynamic (MHD) computations of the solar corona that incorporate observed photospheric magnetic fields into the boundary conditions. These calculations not only describe the magnetic field in the corona and interplanetary spice, but also predict the plasma properties as well. Our computations thus far have been successful in reproducing many aspects of both coronal and interplanetary data, including the structure of the streamer belt, the location of coronal hole boundaries, and the position and shape of the heliospheric current sheet. The most widely used technique for extrapolating the photospheric magnetic field into the corona and heliosphere are potential field models, such as the potential field source-surface model (PFSS),and the potential field current-sheet (PFCS) model

Linker, Jon A.

1998-01-01

218

Corona Associations and Their Implications for Venus  

USGS Publications Warehouse

Geologic mapping principles were applied to determine genetic relations between coronae and surrounding geomorphologic features within two study areas in order to better understand venusian coronae. The study areas contain coronae in a cluster versus a contrasting chain and are (1) directly west of Phoebe Regio (quadrangle V-40; centered at latitude 15??S, longitude 250??) and (2) west of Asteria and Beta Regiones (between latitude 23??N, longitude 239?? and latitude 43??N, longitude 275??). Results of this research indicate two groups of coronae on Venus: (1) those that are older and nearly coeval with regional plains, and occur globally; and (2) those that are younger and occur between Beta, Atla, and Themis Regiones or along extensional rifts elsewhere, sometimes showing systematic age progressions. Mapping relations and Earth analogs suggest that older plains coronae may be related to a near-global resurfacing event perhaps initiated by a mantle superplume or plumes. Younger coronae of this study that show age progression may be related to (1) a tectonic junction of connecting rifts resulting from local mantle upwelling and spread of a quasi-stationary hotspot plume, and (2) localized spread of post-plains volcanism. We postulate that on Venus most of the young, post-resurfacing coronal plumes may be concentrated within an area defined by the bounds of Beta, Atla, and Themis Regiones. ?? 1998 Academic Press.

Chapman, M. G.; Zimbelman, J. R.

1998-01-01

219

Solar cycle variations in F-region Te in the vicinity of the midlatitude trough based on AE-C measurements at solar minimum and DE-2 measurements at solar maximum  

NASA Technical Reports Server (NTRS)

Magnetospheric energy deposited in the plasmasphere produces large enhancements in the electron temperature in the nightside ionosphere at the foot of the geomagnetic L shell that traverses the plasmapause. This temperature peak, which is associated with the midlatitude trough in electron density, often has a great enough amplitude to produce 630 nm emission known as a Sar-arc. The Atmosphere Explorer-C measurements made at solar minimum and the Dynamics Explorer-2 measurements made at solar maximum are used to illustrate how this signature of F-region electron heating changes with solar activity. Global empirical models of the electron temperature and density have not been able to resolve these features thus far because of their large movements with geomagnetic activity and because of the large bin sizes used in the models. It is not yet clear how this major feature of the F-region temperature structure could be included easily in the IRI model.

Brace, Larry H.

1990-01-01

220

Preliminary Global Survey of Circular Lows, A Subset of Venusian Coronae  

NASA Astrophysics Data System (ADS)

We address the mode of formation of coronae on circular lows- coronae with amphitheatre-sized depressions. A major hypothesis is coronae are surface expressions of endogenic rising diapirs but others suggest coronae are exogenic impact craters.

Shankar, B.; Hansen, V. L.

2008-03-01

221

Mapping the Solar Wind from its Source Region into the Outer Corona  

NASA Technical Reports Server (NTRS)

The solar wind not only forms the space environment of Earth and other planets, but is also the cause of many phenomena observed in the Earth's atmosphere, such as aurorae. The expansion of the coronal plasma of the Sun is characteristic to many main sequence stars, and thus provides an example for understanding stellar winds as well. In spite of its importance for both space science and stellar physics, basic solar wind properties remain essentially unresolved. Since its discovery about 50 years ago, the complexity of the Sun corona - solar wind system has complicated the interpretation of observations. Recent progress in remote sensing observations as provided for example by YOHKOH, SOHO, SPARTAN and ULYSSES as well as some ground based techniques such as Interplanetary Scintillation observations, offer a compelling opportunity to unravel the 50 year old puzzle regarding the heat source or sources that cause the expansion of the solar corona. The new era of solar wind observations initiated by SOHO and ULYSSES, have also led to a wealth of new theoretical approaches. The goal of the proposed research was to carry out an integrated study of the coronal and solar wind plasma making use of the opportunities provided by the above spacecraft, as well as plasma emission calculations and new ideas on solar wind expansion theory.

Esser, Ruth; Wagner, William J. (Technical Monitor)

2000-01-01

222

Coronas and iridescence in mountain wave clouds.  

PubMed

We use Fraunhofer diffraction theory and meterological data to determine the nature of cloud-particle distributions and the mean particle sizes required for interpreting photographs of coronas and iridescence in mountain wave clouds. Traditional descriptions of coronas and iridescence usually explain these optical phenomena as diffraction by droplets of liquid water. Our analysis shows that the photographed displays have mean particle sizes from 7.6 to 24.3 microm, with over half the cases requiring diffraction by small (approximatley 20 microm) quasispherical ice particles rather than liquid water droplets. Previous documentation of coronas produced by ice particles are limited to observations in cirrus clouds that appear to be composed of small ice crystals, whereas our observations suggest that coronas and iridescence quite often can be created by tiny quasispherical ice particles that might be unique to mountain wave clouds. Furthermore, we see that the dominant colors in mountain wave-cloud coronas are red and blue, rather than the traditionally described red and green. PMID:12570269

Shaw, Joseph A; Neiman, Paul J

2003-01-20

223

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...

224

Stellar Coronae: The First Twenty - Five Years  

NASA Technical Reports Server (NTRS)

Hot X-ray emitting coronae were detected on stars other than the Sun about twenty-five years ago. Within only a few years of the first detections, the Einstein Observatory had mapped out coronal activity across the HR diagram. These observations provided the foundations for a coarse theoretical understanding of the physical mechanisms responsible for hot coronae on stars that has changed relatively little in the intervening years: plasma trapped in magnetic structures generated by dynamo processes somewhere beneath the photosphere is heated by as yet unidentified mechanisms that appear to transfer kinetic energy from underlying convective regions of the stellar envelope into the outer atmosphere. This review will describe the observational advances that have lead to some further theoretical understanding of stellar coronae, including the first results from high resolution X-ray spectroscopy obtained by Chandra and XMM-Newton, and will highlight the observational directions needed to make further progress.

Drake, Jeremy

2000-01-01

225

Temperature measurements in the inner corona  

NASA Technical Reports Server (NTRS)

To increase the understanding of the acceleration of the solar wind, it is necessary to combine observations and theoretical approaches. The importance of coordinated measurements in the inner corona and interplanetary space to place constraints on solar wind models is demonstrated. Given the fact that the temperature in the inner corona is the most important parameter in solar wind modeling, observations from which reliable temperatures can be deduced are crucial for such coordinated approaches. The derivation of temperatures in the inner corona are addressed, as well as which assumptions and models are inherent in the temperatures derived using different observational techniques. Two examples of extreme ultraviolet (EUV) observations are chosen to demonstrate problems that can arise in the interpretation of measurements.

Esser, Ruth; Habbal, S. R.; Arndt, M. B.

1992-01-01

226

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.; Rybanský, M.; Dorotovi?, I.

2012-12-01

227

Double streamer phenomena in atmospheric pressure low frequency corona plasma  

SciTech Connect

Time-resolved images of an atmospheric pressure corona discharge, generated at 50 kHz in a single pin electrode source, show unique positive and negative corona discharge features: a streamer for the positive period and a glow for the negative period. However, unlike in previous reports of dc pulse and low frequency corona discharges, multistreamers were observed at the initial time stage of the positive corona. A possible physical mechanism for the multistreamers is suggested.

Kim, Dan Bee; Jung, H.; Gweon, B.; Choe, Wonho [Department of Physics, Korea Advanced Institute of Science and Technology, 335 Gwahangno, Yuseong-gu, Daejeon 305-701 (Korea, Republic of)

2010-07-15

228

Hot Plasma Flows in the Solar Corona  

NASA Astrophysics Data System (ADS)

The Solar Corona is a non-equilibrium open system. Energy and mass are supplied from the lower atmosphere and flow upwards through the corona into the interplanetary space. Steady state could be possible but not equilibrium state. Temperature of the corona varies depending on solar activities. However, even under very quite state, coronal temperature is still kept around million degrees. Coronal heating mechanisms have to work under such condition. Temperature of plasma is an averaged kinetic energy of random motion of particles. Motion of charged particles in magnetic field generates Lorenz force and particles gyrate around magnetic field lines. Gyration of charged particles generates magnetic moment which is directed anti-parallel to the surrounding magnetic field. This is the origin of diamagnetism of plasma. Each particle can be considered as a small magnet directed opposite to the surrounding magnetic field. When these magnets are put in inhomogeneous magnetic field, they are pushed toward weak field region. In case of open magnetic field region in the solar corona, plasma particles are pushed upwards. If this force (diamagnetic or mirror force) exceeds the gravity force, plasma flows upwards. Magnetic moment of each charged particle in thermal plasma is proportional to temperature and inversely proportional to magnetic field strength. The condition for plasma to flow upwards in an open magnetic field is that the scale length of the change of magnetic field strength is shorter than the hydrostatic scale length, which is determined by temperature and the gravity acceleration. This can be a mechanism to regulate the coronal temperature around million degree. The solar corona is filled with magnetic field, which is rooted at the photosphere in the form of flux tubes. Flux tubes connect directly the corona and the sub-photospheric layer where temperature is higher than the photosphere. Hot plasma, trapped in the flux tubes when they are generated around the bottom of the convection zone, will be pushed upwards through the flux tubes due to weakening of magnetic field strength upwards and are fed into the corona. This scenario can explain why the solar corona is kept around million degree independent of solar activity. This mechanism can be applied to explain 1) temperature dependent plasma upflows found in the solar atmosphere, 2) solar wind acceleration, 3) loop-top plasma concentration in post flare loops, and 4) various eruptive phenomena, including some of solar flares, caused by flows along curved magnetic field. The MHD equation does not include this force along the field.

Shibasaki, K.

2012-12-01

229

Device for generation of pulsed corona discharge  

DOEpatents

The invention is a method and system for the generation of high voltage, pulsed, periodic corona discharges capable of being used in the presence of conductive liquid droplets. The method and system can be used, for example, in different devices for cleaning of gaseous or liquid media using pulsed corona discharge. Specially designed electrodes and an inductor increase the efficiency of the system, permit the plasma chemical oxidation of detrimental impurities, and increase the range of stable discharge operations in the presence of droplets of water or other conductive liquids in the discharge chamber.

Gutsol, Alexander F. (San Ramon, CA); Fridman, Alexander (Marlton, NJ); Blank, Kenneth (Philadelphia, PA); Korobtsev, Sergey (Moscow, RU); Shiryaevsky, Valery (Moscow, RU); Medvedev, Dmitry (Moscow, RU)

2012-05-08

230

Heating of the corona by magnetic singularities  

NASA Technical Reports Server (NTRS)

Theoretical models of current-sheet formation and magnetic heating in the solar corona are examined analytically. The role of photospheric connectivity in determining the topology of the coronal magnetic field and its equilibrium properties is explored; nonequilibrium models of current-sheet formation (assuming an initially well connected field) are described; and particular attention is given to models with discontinuous connectivity, where magnetic singularities arise from smooth footpoint motions. It is shown that current sheets arise from connectivities in which the photospheric flux structure is complex, with three or more polarity regions and a magnetic null point within the corona.

Antiochos, Spiro K.

1990-01-01

231

Decay of electric charge on corona charged polyethylene  

Microsoft Academic Search

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.

Zhiqiang Xu; Linwen Zhang; George Chen

2007-01-01

232

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

233

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

234

The three-dimensional structure of the solar corona  

Microsoft Academic Search

Due to the rotation of the sun the solar corona can be observed under different directions at different times. Using methods of computer tomography the three-dimensional structure of the emissivity of the solar corona can be reconstructed. We discuss the feasibility of this method for stationary and for non-stationary corona and also for incomplete and finite resolution data. As example

S. Zidowitz; B. Inhester; A. Epple

1995-01-01

235

Unravelling the enigma of Perthes disease.  

PubMed

Perthes disease is an idiopathic avascular necrosis of a juvenile hip. Although 2010 marked a century since it was first described, the aetiology remains unknown. It is suggested that adverse socioeconomic circumstances may be a key precipitant. This work describes recent studies that explore the disease epidemiology. Descriptive studies include a case register from Merseyside, hospital discharge data from Scotland, analysis of the world's largest community disease register (General Practice Research Database [GPRD]) and a systematic review of incidence. Analytical studies include a nested case-controlled study in the GPRD and a hospital case-controlled study. The studies demonstrated a striking north-south divide in the UK incidence of Perthes disease, similar to that seen in many adult diseases. There was a sustained fall in disease frequency in all studies, with a narrowing of the north-south divide. There was a strong association with area deprivation, independent of living in an urban environment. Internationally, equatorial regions were unaffected by disease and northern Europe had the highest incidence, which was primarily a function of race although latitude was an independent predictor. Individual characteristics associated with the disease were congenital anomalies of the genitourinary tract and a structural abnormality of arterial calibre. Despite a falling incidence, Perthes disease remains an important cause of child morbidity and exemplifies socioeconomic inequalities. A deprivation-related exposure, acting early in development, appears critical. The aetiological factor in Perthes disease remains elusive but it is likely that unravelling this enigma may unlock additional secrets pertaining to the developmental origins of this and other diseases. PMID:23838491

Perry, D C

2013-07-01

236

Global Magnetohydrodynamic Modeling of the Solar Corona.  

National Technical Information Service (NTIS)

The coronal magnetic field defines the structure of the solar corona, the position of the heliospheric current sheet, the regions of fast and slow solar wind, and the most likely sites of coronal mass ejections. There are few measurements of the magnetic ...

J. A. Linker

1998-01-01

237

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

238

Differential rotation of the solar electron corona  

Microsoft Academic Search

Autocorrelation analyses of K-coronameter observations made at Haleakala and Mauna Loa, Hawaii, during 1964–1967 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

239

Topological Structure of the Magnetic Solar Corona  

Microsoft Academic Search

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

R. C. Maclean

2007-01-01

240

Patchy reconnection in the solar corona  

Microsoft Academic Search

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

Silvina Esther Guidoni

2011-01-01

241

The Magnetic Field of the Solar Corona  

Microsoft Academic Search

We propose a novel experiment to examine both the magnetic field and electron content of the solar corona. We intend to measure the Faraday rotation and dispersion evident in observations of background pulsar sources as they are occulted by the Sun. As we will be utilising a number of simultaneous lines of sight, that will cut different paths through the

Stephen Ord; Simon Johnston

2006-01-01

242

Protein Corona Significantly Reduces Active Targeting Yield  

PubMed Central

When nanoparticles (NPs) are exposed to the biological environment, their surfaces become covered with proteins and biomolecules (e.g. lipids). Here, we report that this protein coating, or corona, reduces the targeting capability of surface engineered NPs by screening the active sites of the targeting ligands.

Mirshafiee, Vahid; Mahmoudi, Morteza; Lou, Kaiyan; Cheng, Jianjun; Kraft, Mary L.

2013-01-01

243

The Minimum Flux Corona; Theory or Concept.  

National Technical Information Service (NTIS)

The reply to the criticisms of the minimum flux theory is discussed. These criticisms are correct in substance, as well as in detail. Counter arguments that the minimum flux corona theory is untenable, because of errors in its formulation, are presented.

J. H. Underwood S. K. Antiochos

1980-01-01

244

Methane conversion in pulsed corona discharge reactors  

Microsoft Academic Search

This work reports the effect of capacitance, cathode material, gas flow rate and specific energy input on methane conversion, energy efficiency and product selectivity in a co-axial cylinder pulsed corona discharge reactor. Ethane and acetylene appear to be formed from dimerization of CH3 radicals and CH radicals, respectively, while ethylene is formed mainly from the dehydrogenation of ethane. At a

Gui-Bing Zhao; Sanil John; Ji-Jun Zhang; Linna Wang; Suresh Muknahallipatna; Jerry C. Hamann; John F. Ackerman; Morris D. Argyle; Ovid A. Plumb

2006-01-01

245

Black hole accretion disks with coronae  

NASA Technical Reports Server (NTRS)

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, f, of the power released when the cold matter accretes is transported to and dissipated in the corona. This has major effects on the cold disk, making it colder, more geometrically thin, denser, and having larger optical depths. One important consequence is the disappearance of the effectively optically thin zone as well as of the radiation pressure dominated zone for values of f sufficiently closed to unity. The disappearance of the radiation pressure dominated zone will result in a cold disk with only a gas pressure dominated zone that is stable against thermal and viscous instabilities. We also show that the pressure ( and the radiation) from the corona will only affect the surface layers of the cold disk. Our results disagree with those of other recent work on accretion disks with coronae. We find those works to be based on unphysical assumptions.

Svensson, Roland; Zdziarski, Andrzej A.

1994-01-01

246

Corona discharge plasma reactor for decontamination  

Microsoft Academic Search

Summary form only given. The feasibility of using a gas phase corona plasma to sterilize objects from toxic battlefield, medical, and industrial environments was assessed. Plasma chemical processes can be highly effective in promoting oxidation, enhancing molecular dissociation, or producing free radicals to enhance chemical reaction. Until recently, plasma processes were applied in either the high temperature environment of arc

J. G. Birmingham; P. M. Irving

1998-01-01

247

Corona Discharge in Nuclear Excited Dusty Plasma  

SciTech Connect

We considered the possibility of using a corona discharge in a nuclear excited dusty plasma to provide the stability of well ordered dusty plasma structures from a fissionable material and to accomplish a more efficient conversion of nuclear energy into radiation.

Deputatova, L. V.; Fortov, V. E.; Filinov, V. S.; Vladimirov, V. I.; Meshakin, V. I.; Rykov, V. A. [Joint Institute for High Temperatures RAS, Izhorskaya str. 13, bd. 2, Moscow (Russian Federation); Sinkevich, O. A. [Moscow Power Engineering Institute (Technical University) Krasnokazarmennaya str. 14, Moscow (Russian Federation)

2011-11-29

248

Solar Corona Explorer: A mission for the physical diagnosis of the solar corona  

NASA Technical Reports Server (NTRS)

Mission objectives and spacecraft requirements for the Solar Corona Explorer (SCE), a proposed free flying, unmanned solar research craft to be tenatively launched in 1987, were defined. The SCE's purpose is to investigate structure, dynamics and evolution of the corona, globally and in the required physical detail, to study the close coupling between the inner corona and the heliosphere. Investigative objectives are: (1) to understand the corona as the source of varying interplanetary plasma and of varying solar X-ray and extreme ultraviolet fluxes; (2) to develop the capabilities to model the corona with sufficient precision to forecast the Earth's variable environment in space, on the scales from weeks to years; (3) to develop an understanding of the physical processes that determine the dynamics and physical state of the coronal plasma, particularly acceleration processes; and (4) to develop insight and test theory on the Sun applicable to stellar coronae and winds, and in particular, to understand why cool stars put such a large fraction of their energy into X-rays. Considered related factors are: (1) duration of the mission; (2) onboard measuring instrumentation; (3) ground support equipment and procedures; and (4) programs of interpretation and modeling.

1981-01-01

249

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

250

Corona of black holes accretion discs  

NASA Astrophysics Data System (ADS)

The idea that the observed features of the X-ray spectra of galactic black hole can be explained by the presence of a hot corona surrounding a cold accretion disc is not new. Since the end of 70's, when the first disc-corona models were proposed, such models have received much attention. Investigation of X-ray spectra of Active Galactic Nuclears also indicates that the hard X-ray radiation can come from hot regions located above the disk. In the model investigated in paper Galeev, Rosner, Vaiana, 1979, (subsequently referred to as GRV), the corona should by strictly inhomogeneous and heated by reconnecting magnetic loops emerging from the disk. The formation of the hot corona in the GRV model implies that a seed magnetic field is amplified due to processes analogous to a turbulent dynamo. As the magnetic flux tubes with strong magnetic field contain less plasma than their ambient surroundings, they are subject to buoyancy forces. The buoyant magnetic flux tubes emerge from the disk, forming a corona in which reconnection occurs faster than in the disk and providing a mechanism for plasma heating. This model from its appearance have received ample recognition of the astrophysicists and now it is widely used for the explanation of the observational data, However in spite of the new data which are not in agreement with this model the GRV model was not revised. It was found that in hard state the GRV mechanism is able to dissipate only a small fraction of the total energy released from the disk. Recent investigations of MHD turbulence in the accretion disk indicate the presence of the magnetorotational instability. This instability efficiently generates magnetic energy in the disk and helps to explain the rate of energy dissipation in the hard state. We revised the GRV model in the light of new experimental and theoretical results.

Galeev, A.; Sadovski, A.

251

Radio seismology of the outer solar corona  

NASA Astrophysics Data System (ADS)

Observed oscillations of coronal loops in extreme ultraviolet (EUV) lines have been successfully used to estimate plasma parameters in the inner corona (< 0.2R0, where R0 is the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because of rapid decrease in line intensity. We aim to use radio observations to estimate the plasma parameters of the outer solar corona (> 0.2R0). 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. 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 (MHD) 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 may trap the observed oscillations. Seismologically estimated Alfvén 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. 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. The research leading to these results has received funding from the Austrian 'Fonds zur Förderung der wissenschaftlichen Forschung' under project P24740-N27.

Zaqarashvili, Teimuraz; Melnik, Valentin; Brazhenko, Anatoliy; Panchenko, Mykhaylo; Konovalenko, Alexander; Dorovskyy, Vladimir; Rucker, Helmut

2014-05-01

252

Surface temperature profiles of the corona wire in a plate-wire type electrostatic precipitator  

Microsoft Academic Search

The corona wire surface temperature profiles in a plate-wire-type electrostatic precipitator have been measured by an IR thermal image technique and thermocouples under both DC positive and negative corona discharge conditions. The results show that: the corona wire surface temperature profiles under positive coronas are more uniform than those of the negative coronas, where the differences between maximum and minimum

T. OhkuboU; J. S. Chang; A. A. Berezin; Y. Nomoto; T. Adachi

1992-01-01

253

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

254

Structure and dynamics of the solar corona  

NASA Technical Reports Server (NTRS)

Advanced computational techniques were used to study solar coronal heating and coronal mass ejections. A three dimensional, time dependent resistive magnetohydrodynamic code was used to study the dynamic response of a model corona to continuous, slow, random magnetic footpoint displacements in the photosphere. Three dimensional numerical simulations of the response of the corona to simple smooth braiding flows in the photosphere were calculated to illustrate and understand the spontaneous formation of current filaments. Two dimensional steady state helmet streamer configurations were obtained by determining the time asymptotic state of the interaction of an initially one dimensinal transponic solar wind with a spherical potential dipole field. The disruption of the steady state helmet streamer configuration was studied as a response to shearing of the magnetic footpoints of the closed field lines under the helmet.

Schnack, D. D.

1994-01-01

255

Nanoflare Heating of Solar and Stellar Coronae  

NASA Technical Reports Server (NTRS)

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. Kanoflares 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 A.

2010-01-01

256

The puzzling hydrogen corona at Venus  

NASA Astrophysics Data System (ADS)

Although the existence of a hydrogen exosphere around Venus has been established already by the Mariner 5 flyby in 1967, the density and extension of the venusian hydrogen corona is still an open question. It is expected that the hydrogen population consists of a cold part in the lower exosphere and a hot part at higher altitudes. Although the hydrogen exosphere becomes most directly noticeable by means of Lyman-? observations, pick-up planetary hydrogen ions can also be detected through proton cyclotron waves. We present results of magnetic field observations aboard Venus Express, indicating permanent ionization and pick-up of hydrogen by the solar wind upstream of the planetary bow shock up to several planetary radii. In addition, the results of Monte Carlo simulations of the hot hydrogen corona at Venus are shown, suggesting lower neutral densities than those derived from magnetic field observations. The reason for this discrepancy is yet an open issue.

Lichtenegger, H.; Delva, M.; Gröller, H.; Bertucci, C.

2013-09-01

257

Heating the Solar Corona by Magnetic Reconnection  

NASA Astrophysics Data System (ADS)

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 x-ray bright points. Furthermore, it has been shown that the large-scale diffuse corona is heated rather uniformly, so that turbulent reconnection by braiding or ion-cyclotron waves driven by network micro-flares are prime candidates. Finally, reconnection is the natural explanation for a wide variety of phenomena discovered by SOHO including explosive events, blinkers, the magnetic carpet and even possibly tornadoes.

Priest, E. R.

1998-07-01

258

The quiescent corona and slow solar wind  

NASA Technical Reports Server (NTRS)

The observations of the ultraviolet coronagraph spectrometer (UVCS), operating onboard the Solar and Heliospheric Observatory (SOHO) spacecraft, are discussed. The purpose of the UVCS is the study of the quiescent coronal streamer and the slow solar wind. The observations started in January 1996. Polarized radiance data in the visible continuum were obtained. Some characteristics of the coronal streamer from the UVCS recorded data are discussed. A model for the source of the slow solar wind in the inner corona is proposed.

Noci, G.; Kohl, J. L.; Antonucci, E.; Tondello, G.; Huber, M. C. E.; Fineschi, S.; Gardner, L. D.; Korendyke, C. M.; Nicolosi, P.; Romoli, M.; Spadaro, D.; Maccari, L.; Raymond, J. C.; Siegmund, O. H. W.; Benna, C.; Ciaravella, A.; Giordano, S.; Michels, J.; Modigliani, A.; Naletto, G.

1997-01-01

259

EUV Corona in Solar Cycle 23  

Microsoft Academic Search

Extreme-Ultraviolet Telescope (EIT) on board SOHO provides us with unique data since 1996 up to the present time. The solar corona in Extreme-Ultraviolet emissions is visible on the solar disk and demonstrates a good relationship with the magnetic activity (SOHO\\/MDI and NSO\\/Kitt Peak data). We have analysed the EUV data from SOHO\\/EIT in four wavelengths (171A, 195A, 284A, and 304A),

Elena Benevolenskaya

2007-01-01

260

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

261

Ionization fronts in negative corona discharges.  

PubMed

We use a hydrodynamic minimal streamer model to study negative corona discharge. By reformulating the model in terms of a quantity called a shielding factor, we deduce laws for the evolution in time of both the radius and intensity of the ionization fronts. We also compute the evolution of the front thickness under the conditions for which it diffuses due to the geometry of the problem and show its self-similar character. PMID:15903643

Arrayás, Manuel; Fontelos, Marco A; Trueba, José L

2005-03-01

262

Dynamic Tomographic Imaging of the Solar Corona  

Microsoft Academic Search

Three-dimensional (3-D) maps of the electron density and temperature in the solar atmosphere can be tomographically reconstructed from two-dimensional images that are measured by a variety of ground-based and space-based instruments. The electron density and temperature of the solar corona are fundamental parameters for understanding the physical mechanisms that contribute to space weather, or physical phenomena that can, in extreme

Mark D. Butala; Farzad Kamalabadi; Richard A. Frazin; Yuguo Chen

2008-01-01

263

STOCHASTIC COUPLING OF SOLAR PHOTOSPHERE AND CORONA  

SciTech Connect

The observed solar activity is believed to be driven by the dissipation of nonpotential magnetic energy injected into the corona by dynamic processes in the photosphere. The enormous range of scales involved in the interaction makes it difficult to track down the photospheric origin of each coronal dissipation event, especially in the presence of complex magnetic topologies. In this paper, we propose an ensemble-based approach for testing the photosphere-corona coupling in a quiet solar region as represented by intermittent activity in Solar and Heliospheric Observatory Michelson Doppler Imager and Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager image sets. For properly adjusted detection thresholds corresponding to the same degree of intermittency in the photosphere and corona, the dynamics of the two solar regions is described by the same occurrence probability distributions of energy release events but significantly different geometric properties. We derive a set of scaling relations reconciling the two groups of results and enabling statistical description of coronal dynamics based on photospheric observations. Our analysis suggests that multiscale intermittent dissipation in the corona at spatial scales >3 Mm is controlled by turbulent photospheric convection. Complex topology of the photospheric network makes this coupling essentially nonlocal and non-deterministic. Our results are in an agreement with the Parker's coupling scenario in which random photospheric shuffling generates marginally stable magnetic discontinuities at the coronal level, but they are also consistent with an impulsive wave heating involving multiscale Alfvenic wave packets and/or magnetohydrodynamic turbulent cascade. A back-reaction on the photosphere due to coronal magnetic reconfiguration can be a contributing factor.

Uritsky, Vadim M.; Ofman, Leon [Catholic University of America at NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Davila, Joseph M. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Coyner, Aaron J., E-mail: vadim.uritsky@nasa.gov [University of Tulsa, Tulsa, OK 74104 (United States)

2013-05-20

264

Venus' Atla and Beta Regiones: Formation of Chasmata and Coronae  

NASA Astrophysics Data System (ADS)

Two likely areas of current tectonic and volcanic activity on Venus are Atla and Beta Regiones. Both are marked by pronounced topographic and geoid highs and each lies at the intersection of multiple rifts, i.e. the chasmata system. These regiones may be surface expressions of mantle upwellings. We examine the distribution, style, and attitude of coronae with respect to the two geoid highs. Coronae -- circular features unique to Venus -- could be caused by individual rising diapirs. Unlike Earth, Venus shows little evidence of horizontal motion, resulting in juxtaposition of coronae of all ages. Furthermore, there is little erosion to modify features. In our analysis, we use the three-tiered classification (based on the interior morphology) of 394 coronae, hence termed domal, circular, and calderic. These differing styles may reflect different stages in the evolution of a corona: from domal (youngest, possibly still active) features, progressing through increasing degrees of collapse to the calderic coronae. Comparing locations of these features shows the domal coronae average higher elevations, and calderic at lower elevations, with circular in between. Similar comparisons of other characteristics of the coronae, such as size, elongation, or dip, also show the progression from domal through calderic to circular. Both Atla and Beta are ringed by many coronae, but neither has coronae at or near their crests even within 20 m of their geoid highs. Coronae do occur in many rift segments, yet none occurs at or near these intersection points. Perhaps just as remarkable, Atla has a partial ring of four domal coronae, all within a 10-m geoid range of each other, whereas Beta has a partial ring of 6 or so calderic coronae between three and four 10-m contours from its crest. In both instances, the rings parallel geoid contour lines. These are the nearest coronae of their type to the crests. If corona formation is contemporaneous with the uplift process at Atla and Beta, and if the domal are younger than the calderic coronae, then Atla Regio is a recent feature and more active than Beta. This is in agreement with an independent assessment with modified craters. We use stratigraphy, crater modification, and relative tilt of craters and coronae to further test the timing of events implied in our model.

Stoddard, P. R.; Jurdy, D. M.

2004-12-01

265

Dyspraxia or developmental coordination disorder? Unravelling the enigma  

Microsoft Academic Search

Dyspraxia is an enigma to many people, both professional and lay alike—what 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

266

Unravelling Supply and Demand Factors in Work-Related Training  

Microsoft Academic Search

This paper attempts to unravel supply and demand factors of work-related training by exploiting information from workers who wanted to receive such training but did not get it. Worker's willingness to receive training varies with their level of education, background characteristics, and job characteristics. Firms' gains from training vary across industries and with worker's gender and age. Half of the

Hessel Oosterbeek

1998-01-01

267

Alternating Current Corona in Foul Weather II - Below Freezing Point  

Microsoft Academic Search

The mechanism of ac corona caused by the presence of ice particles is shown. Two kinds of precipitation are distinguished: the snow-like and hail-like forms. Conditions of snowcover formation on transmission-line conductors are analyzed. This cover may result in the highest corona energy losses, caused mainly by steady pulseless corona in the positive, and Trichel impulses in the negative, half-cycle.

L. Boulet; L. Cahill; B. J. Jakubczyk

1966-01-01

268

The three-dimensional structure of the solar corona  

NASA Technical Reports Server (NTRS)

Due to the rotation of the sun the solar corona can be observed under different directions at different times. Using methods of computer tomography the three-dimensional structure of the emissivity of the solar corona can be reconstructed. We discuss the feasibility of this method for stationary and for non-stationary corona and also for incomplete and finite resolution data. As example we present reconstructions based on YOHKOH-images, and we compare the results with ground-based optical corona observations. Structures are interpreted in terms of the solar magnetic field topology.

Zidowitz, S.; Inhester, B.; Epple, A.

1995-01-01

269

High Voltage DC Bipolar Corona via Particle-In - Simulation  

NASA Astrophysics Data System (ADS)

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 dissertation, the high voltage dc (HVdc) bipolar corona problem was studied with a two -dimensional particle-in-cell simulation, which allowed us to model the time dependent nonlinear behavior and microscopic phenomena involved in the corona discharge (impact ionization, attachment, mobility, conduction current, displacement current, etc.). The technique follows simulation particles that represent electrons, positive ions, and negative ions, and self-consistently calculates the associated electric field that determines the particle motion. Finite element and charge simulation methods were used to solve Poisson's equation while a finite difference scheme was applied to move simulation particles. Multi-scale techniques (nonuniform triangle mesh and variable time step) were employed to reduce numerical noise and increase simulation efficiency. The particle-in-cell simulation was successfully applied to a cylindrical bipolar corona cage problem. Simulation results included one primitive streamer, multi-electrode induced currents, conductor temperature effects, memory effects, approach to a stationary state, corona saturation on a transient basis, and electric parameters that characterize the dc corona environment (electric field intensity, ion current density, space charge density). Characteristics of the corona current were also obtained through measurements in the laboratory corona cage. Digitizing oscilloscopes have been used to view the anode and cathode corona current at +/- 60kV and +/- 64kV. Cathode current appeared as a nearly quiescent dc current with electron current pulses located at time intervals on the order of 15mu s. Anode current also appeared as a nearly quiescent dc current with electron current pulses located at time intervals on the order of 800mu s. Anode pulses were observed to be about 30 times larger than cathode pulses. Both the laboratory experiment and the particle-in-cell simulation were used to study the influence of load current on corona.

Qin, Bai-Lin

270

The solar extreme ultra-violet corona: Resolved loops and the unresolved active region corona  

NASA Astrophysics Data System (ADS)

In this work, physical characteristics of the solar corona as observed in the Extreme Ultra-Violet (EUV) regime are investigated. The focus will be the regions of intense EUV radiation generally found near the locations of sunspots. These regions are commonly called active regions. Multiple space- based observing platforms have been deployed in the last decade; it is possible to use several of these observatories in combination to develop a more complete picture of the solar corona. Joint Observing Program 146 was created to collect spectroscopic intensities using the Coronal Diagnostic Spectrometer on Solar and Heliospheric Observatory and EUV images using NASA's Transition Region and Coronal Explorer. The emission line intensities are analyzed to develop an understanding of the temperature and density of the active region coronal plasma. However, the performance of the CDS instrument in the spatial and temporal domains is limited and to compensate for these limitations, data collected by the TRACE instrument provide a high spatial and temporal resolution set of observations. One of the most exciting unsolved problems in solar astrophysics is to understand why the corona maintains a temperature roughly two orders of magnitude higher than the underlying material. A detailed investigation of the coronal emission has provided constraints on models of the heating mechanism, since the temperature, density and evolution of emission rates for multiple ionic species are indicative of the mechanism(s) working to heat the corona. The corona appears to consist of multiple unresolved structures as well as resolved active region structures, called coronal loops. The purpose of the present work is to determine the characteristics of the unresolved background corona. Using the characterizations of the coronal unresolved background, results for loops after background subtraction are also presented. This work demonstrates the magnitude of the unresolved coronal emission with respect to the total emission along the line of sight, and the relationship of the coronal background emission to the resolved loop emission. It is apparent from this analysis that the unresolved corona is the dominant source of radiation in active regions. Additionally, the unresolved active region coronal emission can be characterized by hydrostatic scaling laws.

Cirtain, Jonathan Wesley

271

Relationship of coronae, regional plains and rift zones on Venus  

NASA Astrophysics Data System (ADS)

Coronae and rifts are the most prominent volcano-tectonic features on the surface of Venus. Coronae are large radial-concentric structures with diameters of 100 to over 1000 km. They have varied topographical shapes, radial and concentric fracturing and compressional tectonic structures are common for their annuli. Massive volcanism is also connected with some of the structures. Coronae are interpreted to be the result of updoming and fracturing on the surface due to interaction of mantle diapirs with the lithosphere and its subsequent gravitational relaxation. According to Stofan et al. (2001), two types of coronae are observed: type 1 - coronae that have annuli of concentric ridges and/or fractures (407 structures), and type 2 that have similar characteristics to type 1 but lack a complete annulus of ridges and fractures (107 structures). We analyzed 20% of this coronae population (we chose each fifth structure from the Stofan et al. (2001) catalog; 82 coronae of type 1 and 22 coronae of type 2, in total 104 coronae) for the (1) spatial distribution of rift structures and time relationship of rift zones activity with time of regional volcanic plains emplacement, and (2) tectonics, volcanism, age relative to regional plains and relationship with rifts. Two different age groups of rifts on Venus were mapped at the scale 1:50 000 000: old rifts that predate and young rifts that postdate regional plains. Most of young rifts inherit strikes of old rifts and old rifts are reworked by them. This may be evidence of rift-produced uplift zones that were probably mostly stable during both types of rifts formation. Evolution of distribution of rift systems with time (decreasing of distribution and localization of rift zones) imply thickening of the lithosphere with time. Coronae-producing mantle diapirism and uplift of mantle material in rift zones are not well correlated at least in time in most cases, because majority of coronae (77%) of both types has no genetic association with rifts. Majority of coronae (72%) were mostly active before regional plains formation, and only 3% appear to have begun to form after the plains emplacement, which may be also due to thickening of the lithosphere. According to the relationship with regional plains type 2 coronae are in general older than type 1 coronae. Three types of corona-related volcanic activity were observed: shield volcanoes and their clusters, as well as extensive lobate lava flows and smooth volcanic plains. Shield volcanoes during coronae evolution were mostly active before regional plains emplacement. Most active phase of volcanism of corona may not coincide with the time of the major tectonic activity of corona, as majority of coronae (77%) were most active before regional plains formation, but almost half of all coronae have traces of post regional plains volcanism. Detailed mapping and stratigraphic analysis of seven regions with 34 examples of coronae showed a similarity in the sequence of regional geologic units.

Krassilnikov, A. S.; Kostama, V.-P.; Aittola, M.; Guseva, E. N.; Cherkashina, O. S.

2012-08-01

272

Observational Study of the Tridimensional Trajectory of Small White-Light Transients in the Inner Solar Corona  

NASA Astrophysics Data System (ADS)

The physical mechanisms responsible for the low corona origin and subsequent interplanetary development of the small scale white-light transients, known as blobs, is relevant to the formation and acceleration mechanisms of the slow solar wind (Sheeley et al., 1997). Since they are considered to be reliable tracers of the slow solar wind, a statistical kinematical characterization of these faint features should provide to the understanding of its origins and acceleration. The vantage observing points provided by the SECCHI and LASCO imagers aboard the STEREO and SOHO missions, respectively, allows us to get a good estimation of their trajectory in the 3D space and hence perform a detailed analysis of their unprojected kinematical parameters. To address this issue, we have surveyed the SOHO/LASCO C2 and C3, and the STEREO/SECCHI COR 1 and COR 2 databases for the year 2007 through 2010 (i.e., a period comprising the declining phase of the extended past solar minimum and the ascending phase of cycle 24) and selected about 100 blob-like features. The selection of events was facilitated by the scarce presence of coronal mass ejection events during this period, and it was limited to ±30° from the Sun's equator. The restricted latitudinal range is inspired by the work of Wang et al. (1998), who proposed that blobs are liberated from the cusp of helmet steamers. Two methods have been considered for the determination of the 3D kinematical parameters: (1) the tie-pointing and triangulation technique (Thompson W.T., 2008) and (2) the Height-Time analysis as developed by Mierla et al. (2008). In this work, we report on the set of transients studied by both techniques, discuss the limitations encountered on the determination of the 3D trajectories, and explore their significance on understanding the physical mechanisms behind the generation/propagation of the slow solar wind.

Lopez-Portela, C.; Blanco-Cano, X.; Stenborg, G.; Vourlidas, A.

2013-05-01

273

Validation of Spherically Symmetric Inversion by Use of a Tomographic Reconstructed Three-Dimensional Electron Density of the Solar Corona  

NASA Astrophysics Data System (ADS)

Determination of the coronal electron density by the inversion of white-light polarized brightness (pB) measurements by coronagraphs is a classic problem in solar physics. An inversion technique based on the spherically symmetric geometry (Spherically Symmetric Inversion, SSI) was developed in the 1950s, and has been widely applied to interpret various observations. In this study we present the detailed assessment of this method using a model in terms of three-dimensional (3D) electron density in the corona from 1.5 to 4 solar radii reconstructed by tomography method from STEREO/COR1 observations. We first show in theory and observation that the spherically symmetric polynomial approximation (SSPA) method and the Van de Hulst inversion technique are equivalent. Then we assess the SSPA method using synthesized pB images from the 3D density model, and find that the SSPA density values for edge-on streamers are very close to the model inputs in the plane of sky with differences generally less than a factor of two or so; the SSPA density has the lower peak but more spread in latitudinal direction than in the model. Our results confirm the previous suggestion that the SSI method is very suitable to streamers in the solar minimum. In addition, we demonstrate that the SSPA method can be used to reconstruct the 3D coronal density, roughly in agreement with that by tomography in a period of low solar activity. We suggest that the SSI method is complementary to the 3D tomographic technique in some cases, given that the development of the latter is still an ongoing research effort.

Wang, Tongjiang; Kramar, Maxim; Davila, Joseph M.

2014-06-01

274

Rings Around the Sun and Moon: Coronae and Diffraction  

ERIC Educational Resources Information Center

Atmospheric optical effects can teach much about physics and especially optics. Coronae--coloured rings around the sun or moon--are large-scale consequences of diffraction, which is often thought of as only a small effect confined to the laboratory. We describe coronae, how they are formed and experiments that can be conducted on ones in the sky.…

Cowley, Les; Laven, Philip; Vollmer, Michael

2005-01-01

275

Introduction: The High-energy Corona – Waves, Eruptions, Particles  

Microsoft Academic Search

Flares and coronal mass ejections (CME) are the most violent manifestations of solar activity. They are the consequence of the explosive conversion of energy stored in coronal magnetic fields into plasma heating, the kinetic energy of supra-thermal to high energy particles and the mechanical energy of magnetic structures that are propelled through the corona and into interplanetary space. The corona

Karl-Ludwig Klein; Alexander MacKinnon

2007-01-01

276

Thermal Degradation In Composite Insulation Due To Corona Discharges  

Microsoft Academic Search

Composite insulators on overhead lines are frequently subjected to corona discharges due to increased electric field intensities under various conditions. These discharges can cause localized heating on the surface and affect the hydrophobicity of the insulator. A study has been undertaken to quantify and evaluate the thermal degradation that composite insulation is subjected to from corona discharges. This has been

Pradeep Varma Sangaraju Venkateshwara

2010-01-01

277

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

278

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

279

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

280

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

281

RADIO OBSERVATIONS OF THE SOLAR CORONA DURING AN ECLIPSE  

SciTech Connect

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 ({approx}15'') in the corona from where the observed radiation originated.

Kathiravan, C.; Ramesh, R.; Barve, Indrajit V.; Rajalingam, M., E-mail: kathir@iiap.res.in, E-mail: ramesh@iiap.res.in, E-mail: indrajit@iiap.res.in, E-mail: rajalingam@iiap.res.in [Indian Institute of Astrophysics, Bangalore 560 034 (India)

2011-04-01

282

Aspects of nonlinear magnetohydrodynamics in the solar corona  

Microsoft Academic Search

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

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

2004-01-01

283

Subtelescopic Inhomogeneities of Electron Density in the Solar Corona  

Microsoft Academic Search

The brightness of the solar corona due to Thomson scattering depends linearly on the electron density, while the brightness due to the Balmer continuum is proportional to its square. As a consequence, information on the distribution of the electron density in the corona can be obtained by comparing the radial profiles of the surface brightness in both continua. This idea

L. N. Kurochka; O. T. Matsuura; E. Picazzio

1997-01-01

284

Investigating The Solar Corona With Radio Observations Of Pulsars  

Microsoft Academic Search

We propose to examine both the magnetic field and electron content of the solar corona via measurement of the Faraday rotation and dispersion evident in observations of background pulsar sources as they are occulted by the Sun. As we will be utilise a number of simultaneous lines of sight, that will cut different paths through the corona as the Sun

S. Ord

2006-01-01

285

Spitzer's View of the Corona Australis Molecular Cloud  

Microsoft Academic Search

We present preliminary results from a Spitzer study of the Corona Australis molecular cloud region. Corona Australis (CrA) has been observed with IRAC and MIPS as part of the IRAC GTO program and the GO Gould Belt Legacy survey. Relatively nearby at approximately 150 pc, CrA is known to be actively forming stars, particularly within its embedded association, the Coronet.

Dawn E. Peterson; Spitzer IRAC GTO; Gould Belt Legacy Teams

2007-01-01

286

Pulsed power corona discharges for air pollution control  

Microsoft Academic Search

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

Erwin H. W. M. Smulders; Bert E. J. M. van Heesch; Sander S. V. B. van Paasen

1998-01-01

287

Possible lithospheric plate movement on Inverness Corona, Miranda  

Microsoft Academic Search

Miranda is a small icy satellite of Uranus. Two main different types of terrain are usually distinguished in its surface: ancient cratered plains and three endogenically resurfaced areas called coronae. Inverness Corona is located close to the South Pole. It is trapezoidal in shape, and displays an inner, rectangular, dark region, adjacent to a bright chevron-shaped area (the \\

Á. González

2003-01-01

288

Oxidative coupling of methane with ac and dc corona discharges  

Microsoft Academic Search

The oxidative coupling of methane (OCM) is being actively studied for the production of higher hydrocarbons from natural gas. The present study concentrated on the oxidative conversion of methane in an atmospheric pressure, nonthermal plasma formed by ac or dc corona discharges. Methyl radicals are formed by reaction with negatively-charged oxygen species created in the corona discharge. The selectivity to

Changjun Liu; Abdulathim Marafee; Bobby Hill; Genhui Xu; Richard Mallinson; Lance Lobban

1996-01-01

289

CORONAS-F satellite: Tasks for study of particle acceleration  

Microsoft Academic Search

A low altitude satellite with polar orbit, namely CORONAS-F has been launched on July 31, 2001. We briefly list the possibilities of a complex instrument SKL, and on the basis of similar measurements by CORONAS-I we illustrate the possible tasks for magnetospheric studies. Such orbit allows to sample with relatively high time resolution the projection series of various magnetospheric regions

S. N. Kuznetsov; K. Kudela; S. P. Ryumin; Y. V. Gotselyuk

2002-01-01

290

Development of ac corona discharge modes at atmospheric pressure  

SciTech Connect

Corona discharges in gases exist under several distinctive forms. In this paper, a survey study has been made of ac corona discharge modes generated in some different gases fed in a wire-duct reactor with a constant rate of flowing at atmospheric pressure. The properties of different corona modes are analyzed under some condition transitions from Trichel pulses to a steady glow. In the course of the presented experimental work, numerous apparent contradictions with earlier observations necessitated further study and are given to provide more information on the physical mechanisms of the ac corona discharges. Furthermore, we have gained insight into some new technologies and applications of the environmentally friendly corona and plasma discharges.

El-Koramy, Reda Ahmed; Yehia, Ashraf; Omer, Mohamed [Department of Physics, Faculty of Science, Assiut University, 71516 Assiut (Egypt)

2011-02-15

291

Isothermal, Compton-heated coronae above accretion disks  

NASA Technical Reports Server (NTRS)

The structure of Compton-heated coronae above accretion disks is studied here by using analytic and numerical approaches are used here to determine the direct and scattered radiation reaching the base of the corona for a range of central source luminosities. It is found that the outer region of the corona is unaffected by multiple scattering in the interior, provided that the luminosity of the central source is sufficient below the Eddington limit. How attenuation and scattering by the corona affects the strength of chromospheric emission lines is determined, as is the condition for which the irradiation due to the central source exceeds the locally generated flux from the disk. Finally, it is shown that the stability analysis for irradiated accretion disks of Tuchman et al. is not substantially altered by the corona.

Ostriker, Eve C.; Mckee, Christopher F.; Klein, Richard I.

1991-01-01

292

Flexural ridges, trenches, and outer rises around coronae on Venus  

NASA Technical Reports Server (NTRS)

Flexural signatures outboard of Venusian coronal rims are examined with the purpose of inferring the thickness of the planet's elastic lithosphere. Topographic profiles of several prominent coronae which display clear trench and outer rise signatures are presented. Via a thin elastic plate flexure model to characterize the shape of the trench and outer rise, Venusian flexures are found to be similar in both amplitude and wavelength to lithospheric flexures seaward of subduction zones on earth. It is shown that circumferential fractures are concentrated in areas where the topography is curved downward, in good agreement with the high tensile stress predicted by the flexure models. Two scenarios for the development of the ridge-trench-outer rise flexural topography and circumferential fractures of coronae are presented. The first scenario involves reheating and thermal subsidence of the lithosphere interior to the corona, while the second involves expansion of the corona interior and roll back of the subducting lithosphere exterior to the corona.

Sandwell, David T.; Schubert, Gerald

1992-01-01

293

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, Jörg; Musyanovych, Anna; Fetz, Verena; Hecht, Rouven; Schlenk, Florian; Fischer, Dagmar; Kiouptsi, Klytaimnistra; Reinhardt, Christoph; Landfester, Katharina; Schild, Hansjörg; Maskos, Michael; Knauer, Shirley K.; Stauber, Roland H.

2013-10-01

294

On the SORS project of CORONAS I and F  

NASA Astrophysics Data System (ADS)

The scientific experiment SOLAR RADIO SPECTROMETER (abbreviated: SORS) of the CORONAS-I satellite project is described and prospects to the planned mission of CORONAS-F are given. The astrophysical goal of these experiments is the investigation of solar radio emission in a wide frequency band detecting low-frequency solar flare emission outside the terrestrial radio window and its physical interpretation. The principal capacity of SORS could be demonstrated by observation of dynamic spectra of type III bursts during a relatively short operational period aboard CORONAS-I restricted by low solar activity. Using the experience of CORONAS-I it can be anticipated that a new SORS instrument on CORONAS-F will deliver a broader material for the exploration of coronal and heliospheric plasma processes.

Fomichev, V. V.; Oraevsky, V. N.; Pulinets, S. A.; Prutensky, I. S.; Gorgutsa, R. V.; Klos, Z.; Kiraga, A.; Rothkaehl, H.; Kruger, A.; Hildebrandt, J.; Aurass, H.; Klassen, A.; Mann, G.; Kliem, B.; Estel, C.

295

On the SORS project of CORONAS I and F  

NASA Astrophysics Data System (ADS)

The scientific experiment SOLAR RADIO SPECTROMETER (abbreviated: SORS) of the CORONAS-I satellite project is described and prospects to the planned mission of CORONAS-F are given. The astrophysical goal of these experiments is the investigation of solar radio emission in a wide frequency band detecting low-frequency solar flare emission outside the terrestrial radio window. The principal capacity of SORS could be demonstrated by observation of dynamic spectra of type III bursts during a relatively short operational period aboard CORONAS-I restricted by low solar activity. Using the experience of CORONAS-I it can be anticipated that a new SORS equipment on CORONAS-F will deliver a broader material for the exploration of coronal and heliospheric plasma processes.

Fomichev, V. V.; Oraevsky, V. N.; Kruger, A.

296

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

297

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

298

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

299

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

300

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 moiré 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

301

The TESIS experiment on the CORONAS-PHOTON spacecraft  

NASA Astrophysics Data System (ADS)

On February 26, 2009, the first data was obtained in the TESIS experiment on the research of the solar corona using imaging spectroscopy. The TESIS is a part of the scientific equipment of the CORONAS-PHO-TON spacecraft and is designed for imaging the solar corona in soft X-ray and extreme ultraviolet regions of the spectrum with high spatial, spectral, and temporal resolutions at altitudes from the transition region to three solar radii. The article describes the main characteristics of the instrumentation, management features, and operation modes.

Kuzin, S. V.; Zhitnik, I. A.; Shestov, S. V.; Bogachev, S. A.; Bugaenko, O. I.; Ignat'ev, A. P.; Pertsov, A. A.; Ulyanov, A. S.; Reva, A. A.; Slemzin, V. A.; Sukhodrev, N. K.; Ivanov, Yu. S.; Goncharov, L. A.; Mitrofanov, A. V.; Popov, S. G.; Shergina, T. A.; Solov'ev, V. A.; Oparin, S. N.; Zykov, A. M.

2011-04-01

302

Formation of Coronae Structures on Venus by Thermochemical Diapirs  

NASA Astrophysics Data System (ADS)

One of the most prominent features on the surface of Venus are the coronae. They are large scale volcano-tectonic structures, which are approximately circular with a mean diameter of 200 - 300 km [Dombard et al., 2007], with extrema ranging from 60 km to about 2000 km diameter. A total of 515 coronae were found on Venus in the Magellan data [Stofan et al., 2001]. The intruiging point about corona is that there is no counterpart on the other terrestrial planets for these structures. Nine different groups of coronae have been observed on Venus [Smrekar and Stofan, 1997]. Smrekar and Stofan [1997] suggested that these different groups can stand for different steps in the time evolution of coronae. Several mechanisms have been proposed to explain their formation: Dombard et al. [2007] suggested that coronae form in response to magmatic loading of the crust over zones of partial melting above thermally buoyant heads of transient mantle plumes that impinge on the base of the thermal lithosphere. On the other side, the potential importance of crust delamination induced by mantle upwellings as formation mechanisms for coronae was pointed out by Smrekar and Stofan [1997]. Here, we present results on coronae formation using the recently developed 2D finite element code MILAMIN_VEP, which employs MILAMIN technology [Dabrowski et al., 2008]. We apply a temperature and stress-dependent visco-elasto-plastic rheology in a rectangular box, which includes a rising thermochemical diapir beneath the Venusian crust and lithosphere. The rheological parameters are taken from results inferred for Venusian materials [Mackwell et al., 1998]. A free surface is used in our calculations, which allows for the self-consistent computation of topography induced by the buoyant diapir. A hybrid particle-in-cell approach allows remeshing of strongly deformed grid cells. A systematic investigation of the physical conditions under which coronae can form is being performed in 2D. Initial results confirm the delamination hypothesis due to the impinging thermo-chemical diapir. The flattening of the diapir allows for the formation of coronae with radii several times larger than the initial diapir radii. Our calculations strengthen the hypothesis that coronae pass several stages of topographical appearance. They however also indicate that the formation of coronae might happen on much shorter timescales than suggested by previous studies.

Golabek, G. J.; Kaus, B. J. P.; Tackley, P. J.

2009-04-01

303

Corona-discharge-initiated mine explosions  

SciTech Connect

Strong circumstantial evidence suggests that lightning has initiated methane explosions in abandoned and sealed areas of underground coal mines. The Mine Safety and Health Administration (MSHA) investigated several of these occurrences within recent years. The investigated explosions occurred at significant depths, ranging from 700 to 1200 ft. Data from the National Lightning Detection Network indicated a strong correlation between the times and locations of the explosions with those of specific lightning strikes. This paper proposes that corona discharge from a steel borehole casing is the most likely mechanism responsible for these ignitions. A recently investigated mine explosion and fire at a depth greater than 1000 ft was selected for this study. Computer simulations were performed, using data collected at the mine site. CDEGS software from Safe Engineering Services & Technologies, Ltd. and MaxwellSV from Ansoft Corporation were used for the simulations.

Sacks, H.K.; Novak, T. [Virginia Polytechnic Institute & State University, Blacksburg, VA (United States). Dept. of Mining & Minerals Engineering

2005-10-01

304

Magnetohydrodynamic vortices in the solar corona  

NASA Astrophysics Data System (ADS)

Interaction of coronal mass ejections with the plasma of the solar corona is accompanied with the generation of sharp shear flows that cause the induction of Alfvenic vortices. Numerical simulations revealed that for a broad range of parameters, the vortices are essentially compressible, with the perturbations of the density and the absolute value of the magnetic field in the vortex arms reaching 50% of the background density. The typical size of the vortex is about the size of the obstacle. The frequency of the vortex shedding is controlled by a dimensionless parameter known as the Strouhal number. We found that in collisionless low-beta plasma this number is about 0.2. Recent imaging observations with SDO/AIA revealed the generation of Alfvenic vortices at the flanks of emerging plasmoids. The vortices introduce a frictionless aerodynamic drag force, applied to the interacting plasmas. Implication of these findings for the excitation of kink oscillations of coronal loops and CME kinematics is discussed.

Nakariakov, Valery

2012-07-01

305

Solar wind acceleration in the solar corona  

NASA Technical Reports Server (NTRS)

The intensity ratio of the O VI doublet in the extended area is analyzed. The O VI intensity data were obtained with the ultraviolet coronagraph spectrometer (UVCS) during the SOHO campaign 'whole sun month'. The long term observations above the north pole of the sun were used for the polar coronal data. Using these measurements, the solar wind outflow velocity in the extended corona was determined. The 100 km/s level is running along the streamer borders. The acceleration of the solar wind is found to be high in regions between streamers. In the central part of streamers, the outflow velocity of the coronal plasma remains below 100 km/s at least within 3.8 solar radii. The regions at the north and south poles, characterized by a more rapid acceleration of the solar wind, correspond to regions where the UVCS observes enhanced O VI line broadenings.

Giordano, S.; Antonucci, E.; Benna, C.; Kohl, J. L.; Noci, G.; Michels, J.; Fineschi, S.

1997-01-01

306

The X-ray corona of Procyon  

NASA Technical Reports Server (NTRS)

X-ray emission from the nearby system Procyon A/B (F5 IV + DF) was detected, using the IPC (Imaging Proportional Counter) on board the Einstein Observatory. Analysis of the X-ray pulse height spectrum suggests that the observed X-ray emission originates in Procyon A rather than in the white dwarf companion Procyon B, since the derived X-ray temperature, log T = 6.2, agrees well with temperatures found for quiescent solar X-ray emission. Modeling Procyon's corona with loops characterized by some apex temperature Tmax and emission length scale L, it is found that Tmax is well constrained, but L, and consequently the filling factor of the X-ray emitting gas, are essentially unconstrained even when EUV emission from the transition region is included in the analysis.

Schmitt, J. H. M. M.; Harnden, F. R., Jr.; Rosner, R.; Peres, G.; Serio, S.

1985-01-01

307

Untwisting magnetic fields in the solar corona  

NASA Astrophysics Data System (ADS)

The solar corona is the tenuous atmosphere of the Sun characterized by a temperature of the order of million degrees Kelvin, an ambient magnetic field of 10 to 15 Gauss and a very high magnetic Reynolds number because of which it qualifies as a near-ideal magnetofluid system. It is well known that for such a system, the magnetic flux across every fluid surface remains effectively constant to a good approximation. Under this so called ``frozen-in'' condition then, it is possible to partition this magnetofluid into contiguous magnetic subvolumes each entrapping its own subsystem of magnetic flux. Thin magnetic flux tubes are an elementary example of such magnetic subvolumes evolving in time with no exchange of fluid among them. The internal twists and interweaving of these flux tubes, collectively referred as the magnetic topology, remains conserved under the frozen-in condition. Because of the dynamical evolution of the magnetofluid, two such subvolumes can come into direct contact with each other by expelling a third interstitial subvolume. In this process, the magnetic field may become discontinuous across the surface of contact by forming a current sheet there. Because of the small spatial scales generated by steepening of magnetic field gradient, the otherwise negligible resistivity becomes dominant and allows for reconnection of field lines which converts magnetic energy into heat. This phenomenon of spontaneous current sheet formation and its subsequent resistive decay is believed to be a possible mechanism for heating the solar corona to its million degree Kelvin temperature. In this work the dynamics of spontaneous current sheet formation is explored through numerical simulations and the results are presented.

Bhattacharyya, Ramit; Smolarkiewicz, Piotr; Chye Low, Boon

2012-07-01

308

Ionization and Corona Discharges from Stressed Rocks  

NASA Astrophysics Data System (ADS)

Pre-earthquake signals have long been observed and documented, though they have not been adequately explained scientifically. These signals include air ionization, occasional flashes of light from the ground, radio frequency emissions, and effects on the ionosphere that occur hours or even days before large earthquakes. The theory that rocks function as p-type semiconductors when deviatoric stresses are applied offers a mechanism for this group of earthquake precursors. When an igneous or high-grade metamorphic rock is subjected to deviatoric stresses, peroxy bonds that exist in the rock's minerals as point defects dissociate, releasing positive hole charge carriers. The positive holes travel by phonon-assisted electron hopping from the stressed into and through the unstressed rock volume and build up a positive surface charge. At sufficiently large electric fields, especially along edges and sharp points of the rock, air molecules become field-ionized, loosing an electron to the rock surface and turning into airborne positive ions. This in turn can lead to corona discharges, which manifest themselves by flashes of light and radio frequency emissions. We applied concentrated stresses to one end of a block of gabbro, 30 x 15 x 10 cm3, inside a shielded Faraday cage and observed positive ion currents through an air gap about 25 cm from the place where the stresses were applied, punctuated by short bursts, accompanied by flashes of light and radio frequency emissions characteristic of a corona discharge. These observations may serve to explain a range of pre-earthquake signals, in particular changes in air conductivity, luminous phenomena, radio frequency noise, and ionospheric perturbations.

Winnick, M. J.; Kulahci, I.; Cyr, G.; Tregloan-Reed, J.; Freund, F. T.

2008-12-01

309

Measurement and Modeling of Low-Frequency Current From Hybrid AC\\/DC Corona  

Microsoft Academic Search

This paper aims at investigating the mechanism of hybrid ac\\/dc corona which is usually accompanied with the hybrid HVAC\\/HVDC power transmission lines. A coaxial wire-cylinder corona cage is designed in this paper, and the combined ac\\/dc voltage is applied to the wire and cage. The low-frequency component of corona current from the hybrid ac\\/dc corona in this corona cage with

Xiangxian Zhou; Xiang Cui; Tiebing Lu; Yang Liu; Xuebao Li; Chao Fang

2012-01-01

310

Unraveling phosphodiesterase surfaces. Identification of phosphodiesterase 7 allosteric modulation cavities.  

PubMed

The last findings of our group by using chemical genetic approaches have shown that PDE7 is an interesting target in neurodegenerative diseases. The following step in this travel to unravel PDE7 is the design of more selective inhibitors. In this sense we have proposed to perform an analysis of PDE7 surface to identify possible allosteric sites following by a docking study of different PDE7 inhibitors synthesized by our group. Thanks to these studies we have proved the existence of allosteric sites in PDE7 and we have been able to explain the binding modes of the employed PDE7 inhibitors. PMID:24239625

Redondo, Miriam; Soteras, Ignacio; Brea, José; González-García, Alejandro; Cadavid, María Isabel; Loza, María Isabel; Martinez, Ana; Gil, Carmen; Campillo, Nuria E

2013-12-01

311

Study of the solar corona using radio and space observations  

NASA Technical Reports Server (NTRS)

The physics of coronal transients, the characteristics of radiation and accelerated particles at the time of flares, and the density/temperature structure of the transition region and corona and the coronal magnetic field are investigated.

Dulk, G. A.

1984-01-01

312

The X-ray corona and the photospheric magnetic field.  

NASA Technical Reports Server (NTRS)

Soft X-ray photographs of the solar corona have been obtained on four flights of a rocket-borne grazing incidence telescope having a resolution of a few arc sec. The configuration of the X-ray emitting structures in the corona has been compared to the magnetic field distribution measured by photospheric longitudinal magnetograms. The X-ray structures trace the three-dimensional configuration of the magnetic field through the lower corona. Active regions in the corona take the form of tubular structures connecting regions of opposite magnetic polarity within the same or adjacent chromospheric active regions. Higher, larger structures link widely separated active regions into complexes of activity covering substantial fractions of the disk. The complexes are separated by areas of low average field in the photosphere. Interconnections across the solar equator appear to originate over areas of preceding polarity.

Krieger, A. S.; Vaiana, G. S.; Van Speybroeck, L. P.

1971-01-01

313

The origins of hot plasma in the solar corona.  

PubMed

The Sun's outer atmosphere, or corona, is heated to millions of degrees, considerably hotter than its surface or photosphere. Explanations for this enigma typically invoke the deposition in the corona of nonthermal energy generated by magnetoconvection. However, the coronal heating mechanism remains unknown. We used observations from the Solar Dynamics Observatory and the Hinode solar physics mission to reveal a ubiquitous coronal mass supply in which chromospheric plasma in fountainlike jets or spicules is accelerated upward into the corona, with much of the plasma heated to temperatures between ~0.02 and 0.1 million kelvin (MK) and a small but sufficient fraction to temperatures above 1 MK. These observations provide constraints on the coronal heating mechanism(s) and highlight the importance of the interface region between photosphere and corona. PMID:21212351

De Pontieu, B; McIntosh, S W; Carlsson, M; Hansteen, V H; Tarbell, T D; Boerner, P; Martinez-Sykora, J; Schrijver, C J; Title, A M

2011-01-01

314

Decomposition characteristics of toluene by a corona radical shower system.  

PubMed

Non-thermal plasma technologies offer an innovative approach to decomposing various volatile organic compounds(VOCs). The decomposition of toluene from simulated flue gas was investigated using a pipe electrode with nozzles for the generation of free radicals. Corona characteristics and decomposition of toluene were investigated experimentally. In addition, the decomposition mechanism of toluene was explored in view of reaction rate. The experimental results showed that the humidity of additional gas has an important effect on corona characteristics and modes and stable streamer corona can be generated through optimizing flow rate and humidity of additional gas. Applied voltage, concentration of toluene, humidity of toluene and resident time are some important factors affecting decomposition efficiency. Under optimizing conditions, the decomposition efficiency of toluene can reach 80%. These results can give a conclusion that the corona radical shower technology is feasible and effective on the removal of toluene in the flue gas. PMID:15495952

Wu, Zu-liang; Gao, Xiang; Luo, Zhong-yang; Ni, Ming-jiang; Cen, Ke-fa

2004-01-01

315

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

316

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

317

OH generation in steam-air pulsed corona.  

National Technical Information Service (NTIS)

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 depend...

M. Garcia B. Chang

1995-01-01

318

Corona-discharge-induced hydrophobicity loss and recovery of silicones  

Microsoft Academic Search

The effect of corona discharge on the hydrophobicity of polydimethylsiloxane (PDMS) used as high-voltage (HV) insulation and the subsequent recovery of hydrophobicity when exposure ceases is now a well-known phenomenon. Surface characterization studies have established that corona exposure in the laboratory forms a brittle, wettable, very thin silica-like layer on the surface of most PDMS elastomers, consistent with similar effects

J. Kim; M. K. Chaudhury

1999-01-01

319

Properties of the chromosphere-corona transition region in Capella  

NASA Technical Reports Server (NTRS)

Analysis of recent ultraviolet observations of the Capella binary system (Alpha Aur) indicates a dense geometrically narrow chromosphere-corona transition region in the Capella system primary (G5 III) similar in many respects to a solar active region. An examination of the coronal energy balance, together with the coronal base pressure derived from the line fluxes, predicts a corona with a mean temperature of 1.2 million K and a large stellar wind consistent with observations.

Haisch, B. M.; Linsky, J. L.

1976-01-01

320

CORONA DISCHARGE IN FLUID HELIUM: DRASTIC GROWTH OF ELECTRON MOBILITY  

Microsoft Academic Search

Liquid Helium (LHe) at 4.2K was excited using a corona discharge for negative high voltages. The experiments were carried out with temperature increasing and different pressures. Current-voltage characteristics were measured and analyzed. The sharp increasing of the corona current was observed at temperatures 7K and 10K under pressure in the range 0.2-0.4 MPa. The analysis showed the electron mobility increasing

321

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

322

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 Å 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

323

Current Sheet Formation and Reconnection Dynamics in the Solar Corona  

Microsoft Academic Search

Current sheet formation is a necessary consequence of the evolution of the multi-polar magnetic field topologies that are ubiquitous throughout the solar corona. We present a very high-resolution study of 3D MHD current sheet formation and the resulting reconnection dynamics in an environment appropriate for the corona. The initial field consists of a translationally invariant, potential field with a null-point

Justin K. Edmondson; S. K. Antiochos; C. DeVore; T. H. Zurbuchen

2009-01-01

324

Magnetic Structure of Rapidly Rotating FK Comae-type Coronae  

Microsoft Academic Search

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

O. Cohen; J. J. Drake; V. L. Kashyap; H. Korhonen; D. Elstner; T. I. Gombosi

2010-01-01

325

An Industrial Streamer Corona Plasma System for Gas Cleaning  

Microsoft Academic Search

For pulsed corona plasma applications, it becomes important to develop pilot systems with large average power and high-energy conversion efficiency. Since the beginning of 2000, we have been working on an industrial corona plasma system with tasks of 10-30 kW in average power and higher than 90% of total energy conversion efficiency. The pulsed-power source should have the following specifications:

G. J. J. Winands; Keping Yan; A. J. M. Pemen; S. A. Nair; Zhen Liu; E. J. M. van Heesch

2006-01-01

326

Radicals generated from 2-chloro-5-fluorotoluene by corona discharge  

NASA Astrophysics Data System (ADS)

The generation of molecular radicals in corona discharge was investigated spectroscopically by varying the experimental conditions applied to a substituted toluene precursor. Vibronic emission spectra were observed from the corona discharge of 2-chloro-5-fluorotoluene seeded in a large amount of carrier gas helium. From an analysis of emission spectra observed, it was confirmed that bond dissociation energy plays a key role in radical formation. The possible pathway for the formation of benzyl-type radicals is proposed to explain the observation.

Yi, Eun Hye; Yoon, Young Wook; Lee, Sang Kuk

2014-06-01

327

Elastic Thickness Estimates for Coronae Associated with Chasmata on Venus  

NASA Technical Reports Server (NTRS)

Coronae are large-scale circular tectonic features surrounded by annular ridges. They are generally considered unique to Venus and may offer insights into the differences in lithospheric structure or mantle convective pattern between Venus and Earth. 68% of all coronae are associated with chasmata or fracture belts. The remaining 32% are located at volcanic rises or in the plains. Chasmata are linear to arcuate troughs, with trough parallel fractures and faults which extend for 1000 s of kilometers. Estimates of the elastic thickness of the lithosphere (T(sub e)) have been calculated in a number of gravity/topography studies of Venus and for coronae specifically. None of these studies, however, have explored the dependence of T(sub e) on the tectonic history of the region, as implied from the interpretation of relative timing relationships between coronae and surrounding features. We examine the relationship between the local T(sub e) and the relative ages of coronae and chasmata with the aim of further constraining the origin and evolution of coronae and chasmata systems.

Hoogenboom, T.; Martin, P.; Housean, G. A.

2005-01-01

328

How to Channel Photospheric Oscillations into the Corona  

NASA Astrophysics Data System (ADS)

There are now many observations of waves in the solar corona with periods around 5 minutes. The source of these waves is uncertain, although global p-modes in the photosphere are an obvious candidate, given the similarity of the dominant periods. However, p-modes are traditionally considered evanescent in the upper photosphere, and it has been unclear how they could propagate through the chromosphere into the corona. Using a numerical model, we show that photospheric oscillations with periods around 5 minutes can actually propagate into the corona so long as they are guided along an inclined magnetic flux tube. The nonverticality of the flux tube increases the acoustic cutoff period to values closer to the dominant periods of the photospheric oscillations, thus allowing tunneling or even direct propagation into the outer atmosphere. The photospheric oscillations develop into shocks, which drive chromospheric spicules and reach the corona. We suggest that Transition Region and Coronal Explorer (TRACE) observations of propagating magnetoacoustic waves in the corona represent these shocked and tunneled photospheric oscillations. We also explore how seismology of these waves could be exploited to determine the connectivity between photosphere and corona.

De Pontieu, B.; Erdélyi, R.; De Moortel, I.

2005-05-01

329

Orbital fleet dispatched to unravel magnetic storms' roots  

NASA Astrophysics Data System (ADS)

Five satellites at the heart of a unique mission that should greatly improve scientists' understanding of geomagnetic storms in Earth's magnetosphere, which can be highly disruptive to a variety of technologies and a health risk to astronauts, were shifting into orbits as far as halfway to the Moon following the successful Feb. 17 launch of a Delta 2 rocket from Cape Canaveral Air Force Station in Florida. The quintet is designed to detect changes in Earth's space environment including charged particle accelerations and flows, and enhanced plasma waves, all of which occur when the Sun's corona is blasted toward Earth in both the steady stream of the solar wind and during solar storms.

Klotz, Irene

2007-03-01

330

Optimizing the properties of the protein corona surrounding nanoparticles for tuning payload release.  

PubMed

We manipulate the passive release rates of DNA payloads on protein coronas formed around nanoparticles (NPs) by varying the corona composition. The coronas are prepared using a mixture of hard and soft corona proteins. We form coronas around gold nanorods (NRs), nanobones (NBs), and carbon nanotubes (CNTs) from human serum (HS) and find that tuning the amount of human serum albumin (HSA) in the NR-coronas (NR-HS-DNA) changes the payload release profile. The effect of buffer strength, HS concentration, and concentration of the cetyltrimethylammonium bromide (CTAB) passivating the NP surfaces on passive release is explored. We find that corona properties play an important role in passive release, and concentrations of CTAB, HS, and phosphate buffer used in corona formation can tune payload release profiles. These advances in understanding protein corona properties bring us closer toward developing a set of basic design rules that enable their manipulation and optimization for particular biological applications. PMID:24128271

Cifuentes-Rius, Anna; de Puig, Helena; Kah, James Chen Yong; Borros, Salvador; Hamad-Schifferli, Kimberly

2013-11-26

331

Measuring electron temperature in the extended corona  

NASA Technical Reports Server (NTRS)

A technique for measuring electron temperature in the extended corona from the line profile of the electron scattered component of coronal H I Ly alpha produced by Thomson scattering of chromospheric Ly alpha emission is discussed. Because of the high thermal velocity of electrons at coronal temperatures (approximately 6800 km/s at T(sub e) = 1,500,000 K) the effect of nonthermal velocities and solar wind flows on the electron velocity distribution are negligible. However, the low electron mass which is responsible for the high thermal velocity also results in a very wide profile (approximately equal to 50 A). This wide profile, together with an intensity that is three orders of magnitude weaker than the resonantly scattered component of Ly alpha makes the direct measurement of T(sub e) a challenging observational problem. An evaluation of this technique based on simulated measurements is presented and the subsequent instrumental requirements necessary to make a meaningful determination of the electron temperature are discussed. Estimates of uncertainties in the measured electron temperature are related to critical instrument parameters such as grating stray light suppression.

Hassler, Donald M.; Gardner, L. D.; Kohl, John L.

1992-01-01

332

Measuring the Electron Temperature in the Corona  

NASA Technical Reports Server (NTRS)

We report on an experiment to demonstrate the feasibility of a new method to obtain the electron temperature and flow speed in the solar corona by observing the visible Kcoronal spectrum during the total solar eclipse on 29 March 2006 in Libya. Results show that this new method is indeed feasible, giving electron temperatures and speeds of 1.10 $\\pm$ 0.05 MK, 103.0 $\\pm$ 92.0 $kmsA{-l}$; 0.98 $\\pm$ 0.12 MK, 0.0 + 10.0 $kmsA{-1)s; 0.70 $\\pm$ 0.08 MK, 0.0 + 10.0 $kmsA{-l)$ at l.l{\\it R)$ {\\odot}$ in the solar north, east and west, respectively, and 0.93 $\\pm$ 0.12 MK, 0.0 + 10.0 $kmsA{-l}$ at 1.2{\\it R}$ {\\odot}$ in the solar east. This new technique could be easily used from a space-based platform in a coronagraph to produce two dimensional maps of the electron temperature and bulk flow speed at the base of the solar wind useful for the study of heliospheric structure and space weather.

Davila, Joseph; SaintCyr, Orville C.; Reginald, Nelson

2008-01-01

333

Common Periodicities of Gle's and Solar Corona  

NASA Astrophysics Data System (ADS)

Using different techniques of Wavelet Analysis, particularly, cross-wavelet coherence and the Global Wavelet Spectrum, we analyze data of intensity of 70 GLE's of the solar cycles 17 -23 vs data of the solar corona. We have found common periodicities of short period (2.8, 5.2 and 27 days), medium period (0.5, 1.2, 1.8, 3.2) as well as a the 4.6 and 11 yrs. periodicities. The two later are continuous over all the time interval, with a high synchronization and linear phase. In contrast, the short and medium periodicities are rather concentrated around the maximums of solar cycles, with some few cases in the minimums of solar activity, and present in general a complex phase. Results are discussed in terms of the works of others authors related to periodicities of the solar dynamo, solar atmosphere, interplanetary space and cosmic rays. We also evaluated the power anomalies of solar activity by means of sunspots, and have found that anomalies are positives when the GLE 's are of high intensity (higher than 100

Perez-Peraza, Jorge Alberto; Velasco Herrera, Victor Manuel; Miroshnichenko, Leonty I.; Vashenyuk, Eduard V.

334

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)×10-6 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.; Génova-Santos, R.; Luzzi, G.; De Gregori, S.; Rubiño-Martin, J. A.

2007-03-01

335

Indirect detection of the Martian helium corona  

NASA Astrophysics Data System (ADS)

The ion composition mass spectrometer ASPERA on board the PHOBOS 2 spacecraft detected particles with M/q = 4 in the vicinity of Mars. A significant difference between the measured particle velocity and the solar wind velocity suggests that these ions are of planetary origin, apparently He(+) from ionisation within the Martian helium corona. The particles had typical energies of either more than 10 keV or about 500 eV. The former correspond to ion pickup in the solar wind and the latter might be ions extracted from the upper ionosphere by an electric field. The observed density of pickup He(+) ions was 0.02-0.1/cc and the He(+) density in the plasmasheet was of 0.2-0.7/cc. According to a recent model of the Martian neutral atmosphere (Moroz et al, 1991) the He(+) density could reach 0.2/cc at the Phobos orbit. Such values give mass densities comparable to those of the solar wind. Thus, helium may play a role in the solar wind mass loading process near Mars.

Barabash, S.; Norberg, O.

1994-07-01

336

Development of Efficient Models of Corona Discharges Around Tall Structures  

NASA Astrophysics Data System (ADS)

This work concerns with numerical modeling of glow corona and sreamer corona discharges that occur near tall ground structures under thunderstorm conditions. Glow corona can occur when ambient electric field reaches modest values on the order of 0.2 kV/cm and when the electric field near sharp points of ground structure rises above a geometry dependent critical field required for ionization of air. Air is continuously ionized in a small region close to the surface of the structure and ions diffuse out into the surrounding air forming a corona. A downward leader approaching from a thundercloud causes a further increase in the electric field at the ground level. If the electric field rises to the point where it can support formation of streamers in air surrounding the tall structure, a streamer corona flash, or series of streamer corona flashes can be formed significantly affecting the space charge configuration formed by the preceding glow corona. The streamer corona can heat the surrounding air enough to form a self-propagating thermalized leader that is launched upward from the tall structure. This leader travels upward towards the thundercloud and connects with the downward approaching leader thus causing a lightning flash. Accurate time-dependent modeling of charge configuration created by the glow and streamer corona discharges around tall structure is an important component for understanding of the sequence of events leading to lightning attachment to the tall structure. The present work builds on principal modeling ideas developed previously in [Aleksandrov et al., J. Phys. D: Appl. Phys., 38, 1225, 2005; Bazelyan et al., Plasma Sources Sci. Technol., 17, 024015, 2008; Kowalski, E. J., Honors Thesis, Penn State Univ., University Park, PA, May 2008; Tucker and Pasko, NSF EE REU Penn State Annual Res. J., 10, 13, 2012]. The non-stationary glow and streamer coronas are modeled in spherical geometry up to the point of initiation of the upward leader. The model uses an implicit numerical scheme for time integration and employs effective non-uniform grid system allowing very accurate description of non-stationary coronas emitted by sharp points with sub-millimeter dimensions and expanding hundreds of meters in surrounding air. In the talk we will present principal components of the model and its performance under different time dynamics of the applied electric field closely resembling scenarios under thunderstorm conditions, including, in particular, extended periods of time (tens of seconds) when only glow corona is produced, followed by a fast rise in the field (tens of microseconds) describing approach of the downward leader. We will also present comparisons of the numerical model results on time dependent corona radius and current with an analytical corona theory summarized recently by Bazelyan et al. [2008].

Tucker, J.; Pasko, V. P.

2012-12-01

337

Unraveling the Atomic Structure of Ultrafine Iron Clusters  

NASA Astrophysics Data System (ADS)

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; Schwingenschlögl, Udo; Zhang, Xi Xiang; Yang, Wei

2012-12-01

338

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

339

Spectral unraveling by space-selective Hadamard spectroscopy.  

PubMed

Spectral unraveling by space-selective Hadamard spectroscopy (SUSHY) enables recording of NMR spectra of multiple samples loaded in multiple sample tubes in a modified spinner turbine and a regular 5mm liquids NMR probe equipped with a tri-axis pulsed field gradient coil. The individual spectrum from each sample is extracted by adding and subtracting data that are simultaneously obtained from all the tubes based on the principles of spatially resolved Hadamard spectroscopy. The well-known Hadamard spectroscopy has been applied for spatial selection and the method utilizes standard configuration of NMR instrument hardware. The SUSHY method can be easily incorporated in multi-dimensional multi-tube NMR experiments. This method combines the excitation multiplexing, natural advantage of FTNMR, and sample multiplexing and offers high-throughput by reducing the total experimental time by up to a factor of four in a 4-tube mode. PMID:16364668

Murali, Nagarajan; Miller, William Marcus; John, Boban K; Avizonis, Daina A; Smallcombe, Stephen H

2006-04-01

340

Dyspraxia or developmental coordination disorder? Unravelling the enigma  

PubMed Central

Dyspraxia is an enigma to many people, both professional and lay alike—what 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

341

Dissertation talk: The EUV Unresolved Corona and Coronal Loops  

NASA Astrophysics Data System (ADS)

In this work, physical characteristics of the solar corona in the Extreme Ultra-Violet (EUV) regime of the electromagnetic spectrum are investigated. Regions of heightened coronal activity are generally found near the locations of sunspots. These regions are commonly called Active Regions and are the focus of the project. Multiple space based observing platforms have been deployed in the last decade and it is possible to use several of these observatories in combination to develop a more complete picture of the solar corona. Joint Observing Program 146 was created to collect spectroscopic intensities using the Coronal Diagnostic Spectrometer (CDS) on Solar and Heliospheric Observatory (SoHO) and EUV images using NASA's Transition Region and Coronal Explorer (TRACE). The emission line intensities are used to develop an understanding of the temperature and density of the active region coronal plasma. However, the performance of the CDS instrument in the spatial and temporal domains is limited and to compensate for these limitations data collected by the TRACE instrument provide a high spatial and temporal resolution set of observations. The combination of the information contained in the data from these two instruments is used to determine the temperature, density and dynamics of the solar coronal active regions. One of the most exciting unsolved problems in solar astrophysics is to understand why the corona maintains a temperature roughly two orders of magnitude higher than the underlying material. An detailed investigation of the coronal emission has provided constraints on models of the heating mechanism, since the temperature, density and evolution of emission rates for multiple ionic species are indicative of the mechanism(s) working to heat the corona. The observed corona appears to consist of multiple unresolved structures as well as resolved active region structures, called coronal loops. The purpose of the present work is to determine the characteristics of the unresolved background corona. This has two important applicatons. Any model of the corona must account for the emission comprising the unresolved background, and the study of coronal loops can be improved by subtracting the emission along the line-of-sight due to the background contribution to the total intensity. Using the characterizations of the coronal unresolved background, results for loops after background subtraction are also presented. This work demostrates the magnitude of the unresolved coronal emission with respect to the total emission along the line of sight, and how this compares to that of the resolved loops. It is apparent from this analyis that the unresolved corona is the dominant source of radiation in the active region corona.

Cirtain, J.

2005-05-01

342

Positive and negative corona discharges in flowing carbon dioxide  

NASA Astrophysics Data System (ADS)

The effect of the gas flow rate (10-320 cm3 min-1) on the process of ozone formation in both positive and negative corona discharges has been studied using a coaxial cylindrical system of electrodes fed by dry CO2. The source of ozone is electron impact dissociation of carbon dioxide to liberate oxygen atoms and their subsequent formation of oxygen molecules, which may then form ozone by the well-known Chapman mechanism. Small increases in flow rate were found to cause a major increase in the discharge current measured in the negative corona discharge. This effect was found to correspond to observed changes in the ozone concentration within the discharge and is a consequence of dissociative electron attachment to ozone leading to negative ion formation in the discharge. In contrast no direct effect of ozone on the positive corona discharge current was observed. The observed increase in average positive ion mobility in the positive corona is ascribed to the conversion of O_2^+ ions into more mobile O_2^+ ions. Considerably higher ozone concentrations (up to 100 ppm) were found in the negative corona discharge. The effect of the geometry of the system was also explored by using three different stainless steel outer electrodes with diameters of 10, 15 and 27 mm. Ozone concentrations were found to decrease significantly with increasing radius of the outer electrode at the same average input energy density.

Skalny, J. D.; Stoica, A.; Orszagh, J.; Vladoiu, R.; Mason, N. J.

2008-09-01

343

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 Alfvén 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 Alfvén 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

2013-07-01

344

Oxidative coupling of methane with ac and dc corona discharges  

SciTech Connect

The oxidative coupling of methane (OCM) is being actively studied for the production of higher hydrocarbons from natural gas. The present study concentrated on the oxidative conversion of methane in an atmospheric pressure, nonthermal plasma formed by ac or dc corona discharges. Methyl radicals are formed by reaction with negatively-charged oxygen species created in the corona discharge. The selectivity to products ethane and ethylene is affected by electrode polarity, frequency, and oxygen partial pressure in the feed. Higher C{sub 2} yields were obtained with the ac corona. All the ac corona discharges are initiated at room temperature (i.e., no oven or other heat source is used), and the temperature increases to 300--500 C due to the exothermic reactions and the discharge itself. The largest C{sub 2} yield is 21% with 43.3% methane conversion and 48.3% C{sub 2} selectivity at a flowrate of 100 cm{sup 3}/min when the ac corona is at 30 Hz, 5 kV (rms) input power was used. The methane conversion may be improved to more than 50% by increasing the residence time, but the C{sub 2} selectivity decreases. A reaction mechanism including the oxidative dehydrogenation (OXD) of ethane to ethylene is presented to explain the observed phenomena. The results suggest that ac and/or dc gas discharge techniques have significant promise for improving the economics of OCM processes.

Liu, C.; Marafee, A.; Hill, B.; Xu, G.; Mallinson, R.; Lobban, L. [Univ. of Oklahoma, Norman, OK (United States). Inst. of Natural Gas Utilization] [Univ. of Oklahoma, Norman, OK (United States). Inst. of Natural Gas Utilization

1996-10-01

345

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

2013-10-01

346

Review of recent developments in lightning channel corona sheath research  

NASA Astrophysics Data System (ADS)

A review of recent lightning channel corona sheath dynamics research is given. Current state of knowledge about corona sheath conductivity is presented and a brief discussion on the role of radially flowing corona current in longitudinal extension of the channel is given. It is shown that positive transferred charge inside the lightning channel core during the return-stroke stage dominates the total charge when the speed of the return stroke current wave is relatively low and the negative leader line charge density is less than typical values inferred from field measurements. As a result, the positive charge inside the channel during the return-stroke stage can be temporarily greater than the negative charge deposited by the preceding leader. This may explain significant positive overshoots in radial electric fields measured close to the lightning attachment point at ground. Consequences of adoption of corona current concept in the Lumped Current Source (LCS) type models are described, and duality between LCS type models and the Distributed Current Sources (DCS) type models is rigorously demonstrated. Additionally, we discuss the role of corona in making the return-stroke speed lower than the speed of light.

Maslowski, Grzegorz; Rakov, Vladimir A.

2013-07-01

347

INTERCHANGE RECONNECTION IN A TURBULENT CORONA  

SciTech Connect

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. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Ruffolo, D. [Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400 (Thailand); Servidio, S. [Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Velli, M., E-mail: rappazzo@udel.edu [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2012-10-10

348

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

349

Admittance Survey of Type 1 Coronae on Venus: Implications for Elastic Thickness  

NASA Technical Reports Server (NTRS)

Coronae are volcano-tectonic features on Venus which range from 60km to 2600km and are defined by their nearly circular patterns of fractures. Type 1 (regular) coronae are classified as having >50% complete fracture annuli. Previous work has examined the factors controlling the morphology, size, and fracture pattern of coronae, using lithospheric properties, loading signature and geologic characteristics. However, these studies have been limited to Type 2 (topographic) coronae (e.g. coronaes with <50% fracture annuli), and the factors controlling the formation of Type 1 coronae remain poorly understood. In this study, we apply the methodology of to survey the admittance signature for Type 1 coronae to determine the controlling parameters which govern Type 1 coronae formation.

Hoogenboom, T.; Smrekar, S. E.; Anderson, F. S.; Houseman, G.

2003-01-01

350

Comparison of direct current and 50 Hz alternating current microscopic corona characteristics on conductors  

NASA Astrophysics Data System (ADS)

Corona discharge is one of the major design factors for extra-high voltage and ultra-high voltage DC/AC transmission lines. Under different voltages, corona discharge reveals different characteristics. This paper aims at investigating DC and AC coronas on the microscopic scale. To obtain the specific characteristics of DC and AC coronas, a new measurement approach that utilizes a coaxial wire-cylinder corona cage is designed in this paper, and wires of different diameters are used in the experiment. Based on the measurements, the respective microscopic characteristics of DC and AC coronas are analyzed and compared. With differences in characteristics between DC and AC coronas proposed, this study provides useful insights into DC/AC corona discharges on transmission line applications.

Zhang, Shuai; Zhang, Bo; He, Jinliang

2014-06-01

351

Probing the solar corona with very long baseline interferometry  

NASA Astrophysics Data System (ADS)

Understanding and monitoring the solar corona and solar wind is important for many applications like telecommunications or geomagnetic studies. Coronal electron density models have been derived by various techniques over the last 45 years, principally by analysing the effect of the corona on spacecraft tracking. Here we show that recent observational data from very long baseline interferometry (VLBI), a radio technique crucial for astrophysics and geodesy, could be used to develop electron density models of the Sun’s corona. The VLBI results agree well with previous models from spacecraft measurements. They also show that the simple spherical electron density model is violated by regional density variations and that on average the electron density in active regions is about three times that of low-density regions. Unlike spacecraft tracking, a VLBI campaign would be possible on a regular basis and would provide highly resolved spatial–temporal samplings over a complete solar cycle.

Soja, B.; Heinkelmann, R.; Schuh, H.

2014-06-01

352

Biomolecular coronas provide the biological identity of nanosized materials  

NASA Astrophysics Data System (ADS)

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.

Monopoli, Marco P.; Åberg, Christoffer; Salvati, Anna; Dawson, Kenneth A.

2012-12-01

353

On the nature of the prominence - corona transition region  

NASA Astrophysics Data System (ADS)

Due to the complexity of their environment, prominences properties are still a matter of controversy. Prominences cool and dense plasma is suspended in the hot corona by a magnetic structure poorly known. Their thermal insulation from the corona results in a thin geometrical interface called prominence-corona-transition-region (PCTR). Here we will review the main properties of such a region as derived primarily from observations. We will introduce the thermal structure properties, describe the fine structure together with the Doppler-shift and width properties of lines of the emitting plasma. We will introduce the proposed interpretations of such observations and the limits of our knowledge imposed by the present instrumentation. We will conclude with a perspective for the future observations of the PCTR.

Parenti, Susanna; Vial, Jean-Claude

2014-01-01

354

Probing the solar corona with very long baseline interferometry.  

PubMed

Understanding and monitoring the solar corona and solar wind is important for many applications like telecommunications or geomagnetic studies. Coronal electron density models have been derived by various techniques over the last 45 years, principally by analysing the effect of the corona on spacecraft tracking. Here we show that recent observational data from very long baseline interferometry (VLBI), a radio technique crucial for astrophysics and geodesy, could be used to develop electron density models of the Sun's corona. The VLBI results agree well with previous models from spacecraft measurements. They also show that the simple spherical electron density model is violated by regional density variations and that on average the electron density in active regions is about three times that of low-density regions. Unlike spacecraft tracking, a VLBI campaign would be possible on a regular basis and would provide highly resolved spatial-temporal samplings over a complete solar cycle. PMID:24946791

Soja, B; Heinkelmann, R; Schuh, H

2014-01-01

355

HIGH SPATIAL RESOLUTION OBSERVATIONS OF LOOPS IN THE SOLAR CORONA  

SciTech Connect

Understanding how the solar corona is structured is of fundamental importance to determine how the Sun's upper atmosphere is heated to high temperatures. Recent spectroscopic studies have suggested that an instrument with a spatial resolution of 200 km or better is necessary to resolve coronal loops. The High Resolution Coronal Imager (Hi-C) achieved this performance on a rocket flight in 2012 July. We use Hi-C data to measure the Gaussian widths of 91 loops observed in the solar corona and find a distribution that peaks at about 270 km. We also use Atmospheric Imaging Assembly data for a subset of these loops and find temperature distributions that are generally very narrow. These observations provide further evidence that loops in the solar corona are often structured at a scale of several hundred kilometers, well above the spatial scale of many proposed physical mechanisms.

Brooks, David H.; Ugarte-Urra, Ignacio [College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22030 (United States); Warren, Harry P. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Winebarger, Amy R. [NASA Marshall Space Flight Center, ZP 13, Huntsville, AL 35812 (United States)

2013-08-01

356

The solar corona as a quadric surface in three-dimensional space  

Microsoft Academic Search

The topology of the outer solar corona has been analyzed. In so doing the outer corona was treated as a visible manifestation of the heliospheric current sheet base. A generalization of the recent conception of the flat (galaxy-like) solar corona has been suggested. It is shown that the three-dimensional shape of the outer corona is well fitted by the second-degree

R. A. Gulyaev

1994-01-01

357

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, Jérôme; Plantevin, Sophie; Auffan, Mélanie; Bottero, Jean-Yves; Vidaud, Claude

2013-01-01

358

Optical emission spectroscopy of point-plane corona and back-corona discharges in air  

NASA Astrophysics Data System (ADS)

Results of spectroscopic investigations and current-voltage characteristics of corona discharge and back discharge on fly-ash layer, generated in point-plane electrode geometry in air at atmospheric pressure are presented in the paper. The characteristics of both discharges are similar but differ in the current and voltage ranges of all the discharge forms distinguished during the experiments. Three forms of back discharge, for positive and negative polarity, were investigated: glow, streamer and low-current back-arc. In order to characterize ionisation and excitation processes in back discharge, the emission spectra were measured and compared with those obtained for normal corona discharge generated in the same electrode configuration but with fly ash layer removed. The emission spectra were measured in two discharge zones: near the tip of needle electrode and near the plate. Visual forms of the discharge were recorded with digital camera and referred to current-voltage characteristics and emission spectra. The measurements have shown that spectral lines emitted by back discharge depend on the form of discharge and the discharge current. From the comparison of the spectral lines of back and normal discharges an effect of fly ash layer on the discharge morphology can be determined. The recorded emission spectra formed by ionised gas and plasma near the needle electrode and fly ash layer are different. It should be noted that in back arc emission, spectral lines of fly ash layer components can be distinguished. On the other hand, in needle zone, the emission of high intensity N2 second positive system and NO ? lines can be noticed. Regardless of these gaseous lines, also atomic lines of dust layer were present in the spectrum. The differences in spectra of back discharge for positive and negative polarities of the needle electrode have been explained by considering the kind of ions generated in the crater in fly ash layer. The aim of these studies is to better understand the discharge processes encountered in electrostatic precipitators.

Czech, T.; Sobczyk, A. T.; Jaworek, A.

2011-12-01

359

CORONAS-F observations of active phenomena on the Sun  

NASA Astrophysics Data System (ADS)

Complex observations in the framework of the CORONAS-F Mission aimed at the study of active phenomena in the solar corona are described. The main features are given for the following experiments: (1) XUV-imaging spectroscopy with high temporal and spatial resolution (SPIRIT), (2) X-ray spectroscopy (RESIK), (3) X-ray and gamma-ray photometer/spectrometer (HELICON, DIOGENES), (4) Solar cosmic rays (SKL). Examples of new observational results on the structure and dynamics of flares and transient events along with their analysis are discussed.

Oraevsky, V.; Sobelman, I.; Zitnik, I.; Kuznetsov, V.

360

Humidity Influence on Corona Discharge Characteristics on Polymer Insulators under Polluted Conditions  

Microsoft Academic Search

Silicone rubber for polymer insulator has an excellent hydrophobicity with recovery properties, resulting in higher pollution performance. However it is inevitable that even silicone rubber polymer insulators start generating corona discharge with time under humid and polluted conditions. And such a corona discharge causes rubber damage because of acid generation. Since it is assumed that the corona discharge characteristics depend

Tomoki Banno; Itsuki Umeda; Takanori Kondo; Kenji Tanaka; Yoshihiro Suzuki

2009-01-01

361

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

362

From Chemical Kinetics to Streamer Corona Reactor and Voltage Pulse Generator  

Microsoft Academic Search

This paper discusses the global chemical kinetics of corona plasma-induced chemical reactions for pollution control. If there are no significant radical termination reactions, the pollution removal linearly depends on the corona energy density and\\/or the energy yield is a constant. If linear radical termination reactions play a dominant role, the removal rate shows experimental functions in terms of the corona

K. Yan; E. J. M. van Heesch; A. J. M. Pemen; P. A. H. J. Huijbrechts

2001-01-01

363

A Study on Hydrophobicity of Silicone Rubber Exposed to Corona Discharge  

Microsoft Academic Search

This paper describes the degradation of unfilled high temperature vulcanized silicone rubber (HTV-SR) resulting from corona discharges. In this study, corona stress was produced by a needle-plane electrode system, and the chemical and morphological structures at the surface layer of SR before and after corona discharge treatment were analyzed by using the techniques of scanning electron microscope (SEM), Fourier transform

Y. Zhu; K. Haji; H. Yamamoto; T. Miyake; M. Otsubo; C. Honda; K. Kaikake; K. Sugamoto

2006-01-01

364

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

365

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

366

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

367

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

368

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 Å, 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

369

Spontaneous unraveling of hagfish slime thread skeins is mediated by a seawater-soluble protein adhesive.  

PubMed

Hagfishes are known for their ability to rapidly produce vast quantities of slime when provoked. The slime is formed via the interaction between seawater and two components released by the slime glands: mucin vesicles from gland mucous cells, which swell and rupture in seawater to form a network of mucus strands, and intermediate filament-rich threads, which are produced within gland thread cells as tightly coiled bundles called skeins. A previous study showed that the unraveling of skeins from Atlantic hagfish (Myxine glutinosa) requires both the presence of mucins and hydrodynamic mixing. In contrast, skeins from Pacific hagfish (Eptatretus stoutii) unravel in the absence of both mucins and mixing. We tested the hypothesis that spontaneous unraveling of E. stoutii skeins is triggered by the dissolution of a seawater-soluble protein adhesive and the release of stored strain energy within the coiled thread. Here we show that, as predicted by this hypothesis, unraveling can be initiated by a protease under conditions in which unraveling does not normally occur. We also demonstrate, using high resolution scanning electron microscopy, that the treatment of skeins with solutions that cause unraveling also leads to the disappearance of surface and inter-thread features that remain when skeins are washed with stabilizing solutions. Our study provides a mechanism for the deployment of thread skeins in Pacific hagfish slime, and raises the possibility of producing novel biomimetic protein adhesives that are salt, temperature and kosmotrope sensitive. PMID:24744422

Bernards, Mark A; Oke, Isdin; Heyland, Andreas; Fudge, Douglas S

2014-04-15

370

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

371

Imaging and Processing Images of the Solar Corona  

NASA Astrophysics Data System (ADS)

Of all astronomical phenomena visible to the naked eye, none is as spectacular, or as fleeting, as a total eclipse of the Sun. For a few brief minutes, the Moon blocks the Sun's blindingly bright photosphere to reveal the ethereal solar corona. This gossamer halo, forming the outer atmosphere of the Sun, can only be seen in the eerie twilight brought on by totality.

Espenak, Fred

372

Simulation of surface potential decay of corona char ged polyimide  

Microsoft Academic Search

Surface potential decay (SPD) of corona charged polyimide (PI) films has been studied using different initial potentials Vo. It has been noticed that the rate of decay increases with initial charging levels. Surface potential profile over the surface of the PI films and return potential generated after charge neutralization have been also experimentally recorded. In order to analyse and explain

Zehira Ziari; Salah Sahli; Azzedine Bellel; Yvan Segui; Patrice Raynaud

2011-01-01

373

Corona ageing tests of RTV and RTV nanocomposite materials  

Microsoft Academic Search

Silicone rubber insulating materials are superior to conventional porcelain materials, whose special water repellency and transfer of water repellency is favorable in power industry. However, two points are concerned in its application, and these are long-term reliability and lack of methods to assess their long-term performance. Corona and arc are important factors that induce degradation of RTV insulating materials during

Lan Lei; Wen Xishan; Cai Dengke

2004-01-01

374

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...

375

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

376

Energy distribution of nanoflares in the quiet solar corona  

NASA Astrophysics Data System (ADS)

We present a detailed statistical analysis of flare-like events in low layer of solar corona detected with TESIS instrument onboard CORONAS-PHOTON satellite in 171 {Å} during high-cadence (5 sec) time-series. The estimated thermal energies of these small events amount to 10^{23} - 10^{26} erg. According to modern classification flare-like events with such energies are usually referred to as nanoflares. The big number of registered events (above 2000) allowed us to obtain precise distributions of geometric and physical parameters of nanoflares, the most intriguing being energy distribution. Following Aschwanden et al. (2000) and other authors we approximated the calculated energy distribution with a single power law slope: N(E)dE ˜ N^{-?}dE. The power law index was derived to be ? = 2.4 ± 0.2, which is very close to the value reported by Krucker & Benz (1998): ? ? 2.3 - 2.4. The total energy input from registered events constitute about 10^4 erg \\cdot cm^{-2} \\cdot s^{-1}, which is well beyond net losses in quiet corona (3 \\cdot 10^5 erg \\cdot cm^{-2} \\cdot s^{-1}). However, the value of ? > 2 indicates that nanoflares with lower energies dominate over nanoflares with bigger energies and could contribute considerably to quiet corona heating.

Ulyanov, Artyom

2012-07-01

377

Observation of Alfven Waves in the Solar Corona (Invited)  

NASA Astrophysics Data System (ADS)

I will review the extensive progress made in recent years on the observation of Alfven waves in the solar corona, with an emphasis on the measurements made with the Coronal Multi-channel Polarimeter. Application of the wave measurements to coronal seismology will be presented. Future prospects in the field will be discussed.

Tomczyk, S.

2013-12-01

378

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 Švestka

1977-01-01

379

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

380

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

381

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

382

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

383

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

384

Force-Free Magnetic Flux Ropes in the Solar Corona  

Microsoft Academic Search

In the course of an ongoing investigation of force-free magnetic fields in the spherical geometry appropriate to the solar corona, we have found solutions that represent magnetic flux ropes. The magnetic energy stored in these ropes and the surrounding field is larger than that which can be stored in simple magnetic arcades with the same boundary conditions, and in some

R. Wolfson

2003-01-01

385

Reconnection in multiple current sheet configurations in the solar corona  

Microsoft Academic Search

We investigate magnetic reconnection in a multiple current sheet configuration by means of three-dimensional resistive MHD simulations. This configuration might be of interest in the solar corona context, e.g. for coronal helmet streamers. We present results of our simulations of the linear and nonlinear development of the tearing mode instability. In particular, we highlight the changes in magnetic topology and

G. T Birk; A. Otto

1997-01-01

386

Density Structure of the Solar Corona From Radio Occultation Measurements  

Microsoft Academic Search

Starting with angular broadening measurements five decades ago, a wide variety of radio propagation and scattering phenomena have been observed when natural radio sources or spacecraft radio signals happened to pass behind or were occulted by the solar corona. While yielding information on density, velocity and magnetic fields, these unique measurements probe density most directly, and with unprecedented sensitivity, spatial

R. Woo

2003-01-01

387

Evolution of twisted magnetic fields. [Of solar corona  

Microsoft Academic Search

The magnetic field of the solar corona evolves quasi-statically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. It is shown that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, the equilibrium of a thin magnetic flux tube

E. G. Zweibel; A. H. Boozer

1985-01-01

388

Solar corona during the 1994 and 1999 eclipses  

Microsoft Academic Search

The lower and middle layers of the corona are studied analyzing the ground-based observations carried out during the November 3, 1994 and August 11, 1999 total solar eclipses. While the 1994 eclipse took place nearby the solar activity minimum, the 1999 eclipse occurred closer to the solar cycle maximum. Structures, isolines of brightness and polarization, and topology of the magnetic

O. G. Badalyan; J. Sýkora

2008-01-01

389

Investigating The Magnetic Field of The Solar Corona With Pulsars  

Microsoft Academic Search

We propose a novel experiment to examine both the magnetic field and electron content of the solar corona. We intend to measure the Faraday rotation and dispersion evident in observations of background pulsar sources as they are occulted by the Sun. As we will be utilising a number of simultaneous lines of sight, that will cut different paths through the

S. Ord

2006-01-01

390

Complexity of Coronal Mass Ejections in the Corona  

Microsoft Academic Search

Coronal mass ejections (CMEs) present a variety of morphologies and sizes as recorded in white light coronal images. Since magnetic flux is 'frozen' in to the plasma in the highly conducting corona, CME morphologies should be related to the topologies of the magnetic fields they contain. CMEs originating in sites containing complex or multi-polar fields may be expected to have

J. T. Burkepile

2002-01-01

391

Decomposition of toluene by streamer corona discharge with catalyst  

Microsoft Academic Search

The improvement in the decomposition of volatile organic compounds was investigated by combining discharge plasma with photocatalyst (TiO2). A DC streamer corona plasma reactor combined with photocatalyst pellet layer was developed. It was found that the combination of the plasma and TiO2 was effective for improving toluene decomposition when the streamers cover the surface of the pellet layer.

Duan Li; Daisuke Yakushiji; Seiji Kanazawa; Toshikazu Ohkubo; Yukiharu Nomoto

2002-01-01

392

Calculation of corona onset voltage for duct-type precipitators  

Microsoft Academic Search

A pure theoretical method for calculating the onset voltage of corona in duct-type electrostatic precipitators that is independent of the arrangement of discharge wires relative to the collecting plates is described. This method is based on a criterion for self-recurring single electron avalanches in a known electric field distribution in the ionization zone surrounding the discharge wire. The results computed

Mazen Abdel-Salam; Dennis Wiitanen

1993-01-01

393

Flexural ridges, trenches, and outer rises around coronae on Venus  

Microsoft Academic Search

Flexural signatures outboard of Venusian coronal rims are examined with the purpose of inferring the thickness of the planet's elastic lithosphere. Topographic profiles of several prominent coronae which display clear trench and outer rise signatures are presented. Via a thin elastic plate flexure model to characterize the shape of the trench and outer rise, Venusian flexures are found to be

David T. Sandwell; Gerald Schubert

1992-01-01

394

Study on corona suppression for fusion reactor coils  

Microsoft Academic Search

Fusion reactor coils are subjected to 50 Hz ac voltages (for overvoltage tests) and impulsive voltages whose rise time ranges from 1 microsec to 1 ms (for fusion experiments). The paper shows that SiC paint is suitable as a corona suppression coating for such coils. Also, in a fusion reactor, two coils may be arranged in parallel facing each other

Kenzo Kadotani; Takanori Sato; Yasuhiko Kako

1980-01-01

395

Non-thermal processes in coronae and beyond  

NASA Astrophysics Data System (ADS)

This contribution summarizes the splinter session ``Non-thermal processes in coronae and beyond'' held at the Cool Stars 17 workshop in Barcelona in 2012. It covers new developments in high energy non-thermal effects in the Earth's exosphere, solar and stellar flares, the diffuse emission in star forming regions and reviews the state and the challenges of the underlying atomic databases.

Poppenhaeger, K.; Günther, H. M.; Beiersdorfer, P.; Brickhouse, N. S.; Carter, J. A.; Hudson, H. S.; Kowalski, A.; Lalitha, S.; Miceli, M.; Wolk, S. J.

2013-02-01

396

Asymptotic analysis of corona discharge from thin electrodes  

NASA Technical Reports Server (NTRS)

The steady discharge of a high-voltage corona is analyzed as a singular perturbation problem. The small parameter is the ratio of the length of the ionization region to the total gap length. By this method, current versus voltage characteristics can be calculated analytically.

Durbin, P. A.

1986-01-01

397

Corona Formation on Venus via Extension and Lithospheric Instability  

NASA Astrophysics Data System (ADS)

We demonstrate that a mantle plume associated with a rift can create melt that intrudes the lower lithosphere and causes dripping into the upper mantle, extension, surface stresses, and the creation of off-rift coronae at Parga Chasma on Venus.

Piskorz, D.; Elkins-Tanton, L. T.; Smrekar, S. E.

2012-03-01

398

Force-Free Magnetic Flux Ropes in the Solar Corona  

Microsoft Academic Search

Magnetic flux ropes offer a venue for storage of magnetic energy in the solar corona, energy that can contribute to eruptive events such as coronal mass ejections (CMEs). When a flux rope encircles the Sun, the associated magnetic field can store more energy than is needed to open the field fully---one of three energy-demanding tasks required for a CME. This

R. Wolfson

2004-01-01

399

Reticulated vitreous carbon electrodes for gas phase pulsed corona reactors  

Microsoft Academic Search

A new design for gas phase pulsed corona reactors incorporating reticulated vitreous carbon electrodes is demonstrated to be effective for the removal of nitrogen oxides from synthetic air mixtures. The reactor consists of a plexiglass tube with porous reticulated carbon disk electrodes placed perpendicularly to the cylinder axis. Streamers propagate between the reticulated carbon disks providing a uniform exposure of

B. R. Looke; M. Kirkpatrick; H. Hanson; W. C. Finney

1998-01-01

400

Reticulated vitreous carbon electrodes for gas phase pulsed corona reactors  

Microsoft Academic Search

A new design for gas phase pulsed corona reactors incorporating reticulated vitreous carbon (RVC) electrodes is demonstrated to be effective for the removal of nitrogen oxides from various gas mixtures containing O2, N2, water vapor and ethylene. The reactor consists of either a Plexiglass or glass cylindrical tube with macro-porous RVC electrodes placed perpendicularly to the cylinder axis. Streamers propagate

Michael Kirkpatrick; Wright C. Finney; Bruce R. Locke

2000-01-01

401

Unravelling R gene-mediated disease resistance pathways in Arabidopsis.  

PubMed

Abstract Molecular genetic approaches were adopted in the model crucifer, Arabidopsis thaliana, to unravel components of RPP5- and RPP1-mediated disease resistance to the oomycete pathogen, Peronospora parasitica. The products of RPP5 and three genes comprising the RPP1 complex locus belong to a major subclass of nucleotide-binding/leucine-rich repeat (NB-LRR) resistance (R) protein that has amino-terminal homology to the cytoplasmic domains of Drosophila and mammalian Toll and interleukin-1 family receptors (the so called 'TIR' domain). Similarities in the domain architecture of these proteins and animal regulators of programmed cell death have also been observed. Mutational screens revealed a number of genes that are required for RPP5-conditioned resistance. Among these are EDS1 and PAD4. Both EDS1 and PAD4 precede the function of salicylic acid-mediated plant responses. The EDS1 and PAD4 genes were cloned and found to encode proteins with similarity to the catalytic site of eukaryotic lipases, suggesting that they may function by hydrolysing a lipid-based substrate. PMID:20572946

Parker, J E; Feys, B J; van der Biezen, E A; Noël, L; Aarts, N; Austin, M J; Botella, M A; Frost, L N; Daniels, M J; Jones, J D

2000-01-01

402

Unraveling cyanobacteria ecology in wastewater treatment plants (WWTP).  

PubMed

Cyanobacteria may be important components of wastewater treatment plants' (WWTP) biological treatment, reaching levels of 100% of the total phytoplankton density in some systems. The occurrence of cyanobacteria and their associated toxins in these systems present a risk to the aquatic environments and to public health, changing drastically the ecology of microbial communities and associated organisms. Many studies reveal that cyanotoxins, namely microcystins may not act as antibacterial compounds but they might have negative impacts on protozoans, inhibiting their growing and respiration rates and leading to changes in cellular morphology, decreasing consequently the treatment efficacy in WWTP. On the other side, flagellates and ciliates may ingest some cyanobacteria species while the formation of colonies by these prokaryotes may be seen as a defense mechanism against predation. Problems regarding the occurrence of cyanobacteria in WWTP are not limited to toxin production. Other cyanobacterial secondary metabolites may act as antibacterial compounds leading to the disruption of bacterial communities that biologically convert organic materials in WWTP being fundamental to the efficacy of the process. Studies reveal that the potential antibacterial capacity differs according to cyanobacteria specie and it seems to be more effective in Gram (+) bacteria. Thus, to understand the effects of cyanobacterial communities in the efficiency of the waste water treatment it will be necessary to unravel the complex interactions between cyanobacterial populations, bacteria, and protozoa in WWTP in situ studies. PMID:21287346

Martins, Joana; Peixe, Luísa; Vasconcelos, Vítor M

2011-08-01

403

Pulse Propagation Along Transmission Lines in the Presence of Corona and Their Implication to Lightning Return Strokes  

Microsoft Academic Search

Transmission line equations in air in the presence of corona are derived. The analysis shows that the corona caused by a voltage or a current pulse propagating along a transmission line can be represented by a series of corona current sources distributed along the line. Corona has two effects on the voltage or current pulses propagating along a transmission line.

Vernon Cooray; Nelson Theethayi

2008-01-01

404

An XMM-Newton Study of the Coronae of ?2 Coronae Borealis  

NASA Astrophysics Data System (ADS)

We present results of XMM-Newton Guaranteed Time observations of the RS CVn binary ?2 Coronae Borealis. The spectra obtained with the Reflection Grating Spectrometers and the European Photon Imaging Camera MOS2 were simultaneously fitted with collisional ionization equilibrium plasma models to determine coronal abundances of various elements. Contrary to the solar first ionization potential (FIP) effect, in which elements with a low FIP are overabundant in the corona compared to the solar photosphere, and contrary to the ``inverse'' FIP effect observed in several active RS CVn binaries, coronal abundance ratios in ?2 CrB show a complex pattern, as supported by similar findings in the Chandra HETGS analysis of ?2 CrB with a different methodology by Osten and coworkers in 2003. Low-FIP elements (<10 eV) have abundance ratios relative to Fe that are consistent with the solar photospheric ratios, whereas high-FIP elements have abundance ratios that increase with increasing FIP. We find that the coronal Fe abundance is consistent with the stellar photospheric value, indicating that there is no metal depletion in ?2 CrB. However, we obtain a higher Fe absolute abundance than Osten and coworkers did. Except for Ar and S, our absolute abundances are about 1.5 times larger than those reported by Osten and coworkers. However, a comparison of their model with our XMM-Newton data (and vice versa) shows that both models work adequately in general. We find, therefore, no preference for one methodology over the other for deriving coronal abundances. Despite the systematic discrepancy in absolute abundances, our abundance ratios are very close to those obtained by Osten and coworkers. Finally, we confirm the measurement of a low density in O VII (<4×1010 cm-3) but could not confirm the higher densities measured in spectral lines formed at higher temperatures that were derived by other studies of ?2 CrB due to the lower spectral resolution of the XMM-Newton grating spectrometers.

Suh, Jin A.; Audard, Marc; Güdel, Manuel; Paerels, Frederik B. S.

2005-09-01

405

Diagnosing the Prominence-Cavity Connection in the Solar Corona  

NASA Astrophysics Data System (ADS)

The energetic equilibrium of the corona is described by a balance of heating, thermal conduction, and radiative cooling. Prominences can be described by the thermal instability of coronal energy balance which leads to the formation of cool condensations. Observationally, the prominence is surrounded by a density depleted elliptical structure known as a cavity. In this dissertation, we use extreme ultraviolet remote sensing observations of the prominence-cavity system to diagnose the static and dynamic properties of these structures. The observations are compared with numerical models for the time-dependent coronal condensation process and the time-independent corona-prominence magnetic field. To diagnose the density of the cavity, we construct a three-dimensional structural model of the corona. This structural model allows us to synthesize extreme ultraviolet emission in the corona in a way that incorporates the projection effects which arise from the optically thin plasma. This forward model technique is used to constrain a radial density profile simultaneously in the cavity and the streamer. We use a ?2 minimization to find the density model which best matches a density sensitive line ratio (observed with Hinode/Extreme ultraviolet Imaging Spectrometer) and the white light scattered intensity (observed with Mauna Loa Solar Observatory MK4 coronagraph). We use extreme ultraviolet spectra and spectral images to diagnose the dynamics of the prominence and the surrounding corona. Based on the doppler shift of extreme ultraviolet coronal emission lines, we find that there are large regions of flowing plasma which appear to occur within cavities. These line of sight flows have speeds of 10 km/s-1 and projected spatial scales of 100 Mm. Using the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA) dataset, we observe dynamic emission from the prominence-cavity system. The SDO/AIA dataset observes multiple spectral bandpasses with different temperature sensitivities. Time-dependent changes in the observed emission in these bandpass images represent changes in the thermodynamic properties of the emitting plasma. We find that the coronal region surrounding the prominence exhibits larger intensity variations (over tens of hours of observations) as compared to the streamer region. This variability is particularly strong in the cool coronal emission of the 171Å bandpass. We identify the source of this variability as strong brightening events that resemble concave-up loop segments and extend from the cool prominence plasma. Magnetic field lines are the basic structural building block of the corona. Energy and pressure balance in the corona occur along magnetic field lines. The large-scale extreme ultraviolet emission we observe in the corona is a conglomerate of many coronal loops projected along a line of sight. In order to calculate the plasma properties at a particular point in the corona, we use one-dimensional models for energy and pressure balance along field lines. In order to predict the extreme ultraviolet emission along a particular line of sight, we project these one-dimensional models onto the three-dimensional magnetic configuration provided by a MHD model for the coronal magnetic field. These results have allowed us to the establish the first comprehensive picture on the magnetic and energetic interaction of the prominence and the cavity. While the originally hypothesis that the cavity supplies mass to the prominence proved inaccurate, we cannot simply say that these structures are not related. Rather our findings suggest that the prominence and the cavity are distinct magnetic substructures that are complementary regions of a larger whole, specifically a magnetic flux rope. (Abstract shortened by UMI.).

Schmit, D. J.

406

The Effect of a Corona Discharge on a Lightning Attachment  

SciTech Connect

The interaction between the lightning leader and the space charge accumulated near the top of a ground object in the atmospheric electric field is considered using analytical and numerical models developed earlier to describe spark discharges in long laboratory gaps. The specific features of a nonstationary corona discharge that develops in the electric field of a thundercloud and a downward lightning leader are analyzed. Conditions for the development of an upward lightning discharge from a ground object and for the propagation of an upward-connecting leader from the object toward a downward lightning leader (the process determining the point of strike to the ground) are investigated. Possible mechanisms for the interaction of the corona space charge with an upward leader and prospects of using it to control downward lightning discharges are analyzed.

Aleksandrov, N.L. [Moscow Institute of Physics and Technology, Institutskii pr. 9, Dolgoprudnyi, Moscow oblast, 141700 (Russian Federation); Bazelyan, E.M. [Krzhizhanovskii Rower Engineering Institute, Leninskii pr. 19, Moscow, 117927 (Russian Federation); Raizer, Yu.P. [Institute for Problems of Mechanics, Russian Academy of Sciences, pr. Vernadskogo 101, Moscow, 117526 (Russian Federation)

2005-01-15

407

Corona method and apparatus for altering carbon containing compounds  

SciTech Connect

The present invention is a method and apparatus for altering a carbon containing compound in an aqueous mixture. According to a first aspect of the present invention, it has been discovered that for an aqueous mixture having a carbon containing compound with an ozone reaction rate less than the ozone reaction rate of pentachlorophenol, use of corona discharge in a low or non-oxidizing atmosphere increases the rate of destruction of the carbon containing compound compared to corona discharge an oxidizing atmosphere. For an aqueous mixture containing pentachlorophenol, there was essentially no difference in destruction between atmospheres. According to a second aspect of the present invention, it has been further discovered that an aqueous mixture having a carbon containing compound in the presence of a catalyst and oxygen resulted in an increased destruction rate of the carbon containing compound compared to no catalyst.

Sharma, A.K.; Camaioni, D.M.; Josephson, G.B.

1999-11-09

408

Erratum: A Planet Orbiting the Star Rho Coronae Borealis:  

NASA Astrophysics Data System (ADS)

In the Letter, ``A Planet Orbiting the Star ? Coronae Borealis'' by Robert W. Noyes, Saurabh Jha, Sylvain G. Korzennik, Martin Krockenberger, Peter Nisenson, Timothy M. Brown, Edward J. Kennelly, and Scott D. Horner (ApJ, 483, L111 [1997]), a software error caused the sign of the reported radial velocity variations of ? Coronae Borealis to be reversed. This error has no effect on the period, amplitude, or eccentricity of the derived orbit and thus does not affect the main conclusion of the paper. However, the longitude ? of periastron reported in Table 1 is off by 180°, and the predicted time of a possible planetary transit Ttransit is off by approximately 1/2 period. The correct values are ? = 30° +/- 74° and Ttransit = 2,450,657.88 +/- 0.54 HJD.

Noyes, Robert W.; Jha, Saurabh; Korzennik, Sylvain G.; Krockenberger, Martin; Nisenson, Peter; Brown, Timothy M.; Kennelly, Edward J.; Horner, Scott D.

1997-10-01

409

Corona method and apparatus for altering carbon containing compounds  

DOEpatents

The present invention is a method and apparatus for altering a carbon containing compound in an aqueous mixture. According to a first aspect of the present invention, it has been discovered that for an aqueous mixture having a carbon containing compound with an ozone reaction rate less than the ozone reaction rate of pentachlorophenol, use of corona discharge in a low or non-oxidizing atmosphere increases the rate of destruction of the carbon containing compound compared to corona discharge an oxidizing atmosphere. For an aqueous mixture containing pentachlorphenol, there was essentially no difference in destruction between atmospheres. According to a second aspect of the present invention, it has been further discovered that an aqueous mixture having a carbon containing compound in the presence of a catalyst and oxygen resulted in an increased destruction rate of the carbon containing compound compared to no catalyst.

Sharma, Amit K. (Richland, WA); Camaioni, Donald M. (Richland, WA); Josephson, Gary B. (Richland, WA)

1999-01-01

410

Corona Method And Apparatus For Altering Carbon Containing Compounds  

DOEpatents

The present invention is a method and apparatus for altering a carbon-containing compound in an aqueous mixture. According to a first aspect of the present invention, it has been discovered that for an aqueous mixture having a carbon containing compound with an ozone reaction rate less than the ozone reaction rate of pentachlorophenol, use of corona discharge in a low or non-oxidizing atmosphere increases the rate of destruction of the carbon containing compound compared to corona discharge an oxidizing atmosphere. For an aqueous mixture containing pentachlorphenol, there was essentially no difference in destruction between atmospheres. According to a second aspect of the present invention, it has been further discovered that an aqueous mixture having a carbon-containing compound in the presence of a catalyst and oxygen resulted in an increased destruction rate of the carbon containing compound compared to no catalyst.

Sharma, Amit K. (Plainsboro, NJ); Camaioni, Donald M. (Richland, WA); Josephson; Gary B. (Richland, WA)

2004-05-04

411

Acoustic field effects on a negative corona discharge  

NASA Astrophysics Data System (ADS)

For a negative corona discharge under atmospheric pressure in different regimes, we investigated the effects of an acoustic field both on its electrical parameters and on the change in its visual appearance. We found that the application of an acoustic field on the true corona discharge, for particular currents, decreases the discharge voltage. The application of an acoustic field on the discharge in the filamentary streamer regime substantially extends the range of currents for which the discharge voltage remains more or less constant, i.e. it allows a substantial increase in the power delivered to the discharge. The application of an acoustic field on the discharge causes the discharge to spread within the discharge chamber and consequently, a highly reactive non-equilibrium plasma is created throughout the inter-electrode space. Finally, our experimental apparatus radiates almost no acoustic energy from the discharge chamber.

Bálek, R.; ?ervenka, M.; Pekárek, S.

2014-06-01

412

The Structure and Dynamics of the Solar Corona  

NASA Technical Reports Server (NTRS)

This report covers technical progress during the third year of the NASA Space Physics Theory contract "The Structure and Dynamics of the Solar Corona," between NASA and Science Applications International Corporation, and covers the period June 16, 1998 to August 15, 1999. This is also the final report for this contract. Under this contract SAIC, the University of California, Irvine (UCI), and the Jet Propulsion Laboratory (JPL), have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model. During the three-year duration of this contract we have published 49 articles in the scientific literature. These publications are listed in Section 3 of this report. In the Appendix we have attached reprints of selected articles. We summarize our progress during the third year of the contract. Full descriptions of our work can be found in the cited publications, a few of which are attached to this report.

Mikic, Zoran

2000-01-01

413

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

414