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

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Stability analysis of double-peaked proton distribution functions in the solar wind

Twelve proton velocity distribution functions as measured for different solar wind speeds by the plasma analyzer at the Helios spacecraft are modeled analytically by a superposition of two bi-Maxwellians. The stability of these distributions is investigated by solving the linear dispersion equation for parallel propagation of both left- and right-hand polarized modes. Due to the temperature anisotropy of the main proton component the presence of the resonant left-hand ion cyclotron instability is found to be typical for high-speed streams and is independent of an ion beam. The results indicate that the ratio of the beam density to total particle density and the beam drift velocity are generally close to the threshold values necessary to drive a highly unstable nonresonant right-hand mode. This instability is found for one proton distribution and is a consequence of the beam particles. It is concluded that both the ion cyclotron instability and the ion beam instability act as a regulating mechanism on the shape of solar wind double humped proton distribution functions.

Leubner, Manfred P.↗
NASA NTRS1976

Electromagnetic instabilities driven by unequal proton beams in the solar wind

The paper sets forth a numerical investigation of the linear dispersion relation for typical solar wind conditions at 1 AU during those times (high-speed streams) when a secondary beam of protons drifting relative to the main proton component is present. Three beam-driven instabilities were found to occur as the beam drift velocity approaches the Alfven speed: (1) a pure, field-aligned magnetosonic wave that is most important at relatively high beta and/or high beam drift speeds; (2) an oblique magnetosonic wave having highest growth rates 15-30 deg from the magnetic field; and (3) an oblique Alfven wave having maximum growth rates at increasing angle to the magnetic field. The linear growth rates for the field-aligned magnetosonic and the Alfven oblique modes are investigated as a function of relative beam density, varying anisotropic pitch angle distributions for the various components, electron temperature, and electron heat flux.

Montgomery, M. D.↗
NASA NTRS1972

Solar wind interaction with Comet Bennett (1969i

The relations are examined between the solar-wind and Comet Bennett during the period 23 March to 5 April 1970. A large kink was observed in the ion tail of the comet on April 4, but no solar wind stream was observed in the ecliptic plane which could have caused the kink. Thus, either there was no correlation between the solar wind at the earth and that at Comet Bennett (which was 40 deg above the ecliptic) or the kink was caused by something other than a high-speed stream. The fine structure visible in photographs of the kink favors the second of these alternatives. It is shown that a shock probably passed through Comet Bennett on March 31, but no effect was seen in photographs of the comet. A stream preceded by another shock and a large abrupt change in momentum flux might have intercepted the comet between 24 March and 28 March, but again no effect was seen in photographs of the Comet. In view of these results, the possibility must be considered that a large, abrupt change in momentum flux of the solar-wind is neither necessary nor sufficient to cause a large kink in a comet tail.

Burlaga, L. F.↗
NASA NTRS1973

Solar wind interaction with Comet Bennett /1969i/.

Examination of the relations between the solar-wind and Comet Bennett during the period from Mar. 23 to Apr. 5, 1970. A large kink was observed in the ion tail of the comet on April 4, but no solar-wind stream was observed in the ecliptic plane which could have caused the kink. Thus, either there was no correlation between the solar wind at the earth and that at Comet Bennett (which was 40 deg above the ecliptic) or the kink was caused by something other than a high-speed stream. The fine structure visible in photographs of the kink favors the second of these alternatives. It is shown that a shock probably passed through Comet Bennett on March 31, but no effect was seen in photographs of the comet. A stream preceded by another shock and a large abrupt change in momentum flux might have intercepted the comet between March 24 and March 28, but again no effect was seen in photographs of the Comet.

Burlaga, L. F.↗
NASA NTRS2003

CMEs, the Tail of the Solar Wind Magnetic Field Distribution, and 11-yr Cosmic Ray Modulation at 1 AU

Using a recent classification of the solar wind at 1 AU into its principal components (slow solar wind, high-speed streams, and coronal mass ejections (CMEs) for 1972-2000, we show that the monthly-averaged galactic cosmic ray intensity is anti-correlated with the percentage of time that the Earth is imbedded in CME flows. We suggest that this correlation results primarily from a CME related change in the tail of the distribution function of hourly-averaged values of the solar wind magnetic field (B) between solar minimum and solar maximum. The number of high-B (square proper subset 10 nT) values increases by a factor of approx. 3 from minimum to maximum (from 5% of all hours to 17%), with about two-thirds of this increase due to CMEs. On an hour-to-hour basis, average changes of cosmic ray intensity at Earth become negative for solar wind magnetic field values square proper subset 10 nT.

Cliver, E. W.↗
NASA NTRS1994

Neutral hydrogen in the solar wind acceleration region

Observation of solar Ly alpha radiation scattered by coronal neutral hydrogen atoms can be used to investigate the acceleration region of the solar wind. In this paper we focus on the use of these observations to study Alfven waves, which can accelerate the solar wind plasma to flow speeds observed in high-speed streams if their amplitude at the coronal base is 20 km/s or larger. The wave amplitude is then larger than the proton thermal speed in the outer corona, so that the mean proton speed (averaged over a wave period) is significantly larger than the proton thermal speed. For low-frequency wave the hydrogen atoms follow the proton motion in the waves, while for higher frequencies the protons move relative to the neutrals. Nevertheless, in the higher frequency case, the rates for charge exchange and recombination are high enough to broaden the velocity distribution function of neutral hydrogen. Both the wave motion of the hydrogen atoms in low-frequency Alfven waves and the 'heating' by higher frequency waves lead to a broadening of the scattered solar Ly alpha line. For coronal base amplitues of 20 km/s, the line broadening increases with heliocentric distance beyond 4-5 solar radii.

Olsen, Espen Lyngdal↗
NASA NTRS1987

The joint NASA/Goddard-University of Maryland research program in charged particle and high energy photon detector technology

The first measurements of Fe charge states in two coronal hole-association high speed streams, using the sensor on ISEE-3, are presented. Eight event intervals from the January to June 1983 timeframe were chosen for the study of magnetotail dynamics and its relationship to substorm activity and the possible formation of plasmoids. Techniques are being explored for measurement of secondary electrons which are characteristically emitted when ions hit a target material. Efforts are continuing to understand kilometer wavelength shock associated radio events. An all-sky survey of fast X-ray transients of duration of 5 to 10,000 s was completed. Research using high resolution gamma-ray spectroscopy of celestial sources in the 20 keV to 20 MeV range to search for and study narrow lines in low-energy gamma-ray spectrum continues. Research in high energy radiation from pulsars is being conducted.

Source record↗
NASA NTRS1996

The Distant Tail Behavior During High Speed Solar Wind Streams and Magnetic Storms

We have examined the ISEE-3 distant tail data during three intense (Dst< -100(sub n)T) magnetic storms and have identified the tail response to high speed solar wind streams, interplanetary magnetic clouds, and near-Earth storms. The three storms have a peak Dst ranging from -150 to -220 nT, and occur on Jan. 9, Feb. 4, and Aug. 8, 1993.

ISEE-3 solar wind streams solar wind magnetic clou↗
NASA NTRS2008

The Bess Investigation of the Origin of Cosmic-ray Antiprotons and Search for Cosmological Antimatter

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) collaboration has made precise measurements of the spectra of cosmic ray antiprotons and light nuclei and conducted a sensitive search for antinuclei. Ten BESS high-latitude flights, eight from Canada and two from Antarctica, span more than a Solar cycle between 1993 and 2007/2008. BESS measurements of low-energy antiprotons constrain candidate models for dark matter including the possible signature of primordial black hole evaporation. The stringent BESS measurements of antiprotons and the elemental and isotopic spectra of H and He provide strong constraints on models of cosmic-ray transport in the Galaxy and Solar System. BESS has also reported the first antideuterium upper limit. BESS employs a superconducting magnetic-rigity spectrometer with time-of-flight and aerogel Cherenkov detectors to identify incident particles by charge, charge sign, mass, and energy. The BESS-Polar long-duration instrument has reduced lower energy limit of 100 MeV (top of the atmosphere) to increase its sensitivity to possible primary antiproton sources. BESS-Polar II was rebuilt with extended magnet lifetime, improved detector and electronic performance, and greater data storage capacity. It was flown fro Antarctica December 2007-January 2008, recording about 4.6 bission events during 24.5 days at float altitude with the magnet on. During the flight the influence of a high-speed stream in the Solar wind was observed. Details of the BESS-Polar II instrument and flight performance are reported elsewhere at this conference. The successful BESS-Polar II flight at Solar minimum is especially important. Most cosmic-ray antiprotons are secondary products of nuclear interactions of primary cosmic-ray nuclei with the interstellar gas, giving a spectrum that peaks at about 2 GeV and falls rapidly to higher and lower energies. However, BESS data taken in the previous Solar minimum show a small excess over secondary expectations at low energies, possibly suggesting the presence of an additional component that may be masked at higher levels of Solar modulation. The high-statistics Solar minimum data obtained by BESS-Polar II will provide a difinitive test of this component. We will review the BESS program and report the latest results including the antiproton and proton spectra measured in the BESS-Polar I flight, the search for cosmic antinuclei, and the status of the BESS-Polar II analysis.

Mitchell, John↗
NASA NTRS2024

Unveiling the Journey of A Highly Inclined CME: Insights from the March 13, 2012, Event With 110° Longitudinal Separation

Context. A fast (∼2000 km s -1 ) and wide (>110°) coronal mass ejection (CME) erupted from the Sun on March 13, 2012. Its interplanetary counterpart was detected in situ two days later by STEREO-A and near-Earth spacecraft, such as ACE, Wind, and Cluster. We suggest that at 1 au the CME extended at least 110° in longitude, with Earth crossing its east flank and STEREO-A crossing its- west flank. Despite their separation, measurements from both positions showed very similar in situ CME signatures. The solar source region where the CME erupted was surrounded by three coronal holes (CHs). Their locations with respect to the CME launch site were east (negative polarity), southwest (positive polarity) and west (positive polarity). The solar magnetic field polarity of the area covered by each CH matches that observed at 1 au in situ. Suprathermal electrons at each location showed mixed signatures with only some intervals presenting clear counter streaming flows as the CME transits both locations. The strahl population coming from the shortest magnetic connection of the structure to the Sun showed more intensity. Aims. The aim of this work is to understand the propagation and evolution of the CME and its interaction with the surrounding CHs, to explain the similarities and differences between the observations at each spacecraft, and report what one of the most longitudinal expanded CME structures measured in situ would be. Methods. Known properties of the large-scale structures from a variety of catalogues and previous studies were used to have a better overview of this particular event. In addition, multipoint observations were used to reconstruct the 3D geometry of the CME and determine the context of the solar and heliospheric conditions before the CME eruption and during its propagation. The graduated cylindrical shell model (GCS) was used to reproduce the orientation, size and speed of the structure with a simple geometry. Also, the Drag-Based Model (DBM) was utilised to understand the conditions of the interplanetary medium better in terms of the drag undergone by the structure while propagating in different directions. Finally, a comparative analysis of the different regions of the structure through the different observatories was carried out in order to directly compare the in situ plasma and magnetic field properties at each location. Results. The study presents important findings regarding the in situ measured CME on March 15, 2012, detected at a longitudinal separation of 110° in the ecliptic plane despite its initial inclination being around 45° when erupted (March 13). This suggests that the CME may have deformed and/or rotated, allowing it to be observed near its legs with spacecraft at a separation angle greater than 100°. The CME structure interacted with high-speed streams generated by the surrounding CHs. The piled-up plasma in the sheath region exhibited an unexpected correlation in magnetic field strength despite the large separation in longitude. In situ observations reveal that at both locations there was a flank encounter – where the spacecraft crossed the first part of the CME – then encountered ambient solar wind, and finally passed near the legs of the structure. Conclusions. A scenario covering all evidence is proposed for both locations with a general view of the whole structure and solar wind conditions. Also, the study shows the necessity of having multipoint observations of large-scale structures in the heliosphere.

methods: data analysis↗
NASA NTRS1994

Ulysses near-ecliptic observations of differential flow between protons and alphas in the solar wind

The evolution of differential streaming between protons and alpha particles in the solar wind was observed with the solar wind plasma experiment on the Ulysses spacecraft over the solar range of 1.15 to 5.40 AU between November 18, 1990, and May 5, 1992. The correlation of the difference in ion speeds, Delta V = the absolute value of V(sub alpha) - the absolute value of V(sub p), with the proton speed V(sub p) observed by other spacecraft at solar distances less than or equal to 1 AU disappeared at approximately 2 AU. At solar distances greater than or equal to 2.85 AU, the largest values of both V(sub alpha p) = the absolute value of V(sub alpha p) = the absolute value of V(sub alpha) - V(sub p) and the absolute value of Delta V were found in the interaction regions on the leading edges of high-speed streams. The differential streaming was typically enhanced just downstream of strong forward and reverse shocks, and large negative values of Delta V were frequently encountered in the interaction regions. A correlation between V(sub alpha p) and the ratio tau(sub zero)/tau(sub e) of Coulomb collision time to expansion time was observed at all distances, but it is suggested that at the larger values of tau(sub zero)/tau(sub e) observed correlation may arise from enhanced production of differential streaming by processes that also increase the entropy of the solar wind protons.

Neugebauer, M.↗
NASA NTRS1981

Thermal iron ions in high speed solar wind streams. II - Temperatures and bulk velocities

Mitchel and Roelof (1980) reported the detection of iron in high speed solar wind flows using the small, but finite sensitivity of solid state detectors to Fe ions in the low energy (50-200 keV protons) L1 channel of the NOAA/JHU energetic particle experiment (EPE). In the current investigation, the EPE response is modeled to a convected Maxwellian to obtain the thermal velocity, flow angle, and bulk velocity of the iron distribution. It is assumed that the iron bulk flow velocity can be represented as a vector sum of the hydrogen bulk velocity and an interplanetary magnetic field (IMF) aligned velocity increment. It is found that the velocity increment is smaller than the local Alfven speed in magnitude, and that the iron thermal velocity is comparable with or greater than the proton thermal velocity, with the 'thermal' velocity defined as the square root of 2kT/m.

Mitchell, D. G.↗
NASA NTRS1974

Shapes of strong shock fronts in an inhomogeneous solar wind

The shapes expected for solar-flare-produced strong shock fronts in the solar wind have been calculated, large-scale variations in the ambient medium being taken into account. It has been shown that for reasonable ambient solar wind conditions the mean and the standard deviation of the east-west shock normal angle are in agreement with experimental observations including shocks of all strengths. The results further suggest that near a high-speed stream it is difficult to distinguish between corotating shocks and flare-associated shocks on the basis of the shock normal alone. Although the calculated shapes are outside the range of validity of the linear approximation, these results indicate that the variations in the ambient solar wind may account for large deviations of shock normals from the radial direction.

Heinemann, M. A.↗
NASA NTRS1974

The reliability of the daily quick look solar wind velocities as indicators of interplanetary activity

It is shown that the daily quick look solar wind velocities based on the Ames Research Center solar wind plasma data obtained on the Pioneer spacecraft are surprisingly reliable indicators of interplanetary activity. These velocities can appropriately be used in correlation studies with an average accuracy of plus or minus 5%. This accuracy reflects the 'jitter' in the solar wind velocity during quiescent intervals and across high-speed streams.

Intriligator, D. S.↗
NASA NTRS1974

Solar coronal holes as sources of recurrent geomagnetic disturbances

Observations of the solar corona by Oso 7 have been used in a superposed epoch analysis to study the relationships between classes of coronal features and geomagnetic activity. Both bright coronal regions and regions of less than average brightness were investigated. It was found that for the period from January 1972 through January 1973, a significant enhancement in geomagnetic activity occurred 2-3 days after central meridian passage of large coronal holes that extended to within 5 deg of the solar subearth point when they were on the meridian. Large coronal holes appear to satisfy the requirements for 'M regions' which were hypothesized to be responsible for recurrent geomagnetic disturbances (Bartels, 1934). If solar wind high-speed streams originate preferentially in these regions, their velocity at the base of the corona will be substantially higher than that expected from an axisymmetric solar wind model.

Neupert, W. M.↗
NASA NTRS1977

Interplanetary current sheets at 1 AU

The structure and nature of 'discontinuities' in the interplanetary magnetic field at 1 AU in the period from March 18 to April 9, 1971, is determined by using high-resolution magnetic-field measurements from Explorer 43. The discontinuities that were selected for this analysis occurred under a variety of interplanetary conditions at an average rate of 0.5/hour. Both tangential and rotational discontinuities were identified. Tangential discontinuities were observed every day, even among Alfvenic fluctuations. In particular, on one day during which Alfvenic fluctuations were intense and persistent in a high-speed stream, tangential discontinuities (TD's) were seen throughout the day at an average rate of 0.5/hour; rotational discontinuities (RD's) were also observed during this day at a higher than usual rate, the ratio of TD's to RD's being approximately one. The structure of most of the current sheets was simple and ordered; i.e., the magnetic field usually changed smoothly and monotonically from one side of the current sheet to the other. The thickness distributions of the TD's and RD's with very smooth current sheets were similar. The average thickness of the RD's was 1200 km (13 proton Larmor radii), and the average thickness of the TD's was 1300 km (12 proton Larmor radii).

Burlaga, L. F.↗