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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

What causes the warp in the heliospheric current sheet

A comparative discussion of the warp in the heliospheric current sheet is presented. Pioneer 10 and 11 data of the interplanetary magnetic field compared with earlier data (Helios 1 and 2) show a good agreement on the phenomenon of the warp; however, the interpretations differ. One theory (Thomas and Smith, 1980) proposes that fast solar wind streams associated with interaction regions may move the current sheet higher to heliospheric latitudes, thus causing the warp; while the earlier theory (1976) adequately explained the phenomenon by using the observed photospheric magnetic field and the Zeeman effect but omitted the solar wind dynamical considerations as part of the computations. It is shown that the Helios data of the polarity of the interplanetary magnetic field are in good agreement with the computed location of the current sheet, confirming the earlier theory.

Wilcox, J. M.↗
NASA NTRS1983

The effect of the solar field reversal on the modulation of galactic cosmic rays

There is now a growing awareness that solar cycle related changes in the large-scale structure of the interplanetary magnetic field (IMF) may play an important role in the modulation of galactic cosmic rays. To date, attention focussed on two aspects of the magnetic field structure: large scale compression regions produced by fast solar wind streams and solar flares, both of which are known to vary in intensity and number over the solar cycle, and the variable warp of the heliospheric current sheet. It is suggested that another feature of the solar cycle is worthy of consideration: the field reversal itself. If the Sun reverses its polarity by simply overturning the heliospheric current sheet (northern fields migrating southward and vice-versa) then there may well be an effect on cosmic ray intensity. However, such a simple picture of solar reversal seems improbable. Observations of the solar corona suggest the existence of not one but several current sheets in the heliosphere at solar maximum. The results of a simple calculation to demonstrate that the variation in cosmic ray intensities that will result can be as large as is actually observed over the solar cycle are given.

Thomas, B. T.↗
NASA NTRS1995

Ulysses magnetic field observations of fluctuations within polar coronal flows

The Ulysses spacecraft has gathered data from within flows from the Sun's southern polar coronal hole, the first in situ measurement of this region. We present a brief analysis of the heliospheric magnetic field data from this region, using a fractal method. As is the case near the ecliptic, estimated spectral exponents are near 5/3 on spacecraft scales of seconds to minutes. On longer time scales, however, there appears to be a significantly different population in polar flows, which is similar to that found by the Helios spacecraft in fast solar wind flows at 0.3 AU.

Horbury, T.↗
NASA NTRS1997

UVCS/SOHO empirical models of solar coronal holes

A self-consistent empirical model for the major plasma parameters in a solar-minimum coronal hole was developed using the ultraviolet coronagraph spectrometer (UVCS) operating onboard the Solar and Heliospheric Observatory (SOHO). The radial and latitudinal distribution of density, velocity, and kinetic temperature for electrons, neutral hydrogen, and ionized oxygen was obtained. The data were acquired during November 1996 and April 1997. The model provides experimental values which can be used to constrain theoretical models of the fast solar wind. The implications on various models of coronal heating and acceleration are discussed.

Cranmer, S. R.↗
NASA NTRS1999

Microwave Enhancement in Coronal Holes: Structure, Variability and Magnetic Nature

The microwave enhancement in coronal holes in comparison with the quiet Sun is a distinct and easily observed signature related to the magnetic activity. This has proven to be a new tool to study the solar atmospheric layer where the fast solar wind originates. We have developed a catalog of a large number of coronal holes using images obtained by SOHO's Extreme-ultraviolet Imaging Telescope in EUV and by the Nobeyama radioheliograph in microwaves. We also have high resolution longitudinal magnetograms obtained by SOHO's Michelson Doppler Imager. We present the statistical properties of the microwave enhancements and discuss the small-scale dynamics as revealed by the magnetograms and radioheliograms. We also discuss the geoeffectiveness of these coronal holes.

Gopalswamy, N.↗
NASA NTRS2001

Relation Between Pressure Balance Structures and Polar Plumes from Ulysses High Latitude Observations

Ulysses observations have shown that pressure balance structures (PBSs) are a common feature in high-latitude, fast solar wind near solar minimum. Previous studies of Ulysses/SWOOPS plasma data suggest these PBSs may be remnants of coronal polar plumes. Here we find support for this suggestion in an analysis of PBS magnetic structure. We used Ulysses magnetometer data and applied a minimum variance analysis to discontinuities. We found that PBSs preferentially contain tangential discontinuities, as opposed to rotational discontinuities and to non-PBS regions in the solar wind. This suggests that PBSs contain structures like current sheets or plasmoids that may be associated with network activity at the base of plumes.

Yamauchi, Y.↗
NASA NTRS2003

Exploration of the Characteristics of the Time Variable Component of the Coronal Heating Process

By coordinating coronal SOHO observations in white light, ultraviolet, extreme ultraviolet, with radio occultation measurements, and complementing these with modeling, two break-throughs were achieved from this funding: (1) The discovery that minor ions are accelerated much faster than protons in the fast solar wind, and (2) that the imprint of coronal density structures is carried outwards from the Sun into the solar wind. Three refereed papers and one invited review, published in the proceedings of the conference, resulted from this funding. A summary of each is given.

Wagner, William↗
NASA NTRS2002

Relation between Pressure Balance Structures and Polar Plumes from Ulysses High Latitude Observations

Ulysses observations have shown that pressure balance structures (PBSs) are a common feature in high-latitude, fast solar wind near solar minimum. Previous studies of Ulysses/SWOOPS plasma data suggest these PBSs may be remnants of coronal polar plumes. Here we find support for this suggestion in an analysis of PBS magnetic structure. We used Ulysses magnetometer data and applied a minimum variance analysis to magnetic discontinuities in PBSs. We found that PBSs preferentially contain tangential discontinuities, as opposed to rotational discontinuities and to non-PBS regions in the solar wind. This suggests that PBSs contain structures like current sheets or plasmoids that may be associated with network activity at the base of plumes.

Yamauchi, Yohei↗
NASA NTRS2004

Interpretive Tools for Analysis of Coronal Images

Contents include list of publications resulting from grant: Magneto-Hydrodynamic Model of the Solar Corona and Interplanetary Medium. Coronal magnetic field topology and source of fast solar wind. Geophysical Importance of Global Magnetic Field Geometry and Density Distribution in Solar Wind Modeling. Empirical Model of the Corona-Solar Wind with Multiple Current Sheets. Model of the Solar Wind and its Comparison with ULYSSES. Physical properties of a coronal hole from a coronal diagnostic spectrometer, Mauna Loa Coronagraph, and LASCO observations during the Whole Sun Month. Semi-Empirical 2-D MHD Model of the Solar corona and Solar Wind: Energy Flow in the Corona. Source Region of High and Low Speed Wind during the Spartan. Three-dimensional coronal density structure. Cone Model for Halo CME's: Application to Space Weather Forecasting.

Ofman, Leon↗
NASA NTRS2004

Physical Properties of a Coronal Hole from a Coronal Diagnostics Spectrometer, Mauna Loa Coronagraph, and LASCO Observations during the Whole Sun Month

Until recently, inference of electron density distribution in the solar corona was limited by the field of view of white-light coronagraphs (typically out to 6 Rs). Now, for the first time we have a series of white- light coronagraphs (SOHO/LASCO) whose combined field of view extends from 1.1 - 30 Rs. Quantitative information on electron density distribution of coronal hole and coronal plumes/rays are estimated by using white-light, polarized brightness (pB) observations from the SOHO/LASCO/C2 and C3 and HAO/Mauna Loa Mark III coronagraphs from 1.15 to 8.0 Rs. Morphological information on the boundary of the polar coronal hole and streamer interface is determined from the white-light observations in a manner similar to the Skylab polar coronal hole boundary estimate. The average coronal hole electron density in the region 1 - 1.15 Rs is estimated from the density-sensitive EUV line ratios of Si IX 3501342 A observed by the SOHO/coronal diagnostic spectrometer (CDS). We combine these numbers with the estimate from white-light (WL) observations to obtain a density profile from 1 to 8 Rs for the plumes and the polar coronal hole. We find that white light and spectral analysis produce consistent density information. Extrapolated densities inferred from SOHO observations are compared to Ulysses in situ observations of density. Like the density inferred from the Spartan 201-03 coronagraph, the current SOHO density profiles suggest that the acceleration of the fast solar wind takes place very close to the Sun, within 10-15 Rs. The density information is used to put constraints on solar wind flow velocities and effective temperatures. Finally, these results are compared to the recent analysis of the Spartan 201-03 white-light observations.

Guhathakurta, M.↗
NASA NTRS2004

Magnetic Fields and Flows in Open Magnetic Structures

Open magnetic structures connect the solar surface to the heliosphere and are thus of great interest in solar-terrestrial physics. This talk is primarily an observational review of what is known about magnetic fields and particularly flows in such regions with special focus on coronal holes and origins of the fast solar wind. First evidence of the connection between these two features was seen in correlations of Skylab data with in situ measurements of the solar wind soon after the discovery of coronal holes, which are now known to emanate from unipolar magnetic regions at the photosphere. Subsequently many observations of have been made, ranging from oscillations in the underlying photosphere and chromosphere, to possible beginnings of the solar wind as observed by Doppler shifts in high chromospheric and transition-region lines, to coronagraphic time-lapse studies of outward-moving blobs of material which perhaps trace elements of solar-wind plasma. Some of the many unresolved and controversial issues regarding details of these observations and their association with the solar wind will be discussed.

Jones, Harrlson P.↗
NASA NTRS2016

Plasma Deflection Test Setup for E-Sail Propulsion Concept

The Electronic Sail or E-Sail is a novel propulsion concept based on momentum exchange between fast solar wind protons and the plasma sheath of long positively charged conductors comprising the E-Sail. The effective sail area increases with decreasing plasma density allowing an E-Sail craft to continue to accelerate at predicted ranges well beyond the capabilities of existing electronic or chemical propulsion spacecraft. While negatively charged conductors in plasmas have been extensively studied and flown, the interaction between plasma and a positively charged conductor is not well studied. We present a plasma deflection test method using a differential ion flux probe (DIFP). The DIFP measures the angle and energy of incident ions. The plasma sheath around a charged body can measured by comparing the angular distribution of ions with and without a positively charged test body. These test results will be used to evaluate numerical calculations of expected thrust per unit length of conductor in the solar wind plasma. This work was supported by a NASA Space Technology Research Fellowship.

Andersen, Allen↗
NASA NTRS2018

Long-Term Solar Activity Studies Using Microwave Imaging Observations and Prediction for Cycle 25

We use microwave imaging observations from the Nobeyama Radioheliograph at 17 GHz for long-term studies of solar activity. In particular, we use the polar and low-latitude brightness temperatures as proxies to the polar magnetic field and the active-regions, respectively. We also use the location of prominence eruptions as a proxy to the filament locations as a function of time. We show that the polar microwave brightness temperature is highly correlated with the polar magnetic field strength and the fast solar wind speed. We also show that the polar microwave brightness at one cycle is correlated with the low latitude brightness with a lag of about half a solar cycle. We use this correlation to predict the strength of the solar cycle: the smoothed sunspot numbers in the southern and northern hemispheres can be predicted as 89 and 59, respectively. These values indicate that cycle 25 will not be too different from cycle 24 in its strength. We also combined the rush to the pole data from Nobeyama prominences with historical data going back to 1860 to study the north-south asymmetry of sign reversal at solar poles. We find that the reversal asymmetry has a quasi-periodicity of 3-5 cycles.

N. Gopalswamy↗
NASA NTRSDate not supplied

Direct Evidence for the Dynamic Chromospheric Origin of Solar Coronal Plumes

Coronal plumes are long ray-like open structures in coronal holes, and have been considered as possible sources for the fast solar wind. Their origin in the largely unipolar coronal holes has long been a mystery. Earlier spectroscopic and imaging observations have revealed blue-shifted plasma and propagating disturbances (PDs) in plumes that are widely interpreted in terms of flows and/or propagating slow-mode waves, but these interpretations (flows vs waves)are under debate. Recently we discovered an important clue about plume internal structure: dynamic filamentary features called “plumelets”, which account for most of the plume emission. Here we present high-resolution observations from SDO/AIA and IRIS that revealed numerous quasiperiodic tiny jets (so-called “jetlets") associated with transient brightening and plasma heating at the chromospheric footpoints of the plumelets. By analogy to larger coronal jets, these jetlets are most likely produced within the plume base by magnetic reconnection between closed and open flux at a stressed 3D null point. The jetlet-associated brightenings are in phase with plumelet-associated PDs, and vary with a period of ∼3 to 5 minutes, which is remarkably consistent with the photospheric/chromospheric p-mode oscillation. This reconnection at the open-closed boundary in the chromosphere/transition region is likely modulated or driven by local manifestations of the global p-mode waves. We discuss how these quasiperiodic jetlets extend upward to become plumelets, contribute mass to the solar wind, and may be sources of switchbacks recently detected by the Parker Solar Probe.

Pankaj Kumar↗
NASA NTRS1987

The Giotto three-dimensional positive ion analyser

An instrument to measure the three-dimensional energy distribution of positive ions in order to study the interaction between the solar wind and ionized Halley cometary particles was designed. Two sensors measure the distribution from 10 eV to 20 keV once per spacecraft spin and the distribution from 90 eV to 90 keV, with coarse mass discrimination, once every 32 spins. The instrument was turned on September 8, 1985. The performance throughout all testing was nominal. The spacecraft was greater than 10 million km from the earth in the solar wind. The only population identified is the solar wind. The Fast Ion Sensor follows solar wind variations with its autoranging capability. The Implanted Ion Sensor identifies higher mass ions such as O(6+) and O(5+) in the solar wind.

Johnstone, A. D.↗
NASA NTRS1978

ISEE-1 and ISEE-2 fast plasma experiment and the ISEE-1 solar wind experiment

Identical fast plasma experiment (FPE) systems were placed on the ISEE-1 and ISEE-2 spacecraft. The FPE consists of three high efficiency 90 deg spherical section electrostatic analyzers using large secondary emitters and discrete dynode multipliers to detect analyzed particles. Two of them, viewing in opposite directions, produce complete 2D velocity distribution measurements of both protons and electrons every spacecraft revolution. A third FPE analyzer with a divided emitter measures 3D distributions at a slower rate. ISEE-1 also carries a solar-wind experiment (SWE) to measure solar-wind ions with high resolution. The SWE is composed of two 150 deg spherical section analyzers using the same set of plates. The two acceptance fans are tilted with respect to each other so that 3D characteristics of the ion distributions can be derived.

Bame, S. J.↗
NASA NTRS2008

Variations of Strahl Properties with Fast and Slow Solar Wind

The interplanetary solar wind electron velocity distribution function generally shows three different populations. Two of the components, the core and halo, have been the most intensively analyzed and modeled populations using different theoretical models. The third component, the strahl, is usually seen at higher energies, is confined in pitch-angle, is highly field-aligned and skew. This population has been more difficult to identify and to model in the solar wind. In this work we make use of the high angular, energy and time resolution and three-dimensional data of the Cluster/PEACE electron spectrometer to identify and analyze this component in the ambient solar wind during high and slow speed solar wind. The moment density and fluid velocity have been computed by a semi-numerical integration method. The variations of solar wind density and drift velocity with the general build solar wind speed could provide some insight into the source, origin, and evolution of the strahl.

Figueroa-Vinas, Adolfo↗
NASA NTRS1995

Very long baseline IPS observations of the solar wind speed in the fast polar streams

Observations of intensity scintillation (IPS) with two or more spaced antennas have been widely used to measure the solar wind velocity. Such methods are particularly valuable in regions which spacecraft have not yet penetrated, but they are also very useful in improving the spatial temporal sampling of the solar wind, even in regions where spacecraft data are available. The principle of the measurement is to measure the time delay tau(sub d) between the scintillations observed with an antenna baseline b. The velocity estimate is just V = b/tau(sub d). The error in estimation of the time delay delta tau(sub d) is independent of the baseline length, thus the error in the velocity estimate delta V given by delta(V)/V approximately equals to (delta tau(sub d))/tau(sub d) is inversely proportional to tau(sub d) and hence to b. However the use of a long baseline b has a less obvious advantage; it provides a means for separating fast and slow contributions when both are present in the scattering region. Here we will present recent observations made using the large cylinder antenna at Ooty in the Nilgiri Hills of South India, and one of the 45 m dishes of GMRT near Pune in West-Central India. The baseline of 900 km is, by a considerable margin, the longest ever used for IPS and provides excellent velocity resolution. These results compared with the ULYSSES observations and other IPS measurements made closer to the sun with higher frequency instruments such as EISCAT and the VLBA will provide a precise measure of the velocity profile of the fast north-polar stream.

Rao, A. Pramesh↗