SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Interplanetary medium and pulsed solar plasma streams electron number density, structure and behavior determined with radio propagation measurements by Pioneer spacecraft
The paper surveys topics related to the origin, expansion, and acceleration of the solar wind and the plasma physics of the interplanetary medium. The study of the relationship between coronal holes and solar-wind streams, and the associated revision of ideas about solar wind acceleration and heating are reviewed. In addition, topics of hydromagnetic waves and turbulence, and interplanetary electrons, as items of particular importance during the past quadrennium, are discussed. While the research discussed was concerned with data taken near solar minimum, further solar-wind studies will concentrate on observations from the rising and maximum phases of the solar cycle.
The longitudinal distribution of cosmic ray intensity was examined during the years 1974-1976 when the persistent high speed solar wind stream structures produced a well ordered inner heliosphere. Solar wind velocity is mapped back to the Sun and compared with cosmic ray intensity which is represented relative to the solar rotation average. Low solar wind velocity is observed to be a necessary, but not sufficient, condition for the occurrence of higher cosmic ray intensities at 1 AU. These relative enhancements cover a restricted range of heliographic longitudes and persist for several solar rotations. The observed solar wind and cosmic ray intensity relationships are consistent with a simple model suggested here in which cosmic ray modulation is very weak in the inner heliosphere, sunward of the first shock crossing on each field line and more intense in the outer heliosphere.
A unified interpretation of observations of interplanetary fluctuations is presented in terms of nearly incompressible magnetohydrodynamics. Incompressive effects explain the rapid evolution of turbulence in slow wind containing the heliospheric current sheet. The relative constancy of the spectrum of 'inward propagating' fluctuations compared to the rapid decline in 'outward' fluctuations results from incompressive spectral transfer combined with strong dissipation of the outward fluctuations. Secondary compressive effects account for nearly pressure-balanced structures and the density fluctuation levels.
The level of geomagnetic activity near the time of solar activity minimum has been shown to be a reliable indicator for the amplitude of the following solar activity maximum. The geomagnetic activity index aa can be split into two components: one associated with solar flares, prominence eruptions, and coronal mass ejections which follows the solar activity cycle and a second component associated with recurrent high speed solar wind streams which is out of phase with the solar activity cycle. This second component often peaks before solar activity minimum and has been one of the most reliable indicators for the amplitude of the following maximum. The size of the recent maximum in this second component indicates that solar activity cycle 24 will be much higher than average - similar in size to cycles 21 and 22.
The level of geomagnetic activity near the time of solar activity minimum has been shown to be a reliable indicator for the amplitude of the following solar activity maximum. The geomagnetic activity index aa can be split into two components: one associated with solar flares, prominence eruptions, and coronal mass ejections which follows the solar activity cycle and a second component associated with recurrent high speed solar wind streams which is out of phase with the solar activity cycle. This second component often peaks before solar activity minimum and has been one of the most reliable indicators for the amplitude of the following maximum. The size of the recent maximum in this second component indicates that solar activity cycle 24 will be much higher than average - similar in size to cycles 21 and 22 with a peak smoothed sunspot number of 160 plus or minus 25.
Solar wind data obtained with ion mass-energy-spectrometer on the Prognoz 7 satellite are analyzed to study the alpha-particle and proton features in different types of solar wind streams. In the streams from coronal holes the abundance of helium relative to proton slightly increases with increasing solar wind flux and proton density while in the streams from coronal streamers it decreases. These results indicate that the mechanisms of solar wind formation in different regions of solar corona differ. Preferential alpha-particle acceleration and heating are often observed in the streams from coronal holes. Minimum (as well as negative) values of alpha-proton velocity difference are recorded in the heliospheric current sheet, shocked plasma, and coronal mass ejections. Dependences of alpha-proton velocity difference and temperature ratio on several MHD parameters (Alfven velocity, number of Coulomb collisions. etc.) are compared for different types of streams. For velocity difference the dependences in streams from coronal holes and streamers are often similar to each other, and they differ from the ones in the heliospheric current sheet. For temperature ratio the dependences in heliospheric current sheet and streams from coronal streamers are similar, and they differ in streams from coronal holes.
Relation between high velocity plasma streams and solar active regions and data on plasma velocity and temperature obtained from Mariner II SPACECRAFT
This paper addresses specific questions derived from this more general question. How has the structure associated with fast and slow solar wind streams adn their interactions been affected.?.
Electron drainage currents from dilute streaming plasmas to positively biased silicon and cadmium sulfide solar cell arrays
A physically-based strategy for the prediction of geomagnetic/ionospheric disturbances, the Solar-Terrestrial/Environmental Model (STEM 2000), is proposed, with application to the prediction of periods of spacecraft charging. Synoptic solar observations provide input for MHD models for flare occurrence, propagation of coronal disturbances, and high speed solar wind streams. A three-dimensional interplanetary MHD model determines solar wind parameters including the energy flux and the cross-magnetosphere tail electric field. Observational earth data are used to predict local time, high latitude ionospheric disturbances which have an impact on the ionospheric structure.
During the summer of 1979, solar corona structure was such that a sequence of recurrent regions produced a corresponding sequence of corotating solar wind streams with pronounced downstream signatures. One of these stream events passed earth on July 3 and was observed later at Venus late on July 11th, with similar characteristics. Corresponding in situ measurements at earth from the Atmospheric Explorer-E satellite and at Venus from the Pioneer Venus Orbiter are examined for evidence of comparable perturbations of the planetary ionospheres. The passage of the stream shock front is found to be associated with pronounced fluctuations in n(O+) which appear as pronounced local depletion of ion concentrations in both ionospheres. The ionosphere disturbances appear to be closely associated with large variations in the solar wind momentum flux. The implied local ionospheric depletions observed at each planet are interpreted to be the consequence of plasma redistribution, rather than actual depletions of plasma.
A hybrid stream PCRTM-SOLAR model has been proposed for fast and accurate radiative transfer simulation. It calculates the reflected solar (RS) radiances with a fast coarse way and then, with the help of a pre-saved matrix, transforms the results to obtain the desired high accurate RS spectrum. The methodology has been demonstrated with the hybrid stream discrete ordinate (HSDO) radiative transfer (RT) model. The HSDO method calculates the monochromatic radiances using a 4-stream discrete ordinate method, where only a small number of monochromatic radiances are simulated with both 4-stream and a larger N-stream (N ≥ 16) discrete ordinate RT algorithm. The accuracy of the obtained channel radiance is comparable to the result from N-stream moderate resolution atmospheric transmission version 5 (MODTRAN5). The root-mean-square errors are usually less than 5x10(exp -4) mW/sq cm/sr/cm. The computational speed is three to four-orders of magnitude faster than the medium speed correlated-k option MODTRAN5. This method is very efficient to simulate thousands of RS spectra under multi-layer clouds/aerosols and solar radiation conditions for climate change study and numerical weather prediction applications.
All heliospheric current sheet (HCS) crossings and corotating solar wind streams detectedby both WIND and ULYSSES have been identified.
We describe the first results from a self-consistent study of Alfven waves for the time-dependent, single-fluid magnetohydrodynamic (MHD) solar wind equations, using a modified version of the ZEUS MHD code. The wind models we examine are radially symmetrical and magnetized; the initial outflow is described by the standard Parker wind solution. Our study focuses on the effects of Alfven waves on the outflow and is based on solving the full set of the ideal nonlinear MHD equations. In contrast to previous studies, no assumptions regarding wave linearity, wave damping, and wave-flow interaction are made; thus, the models naturally account for the back-reaction of the wind on the waves, as well as for the nonlinear interaction between different types of MHD waves. Our results clearly demonstrate when momentum deposition by Alfven waves in the solar wind can be sufficient to explain the origin of fast streams in solar coronal holes; we discuss the range of wave amplitudes required to obtained such fast stream solutions.
We discuss a type of intense magnetospheric/auroral activity that is not always substorms: High-Intensity, Long-Duration, Continuous AE Activity (HILDCAA) events, which occur during high speed solar wind streams. The high speed streams contain large-amplitude, nonlinear Alfvtn waves. Analyses of POLAR UV images, demonstrate that the AE increases/AL decreases in HILDCAAs are not always substorm expansion phases (although some substorms may occur). The associated auroral W energy deposition is throughout a continuous (360') auroral oval. During some image intervals, the dayside aurora is the most remarkable feature. Our hypothesis is that solar wind energy transfer from the solar wind to the magnetosphere/ionosphere is primarily directly driven due to the finite wavelength Alfv6n waves and the rapid dBz/dt variability.
Evidence for a solar cycle variation in the interplanetary plasma is presented based on direct observations of the solar wind by the Pioneer and Vela spacecraft. These data indicate that between 1965 and 1971 there were more days associated with high speed streams during solar maximum than during solar minimum. These observations provide the first observational explanation for the solar modulation of cosmic rays. At solar maximum the probability is highest that cosmic rays entering the solar system will encounter high speed streams. As a result, there is more modulation of cosmic rays at solar maximum than at other times.
Low-energy solar particle data have been combined from a multi-spacecraft near-earth data set covering most of solar cycle 20 (1966-1976). Particle intensity profiles have been ordered in the natural heliographic coordinate system of the estimated high coronal connection longitude of the foot point of the interplanetary field line. The recurrence trends of approximately 1-MeV solar particles become more apparent in this coordinate system than when plotted versus time, and thereby extend the evidence for regions of continual injection and escape from the corona. Intercomparison of solar particles and solar wind streams in heliographic longitude suggests that the origin of stream-associated spatial particle events seen at 1 AU is solar rather than interplanetary.