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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Direct observation of the latitudinal extent of a high-speed stream in the solar wind

The latitudinal boundaries of stationary fast solar wind streams emerging from equatorward extensions of the sun's polar coronal holes are studied. Simultaneous data from the Helios 1 and Imp spacecraft at different heliographic latitudes are compared. The measured latitudinal speed gradient of 30 km/s/deg shows that large angular speed gradients occur at the leading edges of fast streams and also with respect to latitude. The data indicate that longitudinal speed gradients are steeper near 0.3 AU than at 1.0 AU. Generally, regions with large angular speed gradients are observed to separate fast streams from the surrounding slower plasma. This suggests the existence of mechanisms which diminish longitudinal speed gradients as the plasma travels toward 1.0 AU. It also seems that the distribution of solar wind speeds on a near-sun spherical surface has large mesalike high-speed regions. Comparisons of Helios 1 and Imp data with corona observations supports the hypothesis that high-speed solar wind streams emerge from coronal holes.

Schwenn, R.↗
NASA NTRS1993

Ulysses observations of a recurrent high speed solar wind stream and the heliomagnetic streamer belt

Near-ecliptic solar wind observations by Ulysses on its way to the polar regions of the Sun, compared with those from IMP 8 at 1 AU, showed that high-speed streams decay and broaden with heliocentric distance from IMP 8 to Ulysses, as expected. In July 1992 while traveling south at approximately 13 deg S and 5.3 AU, Ulysses encountered a recurrent high-speed stream, that may also have been observed at IMP 8. The stream has been observed a total of 14 times, once in each solar rotation through June 1993 at approximately 34 deg S. The source of the high-speed stream is an equatorward extension of the south polar coronal hole. From July 1992 through June 1993, averages of solar wind peak speed increased while density decreased with heliographic latitude. Both the stream and a low-speed, high-density flow, presumably associated with the heliomagnetic (coronal) streamer belt encircling the heliomagnetic equator, crossed Ulysses with the solar rotation period until April 1993 when the spacecraft was at approximately 29 deg S heliographic latitude. After this time, as the spacecraft climbed to higher latitudes, the central portion of the streamer belt with lowest speed and highest density disappeared. Therefore, at its maximum inclination, the belt was tilted at approximately 29 deg to the heliographic equator at this point in the solar cycle.

Bame, S. J.↗
NASA NTRS2002

A Search for Solar Sources of High-Speed Solar Wind Streams

This report covers technical progress during the third and fourth years of Subcontract No. 5710000474, 'A Search for Solar Sources of High-speed Solar Wind Streams,' between Science Applications International Corporation (SAIC) and the Massachusetts Institute of Technology (MIT), covering the period November 2000 to December 2002. This is a subcontract originating from NASA SR&T Contract NAG5-7967 with MIT. In the following sections we summarize our progress during this reporting period.

Mikic, Zoran↗
NASA NTRS1976

High-latitude observations of solar wind streams and coronal holes

Interplanetary scintillation observations of the solar wind velocity during 1973 and the first part of 1974 reveal several corotating high-speed streams. These streams, of heliographic latitudes from +40 deg to -60 deg, have been mapped back to the vicinity of the sun and have been compared with coronal holes identified in wide band XUV solar images taken during the manned portions of the Skylab mission. There is some evidence that the high-speed streams are preferentially associated with coronal holes and that they can spread out from the hole boundaries up to about 20 deg in latitude. However, this association is not one to one; streams are observed which do not map back to coronal holes, and holes are observed which do not lie at the base of streams. To the extent that a statistical interpretation is possible the association is not highly significant, but individual consideration of streams and holes suggests that the statistical result is biased somewhat against a strong correlation.

Ricket, B. J.↗
NASA NTRS1975

Relation of large-scale coronal X-ray structure and cosmic rays. I - Sources of solar wind streams as defined by X-ray emission and H-alpha absorption features

The large-scale structure of the corona and the interplanetary medium during Carrington rotations 1601-1607 is discussed relative to recurrent high-speed solar wind streams and their coronal sources. Only streams A, C, D, and F recur on more than one rotation. Streams A and D are associated with coronal holes, while C and F originate in the high corona (20-50 solar radii) over faint X-ray emissions. The association of the streams with holes is confirmed by earlier findings that there are no large equatorial holes without an associated high-speed stream and that the area of the equatorial region of coronal holes is highly correlated with the maximum velocity observed in the associated stream near 1 AU.

Krieger, A. S.↗
NASA NTRS1985

Propagation of energetic electron streams in solar flares

The microscopic stability of an electron stream flowing down to the photosphere from the corona is examined. It is found that, while a power-law distribution is stable in the low-density corona, it is unstable against the generation of magnetized electron plasma waves in the high-density photosphere. The scattering of these energetic electrons may alter their radiation signatures.

Mok, Y.↗
NASA NTRS1991

MeV/n ions associated with corotating high-speed solar wind streams at less than 1 AU during 1978 to 1986

Data from the Goddard Space Flight Center experiments on the ISEE 3/ICE, IMP 8, and Helios 1 spacecraft are used to investigate ion enhancements of more than 1 MeV/n associated with corotating high-speed solar wind streams at least 1 AU during 1978-1986. The observations are consistent with ion acceleration from the solar wind by corotating shocks in the outer heliosphere.

Richardson, I. G.↗
NASA NTRS1995

Coronal roots of solar wind streams: 3-D MHD modeling

Weak (discontinuous) solutions of the 3-D MHD equations look like a promising tool to model the transonic solar wind with structural elements: current sheets, coronal plumes etc. Using the observational information about various coronal emissions one can include these structural elements into the 3-D MHD solar wind model by embedding the discontinuities of given type. Such 3-D MHD structured solar wind is calculated self-consistently: variants are examined via numerical experiments. In particular, the behavior of coronal plumes in the transonic solar wind flow, is modeled. The input information for numerical modeling (for example, the magnetic field map at the very base of the solar corona) can be adjusted so that fast stream arises over the center of the coronal hole, over the coronal hole boundaries and, even, over the region with closed magnetic topology. 3-D MHD equations have the analytical solution which can serve as a model of supersonic trans-alfvenic solar wind in the (5-20) solar radii heliocentric distance interval. The transverse, nonradial total (gas + magnetic field) pressure balance in the flow is the corner-stone of this solution. The solution describes the filamentation (ray-like structure of the solar corona) and streaming (formation of high-speed streams with velocities up to 800 km/sec) as a consequence of the magnetic field spatial inhomogeneous structure and trans-alfvenic character of the flow. The magnetic field works in the model as a 'controller' for the solar wind streaming and filamentation.

Pisanko, Yu. V.↗
NASA NTRS1981

Bi-directional streaming of solar wind electrons greater than 80 eV - ISEE evidence for a closed-field structure within the driver gas of an interplanetary shock

In near time coincidence with the arrival of helium enriched plasma driving the shock wave disturbance of November 12-13, 1978, strong bi-directional streaming of solar wind electrons greater than about 80 eV was observed with Los Alamos instrumentation on ISEE 3. The streaming persisted for many hours simultaneously parallel and anti-parallel to the interplanetary magnetic field which was directed roughly perpendicular to the sun-satellite line. This example of bidirectional streaming cannot be explained by field line connection to the earth's bow shock or the outward propagating interplanetary shock which passed ISEE 3 approximately 16 hours earlier. The event is explained if the local interplanetary field was a part of a magnetic bottle rooted at the sun or a disconnected loop propagating outward.

Bame, S. J.↗
NASA NTRS1977

Nonlinear Alfven waves in high-speed solar wind streams

A nonlinear proton distribution function that is an exact stationary solution of the nonlinear Vlasov equation and Maxwell's equations and which supports a single nonlinear transverse Alfven (ion cyclotron) wave that is circularly polarized and nondispersive is proposed for most of the observations during high-speed solar wind streams. This nonlinear distribution removes the strong Alfven wave instability, inconsistent with the persistence of the observed proton distribution functions in high-speed streams, found by the linear stability analysis. Model temperature anisotropies and drift velocities of the two spatially inhomogeneous bi-Maxwellian components are consistent with typical proton velocity distributions measured in high-speed streams at 1 AU. Two derived relations for each of the wave number and the phase velocity of the wave are obeyed within experimental uncertainties by two typical proton measurements. Our model also predicts that the alpha particle bulk flow velocity exceeds the proton particle bulk flow velocity, as is observed.

Abraham-Shrauner, B.↗
NASA NTRS1984

A hydromagnetic model of corotating conductive solar wind streams

Under the assumption of quasi-azimuthal symmetry the governing equations of a steady hydromagnetic flow in a thermally conductive flux tube possess six invariants. Four of them represent constancy of mass efflux, energy efflux, angular momentum efflux and magnetic flux. Based on the entropy equation we obtain useful approximation in explicit expressions for the two remaining invariants. One of them provides the constraint which determines the compatible heat flux to ensure a vanishing pressure at infinity. Thus, the admissible solution that represents a corotating solar wind stream in terms of specified interplanetary condition can be calculated by an algebraic method, without the necessity of numerical integration. A two-point relationship is then derived, which correlates the solar wind properties at two separated interplanetary sites measured at two properly separated instants. This relationship may be applied to observational data from spacecraft and earth-bound satellites to discern the corotation feature in the solar wind.

Yeh, T.↗