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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Plasma energetics in solar flares

The high-temperature and quasi-thermal aspects of a solar flare are examined along with the basic physical mechanisms related to the primary energization and dissipation processes. Topics covered include the reconnection of the magnetic field, the bulk acceleration of particles, and the thermalization and ultimate radiation of the energy. The complexity of the phenomena involved is emphasized.

Van Hoven, G.↗
NASA NTRS1981

The C I opacity and physical structure of cool, very dense plasma in the solar corona

The physical structure of the cool material in the volume of the solar corona is investigated. The observational evidence is summarized in a table giving the brightness contrast in optical and EUV radiations. The state of ionization and the opacity sources are discussed, and a physical model is described that is consistent with the EUV and optical data. It is noted that a comparison of the EUV raster pictures with H-alpha and Ca K photoheliograms indicates that the material is commonly injected from below into relatively low-lying magnetic loops (fibrils) seen near sunspots and plages.

Foukal, P.↗
NASA NTRS1995

Effects of highly intermittent magnetic fields and plasma flows on solar wind dynamics

Filamentary magnetic fields and intermittent mass flows with highly variant physical parameters as observed in coronal holes provide, from a theoretical point of view, natural conditions for strongly nonlinear dynamics. The presence of sheared mass flows along fine scale magnetic structures results in strong nonlinear instability, most important of which is the explosive instability. We specify the physical conditions for several different manifestations of the onset of explosive instability and its further evolution: (1) fully developed explosive instability - explosive release of the energy; (2) shock formation - stabilization of instability by small scale spatial inhomogeneities leads to formation of subsequent shocks having a number of peculiarities that is determined by the interplay of thermal and viscous losses (for example, in predominance of thermal losses the isothermal jump occurs); and (3) solitary waves - stabilization of explosive instability by nonlinear dispersion effect leads to formation of a 'gas' of solitons which are later either damped away with characteristic time and energy input or evolve to solitons with explosively growing amplitudes. Each scenario is completely determined by the physical parameters of the medium, thus producing a quite uneven distribution of energy in a coronal hole and, respectively, an uneven outward propagation of the energy flux.

Ryutova, M.↗
NASA NTRS1990

Ulysses Launch

Ulysses is a joint mission between the United States National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) to explore the heliosphere over the full range of solar latitudes, especially in the polar regions. The goal of the Ulysses mission is to provide an accurate assessment of our total solar environment. This collaborative ESA/NASA mission will, for the first time, explore the heliosphere -- the region of space that is dominated by the Sun-- within a few astronomical units of the Sun over the full range of heliographic latitudes. The path followed by the spacecraft, using a Jupiter gravity-assist to achieve a trajectory extending to high solar latitudes, will enable the highly sophisticated scientific instruments on board to make measurements in the uncharted third dimension of the heliosphere. The Ulysses spacecraft will carry nine scientific instruments to measure the properties of the solar corona, the solar wind, the Sun/wind interface, the heliospheric magnetic field, solar radio bursts, plasma waves, solar X-rays, solar and galactic cosmic rays, and the interplanetary/interstellar neutral gas and dust. Scientists will take advantage of the enormous distance between the spacecraft and the Earth to perform astrophysical measurements and to search for gravitational waves. In conjunction with instrumentation on Earth-orbiting spacecraft, Ulysses will help to precisely locate the mysterious sources of cosmic gamma bursts. The results obtained will help to solve outstanding problems in solar and heliospheric physics, while undoubtedly revealing new and unanticipated phenomena.

Source record↗
NASA NTRS2010

Observations of Kelvin-Helmholtz Waves Along the Dusk-Side Boundary of Mercury's Magnetosphere During MESSENGER's Third Flyby

During the third MESSENGER flyby of Mercury on 29 September 2009, 15 crossings of the dusk-side magnetopause were observed in the magnetic field data over a 2-min period, during which the spacecraft traveled a distance of 0.2 R(sub M) (where R(sub M) is Mercury's radius). The quasi-periodic nature of the magnetic field variations during the crossings, the characteristic time separations of approx.16 s between pairs of crossings, and the variations of the magnetopause normal directions indicate that the signals are likely the signature of surface waves highly steepened at their leading edge that arose from the Kelvin-Helmholtz instability. At Earth, the Kelvin- Helmholtz instability is believed to lead to the turbulent transport of solar wind plasma into Earth's plasma sheet. This solar wind entry mechanism could also be important at Mercury. Citation: Boardsen, S. A., T. Sundberg, J. A.Slavin, B. J. Anderson, H. Korth, S. C. Solomon, and L. G. Blomberg (2010), Observations of Kelvin-Helmholtz waves along the dusk-side boundary of Mercury s magnetosphere during MESSENGER's third flyby,

Boardsen, Scott A.↗
NASA NTRS2017

Temporal Evolution of the Plasma Sheath Surrounding Solar Cells in Low Earth Orbit

Initial results from the PIC simulation and the LEM simulation have been presented. The PIC simulation results show that more detailed study is required to refine the ISS solar array current collection model and to understand the development of the current collection in time. The initial results from the LEM demonstrate that is it possible the transients are caused by solar array interaction with the environment, but there are presently too many assumptions in the model to be certain. Continued work on the PIC simulation will provide valuable information on the development of the barrier potential, which will allow refinement the LEM simulation and a better understanding of the causes and effects of the transients.

Willis, Emily M.↗
NASA NTRS1982

The Venus ionosphere at grazing incidence of solar radiation - Transport of plasma to the night ionosphere

A quasi-two-dimensional model of the Venusian ionosphere is used to calculate the ion number densities and horizontal ion bulk velocities expected for a range of solar zenith angles near the terminator (80-100 deg). These results are compared with data from the Pioneer Venus Orbiter retarding potential analyzer. It is shown that antisunward horizontal plasma fluxes produced by solar EUV-induced pressure gradients are sufficient to maintain the nighttime ionosphere. While photoionization is the dominant source of ionospheric plasma for solar zenith angles less than 92 deg, plasma transport from the dayside is the dominant plasma source for solar zenith angles greater than 95 deg. It is also shown that the main nightside plasma peak at a height of 140 km is of the F2 type; its height and shape are therefore quite insensitive to the height of the ion source.

Whitten, R. C.↗
NASA NTRS1985

Space test program of high-voltage solar array-space plasma interactions

Future spacecraft, notably the proposed Space Station, will require power systems much larger than have previously been flown. It is recognized that at higher voltages, and at the relatively high plasma density present at low Earth orbital altitudes, undesirable interactions between the high voltage solar array and the space plasma will occur. Space experiments on high voltage solar array space plasma interactions in low Earth orbit are an absolute requirement for confident design of a higher voltage solar array. Experiments are presently being identified to provide the necessary space data for calibration of ground testing, validation of analytical models, and development of design guidelines required for confident design of high voltage solar arrays in space. A proposed flight experiment program which is designed to obtain the required data is summarized.

Carruth, M. R., Jr.↗
NASA NTRS1990

Plasma observations of the solar wind interaction with Mars

Measurements with the plasma analyzers on the Mars-2, 3 and 5 spacecraft show that Mars deflects a large fraction of the incoming solar wind flow to form a strong bow shock. The bow shock is about 1.41 Rm from the center of the planet at the subsolar point and about 2.40 Rm at the terminator. These distances are similar to those for Venus at times of moderate solar activity. The inferred effective obstacle altitude is about 400-700 km. An ion cushion has been found which is similar in its properties to the Venus magnetic barrier. The formation of this cushion appears to cause the deflection of the solar wind. Inside the cushion but well above the ionosphere is found a region where the ions are at the background, the electrons are cool and the magnetic pressure dominates. This region may resemble a planetary magnetosphere.

Vaisberg, O. L.↗
NASA NTRS1967

Interplanetary gas. XIV.

Super-Alfvenic point or distance of effective corotation for loss of angular momentum in solar wind plasma

SOLAR ROTATION↗