Engineering topics

Wolff, C. L.

Publications and source records attributed to Wolff, C. L..

31 records · Page 2

NASA NTRS1975

An anticorrelation between polar and equatorial rotation of the solar photosphere

Published spectroscopic measurements of solar rotation are analyzed to show that when the rotation velocity increases at high latitudes it tends to decrease at low latitudes, and that when the rotation velocity decreases at high latitudes it increases at low latitudes. The high-latitude velocities typically vary over only 20% of the range of those near the equator and the smallest variations of all occurred near latitude 60 deg during the rising portion of the previous solar cycle. The anticorrelation is consistent with a recent suggestion that differential rotation on the sun arises from photospheric wind systems whose strength is determined, ultimately, by oscillations within the sun.

Wolff, C. L.↗

NASA NTRS1974

Rigid and differential rotation driven by oscillations within the sun

Long-period oscillations involving the entire mass of the sun rotate like rigid bodies, and their oscillatory power is distributed nonuniformly across the solar surface. A mostly qualitative theory is constructed showing how the oscillations drive convective flows of global scale, which then organize photospheric and coronal magnetic fields into patterns which rotate rigidly. The convection rises along long graceful curves, creating the magnetic-arcade structures in the corona and unipolar photospheric regions on each side by dynamo action. These are thought to be the origin of the sector structure in the solar wind. The rigid patterns of convective upwelling also force nonrigid horizontal winds on the solar surface. Under the action of the Coriolis force, the main horizontal motions are converted into polar and equatorial wind currents which have the proper directions to drive the differential rotation long observed on the sun's surface.

Wolff, C. L.↗

NASA NTRS1974

Distinctive patterns on the surface of slowly rotating stars whose oscillations are nonlinearly coupled

Slowly rotating stars which are oscillating at small amplitude in a broad spectrum of g-modes should display strong surface nonuniformities if even weak nonlinear coupling exists between the modes. Oscillatory power will be concentrated into distinctive patterns which rotate rigidly in spite of differential rotation in the outer stellar layers. Each pattern rotates at a constant rate slower than the star as a whole according to a very simple law of rotation. Virtually all the rotation rates are within 9 per cent of the stellar rate. Evidence is cited that the sun may be oscillating, so other stars along the main sequence may be oscillating, also. If zones obeying the predicted rotation law can be detected in a star, then the rotation rate of the stellar interior becomes known, and differential rotation is negligible over most of the stellar mass.

Wolff, C. L.↗

NASA NTRS1973

What is the horizontal scale of the 5-min oscillations

Solar oscillations with periods near 5 min were discovered in the photosphere by Leighton et al. (1962) on Doppler photographs which showed the sun to be covered with small velocity cells a few thousand km in diameter. If wrong, all the early reports of a small horizontal scale (about 2000 km) for the 5-min oscillations may be due to unfortunate similarities between the velocity and overturning time of the solar granule convection and the corresponding velocity and period typical of the oscillations. A large horizontal scale (about 30,000 km) for the oscillations seems consistent with the old data and almost required by more recent measurements. The large scales recently measured would imply that a sizable fraction of the solar volume is involved in the oscillation and would cast some doubt on all the old theories of the 5-min oscillations which were based on plane parallel atmospheres.

Wolff, C. L.↗

NASA NTRS1973

Interplanetary gas. XVIII - Models and the mean free path of protons at 1 astronomical unit.

Velocity distribution functions of solar-wind protons obtained by the Vela 3 satellites have been analyzed to obtain a microscopic determination of the momentum flux along magnetic field lines with respect to a reference frame moving at the bulk speed. The determination from macroscopic parameters allows the calculation of an effective mean free path for protons at 1 AU which averages 0.06 AU and is relatively independent of solar-wind velocity w. For quiet times when w is from 300 to 400 km/sec, the experimental mean free path is 2 to 3 times smaller than the value from plasma theory. For w greater than 400 km/sec, the experimental value is 10 to 100 times smaller than the theoretical value.

Brandt, J. C.↗

NASA NTRS1972

The five-minute oscillations as nonradial pulsations of the entire sun.

Calculations of the stability coefficient show that the Sun should be pulsating as a unit in nonradial modes of high order. The pulsations are driven by the superadiabatic gradient of the low photosphere and by the same sensitive changes in opacity that are known to be important in variable stars. The existence of solar pulsations can explain many of the large scale features observed in the well known 5-minute oscillations of the solar atmosphere.

Wolff, C. L.↗

NASA NTRS1972

Free oscillations of the sun and their possible stimulation by solar flares.

The main characteristics of free oscillations of the sun are described, and the sources and sinks of energy are estimated. Adiabatic oscillations and damping are considered. It is shown how a large solar flare can exert a significant mechanical impulse on the sun by causing a wave of compression to move subsonically into the interior. The solar interior does not easily dissipate low-amplitude acoustical energy, and therefore a relatively large fraction of the energy should remain available to go into the normal modes. An estimate is made of how this energy might be distributed among the more interesting modes.

Wolff, C. L.↗

NASA NTRS1972

Solar wind heating.

The difference in objectives, physical assumptions, and results among the most recent detailed models aimed at understanding energy transport in the solar wind are analyzed. Models have been judged primarily by comparing their predictions against spacecraft observations near 1 AU. However, the observed values of flow speed, density, and temperature fluctuate over a wide range so that the criteria for agreement between theory and observation are necessarily somewhat subjective.

Barnes, A.↗

NASA NTRS1972

Gegenschein-Moulton region photography from lunar orbit

Apollo 16 photography during lunar orbit of the Gegenschein-Moulton region was used to determine the libration points of the Sun-Earth system. Triangulation for the system is discussed, along with background experimental information.

Dunkelman, L.↗

NASA NTRS1971