Engineering topics

Rhodes, E. J., Jr.

Publications and source records attributed to Rhodes, E. J., Jr..

27 records · Page 2

NASA NTRS1979

Solar p-mode oscillations as a tracer of radial differential rotation

Photoelectric observations of solar p-modes obtained with improved wavenumber and frequency resolution are presented. The observations are compared with model calculations of the p-modes, and the degree of spatial and temporal coherence of the observed wave pattern is investigated. It is found that the p-mode oscillations pervade the visible surface of the sun with a high degree of coherence in space and time, so that the whole complex pattern of standing waves with its nodes and antinodes can be regarded as a fixed pattern corotating with the solar surface layers. The p-modes are introduced as a tracer of solar rotational flow velocities. The equatorial differential rotation is estimated as a function of effective depth on the basis of the theoretical contribution functions for the p-modes recently derived by Ulrich et al. (1978). The results strongly indicate that the angular speed of rotation is not uniform even in the relatively shallow layer extending about 20,000 km below the photosphere.

Deubner, F.-L.↗

NASA NTRS1979

A new technique for measuring solar rotation

A new technique for measuring solar photospheric and subphotospheric rotation rates is described. The technique utilizes the standing-wave nature of the nonradial p-mode oscillations of the whole sun. Specifically, the technique is based upon the observed concentration of p-mode oscillatory power into well defined ridges in two-dimensional wavenumber-frequency power spectra. The frequencies of the ridges in the eastward- and westward-traveling portions of an individual spectrum are systematically shifted in opposite directions by a drift of the standing-wave pattern across the observing field of view. The magnitudes of these frequency shifts are related to the drift velocity and to the horizontal wavenumber in such a way that measurement of the observed frequency shifts in a spectrum yields the drift velocity for that observing run. By guiding on the solar limbs and observing the velocity field at disk center, the observed drift velocity obtained in this way is exactly the rotational velocity of the solar p-mode pattern, and of the solar gas itself.

Rhodes, E. J., Jr.↗

NASA NTRS1979

The effect of a radial rotational velocity gradient on p-mode eigenfrequencies

The splitting of p-mode eigenfrequencies due to a depth-dependent solar rotation rate is considered. It is shown that to a first approximation this splitting can be treated as resulting from the translation of the wave pattern across the field of view with a velocity equal the actual velocity at a depth called the effective depth. The effective depths for a model solar envelope with l/H = 3 are presented as a function of position on the (kh, omega)-plane. The combination of omega near 0.025/s and kh near 0 yields the deepest probe of the solar envelope. For this same combination of kh and omega it is possible to resolve individual groups of eigenmodes in frequency but not in spatial wavenumber. Achievement of this resolution observationally may permit a determination of the lifetime of these particular modes.

Ulrich, R. K.↗

NASA NTRS1977

Observations of nonradial p-mode oscillations on the sun

Observations of the solar velocity field with a diode array attached to the echelle spectrograph of a vacuum tower telescope are described which resolve the solar five-minute oscillatory motion into distinct bands of power. Previous observations are discussed which show that the solar five-minute oscillations can be resolved into frequencies having the character of nonradial p-mode eigenfrequencies of the solar envelope. The present observations confirm the observed frequencies and sharpen the previous resolution of the five-minute oscillations into ridges on the (wavenumber, frequency) plane. A comparison with earlier calculations indicates that the theoretical frequencies are in good but not perfect agreement with those observed. It is concluded that the identification of the five-minute oscillations as nonradial p-mode oscillations in the solar envelope is established beyond doubt.

Rhodes, E. J., Jr.↗

NASA NTRS1977

The sensitivity of nonradial p mode eigenfrequencies to solar envelope structure

Eigenfrequencies are calculated for nonradial p mode oscillations in the sun. These frequencies are shown to depend on the adiabat of the solar convective envelope. The frequency dependence is greatest for the p2 and p3 modes described by spherical harmonics with l = 500 to 1000. The solar envelope model includes a realistic representation of the chromosphere out to the base of the corona. For the chromospheric model of Vernazza, Avrett, and Loeser (1976) chromospheric modes with a distinct locus of eigenfrequencies exist near an eigenfrequency of 0.026 Hz. The actual frequencies of these eigenmodes depend on the thickness of the chromosphere. Because of the difference in the dependence of eigenfrequency on l for the chromospheric modes as compared with the p modes, the two types of mode can be distinguished observationally. If detected, the chromospheric modes would provide a good way of determining the thickness of the chromosphere.

Ulrich, R. K.↗

NASA NTRS1976

Further evidence of a latitude gradient in the solar wind velocity

Simultaneous Mariner and Explorer data are used in the present paper to show that the large-scale gradient in the bulk velocity of the solar wind observed by Coles (1972) is a heliographic latitude gradient. A value of roughly 15 km/sec/deg for the gradient is derived by a correlation technique employed by Coleman and Rosenberg (1971). A simple model of the velocity/latitude dependence is developed and is shown to be consistent with a direct comparison of the observed Mariner and Explorer velocities. The gradient inferred from the Mariner and Explorer data is compared with values obtained from corresponding analyses of Vela and IPS data.

Rhodes, E. J., Jr.↗

NASA NTRS1976

Evidence of a large-scale gradient in the solar wind velocity

Measurements of the solar wind velocity are compared at two widely separated locations, using plasma data obtained by Mariner 5, en route to Venus, and with the near-earth satellites Explorer 33, 34, and 35. A previous study of the propagation of interplanetary sector boundaries between Mariner and the earth had implied the existence of large scale velocity gradient which was interpreted as a latitude gradient of approximately 13 km/sec per degree of latitude. The results of the present investigation in which the earlier results were extended to the overall solar wind, without regard to the presence of sector boundaries, suggests that a latitude dependence of the solar wind velocity is the most plausible interpretation of the large-scale velocity gradient.

Rhodes, E. J., Jr.↗

NASA NTRS1975

Multispacecraft study of the solar wind velocity at interplanetary sector boundaries

The sector structure of the interplanetary magnetic field and the solar wind velocity at the sector boundaries are compared at separations of up to 0.3 AU, 50 deg in heliocentric longitude, and 7 deg in heliographic latitude, using data from Mariner 5 en route to Venus and from the near-earth Explorer 33, 34, and 35 satellites. The polarity pattern of the magnetic sectors is found to be very similar at the two locations, and 18 pairs of corresponding sector boundaries are identified. One-hour averages of solar wind velocities near the boundaries show that the velocities near earth exceed those measured by Mariner 5 by as much as 30%. Two possible explanations of the observed velocity differences are discussed: a preferential acceleration of sector boundaries with distance, possibly caused by stream-stream interactions; and a dependence of the solar wind velocity on heliographic latitude.

Rhodes, E. J., Jr.↗

NASA NTRS1974

Evidence of a velocity gradient in the solar wind

Sector-boundary velocity data obtained by Mariner 5 near Venus and by Explorers 33, 34, and 35 near earth are analyzed to determine why higher velocities were measured at earth. Differences in the corresponding velocities are plotted as a function of the heliocentric latitude separation of Mariner and earth, and evidence of a significant latitude gradient in the solar wind is found. Several indirect arguments in support of a latitude gradient are presented, and it is concluded that if the solar wind velocity varies with latitude, latitudinal stresses may have a significant effect on the properties of the solar wind, such as the existence and character of the north-south component of the interplanetary magnetic field.

Smith, E. J.↗