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Durney, B. R.

Publications and source records attributed to Durney, B. R..

8 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

On theories of rotating convection zones

It is shown that the time rate of change brought about by turbulent convective motions in the angular momentum of a thin spherical shell is such as to increase the angular velocity of the lower part of the solar convection zone (SCZ) and to decrease the angular velocity of the upper part. Arguments are presented in favor of the following very tentative model of rotation in the SCZ: (1) the lower region is in weaker differential rotation than the surface and not constrained by the Taylor-Proudman theorem, and (2) the observed solar differential rotation at the surface is generated as the SCZ relaxes from the state in the lower part to the state at the surface. In the upper and lower layers of the SCZ, angular-momentum conservation between the turbulent motions and viscous stresses leads to an angular velocity increasing upward.

Durney, B. R.↗
NASA NTRS1985

A search for long-lived velocity fields at the solar poles

A search has been made in the polar regions of the sun for large-scale (50-200 Mm) velocity fields with lifetimes of the order of the solar rotation period (approximately equal to or greater than 30 days). The observations show that any such large-scale, long-lived velocity patterns in the polar regions must have an amplitude less than 5 m/s. Marginally significant detections (at the 2-3 sigma level) were made of two kinds of structures with amplitudes of order 3 m/s. One has a rotation period approximately 38 days (close to the polar rotation period at the sun's surface), and a scale approximately 150 Mm; the other has a period approximately 24 days and a scale approximately 100 Mm. Tentatively, the first structure is interpreted as being of supergranular origin. The second structure is interpreted as the overshooting of the dominant convective mode of the lower solar convection zone - the giant granulation.

Durney, B. R.↗
NASA NTRS1984

On the Influence of Turbulent Motions on Non-radial Oscillations

The effect of turbulent motions on oscillations is studied, considering only the coupling between turbulent and oscillatory velocities. In this case, the turbulence affects the oscillations through the Reynolds stresses in the momentum equation for the pulsations. A simple model of turbulence is adopted to evaluate these Reynolds stresses and the perturbed eigenfrequencies are expressed as a function of certain averages of the turbulent velocities.

Durney, B. R.↗
NASA NTRS1984

On the rotation rate of polar features in the sun

The rotation rate of solar features in the vicinity of the poles is evaluated with the help of a correlation procedure. The average rotation rates for both poles are systematically smaller than those predicted by Howard and Harvey's (1970) formula, but not in serious disagreement with their results.

Durney, B. R.↗
NASA NTRS1983

On the large-scale dynamics of rapidly rotating convection zones

The fact that the values of the eight basic waves present in turbulent flows in the presence of rotation prohibit a tilt of eddy towards the axis of rotation is incorporated into a formalism for rapidly rotating convection zones. Equations for turbulent velocities are defined in a rotating coordinate system, assuming that gravity and grad delta T act in a radial direction. An expression is derived for the lifetime of a basic wave and then for the average velocity vector. A real convective eddy is formulated and the wave vectors are calculated. The velocity amplitude and the stress tensor amplitude are integrated over the eddy domain. Applied to the solar convective zone, it is found that the convective cells are aligned along the axis of rotation at the poles and at the equator, a model that conflicts with nonrotating mixng length theory predictions.

Durney, B. R.↗
NASA NTRS1983

Preliminary observations of velocity fields at the solar poles

Using the 13 m Littrow spectrograph at Sacramento Peak Observatory, the Doppler shift of Fe I 5863 A in the polar regions of the sun over a 20 day interval is studied. The daily observations were assembled into a polar projection of the line-of-sight velocity field. The projection shows a very clear pattern of supergranulation. When a low-pass spatial filter is run over the data, a pattern of large-scale (80-100 Mm) velocity features can be seen. Cross-correlation studies show that the supergranular pattern rotates with a synodic period of 35 days, while there is evidence that the larger features rotate with a shorter period of about 30 days. At present, it is not possible to say whether the large-scale patterns represent a new scale of convection (possibly related to the dominant convective eddy in the lower solar convection zone) or to the low-wavenumber tail of a distribution of supergranular cells.

Cram, L. E.↗
NASA NTRS1978

On the angular momentum loss of late-type stars

The observed surface angular velocity of main-sequence stars shows a sharp decrease at about spectral type F6. It is suggested that stars more massive than F6 cannot experience an appreciable angular-momentum loss because their convection zones cannot sustain a magnetic dynamo: without a magnetic field the angular-momentum loss is very small. The influence of rotation on the convective motions is essential for the existence of a solar-type dynamo. Rotation can influence these convective motions only if the typical convective time is larger than the rotation time. For main-sequence stars of different masses and chemical compositions the dimensionless parameter (convective velocity/sum's angular velocity times mixing length in the lower part of the convection zone) is evaluated. It is shown that this parameter increases very sharply for stars whose mass exceeds that defined by the relation log(star mass/solar mass) is of the order of 0.1. Thus even for large angular velocities, magnetic dynamos are not feasible if log(star mass/solar mass) appreciably exceeds 0.1.

Durney, B. R.↗