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NASA NTRS1986

Steady hydromagnetic flows in open magnetic fields. I - A class of analytic solutions

In the case of an establishment of theoretical models of the hydromagnetic solar wind, the inclusion of the effects of the magnetic field in the solar wind makes it extremely dificult to solve the mathematical problem. This paper has the objective to present a set of particular analytic solutions. The general formulation of Tsinganos (1982) is used to identify a class of analytic solutions to the equations of steady hydromagnetic flows in spherical coordinates. Flow in an open magnetic field are studied, taking into account the problem in dimensionless form, the special case of radial flows with alpha = 0, general radial flows, illustrative examples for flows in which alpha is not equal to 0, a parametric study of nonradial flows in which alpha is not equal to zero, variations in the parameter nu, and variations in the initial speed eta.

Low, B. C.↗
NASA NTRS1987

The influence of strong hydromagnetic turbulence on newborn cometary ions

By means of a test particle model, the time evolution of the velocity distribution function of newborn cometary ions in the presence of strong hydromagnetic turbulence is studied. The test particle model employs a realistic spectrum of hydromagnetic turbulence corresponding to the observations of the International Cometary Explorer spacecraft at Comet Giacobini-Zinner. It is found that pitch-angle scattering processes can rapidly result in the formation of the shell distribution which has been observed near Comets Giacobini-Zinner and Halley. The model also indicates that radial diffusion in velocity space develops on a much longer time scale.

Price, C. P.↗
NASA NTRS1991

Contributions from geomagnetic inverse theory to the study of hydromagnetic conditions near the core-mantle boundary

The Final Report on contributions from geomagnetic inverse theory to the study of hydromagnetic conditions near the core-mantle boundary (CMB) is presented. The original proposal was to study five questions concerning what the surface and satellite magnetic data imply about hydromagnetic and electromagnetic conditions near the CMB. The five questions are: (1) what do the surface and satellite data imply about the geomagnetic field B near the surface of the earth; (2) how does one extrapolate B down through the conducting mantle to the CMB; (3) if B on the CMB is visible, how accurately does it satisfy the frozen-flux approximation; (4) if frozen flux is a good approximation on the CMB, what can be inferred about the fluid velocity v in the upper core; and (5) if v at the CMB is visible, does it suggest any dynamical properties of the core, such as vertical advection, Alfven-inertial waves, link instabilities, or mantle effects. A summary of the research is provided.

Backus, George E.↗
NASA NTRS1994

Disk-driven hydromagnetic winds as a key ingredient of active galactic nuclei unification schemes

Centrifugally driven winds from the surfaces of magnetized accretion disks have been recognized as an attractive mechanism of removing the angular momentum of the accreted matter and of producing the bipolar outflows and jets that are often associated with compact astronomical objects. As previously suggested in the context of young stellar objects, such winds have unique observational manifestations stemming from their highly stratified density and velocity structure and from their exposure to the strong continuum radiation field of the compact object. We have applied this scenario to active galactic nuclei (AGNs) and investigated the properties of hydromagnetic outflows that originate within approximately 10(M(sub 8)) pc of the central 10(exp 8)(M(sub 8)) solar mass black hole. On the basis of our results, we propose that hydromagnetic disk-driven winds may underlie the classification of broad-line and narrow-line AGNs (e.g., the Seyfert 1/Seyfert 2 dichotomy) as well as the apparent dearth of luminous Seyfert 2 galaxies. More generally, we demonstrate that such winds could strongly influence the spectral characteristics of Seyfert galaxies, QSOs, and BL Lac objects (BLOs). In our picture, the torus is identified with the outer regions of the wind where dust uplifted from the disk surfaces by gas-grain collisions is embedded in the outflow. Using an efficient radiative transfer code, we show that the infrared emission of Seyfert galaxies and QSOs can be attributed to the reprocessing of the UV/soft X-ray AGN continuum by the dust in the wind and the disk. We demonstrate that the radiation pressure force flattens the dust distribution in objects with comparatively high (but possibly sub-Eddington) bolometric luminosities, and we propose this as one likely reason for the apparent paucity of narrow-line objects among certain high-luminosity AGNs. Using the XSTAR photoionization code, we show that the inner regions of the wind could naturally account for the warm (greater than or approximately equal to 10(exp 5) K) and hot (greater than or approximately equal to 10(exp 6) K) gas components that have been inferred to exist on scales less than or approximately equal to 10(exp 2) pc in several Seyfert galaxies. We suggest that the partially ionized gas in the inner regions of the wind, rather than the dusty, neutral outflow that originates further out in the disk, could account for the bulk of the X-ray absorption in Seyferts observed at relatively small angles to their symmetry axes. Finally, we discuss the application of this model to the interpretation of the approximately 0.6 keV X-ray absorption feature reported in several BLOs.

Konigl, Arieh↗
NASA NTRS1961

Note on Hydromagnetic Propagation and Geomagnetic Field Stability

In the adjoining letter, Dessler [1961] argues that the interface between the solar wind and the geomagnetic field is stable and cannot, therefore, generate hydromagnetic waves. According to our interpretation, his argument may be paraphrased as follows: He observes that, for many sudden commencement geomagnetic storms, surface magnetograms show no marked change in the level of disturbances from the period before the sudden commencement until well into the initial phase of the storm. He applies the attenuation factors calculated by Francis and Karplus [1960] to the measurements of the 1 cps component of the magnetic disturbances obtained at the surface. From this calculation, he concludes that, during the initial phase of these geomagnetic storms, the amplitudes of hydromagnetic disturbances above the ionosphere are less than 1. Assuming that the sudden commencement indicates the presence of a solar wind, he further concludes that hydromagnetie disturbances are not generated in the region between the geomagnetic field and the solar wind and that this interface is, therefore, inherently stable. He subsequently accounts for the hydromagnetie disturbances which are frequently observed at the earth as having been produced by fluctuations in the energy density of the impinging solar wind.

Coleman, P. J., Jr.↗