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  • ASTROPHYSICS  (4)
  • Solar Physics  (2)
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  • 1
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    Flow downstream of the heliospheric terminal shock: Magnetic field line topology and solar cycle imprint (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The topology of the magnetic field in the heliosheath is illustrated using plots of the field lines. It is shown that the Archimedean spiral inside the terminal shock is rotated back in the heliosheath into nested spirals that are advected in the direction of the interstellar wind. The 22-year solar magnetic cycle is imprinted onto these field lines in the form of unipolar magnetic envelopes surrounded by volumes of strongly mixed polarity. Each envelope is defined by the changing tilt of the heliospheric current sheet, which is in turn defined by the boundary of unipolar high-latitude regions on the Sun that shrink to the pole at solar maximum and expand to the equator at solar minimum. The detailed shape of the envelopes is regulated by the solar wind velocity structure in the heliosheath.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A3; p. 3463-3471
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Radiatively driven winds from magnetic, fast-rotating stars - Wolf-Rayet stars? (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: An analytical procedure is developed to solve the MHD equations for a stellar wind in the strong-magnetic-field, optically thick limit for hot stars. The slow-mode, Alfven, and fast-mode critical points are modified by the radiation terms in the force equation but in a manner that can be easily treated. Once the velocities and distances are known at the critical points, the streamline constants are determined in a straight-forward manner. This shows the structure of the wind with a relatively simple numerical scheme. The magnetic field and a radiation parameter specify the terminal wind velocity. High rotation rates and a modified slow-mode critical point close to the stellar surface determine the high mass-loss rates. Wolf-Rayet stars are modeled with 1000-G fields but require stellar rotational velocities approaching breakup values. The physical conditions that correspond to Wolf-Rayet models are so rare that another mechanism must be operating in these winds.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 321; 355-369
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Stagnation Flow in Thin Streamer Boundaries (2005)
    In:  Other Sources
    Details
    Publication Date: 2018-06-12
    Description: Slow solar wind is believed to arise in the legs or near the cusp of streamers, inside the brightness boundary. In an earlier study, we used an analytic model of flow in this layer to analyze the effect of the magnetic field on the geometry of the flow. That study successfully described those conditions that can lead to a decrease of the flow speed with increasing height near the cusp of the closed magnetic helmet inside a streamer. The model was, however, restricted to a radial brightness boundary on the streamer and hence to a relatively thick outflow region near the cusp. Here this restriction is relaxed through the explicit introduction of a coronal hole-like region outside the brightness boundary. We use the model to describe flow solutions for outflow in a thin layer inside the brightness boundary. The flow geometry now can be constrictive just above the cusp, and we show solutions of this type. Many solutions then show a diverging geometry at greater heights above the cusp, out to at least 5 solar radius. We fail to find solutions in which the geometry alone leads to slow flow but give a more general description than before of conditions favoring slow flow and, consequently, gravitational settling in the legs of streamers.
    Keywords: Solar Physics
    Type: Astrophysical Journal; Volume 624; 378-391
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Flow downstream of the heliospheric terminal shock - The magnetic field on the heliopause (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Modeling the kinematic magnetic field in the solar wind beyond the terminal shock shows that a ridge of magnetic pressure is produced just inside the heliopause. This ridge is sufficiently large that it will cause the layer immediately inside the heliopause to thicken, pushing the heliopause outward and slightly affecting its position relative to the terminal shock. However, the ridge is far too thin to cause an important change in the distance of the terminal shock from the sun. We show that these conclusions are a simple consequence of geometrical arguments for incompressible, steady, laminar flows. Moreover, the heliopause magnetic field originates on the terminal shock near the substagnation point. Consequently, the heliospheric current sheet field reversals are painted onto the inside surface of the heliopause. Alternate magnetic polarity strips will be oppositely directed relative to the interstellar magnetic field, implying that reconnection inevitably occurs on a fine some near the nose of the heliosphere. This suggests that the heliopause is a leaky, diffuse surface.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A9; p. 15,169-15,176.
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Potential Flow Downstream of the Heliospheric Terminal Shock: A Non-Spherical Shock (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We have solved for the potential flow downstream of the terminal shock of the solar wind in the limit of small departures from a spherical shock due to a latitudinal ram pressure variation in the supersonic solar wind. The solution connects anisotropic streamlines at the shock to uniform streamlines down the heliotail because we use a non-slip boundary condition on the heliopause at large radii. The rotational velocity about the heliotail in the near-field solution decays as the fourth power of distance from the shock. The polar divergence of the streamlines will have consequences for the previously discussed magnetic pressure ridge that may build-up just inside the heliopause.
    Keywords: Solar Physics
    Type: NASA-TM-112145 , NAS 1.15:112145 , AGU-95GL01658 , Geophysical Research Letters (ISSN 0094-8534); 22; 13; 1757-1760; AGU-95GL01658
    Format: application/pdf
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  • 6
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    The polar heliospheric magnetic field (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: We describe the large-scale magnetic field morphology in the heliosheath. A simple argument, which depends only on the interstellar wind flowing nearly in the solar equatorial plane, shows that polar heliospheric magnetic fieldlines never approach the heliopause and therefore are accessible to galactic cosmic rays only through perpendicular diffusion. The same argument implies reconnection, at fine scales, on the nose of the heliopause, between the interplanetary magnetic field and the magnetic field in the local interstellar medium. Galactic cosmic rays therefore have direct access across the heliopause to fieldlines connected to equatorial regions of the inner solar system.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 20; 4; p. 329-332.
    Format: text
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