The Transition to Adiabatic Flow in Hydrodynamic Models of the Solar Wind.
Abstract
Quantitative models of the outer solar corona (R/R0. > 2) and interplanetary gas have been constructed by a simultaneous solution of the solar wind equations expressing conservation of mass, energy, and momentum. These models, all of which exhibit supersonic flow beyond some critical distance r~, have vanishing temperature at infinity. For a variety of mass and (total) energy fluxes, models have been calculated and compared for the following situations: (a) Unrestricted heat flow by thermal conduction at all distances (i.e., infinitesimal heat flow theory used to evaluate the transport coefficient for thermal conduction). (b) Heat flow by conduction restricted at large heliocentric distances by the spiralling interplanetary magnetic field. (c) Heat flow depressed at large distances below that of case (a) due to the fact that the solar plasma must support a noninfinitesimal heat flux (or, equivalently, that the fractional temperature change over a mean free path becomes large at great distances, thereby invalidating the linear heat theory approach). (d) Heat flow cut off at large distances by both of the effects (b) and (c). The numerical results indicate that, at least for the equatorial regions of the solar corona, restrictions (b) and (c) on the radial conductive heat flux are sufficient to ensure that the gas flow is rapidly becoming adiabatic by the time the plasma reaches the vicinity of earth. Turbulence and plasma instabilities, which lead to kinking of the magnetic field lines and further reduction of the radial heat flow, should enhance this effect.
- Publication:
-
The Astronomical Journal
- Pub Date:
- 1965
- DOI:
- 10.1086/109562
- Bibcode:
- 1965AJ.....70Q.682K