A three‐dimensional model of corotating streams in the solar wind 2. Hydrodynamic streams

Abstract

This paper explores theoretical aspects of corotating solar wind dynamics on a global scale by means of numerical simulations executed with a nonlinear, inviscid, adiabatic, single-fluid, three-dimensional C3-D) hydrodynamic formulation. The study begins with a simple, hypothetical 3-D stream structure defined on a source surface located at 35 RS and carefully documents its evolution to 1 AU under the influence of solar rotation. By manipulating the structure of this prototype configuration at the source surface, it is possible to'elucidate the factors most strongly affecting stream evolution: 1) the intrinsic correlations among density, temperature, and velocity existing near the source; 2) the amplitude of the stream; 3) the longitudinal breadth of the stream; 4) the latitudinal breadth of the stream; and 5) the heliographic latitude of the centroid of the stream. The action of these factors is best understood in terms of momentum arguments-of relative simplicity and general application (to the extent that waves, conduction, and kinetic effects may be ignored).Corotating structure is viewed as a spiral standing wave (in the rotating frame) in which there is an ongoing competition between the kinematic tendency of the stream to steepen (as high-speed material overtakes slow) and the dynamical reaction of the gas to resist compression (through acceleration and tangential deflection of material by pressure gradients in the interaction region). Longitudinal gradients in the radial velocity distribution determine how fast material is brought into the interaction region, but the detailed momentum balance as a function of position within the stream dictates what happens when the material collides. Reasonable specifications of the five factors mentioned above can so affect this kinematic-dynamic balance that even a high-amplitude stream (e.g., peak-to-trough velocity differences at 1 AU o 480 km/s) may be prevented from shocking inside 1 AU, where the nonradial-flow broadening mechanism operates most efficiently. The nonlinear 3-D capabilities of the model allow quantitative study of the global development of this induced tangential flow in some detail. The nonradial motions lead to the net latitudinal transport of small amounts (a few percent) of mass, energy, and momentum. The effects of the latitudinal transport upon the evolution 2 within an east-west plane are minimal, and the latitudinal spreading of stream material in interplanetary spade, even in the presence of steep meridional gradients (up to 30 km/s/deg), is limited to a few degrees.Thus, for corotating structures, with their favorable spiral geometry, the 2-D approximation adequately describes the dynamical interaction. However, certain important research topics can only be approached in the full 3-D formulation. For example, the systematic pattern of the meridional flow changes across stream-fronts contain information on the 3-D structure of the stream and thus offers promise as a practical diagnostic tool. Also, since the magnetic field is tied ...

Mapping Solar Wind Streams from the Sun to 1 AU: A Comparison of Techniques

“…In a series of successively more sophisticated treatments, V. Pizzo described the effects of, and differences between 1-D, 2-D, and 3-D models as well as the differences between hydrodynamic and MHD solutions under idealized configurations (Pizzo 1978(Pizzo , 1980(Pizzo , 1982.…”

Dynamical evolution of interplanetary magnetic fields and flows between 0.3 AU and 8.5 AU: Entrainment

“…Goldstein and Jokipii (1977), Gosling (1981), Gosling et al (1976), Hundhausen (1973a,b), Hundhausen and Gosling (1976). Pizzo (1980Pizzo ( , 1982, Schubert and Cummings (1967), Simon and Axford (1966), , andWolfe (1977, 1979). The emphasis in most of these papers is on the processes related to the steepening of a corotating stream, particularly: 1) the development of shock pairs, and 2) the acceleration of slow material and deceleration of fast material.…”

Space Weather Quarterly Volume 13, Issue 1, 2016

“…In terms of the effect upon CMEs-in particular, fast CMEs-interacting with the ambient stream structure, there is essentially negligible difference in CME front properties such as arrival time and overall velocity jumps across the CME fronts, as compared with all the very real uncertainties in the inputs. The underlying reason for this is that the distribution of input radial momentum flux dominates the evolution in the interplanetary medium, with the thermal and magnetic pressures playing a secondary role [Pizzo, 1980]. To illustrate, Figure 2 (top row) shows an Enlil time slice pair of plots for an HD simulation wherein a moderate-speed CME has been launched into the back end of an ambient corotating stream front driven by an actual WSA map (the one included in the V2.7e release of the Enlil software).…”