Taking advantage of the advent of massively parallel computers, sophisticated solution-adaptive techniques, and recent fundamental advances in basic numerical methods we have developed a high performance, adaptive-scale MED code capable of resolving many of the critical processes in the Sun-Earth system which range over more than 9 orders of magnitude in scale size. The development of such models are of increasing importance as the impact of space weather on vulnerable technological systems increases, and too, as the severity of space weather increases with solar maximum. There is an increasing need to develop physics-based, high performance models of the Sun-Earth system - from the solar surface to the Earth's upper atmosphere - which can operate faster than real time and which can provide reliable predictions of the near Earth space environment based upon solar observations and upstream solar wind measurements. We report the status of the prototype development of a Comprehensive Space Environment Model for this purpose, to be composed of a core based upon the Michigan MHD code coupled to a high performance inner magnetosphere model and ionosphere/upper atmosphere model. The inner magnetosphere model and ionosphere/upper atmosphere models are derived from the Rice Convection Model (RCM) and the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) respectively, both reformulated for parallel operation using advanced numerics on adaptive grids with significantly higher spatial resolution.

The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms−1 (protons) to 1280 kms−1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to 230 keV/e. The experiment consists of three instruments with a common Data Processing Unit. Each of the three instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made by SMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition SMS results will have an impact on many areas of solar and heliospheric physics, in particular providing important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated; (ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration of particles in the solar wind; and (vii) the physics of the pick-up process of interstellar He as well as lunar particles in the solar wind, and the isotopic composition of interstellar helium.

Models of the transition region — corona — solar wind system are investigated in order to find the coronal helium abundance and to study the role played by coronal helium in controlling the the solar wind proton flux. The thermal force on α-particles in the transition region sets the flow of helium into the corona. The frictional coupling between α-particles and protons and/or the electric polarization field determines the proton flux in the solar wind as well as the fate of the coronal helium content.

日冕物质喷发的观测速度常低于Alfven波速的估计值而高于背景日冕声速,这表明日冕质量喷发可能在日冕中形成慢激波.本文假定日冕物质喷发由冕底的磁通量喷发所驱动,对它在开放磁场中形成的慢激波进行数值模拟。结果表明,慢激波纬度范围有限,外形平坦;一快波与慢激波共存并发生相互作用。快波使背景磁场发生偏转从而在慢激波前方引起稀疏,两侧引起压缩。快波的这些效应对慢激波的位,形和特征具有重要影响。

The coronal transient event of 20–21 November is unusual in that its appearance is distinctly non-loop-like; rather, the transient resembles a confined ray or fan-like volume. Studies of the distribution of the coronal material with time indicate that this is a mass ejection event, involving about 1 × 1015 g of material from the lower corona. Analysis of the polarization signal of the event suggests that the event is associated with chromospheric activity in a region near longitude E68. The observed properties (distributions in brightness and polarization) of the transient are compared with the properties of a well-studied event of typical loop-like appearance, but rotated to simulate an ‘edge-on’ appearance; the differences suggest that the 20–21 November event is not such an edge-on, loop-like transient, but rather is most simply described as an axisymmetric-cylindrical or conical volume, the boundaries of which remain constant over the events' lifetime. On this basis, the variation of the transient spatial density with height and the variation of density with time can be specified rather more certainly than for previously-studied coronal mass ejection events. Densities are found to range from 3 × 10−16 g cm−3 at 2.1 R⊙ heliocentric height early in the event to 1 × 10−18 g cm−3 at 4.0 R⊙ late in the event. Typical temporal variations of the ejected material (at a given heliocentric height) are found to be on the order of 10−18 g cm−3 s−1. The mass and momentum balance in the event have been estimated from the observed parameters, employing a multiparameter approach. We find that a model with modest mass flux typified by material speed u0 ≲ 50 km s−1 and a near balance between the event's pressure gradient force and gravity — with possibly a small hydromagnetic wave contribution to the total pressure — is consistent with the observations. The kinetic energy of the event, determined from the motion of the center of mass of the ejected material, is only about 1026 ergs, and thus is the smallest for any solar mass ejection studied to date.

view Abstract Citations (36) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Fast-mode magnetohydrodynamic waves in coronal holes and the solar wind Fla, T. ; Habbal, S. R. ; Holzer, T. E. ; Leer, E. Abstract Fast-mode MHD waves in the solar corona can propagate in any direction relative to the background magnetic field. In coronal holes, they refract into regions of low Alfven speed and are relatively difficult to damp. These characteristics lead to the possibility that fast-mode waves transport energy from magnetically closed coronal regions into coronal holes, that they are refracted into the central regions of coronal holes, and that they deposit most of their energy in the region of supersonic flow of high-speed solar wind streams emanating from coronal holes. To investigate whether this possibility might be realized and fast-mode waves might play a significant role in driving high-speed streams, a parameter study is carried out to examine the propagation and damping of fast-mode waves in various coronal hole models. This study indicates a broad range of coronal hole parameters for which fast-mode waves can play such a role and emphasizes the need for an improved knowledge of large-scale coronal magnetic structure, which is required before any firm conclusions can be drawn. Publication: The Astrophysical Journal Pub Date: May 1984 DOI: 10.1086/162003 Bibcode: 1984ApJ...280..382F Keywords: Coronal Holes; Magnetohydrodynamic Waves; Propagation Modes; Solar Wind; Energy Transfer; Flux Density; Solar Magnetic Field; Supersonic Flow; Wave Propagation; Solar Physics full text sources ADS |

The increase in mass flux and energy flux from the Sun is calculated for an increasing Alfvén-wave amplitude, δv 0, in the lower corona and fixed values for the coronal pressure, the coronal temperature and the interplanetary magnetic field. The energy per mass and the flow speed at the orbit of the Earth increase with the wave amplitude and reach a maximum for δv 0∼50 km s−1. For reasonable values of the coronal pressure and temperature and of the magnetic field, high-speed solar-wind streams can be driven by Alfvén waves with an amplitude δv 0∼(20÷25) km s−1 in the lower corona.

The connection between geomagnetic disturbances recurring with the 27 day synodic solar rotation period and streams of plasma emitted from particular regions on the Sun (so-called M-regions) has been one of the long-standing problems of solar terrestrial physics. The ‘ plasma streams ’ have been identified with long-lived streams of fast solar wind, imbedded in unipolar magnetic ‘ sectors', for more than a decade. The solar sources of these streams have been identified unequivocally only within the past few years as large-scale coronal regions of open, diverging magnetic fields and abnormally low particle densities, observed as ‘coronal holes’. The temporal evolution of holes and streams seems to reflect the evolution of the large-scale solar magnetic fields; the observed spatial pattern of holes suggests a grand three-dimensional structure of solar wind flow and interplanetary magnetic fields organized by a near-equatorial neutral sheet. The conclusion that much of the solar wind comes from coronal holes implies several important modifications of our ideas regarding the physical origins of the solar wind and any theoretical models of solar wind formation.