Abstract. We present the results of a p•rameter study of the influence of heavy ions on the background solar wind, choosing doubly ionized helium, or alpha particles, and O +•, as examples. Using a three-fluid solar wind model, we keep the input parameters to the electrons and protons unchanged and investigate the effects of changing the input energy flux to the heavy ions and their coronal abundance, i.e., their abundance at 1 R•, on the background electron-proton solar wind. Our results confirm earlier studies that alpha particles can have a dramatic effect on the thermodynamic and flow properties of the protons in the solar wind. The maximum coronal abundance for which the changes in the energy input to the heavy ions has no effect on the protons is 5 x 10 -4 for the alphas and 5 x 10 -• for the oxygen ions, which are well below the photospheric values. For larger coronal abundances, the sensitivity of the changes of the flow speed and proton mass flux to changes in the energy input to the heavy ions increases sharply with increasing abundance. When the heavy ions are not heated, the increase in the coronal abundance leads to an increase in flow speed, a decrease in proton mass flux, and an increase in proton temperature at 1 AU. However, as the heat input to the heavy ions increases, the dependence of these parameters on the abundance goes through a transition and starts to follow the opposite pattern, namely a decrease in flow speed and proton temperature at 1 AU, and an increase in proton mass flux. This study shows that, for currently known photospheric elemental abundances, the flow properties of heavy ions cannot be investigated independently of those of the bulk protonelectron solar wind. The effect of heavy ions on the electron-proton bulk solar wind is determined primarily by the collisions occurring very close to the coronal base. Hence including physical processes responsible for the preferential heating of heavy ions to temperatures exceeding those of protons in the inner corona cannot be done without considering the subsequent implications for the protons and electrons in a self-consistent manner.
Using the recently developed PPMLR-MHD code, we present 3D global simulation of the interaction of the interplanetary (IP) shock with the magnetosphere with emphasis on the the effect of shock orientation. We investigate its impact on the sudden commencement (SC) of geomagnetic storms and the magnetospheric responses. Generally speaking, a highly oblique shock causes asymmetric compression of the magnetosphere with respect to the noon-midnight meridian, and requires more time to compress the forward part of the magnetosphere, which producing longer rise time of SC. Even if the solar wind dynamic pressure changed similarly at a solar wind monitor, the responses of the magnetosphere could vary depending on the orientation of the causative IP shock. The effect of the shock orientation is of great help to understand space weather processes.
A two‐dimensional, two‐component MHD model and the PPM scheme are used to investigate distribution of the density ratio (), magnetic field strength ratio (), gas pressure ratio (), and kinetic pressure jump() on the shock wave front at 1 AU in the inner helioshperic equatorial plane (the subscripts 1 and 2 represent the upstream and downstream sides respectively). Effects of the background solar wind velocity, the width and initial propagation direction of the disturbance source, and the presence of the interplanetary current sheet on the distribution are also studied. The main conclusions are as follows. (1) In an axial symmetric background, the stronger magnetic field region is situated at the western part of the shock wave front, whereas the kinetic pressure jump is larger at the eastern part. On the other hand, the density and gas pressure ratio are essentially symmetrical with respect to the normal across the source center. (2) The velocity of the background solar wind exerts a great influence on the kinetic pressure jump and the magnetic field ratio. The width of the disturbance source has no appreciable effect but the initial propagation direction of the disturbance has a significant effect on the distribution of the relevant parameters. (3) The presence of the current sheet directly affects the distribution of the parameters along the shock wave front. When the initial position of the current sheet does not coincide with the disturbance source, the peaks of the ratios of density, gas pressure and magnetic field strength deviate westward in longitude, whereas the peak of the kinetic pressure jump and the normal across the source center are located at the same side of the current sheet. When the center coincides with the current sheet, there exists a peak on each part of the shock wave front, i.e. a double peak structure, and moreover, the kinetic pressure jump is larger on the eastern part while the magnetic field strength is stronger on the western part.
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