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Journal Articles
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Pages: 1-10
Year: Issue:  1
Journal: Chinese Journal of Geophysics

Keyword:  均匀磁场数值积分地球半径阿尔芬初始速度特征速度磁暴急始气体动力学扰动波几何平均值;
Abstract: Chisnell- no’s method is applied to studying the propagation of a perpendicular hydromagnetic shock wave in the inhomogeneous magnetic field. A new shock parameter, the characteristic velocity of shock wave representing’ the geometric mean of the shock velocities in both sides of the front, has been introduced. The propagation equation thus obtained is greatly simplified. The equation is integrated by numerical method in the case of "strong magnetic medium", where the Alfvén velocity is much greater than the sound velocity. Three types of particle density distribution are considered: (1) the Alfvén velocity is constant, (2) the density is uniform and (3) the ratio of the density to the field intensity remains constant. It is shown that when a shock wave propagates from a weak field into a strong one, its strength measured by the jump ratio of field intensity always decreases. For medium with a constant Alfvén velocity the shock wave decays most slowly; for a medium of uniform density the shock wave attenuates most quickly; while for the constant density-field ratio medium the attenuation rate appears to be intermediate. In the weak shock limit, the amplitude of wave is inversely proportional to the square root of the Alfvén velocity. These results are discussed in relation to the magnetic shock propagating in the earth’s magnetosphere on the assumption that the whole space is filled with wholly ionized hydrogen plasma whose density is proportional to the field intensity, as confirmed by whistler observation from 2 to 5 earth’s radii distance. In this case, it is shown that a shock wave of initial velocity 10~8cm/sec at 10 earth’s radii distance will excite a 60γ field change in the earth’s surface, comparable to the order of magnetitude of the sudden commencement of a strong storm in the lower latitudes.
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