| 磁流体冲激波在非均匀磁场中的传播 |
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| 引用本文： | 章公亮.磁流体冲激波在非均匀磁场中的传播[J].地球物理学报,1964,13(1):1-10. |
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| 作者姓名： | 章公亮 |
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| 作者单位： | 中国科学院地球物理研究所 |
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| 摘 要： | 本文应用Chisnell- no方法,求解了在理想介貭中,垂直磁流体冲激波在非均勻磁場中的传播問題。这种方法,把非均勻介貭分解成无限小的弱間断面,根据气体动力学中波与間断面相互作用的原理,算出激波通过弱間断面时的强度变化,然后用积分求得激波通过整个非均勻区时的强度变化。作者引入了激波的特征速度（它是激波在波前后介貭中传播速度的几何平均值）作为輔助参量,得到形式上比較簡单的激波传播方程。然后考虑了磁压力远大于气体压力的强磁介貭中的激波传播問題,并进行了数值积分。采用的介貭密度模型有三种:（1）阿尔芬波速为常数;（2）密度不变;（3）密度与磁場强度成正比。計算結果表明:当激波由弱磁場向强磁場传播时,激波的强度逐漸变弱。其中,在阿尔芬波速为常数的介貭中,激波强度的衰减最为緩慢;在密度不变的介貭中,激波强度的衰減最为迅速;而在密度与磁場成正比的介貭中,激波强度的衰減則介乎上述两种密度分布之間。作者联系磁流体冲激波在地球外层空間的传播問題进行了討論,密度的模型采取大气啃昔的观測結果（卽上述第三种密度分布）,并进行了适当的外推,估計了在十个地球半径处的磁流体冲激波传到地面时的强度,求出了激波在地面引起的磁場变化与激波初始速度之間的关系。根据上述簡化模型,計算結果表明,在十个地球半径处初始速度为108厘米/秒的激波,传到地面引起的磁場变化大約为60伽（亻馬）,这个数值的量級恰好与中低緯度强磁暴的急始变幅相符。
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| 关 键 词： | 弱激波 磁流体 阿尔芬波 激波强度 特征速度 密度分布 传播速度 激波传播 数值积分 球半径 |
PROPAGATION OF HYDROMAGNETIC SHOCK WAVE IN THE INHOMOGENEOUS MAGNETIC FIELD |
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| ZHANG GONG-LIANG.PROPAGATION OF HYDROMAGNETIC SHOCK WAVE IN THE INHOMOGENEOUS MAGNETIC FIELD[J].Chinese Journal of Geophysics,1964,13(1):1-10. |
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| Authors: | ZHANG GONG-LIANG |
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| Institution: | Institute of Geophysics and Meteorology, Academia Sinica |
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| 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 108cm/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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