Response of the Magnetosphere -ionosphere- earth system to solm Wind Dynamic Prssure Variation

1. 详细分析了1991年3月24日发生的一次地磁突然开始（SC）。发现(1)大(202元Kakioka)正H-component脉冲的时间短(约1分钟)出现在初始阶段SC.Such大幅脉冲以前从未被观察到,(2)这个脉冲是由传播的效果突然压缩整个磁气圈的光面阴面,(3)大幅脉冲的动态压力应该存在于太阳风为了产生脉冲,(4)至于地球附近的脉冲的传播,脉冲的峰值在电离层中以HM波速度传播，但其起始在电离层与地球之间的空间中几乎是瞬间传播的。(5)在大约6小时后，在世界范围内观测到一个相干的Pc-5地磁脉冲。结果表明：(1)1940年3月24日在Kakioka观测到最大的SC，其振幅为273nT；(2) 1924 ~ 1994年期间观测到12个振幅大于100nT的SC；(3)大振幅SC多出现在太阳黑子数量下降的阶段。Dst指数与太阳风动压（Pd）平方根的散点图显示，上层包络线呈线性增加。我们解释说，这个包络显示了Pd的依赖性。我们还分析了(1)连续的地面负地磁脉冲观测，(2)地球同步磁层顶交叉，(3)1994年2月21日的SC。

1. A geomagnetic sudden commencement (SC) occurred on March 24,1991 was analyzed in detail. It was found that (1) A large (202nT at Kakioka) positive H-component pulse of short duration (about 1 min) appeared in the initial stage of SC.Such a sharp pulse has never been observed before, (2) This pulse was caused by propagation of the effect of a sudden compression of the whole magnetosphere from dayside to nightside, (3) A sharp pulse of the dynamic pressure should exist in the solar wind in order to produce the pulse, (4) As for the propagation of the pulse near the earth, the peak of the pulse propagated with HM wave velocity in the ionosphere but its onset propagated nearly instantaneously in the space between the ionosphere and the earth, (5) A coherent Pc-5 geomagnetic pulsation was observed world-widely after about 6 hours.2. We analyzed past large SCs observed at Kakioka and found that (1) The largest SC occurred on March 24,1940 and its amplitude was 273nT,(2)Twelve SCs with amplitude larger than 100nT were observed in the period between 1924 and 1994, (3)large amplitude SCs tend to occur in the declining phase of the sunspot number.3. A scatter plot of the Dst index versus the square root of the solar wind dynamic pressure (Pd) shows a upper envelope increasing linearly. We interpret that this envelope shows Pd dependence of Dst.4. We also analyzed (1) successive negative geomagnetic impulses observed on the ground, (2) geosynchronous magnetopause crossings, and (3) SC on February 21,1994.