Sources of geomagnetic activity over the solar cycle: Relative importance of coronal mass ejections, high‐speed streams, and slow solar wind
Sources of geomagnetic activity over the solar cycle: Relative importance of coronal mass ejections, high‐speed streams, and slow solar wind
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DOI：
10.1029/1999ja000400
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发表时间：
2000-08
影响因子：
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通讯作者：
I. Richardson;E. Cliver;H. Cane
中科院分区：
文献类型：
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作者：
I. Richardson;E. Cliver;H. Cane
我们评估了太阳周期期间各种类型的太阳风结构（日冕物质抛射 (CME)、高速流和慢速太阳风）对 aa 地磁活动指数 ( ) 平均值的贡献。我们使用太阳风等离子体、磁场和高能粒子数据来识别 1972 年至 1986 年期间近地太阳风中存在的流动类型（包括太阳周期 20 和整个周期 21 的衰退）。同步旋转的高速水流在太阳活动极大期之外贡献了约 70%，在太阳活动极大期贡献了约 30%（1978-1982 年）。与日冕物质抛射相关的结构（震波/震后流/喷射物）占太阳活动极大期的 ∼ 50%，在太阳活动极大期之外的比例<10%。慢速太阳风在整个太阳周期中贡献约 20%。我们的分析深入了解了地磁活动中所谓的“格涅维雪夫间隙”的原因，其特征是太阳黑子周期峰值附近的减少。这种现象的一个例子发生在 1980 年第 21 个周期的最大值时，记录的值低于之前太阳活动极小值时观测到的值。我们将 1980 年的低气压归因于平均太阳风速的暂时降低（这在日冕物质抛射和同转流相关组件中都很明显），以及所有类型太阳风结构中平均磁场的降低。所有太阳风结构的参与表明了一种全球性太阳现象，显然与太阳磁场极性反转时观察到的太阳开放磁通量的下降有关。日冕物质抛射和地磁流都会对该最小值两侧的地磁活动产生影响。因此，至少对于第 21 个周期，格涅维雪夫间隙不反映太阳活动极大期之前的日冕物质抛射导致的地磁活动水平增强时期与下降阶段期间的同步旋转流导致的第二次增强时期之间的过渡。在格涅维雪夫间隙峰值之后，高速流最终将在周期下降时主导地磁活动，并且有时（如第 20 个太阳周期）可能会产生平均地磁活动的后期峰值，而日冕物质抛射的贡献相对较小。
We assess the contribution of various types of solar wind structures (coronal mass ejections (CMEs), high-speed streams, and slow solar wind) to averages of the aa geomagnetic activity index ( ) during the solar cycle. We used solar wind plasma, magnetic field, and energetic particle data to identify the flow types present in the near-Earth solar wind during 1972–1986 (encompassing the decline of solar cycle 20 and all of cycle 21). Corotating high-speed streams contribute ∼ 70% of outside of solar maximum and ∼ 30% at solar maximum (1978–1982). CME-related structures (shocks/postshock flows/ejecta) account for ∼ 50% of at solar maximum and <10% outside of maximum. Slow solar wind contributes ∼ 20% throughout the solar cycle. Our analysis provides insight into the cause of the so-called “Gnevyshev Gap” in geomagnetic activity, characterized by a decrease in near the peak of the sunspot cycle. An example of this phenomenon occurred in 1980 at the maximum of cycle 21 when registered a value lower than that observed at the preceding solar minimum. We attribute the 1980 depression in to a temporary reduction in average solar wind speed, evident in both CME and corotating stream related components, and a reduction in mean magnetic fields in all types of solar wind structure. This involvement of all solar wind structures is indicative of a global solar phenomenon, apparently related to an observed depression in the solar open magnetic flux at the time of solar magnetic field polarity reversal. Both CMEs and streams contribute to geomagnetic activity on either side of this minimum. Thus, at least for cycle 21, the Gnevyshev Gap does not reflect a transition between a period of enhanced geomagnetic activity levels due to CMEs just prior to solar maximum and a second enhancement, due to corotating streams, during the descending phase. Beyond the post Gnevyshev Gap peak, high-speed streams will eventually dominate geomagnetic activity on the decline of the cycle and may, on occasion (as in solar cycle 20), produce a late peak in average geomagnetic activity with relatively little contribution from CMEs.