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Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

【标题】Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

【Title】Spontaneous and trigger-associated substorms compared: Electrodynamic parameters in the polar ionosphere

【作者】 刘俊明; 张北辰; Y. Kamide ; Zhen-Sen Wu ; 胡泽骏; 杨惠根

【Author】 Liu Junming ; Zhang Beichen ; Y. Kamide ; Zhen-Sen Wu ; Hu Zejun ; Yang Huigen

【期刊】Journal of Geophysical Research: Space Physics

【Journal】Journal of Geophysical Research: Space Physics

【期刊年份】2011

【卷】116

【期】A1

【关键词】 trigger-associated substorms; spontaneous substorm; ionosphere; solar wind

【Keywords】 trigger-associated substorms; spontaneous substorm; ionosphere; solar wind

【摘要】 An attempt is made to study the difference, if any, between the response of the polar ionosphere to spontaneous substorms and that to trigger-associated substorms in terms of electrodynamic parameters including ionospheric current vectors, the electric potential, and the current function. The results show that, in the first approximation, the ionospheric parameters for the two types of substorms are quite similar. It is therefore conceived that spontaneous substorms are not very different from trigger-associated substorms in the development of substorm processes in the magnetosphere-ionosphere system. We demonstrate, however, that spontaneous substorms seem to have a more clearly identifiable growth phase, whereas trigger-associated substorms have a more powerful unloading process. Changes in the current intensity and the electric potential drop across the polar cap in the recovery phase are also quite different from each other. Both the current intensity and the cross-polar cap potential drop show a larger decrease in the recovery phase of trigger-associated substorms, but the potential drop decreases only slightly and the currents in the late morning sector are still strong for spontaneous substorms. We interpret these findings as an indication of the relative importance of the unloading process and the directly driven process in conjunction with the north-south polarity of the interplanetary magnetic field. There still exists a strong directly driven process in the recovery phase of spontaneous substorms. For trigger-associated substorms, however, both the directly driven process and the unloading process become weak after the peak time.

【Abstract】 An attempt is made to study the difference, if any, between the response of the polar ionosphere to spontaneous substorms and that to trigger-associated substorms in terms of electrodynamic parameters including ionospheric current vectors, the electric potential, and the current function. The results show that, in the first approximation, the ionospheric parameters for the two types of substorms are quite similar. It is therefore conceived that spontaneous substorms are not very different from trigger-associated substorms in the development of substorm processes in the magnetosphere-ionosphere system. We demonstrate, however, that spontaneous substorms seem to have a more clearly identifiable growth phase, whereas trigger-associated substorms have a more powerful unloading process. Changes in the current intensity and the electric potential drop across the polar cap in the recovery phase are also quite different from each other. Both the current intensity and the cross-polar cap potential drop show a larger decrease in the recovery phase of trigger-associated substorms, but the potential drop decreases only slightly and the currents in the late morning sector are still strong for spontaneous substorms. We interpret these findings as an indication of the relative importance of the unloading process and the directly driven process in conjunction with the north-south polarity of the interplanetary magnetic field. There still exists a strong directly driven process in the recovery phase of spontaneous substorms. For trigger-associated substorms, however, both the directly driven process and the unloading process become weak after the peak time.

【基金/项目】 空间灾害性天气的电离层和中高层大气研究 ; 极隙区空间天气现报和预报模式研究 ; 极区能量沉积过程及其对120E子午面电离层影响的研究 ; 极区电离层南北极对比研究 ; 日侧冕状极光的分类及其产生机制研究 ; 日侧极光粒子沉降的能谱特征研究 ; 日侧极光分类及其在空间天气监测中的应用

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