Abstract. Based on assumptions that substorm field line dipolarization at geosynchronous altitudes is associated with the arrival of high-velocity magnetotail flow bursts referred to as bursty bulk flows, the following sequence of field line dipolarization is proposed: (1) slow magnetoacoustic wave excited through ballooning instability by enhanced inflows in pre-onset intervals towards the equatorial plane; (2) in the equatorial plane, slow magnetoacoustic wave stretching of the flux tube in dawn–dusk directions resulting in spreading plasmas in dawn–dusk directions and reduction in the radial pressure gradient in the flux tube. As a consequence of these processes, the flux tube assumes a new equilibrium geometry in which the curvature radius of new field lines increased in the meridian plane, suggesting an onset of field line dipolarization. The dipolarization processes associated with changing the curvature radius preceded classical dipolarization caused by a reduction of cross-tail currents and pileup of the magnetic fields. Increasing the curvature radius induced a convection surge in the equatorial plane as well as inductive westward electric fields of the order of millivolts per meter (mV m −1 ). Electric fields transmitted to the ionosphere produce an electromotive force in the E layer for generating a field-aligned current system of Bostrom type. This is also equivalent to the creation of an incomplete Cowling channel in the ionospheric E layer by the convection surge.

中文翻译：

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经典偶极化前地磁场线曲率半径的增加

摘要。基于地球同步高度的亚暴场线偶极化与称为突发体流的高速磁尾流爆发的到来相关的假设，提出了以下场线偶极化序列：（1）通过膨胀不稳定性激发的慢磁声波通过在发病前的间隔内向赤道平面增加流入量；(2) 在赤道平面上，通量管在黎明-黄昏方向的缓慢磁声波拉伸导致等离子体在黎明-黄昏方向扩散，并降低通量管中的径向压力梯度。作为这些过程的结果，通量管呈现出一种新的平衡几何形状，其中新场线的曲率半径在子午面增加，表明场线双极化的开始。与改变曲率半径相关的偶极过程先于由交叉尾电流减少和磁场堆积引起的经典偶极。增加曲率半径会导致赤道平面中的对流浪涌以及每米毫伏 (mV m -1 ) 数量级的感应西向电场。传输到电离层的电场在 E 层中产生电动势，用于产生 Bostrom 型场对齐电流系统。这也等同于对流浪涌在电离层 E 层中形成了一个不完整的 Cowling 通道。增加曲率半径会导致赤道平面中的对流浪涌以及每米毫伏 (mV m -1 ) 数量级的感应西向电场。传输到电离层的电场在 E 层中产生电动势，用于产生 Bostrom 型场对齐电流系统。这也等同于对流浪涌在电离层 E 层中形成了一个不完整的 Cowling 通道。增加曲率半径会导致赤道平面中的对流浪涌以及每米毫伏 (mV m -1 ) 数量级的感应西向电场。传输到电离层的电场在 E 层中产生电动势，用于产生 Bostrom 型场对齐电流系统。这也等同于对流浪涌在电离层 E 层中形成了一个不完整的 Cowling 通道。