Although the postmidnight‐to‐dawn sector of the auroral ionosphere contains interesting dynamic phenomena that may significantly impact the magnetosphere‐ionosphere‐thermosphere system, it has been much less studied than the dusk‐to‐premidnight sector. We discuss a dynamic phenomenon in the postmidnight‐to‐dawn sector of the auroral oval, eastward fast flows mainly within the expanse of the Region 1 current (its part equatorward of the polar cap). These flows peak and have a steep speed gradient (increase from low to high latitude) near the interface between the Region 1 and Region 2 currents. Because such flows correspond to an electric field that most likely comes from enhanced Region 2 currents and an associated spatial conductivity gradient, their generation mechanism is analogous to that of a subauroral polarization stream. Therefore, we refer to such an eastward flow as a dawnside auroral polarization stream (DAPS). We show several examples of the presence and absence of DAPS under different geomagnetic activity levels. A DAPS' electric field can heat the ionosphere (and thus the thermosphere), change the convection pattern of the magnetosphere‐ionosphere system, and modify the drift path of magnetospheric particles. Because a DAPS' flow peak maps to a major site of magnetic‐kinetic energy conversion in the magnetosphere (the transition region between dipole and stretched field), it may be important for the conversion. A DAPS' steep flow gradient is also potentially important; it may lead to instabilities, such as that responsible for auroral Omega bands. Given its potential importance, knowledge of DAPS is fundamental for understanding the magnetosphere‐ionosphere‐thermosphere system.

中文翻译：

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黎明极光极化流

尽管极光电离层的午夜后至黎明部分包含有趣的动力学现象，这些现象可能会显着影响磁层-电离层-热球系统，但与黄昏至午夜部分相比，它的研究少得多。我们讨论了极光椭圆形的从午夜到黎明的动态现象，主要是在1区洋流（其极地赤道的一部分）的范围内向东快速流动。这些流量达到峰值并在1区和2区电流之间的界面附近具有陡峭的速度梯度（从低纬度增加到高纬度）。由于此类流对应的电场很可能来自增强的区域2电流和相关的空间电导率梯度，因此它们的生成机制类似于耳下极化流的生成机制。因此，我们将这种向东的流动称为黎明极光极化流（DAPS）。我们显示了在不同地磁活动水平下存在和不存在DAPS的几个示例。DAPS的电场可以加热电离层（进而加热热层），改变磁层-电离层系统的对流方式，并改变磁层颗粒的漂移路径。由于DAPS的流量峰值映射到磁层中磁动能转换的主要部位（偶极子和拉伸场之间的过渡区域），因此对于转换来说很重要。DAPS陡峭的流量梯度也很重要。它可能导致不稳定，例如导致极光Omega波段的不稳定。鉴于其潜在的重要性，