This paper reviews our current understanding of auroral features that appear poleward of the main auroral oval within the polar cap, especially those that are known as Sun-aligned arcs, transpolar arcs, or theta auroras. They tend to appear predominantly during periods of quiet geomagnetic activity or northwards directed interplanetary magnetic field (IMF). We also introduce polar rain aurora which has been considered as a phenomenon on open field lines. We describe the morphology of such auroras, their development and dynamics in response to solar wind-magnetosphere coupling processes, and the models that have been developed to explain them.

中文翻译：

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极光中的极光：回顾

本文回顾了我们目前对极冠内主极光椭圆极光特征的理解，尤其是那些被称为太阳对齐弧、跨极弧或θ极光的极光。它们往往主要出现在地磁活动平静或向北的行星际磁场 (IMF) 期间。我们还介绍了极雨极光，它被认为是开放场线上的一种现象。我们描述了此类极光的形态、它们的发展和响应太阳风-磁层耦合过程的动力学，以及已开发的用于解释它们的模型。