Morphological evolution and spatial profile changes of poleward moving auroral forms
Morphological evolution and spatial profile changes of poleward moving auroral forms
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DOI：
10.5194/angeo-41-115-2023
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发表时间：
2023-03
影响因子：
1.9
通讯作者：
A. Goertz;N. Partamies;D. Whiter;L. Baddeley
中科院分区：
文献类型：
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作者：
A. Goertz;N. Partamies;D. Whiter;L. Baddeley
抽象的。通过对全天相机(ASC)图像的目测和弧度指数的定量研究，定性地研究了极光运动形式(PMAF)的形态。这项研究中的PMAF最初是通过位于斯瓦尔巴特群岛谢尔·亨里克森天文台(KHO)的子午线扫描光度计(MSP)识别的，并使用KHO和斯瓦尔巴特群岛NY-älesund的相机拍摄的ASC图像进行了分析。我们给出了PMAF形态在两个维度上的详细的六步演化。这种演化包括：(1)极光椭圆形向赤道方向扩展和极光开闭边界(OCB)亮度的增强，(2)椭圆形内出现弧形结构，(3)极地和可能的西/东传播，(4)方位向扩展事件，(5)PMAF重新变亮，最终(6)逐渐消失。这是第一个致力于极光的形态演化的工作，它包括更详细的讨论和新颖的方面，例如观察到557.7 nm极光斑块的初始合并形成了极光。此外，还使用弧度指数对PMAF的形态进行了量化，该指数描述了弧形极光如何在ASC图像中出现。这使得对极光形态进行无偏见的统计调查成为可能。我们提出了与PMAF发生相关的弧度的叠加时代分析的结果。这一分析发现，在PMAF事件开始期间，幸福感突然增加，并在PMAF寿命期间下降，直到事件结束后返回到其基准值。这一行为可以基于PMAF形态的变化来理解，并验证了我们对PMAF形态的理解。此外，我们关于爱笑的发现可能会使自动识别PMAF成为可能，这已经被发现是出了名的困难。
Abstract. We investigated the morphology of poleward moving auroral forms (PMAFs) qualitatively by visual inspection of all-sky camera (ASC) images and quantitatively using the arciness index. The PMAFs in this study were initially identified with a meridian scanning photometer (MSP) located at the Kjell Henriksen Observatory (KHO), Svalbard, and analyzed using ASC images taken by cameras at the KHO and in Ny-Ålesund, Svalbard. We present a detailed six-step evolution of PMAF morphology in two dimensions. This evolution includes (1) an equatorward expansion of the auroral oval and an intensification of auroral brightness at the open–closed boundary (OCB), (2) the appearance of an arc-like structure in the oval, (3) poleward and possible west/eastward propagation, (4) azimuthal expansion events, (5) re-brightening of the PMAF and eventual (6) fading away. This is the first work dedicated to the morphological evolution of PMAFs and it includes more detailed discussion and novel aspects, such as the observation of initial merging of 557.7 nm auroral patches to form a PMAF. Moreover, the morphology of PMAFs is quantified using the arciness index, which is a number describing how arc-like auroral forms appear in ASC images. This allows an unbiased statistical investigation of auroral morphology. We present the results of a superposed epoch analysis of arciness in relation to PMAF occurrence. This analysis uncovered that arciness increases suddenly during the onset of a PMAF event and decreases over the PMAF lifetime to return to its baseline value once the event has concluded. This behavior may be understood based on changes in the morphology of PMAFs and validates our understanding of PMAF morphology. Furthermore, our findings relating to arciness may enable automatic identification of PMAFs, which has been found to be notoriously difficult.