Multi-Scale Experimental Investigations of Extreme Plasma Density Depletions in the Polar Ionosphere

该项目将研究极地电离层中被称为“极地空穴”的现象，这是由于太阳辐射而高度电离的大气区域（海拔80至1000公里），具有高浓度的带电粒子，即电子和离子。极洞指的是带电粒子（称为等离子体）的大量减少，这种减少不时出现在所谓的f区（150至500公里），并且被认为在太阳辐射处于最低水平的太阳极小期更经常发生。这种空穴的形成与带电粒子与电磁场和大气环流的复杂相互作用有关，这在极地地区是独一无二的。了解极洞的形成和内部结构填补了我们对这种相互作用的理解的空白，并有助于改进极地电离层的模型模拟。当前的太阳极小期为研究这一现象提供了一个很好的机会。本项目将实验研究极空穴及其等离子体对流在其形成和演化中的作用。极洞被认为是在非常缓慢的反太阳对流期间形成的，当等离子体在没有任何电离源的情况下被困在统计极光椭圆的正极方向时。同时，伴随等离子体垂直输运的快速对流也与极空穴的形成有关。结合位于北极帽的先进模块化非相干散射雷达（AMISR）的多点能力、ASTRA开发的最新变分数据同化工具IDA4D，以及超级双极光雷达网络（SuperDARN）阵列的对流数据，研究等离子体对流在极地空穴形成中的作用。在极洞附近的密度被认为是非常有结构的。本研究将探索极孔的内部结构，分析极孔内部及其边缘的梯度，并评估其对高频雷达后向散射的影响。最后，为了提高极帽区域电子密度条件的可预测性，这是建模中最困难的问题，将对太阳极小期条件下的极帽密度进行统计分析。利用IDA4D运行和COSMIC I任务在南北两极地区收集的大量无线电掩星数据来研究极帽密度的变异性，以找到模型参数和数据导出参数差异最大的问题最严重的时段。这项工作将提高我们对太阳活动极小期极帽中等离子体消耗的认识。冬季和太阳活动极小期的极帽是电离层模型在卫星通信、卫星导航、数据链和空间态势感知等应用领域中最具问题的区域之一。这项工作将通过对极帽区最低极值的直接调查和对其变异性的统计调查，提高模拟极帽区电子密度的能力。该项目将支持一名早期职业女性研究人员，她有良好的外展活动记录，包括为老年人提供空间物理学讲座，并开发www.sheisaphysicist.com网络空间，通过发布有关女性物理学家职业道路的故事来促进和培养女性在物理学领域的成功。当一个新的采访发布时，该网站达到了约2000个独立观点，激励高中和本科女生选择物理作为她们的职业道路。这将有助于扩大代表性不足的少数民族在STEM领域的参与。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will investigate a phenomenon called ‘polar holes’ in the polar ionosphere, which is a region of atmosphere (80 to 1000 km above sea level) that is highly ionized due to solar radiation, with high concentration of charged particles, i.e. electrons and ions. The polar hole refers to the large reduction of charged particles (called plasma) that appears from time to time in the so-called F-region (150 to 500 km) and is believed to happen more often during the solar minimum when the solar radiation is at its lowest level. The formation of such holes is related to the complex interactions of the charged particles with the electromagnetic field and atmospheric circulation that are unique in the polar region. Understanding the formation and internal structures of the polar holes fills the gap of our understanding of such interactions and helps improve model simulation of the polar ionosphere. The current solar minimum provides a good opportunity to study this phenomenon.This project will experimentally investigate the polar holes and the role of the plasma convection in their formation and evolution. Polar holes are believed to be formed during the periods of the very slow anti-sunward convection, when the plasma is trapped just poleward of the statistical auroral oval in the absence of any ionization sources. At the same time, fast convection with rapid vertical plasma transport has also been associated with the polar hole formation. Combining the multi-point capability of the Advanced Modular Incoherent Scatter Radar (AMISR) located in the northern polar cap, the state of art variational data assimilation tool IDA4D developed at ASTRA, and the convection data from the Super Dual Auroral Radar Network (SuperDARN) array, the role of plasma convection in the polar hole formation will be investigated. The density in the vicinity of the polar holes is thought to be very structured. This study will explore the polar hole internal structure, analyze the gradients that are present inside the polar hole and on its edges, and evaluate their effects on high-frequency radar backscatter. Finally, to improve the predictability of the electron density conditions in polar cap regions, which are most problematic for modeling, a statistical analysis of the polar cap density during the solar minimum conditions will be performed. Variability of the polar cap density will be investigated using IDA4D runs and large amounts of collected radio occultation data from COSMIC I mission in the northern and southern polar regions to find the most problematic time periods where the model parameters and data-derived parameters have the largest differences.The work will improve our knowledge of the plasma depletions in the polar cap during solar minimum conditions. The polar cap during the winter and during the solar minimum is one of the most problematic zones for the ionospheric models used in application areas, such as satellite communications, satellite-based navigation, data links, and space situational awareness. This work will improve the ability to model the electron density in the polar cap region by direct investigation of its lowest extremes and by statistical investigation of its variability. This project will support an early-career female researcher who has a strong track record of outreach activities, including delivering Space Physics lectures for senior people and developing the www.sheisaphysicist.com web space that promotes and cultivates the success of women in physics by publishing stories about the career path of female physicists. When a new interview is published, the website reaches ~2000 independent views, inspiring high-school and undergraduate female students to choose physics as their career path. This will contribute to broadening of participation of underrepresented minorities in STEM fields.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.