Collaborative Research: CEDAR--Large-Scale Characterization of the Sub-Auroral Polarization Stream and Its Impacts on the Ionosphere-Thermosphere System

在地磁暴期间，位于极光区赤道正对面的电离层区域经常受到高速(1公里/S)等离子体流的纵向扩展通道的扰动，称为亚极光极化流(SAPS)。研究人员将分析在当前太阳活动周期高峰期观测到的电离层扰动，目的是得出一个全面的、以观测为基础的SAPS模型。这项研究将检验SAPS流的开始、扩散和衰减，并绘制观察到的总电子含量(TEC)的伴随变化。将与米尔斯通山最近翻新的非相干散射雷达进行协调实验，以便将SAPS电场动态与电离层密度和化学变化联系起来，并衡量其对中性大气的影响。SAPS现象与强烈的极向电场(50 mV/m)和电离层密度的深凹陷或低谷有关。SAPS被认为是反馈过程的结果，在反馈过程中，起源于磁层的磁场对齐电流关闭整个电离层槽，引发化学变化，进一步降低电离层密度，同时以保持电流连续性的方式增加电场。SAPS现象对电离层等离子体的结构、电离层成分、等离子体不规则的形成以及与中性大气的耦合都有重要的影响。以观测为基础全面了解SAPS及其对热层的影响将是一大进步。SAPS传统上是用单一雷达和卫星来研究的，导致对SAPS作为一种多维、全球尺度现象的演变和影响的了解作用有限。观测技术的最新进展从根本上改变了研究的格局。由于在北美建造了中纬度SuperDARN雷达链，有可能同时(~1分钟)看到多个小时的SAPS等离子体流动和电场，而全球定位系统接收器网络的扩大使在类似时间尺度上绘制大陆尺度的TEC图成为可能。初步比较表明，雷达观测到的SAPS位于TEC绘制的增强的槽状密度特征中。这项工作将导致开发适用于检验理论想法的SAPS现象学模型，并开发风暴时间电离层模型，向更广泛的社区传播关于SAPS最近事件的全球范围的信息，将全球定位系统TEC数据库更多地应用于科学研究，并指导科学家使用这些数据。此外，弗吉尼亚理工大学的一名研究生将接受新的实验技术以及来自SuperDARN雷达、GPS和非相干散射雷达的数据合并方面的培训。

During geomagnetic storms the region of the ionosphere that lies just equatorward of the auroral zone is often perturbed by a longitudinally-extended channel of high-speed (1 km/s) plasma flow known as the sub-auroral polarization stream (SAPS). The investigators will analyze observations of ionospheric disturbances through the current period of solar cycle maximum with the aim of deriving a comprehensive, observationally based model of SAPS. The study will examine the onset, spread, and decay of SAPS flows and chart the accompanying changes observed in total electron content (TEC). Coordinated experiments will be conducted with the recently refurbished Incoherent Scatter Radar (ISR) at Millstone Hill in order to relate the SAPS electric field dynamics to changes in ionospheric density and chemistry and to gauge their effects on the neutral atmosphere. The SAPS phenomenon is associated with strong poleward-directed electric fields (50 mV/m) and a deep depression, or trough, in ionospheric densities. SAPS is believed to be a consequence of a feedback process whereby magnetic field-aligned current of magnetospheric origin closes across the ionospheric trough, eliciting chemical changes that further reduce the ionospheric density while increasing the electric field in a manner that maintains current continuity. The SAPS phenomenon has important consequences for structuring ionospheric plasma, ionospheric composition, formation of plasma irregularities, and coupling to the neutral atmosphere. The attainment of a comprehensive, observationally-based understanding of SAPS and its impacts on the thermosphere would be a major advance. SAPS has traditionally been studied with single radars and satellites, leading to characterizations that are limited in their utility for understanding the evolution and impacts of SAPS as a multi-dimensional, global-scale phenomenon. Recent advances in observational techniques have fundamentally altered the research landscape. The construction of a mid-latitude chain of SuperDARN radars in North America has made possible simultaneous (~1 min) views of SAPS plasma flows and electric fields across many hours of MLT while the expansion of the network of Global Positioning System (GPS) receivers has made possible continental-scale mapping of TEC on similar time scales. Initial comparisons indicate that the SAPS observed by the radars are seated in an enhanced trough-like density feature that is mapped by TEC. This work will lead to the development of a phenomenological model of SAPS that is suitable for testing theoretical ideas and the development of storm-time ionospheric models, the dissemination of global-scale information on recent SAPS events to the wider community, the increased application of the GPS TEC database to scientific research, and the instruction of scientists on the use of these data. In addition, a graduate student at Virginia Tech will be trained in the new experimental techniques and in the merging of data from the SuperDARN radars, GPS, and incoherent scatter radar.