Collaborative Research: CEDAR--Three-dimensional Large Electron Density Gradients at Mid-latitudes from a TEC-based Ionospheric Data Assimilation system (TIDAS)

该项目将调查中纬度电离层中两个重要的、有时同时发生的现象，电离层是一个在大约60公里至1 000公里高度上带电粒子浓度相对较高的大气层区域。 这两种现象被称为风暴增强密度（SED）羽流和主电离层槽。 它们指的是电离层中电子密度（Ne）的巨大空间变化，通常与地球空间风暴有关，地球空间风暴是由于太阳能输入的突然变化而对地球磁场造成的扰动。 众所周知，这些大的电子密度梯度会对导航和通信系统造成重大的有害空间气象影响，本项目的总体目标是在三维域中确定这些电离层密度梯度的特征，并了解造成梯度形成和发展的基本物理过程。这将通过开展三项任务来完成：（a）建立2006年以来中到大型地球空间风暴的三维电子密度剖面数据库，使用数据同化系统生成该数据库;（B）建立第一个SED羽流和主槽的区域三维经验模型，其中包含关于其详细的时空变化和地球物理依赖性的信息;以及（c）通过基于物理学和数据驱动的综合建模方法，促进对SED和主槽机制的理解，包括电动力学和中性动力学的相对作用以及相关的电离层-热层耦合过程。科学研究[任务（B）和（c）]将调查SED和槽的统计形态，重点是它们与风暴时间的相互关系，地球物理的依赖性和驱动过程的可变性。这些过程及其在梯度形成和演变中的作用将利用热层-电离层-电动力学环流模式进行研究。由数据同化和经验模型[任务（a）和（B）]提供的具有SED和波谷的全球Ne的实际初始状态规格将在梯度模拟的每个时间步输入TIEGCM。然后，这些过程将估计使用Encourage卡尔曼滤波算法和理解其显着的风暴时间的变化可以解决。该项目的目标是应对社区在了解三维域中动态电离层密度梯度方面的重大挑战。SED和波谷特性不仅将在总电子含量（TEC）中进行研究，而且还将在NmF 2（F2区域峰值电子密度）、hmF 2（F2区域峰值电子密度的高度）和全Ne分布中进行研究。 此外，通过使用TIDAS（TEC为基础的电离层数据同化系统）的结果作为初始条件的第一性原理模式模拟，本研究解决了显着的和独特的变化的物理驱动过程的梯度在一个新的方式，通过比较分析的模拟和观测。将生成若干独特和开放获取的社区数据产品，包括2006年以来的风暴时三维电离层数据集。它将为今后以与现有的马德里加尔电子技术中心数据库同步的方式针对常规电离层三维规格的工作奠定基础，为广泛的研究界服务。将制作SED和槽的社区经验模型，直接满足梯度规范中的空间气象应用需要。本科生将参与数据分析和模拟。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

This project will investigate two significant and sometimes concurrent phenomena in the mid-latitude ionosphere, which is a region of atmosphere with relatively higher concentration of charged particles from about 60 km to 1000 km altitude. These two phenomena are called storm-enhanced density (SED) plumes and the main ionospheric trough. They refer to large spatial variations in electron density (Ne) in the ionosphere, often associated with geospace storms which are disturbances in the Earth’s magnetic fields due to sudden changes in solar energy input. These large electron density gradients are known for imposing substantial and detrimental space weather effects on navigation and communication systems.The overall goal of this project is to characterize these ionospheric density gradients in a three-dimensional (3-D) domain, and to understand the fundamental physical processes responsible for gradient formation and development. This will be accomplished by conducting three tasks: (a) creation of a 3-D electron density profile database for moderate-to-major geospace storms since 2006, using a data assimilation system to produce the database; (b) construction of the first regional 3-D empirical models of SED plumes and the main trough, containing information on their detailed spatial-temporal variations and geophysical dependence; and (c) through a combined physics-based and data-driven modeling approach, advancing understanding of SED and main trough mechanisms, including relative roles of electrodynamics and neutral dynamics as well as associated ionosphere-thermosphere coupling processes.Scientific studies [Tasks (b) and (c)] will investigate SED and trough statistical morphology, focusing on their storm-time inter-relationship, geophysical dependence, and variability of the driving processes. These processes and their roles in the formation and evolution of gradients will be investigated using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). A realistic initial state specification of global Ne with SED and trough, provided by data assimilation and empirical models [Tasks (a) and (b)], will feed into TIEGCM at each time step for the gradient simulation. These processes will then be estimated using the Ensemble Kalman filter algorithm and understanding of their significant storm-time variability can be addressed. This project targets the important community challenge of understanding extremely dynamic ionospheric density gradients in a 3-D domain. SED and trough characteristics will be investigated not only in the Total Electron Content (TEC) but also in NmF2 (F2 region peak electron density), hmF2 (height of the peak electron density in F2 region), and full Ne profiles. Furthermore, through use of TIDAS (TEC-based Ionospheric Data Assimilation System) results as initial conditions for first-principle model simulations, this study addresses significant and unique variability of physical driving processes of the gradients in a novel way through comparative analysis of the simulations and observations. Several unique and open-access community data products will be generated, including storm-time 3-D ionospheric dataset since 2006. It will lay the foundation for future efforts targeting regular ionospheric 3-D specification in a synchronized fashion with the existing Madrigal TEC database, serving a broad research community. Community empirical models of SED and the trough will be produced that directly address space weather application needs in gradient specification. Undergraduate students will be involved with data analysis and simulation.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.