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

该项目将研究中纬度电离层的两种重要且有时同时发生的现象，电离层是海拔约60公里至1000公里的带电粒子浓度相对较高的大气区域。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量输入的突然变化而引起的地球磁场的扰动。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巨大而有害的空间天气影响。该项目的总体目标是在三维（3-D）域描述这些电离层密度梯度，并了解负责梯度形成和发展的基本物理过程。为此，我们将进行三项工作：(a)利用数据同化系统，建立2006年以来中至大型地球空间风暴的三维电子密度分布图数据库；(b)建立了首个SED羽流和主槽的区域三维经验模型，包含了它们的详细时空变化和地球物理相关性信息；(c)通过结合基于物理和数据驱动的建模方法，推进对SED和主要槽机制的理解，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)]将通过统计形态学调查SED和SED，重点关注它们的风暴时间相互关系、地球物理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化中的作用将使用热层-电离层-电动力学环流模式（TIEGCM）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和槽的全局Ne的现实初始状态规范将在每个时间步输入TIEGCM进行梯度模拟。然后，这些过程将使用集合卡尔曼滤波算法进行估计，并了解其显著的风暴时间变异性。这个项目的目标是在三维领域理解极端动态电离层密度梯度的重要社区挑战。SED和槽特性将不仅研究总电子含量（TEC），还研究NmF2 （F2区峰电子密度）、hmF2 （F2区峰电子密度高度）和全Ne谱。此外，利用基于tec的电离层数据同化系统（TIDAS）结果作为第一原理模式模拟的初始条件，通过模拟和观测的对比分析，以一种新颖的方式解决了梯度物理驱动过程的显著和独特的变异性。将生成几个独特和开放获取的社区数据产品，包括自2006年以来的风暴时间三维电离层数据集。它将为未来的工作奠定基础，目标是与现有的Madrigal TEC数据库同步进行常规电离层3-D规格，为广泛的研究社区服务。将产生SED和槽的社区经验模型，直接解决梯度规范中的空间天气应用需求。本科学生将参与数据分析和模拟。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 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.