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

这个项目将研究中纬度电离层中的两个重要现象，有时是同时发生的，电离层是在大约60公里至1000公里高度具有相对较高带电粒子浓度的大气区域。这两种现象被称为风暴增强密度(SED)羽流和电离层主槽。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和有害的空间天气影响。该项目的总体目标是在三维(3-D)域中表征这些电离层密度梯度，并了解导致梯度形成和发展的基本物理过程。为此，将开展三项工作：(A)自2006年以来，利用数据同化系统建立一个中到大的地球空间风暴的三维电子密度剖面数据库；(B)建立第一个关于SED羽流和主槽的区域三维经验模型，其中载有关于其详细的时空变化和地球物理相关性的信息；科学研究[任务(B)和(C)]将研究SED和槽的统计形态，重点研究它们在风暴时间的相互关系、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-电动力学大气环流模式(TIEGCM)进行研究。由资料同化和经验模式[任务(A)和(B)]提供的具有SED和槽的全球Ne的真实初始态规范将在每个时间步长输入TIEGCM用于梯度模拟。然后，将使用集合卡尔曼滤波算法估计这些过程，并了解它们在风暴时间的显著变化。该项目的目标是在3-D领域中理解极其动态的电离层密度梯度这一重要的社区挑战。SED和沟槽特性不仅将在总电子含量(TEC)中进行研究，还将在NmF2(F2区峰值电子密度)、hmF2(F2区峰值电子密度高度)和全Ne分布中进行研究。此外，通过使用TIDAS(基于TEC的电离层数据同化系统)结果作为第一原理模式模拟的初始条件，本研究通过模拟和观测的对比分析，以一种新的方式解决了梯度物理驱动过程的显著和独特的可变性。将产生若干独特和开放获取的社区数据产品，包括2006年以来的风暴时间3-D电离层数据集。它将为今后以常规电离层3-D规范为目标的工作奠定基础，使之与现有的Madrigal TEC数据库同步，为广泛的研究界服务。将产生SED和低谷的社区经验模式，直接解决梯度规范中的空间天气应用需求。本科生将参与数据分析和模拟。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.