Data Assimilation of Ground‐Based GPS and Radio Occultation Total Electron Content for Global Ionospheric Specification

Abstract

This study presents an approach based on the Gauss‐Markov Kalman filter to assimilate the total electron content observed from ground‐based GPS receivers and space‐based radio occultation instrumentations (such as FORMOSAT‐3/COSMIC (F3/C) and FORMOSAT‐7/COSMIC‐2 (F7/C2)) into the International Reference Ionosphere. Observing System Simulation Experiments (OSSEs) show that the data assimilation procedure consisting of the forecast and the measurement update steps can better improve the accuracy of the data assimilation analysis than the assimilation procedure using the measurement update alone. Compared with F3/C, the denser F7/C2 occultation observations can improve the analysis accuracy significantly as suggested by OSSEs. The real data assimilation results are further validated with global ionosphere maps, the global ground‐based GPS measurements, and the ionospheric F2 peak height and electron density sounded by ionosondes. Both the OSSEs and validation results confirm that a number of improvements to the data assimilation procedure presented in this paper can indeed be used to reconstruct the three‐dimensional ionospheric electron density adequately.

Revisiting the Modulations of Ionospheric Solar and Lunar Migrating Tides During the 2009 Stratospheric Sudden Warming by Using Global Ionosphere Specification

“…As the assimilation cycle progresses along time, the analysis ionosphere is continuously updated, and the influence of initial ionosphere conditions given by International Reference Ionosphere is replaced by the prior state of the assimilation after 8 hr (Lin et al, ). The GIS product has been verified by observing system simulation experiments, demonstrating that the data assimilation procedure, consisting of both the forecast and the measurement update steps, can greatly improve the accuracy of the data assimilation analysis compared to the assimilation procedure using solely the measurement update alone (Lin et al, ). The domain of GIS consists of 5° × 2.5° × 20 (km) grid in geographic longitude, magnetic latitude (between ±40°), and altitude (from 100 to 1,000 km) with time interval of 1 hr in UT.…”

“…However, previous studies using FORMOSAT‐3/COSMIC (F3/C) electron density profiles could not resolve and distinguish daily SW2 and M2 variabilities as it requires at least a 20‐day accumulated window to ensure sufficient radio occultation measurements in the global three‐dimensional grid covering 24‐hr local time period for constructing the median ionospheric electron density (J. T. Lin et al, ). In the present study, we utilize a new approach of assimilated electron density product (Lin et al, ), referred to as global ionosphere specification (GIS). GIS assimilates both radio occultation and ground‐based Global Positioning System (GPS) slant TECs and provides hourly global electron density distribution every day.…”

Generation of Regional Ionospheric TEC Maps With EIA Nowcasting/Forecasting Capability During Geomagnetic Storm Conditions

“…A linear Gauss Markov process is used in the Kalman filter model forecast step to time-forward the ionospheric TEC state from k time step to k + k time step as given below (2) [11].…”

“…Chen et al [18] assimilated ground-based GPS TEC observations into the TIEGCM model with 10 min assimilation-forecast cycling process and achieved greater forecast accuracy. Lin et al [11] assimilated the global data sets of ground-based TEC observations and COSMIC F3/C radio occultation datapoints onto International Reference Ionosphere (IRI) including forecasting capability.…”

Exploration of a Composite Index to Describe Magnetospheric Activity: Reduction of the Magnetospheric State Vector to a Single Scalar

“…Magnetospheric measures that certainly would be of interest if they became available for extended periods of time are measures of the state of the plasmasphere, the state of the electron plasma sheet, the area of the polar cap, the dayside reconnection rate (measured from dayside ionospheric radars), the total radiation belt content (C.-L. Huang, private communication, August 31, 2015;Forsyth et al, 2016), a nightside stretching index (S. Wing, private communication, June 18, 2014), the mass composition of the magnetospheric plasmas, and the intensities of plasma waves in the magnetosphere (in particular electromagnetic ion cyclotron waves and whistler-mode chorus waves). Ionospheric measures that would be of interest if they became available are the ionospheric ion outflow rates from the polar cap and from the auroral zone (Welling et al, 2015;Wilson et al, 2004), the global total electron content (Emmert et al, 2017;Lin et al, 2017), the global Joule heating rate (Weimer, 2005;Zhang et al, 2005), and the Q-value of the Schumann resonance cavity (Fullenkrug et al, 2002;Toledo-Redondo et al, 2016). A storm time atmospheric measure that would be of interest for atmospheric drag if it became available is the thermospheric density (Rhoden et al, 2000;Vallardo & Finkleman, 2014).…”