The Early Results and Validation of FORMOSAT‐7/COSMIC‐2 Space Weather Products: Global Ionospheric Specification and Ne‐Aided Abel Electron Density Profile

Abstract

The FORMOSAT-7/COSMIC-2 (F7/C2) satellite mission was launched on 25 June 2019 with six low-Earth-orbit satellites and can provide thousands of daily radio occultation (RO) soundings in the low-latitude and midlatitude regions. This study shows the preliminary results of space weather data products based on F7/C2 RO sounding: global ionospheric specification (GIS) electron density and Ne-aided Abel and Abel electron density profiles. GIS is the ionospheric data assimilation product based on the Gauss-Markov Kalman filter, assimilating the ground-based Global Positioning System and space-based F7/C2 RO slant total electron content, providing continuous global three-dimensional electron density distribution. The Ne-aided Abel inversion implements four-dimensional climatological electron density constructed from previous RO observations, which has the advantage of providing altitudinal information on the horizontal gradient to reduce the retrieval error due to the spherical symmetry assumption of the Abel inversion. The comparisons show that climatological structures are consistent with each other above 300 km altitude. Both the Abel electron density profiles and GIS detect electron density variations during a minor geomagnetic storm that occurred within the study period. Moreover, GIS is further capable of reconstructing the variation of equatorial ionization anomaly crests. Detailed validations of all the three products are carried out using manually scaled digisonde N m F 2 (h m F 2), yielding correlation coefficients of 0.885 (0.885) for both Abel inversions and 0.903 (0.862) for GIS. The results show that both GIS and Ne-aided Abel are reliable products in studying ionosphere climatology, with the additional advantage of GIS for space weather research and day-today variations. Plain Language Summary This study presents two ionosphere products from the innovative satellite constellation mission launched recently. Global ionospheric specification is an ionospheric data product that assimilates ground-based Global Positioning System and FORMOSAT-7/COSMIC-2 radio occultation observation of total electron content, to generate hourly global three-dimensional electron density for monitoring space weather condition. Ne-aided Abel electron density profile is an improved retrieval product of FORMOSAT-7/COSMIC-2 radio occultation observations by imposing asymmetry information of ionosphere to mitigate the error introduced by the assumption of spherical symmetry in the Abel inversion. The comparisons and validations confirm that these two data products are reliable for the study of ionosphere climatology and weather. They are operationally produced and released at Taiwan Analysis Center for COSMIC.

Local‐Time and Vertical Characteristics of Quasi‐6‐Day Oscillation in the Ionosphere During the 2019 Antarctic Sudden Stratospheric Warming

“…GIS products have been verified by observing system simulation experiments (OSSEs), demonstrating that the data assimilation accurately reproduces the simulation truth (Lin et al, 2017). It is also validated by extensive ground‐based ionospheric sounding observations (Lin et al, 2020). The domain of GIS used in this study consists of 5° × 2.5° × 20 (km) grid in geographic longitude, ±60° magnetic latitude (MLAT), and altitude (100–1,000 km), with a time interval of 1 hr.…”

“…The ionospheric data (TEC/electron density) used in this study are from Global Ionosphere Specification (GIS) (Lin et al, 2015(Lin et al, , 2017, which is an observational product based on the Gauss-Markov Kalman filter to assimilate the slant TECs from ground-based GPS receivers and space-based radio occultation receivers onboard the recently launched FORMOSAT-7/COSMIC-2 mission (Lin et al, 2020). GIS products have been verified by observing system simulation experiments (OSSEs), demonstrating that the data assimilation accurately reproduces the simulation truth (Lin et al, 2017).…”

Near Real‐Time Global Plasma Irregularity Monitoring by FORMOSAT‐7/COSMIC‐2

“…F7/C2 is a follow‐on mission of the experimental F3/C, having six identical small satellites in low inclination orbits, which is expected to reveal new phenomena or underlying physics of space weather events in mid‐ and low‐latitude ionosphere. RO measurements by F7/C2, operating at low inclination (24°) and low earth orbitLEO at 550 km altitude, have already been extensively validated (C. Y. Lin et al., 2020), and applied for investigating new characteristics of ionospheric modulations related to 2019 sudden stratospheric warmingSSW event (J. T. Lin et al., 2020). In addition to the electron density information from the RO data, the L1 band signal from GLONASS and GPS, received by the on‐board GNSS receiver of F7/C2 is further used to compute S4 scintillation index.…”

Wave Steepening in Ionospheric Total Electron Density due to the 21 August 2017 Total Solar Eclipse

“…As more and more RO satellites being launched into space, the dense space‐based vertical RO soundings give a greater chance for capturing the transient evolution of ionospheric disturbances or instabilities from the bottom to the top ionosphere (Chen et al., 2020; Chou, Pedatella, et al., 2020). The combination of the dense space‐ and ground‐based soundings can be utilized to better construct and study the three‐dimensional ionospheric structures and perturbations (Chen et al., 2016; Lin et al., 2020). The comprehensive observations can be expected to complete the story of the wave steepening and its subsequent phenomena in the vertical directions.…”