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

摘要

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 NmF2 (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-to-day 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.