The formation of the sporadic E (E s ) layer can be interpreted in several different ways, with wind shear theory and the meteor ionization mechanism being the most commonly used explanations. Nevertheless, neither the wind shear theory nor the meteor ionization mechanism alone can completely explain the formation of the E s layer. The meteor ionization mechanism cannot interpret the different activity in this layer between the Northern and Southern Hemispheres, while the wind shear theory cannot explain the source of the large amount of ionized particles in the E s layer. In this study, the activity in the E s layer is compared with information about meteors and the global vertical speed of ionized particles. The information about meteors is obtained from International Meteor Organization and Radio Meteor Observing Bulletin. The global vertical speed information for ionized particles is calculated using the International Geomagnetic Reference Field model, Horizontal Wind Model (HWM07), and Mass Spectrometer-Incoherent Scatter model. The activity in the E s layer is based on the value of the irregular degree index, which is derived from the signal-to-noise ratio obtained from Formosa Satellite Mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) Global Positioning System radio occultation mission. Taking both wind shear theory and the meteor ionization mechanism together, the source of the ionized particles in the E s layer and the difference in the activity in the E s layer between Northern and Southern Hemispheres can thus be explained more completely.

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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.

[1] Using the Global Positioning System radio occultation (GPSRO) technique, the observation of the global ionosphere becomes possible. The irregularity in the ionospheric sporadic-E (Es) layer, which is probably caused by wind shear, can be investigated by analyzing the signal-to-noise ratio (SNR) of RO signal. In this study, the relation between the amplitude of RO signals and the electron density profiles of the ionosphere is simulated, and RO data recorded in the time period from mid-2008 to mid-2011 are used for the analysis. Based on the simulation results, the multiple-layer-type (MLT) and the single-layer-type (SLT) Es layers which are defined by the shape of SNR, are used to analyze the global distribution of Es layer. The seasonal MLT Es layer is compared with the seasonal wind shear, which is obtained from the Horizontal Wind Model (HWM07). Furthermore, the seasonal MLT Es layer is compared with the SLT Es layer, and the global altitude distributions of MLT and SLT Es layers are similar while the magnitude distributions are different. Unlike the MLT Es layer, the global distribution of the SLT Es layer is similar to the distribution of E region peak electron density (N m E), which is related to the solar zenith angle.

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