<p>Many of the modern Low-Earth-Orbiting satellites are now equipped with dual-frequency GPS receivers for Radio Occultation (RO) and Precise Orbit Determination (POD). The space-borne GPS measurements can be successfully utilized for ionospheric climatology and space weather monitoring. The combination of GPS measurements, which include RO observations and POD measurements from the upward-looking GPS antenna, provides information about electron density distribution (profile) below the satellite orbit and an integrated Total Electron Content (TEC) above the satellite representing an important data source for electron density climatology above the F2 layer peak on a global scale. We demonstrate the advantages of using space-borne LEO GPS measurements, both RO and upward-looking, for Space Weather activity monitoring including specification of ionospheric plasma density structures at different altitudinal domains of the ionosphere in quiet and disturbed conditions. After the great success of the COSMIC-1 (Constellation Observing System for Meteorology, Ionosphere, and Climate) mission operating since 2006, the six COSMIC-2 satellites were launched into a 24 deg inclination orbit in June 2019. The COSMIC-2 scientific payloads with the advanced Tri-GNSS Radio-Occultation Receiver System provide multiple observation types including multi-GNSS TEC (limb and overhead), RO electron density profiles, amplitude/phase scintillation indices, in-situ ion densities and velocities. The COSMIC-2 advanced instruments allow detection of ionospheric plasma density structures of various scales, and the monitoring of high-rate amplitude and phase scintillations both above and below a satellite orbit. The COSMIC-2 multi-instrumental observations will contribute to a better understanding of the equatorial ionosphere morphology and future forecasting of ionospheric irregularities and radio wave scintillations that harmfully affect satellite-to-Earth communication and navigation systems. We present results of post-event analyses for severe space weather events demonstrating a great potential and contribution of the COSMIC-1/2 missions in combination with the ground-based GNSS receivers and other LEO missions like C/NOFS, DMSP, MetOp, TerraSAR-X, and Swarm for monitoring the space weather effects in the Earth&#8217;s ionosphere.</p>
Space Weather Observations by GNSS Radio Occultation: From FORMOSAT‐3/COSMIC to FORMOSAT‐7/COSMIC‐2
