## 1 Introduction  
Since its launch in 2006, the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) 1 mission and Formosa Satellite Mission 3 (COSMIC-1/FORMOSAT-3,hereafter COSMIC-1) has provided more than 7.0 million (as of the middle of 2019) global neutral atmospheric profiles in the lower stratosphere and troposphere [1]. With a six-satellite constellation in Low-Earth-Orbiting (LEO) satellites, COSMIC-1 occultations are of a uniform temporal coverage globally. Using the Global Positioning System (GPS) radio occultation (RO) technique, COSMIC data are of all-weather capability and high vertical resolution (~200-600 m, [2]). Studies have demonstrated that the high vertical resolution COSMIC-1 neutral atmospheric profiles, which are not very sensitive to clouds and precipitation [3], are very useful for studying atmospheric processes [4; 5; 6; 7]. Almost all global operational numerical weather prediction (NWP) centers showed significant impacts on the global weather forecast when they started to assimilate COSMIC data into their forecast systems ([8; 9; 10; 11; 12; 13; 14; 15]). Ref. [16; 17] and ref. [1] have summarized the accomplishment of the COSMIC-1 mission for atmospheric studies, NWP, climate, and space weather since 2006. After passing its planned lifetime, the number of COSMIC-1 neutral atmospheric profiles has decreased to less than 300 per day since the middle of 2019 [1]. To continue providing highly accurate neutral atmospheric profiles for atmospheric researches and NWP, a COSMIC follow-up mission, COSMIC-2/Formosa Satellite Mission 7 (COSMIC-2/FORMSAT-7, COSMIC-2 hereafter), was launched on 25 June 2019. COSMIC-2 is also a-six satellite constellation mission. COSMIC-2 is equipped with the advanced TriG (Global Positioning System--GPS, GALILEO, and GLObal NAvigation Satellite System--GLONASS) GNSS (Global Navigation Satellite System) RO Receiver System (TGRS). TGRS is with beam steering and beamforming capability to improve the gain and signal quality. The secondary payloads are an ion velocity meter and Radio Frequency beacon transmitter, mainly for space weather detection. With a 24-degree inclination orbit at 720 km altitude, COSMIC-2 occultations primarily distribute from 45\({}^{\circ}\) N and 45\({}^{\circ}\) S. COSMIC-2 has provided at least 4000 high quality atmospheric and ionospheric profiles per day since it launched. COSMIC-2 is an international and inter-agency RO mission. The NOAA (National Oceanic and Atmospheric Administration) is the lead U.S. agency partnering with the U.S. Air Force (USAF), Taiwan's National Space Organization (NSPO), and the University Corporation for Atmospheric Research (UCAR) for the COSMIC-2 satellite program. The UCAR COSMIC Data Archive Center (CDAAC) is the COSMIC-2 data processing center (DPC). The National Environmental Satellite, Data, and Information Service (NESDIS) Center for Satellite Applications and Research (STAR) is the COSMIC-2 validation and quality monitoring center in NOAA. STAR also processes COSMIC-2 data independently in a post-processing mode [18; 19; 20]. UCAR CDAAC has adapted the COSMIC data processing package to convert the COSMIC-2 phase delay into vertical profiles of bending angle, refractivity, temperature, and moisture. This COSMIC processing package has also been used to process not only COSMIC data but also RO data from Challenging Minisatellite Payload, Korea Multi-Purpose Satellite-5 (KOMPSAT-5), and Meteorological Operational Series (i.e., MetOp-A, -B, -C) Receiver for Atmospheric Sounding (GRAS).