COSMIC-2 RO Profile Ending at PBL Top with Strong Vertical Gradient of Refractivity

The Formosa Satellite-7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (Satellite-7/COSMIC-2), which was successfully launched on 25 June 2019, provides dense radio occultation (RO) observations over the tropics subtropics. This study examines RO-observed lowest altitude its possible relationship to refractivity gradients planetary boundary layer (PBL) heights. COSMIC-2 RO data Southeast Pacific region (SEP) South-Central (SCP) from August 2020 are employed determine their altitudes, European Centre Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis used obtain of refractivity. Results show that there no ray perigees below PBL top when vertical gradient N?N(r) is strong (<?65 N-unit km?1), where N(r) represents profile spherically symmetric Significantly local due atmospheric ducting occur more frequently SEP than SCP areas. For some cases, a horizontal in tangent direction near perigee point can also limit going further even relatively weak. Fortunately, only about 0.6% profiles unaffected by above factors but cannot observe 2-km altitude.