Exploring commercial Global Navigation Satellite System (GNSS) radio occultation (RO) products for planetary boundary layer studies in the Arctic

Abstract. Commercial radio occultation (RO) satellites that utilize the Global Navigation Satellite System (GNSS) signals are emerging as key tools for observing the polar regions, which are not covered by the second-generation Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) mission. This study evaluates the value of commercial RO measurements, specifically Spire and GeoOptics, for planetary boundary layer (PBL) investigations in the Arctic, a region where favorable lower-atmospheric penetration of GNSS RO is vital for observing the persistently shallow PBL. The lower tropospheric penetration capability of both Spire and GeoOptics over the Arctic Ocean, with nearly 80 % observations reaching an altitude of 500 m above mean sea level, is comparable to other RO missions such as the current Meteorological Operational satellite programme (MetOp) and the discontinued COSMIC-1 missions. A seasonal cycle in RO penetration probability, with the minimum occurring during the Arctic warm season, was observed in most RO datasets, except NASA-purchased Spire data. Monthly mean Arctic PBL height (PBLH) derived from Spire and GeoOptics compares well with MetOp observations and the reanalysis from Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2). A minimum penetration threshold of 500 m generally suffices for determining Arctic PBLH, although a 300 m threshold improves performance of NASA-purchased Spire data. Arctic PBLH representation is influenced less by the number of observations or instrument type and more by the algorithms used for bending angle and refractivity retrievals. These findings underscore the importance of processing algorithms in achieving accurate lower-atmospheric soundings and Arctic PBLH representation.