The Planetary Boundary Layer Height Climatology Over Oceans Using COSMIC-2 and Spire GNSS RO Bending Angles From 2019 to 2023: Comparisons to CALIOP, ERA-5, MERRA2, and CFS Reanalysis

The bending angle (BA) vertical profiles from two recent Global Navigation Satellite System (GNSS) Radio Occultation (RO) missions, Formosa Satellite Mission 7–Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) and Spire, are used to detect the planetary boundary layer height (PBLH) over global oceans. While COSMIC-2 is mainly distributed from 45°N to 45°S with relatively uniform temporal distribution, Spire RO profiles cover the global but focus on 2–3, 9–10, 14–15, and 21–22 local time. We compared the RO PBLH to the height of the boundary-layer-cloud-top (BLCTH), derived from the lidar measurements taken by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument at regions with stratocumulus clouds over oceans. The remarkable consistency and strong correlation between RO PBLH and BLCTH estimations over tropical-subtropical oceans confirm the RO PBLH accuracy. These results also demonstrate the consistency between Spire and COSMIC-2 PBLH. We further compared the RO PBLH with the PBLH outputs from the European Centre for Medium-Range Weather Forecasts (ECMWFs) Atmospheric Reanalysis Version 5 (ERA-5), Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2), and National Center of Environmental Prediction (NCEP)-Climate Forecast System (CFS). Consistent PBLH patterns from ERA-5, MERRA-2, and CFS with those from RO showed that the RO PBLH has substantial seasonal variation over various ocean basins, reflecting evident seasonal evolution within the coupled atmosphere-ocean system. Longitudinal RO PBLH variations are prominent in the southeastern Pacific region, indicating that PBLH is sensitive to surface temperature and large-scale circulations in the mid-upper troposphere. We also converted ERA-5 thermal profiles into BA profiles. The minimum gradient (MG) method used in RO PBLH detection is also applied to the ERA-5 BA profiles to derive the ERA-5 (MGBA) PBLH. The RO PBLH is highly consistent with the ERA-5 (MGBA) PBLH, while the latter is about 100 m lower.