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 degrees N to 45 degrees 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.