Intercomparison of the Planetary Boundary Layer Height Estimates from COSMIC-2 and Spire RO, CALIPSO, and Reanalysis Products

Retrievals from two recent Global Navigation Satellite System (GNSS) Radio Occultation (RO) missions have been analyzed to estimate the planetary boundary layer height (PBLH) with a focus on global oceans. The first RO mission, the Constellation Observing System for Meteorology, Ionosphere, and Climate-2/Formosa Satellite Mission 7 (COSMIC-2), is a successor to COSMIC-1 and covers the period after 2019 between 45°N and 45°S. The second mission, Spire, is a commercial satellite constellation from approximately 110 CubeSats. The Spire data has global coverage for the post-2021 period with 3000 to 5000 occultation profiles daily in our study. The primary objectives of this investigation are to evaluate the accuracy of PBLH estimation from RO data and examine the spatiotemporal variations of PBLH over recent years.

To validate the RO-based PBLH estimates, a comparison is made with boundary-layer-cloud-top height (BLCTH) obtained from lidar measurements from the CALIOP instrument onboard the CALIPSO satellite. This assessment is focused on tropical-subtropical stratiform cloud regions. The strong agreement and correlation between the two PBLH estimation methods affirm the efficacy and precision of RO-derived PBLH data. Furthermore, a comparative analysis is conducted between RO-PBLH and PBLH outputs from two widely-used reanalyses: ERA-5 and MERRA-2, and one forecast model (NCEP-CFS). While the reanalysis/model results generally exhibit similar spatial patterns and seasonal variability as RO-PBLH, they tend to yield smaller values than RO-PBLH and BLCTH. This discrepancy suggests noteworthy deficiencies in the present reanalyses and climate models with respect to their representation of PBLH.

The study further delves into the spatial distribution and temporal variations of PBLH using RO-based estimations. Despite differences in sampling between COSMIC-2 and Spire missions, they exhibit a high level of consistency. Diurnal variations in PBLH are relatively subdued over oceans yet discernible. The PBLH over oceans displays robust seasonal variations, reflecting distinct seasonal evolutions within the coupled atmosphere-ocean system. This is particularly pronounced in the tropical-subtropical eastern ocean basins. Notably, distinct longitudinal variability emerges, particularly in the southeastern Pacific, underscoring the sensitivity of PBLH to surface temperature and large-scale mid-upper tropospheric circulations.