Improving the Estimate of Summer Daytime Planetary Boundary Layer Height Over Land From GPS Radio Occultation Data

Global Positioning System (GPS) radio occultation measurements have been widely used to estimate global planetary boundary layer heights (H) using the minimum refractivity gradient method. This method is directly tested here using radiosonde data in China and is found to overestimate summer daytime H over land primarily in the presence of multi-inversions in the lower troposphere. This deficiency is largely reduced by adding a constraint with lifting condensation level (LCL) in the derivation of H, particularly for LCL < 2 km (usually over humid regions). The primary reason is that our new method effectively avoids estimating H near the strong inversion corresponding to the minimum refractivity gradient in the free atmosphere. Applying our new method to the GPS radio occultation data, with LCL derived from surface automatic weather stations, yields more reasonable daytime variation and spatial distribution of H over land in China as compared to the ERA5 reanalysis and radiosonde data.