Observed diurnal cycle climatology of PBLH and CWRF sensitivity to PBL schemes

Description

The first observed climatology of the planetary boundary layer height (PBLH) diurnal cycle is provided. PBLHs are diagnosed rom fine-resolution sounding data collected in many major field campaigns across the world over various surface types. An objective algorithm determining PBLH from sounding profiles is first developed and then verified by available lidar and sodar retrievals. The algorithm is robust and produces realistic PBLH as validated by visual examination of several thousand additional soundings. This data set provides a unique observational data base for critical model evaluation on the PBLH diurnal cycle and its temporal/spatial variability.

As the state-of-the-art regional climate model (RCM), CWRF (Climate extension of Weather Research Forecasting model) was developed, incorporating numerous improvements that are crucial to climate scales, thus providing the best platform for PBL schemes evaluation. CWRF-simulated PBLH diurnal cycles with various PBL schemes (MYJ, QNSE, UW, ACM, CAM, YSU) are compared against the best diagnostic climatology at the Southern Great Plains site (97°30'W, 36°36'N) of the Atmospheric Radiation Measurement (ARM) Climate Research Facility. All TKE-based schemes (MYJ, QNSE, UW) substantially underestimate convective or residual PBL heights from noon toward evening, while others (ACM, CAM, YSU) well capture the observed diurnal cycle except for the GFS with systematic overestimation. These differences among the schemes are representative over most areas of the domain, suggesting systematic behaviors of the parameterizations. Lower PBL heights simulated by the QNSE and MYJ are consistent with their smaller Bowen ratios and heavier rainfalls, while higher PBL tops by the GFS correspond to warmer surface temperatures.