Objectively determined fair-weather CBL depths in the ARW-WRF Model and their comparison to CASES-97 observations

High-resolution 24-h runs of the Advanced Research version of the Weather Research and Forecasting Model are used to test eight objective methods for estimating convective boundary layer (CBL) depth h, using four planetary boundary layer schemes: Yonsei University (YSU), Mellor-Yamada-Janjic (MYJ), Bougeault-LaCarrere (BouLac), and quasi-normal scale elimination (QNSE). The methods use thresholds of virtual potential temperature Od, turbulence kinetic energy (TKE), Od,z, or Richardson number.

Those that identify h consistent with values found subjectively from modeled Od profiles are used for comparisons to fair-weather observations from the 1997 Cooperative Atmosphere-Surface Exchange Study (CASES-97). The best method defines h as the lowest level at which Od,z = 2 K km-1, working for all four schemes, with little sensitivity to horizontal grid spacing. For BouLac, MYJ, and QNSE, TKE thresholds did poorly for runs with 1- and 3-km grid spacing, producing irregular h growth not consistent with Od-profile evolution.