Single Column Model study of Planetary Boundary Layer parameterizations with respect to the representation of the effects of subsidence on the evolution of stably-stratified boundary layers

A recent analysis of observations from the Surface Heat Budget of the Arctic Ocean (SHEBA) field study has indicated that during the polar winter, under clear-sky, high pressure conditions, vertical advection, or subsidence, can have a dramatic effect on the evolution of the stably stratified atmospheric boundary layer (ABL). Mirocha et al. (2005) inferred that a modest subsidence rate of 0.001-0.002 m s-1 could provide sufficient advective heating at the ABL top to balance the cooling at the surface, resulting in a nearly-steady boundary layer structure. A follow-up numerical study using large-eddy simulation (LES) demonstrated that imposing the mean vertical velocities identified in Mirocha et al. (2005) resulted in nearly-steady stably-stratified ABL structures that more closely matched the observations than simulations conducted with no mean subsidence (Mirocha and Kosović, 2010). Furthermore, this study showed that the heat flux profile in the ABL is significantly different from that observed when subsidence is not present, displaying an elevated maximum in magnitude.

In this work we explore the effects of subsidence on the boundary layer structure as accounted for by planetary boundary layer (PBL) parameterizations commonly used in mesoscale models. For that purpose we use WRF in Single Column Model (SCM) mode with Mellor-Yamada-Janic (MYJ), Mellor-Yamada-Nakanishi-Niino (MYJNN), Yonsei University (YSU) and, Quasi Normal Scale Elimination (QNSE) PBL parameterizations. We use the SCM to simulate periods of interest in January, 1998, previously studied using LES. Initial and boundary conditions as well as advective forcing for these simulations are derived from the North American Regional Reanalysis (NARR) data set. We compare SCM model results with LES results and observations, present detailed analysis ABL structure obtained using the SCM, and make recommendations for modifications of PBL schemes to accurately account for the effects of subsidence. Considering that inaccurate prediction of the thermodynamic structure and evolution of the stably-stratified ABL can have detrimental effects on the prediction of, for example, ice formation in polar regions, it is critical that the effects of subsidence be accurately represented.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-427570