Sensitivity of PBL Schemes of WRF-ARW Model in Simulating Mesoscale Atmospheric Flow-Field Parameters over a Complex Terrain

Abstract:

In the present study planetary boundary layer (PBL) flow-field parameters over the complex topographic region of Jharkhand state of tropical India are simulated using WRF-ARW mesoscale model. High resolution simulations are conducted with triple nested domains having horizontal resolution of 27, 9 and 3 km; 51 vertical levels by using the 1x1 degree NCEP Final Analysis meteorological fields for initial and boundary conditions. In the study, eight fair weather days in each season (winter, pre-monsoon, monsoon, and post-monsoon) with no significant synoptic activity are chosen. Sensitivity experiments are conducted with two non-local [Yonsei University (YSU), Asymmetric Convective Model version 2 (ACM2)] and three local turbulence kinetic energy (TKE) closure [Mellor- Yamada Nakanishi and Niino Level 2.5 PBL (MYNN2), Mellor-Yamada-Janjic (MYJ), and quasi-normal scale elimination (QNSE)] turbulence diffusion parameterisations to study the evolution of PBL parameters and thermodynamic structure during the all seasons. The model simulated parameters are validated with the available in situ meteorological observations at Ranchi. Simulations reveal that the low-level flow field is highly influenced by the topography and widely varies in different seasons. Results indicates the non-local PBL schemes ACM2 followed by YSU and the TKE closure MYNN2 could capture the local scale circulations and the diurnal trends in surface meteorological variables, surface layer fluxes and the vertical atmospheric structure in better agreement with observations over the Ranchi. The better performance of ACM2, YSU, MYNN2 is evident in the lesser bias, MAE and RMSE for various parameters relative to other PBL schemes.

Key words: WRF model, Planetary Boundary layer Parameterization, Complex Terrain