Evaluation of ABL parametrization schemes in the COSMO, a regional non-hydrostatic atmospheric model over an inhomogeneous environment

Abstract

The boundary-layer processes characterized through turbulent motion are generally very small scale and sub grid and are represented through different parametrization schemes in the atmospheric models. Here, we evaluate the performance of the atmospheric boundary layer (ABL) parametrization schemes in the COnsortium for Small-scale MOdelling (COSMO), a non-hydrostatic atmospheric model by comparing the model simulations with the concurrent in situ observations over Thiruvananthapuram (8.5 $$^{\circ }$$ N, 76.9 $$^{\circ }$$ E, India). With a view to investigating the role of master length scale (l) in simulation of the ABL features, the default parametrization scheme based on the 1-D diagnostic closure, is modified by adopting a new mathematical formulation for l, and the new approach is implemented in the COSMO model. A total of three parametrization approaches, including the two in-built schemes, are designed and the model simulations with these three distinct schemes are carried out for a total of 9 days. Results obtained from the present study reveal the role of l in the estimation of eddy diffusivity coefficients ( $$K_m$$ and $$K_h$$ ) and the associated vertical turbulent mixing. The study also attempts to highlight the significance of ABL parametrization schemes over non-homogeneous environment, hitherto least explored.