Sensitivity study of planetary boundary layer scheme in numerical simulation of western disturbances over Northern India

A numerical weather forecasting model (WRF-ARW) is used to simulate the weather during western disturbances over India. The horizontal resolution of the model is 27 km, and the model covers a region extending from 40 degrees E to 105 degrees E and 10 degrees N to 48 degrees N. The Asymmetric Convective Model, version 2 (ACM2) scheme is used to parameterize planetary boundary layer in the simulations. This scheme uses several parameters which are hidden or implicit from the model users. Literature shows that a particular parameter 'p' used in this scheme to prescribe the vertical profile of eddy exchange coefficient has significant impact on mixing within the planetary boundary layer. Thus, the default value of 'p' may not be the most appropriate choice for all types of atmospheric conditions. In the present study, attempt has been made to study the effect of'p'on the parameters like potential temperature and relative humidity within planetary boundary layer and also to prescribe an appropriate value of 'p'for the region under study. Our study reveals that the WRF-ARW model embedded with PBL parameterization (ACM2) is capable of more appropriately simulating the potential temperature and relative humidity by using 'p'value of 1.25 to prescribe the vertical profile of eddy exchange coefficient within the boundary layer especially during the daytime when the system is dominated by convective-scale eddies at least for the chosen domain and period of study.