LAUSR

Abstract In this study the influence of land surface physics on the simulation of Planetary Boundary Layer (PBL) characteristics in the Advanced Research Weather Research and Forecast (WRF-ARW) is examined at the tropical costal station Kalpakkam. High resolution simulations were conducted using WRF-ARW with two land surface models (LSM) (Noah and Noah MP) for winter (2–5 February 2011) and South West (SW) monsoon (15–18 September 2010). Data from a Lower Atmospheric Wind Profiler (LAWP), GPS-Sonde, meteorological towers and sonic anemometer were used to analyze the PBL properties. Significant variation in the surface and PBL properties were noticed in the simulations with the two LSMs and various features of the PBL were produced better by Noah MP than Noah. The Noah because of higher exchange coefficients simulated more warm and humid boundary layers compared to the Noah MP. In the study region higher (lower) sensible heat flux is simulated compared to the latent and soil heat fluxes during the dry winter (rainy SW monsoon). The variation in the surface energy partitioning resulted in a variation in the simulated PBL depth by the two LSMs. The PBL simulated by Noah MP was shallower than the Noah. During winter higher Bowen ratio associated with the Noah MP resulted in stronger entrainment of upper dry air which suppressed the vertical growth of the PBL. Whereas in SW monsoon, the convective and mechanical turbulence simulated by Noah MP was less than that of Noah, which has lead to a shallow PBL in Noah MP. Overall, the Noah MP simulated the thermodynamical structure, winds and vertical extent of the PBL better than Noah. The improvement in simulations with Noah MP are due to the explicit treatment of plant canopy, snow and ground surface, tiling scheme for vegetation and bare soil, and due to moderate exchange coefficients for soil heat and moisture.