The representation of the stable boundary layer over the Greenland Ice Sheet using the regional atmospheric climate model RACMO2.3

Abstract

Accurate modelling of the Greenland Ice Sheet is of paramount importance as it is a frontier of climate change. This study analyses the result of implementing a Turbulent Kinetic Energy (TKE) turbulence scheme in the regional climate model RACMO2.3 in place of the default Monin Obukhov diffusion scheme. RACMO2.3, initialised with ERAInterim data, is run with the new turbulence scheme over the region of Greenland from 2003 to 2015, and then compared with a simulation using the default turbulence scheme. Climatological differences are assessed in combination with the differing performance of the two schemes in specific conditions. Generally, the TKE scheme simulates a lower near surface temperature and a higher humidity over Greenland and it’s surrounding ocean. The TKE scheme reduces instances of high sensible heat flux and high wind speeds showing that the scheme produces less turbulent mixing compared to the default scheme. Counter to this the katabatic jet is modelled stronger and closer to the surface, creating more near surface turbulence. To determine whether these differences are significant improvements to model performance or not, model output is compared to observations from automated weather stations. From this comparison, it is thought that the TKE boundary layer scheme has made a statistically insignificant improvement to the performance of RACMO2.3 over Greenland. This is still a positive result for the TKE scheme as certain features are represented more realistically, whilst not significantly degrading the model output. Over the oceans, an evaluation of the differences is not possible due to no static long-term observations being available. The TKE scheme performs as successfully as the default Monin-Obukhov diffusion scheme, meaning that the scheme can be regarded as a robust alternative for polar regional climate modelling