| The aim of this study is to improve the understanding and prediction of thermally induced slope winds. This is motivated by the important role of slope winds in local air quality, weather and climate in complex, mountainous terrain. Accurate numerical modeling of atmospheric boundary layer (ABL) flows requires adequate representation of the effects of turbulence. To this end, a comparison of turbulence closures is made in modeling katabatic winds.;First, a one-dimensional atmospheric boundary layer model for studying slope winds has been developed and six turbulence closure schemes commonly used for simulations of the atmospheric boundary layer are implemented in the model. Then, the model is used to investigate the impacts of different turbulence closures on model results in the context of katabatic winds. In this study the E --ℓ closure, two versions of q 2ℓ Level 2.5, E--epsilon closure and its planetary boundary layer (PBL) modifications are compared. The different turbulence closures are compared in terms of their influence on mean variables, turbulent fluxes, turbulent kinetic energy and eddy diffusivity. Analyses of momentum, heat and turbulent kinetic energy budgets of the predicted slope flows are also carried out. Model sensitivity to physical parameters such as ambient atmospheric stability, slope angle and roughness are also investigated using the q2ℓ _I closure based on its good performance. Effects of these parameters on steady state slope winds are discussed. Model simulations with the q 2ℓ _I closure are compared with published measurements of katabatic winds taken over the sloping ice surfaces in Vatnajokull, Iceland and Pasterze, Austria. In addition, model results are also compared with second- order closure modeling and large eddy simulations in relation to these observations. Model results demonstrate that the q 2ℓ _I closure performs well in modeling slope winds in spite of some deficiencies. Finally, we investigate whether slope winds may explain surface wind measurements reported from the Phoenix mission to Mars in terms of the observed diurnal variation of wind direction. |
