Extension and Evaluation of University of Washington Moist Turbulence Scheme to Gray‐Zone Scales

Abstract

AbstractWith the rapid improvement in computational resources, it has become possible to structure numerical weather model simulations to use sub‐kilometer grid spacing. Traditional turbulence‐mixing closures have become obsolete within the context of the gray zone of turbulence. Here, a new scale‐aware algorithm (SA‐UW) is developed based on the UW (University of Washington Moist Turbulence) scheme. By dividing both the local and nonlocal vertical turbulence flux into sub‐grid and resolved parts, the partition of sub‐grid turbulence is tuned by a set of well‐acknowledged scale‐dependent relationships. Idealized simulations confirm that the newly developed scheme can adequately reproduce sub‐grid turbulence transport at gray‐zone scales. The inclusion of a nonlocal transport term in the SA‐UW scheme is essential, as it vastly improves the distribution and intensity of coherent structures. The SA‐UW scheme recovers the conventional UW scheme when grid spacing is larger than the turbulence length scale, thereby evincing the sale‐aware capability of the new method. For real‐case simulations, the SA‐UW scheme can capture the diurnal cycle and provide a more accurate vertical structure of temperature and humidity.