Impact of Turbulent Mixing in the Stratocumulus-Topped Boundary Layer on Numerical Weather Prediction

• Published in: Asia-Pacific journal of atmospheric sciences Vol. 54; no. Suppl 1; pp. 371 - 384
• Main Authors: Lee, Eun-Hee, Lee, Eunjung, Park, Raeseol, Kwon, Young Cheol, Hong, Song-You
• Format: Journal Article
• Language: English
• Published: Seoul Korean Meteorological Society 01.06.2018; Springer Nature B.V; 한국기상학회
• Subjects: Advection; Advection fog; Atmospheric Sciences; Boundary layer; Boundary layers; Climatology; Cloud amount; Cooling; Earth and Environmental Science; Earth Sciences; Educational institutions; Entrainment; Fog; Geophysics/Geodesy; Humidity; Lower troposphere; Mathematical models; Parameterization; Planetary boundary layer; Radiation; Radiative cooling; Regions; Simulation; Surface temperature; Temperature; Tropical environments; Troposphere; Turbulent mixing; Weather; Weather forecasting; 대기과학; Yellow Sea; numerical weather prediction; planetary boundary layer parameterization; Fog dissipation; stratocumulus-topped boundary layer
• ISSN: 1976-7633; 1976-7951
• DOI: 10.1007/s13143-018-0024-0

The impact of enhanced turbulent mixing induced by radiative cooling at the top of the stratocumulus-topped boundary layer (STBL) on numerical weather prediction is examined. An additional term involving top-down turbulent mixing via in-cloud radiative cooling is applied to the Yonsei University (YSU) planetary boundary layer (PBL) parameterization scheme using a top-down diffusivity profile and cloud-top entrainment. The modified scheme is evaluated in an advection fog case over the Yellow Sea of Korea using the Weather Research and Forecasting (WRF) model and in global medium-range forecasts using the Global/Regional Integrated Model system (GRIMs). In the fog case simulation, consideration of the additional top-down mixing parameterization in the YSU PBL simulates less formation and more rapid dispersion of the fog. As a result, the modified scheme simulates a drier and warmer boundary layer and a moister and cooler layer above the PBL. The modified algorithm also improves surface temperature prediction over the Yellow Sea accompanying early dissipation of the fog. In the global medium-range forecast experiment, the modified scheme simulates overall enhanced PBL mixing over the STBL in the tropics and subtropical ocean, showing drier and warmer regions near the surface and moister and cooler regions above the PBL, resulting in prediction of reduced low level cloud amount and increased downward shortwave radiation at the surface. The modified scheme appears to improve systematic bias in temperature and humidity in the lower troposphere compared to the control simulation.