EFFECT OF LARGE EDDY RESOLUTION ON SIMULATION OF STRUCTURE AND EVOLUTION OF THE MARINE TRADE-WIND BOUNDARY LAYER

REN Yan; HUANG Qian; ZHANG Jun-xia; WANG Chan

doi:10.16032/j.issn.1004-4965.2018.01.003

Abstract：The effects of turbulent eddies with various scales on the structure and evolution of mixed layer and cumulus layer are analyzed by using the sounding data from the Barbados Oceanographic and Meteorological Experiment (BOMEX) and a large eddy simulation (LEM) sensitivity test with different horizontal grid spacings.The results showed that a fine structure of the boundary layer convection with a warm and dry mixed layer is simulated with smaller model horizontal grid spacings.Strong convection and entrainment also were modeled using high-resolution tests due to small turbulent eddies being resolved.If larger model horizontal grid spacings were used,larger turbulent eddies led to a weaker boundary layer convection with cooler and wetter mixed layer and weaker entrainment.The simulated scale of turbulent eddies were also shown to affect the simulation of liquid water mixing ratio in the trade-wind cumulus layer.If small turbulent eddies were modeled,this led to an early formation of trade-wind cumulus and a high cloud top.Large liquid water content with small volume of single cloud was found in the trade-wind cumulus layer.It gave the opposite results if large turbulent eddies were simulated.Considering the effects of noise signals generated by the high resolution simulations and computing time,the use of 100 m grid spacing as LEM horizontal resolution in simulating marine trade-wind cumulus boundary layer is a ideal choice,although the characteristics of mixed layer and cumulus layer from a fine trade-wind boundary layer could be modeled by using the simulation with 50 m or 100 m grid spacings.