Characteristics of Secondary Circulations in the Convective Boundary Layer over Two-Dimensional Heterogeneous Surfaces  

作　　者：SHEN Lidu SUN Jianning and LIU Peng 沈历都;孙鉴泞;袁仁民;刘鹏

机构地区：[1]School of Atmospheric Sciences & Institute for Climate and Global Change, Nanjing University [2]Jiangsu Provincial Collaborative Innovation Centre of Climate Change [3]School of Earth and Space Sciences, University of Science and Technology of China

出　　处：《Journal of Meteorological Research》2016年第6期944-960,共17页气象学报（英文版）

基　　金：Supported by the National Natural Science Foundation of China(41475012 and 40975004);National Key Basic Research and Development(973)Program of China(2010CB428501)

摘　　要：Large-eddy simulations are conducted to investigate the impacts of the scale of chessboard-like heteroge- neous surface heating and the background wind on secondary circulations （SCs） in the convective boundary layer （CBL）. When the wind blows along the diagonal of the chessboard pattern, the cases with different heterogeneity length scales （λ = 1.2, 2.4, and 4.8 km） and weak background wind （U = 2.5 m s-1） suggest that there exists a threshold for the roll-like SCs, which is satisfied when the heterogeneity length scale is 1.6 times the boundary layer height （λ = 1.6zi）. During the CBL development, the SC intensity increases before this threshold is met, whereas it decreases thereafter. The cases with different background wind speeds （U = 2.5, 5.0, and 10.0 m s-1） and relatively large heterogeneity length scale （λ = 4.8 km） show that the SCs are strengthened by larger wind speeds when the heterogeneity length scale is so large that the threshold cannot be met during the CBL development. Another case with wind direction along neither the diagonal nor the side of the chessboard pattern shows that the roll-like SCs can still be triggered, but the roll axes are orientated along the diagonal of the chessboard pattern rather than along the wind direction.Large-eddy simulations are conducted to investigate the impacts of the scale of chessboard-like heteroge- neous surface heating and the background wind on secondary circulations （SCs） in the convective boundary layer （CBL）. When the wind blows along the diagonal of the chessboard pattern, the cases with different heterogeneity length scales （λ = 1.2, 2.4, and 4.8 km） and weak background wind （U = 2.5 m s-1） suggest that there exists a threshold for the roll-like SCs, which is satisfied when the heterogeneity length scale is 1.6 times the boundary layer height （λ = 1.6zi）. During the CBL development, the SC intensity increases before this threshold is met, whereas it decreases thereafter. The cases with different background wind speeds （U = 2.5, 5.0, and 10.0 m s-1） and relatively large heterogeneity length scale （λ = 4.8 km） show that the SCs are strengthened by larger wind speeds when the heterogeneity length scale is so large that the threshold cannot be met during the CBL development. Another case with wind direction along neither the diagonal nor the side of the chessboard pattern shows that the roll-like SCs can still be triggered, but the roll axes are orientated along the diagonal of the chessboard pattern rather than along the wind direction.

关 键 词：background wind convective boundary layer heterogeneous surface large-eddy simulation secondary circulation TURBULENCE 

分 类 号：P434[天文地球—大气科学及气象学]