Abstract
Abstract. Lake breezes are proved by downdrafts and the divergence flows of zonal wind in the source region of the Yellow River (SRYR) in the daytime based on ERA-Interim reanalysis data. In order to depict the effect of the circulations induced by surface anomaly heating (patches) on the boundary-layer turbulence, the UK Met Office Large Eddy Model was used to produce a set of 1D strip-like surface heat flux distributions based on observations, which were obtained by a field campaign in the Ngoring Lake basin in the summer of 2012. The simulations show that for the cases without background wind, patch-induced circulations (SCs) promote the growth of convective boundary layer (CBL), enhance the turbulent kinetic energy (TKE), and then modify the spatial distribution of TKE. Based on phase-averaged analysis, which separates the attribution from the SCs and the background turbulence, the SCs contribute no more than 10 % to the vertical turbulent intensity, but their contributions to the heat flux can be up to 80 %. The thermal internal boundary layer (TIBL) reduces the wind speed and forms the stable stratification, which produces the obvious change of turbulent momentum flux and heat flux over the heterogeneous surfaces. The increased downdrafts, which mainly occur over the lake patches, carry more warm, dry air down from the free atmosphere. The background wind inhibits the SCs and the development of the CBL; it also weakens the patch-induced turbulent intensity, heat flux, and convective intensity.
Highlights
Turbulence in the planetary boundary layer (PBL), which is derived from surface heating and surface fraction, plays an important role in the exchange of heat, momentum, moisture, and chemical constituents between the surface and free atmosphere (Zhang et al, 2018)
The wind speed derived from the GPS sounding at 12:30 LT is larger than that at 18:30 LT below 2 km, indicating that the larger background wind covered up the divergent wind at 12:30 LT
Ten runs of the 1D strip-like distribution of the surface heat flux and two homogeneous runs based on the observations made during the summer of 2012 in the Ngoring Lake basin were conducted in order to investigate the effects of the patch-induced circulations on the boundary-layer turbulence and its energy transport at the lake–air and grass–air interfaces, and the influence of the background wind was considered
Summary
Turbulence in the planetary boundary layer (PBL), which is derived from surface heating and surface fraction, plays an important role in the exchange of heat, momentum, moisture, and chemical constituents between the surface and free atmosphere (Zhang et al, 2018). Previous studies on the turbulence and turbulent exchange over homogeneous surfaces based on Monin–Obukhov similarity theory were conducted before the 1990s (Sommeria and LeMone, 1978; Moeng, 1984). Thermal surface heterogeneity is a typical issue and leads to the formation of local/secondary circulations. Sea and lake breezes are a well-known example of flows that are generated by heterogeneous surface heating between the land and water (Crosman and Horel, 2012). Observations have revealed the imbalance in the surface energy bud-
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