Abstract: Data of turbulence, net radiation and temperature profiles obtained in International Energy Balance Experiment (EBEX-2000) are used to study characteristics of turbulence cospectra, temperature profiles and turbulent fluxes at 8.7 m and 2.7 m in the atmospheric surface layer. Interaction of large eddies with local turbulence in a disturbed surface layer induced by patch-to-patch irrigation is emphasized, as well as their influence on turbulent fluxes. Results indicate that peak frequencies of cospectra in the low frequency range at the two levels are well consistent, revealing that low frequency turbulence obeys the OLS law. High frequency turbulence obeys the local isotropy theory. Spectral energy in low frequency range is greatly enhanced by large eddies, and this enhancement is more notable at 8.7 m than that at 2.7 m. Multiple peak frequencies are observed at low frequency range of cospectra, and their scales correspond well with thermal heterogeneous scale of the underlying surface. Three dominant scales of these large eddies are 800, 400 and 200 m. Furthermore, large eddies have greater influence on turbulence at higher levels than lower levels and in unstable atmospheric surface layer than stable atmospheric surface layer.

Key words: disturbed surface layer, turbulence cospectra, turbulent flux

摘要： 运用国际能量平衡实验(EBEX-2000)的湍流、净辐射和温度梯度资料, 对近地层8.7 m和2.7 m两个高度的湍流互谱结构、温度廓线和湍流通量的特征进行了分析, 重点研究了逐块灌溉所致的扰动近地层内大涡与局地湍流的相互作用以及大涡对地表通量的影响。研究结果显示, 低频湍流互谱的峰值频率在两个高度趋于一致, 基本遵循外层标度律(OLS)模型; 高频湍流符合局地各向同性湍流理论。由于大涡的影响, 湍流互谱低频能量显著增强, 且该增强作用在8.7 m高度比2.7 m高度更为突出。湍流谱的低频部分出现多峰值, 峰值频率对应的涡旋尺度与热力非均匀性的尺度有较好的对应关系, 主要的3个涡旋尺度分别为800, 400和200 m。大尺度涡旋扰动对局地湍流的影响: 上层大于下层, 不稳定时大于稳定时。

关键词: 扰动近地层, 湍流互谱, 湍流通量