华东沿海高标准农田大气湍流特征的观测分析
Observation and Analysis on Atmospheric Turbulence Characteristics over a High Standard Farmland along the East China Coast
中文摘要：
为评估Monin-Obukhov相似理论和涡度相关系统在高标准农田的适用性，利用南通高标准农田水稻下垫面涡度相关观测数据，分析了大气稳定度、湍流方差相似性、湍流谱特征、湍流强度和湍流动能等。结果表明：该高标准稻田上方大气呈现白天不稳定、夜晚稳定的昼夜变化特征；Monin-Obukhov相似理论在该高标准农田适用，三维风速归一化标准差随大气稳定度的变化符合“1/3”次方规律，温度、比湿、CO2密度归一化标准差随大气稳定度的变化在大气不稳定时符合“1/3”次方规律；在惯性子区，三维风速的湍流能谱符合“－2/3”次方斜率，垂直风速与温度、湿度和CO2密度的协谱符合“－4/3”次方斜率，可见涡度相关系统能够观测该高标准农田的水热和CO2通量；三个方向上的湍流强度均随风速增大而减小，且水平方向湍流强度大于垂直方向；湍流动能随风速呈二次函数增大，呈现昼高夜低的日变化特征，大气中性时达到最大，且以动力湍流贡献为主。研究结果可为揭示华东地区高标准农田生态系统与大气之间的物质和能量交换特征以及机制提供参考。
中文关键词：
高标准农田，大气湍流特征，湍流强度，湍流谱，湍流动能
KeyWords：
high-standard farmland, atmospheric turbulence
Abstract：
In order to evaluate the applicability of Monin-Obukhov similarity theory and the eddy covariance system in high-standard farmland, this paper analyzed the atmospheric characteristics, including atmospheric stability, turbulent variance similarity, power spectra and cospectrum, turbulent intensity and turbulence kinetic energy, using the observation data of the eddy covariance system over the underlying surface of a high-standard farmland in Nantong, Jiangsu Province. The results show that the atmosphere over the farmland is unstable during the daytime and stable at night. The variation of normalized standard deviation of three-dimensional wind components with atmospheric stability obeys the “1/3” power law. The normalized standard deviation of temperature, specific humidity and CO2 density with atmospheric stability follows the “1/3” power law when atmosphere is unstable. Therefore, Monin-Obukhov similarity theory is applicable at such a high-standard farmland. In the inertia subregion, the power spectra of three-dimensional wind speeds follows the “－2/3” slope relation, and the cospectrum of vertical wind speed and scalar quantities follows the “－4/3” slope relation. So, the sensible heat, latent heat and CO2 fluxes over the high-standard farmland can be correctly observed by the eddy covariance system. The three-dimensional turbulence intensities decrease with the increase of wind speed, showing horizontal results stronger than those in vertical direction. The turbulent kinetic energy (TKE) increases with the increase of wind speed, following a quadratic function. TKE is high during the daytime and low at night, reaching its maximum under neutral atmosphere. Compared to thermal turbulence, mechanical turbulence contributes more to TKE. The research can advance our understanding of the energy and mass exchanges between high-standard farmland and atmosphere in East China.