Sim So-Kumneth, Peinke Joachim, Maass Philipp
Fachbereich Physik, Universität Osnabrück, Barbarastraße 7, 49076, Osnabrück, Germany.
Institut für Physik & ForWind, Universität Oldenburg, Küpkersweg 70, 26129, Oldenburg, Germany.
Sci Rep. 2023 Aug 17;13(1):13411. doi: 10.1038/s41598-023-40450-9.
We analyze offshore wind speeds with a time resolution of one second over a long period of 20 months for different heights above the sea level. Energy spectra extending over more than seven decades give a comprehensive picture of wind fluctuations, including intermittency effects at small length scales and synoptic weather phenomena at large scales. The spectra S(f) show a scaling behavior consistent with three-dimensional turbulence at high frequencies f, followed by a regime at lower frequencies, where fS(f) varies weakly. Lowering the frequency below a crossover frequency [Formula: see text], a rapid rise of fS(f) occurs. An analysis of the third-order structure function [Formula: see text] of wind speed differences for a given time lag [Formula: see text] shows a rapid change from negative to positive values of [Formula: see text] at [Formula: see text]. Remarkably, after applying Taylor's hypothesis locally, we find the third-order structure function to exhibit a behavior very similar to that obtained previously from aircraft measurements at much higher altitudes in the atmosphere. In particular, the third-order structure function grows linearly with the separation distance for negative [Formula: see text], and with the third power for positive [Formula: see text]. This allows us to estimate energy and enstrophy dissipation rates for offshore wind. The crossover from negative to positive values occurs at about the same separation distance of 400 km as found from the aircraft measurements, suggesting that this length is independent of the altitude in the atmosphere.
我们在长达20个月的时间里，以1秒的时间分辨率分析了不同海平面高度处的海上风速。跨越七个多数量级的能谱全面呈现了风的波动情况，包括小尺度的间歇性效应和大尺度的天气现象。能谱S(f)在高频f处呈现出与三维湍流一致的标度行为，随后在低频区域，fS(f)变化较弱。当频率低于交叉频率[公式：见正文]时，fS(f)会迅速上升。对给定时间滞后[公式：见正文]的风速差的三阶结构函数[公式：见正文]进行分析表明，在[公式：见正文]处，[公式：见正文]从负值迅速变为正值。值得注意的是，在局部应用泰勒假设后，我们发现三阶结构函数呈现出与之前在大气中更高海拔处通过飞机测量得到的行为非常相似的特征。特别是，对于负的[公式：见正文]，三阶结构函数随分离距离线性增长，而对于正的[公式：见正文]，则随分离距离的三次方增长。这使我们能够估算海上风的能量和涡量耗散率。从负值到正值的转变发生在与飞机测量结果相同的约400公里的分离距离处，这表明该长度与大气中的海拔高度无关。
