论文标题
电源光谱中的地球湍流和离岸风速波动的三阶结构功能的签名
Signatures of geostrophic turbulence in power spectra and third-order-structure function of offshore wind speed fluctuation
论文作者
论文摘要
我们以20个月的长时间分析了一秒钟的时间分析海上风速，以高于海平面的不同高度。延伸超过七十年的能源光谱给出了风波动的全面图片，包括在小长度上的间歇性效应和大尺度上的天气天气现象。 Spectra $ s（f）$显示出与高频$ f $的三维湍流一致的缩放行为，其次是较低频率的政权，其中$ fs（f）$差异很小。将频率降低到交叉频率$ f _ {\ rm \ scriptscriptstyle 2d} $下方，发生$ fs（f）$的快速上升。 An analysis of the third-order structure function $D_3(τ)$ of wind speed differences for a given time lag $τ$ shows a rapid change from negative to positive values of $D_3(τ)$ at $τ\simeq 1/f_{\rm\scriptscriptstyle 2D}$.值得注意的是，在局部应用泰勒的假设后，我们发现三阶结构函数表现出与以前从飞机测量值获得的行为非常相似的行为。特别是，三阶结构功能随着负$ d_3 $的分离距离而线性增长，并带有第三个功率，用于正$ d_3 $。这使我们能够估算离岸风能的能量和胚胎耗散率。从负值到正值的交叉发生在飞机测量值中的400 km的相同分离距离处发生，这表明该长度与大气中的高度无关。
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 $f_{\rm\scriptscriptstyle 2D}$, a rapid rise of $fS(f)$ occurs. An analysis of the third-order structure function $D_3(τ)$ of wind speed differences for a given time lag $τ$ shows a rapid change from negative to positive values of $D_3(τ)$ at $τ\simeq 1/f_{\rm\scriptscriptstyle 2D}$. 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 $D_3$, and with the third power for positive $D_3$. 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.
