Observations of small-scale turbulence and energy dissipation rates in the cloudy boundary layer
Observations of small-scale turbulence and energy dissipation rates in the cloudy boundary layer
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DOI：
10.1175/jas3687.1
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发表时间：
2006-05-01
影响因子：
3.1
通讯作者：
Wendisch, Manfred
中科院分区：
文献类型：
--
作者：
Siebert, Holger;Lehmann, Katrin;Wendisch, Manfred
提出了在多云边界层中分辨率约为 10 厘米的系留气球测量。讨论了在不同条件下采样的有关云生命阶段的两个例子。这里测试的假设是边界层云中经典湍流理论的基本思想即使在分米尺度上也是有效的。气温、液态水含量和风速分量的功率谱密度 S(f) 显示出低至约 20 cm 的惯性子范围行为。两个数据集的平均能量耗散率 epsilon 类似于 10(-3) m(2) s(-3)。估计的泰勒雷诺数 (Re-lambda) 与 10(4) 类似，这表明湍流已完全发展。纵向和横向 S(f) 之间的比率收敛到接近 4/3 的值，这是局部各向同性条件下的经典湍流理论所预测的。推导出风速增量 Delta(u) 的概率密度函数 (PDF)。 PDF 显示与间歇流典型的长尾高斯分布的显着偏差。局部能量耗散率 epsilon(tau) 来自持续时间为 tau = 1 s 的子序列。当平均水平风速为 8 in s(-1) 时，tau 对应的空间尺度为 8 m。 epsilon(tau) 的 PDF 可以用符合经典理论的对数正态分布来很好地近似。在分析的云中发现 epsilon(tau) 的最大值近似于 10(-1) m(2) s(-3)。讨论了粒子-湍流相互作用的大范围 epsilon(tau) 值的后果。
Tethered balloon-borne measurements with a resolution in the order of 10 cm in a cloudy boundary layer are presented. Two examples sampled under different conditions concerning the clouds' stage of life are discussed. The hypothesis tested here is that basic ideas of classical turbulence theory in boundary layer Clouds are valid even to the decimeter scale. Power spectral densities S(f) of air temperature, liquid water content, and wind velocity components show an inertial subrange behavior down to approximate to 20 cm. The mean energy dissipation rates epsilon are similar to 10(-3) m(2) s(-3) for both datasets. Estimated Taylor Reynolds numbers (Re-lambda) are similar to 10(4), which indicates the turbulence is fully developed. The ratios between longitudinal and transversal S(f) converge to a value close to 4/3, which is predicted by classical turbulence theory for local isotropic conditions. Probability density functions (PDFs) of wind velocity increments Delta(u) are derived. The PDFs show significant deviations from a Gaussian distribution with longer tails typical for an intermittent flow. Local energy dissipation rates epsilon(tau) are derived from subsequences with a duration of tau = 1 s. With a mean horizontal wind velocity of 8 in s(-1), tau corresponds to a spatial scale of 8 m. The PDFs of epsilon(tau) can be well approximated with a lognormal distribution that agrees with classical theory. Maximum values of epsilon(tau) approximate to 10(-1) m(2) s(-3) are Found in the analyzed clouds. The consequences of this wide range of epsilon(tau) values for particle-turbulence interaction are discussed.