Turbulence in a small arctic pond: Turbulence in an arctic pond
Turbulence in a small arctic pond: Turbulence in an arctic pond
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北极小池塘中的湍流： 北极池塘中的湍流
DOI：
10.1002/lno.10941
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发表时间：
2018
影响因子：
4.5
通讯作者：
Arneborg, Lars
中科院分区：
文献类型：
--
作者：
MacIntyre, Sally;Crowe, Adam. T.;Cortés, Alicia;Arneborg, Lars
北极地区遍布许多小池塘，其中的气候强迫微量气体往往过饱和。改善排放量的估计需要量化（1）它们的混合动力学和（2）近地面湍流，这将使排放。为此，我们仪表北极池塘（510平方米，1米深）与气象站，热敏电阻阵列，和垂直定向的声学多普勒测速仪。我们将测量的湍流（作为湍流动能耗散率ε）与基于风切变asu*w、水摩擦速度和浮力通量β的莫宁-奥布霍夫相似性理论（MOST）预测值进行了对比。层结随昼夜循环而变化;温跃层随着风的变化而上升，使近底层水通风。近地表温度分层高达每米7°C。关于MOST的预测：（1）在加热和强近地表层结条件下，β为正，湍流受到抑制;（2）在加热和中度层结条件下，在冷却和轻至中度风条件下，测得的ε与MOST一致;（3）在冷却和无风条件下，当表面电流停止时，如发生20%的时间，湍流可测量并根据β进行预测。由于不稳定大气下阻力系数值较高，相对于中性大气下，冷却和微风下的近地表湍流增强。小型池塘是动态系统，具有风引起的温跃层倾斜，能够进行垂直交换。与大型系统中的湍流类似，近地表湍流可以通过地表气象学计算，从而能够准确估计气体传输系数和排放。
Small ponds, numerous throughout the Arctic, are often supersaturated with climate‐forcing trace gases. Improving estimates of emissions requires quantifying (1) their mixing dynamics and (2) near‐surface turbulence which would enable emissions. To this end, we instrumented an arctic pond (510 m2, 1 m deep) with a meteorological station, a thermistor array, and a vertically oriented acoustic Doppler velocimeter. We contrasted measured turbulence, as the rate of dissipation of turbulent kinetic energy,ε, with values predicted from Monin–Obukhov similarity theory (MOST) based on wind shear asu*w, the water friction velocity, and buoyancy flux,β, under cooling. Stratification varied over diel cycles; the thermocline upwelled as winds changed allowing ventilation of near‐bottom water. Near‐surface temperature stratification was up to 7°C per meter. With respect to predictions from MOST: (1) With positiveβunder heating and strong near‐surface stratification, turbulence was suppressed; (2) under heating with moderate stratification and under cooling with light to moderate winds, measuredεwas in agreement with MOST; (3) under cooling with no wind and when surface currents had ceased, as occurred 20% of the time, turbulence was measurable and predicted fromβ. Near‐surface turbulence was enhanced under cooling and light winds relative to that under a neutral atmosphere due to higher values of drag coefficients under unstable atmospheres. Small ponds are dynamic systems with wind‐induced thermocline tilting enabling vertical exchanges. Near‐surface turbulence, similar to that in larger systems, can be computed from surface meteorology enabling accurate estimates of gas transfer coefficients and emissions.