Poincare wave-induced mixing in a large lake
Poincare wave-induced mixing in a large lake
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DOI：
10.4319/lo.2012.57.4.1201
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发表时间：
2012-07-01
影响因子：
4.5
通讯作者：
Rao, Yerubandi R.
中科院分区：
文献类型：
--
作者：
Bouffard, Damien;Boegman, Leon;Rao, Yerubandi R.
在大多数年份里，在伊利湖的中央盆地形成了一个10,000平方公里的缺氧“死亡区”。为了研究缺氧的驱动过程，我们进行了为期2年的实地活动，在分层期间，在湖内部的混合进行了检查，使用电流计和温度记录仪的数据，以及。600个温度微观结构曲线，从中计算湍流混合。近惯性庞加莱波驱动剪切不稳定性，产生类似于1米的振幅和10米波长的高频内波与类似于1米的密度翻转，导致湍流耗散增加一个数量级。不稳定性与增强的垂直剪切波的波峰和波谷的庞加莱波，并可能与当地梯度理查森数。当Burger数< 0.25时，Poincare波诱导混合是一个重要因素。庞加莱波活动引起的强烈的穿壁混合也将显著地改变能量通量路径。例如，我们估计，在伊利湖，0.85%的风能被转移到湖泊内部（低于表层），其中，40%是消散在内部metalimnion和60%是消散在底部边界。在较小的湖泊中，0.42%的风能被转移到更深的水中，90%的风能在边界消散，10%的风能在内部超水层中消散。
A 10,000-km(2) hypoxic 'dead zone' forms, during most years, in the central basin of Lake Erie. To investigate the processes driving the hypoxia, we conducted a 2-yr field campaign where the mixing in the lake interior during the stratification period was examined using current meters and temperature-loggers data, as well as. 600 temperature microstructure profiles, from which turbulent mixing was computed. Near-inertial Poincare waves drive shear instability, generating similar to 1-m amplitude and 10-m wavelength high-frequency internal waves with similar to 1-m density overturns that lead to an increase in turbulent dissipation by one order of magnitude. The instabilities are associated with enhanced vertical shear at the crests and troughs of the Poincare waves and may be correlated with the local gradient Richardson number. Poincare wave-induced mixing should be an important factor when the Burger number < 0.25. The strong diapycnal mixing induced by the Poincare wave activity will also significantly modify the energy-flux paths. For example, we estimate that, in Lake Erie, 0.85% of the wind energy is transferred to the lake interior (below the surface layer); of this, 40% is dissipated in the interior metalimnion and 60% is dissipated at the bottom boundary. In smaller lakes, 0.42% of wind energy is transferred to the deeper water, with 90% dissipated in the boundary and 10% in the interior metalimnion.