Dissipation and mixing during the onset of stratification in a temperate lake, W indermere
Dissipation and mixing during the onset of stratification in a temperate lake, W indermere
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温德米尔温带湖泊分层开始时的消散和混合
DOI：
10.1002/lno.10008
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发表时间：
2014
影响因子：
4.5
通讯作者：
Simpson J
中科院分区：
文献类型：
--
作者：
Simpson J
声学多普勒海流剖面仪和温度传感器链被用来观察春季过渡到稳定分层超过55天的时间在温带湖泊。流结构的观测得到补充的耗散测量，基于结构功能方法，在湖床附近和水柱的上部。在完全垂直混合期间，风驱动运动具有水平各向同性速度，正压和斜压动能大致相等。耗散与风速的立方密切相关，表明了壁面缩放的规律，在最大风强迫（W <$15 m s−1）时，10米深度处的耗散峰值为<$1 × 10−5.5W kg− 1。随着层化的发展，气流演变成一个主要的斜压状态，由第一模态内部假潮主导，均方根轴向流速为1.2 -3 cm−1，是横向分量的2.5倍。在河床上方2.8 m处，大部分耗散发生在与近床水流峰值相一致的多个强极大值中。在密度跃层中，大部分时间耗散都很低，但有明显的最大值（达到101 × 10− 5 W kg−1），与当地的速度切变密切相关。在27.5 d内，跃层的向下扩散热通量占其下水柱温升的70%左右。总湖动能增加了三个因素之间的混合和分层制度，尽管减少风强迫，表明在稳定条件下有效的阻尼。
Acoustic Doppler Current Profilers and chains of temperature sensors were used to observe the spring transition to stable stratification over a 55‐d period in a temperate lake. Observations of the flow structure were complemented by measurements of dissipation, based on the structure function method, near the lake bed and in the upper part of the water column. During complete vertical mixing, wind‐driven motions had horizontally isotropic velocities with roughly equal barotropic and baroclinic kinetic energy. Dissipation was closely correlated with the wind‐speed cubed, indicating law of the wall scaling, and had peak values of ∼ 1 × 10−5.5W kg−1at ten meters depth during maximum wind forcing (W∼ 15 m s−1). As stratification developed, the flow evolved into a predominantly baroclinic regime dominated by the first mode internal seiche, with root mean square axial flow speeds of ∼ 2–3 cm−1; ∼ 2.5–times the transverse component. At 2.8 m above the bed, most of the dissipation occurred in a number of strong maxima coinciding with peaks of near‐bed flow. In the pycnocline, dissipation was low most of the time, but with pronounced maxima (reaching ∼ 1 × 10−5W kg−1) closely related to the local velocity shear. The downward diffusive heat flux across the pycnocline over 27.5 d accounted for ∼ 70% of the temperature rise in the water column below. Total lake kinetic energy increased by a factor of three between mixed and stratified regimes, in spite of reduced wind forcing, indicating less efficient damping in stable conditions.