The Clyde Sea: a model of the seasonal cycle of stratification and mixing
The Clyde Sea: a model of the seasonal cycle of stratification and mixing
复制标题
克莱德海：分层和混合的季节循环模型
DOI：
10.1006/ecss.1993.1047
复制
发表时间：
1993
影响因子：
2.8
通讯作者：
T. Rippeth
中科院分区：
文献类型：
--
作者：
J. Simpson;T. Rippeth
在克莱德海峡湾系统的系泊观测表明，1990年11月下旬，由于冷却和风的搅动，深水沃茨中出现了完全的垂直混合。ADCP观测之前和混合过程中表明，分层的崩溃大大改变了流通，并在很大程度上消除了垂直剪切与密度驱动流。尽管现有记录有限，但以前没有记录完全混合的病例。历史资料的汇编表明，克莱德系统通常是由热浮力和淡水浮力输入的组合而分层的，在夏季，当Δσ l可能超过1·5 kg m-3时，分层最为明显。冬季层结一般较弱，在冷却阶段出现逆温。控制分层的过程表示在一个填充箱模型的克莱德系统，其中与北槽的交换流是有关的表面密度差在窗台。浮力输入的分层效果，如热量和淡水是反对机械搅拌，由于（i）风应力和（ii）正压潮汐。来自（iii）与深水置换相关的对流效应和（iv）Stigebrandt（1976年）提出的内波机制的额外搅动作用也可能有所贡献。模型运行仅使用机制（一）和（二）没有表现出在夏季观察到的底部温度上升，因此，高估密度分层。额外的输入（iii），特别是（iv），使用最佳估计的效率因素，产生了一个更现实的平衡，并给出了合理的一阶帐户的季节性周期的密度分层。它还提供了一个公平的模拟温度和盐度的季节演变，包括在11月和12月观察到的温度逆温。结果表明，在克莱德系统中，浮力和搅拌的年平均输入之间存在良好的平衡，从而使每年冬季混合的可能性成为可能。
Abstract Mooring observations in the fjordic system of the Clyde Sea show complete vertical mixing in the deep waters during late November 1990 as a result of cooling and wind stirring. ADCP observations before and during mixing indicate that the breakdown of stratification drastically modified the circulation and largely removed the vertical shear associated with the density driven flow. There are no previous documented cases of complete mixing though the available records are limited. A compilation of the historical data indicates that the Clyde system is usually stratified by a combination of thermal and freshwater buoyancy inputs with most pronounced stratification in the summer months when Δσ l may exceed 1·5 kg m -3 . Winter stratification is generally weaker with temperature inversions occurring during the cooling phase. The processes controlling stratification are represented in a filling box model of the Clyde system in which the exchange flow with the North Channel is related to the surface density difference across the sill. The stratifying effect of buoyancy inputs as heat and freshwater is opposed by mechanical stirring due to (i) wind-stress and (ii) the barotropic tide. Additional stirring contributions from (iii) convective effects associated with deep-water replacement and (iv) the internal wave mechanism proposed by Stigebrandt (1976) may also contribute. Model runs using only mechanisms (i) and (ii) did not exhibit the rise in bottom temperature observed during the summer season and, as a consequence, over-estimated density stratification. Additional inputs from (iii) and, in particular (iv), using best estimates of the efficiency factors, produced a more realistic balance and gave a reasonable first order account of the seasonal cycle of density stratification. It also provides a fair simulation of the seasonal evolution of temperature and salinity including the temperature inversions observed in the November and December. The results point to a fine balance between the annual mean inputs of buoyancy and stirring in the Clyde system thus allowing the possibility of annual winter mixing.