Temporal variability of internal waves and vertical mixing in the North Atlantic

该项目的总体目标是研究与北大西洋洋流及其涡场有关的内波能和垂直混合强度的时间变化。因此，将使用中大西洋海岭以西部分的三个系泊处的系泊电流计和温度/电导率记录仪进行5-6年的观测，以及船上的LADCP/CTD测量。具体的科学目标是：-从对海流和分层的观测中产生内波能的时间序列-研究与风输入、NAC和涡旋位置相关的变率的时间尺度-确定观测到的变率的产生过程，例如潮汐、风暴、季节周期、涡旋、NAC分支（本地/远程强迫）-确定混合变率(温度逆温、索普尺度、为了实现上述目标，将计算和研究内波势和动能谱与各种背景特性的关系，例如风强迫、潮汐、经过的涡流、NAC分支的分层和变率，以及它们对局部MAR地形的依赖。自2012年夏季以来，系泊仪器还允许计算内波垂直模态和能量通量，这将提供有关北大西洋内波输送能量的大小和时间变化的信息。将计算出的能量通量与射线追踪法结合起来，对MAR产生的内波也可以估计出研究区域MAR地形对内波产生的相对重要性。从2015年夏季开始，分析将通过计算索普尺度的时间序列和温度-压力测量的耗散率进一步扩展。结果将通过使用细尺度参数化方法从五次巡航的船上LADCP/CTD数据中获得的典型扩散系数估计来补充。这样就可以进一步分析内波的主要来源，定量估计垂直混合率及其时空变异性

The general objective of this project is the investigation of temporal variability in internal wave energy and the intensity of vertical mixing in relation to the North Atlantic Current and its eddy field. Thereby 5-6 year long observations from moored current meters and temperature/conductivity recorders from three moorings along a section west of the Mid-Atlantic Ridge as well as shipboard LADCP/CTD measurements will be used. Specific scientific goals are:- produce time series of internal wave energy from moored observation of currents and stratification - investigate time scales of variability in relation to wind input, position of NAC and eddies- identify generating processes of the observed variability, e.g. tides, storms, seasonal cycle, eddies, NAC branches (local/remote forcing)- determine variability of mixing (temperature inversions, Thorpe scales, finescale parameterization) in dependence on changing background propertiesTo achieve the above objectives, internal wave potential and kinetic energy spectra will be calculated and studied for their relation to variable background properties e.g. wind forcing, tides, passing eddies, stratification and variability in the NAC branches as well as for their dependence on the local MAR topography. Mooring instrumentation since summer 2012 additionally permits the calculation of internal wave vertical modes and energy fluxes which will yield information about the magnitude and temporal variability of energy transported by internal waves in the North Atlantic. Combining calculated energy fluxes with ray tracing methods for internal waves generated at the MAR will also enable the estimation of the relative importance of the MAR topography for the generation of internal waves in the study area. From summer 2015 onward analyses will be further extended by the calculation of time series of Thorpe scales and dissipation rates from temperature-pressure measurements. Results will be supplemented by the estimation of diapycnal diffusivities obtained from shipboard LADCP/CTD data from five cruises using a finescale parameterization. This allows the further analysis of dominant sources of internal waves and quantitative estimates of vertical mixing rates as well as their temporal and spatial variability