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旋场有关的内波能量和垂直混合强度的时间变异性。因此，将使用中大西洋海脊以西一段三个系泊处的系泊海流计和温度/电导率记录仪进行的5-6年长时间观测以及船上的LADCP/CTD测量。具体的科学目标是：-通过对海流和层结的系泊观测产生内波能的时间序列-调查与风输入、NAC位置和涡旋有关的可变性的时间尺度-确定观测到的可变性的产生过程，例如潮汐、风暴、季节周期、涡旋、NAC分支(本地/远程强迫)-根据变化的背景特性确定混合的可变性(温度逆、索普尺度、精细尺度参数化)为实现上述目标，将计算和研究内波势和动能谱，以了解它们与不同背景特性的关系，例如风力、潮汐、通过涡旋、NAC分支的层化和变异性以及它们对当地MAR地形的依赖。自2012年夏季以来的系泊仪器还允许计算内波垂直模式和能量通量，这将提供有关北大西洋内波输送的能量的量级和时间变化性的信息。将计算的能量通量与MAR产生的内波的射线追踪方法相结合，也将能够估计MAR地形对研究区域内产生内波的相对重要性。从2015年夏季开始，将通过计算索普尺度的时间序列和温度-气压测量的耗散率来进一步扩大分析范围。利用FineScale参数化法从五个航次的船上LADCP/CTD资料中获得的日平均扩散系数的估算结果将得到补充。这使得进一步分析内波的主要来源和垂直混合率及其时间和空间变异性的定量估计成为可能。

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