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

• Applicant: Dr. Janna Köhler
• Subject Area: Oceanography
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257192667

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

• DFG Programme: Research Grants
• Participating Persons: Dr. Birgit Klein; Dr. Christian Mertens; Professorin Dr. Monika Rhein; Dr. Uwe Stöber; Dr. Maren Walter