Atmosphere Ocean Science Friday Seminar

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Estimating Mixing Strenghts Using Hydrographic Data

Speaker: Niek Kusters, NIOZ, Netherlands

Location: Warren Weaver Hall 1314

Date: Friday, April 28, 2023, 4 p.m.

Synopsis:

Ocean mixing affects the uptake, transport and storage of tracers such as heat and carbon in the ocean, subsequently impacting the climate and its future changes. Ocean mixing is caused by many different physical processes that take place on a large range of spatiotemporal scales. This makes mixing difficult to observe, or resolve in numerical ocean models. Consequently, ocean models use parameterizations of mixing that determine its strength and distribution. However, it turns out that models can be sensitive to unconstraint choices required for construction of these parameterizations. These mixing parameterizations can be improved by using observationally based constraints.

In this talk I will introduce the Spiralling Inverse Method (SIM) that provides estimates of the mixing strength. The SIM uses a vertical integral over a balance between the watermass transformation equation and the thermal wind balance. The result is an equation where all terms, except for the mixing strengths, can be obtained from hydrographic data of temperature and salinity. As an advantage, the SIM estimates the mixing strengths without the need of further knowledge of for example a reference velocity or streamfunction. The SIM therefore has potential to improve and constrain parameterizations used for climate and ecosystem modelling using readily available hydrographic data.

Furthermore, I will discuss some current work on parameter estimation and show some preliminary results. In this study we aim to estimate the buoyancy or GM diffusivity, given knowledge of the passive tracer or Redi diffusivity. This gives us a way to estimate the GM diffusivity and related parameters using hydrographic data.