NorthWest Research Associates

Pascale LeLong (NorthWest Research Associates -NWRA)

The unifying theme of this two-part talk is the role of inertia-gravity waves (IGWs) and eddy motions in the dynamics of rotating, stratified flows, with an emphasis on oceanic applications on scales of 100 m to 10 km. In the first part, I will present a mathematical solution based on mul- tiple time-scale expansions demonstrating the generation of inertia-gravity waves following a resonant interaction between a tidal current and a field of geostrophic eddies. The generated IGWs exhibit the frequency of the tide and the vertical scale of the eddies while their horizontal wavelength is deter- mined by the sum/difference of tidal and eddy horizontal scales. Resonance is strongest when the horizontal scale of the tidal current is within a factor of 2 of the eddy scale. Numerical simulations of broadband eddy fields forced by tidal currents confirm the occurrence of this resonance.

In the second part, I will address the lateral dispersion of a passive tracer in oceanic ambient conditions dominated by (i) small-scale (submesoscale) eddies, (ii) spectra of weakly nonlinear waves and (iii) a combination of both. Surprisingly, we find that significant dispersion, of O (1 m2s?1), is possible even in cases such as (ii) through a mechanism akin to Stokes drift.

ChuanLi Jiang (Research Scientist, ESR)

Southern Ocean modulates the global climate system through air-sea heat and CO2 fluxes which are both associated with the sea surface temperature and the surface winds. In this talk, I will focus on two key factors controlling the accuracy of the air-sea heat and CO2 fluxes in the Southern Ocean: the air-sea eddy-resolving turbulent (latent and sensible) heat fluxes and the surface water partial pressure of CO2 (pCO2). In the first part of the talk, I will examine the spatial scales of the turbulent heat fluxes determined from the underway high-resolution shipboard measurements in the Drake Passage. These length scales will later be used to evaluate the performance of the recent high-resolution air-sea heat flux products. In the second part of the talk, I will examine the variations of the oceanic pCO2 using both in-situ observations and the newly available CMIP5 Carbon/Climate coupled models. In particular, I will focus on the role of physical processes in the accuracy of the surface water pCO2. In the end, I will touch on the implications and future directions of these two topics.