Physical oceanography studies the physical processes connected to our oceans. Our research on physical oceanography follows three main strands: ocean-atmosphere interactions, the connection between the wind-driven and the thermohaline circulation, and nonlinear data assimilation for the ocean.
Understanding ocean-atmosphere interactions is crucial for understanding the functioning of both systems. For instance, the atmosphere generates large- and small-scale ocean circulations via the stress exerted by the atmospheric wind on the ocean surface. Examples are the so-called gyre circulations, basin-wide circulations with ranges up to thausants of km that are crucial for the surface heat and salt transport in the world oceans. On the other hand heat and water from the oceans is transported into the atmosphere, important for cloud formation and atmospheric frontal systems. It has been observed that sometimes an impression of the GulfStream ocean front can be found back in the atmosphere at 5 km height.
Our research in this area concentrates on ocean-atmosphere interactions in relation to the Madden-Julian Oscillation (MJO). We inverstigate the influence of rain-water layers on the ocean-atmosphere heat and humidity exchange using high-resolution atmospheric models coupled to mixed-layer ocean models. This research is conducted with Charlotte DeMott.
The connection between the wind-driven and the global thermohaline circulation
A long standing research question in physical oceanography is how the wind-driven ocean circulation (e.g. the ocean gyres) interact with the global thermohaline circulation. Extensive studies have been performed in the Southern Ocean, i.e. the Antarctic Circumpolar Current (ACC) where a direct exchange via Ekman pumping is present. Large efforts have also been devoted to those places where oceans meet, the so-called interocean exchange regions. An example is the connection between the Indian and the South Atlantic Ocean, just south of the African continent.
Using integrated balances over different ocean basins, or parts of ocean basins, it is possible to investigate the possibility of certain circulation configurations. An example is the integrating the zonal momentum balance over an ocean basin and determine which inflow and outflow configutaions are possible or compatible with the internal circulation within the basin. This powerful tool allows us to understand better why the ocean circulations are as they are. This is because several at first sight plausible flow configurations turn out to violate e.g. the zonal or meridional integrated momentum balance.
As an example of this procedure, it turns out that a retrun flow of the thermohaline circulation via Drake Passage alone cannot fulfil the integrated balences in the South Atlantic. An inflow via the Agulhas does allow for closed balances, but only if part of that inflow leaves the South Atlantic at its southern boundary.
Another line of research is to apply our new causal discovery method to infer the connection between the wind-driven and the thermohaline ocean circulation. This is work in progress.
Nonlinear data assimilation
We are developing cutting edge nonlinear data-assimilation methods for ocean forecasting, but also to help increase understanding of the ocean circulation, and to systematically improve ocean models. This is work with Polly Smith, Nick Byrne, and Maria Broadridge. More information can be found on the Data Assimilation page.