Numerical modelling

Numerical simulation of internal waves

The modelling group investigates a wide variety of oceanic processes using the state of the art oceanic numerical models. The area of interests includes:

  • oceanic internal waves
  • baroclinic tides
  • dynamics of straits and channels
  • deep-water circulation in the North Atlantic
  • sea-river interaction

Projects

Modelling Oceanic Internal Waves

Oceanic internal waves (Figure 1) have great implications for the efficiency of vertical water mixing, transport of pollutants and suspended matter. They produce shear currents and turbulence that mix water and supply nutrients from the abyss to the surface photic layer. These effects, in turn, play a major role in primary biological productivity and water quality of the basins. On a global scale oceanic internal waves play a fundamental role in setting smooth vertical oceanic stratification that allows meridional overturning circulation - the key element of the Earth climate system.

Modelling Dynamics of Straits and Channels

Straits and channels such as the Strait of Gibraltar that connects the Mediterranean with the Atlantic Ocean, Bosporus and Dardanelles connecting the Black and Aegean Seas through the Marmara Sea, or the Luzon Strait between the South China Sea and the Pacific Ocean and others, have great impact on the environment of the connected basins. In many cases they also make an important contribution to the formation of the global oceanic circulation, e.g. the Strait of Gibraltar, supplying nutrient-rich salty waters from the Mediterranean Sea to the Atlantic Ocean. Understanding the mechanisms which transport and disperse water-borne materials (e.g., nutrients, pollutants, plankton, etc) is a high priority objective which has great importance for the population. The modelling group has recently made a major advance in the area applying the-state-of-the-art numerical models for theoretical investigation of the dynamics of straits and channels (Figure 2).

Figure 1: Large-amplitude internal waves in the Alboran Sea: in-situ measured (top), modelled (middle), and remotely observed (bottom).

Figure 2: Model predicted spatial structure of an internal wave packet in the Strait of Gibraltar 9 hours after its generation over the Camarinal Sill.

Modelling Deep Water Circulation

The water exchange between the Nordic Seas and the North Atlantic Ocean is a part of the global thermo-haline circulation in which warm, saline water flows northwards in the near/surface layers while cold fresher water returns southwestwards at depth. The strength and variability of this circulation is thought to have significant consequences for the climate of northern Europe. Important exit pathways for the cold, dense bottom water are found all along the topographic barrier presented by the Greenland Scotland Ridge - the eastern section of which (between Iceland and Scotland) carries about one third of the total overflow transport into the N Atlantic. The modelling efforts were focused on the structure and hydraulic conditions of the bottom currents in the Faroe Bank Channel and the portion of the overflow that is diverted over the Wyville-Thomson Ridge and eventually into the Rockall Trough (Figure 3). More details on the dynamics and structure of the bottom water current in the Faroese Channels are discussed in the following papers:

Modelling Plume Dynamics

Much of the riverine waters discharged from the rivers onto a relatively shallow continental shelf spread as plumes, buoyant surface layers bound by sharp interfaces or fronts (Figure 4). It is believed that these plumes are of dominant importance for mixing and dispersion of land-based water into coastal seas. The intensive mixing in plumes starts from a so-called ‘€œlift-off’ zone where the plume loses contact with the bottom. There is still a gap in the understanding of how this mixing and dispersion takes place. Key unresolved questions are whether plume fronts mix by entrainment of ambient water or by de-etrainment of plume water, whether internal waves and billows on the interface between plume and ambient waters play a significant role, and whether along-front baroclinic instabilities play a role in the ultimate break-up of a plume. Some of the modelling group efforts were applied to address these questions through a series of numerical experiments summarized in the following papers:

Figure 3: (Left) Plan view of the depth integrated tracer field (white isolines) overflowed from the Faroe Bank Channel (FBC) into the Ymir Trough (YT) and Cirolana Deep (CD) through the Wyville Thompson Ridge (WTR) overlaid with topography 2 days and 2 hours after the beginning of the lock exchange experiment. (Right)Cross-sections of the temperature and tracer along the thalweg of the Ymir Trough.
 

Figure 4: Model-predicted structure of the Columbia River plume (dark blue) 6 hours after the ebbing tidal flow was released from the mouth. The fronts of the generated internal waves detached from the plume are shown in red.