New finding will lead to better climate simulations
Consider the Gulf Stream as Northern Europe’s hot-water heating system. As like the Kuroshio (its counterpart in the Pacific), its currents play an important role in the development of the global climate. And now, researchers have demonstrated that the strength of the currents are dependent on the energy exchange between current-generated eddies and the atmosphere.
Major western boundary currents like the Gulf Stream and the Kuroshio transport up to 100 million cubic metres of water per second from the subtropics to the higher latitudes. Making a large contribution to the energy flux that takes place on our planet, they play a major role in influencing weather patterns at the mid-latitudes and our global climate. Without them, the climate in parts of Europe and North America would have been much colder. Now, an international team of researchers have shown that the dynamics and control of these ocean currents depend on the energy exchange between smaller vortices in the ocean currents and the atmosphere, a process which has not been sufficiently taken into account in many of the climate models so far. The findings of the team’s study has been published in the latest issue of Nature.
“From listening to weather forecasts, many people are familiar with the concept of a front, known as the boundary between air masses of different characteristics, usually associated with rainfall,” said Prof Dr Peter Brandt, one of the study’s co-authors. “Such fronts are also associated with large ocean currents where they separate areas with very different temperatures. At these interfaces, the western boundary currents, such as the Gulf Stream and the Kuroshio, form eddies with diameters of a few hundred kilometres. There is where the energy exchange between ocean and atmosphere is greatest,” he continued.
Dr Richard Greatbatch, Professor of Theoretical Oceanography at GEOMAR and the study’s co-author, explained that most of the climate models previously used to carry out numerical integrations over longer periods did not have the necessary resolution to map the processes properly, leading to the fact that the models were unable to correctly reproduce reality.
He added, “We have found that some portions of the Kuroshio in the Pacific are weakened by about one-third if this interaction between the atmosphere and ocean is not considered.” And, as a result, this leads to consequences for the simulation and prediction of extratropical storm systems and other extreme events, as well as their potential modification through climate change.
“To carry out such studies, we operate very high resolution ocean models at GEOMAR, and the results are then used to further the quality of forecasts with coupled ocean-atmosphere models which cannot be operated with such detailed resolution,” said Prof Brandt.
More information: www.geomar.de