To investigate the climate phenomenon El Niño Southern Oscilliation (ENSO), scientific focus was so far mainly on changes in sea surface dynamics, like deviations in temperature and sea level from long term mean values. A team of scientists from GFZ section Earth System Modelling, now proposes another option: The examination of oceanic magnetic fields, which result from the interactions between Earth’s magnetic field and tidal ocean currents. This may improve the forecast of ENSO events and add to a better understanding of underlying processes.
Approximately every four years, sea surface temperatures increase offshore the Peruvian coast around Christmas time. Weakened trade winds push less water away from the coast so that the stream of cold and nutrient rich water from deeper ocean regions to the surface subsides. Such an event is called El Niño event (Spanish for 'Christ Child') and it impacts the local fishing industry as well as global climate. These warm events are usually followed by phases of especially cold sea surface temperatures being called La Niña. Both phases have global effects on, for example, European weather or the monsoon, and are referred to as ENSO.
Temperature changes in seawater in concert with changing salinity have a direct impact on the electrical conductivity of sea water. The conductivity together with the current field in return determines the strength of the ocean tide induced magnetic field. The scientists were now able to show in a model simulation that measurements of changes in these magnetic field strength have the potential to serve as an early indicator of El Niño and La Niña events. Their results are now published as a highlight article in Ocean Science.
Using a coupled ocean-atmosphere model, the scientists simulated the ocean currents, temperature, and salinity for a time period of 50 years and calculated the resulting oceanic magnetic field strength. Johannes Petereit, first author and PhD student in the section: „We were able to show that within our simulation an ENSO event is preceded by changes in the amplitude of the ocean tide induced magnetic field. These changes occur on average already four months before the typical changes in temperature occur at the sea surface”. The reason for this are changes in the vertical temperature profile of the equatorial Pacific. These changes cause variations in the oceanic conductivity and thus changes in the ocean tide induced magnetic field strength.
So far, magnetic field measurements with sufficient precision for an ENSO prediction are only possible under laboratory conditions. With an improved technique, however, a prediction of ENSO events based on variations of oceanic tide induced magnetic fields may be an option for the future. Like this, negative effects of ENSO events for example for the fishing industry may be mitigated.
The realization of continuous measurements of oceanic induced electromagnetic signals would not only enhance ENSO prediction skills but would also improve the basic understanding of processes behind ENSO phenomenon within the ocean-atmosphere system. (ak)
Original study: Petereit, J., Saynisch, J., Irrgang, C., Weber, T., Thomas, M., 2018. Electromagnetic characteristics of ENSO. Ocean Science 14, pp 515-524. DOI: https://doi.org/10.5194/os-14-515-2018