Electromagnetic characteristics of ENSO
2018
Abstract. The motion of electrically conducting sea water through Earth's magnetic
field induces secondary electromagnetic fields. Due to its periodicity, the
oceanic tidally induced magnetic field is easily distinguishable in magnetic
field measurements and therefore detectable. These tidally induced signatures
in the electromagnetic fields are also sensitive to changes in oceanic
temperature and salinity distributions. We investigate the impact of oceanic
heat and salinity changes related to the El Nino–Southern Oscillation (ENSO)
on oceanic tidally induced magnetic fields. Synthetic hydrographic
data containing characteristic ENSO dynamics have been derived from a coupled
ocean–atmosphere simulation covering a period of 50 years. The corresponding
tidally induced magnetic signals have been calculated with the 3-D induction
solver x3dg. By means of the Oceanic Nino Index (ONI), based on sea surface
temperature anomalies, and a corresponding Magnetic Nino Index (MaNI),
based on anomalies in the oceanic tidally induced magnetic field at sea
level, we demonstrate that evidence of developing ENSO events can be found in
the oceanic magnetic fields statistically 4 months earlier than in sea
surface temperatures. The analysis of the spatio-temporal progression of the
oceanic magnetic field anomalies offers a deeper understanding on the
underlying oceanic processes and is used to test and validate the initial
findings.
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