Geomagnetic secular variation

{
  "id": "MLC-T-OAG-001675",
  "term": "Geomagnetic secular variation",
  "field": "Oil and gas",
  "definition": "The slow, long-term change in the Earth's magnetic field over decades to centuries, distinct from daily variations or magnetic storms. This variation is caused by fluid motion within the Earth's outer core. It must be accounted for when processing magnetic survey data to isolate anomalies related to subsurface geology.",
  "subject": "Geophysics",
  "url": "https://mlchart.com/terminology/oil-and-gas/geomagnetic-secular-variation/"
}