Secular variation

{
  "id": "MLC-T-MET-008755",
  "term": "Secular variation",
  "field": "Meteorology and atmospheric science",
  "definition": "A slow, non-periodic change in a climatic or geophysical quantity that persists over decades to centuries, as distinct from diurnal, seasonal and interannual fluctuations. In geomagnetism it denotes the gradual drift of the Earth's main field, such as the yearly change of magnetic declination at an observatory, which reaches tens of nanotesla per year in field strength in some regions.",
  "url": "https://mlchart.com/terminology/meteorology/secular-variation/"
}