Field mill

{
  "id": "MLC-T-MET-005564",
  "term": "Field mill",
  "field": "Meteorology and atmospheric science",
  "definition": "An instrument used to measure the strength and polarity of the atmospheric electric field at the ground. It operates by rotating a grounded shutter over an exposed sensing electrode, inducing an alternating current proportional to the ambient electric field. Field mills are commonly deployed in thunderstorm research and lightning warning systems.",
  "url": "https://mlchart.com/terminology/meteorology/field-mill/"
}