Critical frequency

{
  "id": "MLC-T-MET-004759",
  "term": "Critical frequency",
  "field": "Meteorology and atmospheric science",
  "definition": "The highest frequency at which a radio wave, when transmitted vertically, is reflected back to Earth by an ionospheric layer. Frequencies above this value penetrate the layer and are not returned. This frequency varies with the time of day, season, and solar activity, and is measured by an ionosonde.",
  "url": "https://mlchart.com/terminology/meteorology/critical-frequency/"
}