Modified refractive index

{
  "id": "MLC-T-MET-010625",
  "term": "Modified refractive index",
  "field": "Meteorology and atmospheric science",
  "definition": "A quantity used in radio wave propagation analysis that accounts for both the standard atmospheric refraction and the curvature of the Earth. It is defined as M = N + (h/a) x 10^6, where N is the refractivity, h is the height above the surface, and a is the Earth's radius. A negative vertical gradient of M indicates the presence of a ducting layer, where radio waves can be trapped and travel far beyond the normal horizon.",
  "see_also": [
    "modified refractivity"
  ],
  "url": "https://mlchart.com/terminology/meteorology/modified-refractive-index/"
}