Umkehr effect

{
  "id": "MLC-T-MET-009871",
  "term": "Umkehr effect",
  "field": "Meteorology and atmospheric science",
  "definition": "The reversal in the trend of the intensity ratio of zenith-sky light at two ultraviolet wavelengths as the sun nears the horizon. It occurs because at large solar zenith angles the scattering that supplies the sky light happens at progressively higher altitudes, so the ratio responds to ozone at different levels. Ground-based Dobson spectrophotometers record it, and inverting the measurements yields an ozone profile in roughly ten layers, each several kilometers thick.",
  "url": "https://mlchart.com/terminology/meteorology/umkehr-effect/"
}