Individual #D-layer__D_region  the lowest region of the ionosphere (35 to 50 miles up) that reflects low-frequency radio waves
  instance of:  region.location
  part of:  ionosphere  the outer region of the Earth's atmosphere; contains a high concentration of free electrons
     part of:  atmosphere  the mass of air surrounding the Earth; "there was great heat as the comet entered the atmosphere"
        part of:  Earth.terrestrial_planet__earth__globe  the 3rd planet from the sun; the planet on which we live; "the Earth moves around the sun"; "he sailed around the world"

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