Definitions:

1. A layer within the D region of the ionosphere. NOUN
   • During solar eclipses, scientists observe the D-layer closely to study its response to the sudden decrease in solar radiation.
2. The lowermost portion of the mantle, sits just above the molten iron-rich outer core. NOUN
   • The ionospheric D-layer's lower altitude compared to other layers makes it particularly sensitive to changes in solar activity.
3. The lowest layer of the ionosphere, able to reflect low-frequency radio waves. NOUN
   • Amateur radio operators often adjust their frequencies based on the time of day to account for the changing conditions in the D-layer.
   • The D-layer of the Earth's ionosphere experiences significant fluctuations in ionization levels, affecting radio wave propagation.
4. The lowest region of the ionosphere, characterized by mounting electron and ion density. NOUN
   • Research into the D-layer's behavior during geomagnetic storms provides valuable insights into Earth's atmospheric dynamics.

Synonyms:

• d region
• ionospheric absorption layer
• lowest ionospheric layer
• solar radiation-affected layer