What does this image represent?

During moderate to strong solar flare events, intense ionization within the D-layer propagation region is observed on the sunlit side of Earth, and affects a wide range of frequncies within the HF Spectrum (3 - 30 MHz). These events can degrade HF radio communications and are also known as radio blackouts. This model represents the areas most affected by these radio blackouts. For more detailed information, please visit the following link. http://www.swpc.noaa.gov/drap/dregion_absorption_documentation.html

Example of a radio blackout event detected by the Global D model