Sporadic E propagation

Sporadic E propagation, often abbreviated as Es propagation, is a type of ionospheric propagation that affects radio waves in the high frequency (HF) band, typically between 30 MHz and 300 MHz. This phenomenon occurs when patches of the E-layer of the ionosphere become ionized irregularly, resulting in the reflection of radio waves back to Earth over distances that can exceed 1,500 kilometers (about 930 miles).