Which of the following types of propagation is most commonly associated with occasional strong signals on the 10-, 6-, and 2-meter bands from beyond the radio horizon?

Sporadic E is a type of propagation where temporary, highly ionized clouds form in the E region of the ionosphere. These clouds can act like a mirror for higher frequency signals that would normally pass straight into space, abruptly enabling long-distance contacts. This phenomenon is particularly famous for opening up the 10-meter, 6-meter, and occasionally 2-meter bands for hundreds or thousands of miles. It is most common during the summer months but can happen anytime, completely surprising operators with suddenly strong, crystal-clear signals from far beyond the normal radio horizon.