Ham Amateur Radio Technician 2025 – 400 Free Practice Questions to Pass the Exam

A coronal mass ejection (CME) can take 15 hours to several days to affect radio propagation on Earth due to the nature of its travel through space. When a CME is expelled from the Sun, it travels through the solar wind and interplanetary medium before reaching Earth. The precise time it takes for the CME to arrive depends on various factors, including its speed and the distance it has to cover.

Typically, slower CMEs can take up to five days to reach Earth, while faster ones may arrive within a shorter timeframe, but many will fall within the 15-hour to several days window. This delay means that any potential impacts on radio propagation—like increased ionospheric disturbances that can affect HF communications—are not immediate but occur after the CME has reached the Earth’s magnetosphere.

Understanding the timing of CMEs is crucial for amateur radio operators, as awareness of these events helps in predicting and preparing for possible disruptions in radio propagation, especially for high-frequency communication that relies on ionospheric conditions.