Radar attenuation occurs when:

Radar attenuation occurs primarily when a precipitation cell near the airplane absorbs or reflects all the radio energy from a radar pulse, thus masking precipitation that might exist behind it. This phenomenon is particularly significant during heavy rainfall or when there are intense precipitation echoes. When the radar signal encounters dense precipitation, it can be significantly weakened or completely absorbed, making it difficult for the radar to detect or display precipitation that is further behind the absorbing cell.

This principle is essential for pilots to understand as it can lead to dangerous situations where they might not be aware of severe weather conditions that are obscured by nearby precipitation. On the other hand, while the other choices describe different phenomena related to radar operation and its interpretation, they do not encapsulate the concept of radar attenuation in the same way that the first choice does. Therefore, recognizing how attenuation directly impacts radar data allows pilots to make informed decisions while flying through various weather conditions.