Elves and Sirens

Elves noun - An acronym for emissions of light and very low frequency perturbations due to electromagnetic pulse sources; extremely bright extremely short (less than a msec) electrical flashes forming a huge ring (up to 400 km diameter) in the ionosphere.

Sirens and elves are semantically related. In some cases you can use "Sirens" instead a noun "Elves".

Elves and sirens are semantically related. Sometimes you can use "Elves" instead a noun "Sirens".