noun, noun which may take the genitive case particle 'no'
low altitude; low sky
Refers to a low altitude or the sky near the ground. Often used attributively with の to modify nouns like 飛行 (flight) or 雲 (clouds).
飛行機が低空を飛んでいる。
The airplane is flying at a low altitude.
低空の雲が山の頂上を隠している。
Low clouds are hiding the mountain top.