This is the 4830th most frequent Japanese word.
涼しく
"涼しく" means "coolly" or "refreshingly."
涼しく is used as an adjective describing 'morning' to convey a sense of coolness.
夏の朝は涼しくて気持ちがいいです。
Summer mornings are cool and pleasant.
涼しく modifies '吹いています' as an adverb to describe the manner of the wind blowing.
風が涼しく吹いています。
The wind is blowing coolly.
涼しく indicates a change to becoming cool as part of a phrase expressing a process.