exact meaning of 気持ちのいい

Hello everyone,
I just stumbled across the sentence 気持ちのいい朝です in the anki deck I'm learning with and was wondering, what the meaning of the particle の in this context was.
My dictionary says, 気持ち can either be a noun (meaning "feeling"), or an adverb (meaning "somewhat"). Is the 気持ち in this sentence an adverb, thus modifying an other adjective (いい) with の, or is it completely different?
Thanks in advance

It's the same as 気持ちがいい朝です. 気持ち is a noun, and の is the subject marker here. See the following thread.

Questions about a sentence. | Japan Forum