The retrieved literature consistently confirms that noctilucent clouds form in the cold mesosphere during high-latitude summers and are typically observed under twilight conditions.
The claim states that noctilucent clouds are visible primarily in high-latitude summer mesospheres during twilight. Papers [0], [1], and [4] directly corroborate the high-latitude summer mesosphere occurrence and twilight visibility conditions of noctilucent clouds. None of the papers refute this well-established meteorological phenomenon.