noctilucent clouds
高緯度地域特有の現象だった「夜光雲」が最近は中緯度でも頻繁に出現するようになったということです。夜光雲は高緯度で発生する雲が、地平線下の太陽の光を下から受けて反射する気象現象とのことで、その増加にはやはり気候変動がかかわっていると専門家は指摘しています。
Noctilucent Clouds Above Finland
Shimmering noctilucent, or "night shining," clouds have long graced high-latitude sunsets around the globe. But recently, the clouds have been mysteriously appearing as far south as the U.S. states of Colorado and Utah. "They are becoming brighter and seem to be coming to lower latitudes than in the past," James Russell, principal investigator for
NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite, said last week at an American Geophysical Union meeting in San Francisco. Scientists suspect that the increase in night-shining clouds may be due to climate change: Even as surface temperatures rise, the upper atmosphere is getting colder due to the buildup of carbon dioxide, creating perfect conditions for cloud formation, experts say.
夜光雲は英語の「夜の」語形変化（noct(i)-）と「光っている」（lucent）を合成したことばでしょう。night shiningと言った方がわかりやすいですね。そう言えば、「夜光虫」noctilucaも
同形の単語です。（UG）
