Two interesting posts on noctilucent clouds and the solar minimum – we are currently at the end of one solar cycle and just entering another. It seems that during solar minimum the atmosphere shrinks and this is why this year, last year, and next year will have lots of noctilucent clouds (just after sunset). In the two links below, 2018 and 2019, there is each a video of the phenomenon, created by meteor smoke and water crystals high in the upper atmosphere. The comments are also interesting as this phenomenon affects C14 entering the upper atmosphere, implying a question mark on how reliable this dating methodology might be. However, as calibration involves joining at the hip C14 dates to tree rings (and other data) it is thought this does not affect the main thrust of the dating method. It is being brought into line with other factors all the time and C14 is not a stand alone dating method (although sometimes archaeologists seem to rely excessively on dates sent back by C14 laboratories). Go to https://wattsupwiththat.com/2018/07/08/meteor-activity-produces-glowing-… …. and https://wattsupwiththat.com/2019/06/11/electric-blue-night-clouds-are-in… … but see also http://spaceweatherarchive.com/2019/06/12/record-setting-noctilucent-clo… … which discusses the recent outbreak over the US and provides a gallery of photographs and the odd video
such as this.