At the "UFO Truth" Conference in Watford on 29 April 2017, a very kind gentleman gave me a copy of a book simply called "Clouds" by C.J.P. Cave published in 1943 by Cambridge University Press. The reason he gave me this is because it has, for the time, a very nice selection of photos.
Whilst I am not trying to debunk anything, these photos provide good evidence that certain types of cloud have been around for at least 70 years. Though I myself am very suspicious of the regularity with which I see "linear" type clouds – because I am fairly sure, that at least in some cases, these indicate active weather modification, these images show a few examples of these sorts of clouds – during WWII. This of course predates the construction of facilities like HAARP.
Figure 42 is particularly interesting…. Many thanks to this anonymous donor for sharing this evidence! If you want to download the whole book, use this link.