This is a schematic produced by Dr. <a href="https://en.wikipedia.org/wiki/Ted_Fujita" class="extiw" title="en:Ted Fujita">Ted Fujita</a> (1920-1998) when explaining the technical details of the Fujita tornado intensity scale when he introduced it. It was originally published in a science journal but he and his family have released all his available works for public use. Proper citation is still warranted, of course.
Fujita, T.T. ,SVG Version - <a href="https://en.wikipedia.org/wiki/User:Rugby471" class="extiw" title="w:User:Rugby471">Rugby471</a>
Attribution
"Proposed characterization of tornadoes and hurricanes by area and intensity". <i>Satellite Mesometeorology Research Program Research Paper Number 91</i>, Department of Geophysical Sciences, University of Chicago. 42pp. (pdf version <a rel="nofollow" class="external free" href="https://archive.org/download/nasa_techdoc_19720008829/19720008829.pdf">https://archive.org/download/nasa_techdoc_19720008829/19720008829.pdf</a>)