Bubble or vortex ring thermal model
U.S. Dept. of Transportation, Federal Aviation Administration
Glider Flying Handbook, FAA-H-8083-13, <a rel="nofollow" class="external free" href="https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/glider_handbook/media/faa-h-8083-13a.pdf">https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/glider_handbook/media/faa-h-8083-13a.pdf</a>