Clouds form spontaneously when air reaches the necessary pressure/temperature. Near mountains you will often see clouds trailing from peaks as air is forced by the lay of the land to the necessary altitude, they also often disappear if the air mass then decends in altitude. Such rings around the top of peaks normally require very low wind speeds and a local change in air pressure to cause uniform ring-shaped cloud formation. I suppose that the shockwave of a jet's sonic boom caused the cloud formation because the air was already very near the critical point.

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"Those who cannot remember the past are condemned to repeat it" - George Santayana