from defenselink.mil:
Navy Lt. Ron Candiloro's F/A-18 Hornet creates a shock wave as he breaks the sound barrier July 7. The shock wave is visible as a large cloud of condensation formed by the cooling of the air. A smaller shock wave can be seen forming on top of the canopy.(Oh, and about the name of the photographer, please feel free to infer a "don't ask, don't tell" joke.)
It is possible for a skilled pilot to work the plane's throttle to move the shock wave forward or aft.
Candiloro is assigned to Fighter Squadron 151, currently deployed with the USS Constellation battle group. (U.S. Navy photo by Ensign John Gay)