As an object collides and moves through Jupiter's atmosphere, it compresses the air in front of it - this is called atmospheric ram pressure. The compressed air reaches tens of thousands of degrees, heating the object.
The explosion blasts out along the trail that the massive meteor created. A huge fireball of heated atmosphere rises high above Jupiter's cloud tops from this superheated column. The fireball's debris rapidly cools into dark jovian "soot" and collapses onto Jupiter's cloud tops, making a characteristic dark impact site.