A 62 thousand ton stationary asteroid explodes with an energy of 5 megatons at 5 km above the surface.  The movie window is 15 km wide and about 8 km high.  Bright colors of the fireball indicate temperature, ranging from steam (dull red) to rock vapor (white).  Gray background indicates air density and shows a spherical blast wave that reflects from the ground.  The fireball rises buoyantly and cools as it recedes, limiting the thermal effects on the surface.  This simulation shows what happens when momentum is ignored to simplify the problem as scientists have done in the past. The airburst is approximated by a "point source" explosion similar to a nuclear detonation. -- Sandia

This simulation shows what happens when momentum is not ignored, an approach that is allowed with modern supercomputers and codes.  The same asteroid is now moving through the atmosphere at a typical impact velocity (20 km/s).  For illustration purposes, extra energy is deposited into the asteroid when it reaches 5 km, for a total of 5 megatons.  Momentum carries the hot fireball down to the surface, which enhances heat and wind effects on the ground.

3D simulation of a 15 megaton explosion that is initiated 18 km above the surface, for an asteroid entering at an angle of 35 degrees above the horizontal.  Box dimensions are 40 km wide, 20 km high.  Colors indicate speed.  The hot fireball decends to the surface and slides downrange at high velocities, subjecting the landscape to blast-furnace condtions.  This did not happen at Tunguska.

Map view of blast zone from 3-D simulation of a 15 megaton explosion.  Axes are labeled in centimeters, and colors indicate wind speed.  Expanding oblong shape is the blast wave moving along the surface, blowing down trees with wind speeds decreasing from high hurricane force of 60 m/s (magenta) to below 20 m/s (yellow).  Blast-furnace conditions are sustained downrange (left) of the origin where the fireball contacted the surface.  This did not happen at Tunguska, so the asteroid must have been smaller (less energetic).

3D simulation of a 5 megaton explosion that is initiated 12 km above the surface, for an asteroid entering at an angle of 35 degrees above the horizontal.  Box dimensions are 40 km wide, 20 km high.  Colors indicate speed.  The hot fireball does not reach the surface, but descends to an altitude of 5 km before buoyantly rising.  At ground zero, the blast wave comes from directly above, consistent with observations of standing trees at the Tunguska epicenter.