A very large convection cell that forms within a cumulonimbus by the merging of several smaller convective cells. Inside the supercell air may rise at 45 m/s and the cell may extend to a height of more than 16 km, breaking through the tropopause. Supercells last much longer than ordinary convective storm cells, because the warm updraughts rise at an angle to the vertical and the cold downdraughts associated with precipitation subside to the side of them, so the sinking cold air does not chill the rising warm air, thereby suppressing the vertical circulation. Supercells produce extremely violent storms, and they can trigger tornadoes. See also mesocyclone.