Firestorm

"But then, through the darkness, fire erupted: crimson and gold, a ring of fire that surrounded the rock so that the Inferi holding Harry so tightly stumbled and faltered... Dumbledore was on his feet again, pale as any of the surrounding Inferi, but taller than any, too, the fire dancing in his eyes; his wand was raised like a torch and from its tip emanated the flames, like a vast lasso, encircling them all with warmth."

- Description

The Firestorm charm is one which produces a large ring of fire from around the caster's wand. When the caster moves, so the ring of flame will move with them in the same direction, swirling like a flaming lasso. The caster may also shoot jets or balls of flame at individual targets or opponents while the fire is still being produced, which will inflict a small amount of damage to them. The spell Partis Temporus will temporarily create a gap in the flames to allow safe passage through.

Uses
In June of 1997, Professor Albus Dumbledore and his student Harry Potter entered a seaside cave in an attempt to locate one of Lord Voldemort's Horcruxes. When the Inferi guarding the horcrux attacked them, Dumbledore used this spell, (with the Elder Wand) to drive them back into the water and protect Harry and himself until they reached their boat, therefore saving Harry's life.

Behind the scenes

 * In the book, the spell merely conjured a lasso of flames, like a rope made of fire. In the films, however, this was dramatised to have a wall of flame swirling around them, filling up most of the cave, with Dumbledore shooting fireballs at the Inferi underwater.
 * Due to the increased intensity in the film portrayal, on par with Fiendfyre, it is unknown whether Aguamenti or Aqua Eructo would work to extinguish the fire rope. It may not work, as Dumbledore was able to launch fireballs into the water to attack the Inferi holding Harry.
 * It is possible that the spell, as it appears in the book, is the Fire rope charm, due to the novel's description of the fire as "a vast lasso" of flames produced from Dumbledore's wand.
 * This spell is one of the last and most powerful spells that Albus Dumbledore uses with the Elder Wand, before his death.

Appearances

 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)
 * Harry Potter and the Half-Blood Prince (video game)
 * Harry Potter and the Deathly Hallows: Part 1
 * Harry Potter for Kinect
 * Harry Potter: The Creature Vault (mentioned only)

Notes and references
Tempête de feu Firestorm Огненный шторм