Polar Vortex

Version 0.30: This article may not be up to date for the latest stable release of Crawl.

Polar Vortex
Level	9
School1	Ice
Source(s)	Book of Ice
Casting noise	5
Spell noise	15
Power Cap	200
Range	5
Flags	Area

Turns the air around the caster into a freezing vortex, doing tremendous damage to everyone caught in it that can only partially be mitigated by resistance to cold. Those affected will also be swept up into the air and tossed around. Only the eye of the storm is a safe place, and it follows the caster. The vortex is unable to follow the caster through long-distance translocations. The spell's effectiveness is greatly diminished in closed areas. After the vortex fades, it cannot be called forth again for a short time.

Polar Vortex is a level 9 Ice Magic spell that creates a frenzy of raging wind up to 6 tiles around you, dealing catastrophic cold damage.

Useful Info

Polar Vortex creates clouds of raging wind, dealing a base of 12d(pow/15) damage per 1.0 turn. Only 50% of damage is affected by cold resistance.

The damage is then adjusted by:

• Percentage of tiles open. In tight spaces, damage is reduced. Damage is multiplied by the ratio, (tiles with wind) / (tiles that could have wind).
• "Duration-radius" factor. Creatures on the outside of the vortex will receive the most damage.

The vortex's radius is equal to sqrt(aut_passed) * 7/5, or roughly 1 tile per 1.0 turn, with a max. of 5 tiles. Creatures and clouds caught inside will rotate in a counterclockwise fashion. The "rotation" is a square shape, and done at a rate of ~1 full rotation per 6 turns.

While casting the spell, the caster and anything caught inside will fly for a short period of time. Once it ends, there's a grace period of 1 turn until flight ends. Monsters won't make any effort to avoid falling into deep water or lava.

Polar Vortex lasts for 6 turns. The vortex immediately ends if you blink or teleport via any means, or if you enter another floor. After it ends, it has a cooldown of 3.5 - 4.5 turns.

Creatures who are currently casting Polar Vortex (including twisters) are immune to other creatures' Polar Vortex. No other monster is immune.

Strategy

While Polar Vortex has poor damage/turn compared to other level 9 spells, it has great MP efficiency. For a single, 9 MP cast, you'll get up to 6 turns of damage. Plus, you can cast other spells while the vortex is running. Great in an open area, especially against crowds. The ability to pierce cold resistance is also useful for Ice Magic specialists.

The downsides (other than damage/turn) mostly stem from the vortex mechanic itself. It is much weaker in a cramped area. For most of the duration, the vortex has a short radius. And the spell has a lengthy cooldown.

As a single school spell, Polar Vortex is easier to train than the likes of Fire Storm or Chain Lightning, but it's still a significant XP investment. In a 3 rune game, training for a level 9 spell usually means sacrificing on your defenses. But, for a low-range, damage over time spell that excels in open areas, you'll want good defenses. Polar Vortex can still be worth using, but don't rush for it.

Tips & Tricks

• When the radius is 5, the amount of noise is 15. This number is multiplied by the delay of your last action (in auts) and divided by 10.
• Be careful not to use Blink while the spell is up, unless you specifically want to end its effects.
• Any trees within Polar Vortex's range have a chance of being destroyed by the spell.

History

• Prior to 0.30, Polar Vortex was 60% irresistible.
• Prior to 0.28, Polar Vortex's power was not stored on cast. Using Sif Muna's Divine Exegesis would cause a 0 power vortex after the first turn. Also, switching gear would recheck the power.
• Polar Vortex was added in 0.27, as a rethemed version of Tornado. Comparative to Tornado, Vortex deals 33% more damage, but is partially resistible. In addition, a few monsters lost rTornado.