the Warden's Class Mastery signature script has charm:
Create an 8 meter area for 2 seconds under your target once every 8 seconds that snares enemies by 70%, and charms for 3 seconds when it expires. If no enemies are charmed, you restore 70 Magicka and Stamina.

you can add the script to any grimoire.
you need to find 50 class scraps to get the script though.
you can find them when handing in trial quests, master writ quests, daily infinite archive quests as examples.

the 20~ meter white area could be frost damage Elemental Explosion.