Arcane Barrier

When you, or an ally within 30ft of you, is the target of a successful attack roll you may cast Arcane Barrier before the damage is rolled.  You hold the pearl in your hands in front of your chest and focus your arcane ability into it.  You then push your arms out expanding a thin but strong magical arcane barrier from the pearl outward to a sphere of 30ft radius.  Until the start of your next turn all allies within the sphere gain a +10 to their AC and cannot be targeted by ranged attacks, including attack roll spells.  All creatures of your choice within the sphere must make a Strength saving throw or be knocked prone, additionally any creature wishing to enter the barrier must make a Strength saving throw to enter.  Magical Missle cannot pass through the barrier and the barrier can be targeted by the disintegrate spell which destroys it.