Is it possible to "turn off" the ability to fly?

I'm asking this because I was wondering whether it was possible to announce that, for example, your Storm was "grounded" at that time, meaning she could make a ranged attack at an adjacent flier?

I know that you can outwit the ability to soar, but can you cancel the ability to fly full stop?

You cannot voluntarily chagne your speed mode, no - a flyer is a flyer, at least until it gets Earthbound.
However, fliers can always make ranged attacks, so Storm would get no benefit from cancelling her fligth - she would still be able to make a ranged combat attack against an adjacet enemy, whether it was flying or not.

Although the first part of the sentence is over-simplified (statements with "always" usually are), this is quoted for truthery.

Also, a flier can be "grounded" without gaining Earthbound. Grounded means "not soaring and not elevated." (There is no specific term for someone who isn't flying except for the term "non-flier.")

Wow!

This is news to me!

I love. Storm wins again!

/That's a really unbalanced rule, I always thought if a flier was based by a flier they couldn't do a range against them.

You can always play the crosswind battlefield condition so all fliers gain earthbound. No more flying.