Transition on randomly generated circles

ei guys,
i actually would have searched,but i dont know how to call it…anyways, here’s my problem.

i have this AS where it generates objects(let’s say "bubble.mc"having random alpha,scale,speed) to move upwards (more like bubbles in a bottle). so what i would want to happen is that, when i click another button to go to another section,ill have transitions for the other objects to disappear, alongwith the bubble.mc but in a smooth kinda way (more like disappearing until the last drop)… so that it wont look like just dissappearing and moving into the next section.

hope you can understand what im trying to say.

thanks guys