it should be modelled like a flattened half-sphere and should be textured with
this Texture:

that has this Alpha:

The Feature should Collisionwise be very small, the collision placed in the Center and very high above the Surface of the Map. (so that the feature only gets visibible when zoomed out)
The Feature is needed in two Sizes one Time 40x40 and the second Time 20x20.. Thx for anyone doing it..
The Intention is to make popping up clouds of atmoshpere