STRIP AT BOTTOM EDGE OF TOP WINDOW

I'm not really sure what you have or how it reattaches. It would depend on what you have. It sounds like weatherstripping, but there are about a million different kinds of weatherstripping around. Some have a straight, ribbed kerf that pushes into a slot. Others have a "T" shaped base that slides in from the edges of the window. Others are nailed in, or stick on with glue, and if your windows are particularly old then they could even be held in with caulk. There's no industry standard.