A unique aero-related observation...

[SL8Brick]

In past posts, I've mentioned the addition of a 1"x1.5" rear lip spoiler to the rear hatch of my Volvo 240 wagon. Over the past several months, I've been noticing something different happening behind the car @ speeds over 45mph. While driving on rain soaked roads, there appears to be a "wall" of upward flowing water mist that seems to extend from under the rear bumper(@ ~45deg.) and disapates somewhere above the roofline. Now that Fall is upon us, I've also noticed a similar pattern with fallen leaves on the road. Prior to the installation of the spoiler, there were no noticeable flow patterns behind the car. I realize that this observation is non-scientific, but there clearly is something different happening back there.

Any thoughts??