Alpha is the Greek letter used in engineering to represent angle-of-attack in equations.

As for the harrier, I don't think anyone can say for 100% sure what the aero is. Even though your airspeed is low, the prop blast over the wing gives airspeed and lift over that section of the wing's surface. This may be the reason that the very low aspect ratio wings tend to harrier easily; they have a large portion of the wing "blown" by the prop. The majority of good 3D harrier planes have either a low aspect ratio or a wide root chord.