The mathematical side:
Cl = L / qA
Cl = Coefficient of lift
L = lift force
q = dynamic pressure
A = wing area
Dynamic pressure is a function of fluid density (air which will remain unchanged) and velocity of that fluid (also will not change).
Lift force in its plain form is 1/2 (p V2 A Cl)
p = air density
V = velocity
Well again air density won't change and velocity won't
? If non of these go up, how does Cl go up when in ground effect?
These two formulas, often given as the be all end all in production of lift, leave one thinking lift cannot go up in ground effect. They leave out advanced lift ideas like, circular flow and pressure changes from the lack of suction of tip vortices, out of the picture (as they well should for pilots).
These all have a small effect which increases the lifting force when in ground effect, causing an increase in lift coefficient. My apologies, I am not an engineer so I do not know how to apply all the formulas for a demonstration. Point is, Cl does go up in ground effect which increases lift.
Edit: Cubdriver, there are truths in what you posted, the aircraft exhibits a flow pattern that acts as a form of suction pulling the aircraft downward. I however don't understand how it works and that article doesn't help much. It was just in my flight dynamics notes, noted as advanced airflow. Anyone have more insight?