Refer to fig 11-3-8. The fig shows three airfoils. The top one
shows 2 dimensional flow, ie no induced flow.
The centre airfoil shows how the induced flow now deflects the relative air
flow and we get what is called the effective airflow. The angle between the
chord line and effective airflow is the effective angle of attack. The angle
between effective airflow and the horizontal flow that was the relative airflow
is called the induced angle of attack, which is equal to the down wash angle.
On entering ground effect induce flow reduces and the induced angle of attack
decreases, with an increase in the effective angle of attack. Lift increases
and induced drag and down wash reduce.