Before revision: The airfoil speed is denoted with V and is constant, the lift force on the airfoil is given by L, and its moment of force by M. The gust has a transverse (vertical) velocity w, which is assumed to be a constant in the gust region, left of the dashed line.
After revision: The airfoil speed is denoted with V and is constant, the lift force on the airfoil is given by L, and its pitching moment by M. The gust has a transverse (vertical) velocity w, which is assumed to be a constant in the gust region, left of the dashed line.