The snowboarder is sitting down.
The snowboarder is sitting on the snow.
One who is snowboarding and sitting down can be expected to be sitting on the snow.
exists e1 s1 x1.(n_snowboarder(x1) & a_down(s1) & Manner(e1,s1) & Actor(e1,x1) & v_sit(e1))
exists e1 x1 x2.(n_snow(x2) & n_snowboarder(x1) & on(e1,x2) & Actor(e1,x1) & v_sit(e1))