A: clockwise around, and away from the centre of, a low pressure area
B: from a low pressure area to a high pressure area
C: counter-clockwise around, and toward the centre of, a low pressure area
D: counter-clockwise around, and away from the centre of, a high pressure area.
A: at the top of a marked surface-based inversion.
B: at the condensation level when there is no night radiation.
C: at the condensation level when there is strong surface friction.
D: at the top of the friction layer.