Cold air outbreak during MASEX: Lidar observations and boundary-layer model test

Lidar observations of boundary-layer development during a cold air outbreak over the Atlantic Ocean were examined. Very rapid rise rates were measured in the first 20 km off the coast. A large region of partial cloudiness was found to exist between the totally clear region near shore and the overcast region far from the coast. As the layer became overcast, rise rate of the boundary layer tripled, suggesting a direct relation between cloudiness and entrainment. Boundary-layer evolution was reasonably well simulated by a simple slab model. The model was not capable of predicting the area of partial cloudiness, nor the region of rapid entrainment near the coast.