The 3-D model characteristics of a Cb cloud which moves along a valley

Summary The three-dimensional cloud-resolving mesoscale model is used to simulate an individual Cb cloud in condition of real orography. We have conducted our numerical experiments over an area known as hail bearing clouds source. Once formed such clouds regenerate and propagate along the valley if the shallow layer of strong wind shear exists. The orographic effects on model Cb cloud are recognized through comparison of simulated cloud characteristics with those calculated for the flat terrain. Sensitivity experiments with respect to the wind shear layer depth are also conducted.Our results demonstrate the model capability to simulate well some observational Cb cloud characteristics. It is shown that the river valley is of essential importance for Cb cloud development. The most prominent features of the model cloud in this case are as follows: fast propagation along the river valley; considerable depth of the cold air nose with pronounced pulsation mechanism and intense cell regeneration at the leading edge of cold air outflow. Model and observed radar reflectivities in the vertical cross-section are in agreement. Some characteristics of surface cumulative rain precipitation are also well reproduced by the model. In contrast with the real orography case, the model cloud is more intense and it propagates freely in lateral direction for the flat terrain. The cell regeneration associated with forced updraft above the cold air nose is not pronounced in contrast with earlier considerations. Reflectivity pattern near the ground, having mainly bat-like wings, encircles much larger area with altitude compared to the case of real orography. Finally, the model cloud characteristics depend strongly on shear layer.Received June 2002; revised August 22, 2002; accepted October 1, 2002 Published online: April 10, 2003