Atmospheric Factors Governing Banded Orographic Convection

Daniel J. Kirshbaum, Dale R. Durran
2005 Journal of the Atmospheric Sciences  
The three-dimensional structure of shallow orographic convection is investigated through simulations performed with a cloud-resolving numerical model. In moist flows that surmount a given topographic barrier to form statically unstable cap clouds, the organization of the convection depends on both the atmospheric structure and the mechanism by which the convection is initiated. Convection initiated by thermal perturbations over a smooth mountain (without any small-scale topographic features) is
more » ... raphic features) is cellular and disorganized except that shear-parallel bands may form in flows with strong vertical shear, when there is weak instability (or potential instability) inside the cloud, and when the air surrounding the cloud is strongly stable. These bands, which travel with the prevailing wind and distribute precipitation evenly over the mountain, also develop in flows where convection is initiated by small-scale topographic roughness elements. However, a more dominant quasi-stationary mode parallel to the mean low-level wind direction also develops when the convection is initiated by topographic roughness. This robust flow-parallel mode is less sensitive to the atmospheric structure and to the strength of forcing, and can produce locally heavy precipitation due to the stationarity of the bands with respect to the underlying topography.
doi:10.1175/jas3568.1 fatcat:q4mt4gzzzjc5znbj3bmi4kbfze