The spacing of orographic rainbands triggered by small-scale terrain

Elongated and stationary rainbands aligned parallel to the flow direction tend to occur in areas where oceanic air laden with low-level moisture and potential instability is forced to flow over coastal mountain ridges. Due to their considerable precipitation-enhancing abilities, these bands have direct implications upon regional hydrology and may lead to flash-flooding events. Recent research has led to a novel hypothesis for the triggering and organization of the bands, but no general theory exists to explain the observed spacing between adjacent bands. In this study, a suite of numerical simulations is conducted to determine the environmental and terrain-related parameters that govern the inter-band spacing. It is found that the spacing of the bands, which cannot be predicted by linear theory of moist flow over an irregular surface, is controlled by complex interactions between lee waves upstream of the bands and moist convection within the bands.