Dynamics of Heavy Precipitation over Mesoscale Mountains

North Carolina State University, Raleigh NC

Investigators

Abstract

The objective of this research is to advance scientific understanding of orographic rainfall. Three major questions will be addressed: (1) In addition to the moist Froude number, what are other major non dimensional parameters that control the propagation of orographically induced mesoscale convective systems over mountains? (2) What are the formation and propagation mechanisms of convective cells embedded in an orographic mesoscale convective system? (3) How does an upper-level jet streak couple with the low-level flow to create an environment that is highly favorable for heavy orographic precipitation? In order to address the first question, the Principal Investigator will extend previous studies to investigate other major control parameters for a conditionally unstable orographic flow. A series of idealized numerical experiments will be performed using a mesoscale numerical model to study the effects of basic flow speed, instability, moisture content, aspect ratio of the mountain, Coriolis force and vertical wind shear on moist flow regimes. In order to address the second question, the Principal Investigator hypothesizes that advection is the major mechanism for the generation of convective cells. This advection mechanism will be tested by performing a series of numerical experiments. Regarding the third question, it is hypothesized that there is a vertical coupling process between the boundary layer flow and upper-level jet streak that creates an environment that is highly favorable for heavy orographic precipitation. A mesoscale numerical model will be adopted to perform real-case numerical experiments to help answer this question. The intellectual merit of this approach is largely derived from the unique multi-faceted synthesis of idealized numerical modeling, real data numerical modeling and observational data analyses as applied to the problem of why heavy orographic rainfall occurs over mesoscale mountains. The broader impacts will be achieved by utilizing the research findings for the development of improved forecast techniques of extreme orographic rainfall predictions. It is anticipated that this will result in the saving of lives and the reduction of property losses.