P70 Effect of Lateral Boundary Condition (LBC) errors on regional simulations

Ha, Soyoung, Chris Snyder, Bill Skamarock, Michael Duda and Laura Fowler, National Center for Atmospheric Research

High-resolution regional simulations can produce realistic forecasts of mesoscale convective systems, but are always constrained by large-scale forcing through lateral boundary conditions (LBCs), particularly in the fast-moving synoptic circulation that creates rapidly changing cross-boundary flows.

In contrast, the global Model for Prediction Across Scales (MPAS) allows high-resolution simulations in the region of interest without any artificial lateral boundaries using its horizontally variable-resolution unstructured grids.

A new capability of providing initial and boundary conditions from MPAS global forecasts for the WRF regional simulations is recently incorporated in the latest version of WRF preprocssing and initialization programs. This enables to examine the effect of artificial LBCs in the convection simulations by comparing MPAS global forecasts in the local refinement area with the WRF forecasts that use the initial and boundary conditions from the same MPAS global simulations.

Through convective case studies, we discuss how large and important LBC errors would be in the convective simulations and how they affect the forecast error growth at different scales given the same large-scale forcing.