Sensitivity of a regional climate model to the resolution of the lateral boundary conditions

The sensitivity of a one-way nested regional climate model (RCM) to the spatial and temporal levels of information provided at its lateral boundaries is studied. To unambiguously address these two issues, a perfect-prognosis approach called the Big-Brother Experiment (BBE) is employed. It consists in first establishing a reference climate simulation (called the Big Brother) over a large domain and then using the simulated data for nesting another RCM (called Little Brother) integrated over a smaller domain. The effect of degrading the resolution of lateral boundary conditions (LBC), spatially and temporally, is investigated by comparing the big- and little-brother climate statistics for the total and fine-scale components of the fields, as well as for their stationary and transient components. Within the BBE framework using a 45-km grid-point RCM, it is found that the one-way nesting approach gives satisfactory results for most fields studied when spatial resolutions degraded by up to a factor of 12 are imposed between the nesting data and the Little Brother. For the LBC update interval, 12 h appears to be the upper limit, while little difference is found between update intervals of 3 and 6 h.