September 2004: A nested grid formation for chemical transport over Asia: applications to CO
The GEOS-CHEM global model was modified to permit treatment of a limited spatial regime with resolution 1ox1o, higher than that adopted for the global background (4ox5o or 2ox2.5o). Identified as a one-way nested grid formulation, the model was applied to a simulation of CO over Asia during spring 2001. The top panels compare mixing ratios of CO for March 2001 in the boundary layer obtained using the nested grid, with resolution 1ox1o (left panel), the coarse global model, resolution 4ox5o (middle panel), and the intermediate global model, resolution 2ox2.5o (right panel) . The higher resolution model allows for more efficient, advection-related, ventilation of the lower atmosphere, reflecting the significance of localized regions of intense upward motion not resolved in a coarser-resolution simulation.
The nested-grid model is shown to provide good agreement with measurements made during the TRACE-P campaign in spring 2001, notably better than the low-resolution model in simulating frontal lifting process and differences across the boundary separating the regions of cyclonic and anticyclonic flow. The high-resolution window approach al so allows us to differentiate transport mechanisms for individual sub-regions of China on a much finer scale than was pos sible previously. The above figure presents a summary of correlation coefficients (R) evaluated by comparing mo del results with the observational data for each of the individual flights on the model scale (upper panel) and the o bservation scale (lower panel). For a full account of this work, please see Wang et al. [2004] .