Analysis of tropospheric transport in the Pacific Basin using the adjoint technique

An adjoint sensitivity analysis is performed within a regional episodic chemical transport model covering the Pacific Basin. The analysis is performed with respect to the concentration over Hawaii of a soluble and insoluble chemically inert species, with the same emissions as NOx The sensitivity is examined at times of elevated tracer mixing ratio at 300, 680, and 900 mbar. The sensitivity to the average mixing ratio at 680 mbar is also examined. The meteorological conditions of April and May 1992 are used for the transport. The adjoint analysis includes the effect of the entire model transport function. It provides a method to analyze the transport of modeled emissions to Hawaii, including the effect of various emission regions, and the associated transport pathways and timescales. The boundary layer mixing ratio at Hawaii is most sensitive to local emissions, with emissions from North America and Asia also contributing to the modeled concentration. In the free troposphere the concentration over Hawaii is most sensitive to emissions from Asia. The adjoint also allows modeled processes to be ranked by their importance in determining the concentration of a species at a particular location. At Hawaii, emissions are ranked first and second in order of importance for the insoluble and soluble species, respectively. For the soluble species the solution is most sensitive to the modeled wet deposition by nonconvective rain. Free tropospheric mixing is generally next in order of importance. Deep convection is important in some locations, particularly for the 300 mbar concentrations. Boundary layer processes, including dry deposition, are generally not important to the free tropospheric solution at Hawaii.