Chemistry-transport modeling of the satellite observed distribution of tropical troposheric ozone

[摘要] We have compared the 14-year record of satellite derived tropicaltropospheric ozone columns (TTOC) from the NIMBUS--7 Total Ozone Mapping Spectrometer (TOMS) to TTOC calculated byachemistry-transport model (CTM). An objective measure of error, based on the zonal distribution of TTOC in thetropics, is applied to perform this comparison systematically. In addition,the sensitivity of the model to several key processes in the tropics is quantified to select directions for future improvements. The comparisonsindicate a widespread, systematic (20%) discrepancy over the tropical Atlantic Ocean, which maximizes during austral Spring. Although independentevidence from ozonesondes shows that some of the disagreement is due to satellite overestimate of TTOC, the Atlantic mismatch is largely due to amisrepresentation of seasonally recurring processes in the model. Only minordifferences between the model and observations over the Pacific occur, mostlydue to interannual variability not captured by the model. Although chemicalprocesses determine the TTOC extent, dynamical processes dominate the TTOCdistribution, as the use of actual meteorology pertaining to the year of observations always leads to a better agreement with TTOC observations thanusing a random year or a climatology. The modeled TTOC is remarkably insensitive to many model parameters due to efficient feedbacks in the ozonebudget. Nevertheless, the simulations would profit from an improved biomassburning calendar, as well as from an increase in NO_x abundances infree tropospheric biomass burning plumes. The model showed the largest response to lightningNO_x emissions, but systematic improvements could not be found. The use of multi-year satellite derived tropospheric datato systematically test and improve a CTM is a promising new addition to existing methods of model validation, and is a first step to integratingtropospheric satellite observations into global ozone modeling studies. Conversely, the CTM may suggest improvements to evolving satellite retrievalsfor tropospheric ozone.

[学科分类] 大气科学