| Abstract: | The purpose of this work is to simulate water vapor (H₂O), ozone (O₃), and carbon monoxide (CO) in the upper troposphere and lower stratosphere (UTLS) using a domain-filling, forward trajectory model. The influx of H₂O to the UTLS is largely determined by the large-scale troposphere-to-stratosphere transport in the tropics, during which air is dehydrated across the cold tropical tropopause. In the domain-filling, forward trajectory model, trajectories are initialized in the upper troposphere, and the circulation is based on reanalysis wind fields. Along the trajectories, winds determine the pathways of parcels and temperature determines the H₂O content through an idealized saturation calculation. Compared with the Aura Microwave Limb Sounder (MLS) measurements, this simple advection-condensation strategy yields reasonable results for H₂O in the stratosphere in terms of both seasonal variability and vertical structures. The detailed global dehydration patterns are also revealed from this model and it improves our understanding of the H₂O and its transport within the UTLS. Besides H₂O, ozone (O₃) and carbon monoxide (CO) are also important trace gases in the UTLS linked to circulation, transport and climate forcing (for O₃). Combined with simple parameterization of chemical production and loss rates from the Whole Atmosphere Community Climate Model (WACCM), we also managed to simulate O₃ and CO transport in the UTLS via this trajectory model. The trajectory modeled O₃ and CO show good overall agreement with satellite observations from the MLS and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) in terms of spatial structure and seasonal variability. The trajectory model results also agree well with the Eulerian WACCM simulations. Analysis of the simulated tracers shows that seasonal variations in tropical upwelling exerts strong influence on O₃ and CO in the tropical lower stratosphere, and the coupled seasonal cycles provide a useful test of the transport simulations. Interannual variations in the tracers are also closely coupled to changes in upwelling, and the trajectory model can accurately capture and explain observed changes. This demonstrates the importance of variability in tropical upwelling in forcing chemical changes in the tropical UTLS. Trajectory modeling of O₃ and CO can provide useful tests for simplified understanding of transport and chemical processes in the UTLS, and provide complementary information to the H₂O simulations, which are primarily constrained by tropopause temperatures. This model is easy to use, easy to diagnose, and the Lagrangian perspective makes it exceptionally useful in studying transport processes within the UTLS. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152437 |
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