Abstract
Abstract. A domain-filling, forward trajectory model originally developed for simulating stratospheric water vapor is used to simulate ozone (O3) and carbon monoxide (CO) in the lower stratosphere. Trajectories are initialized in the upper troposphere, and the circulation is based on reanalysis wind fields. In addition, chemical production and loss rates along trajectories are included using calculations from the Whole Atmosphere Community Climate Model (WACCM). The trajectory model results show good overall agreement with satellite observations from the Aura Microwave Limb Sounder (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 during 2005–2011. This demonstrates the importance of variability in tropical upwelling in forcing chemical changes in the tropical lower stratosphere.
Highlights
The influx of water vapor (H2O) to the stratosphere is largely determined by the large-scale troposphere-to-stratosphere transport in the tropics, during which air is dehydrated across the cold tropical tropopause (e.g., Fueglistaler et al, 2009, and references therein)
We focus on analyzing the model results during 2005–2011, to overlap the Microwave Limb Sounder (MLS) and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) observations
carbon monoxide (CO) experiences a net increase in the middle stratosphere due to oxidation of methane (CH4), this has little influence on the results shown here
Summary
The influx of water vapor (H2O) to the stratosphere is largely determined by the large-scale troposphere-to-stratosphere transport in the tropics, during which air is dehydrated across the cold tropical tropopause (e.g., Fueglistaler et al, 2009, and references therein) Observations such as the entry mixing ratios (Dessler, 1998; Dessler et al, 2013), the coherent relations between water vapor and temperature (Mote et al, 1996), and the extensive cirrus clouds near the tropopause (e.g., Winker and Trepte, 1998; Wang and Dessler, 2012) all support this understanding. A newly designed domain-filling forward trajectory model driven by reanalysis wind and temperature has demonstrated success at simulating the transport of H2O in the stratosphere (Schoeberl and Dessler, 2011; Schoeberl et al, 2012, 2013) In this trajectory model, winds determine the pathways of parcels and temperature determines the H2O content through an idealized saturation calculation. O3 and CO exhibit relatively large out-of-phase seasonal cycles in the tropical lower stratosphere (Randel et al, 2007), and these coupled variations provide a sensitive test of the trajectory model simulations in this region
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