| dc.description.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. | en |
