Browsing by Subject "dehydration"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Seasonal and Regional Variability of Stratospheric Dehydration(2012-07-16) Christenberry, Aaron JosephWe analyze output from a domain-filling forward trajectory model in order to better understand the annual cycle of water vapor entering the stratosphere. To do this, we determine the minimum water vapor saturation mixing ratio along each trajectory (the final dehydration point or FDP) and assume that the parcel carries that much water vapor into the stratosphere. In the annual average, the tropical Western Pacific, equatorial Africa and South America, and Southeast Asia are found to be the locations of the most frequent FDPs. Looking at individual seasons, we find that FDPs in the tropical western Pacific tend to occur in the summer hemisphere, with FDPs over South America and Africa occurring predominantly during the boreal winter. During boreal summer, a dehydration maximum occurs in the Asian monsoon region. In the annual average, FDP maxima occur at 99 and 84 hPa. Looking at individual seasons, we find that FDPs occur at higher altitudes (centered at 84 hPa) during boreal winter and at lower altitudes (99 hPa) during boreal summer. The annual cycle in FDP altitude combines with the annual cycle in tropical tropopause layer temperatures to generate the observed annual variations in water vapor entering the stratosphere.Item Trajectory Simulations of H2O, O3, and CO in the Upper Troposphere and Lower Stratosphere (UTLS)(2014-05-05) Wang, TaoThe 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.