A two‐dimensional model of stratospheric chemistry and transport (original) (raw)
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STRATAQ: A three-dimensional Chemical Transport Model of the stratosphere
Annales Geophysicae, 2002
A three-dimensional (3-D) Chemical Transport Model (CTM) of the stratosphere has been developed and used for a test study of the evolution of chemical species in the arctic lower stratosphere during winter 1996/97. This particular winter has been chosen for testing the model's capabilities for its remarkable dynamical situation (very cold and strong polar vortex) along with the availability of sparse chlorine, HNO 3 and O 3 data, showing also very low O 3 values in late March/April. Due to those unusual features, the winter 1996/97 can be considered an excellent example of the impact of both dynamics and heterogeneous reactions on the chemistry of the stratosphere. Model integration has been performed from January to March 1997 and the resulting long-lived and short-lived tracer fields compared with available measurements. The model includes a detailed gas phase chemical scheme and a parameterization of the heterogeneous reactions occurring on liquid aerosol and polar stratospheric cloud (PSC) surfaces. The transport is calculated using a semi-lagrangian flux scheme, forced by meteorological analyses. In such form, the STRATAQ CTM model is suitable for short-term integrations to study transport and chemical evolution related to "real" meteorological situations. Model simulation during the chosen winter shows intense PSC formation, with noticeable local HNO 3 capture by PSCs, and the activation of vortex air leading to chlorine production and subsequent O 3 destruction. The resulting model fields show generally good agreement with satellite data (MLS and TOMS), although the available observations, due to their limited number and time/space sparse nature, are not enough to effectively constraint the model. In particular, the model seems to perform well in reproducing the rapid processing of air inside the polar vortex on PSC converting reservoir species in active chlorine. In addition, it satisfactorily reproduces the morphology of the continuous O 3 decline as shown by the satellite during the investigated period, with a tendency, however, to underestimate the total column val-Correspondence to: B. Grassi (Barbara.grassi@aquila.infn.it) ues inside the polar vortex during late winter. As possible causes of this model/observation difference we suggest an incorrect estimation of the vertical transport and of the tropospheric contribution.
Evaluation of transport in the lower tropical stratosphere in a global chemistry and transport model
Journal of Geophysical Research, 2003
Off-line chemistry and transport models (CTMs) use meteorological information from a general circulation model (GCM) or from a data assimilation system (DAS) to calculate the evolution of stratospheric constituents. Here constituent fields from two CTM simulations are compared with each other and with observations from satellite, aircraft, and sondes to judge the realism of the tropical transport. One simulation uses winds from a GCM and the second uses winds from a DAS that has the same GCM at its core. A simulation using the GCM fields reproduces many observed features for O 3 , CH 4 , and the age of air. The same comparisons for a simulation using DAS fields show rapid upward tropical transport and excessive mixing between the tropics and middle latitudes. The assimilation system changes the temperature and wind fields to produce consistency between a GCM forecast and observations, behaving like an additional forcing has been added to the equations of motion and possibly leading to the unrealistic transport produced by the DAS fields. These comparisons highlight aspects of the transport in the lower tropical stratosphere, and suggest that while a CTM driven by DAS fields provides good short-term simulations when event-by-event comparisons with observations are desired, a CTM driven by GCM fields may be more appropriate for long-term calculations such as required to assess the impact of changes in stratospheric composition.
Evaluation of transport in stratospheric models
Journal of Geophysical Research, 1999
We evaluate transport characteristics of two-and three-dimensional chemical transport models of the stratosphere by comparing their simulations of the mean age of stratospheric air and the propagation of annually periodic oscillations in tracer mixing ratio at the tropical tropopause into the stratosphere to inferences from in situ and satellite observations of CO2, SFe, and water vapor. The models, participants in the recent NASA "Models and Measurements II" study, display a wide range of performance. Most models propagate annual oscillations too rapidly in the vertical and overattenuate the signal. Most models also significantly underestimate mean age throughout the stratosphere, and most have at least one of several unrealistic features in their mean age contour shapes. In the lower stratosphere, model-to-model variation in N20, NO•, and CI• is well correlated with variation in mean age, and the magnitude of N O• and Cly variation is large. We conclude that model transport inaccuracies significantly affect simulations of important long-lived chemical species in the lower stratosphere. Age spectrum 0 everywhere Sin tracer 1 everywhere Cos tracer 1 everywhere SF6 0 everywhere Within zonal band 4-10 ø and surface to 2 km, mixing ratio held 1 for January, then 0 for rest of 20 year run. No-flux elsewhere. Same region as age spectrum; time dependence is 1 + sin(2•rt/1 year) Same as sin tracer, but 1 + cos(2•r/1 year) Flux into surface layer 30 ø to 60 øN, uniform per unit area, with steady increase such that total kilotons released during year t is 0.2(t-1966). Run from t = 1966 to 2000. may be reconstructed from the age spectrum. Section 4 focuses on the global mean age distribution, making comparisons to observations, identifying components of model transport that have strong leverage over mean age, and discussing similarities of mean age variations to variations of other long-lived trace gases. Model transport in the tropics is analyzed in section 5 by comparing the propagation of periodic signals and the mean age distribution in models to derivations from observations.
Journal of Geophysical Research, 1995
Constituent distributions are presented from the NASA Langley threedimensional general circulation model, incorporating a comprehensive chemistry scheme. A 7-year, gas phase model simulation was performed to investigate long-term model stability. In addition, a 1-year simulation was made using parameterized polar heterogeneous processes and reactions occurring on sulfate aerosols. The results of these simulations are compared with species climatologies and with satellite data sets in order to characterize and evaluate model performance and identify aspects of the chemical scheme requiting improvement. The agreement between the modeled seasonal variation of total ozone and the measurement climatologies is satisfactory but with some differences with respect to the depth and persistence of the southern springtime ozone depletion. Comparisons of the model simulation with observations made from UARS were performed. There is good accord between the microwave limb sounder observations of ozone and the model. Areas of agreement and disagreement are revealed between the model and the cryogenic array etalon spectrometer measurements of HNO3 and C1ONO2, suggesting the need for a more detailed representation of sulfate aerosol processes in the model. The comparison between the modeled and the measured partitioning of odd chlorine species is improved in the upper stratosphere by the inclusion of an additional pathway to HC1 from the reaction of C10 + OH. 13,951 13,952 ECKMAN ET AL.: THREE-DIMENSIONAL GCM MORPHOLOGY 13,962 ECKMAN ET AL.: THREE-DIMENSIONAL GCM MORPHOLOGY
A domain-filling, forward trajectory model originally developed for simulating stratospheric water vapor is used to simulate ozone (O 3 ) and carbon monoxide (CO) in the upper troposphere and lower stratosphere (UTLS). Trajectories are initialized in the upper troposphere, and the circulation is based on reanalysis wind fields. In addi-5 tion, 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 variabil-10 ity. 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 O 3 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 15 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 UTLS. 25 1998; Wang and Dessler, 2012) all support this understanding. Back trajectory models 5992 ACPD 14, 5991-6025, 2014
Assimilation of Tropospheric Species into a Chemistry Transport Model
This proposal aims at assimilating chemical satellite data from present and future instruments into the MOCAGE chemistry-transport model. The goal is to construct assimilated fields of CO and O 3 by using data from MOPITT, IASI (launch in 2006) in the troposphere and Odin in the lower stratosphere.
Atmospheric Chemistry and Physics, 2006
In this paper we study the impact of the modelling of N 2 O on the simulation of NO 2 and HNO 3 by comparing in situ vertical profiles measured at mid-latitudes with the results of the Reprobus 3-D CTM (Three-dimensional Chemical Transport Model) computed with the kinetic parameters from the JPL recommendation in 2002. The analysis of the measured in situ profile of N 2 O shows particular features indicating different air mass origins. The measured N 2 O, NO 2 and HNO 3 profiles are not satisfyingly reproduced by the CTM when computed using the current 6hourly ECMWF operational analysis. Improving the simulation of N 2 O transport allows us to calculate quantities of NO 2 and HNO 3 in reasonable agreement with observations. This is achieved using 3-hourly winds obtained from ECMWF forecasts. The best agreement is obtained by constraining a one-dimensional version of the model with the observed N 2 O. This study shows that the modelling of the NO y partitioning with better accuracy relies at least on a correct simulation of N 2 O and thus of total NO y .
A three-dimensional general circulation model with coupled chemistry for the middle atmosphere
Journal of Geophysical Research, 1995
We document a new middle atmosphere general circulation model that includes ozone photochemistry. The dynamical model component is based on the NCAR middle atmosphere version of the Community Climate Model. The chemistry model component simulates the evolution of 24 chemically reactive gases. The horizontal resolution is approximately 3 ø in latitude and 6 ø in longitude. It includes 44 levels, with a maximum vertical grid spacing of about 2.5 km and a top level at around 75 km. The chemical model distinguishes between species where we judge transport to be critical and those for which it may be neglected. Nine longer-lived species (N20, CH4, H20, HNO3, N205, CO, C1ONO2, HC1, and HOC1) and four chemical families (NOy, NOx, Ox and Cix) are advected. Concentrations of 15 species which are typically shorter-lived or are members of the chemical families are diagnosed using quasi-equilibrium assumptions (O(1D),