Scenarios for modeling multiphase tropospheric chemistry (original) (raw)
Related papers
Journal of Geophysical Research, 2001
We present a first description and evaluation of GEOS-CHEM, a global threedimensional (3-D) model of tropospheric chemistry driven by assimilated meteorological observations from the Goddard Earth Observing System (GEOS) of the NASA Data Assimilation Office (DAO). The model is applied to a 1-year simulation of tropospheric ozone-NO•-hydrocarbon chemistry for 1994, and is evaluated with observations both for 1994 and for other years. It reproduces usually to within 10 ppb the concentrations of ozone observed from the worldwide ozonesonde data network. It simulates correctly the seasonal phases and amplitudes of ozone concentrations for different regions and altitudes, but tends to underestimate the seasonal amplitude at northern midlatitudes. Observed concentrations of NO and peroxyacetylnitrate (PAN) observed in aircraft campaigns are generally reproduced to within a factor of 2 and often much better. Concentrations of HNO3 in the remote troposphere are overestimated typically by a factor of 2-3, a common problem in global models that may reflect a combination of insufficient precipitation scavenging and gas-aerosol partitioning not resolved by the model. The model yields an atmospheric lifetime of methylchloroform (proxy for global OH) of 5.1 years, as compared to a best estimate from observations of 5.5 +/-0.8 years, and simulates H202 concentrations observed from aircraft with significant regional disagreements but no global bias. The OH concentrations are •20% higher than in our previous global 3-D model which included an UV-absorbing aerosol. Concentrations of CO tend to be underestimated by the model, often by 10-30 ppb, which could reflect a combination of excessive OH (a 20% decrease in model OH could be accommodated by the methylchloroform constraint) and an underestimate of CO sources (particularly biogenic). The model underestimates observed acetone concentrations over the South Pacific in fall by a factor of 3; a missing source from the ocean may be implicated. examine aerosol-chemistry-climate interactions [Roelofs et aL, 1997; Mickley et al., 1999; Adams et aL, 2001], and to guide international environmental policy assessments [Intergovernmental Panel on Climate Change (IPCC), 1995, 2001 ]. Several community intercomparisons of global tropospheric chemistry models have been conducted recently, demonstrating the rapid growth of the field [Jacob et al.
Simulation of tropospheric chemistry and aerosols with the climate model EC-Earth
Geoscientific Model Development, 2014
We have integrated the atmospheric chemistry and transport model TM5 into the global climate model EC-Earth version 2.4. We present an overview of the TM5 model and the two-way data exchange between TM5 and the IFS model from the European Centre for Medium-Range Weather Forecasts (ECMWF), the atmospheric general circulation model of EC-Earth. In this paper we evaluate the simulation of tropospheric chemistry and aerosols in a oneway coupled configuration. We have carried out a decadal simulation for present-day conditions and calculated chemical budgets and climatologies of tracer concentrations and aerosol optical depth. For comparison we have also performed offline simulations driven by meteorological fields from ECMWF's ERA-Interim reanalysis and output from the EC-Earth model itself. Compared to the offline simulations, the online-coupled system produces more efficient vertical mixing in the troposphere, which reflects an improvement of the treatment of cumulus convection. The chemistry in the EC-Earth simulations is affected by the fact that the current version of EC-Earth produces a cold bias with too dry air in large parts of the troposphere. Compared to the ERA-Interim driven simulation, the oxidizing capacity in EC-Earth is lower in the tropics and higher in the extratropics. The atmospheric lifetime of methane in EC-Earth is 9.4 years, which is 7 % longer than the lifetime obtained with ERA-Interim but remains well within the range reported in the literature. We further evaluate the model by comparing the simulated climatologies of surface radon-222 and carbon monoxide, tropospheric and surface ozone, and aerosol optical depth against observational data. The work presented in this study is the first step in the development of EC-Earth into an Earth system model with fully interactive atmospheric chemistry and aerosols.
Journal of Geophysical Research, 2010
1] The goal of the Chemistry-Climate Model Validation (CCMVal) activity is to improve understanding of chemistry-climate models (CCMs) through process-oriented evaluation and to provide reliable projections of stratospheric ozone and its impact on climate. An appreciation of the details of model formulations is essential for understanding how models respond to the changing external forcings of greenhouse gases and ozonedepleting substances, and hence for understanding the ozone and climate forecasts produced by the models participating in this activity. Here we introduce and review the models used for the second round (CCMVal-2) of this intercomparison, regarding the implementation of chemical, transport, radiative, and dynamical processes in these models. In particular, we review the advantages and problems associated with approaches used to model processes of relevance to stratospheric dynamics and chemistry. Furthermore, we state the definitions of the reference simulations performed, and describe the forcing data used in these simulations. We identify some developments in chemistry-climate modeling that make models more physically based or more comprehensive, including the introduction of an interactive ocean, online photolysis, troposphere-stratosphere chemistry, and non-orographic gravity-wave deposition as linked to tropospheric convection. The relatively new developments indicate that stratospheric CCM modeling is becoming more consistent with our physically based understanding of the atmosphere. Citation: Morgenstern, O., et al. (2010), Review of the formulation of present-generation stratospheric chemistry-climate models and associated external forcings,
Atmospheric Environment, 1995
Limitations on comprehensive tropospheric chemistry/transport models are discussed within the context of a ~et of issues currently facing the environmental scientific and policy-making communities. A number of central improvements are discussed in a prioritized manner, with consideration of the key progress nece ~sary to include feedback processes between meteorology and chemistry, aerosol formatiot~ in cloud development with subsequent effects on wet removal, dry deposition and surface exchangeprocesses, and impacts of chemical perturbations on radiation, climate, and weather. These improvements would result in a "third-generation model". The computational framework for this code is outlined, and estimates of required computer resources presented.
Environmental Modelling & Software, 2004
We have used a three-dimensional off-line chemistry transport model to identify the role of t mixing processes in the planetary boundary layer (PBL) and of convection on the global distributions of O 3 , and O 3 precursors, processes whose effects are yet to be fully quantified. These effects are investigated in the model performing a sensitivity test, which takes the difference between a base run and a run where either convection or the PBL scheme have been switched off. With both PBL processes and convection, chemical species are redistributed in the troposphere, so that their mixing ratio profile becomes more uniform with height. In areas of strong convection, O 3 is brought rapidly from the upper troposphere downwards to regions where its lifetime is shorter due to higher photochemical activity and the higher water vapour mixing ratio (the major sink for O 3 ) than in the upper troposphere. This indicates that a direct effect of convection is to reduce the lifetime of O 3 and thus lower the amount of tropospheric O 3 . More specifically, convection lowers O 3 values by up to 5 ppbv in the upper troposphere, since it transports O 3 -poor surface air upwards. In regions where surface emissions are important, nitrogen species in the upper troposphere, most notably HNO 3 , show an increase of about 50 pptv. Conversely, in areas with strong lightning activity and low surface emissions, HNO 3 decreases by about 10 pptv since convection dilutes locally produced nitrogen by lightning. The PBL acts primarily as a cleansing mechanism of the surface, transporting surface pollutants upwards and hence affecting the upper troposphere chemical concentrations as well. For instance, surface CO values decrease within areas of strong surface emissions by more than 100 pptv but in the lower free troposphere, CO values increase by more than 40 pptv through the injection of surface air rich in CO. Furthermore, the sensitivity of local, time varying concentrations to the processes in the PBL and convection is considered using a time series analysis, which reveals whether chemistry or transport dominates on particular days.
Journal of Geophysical Research, 1995
We present results of global tropospheric chemistry simulations with the coupled chemistry/atmospheric general circulation model ECHAM. Ultimately, the model will be used to study climate changes induced by anthropogenic influences on the chemistry of the atmosphere; meteorological parameters that are important for the chemistry, such as temperature, humidity, air motions, cloud and rain characteristics, and mixing processes are calculated on-line. The chemical part of the model describes background tropospheric CH4-CO-NOx-HOx photochemistry. Emissions of NO and CO, surface concentrations of CH4, and stratospheric concentrations of 03 and NOy are prescribed as boundary conditions. Calculations of the tropospheric 03 budget indicate that seasonal variabilities of the photochemical production and of injection from the stratosphere are represented realistically, although some aspects of the model still need improvement. Comparisons of calculated 03 surface concentrations and 03 profiles with available measurements show that the model reproduces 03 distributions in remote tropical and midlatitudinal sites. Also, the model matches typical profiles connected with deep convection in the Intertropical Convergence Zone (ITCZ). However, the model tends to underestimate 0 3 concentrations at the poles and in relatively polluted regions. These underestimates are caused by the poor representation of tropopause foldings in midlatitudes, which form a significant source of tropospheric 03 from the stratosphere, too weak transport to the poles, and the neglect of higher hydrocarbon chemistry. Also, mixing of polluted continental boundary layer air into the free troposphere may be underestimated. We discuss how these model deficiencies will be improved in the future. 20,983 20,984 ROELOFS AND LELIEVELD: TROPOSPHERIC O3 IN A CHEMISTRY GCM Institute for Meteorology in Hamburg, Germany [Roeckner et al. , 1992]. All meteorological data needed to evaluate chemical tracer concentrations in the atmosphere are calculated on-line by ECHAM with a time resolution of 40 min. As a result of the meteorology calculations, more CPU time is required than with an off-line model with the same spatial resolution and chemistry. In our model the calculations associated with chemical species (i.e., the processes described in section 2 and transport in the atmosphere) need approximately the same amount of CPU time as the meteorology calculations. However, the use of an off-line model requires substantial CPU time and memory to read and store data for the calculation of transport and the complex interactions between meteorological and chemical processes, whereas a large amount of data may be needed to cover different model resolutions. Further, a chemistry GCM interactively calculates concentrations of radiatively active species such as 03 that directly drive the radiation scheme and the GCM meteorology. When fully developed and tested, a coupled chemistry GCM is a powerful tool in the study of the intricate interactions between atmospheric chemistry and global climate.
Journal of Geophysical Research, 1999
A new middle-atmosphere general circulation model that includes the photochemistry for ozone and other chemical species (19 photolysis and 52 chemical reactions) has been constructed. The horizontal spectral resolution is T21 (about a 600 km horizontal grid spacing) with 30 layers in the vertical. Preliminary results from over 10 years of model integration are presented. The distributions of longlived species, such as N20, are rather similar to those of satellite observations in a climatological sense, although the sharp meridional gradient around 30 ø latitude is not well simulated in the model stratosphere. Neither is the double peak structure that occurs during equinox periods well reproduced. This result is consistent with the fact that the westerly phase of the semiannual oscillation is weak in this model. This may be due to the coarse resolution of the model. The seasonal evolution of the ozone column abundance is quite realistic, although the model slightly underestimates total tropical ozone. The model also underestimates ozone amounts around the equatorial tropopause. The February midlatitude number density of OH in the model upper stratosphere is about 1.8 x 107 cm -3, which is slightly less than that observed. The horizontal distributions of short-lived species, such as NO, suggest a reasonable model diurnal variation. The model has a cold bias of about 25 K in the lower stratospheric Northern Hemisphere winter and 5 K in the Southern Hemisphere winter. The model residual mean vertical velocity in the equatorial lower stratosphere is too weak (about 0.1 mm/s) during the Northern Hemisphere winter, compared with the observed (about 0.4 mm/s), while the model temperature around the equatorial tropopause is cooler than that observed.
Atmospheric Chemistry and Physics, 2006
The new Modular Earth Submodel System (MESSy) describes atmospheric chemistry and meteorological processes in a modular framework, following strict coding standards. It has been coupled to the ECHAM5 general circulation model, which has been slightly modified for this purpose. A 90-layer model version up to 0.01 hPa was used 5 at T42 resolution (≈2.8 • latitude and longitude) to simulate the lower and middle atmosphere. The model meteorology has been tested to check the influence of the changes to ECHAM5 and the radiation interactions with the new representation of atmospheric composition. A Newtonian relaxation technique was applied in the tropospheric part of the domain to weakly nudge the model towards the analysed meteorology during the 10 period 1998-2005. It is shown that the tropospheric wave forcing of the stratosphere in the model suffices to reproduce the Quasi-Biennial Oscillation and major stratospheric warming events leading e.g. to the vortex split over Antarctica in 2002. Characteristic features such as dehydration and denitrification caused by the sedimentation of polar stratospheric cloud particles and ozone depletion during winter and spring are 15 simulated accurately, although ozone loss in the lower polar stratosphere is slightly underestimated. The model realistically simulates stratosphere-troposphere exchange processes as indicated by comparisons with satellite and in situ measurements. The evaluation of tropospheric chemistry presented here focuses on the distributions of ozone, hydroxyl radicals, carbon monoxide and reactive nitrogen compounds. In spite 20 of minor shortcomings, mostly related to the relatively coarse T42 resolution and the neglect of interannual changes in biomass burning emissions, the main characteristics of the trace gas distributions are generally reproduced well. The MESSy submodels and the ECHAM5/MESSy1 model output are available through the internet on request. 6, 2006 EGU 20 5th generation European Centre Hamburg GCM, ECHAM5 (Roeckner et al., 2003. We pursue a rigorous modularisation and apply coding standards to face the challenges associated with increasing model complexity . The resulting Modular Earth Submodel System (MESSy) is portable, user-friendly and flexible, well-documented and easily expandable (see http://www.messy-interface.org).