Interaction of atmospheric chemistry and climate and its impact on stratospheric ozone (original) (raw)
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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,
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.
Journal of Climate, 2010
The temperature of the stratosphere has decreased over the past several decades. Two causes contribute to that decrease: well-mixed greenhouse gases (GHGs) and ozone-depleting substances (ODSs). This paper addresses the attribution of temperature decreases to these two causes and the implications of that attribution for the future evolution of stratospheric temperature. Time series analysis is applied to simulations of the Goddard Earth Observing System Chemistry–Climate Model (GEOS CCM) to separate the contributions of GHGs from those of ODSs based on their different time-dependent signatures. The analysis indicates that about 60%–70% of the temperature decrease of the past two decades in the upper stratosphere near 1 hPa and in the lower midlatitude stratosphere near 50 hPa resulted from changes attributable to ODSs, primarily through their impact on ozone. As ozone recovers over the next several decades, the temperature should continue to decrease in the middle and upper stratosp...
Quarterly Journal of the Royal Meteorological Society, 2005
We have created a new interactive model for coupled chemistry-climate studies of the stratosphere. The model combines the detailed stratospheric chemistry modules developed and tested in the SLIMCAT/ TOMCAT off-line chemical transport models (CTM) with a version of the Met Office Unified Model (UM). The resulting chemistry-climate model (CCM), called UMCHEM, has a detailed description of stratospheric gasphase and heterogeneous chemistry. The chemical fields of O 3 , N 2 O, CH 4 and H 2 O are used interactively in the radiative heating calculation.
Journal of Geophysical Research, 2006
1] Simulations of the stratosphere from thirteen coupled chemistry-climate models (CCMs) are evaluated to provide guidance for the interpretation of ozone predictions made by the same CCMs. The focus of the evaluation is on how well the fields and processes that are important for determining the ozone distribution are represented in the simulations of the recent past. The core period of the evaluation is from 1980 to 1999 but long-term trends are compared for an extended period . Comparisons of polar high-latitude temperatures show that most CCMs have only small biases in the Northern Hemisphere in winter and spring, but still have cold biases in the Southern Hemisphere spring below 10 hPa. Most CCMs display the correct stratospheric response of polar temperatures to wave forcing in the Northern, but not in the Southern Hemisphere. Global long-term stratospheric temperature trends are in reasonable agreement with satellite and radiosonde observations. Comparisons of simulations of methane, mean age of air, and propagation of the annual cycle in water vapor show a wide spread in the results, indicating differences in transport. However, for around half the models there is reasonable agreement with observations. In these models the mean age of air and the water vapor tape recorder signal are generally better than reported in previous model intercomparisons. Comparisons of the water vapor and inorganic chlorine (Cl y ) fields also show a large intermodel spread. Differences in tropical water vapor mixing ratios in the lower stratosphere are primarily related to biases in the simulated tropical tropopause temperatures and not transport. The spread in Cl y , which is largest in the polar lower stratosphere, appears to be primarily related to transport differences. In general the amplitude and phase of the annual cycle in total ozone is well simulated apart from the southern high latitudes. Most CCMs show reasonable agreement with observed total ozone trends and variability on a global scale, but a greater spread in the ozone trends in polar regions in spring, especially in the Arctic. In conclusion, despite the wide range of skills in representing different processes assessed here, there is sufficient agreement between the majority of the CCMs and the observations that some confidence can be placed in their predictions. Citation: Eyring, V., et al. (2006), Assessment of temperature, trace species, and ozone in chemistry-climate model simulations of the recent past,
Climate Change - Geophysical Foundations and Ecological Effects, 2011
Climate Change-Geophysical Foundations and Ecological Effects 4 stratosphere was explained as a combination of special meteorological conditions and changed chemical composition induced by industrially manufactured (anthropogenic) chlorofluorocarbons (CFCs) and halons. 1.1 Ozone chemistry In the atmosphere, ozone (O 3) is produced exclusively by photochemical processes. Ozone formation in the stratosphere is initiated by the photolysis of molecular oxygen (O 2). This produces two oxygen atoms (O) which recombine with molecular oxygen to form ozone. Since ozone is created by photochemical means, it is mainly produced in the tropical and subtropical stratosphere, where sunshine is most intensive throughout the year. At the same time, the ozone molecules formed in this way are destroyed again by the photolysis of ozone and by reaction with an oxygen atom. These reactions form the basis of stratospheric ozone chemistry, the so-called Chapman mechanism (Chapman, 1930). But if stratospheric ozone amounts are determined via this simple reaction system and the known rate constants and photolysis rates, the results obtained are about twice as high as the measured values. Since the early 1950ies, it has been known that fast so-called catalytic cycles reduce the determined ozone amounts to the observed values. By the early 1970ies, the catalysts had been identified as the radical pairs OH/HO 2 and NO/NO 2 , which are formed from water vapour (H 2 O) and nitrous oxide (N 2 O) respectively (Bates and Nicolet, 1950; Crutzen, 1971; Johnston, 1971). In the mid-1970ies, the radical pairs Cl/ClO (from CFCs) and Br/BrO (from halons) were identified as further significant contributors (Molina and Rowland, 1974; Wofsy et al., 1975). The important point is that a catalyst can take part in the reaction cycle several thousand times and therefore is very effective in destroying ozone molecules. The increased occurrence of CFCs and halons due to anthropogenic emissions has significantly accelerated stratospheric ozone depletion cycle over recent decades, triggering a negative stratospheric ozone trend which is most obvious in the Southern polar stratosphere during spring time where the ozone hole is found. In the troposphere, CFCs and halons are mostly inert. Over time (several years), they are transported into the stratosphere. Only there they are photolysed and converted into active chlorine or bromine compounds. In particular, ozone is depleted via the catalytic Cl/ClO-cycle in polar spring. However, the kinetics of these processes are very slow, because the amount of UV radiation is limited due to the prevailing twilight conditions. In the polar stratosphere, it is mainly chemical reactions on the surface of stratospheric ice particles that are responsible for activating chlorine (and also bromine) and then driving ozone depletion immediately after the end of polar night (Solomon et al., 1986). In the very cold lower polar stratosphere, polar stratospheric clouds (PSCs) form during polar night (Figure 1). PSCs develop at temperatures below about 195 K (=-78 °C) where nitric acid trihydride crystals form (NAT, HNO 3 •3H 2 O). Under the given conditions in the lower stratosphere ice particles develop at temperatures below approx. 188 K (=-85 °C). Due to different land-sea distributions on the Northern and Southern Hemisphere, the lower stratosphere over the south pole cools significantly more in winter (June-August) than the north polar stratosphere (December-February) (see Section 1.2). The climatological mean of polar winter temperatures of the lower Arctic stratosphere is around 10 K higher than that of the lower Antarctic stratosphere. While the Antarctic stratosphere reaches temperatures below PSC-forming temperatures for several weeks every year, there is a pronounced year-on-year variability in the north polar stratosphere: relatively warm winters, where hardly any PSCs develop are www.intechopen.com
Journal of Geophysical Research, 2000
We present an improved version of the global chemistry-general circulation model of Roelofs and Lelieveld [1997]. The major model improvement is the representation of higher hydrocarbon chemistry, implemented by means of the Carbon Bond Mechanism 4 (CBM-4). Simulated tropospheric ozone concentrations at remote locations, which agreed well with observations in the previous model version, are not affected much by the chemistry of higher hydrocarbons. However, ozone formation in the polluted boundary layer is significantly enhanced, resulting in a more realistic simulation of surface ozone in regions such as North America, Europe, and Southeast Asia. Our model simulates a net global tropospheric ozone production of 73 Tg yr -• when higher hydrocarbon chemistry is considered, and -36 Tg yr-• without higher hydrocarbon chemistry. The simulated seasonality of surface CO agrees well with observations. However, the southern hemispheric maximum for O3 and CO associated with biomass burning emissions is delayed by 1 month compared to the observations, which demonstrates the need for a better representation of biomass burning emissions. Simulated peroxyacetyl nitrate (PAN) concentrations agree well with observed values, although the variability is underestimated. OH decreases strongly in the continental boundary layer due to its reaction with higher hydrocarbons. However, this is almost compensated by an increase of OH over oceans in the lower half of the troposphere. Consideration of higher hydrocarbon chemistry decreases the global annual tropospheric OH concentration by about 8% compared to a background tropospheric chemistry scheme. Further, the radiative forcing by anthropogenically increased tropospheric ozone on the northern hemisphere increases, especially in July. The forcing also increases on the southern hemisphere where biomass burning emissions produce tropospheric ozone, except between December and June, that is, outside the biomass burning season, when ozone formation is suppressed due to formation of PAN and MPAN from isoprene oxidation. Globally and annually averaged, the forcing increases only by a few percent due to higher hydrocarbon chemistry. al., 1990]. The seasonality of ozone in the troposphere is determined by two main processes. First, ozone-rich air is transported from the stratosphere to the troposphere by stratosphere-troposphere exchange (STE). These transports maximize at extratropical latitudes on both hemispheres in winter and early spring when ozone concentrations in the stratosphere are relatively high and the stratospheric wave forcing is strongest [Holton et al., 1995]. Second, ozone is produced and destroyed through photochemistry from emissions of ozone precursors such as NO, c, CO, CH4, and higher hydrocarbons from natural and anthropogenic sources. In the NH where anthropogenic emissions are relatively large throughout the year, a summer ozone maximum is observed in the polluted boundary layer and in the extratropical free troposphere, whereas a spring maximum and summer minimum are observed at the surface in remote regions. The ozone seasonality in the southern hemisphere (SH) is strongly influenced by biomass burning activities which cause elevated ozone levels over a large part of the SH between September and November, and by STE which maximizes around August [Fishman et al., 1990; Thompson et al., 1996]. Three-dimensional global chemistry-transport and chemistry-climate models of the atmosphere are invaluable tools to study transports and chemistry of ozone in the troposphere and 22,697 22,698 ROELOFS AND LELIEVELD: TROPOSPHERIC OZONE SIMULATION to assess the anthropogenic influence on tropospheric ozone levels and associated climate effects [Lelieveld and van Dorland, 1995; Roelofs et al., 1997a; Berntsen et al., 1997; Haywood et al., 1998]. In this study we present an improved version of a global chemistry-climate model that has previously been applied to several studies of tropospheric ozone. In the work of Roelofs and Lelieveld [1997] the contribution of ozone from stratospheric origin to tropospheric ozone levels was investigated; in the work of Roelofs et al. [1997b], simulated ozone distributions in the South Atlantic Ocean region during the biomass burning season are compared with ship measurements and observations from satellites; and in the work of Roelofs et al. [1997a, 1998] and Roelofs [1999a], simulations of the increase of tropospheric ozone due to anthropogenic activities and associated radiative climate forcings are discussed. By using a nudged version of the model, which assimilates European Centre for Medium-Range Weather Forecasts (EC-MWF) to represent actual meteorology [Jeuken et al., 1996], studies have been made of cross-tropopause ozone transports in synoptic-scale disturbances [Kentarchos et al., 1999, 2000], of transports and chemistry in the Indian Ocean region as part of the Indian Ocean Experiment (INDOEX) project [De Laat et al., 1999], and of ozone distributions in the tropopause region associated with the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program [Roelofs, 1999b]. The chemistry module used thus far describes background tropospheric chemistry. Generally, this version provided a fair representation of the magnitude and seasonality of ozone concentrations in relatively remote regions of the troposphere [Roelofs and Lelieveld, 1995, 1997; Kanakidou et al., 1999]. Two important shortcomings of the model were found. First, the model was not able to capture the large, synoptic-scale, variability of ozone concentrations in the upper troposphere because stratospheric ozone concentrations were parameterized based on monthly averaged values. A new parameterization, which relates lower stratospheric ozone concentrations to the modeled potential vorticity, is presented in detail by Roelofs and Lelieveld [2000] and will be briefly discussed in section 2. Second, the model underpredicted lower tropospheric ozone concentrations over the NH continents in summer [Roelofs and Lelieveld, 1995, 1997]. Also, simulated tropospheric ozone columns over the tropical $H Atlantic Ocean during the biomass burning season were underestimated compared to measurements [Roelofs et al., 1997b]. We attributed the underestimation of ozone by the model to the neglect of higher hydrocarbon chemistry. The influence of higher hydrocarbons on ozone levels, even at continental but relatively clean locations, can be significant [e.g., Liu et al., 1987]. Additionally, peroxyacetyl nitrate (PAN) formation and transport is an efficient means to carry NO,• from polluted to remote regions [Moxim et al., 1996; Horowitz and Jacob, 1999]. Previous model studies have demonstrated the potential importance of higher hydrocarbons to global ozone distributions [e.g., Kanakidou et al., 1991; Houweling et al., 1998; Wang et al., 1998a, b].
The new UKCA climate-chemistry model: Evaluation of the stratospheric performance
2009
The UK Chemistry and Aerosols (UKCA) model is a new chemistry module coupled to the Met Office Unified Model capable of simulating composition and climate from the troposphere to the mesosphere. Here we assess its performance in the stratosphere. We present basic and derived dynamical and chemical model results and compare to ERA-40 reanalyses and satellite climatologies. Polar temperatures and the lifetime of the southern polar vortex are well captured, indicating that the model is suitable for assessing the ozone hole; this is partly a consequence of a good representation of meridional heat fluxes in the model. Ozone and long- lived tracers compare favourably to observations. Chemical-dynamical coupling, as evidenced by the anticorrelation between winter-spring northern polar ozone columns and the strength of the polar jet, is also well captured. We discuss remaining weaknesses and ways to improve the model. The simulation presented here forms part of our contribution to the CCMVal-2 model intercomparison.
Multimodel projections of stratospheric ozone in the 21st century
Journal of Geophysical Research, 2007
Simulations from eleven coupled chemistry-climate models (CCMs) employing nearly identical forcings have been used to project the evolution of stratospheric ozone throughout the 21st century. The model-to-model agreement in projected temperature trends is good, and all CCMs predict continued, global mean cooling of the stratosphere over the next 5 decades, increasing from around 0.25 K/decade at 50 hPa to around 1 K/ decade at 1 hPa under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario. In general, the simulated ozone evolution is mainly determined by decreases in halogen concentrations and continued cooling of the global stratosphere due to increases in greenhouse gases (GHGs). Column ozone is projected to increase as stratospheric halogen concentrations return to 1980s levels. Because of ozone increases in the middle and upper stratosphere due to GHGinduced cooling, total ozone averaged over midlatitudes, outside the polar regions, and globally, is projected to increase to 1980 values between 2035 and 2050 and before lowerstratospheric halogen amounts decrease to 1980 values. In the polar regions the CCMs simulate small temperature trends in the first and second half of the 21st century in midwinter. Differences in stratospheric inorganic chlorine (Cl y) among the CCMs are key to diagnosing the intermodel differences in simulated ozone recovery, in particular in the Antarctic. It is found that there are substantial quantitative differences in the simulated Cl y , with the October mean Antarctic Cl y peak value varying from less than 2 ppb to over 3.5 ppb in the CCMs, and the date at which the Cl y returns to 1980 values varying from before 2030 to after 2050. There is a similar variation in the timing of recovery of Antarctic springtime column ozone back to 1980 values. As most models underestimate peak Cl y near 2000, ozone recovery in the Antarctic could occur even later, between 2060 and 2070. In the Arctic the column ozone increase in spring does not follow halogen decreases as closely as in the Antarctic, reaching 1980 values before Arctic halogen amounts decrease
Izvestiya, Atmospheric and Oceanic Physics, 2011
The solar climate ozone links (SOCOL) three dimensional chemistry-climate model is used to estimate changes in the ozone and atmospheric dynamics over the 21st century. With this model, four numer ical time slice experiments were conducted for 1980, 2000, 2050, and 2100 conditions. Boundary conditions for sea surface temperatures, sea ice parameters, and concentrations of greenhouse and ozone depleting gases were set following the IPCC A1B scenario and the WMO A1 scenario. From the model results, a statis tically significant cooling of the model stratosphere was obtained to be 4-5 K for 2000-2050 and 3-5 K for 2050-2100. The temperature of the lower atmosphere increases by 2-3 K over the 21st century. Tropospheric heating significantly enhances the activity of planetary scale waves at the tropopause. As a result, the Elias sen-Palm flux divergence considerable increases in the middle and upper stratosphere. The intensity of zonal circulation decreases and the meridional residual circulation increases, especially in the winter-spring period of each hemisphere. These dynamic changes, along with a decrease in the concentrations of ozone depleting gases, result in a faster growth of O 3 outside the tropics. For example, by 2050, the total ozone in the middle and high latitudes approaches its model level of 1980 and the ozone hole in Antarctica fills up. The super recovery of the model ozone layer in the middle and high latitudes of both hemispheres occurs in 2100. The tropical ozone layer recovers far less slowly, reaching a 1980 level only by 2100.