Relaxing the well‐mixed greenhouse gas approximation in climate simulations: Consequences for stratospheric climate

Curry, Charles L.; McFarlane, N. A.; Scinocca, John

doi:10.1029/2005jd006670

Cited by 5 publications

(5 citation statements)

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“…Note that for weather forecasting it is generally not necessary to represent changes to trace gases during the simulation, so one may combine all wellmixed gases with carbon dioxide into a ''composite'' gas (e.g., Ritter and Geleyn 1992). Curry et al (2006) showed that the global-mean temperature error resulting from assuming methane and nitrous oxide to be well mixed is less than 0.2 K below 30 km, rising to 1 K above 50 km, while the error due to treating CFC11 and CFC12 as well mixed is less than 0.1 K everywhere below 50 km. These small errors will have no detectable impact on the accuracy of weather forecasts.…”

Section: Results For a Single Absorbing Gasmentioning

confidence: 99%

“…The computational time spent resolving the spectrum is also not matched by the time spent resolving the spatial structure of clouds within a grid box, leading to substantial radiative biases (Cahalan et al 1994;Shonk and Hogan 2008). Moreover, while it is necessary to represent trace gases individually for climate forecasts and reanalysis projects, the accuracy of day-to-day numerical weather forecasts is largely insensitive to errors in their representation; Curry et al (2006) showed that assuming trace gases to be vertically well mixed led to a temperature error of less than 0.2 K below 30 km, rising to 1 K above 50 km. It is therefore highly desirable to explore ways to treat gaseous absorption more efficiently.…”

Section: Introductionmentioning

confidence: 98%

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The Full-Spectrum Correlated-k Method for Longwave Atmospheric Radiative Transfer Using an Effective Planck Function

Hogan

2010

Journal of the Atmospheric Sciences

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The correlated-k-distribution (CKD) method is widely used in the radiative transfer schemes of atmospheric models; it involves dividing the spectrum into a number of bands and then reordering the gaseous absorption coefficients within each one. The fluxes and heating rates for each band may then be computed by discretizing the reordered spectrum into O(10) quadrature points per major gas and performing a pseudomonochromatic radiation calculation for each point. In this paper it is first argued that for clear-sky longwave calculations, sufficient accuracy for most applications can be achieved without the need for bands: reordering may be performed on the entire longwave spectrum. The resulting full-spectrum correlated-k (FSCK) method requires significantly fewer pseudomonochromatic calculations than standard CKD to achieve a given accuracy. The concept is first demonstrated by comparing with line-by-line calculations for an atmosphere containing only water vapor, in which it is shown that the accuracy of heating rate calculations improves approximately in proportion to the square of the number of quadrature points. For more than around 20 points, the root-mean-square error flattens out at around 0.015 K day 21 due to the imperfect rank correlation of absorption spectra at different pressures in the profile. The spectral overlap of m different gases is treated by considering an m-dimensional hypercube where each axis corresponds to the reordered spectrum of one of the gases. This hypercube is then divided up into a number of volumes, each approximated by a single quadrature point, such that the total number of quadrature points is slightly fewer than the sum of the number that would be required to treat each of the gases separately. The gaseous absorptions for each quadrature point are optimized such that they minimize a cost function expressing the deviation of the heating rates and fluxes calculated by the FSCK method from line-by-line calculations for a number of training profiles. This approach is validated for atmospheres containing water vapor, carbon dioxide, and ozone, in which it is found that in the troposphere and most of the stratosphere, heating rate errors of less than 0.2 K day 21 can be achieved using a total of 23 quadrature points, decreasing to less than 0.1 K day 21 for 32 quadrature points. It would be relatively straightforward to extend the method to include other gases.

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Section: Results For a Single Absorbing Gasmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

The Full-Spectrum Correlated-k Method for Longwave Atmospheric Radiative Transfer Using an Effective Planck Function

Hogan

2010

Journal of the Atmospheric Sciences

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“…Since both CH 4 concentrations and land area are largest in the NH, using a more realistic surface concentration distribution should lead to an even larger north/south imbalance in the methane sink than already seen (approximately 60/40, according to Paper I), and a slightly larger global uptake. Furthermore, the parameterization of methane consumption utilized in this paper can be combined with a simplified atmospheric CH 4 chemistry scheme, already tested in AGCM3 (Curry et al, 2006), to enable completely prognostic methane sinks in a coupled GCM. For a prescribed surface CH 4 concentration field, running the model to equilibrium would then determine the relative contributions of the atmosphere and soil to the total CH 4 sink.…”

Section: Discussionmentioning

confidence: 99%

The consumption of atmospheric methane by soil in a simulated future climate

Curry

2009

Biogeosciences

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Abstract.A recently developed model for the consumption of atmospheric methane by soil (Curry, 2007) is used to investigate the global magnitude and distribution of methane uptake in a simulated future climate. In addition to solving the one-dimensional diffusion-reaction equation, the model includes a parameterization of biological CH 4 oxidation that is sensitive to soil temperature and moisture content, along with specified reduction factors for land cultivation and wetland fractional coverage. Under the SRES emission scenario A1B, the model projects an 8% increase in the global annual mean CH 4 soil sink by 2100, over and above the 15% increase expected from increased CH 4 concentration alone. While the largest absolute increases occur in cool temperate and subtropical forest ecosystems, the largest relative increases in consumption (>40%) are seen in the boreal forest, tundra and polar desert environments of the high northern latitudes. Methane uptake at mid-to high northern latitudes increases year-round in 2100, with a 68% increase over present-day values in June. This increase is primarily due to enhanced soil diffusivity resulting from lower soil moisture produced by increased evaporation and reduced snow cover. At lower latitudes, uptake is enhanced mainly by elevated soil temperatures and/or reduced soil moisture stress, with the dominant influence determined by the local climate.

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“…Collins et al, 2006); that is, these models consider CH 4 as a well-mixed gas, which is unrealistic above the tropopause. Using a simpler parameterisation approach than CoMeCAT, Curry et al (2006) showed the impact that relaxing the wellmixed approximation for some greenhouse gases (GHGs) 9654 B. M. Monge-Sanz et al: Stratospheric methane and water in global models had in the stratosphere. They used the Canadian AGCM3 general circulation model (McFarlane et al, 1992) with a simplified treatment for the chemical loss of N 2 O, CH 4 , CFC-11 and CFC-12.…”

Section: Stratospheric Methane Radiation and Temperaturementioning

confidence: 99%

On the uses of a new linear scheme for stratospheric methane in global models: water source, transport tracer and radiative forcing

et al. 2013

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This study evaluates effects and applications of a new linear parameterisation for stratospheric methane and water vapour. The new scheme (CoMeCAT) is derived from a 3-D full-chemistry-transport model (CTM). It is suitable for any global model, and is shown here to produce realistic profiles in the TOMCAT/SLIMCAT 3-D CTM and the ECMWF (European Centre for Medium-Range Weather Forecasts) general circulation model (GCM). Results from the new scheme are in good agreement with the full-chemistry CTM CH₄ field and with observations from the Halogen Occultation Experiment (HALOE). The scheme is also used to derive stratospheric water increments, which in the CTM produce vertical and latitudinal H₂O variations in fair agreement with satellite observations. Stratospheric H₂O distributions in the ECMWF GCM show realistic overall features, although concentrations are smaller than in the CTM run (up to 0.5 ppmv smaller above 10 hPa). The potential of the new CoMeCAT tracer for evaluating stratospheric transport is exploited to assess the impacts of nudging the free-running GCM to ERA-40 and ERA-Interim reanalyses. The nudged GCM shows similar transport patterns to the offline CTM forced by the corresponding reanalysis data. The new scheme also impacts radiation and temperature in the model. Compared to the default CH₄ climatology and H₂O used by the ECMWF radiation scheme, the main effect on ECMWF temperatures when considering both CH₄ and H₂O from CoMeCAT is a decrease of up to 1.0 K over the tropical mid/low stratosphere. The effect of using the CoMeCAT scheme for radiative forcing (RF) calculations is investigated using the offline Edwards–Slingo radiative transfer model. Compared to the default model option of a tropospheric global 3-D CH₄ value, the CoMeCAT distribution produces an overall change in the annual mean net RF of up to −30 mW m⁻²

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Relaxing the well‐mixed greenhouse gas approximation in climate simulations: Consequences for stratospheric climate

Cited by 5 publications

References 69 publications

The Full-Spectrum Correlated-k Method for Longwave Atmospheric Radiative Transfer Using an Effective Planck Function

The Full-Spectrum Correlated-k Method for Longwave Atmospheric Radiative Transfer Using an Effective Planck Function

The consumption of atmospheric methane by soil in a simulated future climate

On the uses of a new linear scheme for stratospheric methane in global models: water source, transport tracer and radiative forcing

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