A global signature of enhanced shortwave absorption by clouds

Collins, William D.

doi:10.1029/1998jd200022

Cited by 40 publications

(30 citation statements)

References 56 publications

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“…In the shortwave radiation package, Raleigh scattering, absorption by ozone, water vapor and other absorptive gases, and aerosol and cloud scattering and extinction are considered (Briegleb, 1992;Collins et al, 1998Collins et al, , 2001). The optical depth, single scattering albedo, and asymmetry factor for ice clouds, are parameterized as a function of ice cloud effective radius (Ebert and Curry, 1992).…”

Section: Methods Used To Calculate Ice Crystal Number Concentration Amentioning

confidence: 99%

Possible influence of anthropogenic aerosols on cirrus clouds and anthropogenic forcing

et al. 2009

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Abstract. Cirrus clouds have a net warming effect on the atmosphere and cover about 30% of the Earth's area. Aerosol particles initiate ice formation in the upper troposphere through modes of action that include homogeneous freezing of solution droplets, heterogeneous nucleation on solid particles immersed in a solution, and deposition nucleation of vapor onto solid particles. Here, we examine the possible change in ice number concentration from anthropogenic soot originating from surface sources of fossil fuel and biomass burning, from anthropogenic sulfate aerosols, and from aircraft that deposit their aerosols directly in the upper troposphere. We use a version of the aerosol model that predicts sulfate number and mass concentrations in 3-modes and includes the formation of sulfate aerosol through homogeneous binary nucleation as well as a version that only predicts sulfate mass. The 3-mode version best represents the Aitken aerosol nuclei number concentrations in the upper troposphere which dominated ice crystal residues in the upper troposphere. Fossil fuel and biomass burning soot aerosols with this version exert a radiative forcing of −0.3 to −0.4 Wm −2 while anthropogenic sulfate aerosols and aircraft aerosols exert a forcing of −0.01 to 0.04 Wm −2 and −0.16 to −0.12 Wm −2 , respectively, where the range represents the forcing from two parameterizations for ice nucleation. The sign of the forcing in the mass-only version of the model depends on which ice nucleation parameterization is used and can be either positive or negative. The magnitude of Correspondence to: J. E. Penner (penner@umich.edu) the forcing in cirrus clouds can be comparable to the forcing exerted by anthropogenic aerosols on warm clouds, but this forcing has not been included in past assessments of the total anthropogenic radiative forcing of climate.

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Section: Methods Used To Calculate Ice Crystal Number Concentration Amentioning

confidence: 99%

Possible influence of anthropogenic aerosols on cirrus clouds and anthropogenic forcing

et al. 2009

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“…Below approx. 60 km the SW radiation of CAM4 is retained, employing 19 spectral bands between 200 and 5000 nm (Collins, 1998). For the transition zone (60-70 km) SW heating rates are calculated as weighted averages of the two approaches.…”

Section: Chemistry-climate Model Descriptionsmentioning

confidence: 99%

Solar forcing for CMIP6 (v3.2)

et al. 2017

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Abstract. This paper describes the recommended solar forcing dataset for CMIP6 and highlights changes with respect to CMIP5. The solar forcing is provided for radiative properties, namely total solar irradiance (TSI), solar spectral irradiance (SSI), and the F10.7 index as well as particle forcing, including geomagnetic indices Ap and Kp, and ionization rates to account for effects of solar protons, electrons, and galactic cosmic rays. This is the first time that a recommendation for solar-driven particle forcing has been provided for a CMIP exercise. The solar forcing datasets are provided at daily and monthly resolution separately for the CMIP6 preindustrial control, historical (1850CMIP6 preindustrial control, historical ( -2014, and future (2015-2300) simulations. For the preindustrial control simulation, both constant and time-varying solar forcing components are provided, with the latter including variability on 11-year and shorter timescales but no long-term changes. For the future, we provide a realistic scenario of what solar behavior could be, as well as an additional extreme Maunderminimum-like sensitivity scenario. This paper describes the forcing datasets and also provides detailed recommendations as to their implementation in current climate models.For the historical simulations, the TSI and SSI time series are defined as the average of two solar irradiance models that are adapted to CMIP6 needs: an empirical onePublished by Copernicus Publications on behalf of the European Geosciences Union. A new and lower TSI value is recommended: the contemporary solar-cycle average is now 1361.0 W m −2 . The slight negative trend in TSI over the three most recent solar cycles in the CMIP6 dataset leads to only a small global radiative forcing of −0.04 W m −2 . In the 200-400 nm wavelength range, which is important for ozone photochemistry, the CMIP6 solar forcing dataset shows a larger solar-cycle variability contribution to TSI than in CMIP5 (50 % compared to 35 %).We compare the climatic effects of the CMIP6 solar forcing dataset to its CMIP5 predecessor by using timeslice experiments of two chemistry-climate models and a reference radiative transfer model. The differences in the long-term mean SSI in the CMIP6 dataset, compared to CMIP5, impact on climatological stratospheric conditions (lower shortwave heating rates of −0.35 K day −1 at the stratopause), cooler stratospheric temperatures (−1.5 K in the upper stratosphere), lower ozone abundances in the lower stratosphere (−3 %), and higher ozone abundances (+1.5 % in the upper stratosphere and lower mesosphere). Between the maximum and minimum phases of the 11-year solar cycle, there is an increase in shortwave heating rates (+0.2 K day −1 at the stratopause), temperatures (∼ 1 K at the stratopause), and ozone (+2.5 % in the upper stratosphere) in the tropical upper stratosphere using the CMIP6 forcing dataset. This solar-cycle response is slightly larger, but not statistically significantly different from that for the CMIP5 forcing dataset.CMIP6 models wi...

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“…The solar spectrum is divided into 19 discrete spectral and pseudospectral intervals: 7 for O 3 , 1 for the visible, 7 for H 2 O including water-vapor continuum, 3 for CO 2 , and 1 for the near-infrared following Collins (1998). The solar absorption by water vapor between 1000 and 18 000 cm −1 is treated using seven pseudo-spectral intervals with a constant specific extinction specified for each interval.…”

Section: A23 Model #26 Cam Radiation Scheme (Car-cam F Zhang)mentioning

confidence: 99%

Intercomparison of shortwave radiative transfer schemes in global aerosol modeling: results from the AeroCom Radiative Transfer Experiment

et al. 2013

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Abstract. In this study we examine the performance of 31 global model radiative transfer schemes in cloud-free conditions with prescribed gaseous absorbers and no aerosols (Rayleigh atmosphere), with prescribed scattering-only aerosols, and with more absorbing aerosols. Results are compared to benchmark results from high-resolution, multi-angular line-by-line radiation models. For purely scattering aerosols, model bias relative to the line-by-line models in the top-of-the atmosphere aerosol radiative forcing ranges from roughly −10 to 20%, with over- and underestimates of radiative cooling at lower and higher solar zenith angle, respectively. Inter-model diversity (relative standard deviation) increases from ~10 to 15% as solar zenith angle decreases. Inter-model diversity in atmospheric and surface forcing decreases with increased aerosol absorption, indicating that the treatment of multiple-scattering is more variable than aerosol absorption in the models considered. Aerosol radiative forcing results from multi-stream models are generally in better agreement with the line-by-line results than the simpler two-stream schemes. Considering radiative fluxes, model performance is generally the same or slightly better than results from previous radiation scheme intercomparisons. However, the inter-model diversity in aerosol radiative forcing remains large, primarily as a result of the treatment of multiple-scattering. Results indicate that global models that estimate aerosol radiative forcing with two-stream radiation schemes may be subject to persistent biases introduced by these schemes, particularly for regional aerosol forcing.

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A global signature of enhanced shortwave absorption by clouds

Cited by 40 publications

References 56 publications

Possible influence of anthropogenic aerosols on cirrus clouds and anthropogenic forcing

Possible influence of anthropogenic aerosols on cirrus clouds and anthropogenic forcing

Solar forcing for CMIP6 (v3.2)

Intercomparison of shortwave radiative transfer schemes in global aerosol modeling: results from the AeroCom Radiative Transfer Experiment

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