Radiative Fluxes in the ECHAM5 General Circulation Model

Wild, Martin; Roeckner, Erich

doi:10.1175/jcli3823.1

Cited by 65 publications

(45 citation statements)

References 36 publications

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“…Discrepancies between modelled and observed SW and LW cloud forcings suggest that the amount of low clouds may be overestimated in the model (Wild and Roeckner, 2006). It is not clear whether the overestimation involves liquid or ice clouds, or is associated with the cloud cover or the cloud lifetime.…”

Section: Conclusion and Discussionmentioning

confidence: 95%

Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM

et al. 2006

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Abstract.A parameterization for cloud processing is presented that calculates activation of aerosol particles to cloud drops, cloud drop size, and pH-dependent aqueous phase sulfur chemistry. The parameterization is implemented in the global aerosol-climate model ECHAM5-HAM. The cloud processing parameterization uses updraft speed, temperature, and aerosol size and chemical parameters simulated by ECHAM5-HAM to estimate the maximum supersaturation at the cloud base, and subsequently the cloud drop number concentration (CDNC) due to activation. In-cloud sulfate production occurs through oxidation of dissolved SO 2 by ozone and hydrogen peroxide. The model simulates realistic distributions for annually averaged CDNC although it is underestimated especially in remote marine regions. On average, CDNC is dominated by cloud droplets growing on particles from the accumulation mode, with smaller contributions from the Aitken and coarse modes. The simulations indicate that in-cloud sulfate production is a potentially important source of accumulation mode sized cloud condensation nuclei, due to chemical growth of activated Aitken particles and to enhanced coalescence of processed particles. The strength of this source depends on the distribution of produced sulfate over the activated modes. This distribution is affected by uncertainties in many parameters that play a direct role in particle activation, such as the updraft velocity, the aerosol chemical composition and the organic solubility, and the simulated CDNC is found to be relatively sensitive to these uncertainties.

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Section: Conclusion and Discussionmentioning

confidence: 95%

Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM

et al. 2006

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“…The tracer advection is calculated with a mass conserving flux form semi-Lagrangian scheme (Lin and Rood, 1996). The ECHAM5 radiation scheme distinguishes four UV-VIS and near-IR, and 16 thermal IR spectral regions (Wild and Roeckner, 2006), and it utilizes the online computed tracer distributions. Photolysis rate calculations for the troposphere up to the mesosphere are based on the eight spectral band approach described in Landgraf and Crutzen (1998), considering absorption and scattering by gases, aerosols and clouds in a delta-two-stream method.…”

Section: Numerical Modelmentioning

confidence: 99%

Stratospheric dryness: model simulations and satellite observations

et al. 2007

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Abstract. The mechanisms responsible for the extreme dryness of the stratosphere have been debated for decades. A key difficulty has been the lack of comprehensive models which are able to reproduce the observations. Here we examine results from the coupled lower-middle atmosphere chemistry general circulation model ECHAM5/MESSy1 together with satellite observations. Our model results match observed temperatures in the tropical lower stratosphere and realistically represent the seasonal and inter-annual variability of water vapor. The model reproduces the very low water vapor mixing ratios (below 2 ppmv) periodically observed at the tropical tropopause near 100 hPa, as well as the characteristic tape recorder signal up to about 10 hPa, providing evidence that the dehydration mechanism is well-captured. Our results confirm that the entry of tropospheric air into the tropical stratosphere is forced by large-scale wave dynamics, whereas radiative cooling regionally decelerates upwelling and can even cause downwelling. Thin cirrus forms in the cold air above cumulonimbus clouds, and the associated sedimentation of ice particles between 100 and 200 hPa reduces water mass fluxes by nearly two orders of magnitude compared to air mass fluxes. Transport into the stratosphere is supported by regional net radiative heating, to a large extent in the outer tropics. During summer very deep monsoon convection over Southeast Asia, centered over Tibet, moistens the stratosphere.

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“…Aspects of the radiation parameterization and its validation are described in Roeckner et al (2003) and Wild and Roeckner (2006), respectively. The standard spectral resolution of the solar radiation parameterization is 4 bands (referenced here as SW4, see Table 1), with 1 band for the UV and visible (250 to 690 nm) and three bands for the near-infrared (690 to 4000 nm).…”

Section: Radiation Parameterizationsmentioning

confidence: 99%

Impact of an improved shortwave radiation scheme in the MAECHAM5 General Circulation Model

et al. 2007

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Abstract. In order to improve the representation of ozone absorption in the stratosphere of the MAECHAM5 general circulation model, the spectral resolution of the shortwave radiation parameterization used in the model has been increased from 4 to 6 bands. Two 20-years simulations with the general circulation model have been performed, one with the standard and the other with the newly introduced parameterization respectively, to evaluate the temperature and dynamical changes arising from the two different representations of the shortwave radiative transfer. In the simulation with the increased spectral resolution in the radiation parameterization, a significant warming of almost the entire model domain is reported. At the summer stratopause the temperature increase is about 6 K and alleviates the cold bias present in the model when the standard radiation scheme is used. These general circulation model results are consistent both with previous validation of the radiation scheme and with the offline clear-sky comparison performed in the current work with a discrete ordinate 4 stream scattering line by line radiative transfer model. The offline validation shows a substantial reduction of the daily averaged shortwave heating rate bias (1-2 K/day cooling) that occurs for the standard radiation parameterization in the upper stratosphere, present under a range of atmospheric conditions. Therefore, the 6 band shortwave radiation parameterization is considered to be better suited for the representation of the ozone absorption in the stratosphere than the 4 band parameterization. Concerning the dynamical response in the general circulation model, it is found that the reported warming at the summer stratopause induces stronger zonal mean zonal winds in the middle atmosphere. These stronger zonal mean zonal winds thereafter appear to produce a dynamical feedback that results inCorrespondence to: C. Cagnazzo (cagnazzo@bo.ingv.it) a dynamical warming (cooling) of the polar winter (summer) mesosphere, caused by an increased downward (upward) circulation in the winter (summer) hemisphere. In addition, the comparison of the two simulations performed with the general circulation model shows that the increase in the spectral resolution of the shortwave radiation and the associated changes in the cloud optical properties result in a warming (0.5-1 K) and moistening (3%-12%) of the upper tropical troposphere. By comparing these modeled differences with previous works, it appears that the reported changes in the solar radiation scheme contribute to improve the model mean temperature also in the troposphere.

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Radiative Fluxes in the ECHAM5 General Circulation Model

Cited by 65 publications

References 36 publications

Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM

Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM

Stratospheric dryness: model simulations and satellite observations

Impact of an improved shortwave radiation scheme in the MAECHAM5 General Circulation Model

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