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  • 1
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    ICON‐A, the Atmosphere Component of the ICON Earth System Model: I. Model Description (2018)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2023-01-03
    Description: ICON-A is the new icosahedral nonhydrostatic (ICON) atmospheric general circulation model in a configuration using the Max Planck Institute physics package, which originates from the ECHAM6 general circulation model, and has been adapted to account for the changed dynamical core framework. The coupling scheme between dynamics and physics employs a sequential updating by dynamics and physics, and a fixed sequence of the physical processes similar to ECHAM6. To allow a meaningful initial comparison between ICON-A and the established ECHAM6-LR model, a setup with similar, low resolution in terms of number of grid points and levels is chosen. The ICON-A model is tuned on the base of the Atmospheric Model Intercomparison Project (AMIP) experiment aiming primarily at a well balanced top-of atmosphere energy budget to make the model suitable for coupled climate and Earth system modeling. The tuning addresses first the moisture and cloud distribution to achieve the top-of-atmosphere energy balance, followed by the tuning of the parameterized dynamic drag aiming at reduced wind errors in the troposphere. The resulting version of ICON-A has overall biases, which are comparable to those of ECHAM6. Problematic specific biases remain in the vertical distribution of clouds and in the stratospheric circulation, where the winter vortices are too weak. Biases in precipitable water and tropospheric temperature are, however, reduced compared to the ECHAM6. ICON-A will serve as the basis of further development and as the atmosphere component to the coupled model, ICON-Earth system model (ESM). Key Points: - Physics package for climate modeling is coupled to a nonhydrostatic dynamical core - Tuning in five steps to obtain a balanced net radiation at top of atmosphere - Overall biases of ICON-A are comparable to ECHAM6.3, but circulation biases remain due to problems with parameterized drag
    Type: Article , PeerReviewed
    Format: text
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  • 2
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    On the sensitivity of anthropogenic aerosol forcing to model‐internal variability and parameterizing a T womey effect (2017)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2023-01-03
    Description: Despite efforts to accurately quantify the effective radiative forcing (ERF) of anthropogenic aerosol, the historical evolution of ERF remains uncertain. As a further step toward a better understanding of ERF uncertainty, the present study systematically investigates the sensitivity of the shortwave ERF at the top of the atmosphere to model-internal variability and spatial distributions of the monthly mean radiative effects of anthropogenic aerosol. For this, ensembles are generated with the atmospheric model ECHAM6.3 that uses monthly prescribed optical properties and changes in cloud-droplet number concentrations designed to mimic that associated with the anthropogenic aerosol using the new parameterization MACv2-SP. The results foremost highlight the small change in our best estimate of the global averaged all-sky ERF associated with a substantially different pattern of anthropogenic aerosol radiative effects from the mid-1970s (–0.51 Wm–2) and present day (–0.50 Wm–2). Such a small change in ERF is difficult to detect when model-internal year-to-year variability (0.32 Wm–2 standard deviation) is considered. A stable estimate of all-sky ERF requires ensemble simulations, the size of which depends on the targeted precision, confidence level, and the magnitude of model-internal variability. A larger effect of the pattern of the anthropogenic aerosol radiative effects on the globally averaged all-sky ERF (15%) occurs with a strong Twomey effect through lowering the background aerosol optical depth in regions downstream of major pollution sources. It suggests that models with strong aerosol-cloud interactions could show a moderate difference in the global mean ERF associated with the mid-1970s to present-day change in the anthropogenic aerosol pattern. Key Points: - Ensembles of atmosphere-only experiments with MACv2-SP allow a sensitivity assessment of instantaneous and effective radiative forcing (ERF) - Global mean all-sky ERFs with aerosol patterns of mid-1970s and today difficult to distinguish, when atmospheric variability considered - A moderate pattern effect on ERF could occur in models with presumably strong aerosol-cloud interaction
    Type: Article , PeerReviewed
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  • 3
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    ICON‐A, The Atmosphere Component of the ICON Earth System Model: II. Model Evaluation (2018)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2023-01-03
    Description: We evaluate the new icosahedral nonhydrostatic atmospheric (ICON-A) general circulation model of the Max Planck Institute for Meteorology that is flexible to be run at grid spacings from a few tens of meters to hundreds of kilometers. A simulation with ICON-A at a low resolution (160 km) is compared to a not-tuned fourfold higher-resolution simulation (40 km). Simulations using the last release of the ECHAM climate model (ECHAM6.3) are also presented at two different resolutions. The ICON-A simulations provide a compelling representation of the climate and its variability. The climate of the low-resolution ICON-A is even slightly better than that of ECHAM6.3. Improvements are obtained in aspects that are sensitive to the representation of orography, including the representation of cloud fields over eastern-boundary currents, the latitudinal distribution of cloud top heights, and the spatial distribution of convection over the Indian Ocean and the Maritime Continent. Precipitation over land is enhanced, in particular at high-resolution ICON-A. The response of precipitation to El Niño sea surface temperature variability is close to observations, particularly over the eastern Indian Ocean. Some parameterization changes lead to improvements, for example, with respect to rain intensities and the representation of equatorial waves, but also imply a warmer troposphere, which we suggest leads to an unrealistic poleward mass shift. Many biases familiar to ECHAM6.3 are also evident in ICON-A, namely, a too zonal SPCZ, an inadequate representation of north hemispheric blocking, and a relatively poor representation of tropical intraseasonal variability. Key Points: - Article presents evaluation of atmosphere component of new ICON Earth system model - The new MPI atmospheric ICON-A model partly outperforms ECHAM6.3 - ICON-A is flexible to be run at grid spacings from a few tens of meters to hundreds of kilometers
    Type: Article , PeerReviewed
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  • 4
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    Bounding Global Aerosol Radiative Forcing of Climate Change (2020)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-02-08
    Description: Aerosols interact with radiation and clouds. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the Earth's radiation budget caused by anthropogenic aerosols, called aerosol radiative forcing, but uncertainties remain large. This review provides a new range of aerosol radiative forcing over the industrial era based on multiple, traceable, and arguable lines of evidence, including modeling approaches, theoretical considerations, and observations. Improved understanding of aerosol absorption and the causes of trends in surface radiative fluxes constrain the forcing from aerosol-radiation interactions. A robust theoretical foundation and convincing evidence constrain the forcing caused by aerosol-driven increases in liquid cloud droplet number concentration. However, the influence of anthropogenic aerosols on cloud liquid water content and cloud fraction is less clear, and the influence on mixed-phase and ice clouds remains poorly constrained. Observed changes in surface temperature and radiative fluxes provide additional constraints. These multiple lines of evidence lead to a 68% confidence interval for the total aerosol effective radiative forcing of -1.6 to -0.6 W m−2, or -2.0 to -0.4 W m−2 with a 90% likelihood. Those intervals are of similar width to the last Intergovernmental Panel on Climate Change assessment but shifted toward more negative values. The uncertainty will narrow in the future by continuing to critically combine multiple lines of evidence, especially those addressing industrial-era changes in aerosol sources and aerosol effects on liquid cloud amount and on ice clouds. Key Points: - An assessment of multiple lines of evidence supported by a conceptual model provides ranges for aerosol radiative forcing of climate change - Aerosol effective radiative forcing is assessed to be between -1.6 and -0.6 W m−2 at the 16–84% confidence level - Although key uncertainties remain, new ways of using observations provide stronger constraints for models
    Type: Article , PeerReviewed
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  • 5
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    Climate Change Feedbacks in Aquaplanet Experiments With Explicit and Parametrized Convection for Horizontal Resolutions of 2,525 Up to 5 km (2021)
    Details
    Publication Date: 2021-10-13
    Description: Earth's equilibrium climate sensitivity (ECS) is the long-term response to doubled atmospheric CO2 and likely between 1.5 and 4.5 K. Conventional general circulation models do not convincingly narrow down this range, and newly developed nonhydrostatic models with relatively fine horizontal resolutions of a few kilometers have thus far delivered diverse results. Here we use the nonhydrostatic ICON model with the physics package normally used for climate simulations at resolutions as fine as 5 km to study the response to a uniform surface warming in an aquaplanet configuration. We apply the model in two setups: one with convection parametrization employed and one with explicit convection. ICON exhibits a negative total feedback independent of convective representation, thus providing a stable climate with an ECS comparable to other general circulation models, though three interesting new results are found. First, ECS varies little across resolution for both setups but runs with explicit convection have systematically lower ECS than the parametrized case, mainly due to more negative tropical clear-sky longwave feedbacks. These are a consequence of a drier mean state of about 6% relative humidity for explicit convection and less midtropospheric moistening with global warming. Second, shortwave feedbacks switch from positive to negative with increasing resolution, originating foremost in the tropics and high latitudes. Third, the model shows no discernible high cloud area feedback (iris effect) in any configuration. It is possible that ICON's climate model parametrizations applied here are less appropriate for cloud resolving scales, and therefore, ongoing developments aim at implementing a more advanced prognostic cloud microphysics scheme.
    Keywords: 551.6 ; ICON ; climate change feedbacks ; aquaplanet ; high resolution ; explicit convection ; ECS
    Language: English
    Type: map
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