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  • 1
    Online Resource
    Online Resource
    Quantifying the importance of the atmospheric sink for polychlorinated dioxins and furans relative to other global loss processes
    American Geophysical Union (AGU) ; 2006
    In:  Journal of Geophysical Research Vol. 111, No. D21 ( 2006-11-10)
    Details
    In: Journal of Geophysical Research, American Geophysical Union (AGU), Vol. 111, No. D21 ( 2006-11-10)
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2005JD006923
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2006
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    detail.hit.zdb_id: 2016800-7
    detail.hit.zdb_id: 161666-3
    detail.hit.zdb_id: 161667-5
    detail.hit.zdb_id: 2969341-X
    detail.hit.zdb_id: 161665-1
    detail.hit.zdb_id: 3094268-8
    detail.hit.zdb_id: 710256-2
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    detail.hit.zdb_id: 3094219-6
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    SSG: 16,13
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  • 2
    Online Resource
    Online Resource
    Addressing Complexity in Global Aerosol Climate Model Cloud Microphysics
    American Geophysical Union (AGU) ; 2023
    In:  Journal of Advances in Modeling Earth Systems Vol. 15, No. 5 ( 2023-05)
    Details
    In: Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), Vol. 15, No. 5 ( 2023-05)
    Abstract: Model scheme complexity brings about a bouquet of problems, from hindering interpretability to hiding unforced modeler choices Using sensitivity analysis on an emulated perturbed parameter ensemble we characterize the two cloud microphysics schemes of ECHAM‐HAM We find potential for process simplifications as well as instances where model sensitivities deviate from a priori physical understanding
    Type of Medium: Online Resource
    ISSN: 1942-2466 , 1942-2466
    URL: Article
    DOI: 10.1029/2022MS003571
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2023
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  • 3
    Online Resource
    Online Resource
    Assessing the potential for simplification in global climate model cloud microphysics
    Copernicus GmbH ; 2022
    In:  Atmospheric Chemistry and Physics Vol. 22, No. 7 ( 2022-04-12), p. 4737-4762
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 22, No. 7 ( 2022-04-12), p. 4737-4762
    Abstract: Abstract. Cloud properties and their evolution influence Earth's radiative balance. The cloud microphysical (CMP) processes that shape these properties are therefore important to represent in global climate models. Historically, parameterizations in these models have grown more detailed and complex. However, a simpler formulation of CMP processes may leave the model results mostly unchanged while enabling an easier interpretation of model results and helping to increase process understanding. This study employs sensitivity analysis of an emulated perturbed parameter ensemble of the global aerosol–climate model ECHAM-HAM to illuminate the impact of selected CMP cloud ice processes on model output. The response to the perturbation of a process serves as a proxy for the effect of a simplification. Autoconversion of ice crystals is found to be the dominant CMP process in influencing key variables such as the ice water path and cloud radiative effects, while riming of cloud droplets on snow has the most influence on the liquid phase. Accretion of ice and snow and self-collection of ice crystals have a negligible influence on model output and are therefore identified as suitable candidates for future simplifications. In turn, the dominating role of autoconversion suggests that this process has the greatest need to be represented correctly. A seasonal and spatially resolved analysis employing a spherical harmonics expansion of the data corroborates the results. This study introduces a new application for the combination of statistical emulation and sensitivity analysis to evaluate the sensitivity of a complex numerical model to a specific parameterized process. It paves the way for simplifications of CMP processes leading to more interpretable climate model results.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-22-4737-2022
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2022
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  • 4
    Online Resource
    Online Resource
    How frequent is natural cloud seeding from ice cloud layers ( 〈 −35 °C) over Switzerland?
    Copernicus GmbH ; 2021
    In:  Atmospheric Chemistry and Physics Vol. 21, No. 6 ( 2021-04-01), p. 5195-5216
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 21, No. 6 ( 2021-04-01), p. 5195-5216
    Abstract: Abstract. Clouds and cloud feedbacks represent one of the largest uncertainties in climate projections. As the ice phase influences many key cloud properties and their lifetime, its formation needs to be better understood in order to improve climate and weather prediction models. Ice crystals sedimenting out of a cloud do not sublimate immediately but can survive certain distances and eventually fall into a cloud below. This natural cloud seeding can trigger glaciation and has been shown to enhance precipitation formation. However, to date, an estimate of its occurrence frequency is lacking. In this study, we estimate the occurrence frequency of natural cloud seeding over Switzerland from satellite data and sublimation calculations. We use the DARDAR (radar lidar) satellite product between April 2006 and October 2017 to estimate the occurrence frequency of multi-layer cloud situations, where a cirrus cloud at T 〈 −35 ∘C can provide seeds to a lower-lying feeder cloud. These situations are found to occur in 31 % of the observations. Of these, 42 % have a cirrus cloud above another cloud, separated, while in 58 % the cirrus is part of a thicker cloud, with a potential for in-cloud seeding. Vertical distances between the cirrus and the lower-lying cloud are distributed uniformly between 100 m and 10 km. They are found to not vary with topography. Seasonally, winter nights have the most multi-layer cloud occurrences, in 38 % of the measurements. Additionally, in situ and liquid origin cirrus cloud size modes can be identified according to the ice crystal mean effective radius in the DARDAR data. Using sublimation calculations, we show that in a significant number of cases the seeding ice crystals do not sublimate before reaching the lower-lying feeder cloud. Depending on whether bullet rosette, plate-like or spherical crystals were assumed, 10 %, 11 % or 20 % of the crystals, respectively, could provide seeds after sedimenting 2 km. The high occurrence frequency of seeding situations and the survival of the ice crystals indicate that the seeder–feeder process and natural cloud seeding are widespread phenomena over Switzerland. This hints at a large potential for natural cloud seeding to influence cloud properties and thereby the Earth's radiative budget and water cycle, which should be studied globally. Further investigations of the magnitude of the seeding ice crystals' effect on lower-lying clouds are necessary to estimate the contribution of natural cloud seeding to precipitation.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-21-5195-2021
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
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  • 5
    Online Resource
    Online Resource
    Cloud Ice Processes Enhance Spatial Scales of Organization in Arctic Stratocumulus
    American Geophysical Union (AGU) ; 2019
    In:  Geophysical Research Letters Vol. 46, No. 23 ( 2019-12-16), p. 14109-14117
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 46, No. 23 ( 2019-12-16), p. 14109-14117
    Abstract: Mixed‐phase clouds in the Arctic feature organized open‐cell structures, similar to warm‐phase stratocumuli For an ice to liquid water path ratio of 1:2, ice processes strengthen cold pools and impact cell size A reduction of the cloud condensation nuclei concentration also impacts precipitation intensity, cold pool strength, and cell size
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Article
    DOI: 10.1029/2019GL084959
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2019
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    SSG: 16,13
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  • 6
    Online Resource
    Online Resource
    Cloud response and feedback processes in stratiform mixed‐phase clouds perturbed by ship exhaust
    American Geophysical Union (AGU) ; 2017
    In:  Geophysical Research Letters Vol. 44, No. 4 ( 2017-02-28), p. 1964-1972
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 44, No. 4 ( 2017-02-28), p. 1964-1972
    Abstract: Increases in cloud top radiative cooling lead to increased immersion freezing rates near cloud top Feedback mechanisms involving the ice phase reduce, if not suppress, changes to the cloud liquid water path triggered by ship exhaust Changes in cloud condensation nuclei concentrations of 100 cm −3 were sufficient to shift the cloud state beyond its background variability
    Type of Medium: Online Resource
    ISSN: 0094-8276 , 1944-8007
    URL: Issue
    URL: Article
    DOI: 10.1002/grl.v44.4
    DOI: 10.1002/2016GL071358
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2017
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    detail.hit.zdb_id: 7403-2
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  • 7
    Online Resource
    Online Resource
    Modeling the Effects of Geoengineering
    American Geophysical Union (AGU) ; 2018
    In:  Eos Vol. 99 ( 2018-08-07)
    Details
    In: Eos, American Geophysical Union (AGU), Vol. 99 ( 2018-08-07)
    Abstract: Report on the Eighth Annual GeoMIP Meeting; Z�rich, Switzerland, 16–17 April 2018
    Type of Medium: Online Resource
    ISSN: 2324-9250
    URL: Article
    DOI: 10.1029/2018EO103333
    Language: Unknown
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2018
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  • 8
    Online Resource
    Online Resource
    Tropospheric sulfur cycle in the Canadian general circulation model
    American Geophysical Union (AGU) ; 1999
    In:  Journal of Geophysical Research: Atmospheres Vol. 104, No. D21 ( 1999-11-20), p. 26833-26858
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 104, No. D21 ( 1999-11-20), p. 26833-26858
    Abstract: Emission, transport, chemistry, and scavenging of the gaseous sulfur species dimethyl sulfide and sulfur dioxide (SO 2 ) and sulfate aerosols are calculated on‐line with the meteorology in the general circulation model (GCM) of the Canadian Centre for Climate Modelling and Analysis (CCCMA). Additionally, prognostic equations for cloud water and cloud ice have been introduced. The sensitivity of this sulfur cycle to differences in GCM physics and dynamics has been studied by comparing the results to those obtained with the ECHAM GCM which has a very similar sulfur cycle and cloud scheme, but a different turbulent diffusion and convection scheme. The differences in the global mean burdens of SO 2 and sulfate are less than 2%. Simulated surface SO 2 concentrations with CCCMA in winter as well as the seasonal cycle are in better agreement with observations at several sites than those simulated with ECHAM because of stronger boundary layer mixing in CCCMA. The simulated surface SO 4 2− with CCCMA, however, is often higher than observed and in ECHAM. Additionally, sensitivity experiments showed that the global sulfur budgets are most sensitive to changes in the cloud cover parameterization and less sensitive to changes in pH calculation and oxidation of SO 2 in convective clouds. The results of the sensitivity experiments give evidence for the importance of all of these effects on the geographical and vertical distribution of sulfur and cloud liquid water.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JD900343
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1999
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    detail.hit.zdb_id: 161666-3
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    SSG: 16,13
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  • 9
    Online Resource
    Online Resource
    Prediction of the number of cloud droplets in the ECHAM GCM
    American Geophysical Union (AGU) ; 1999
    In:  Journal of Geophysical Research: Atmospheres Vol. 104, No. D8 ( 1999-04-27), p. 9169-9198
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 104, No. D8 ( 1999-04-27), p. 9169-9198
    Abstract: In this paper a prognostic equation for the number of cloud droplets (CDNC) is introduced into the ECHAM general circulation model. The initial CDNC is based on the mechanistic model of Chuang and Penner [1995], providing a more realistical prediction of CDNC than the empirical method previously used. Cloud droplet nucleation is parameterized as a function of total aerosol number concentration, updraft velocity, and a shape parameter, which takes the aerosol composition and size distribution into account. The total number of aerosol particles is obtained as the sum of marine sulfate aerosols produced from dimethyl sulfide, hydrophylic organic and black carbon, submicron dust, and sea‐salt aerosols. Anthropogenic sulfate aerosols only add mass to the preexisting aerosols but do not form new particles. The simulated annual mean liquid water path, column CDNC, and effective radius agree well with observations, as does the frequency distributions of column CDNC for clouds over oceans and the variations of cloud optical depth with effective radius.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JD900046
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1999
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    SSG: 16,13
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  • 10
    Online Resource
    Online Resource
    Simulation of the tropospheric sulfur cycle in a global model with a physically based cloud scheme
    American Geophysical Union (AGU) ; 2002
    In:  Journal of Geophysical Research: Atmospheres Vol. 107, No. D21 ( 2002-11-16)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 107, No. D21 ( 2002-11-16)
    Abstract: The treatment of the sulfur cycle in the CSIRO global climate model (GCM) is described. It is substantially based on the scheme developed previously for the European Center/Hamburg (ECHAM) model, but the treatment of wet scavenging has been completely rewritten to better reflect the different properties of liquid and frozen precipitation, and the treatment of these in the model's cloud microphysical scheme. The model is able to reproduce the observed finding that wet deposition of sulfur over Europe and North America is larger in summer than in winter, but the seasonal cycle of sulfate over Europe is not well simulated. The latter is improved when the amplitude of the seasonal cycle of European emissions is increased. Below‐cloud scavenging makes an important contribution in our scheme: On omitting it, the global sulfate burden increases from 0.67 to 0.93 Tg S. On reverting to the less efficient scavenging treatment used in ECHAM, the global sulfate burden again increases from 0.67 to 0.93 Tg S, and excessive sulfate concentrations are obtained in Europe and North America. Some deficiencies in the simulation are investigated via further sensitivity tests. In particular, during the Arctic winter, the modeled sulfur dioxide (SO 2 ) concentrations are too large, and the modeled sulfate concentrations are too small (as in most global sulfur‐cycle models). Recent laboratory experiments suggest that SO 2 oxidation in ice clouds is nonnegligible. We obtain a much improved Arctic simulation when a simple treatment of SO 2 oxidation in ice clouds is included.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2002JD002128
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2002
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    detail.hit.zdb_id: 161667-5
    detail.hit.zdb_id: 2969341-X
    detail.hit.zdb_id: 161665-1
    detail.hit.zdb_id: 3094268-8
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016804-4
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    detail.hit.zdb_id: 2220777-6
    detail.hit.zdb_id: 3094197-0
    SSG: 16,13
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