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  • 1
    Publication Date: 2020-11-16
    Description: The double-intertropical convergence zone (DI) systematic error, affecting state-of-the-art coupled general circulation models (CGCM) is examined in the multi-model Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) ensemble of simulations of the twentieth-century climate. Aim of this study is to quantify the DI error on precipitation in the tropical Pacific, with a specific focus on the relationship between the DI error and the representation of large-scale vertical circulation regimes in climate models. The DI rainfall signal is analysed using a regime sorting approach for the vertical circulation regimes. Through the use of this compositing technique, precipitation events are regime-sorted based on the large scale vertical motions, as represented by the mid-tropospheric lagrangian pressure tendency omega500 dynamical proxy. This methodology allows the partition of the precipitation signal into deep and shallow convective components. Following the regime-sorting diagnosis, the total DI bias is split into an error affecting the magnitude of precipitation associated with individual convective events and an error affecting the frequency of occurrence of single convective regimes. It is shown that, despite the existing large intra-model differences, CGCMs can be ultimately grouped into a few homegenous clusters, each featuring a well defined rainfall-vertical circulation relationship in the DI region. Three major behavioural clusters are identified within the AR4 models ensemble: two unimodal distributions, featuring maximum precipitation under subsidence and deep convection regimes, respectively, and one bimodal distribution, displaying both components. Extending this analysis to both coupled and uncoupled (atmosphere-only) AR4 simulations reveals that the DI bias in CGCMs is mainly due to the overly frequent occurrence of deep convection regimes, whereas the error on rainfall magnitude associated with individual convective events is overall consistent with errors already present in the corresponding atmosphere stand-alone simulations. A critical parameter controlling the strength of the DI systematic error is identified in the model-dependent sea surface temperature (SST) threshold leading to the onset of deep convection (THR), combined with the average SST in the south-eastern Pacific.
    Description: Published
    Description: 1127–1145
    Description: 4A. Oceanografia e clima
    Description: JCR Journal
    Description: open
    Keywords: double ITCZ ; climate models ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
    Publication Date: 2021-09-21
    Description: Simulation characteristics from eighteen global ocean–sea-ice coupled models are presented with a focus on the mean Atlantic meridional overturning circulation (AMOC) and other related fields in the North Atlantic. These experiments use inter-annually varying atmospheric forcing data sets for the 60- 1 Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site year period from 1948 to 2007 and are performed as contributions to the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II). The protocol for conducting such CORE-II experiments is summarized. Despite using the same atmospheric forcing, the solutions show significant differences. As most models also differ from available observations, biases in the Labrador Sea region in upper-ocean potential temperature and salinity distributions, mixed layer depths, and sea-ice cover are identified as contributors to differences in AMOC. These differences in the solutions do not suggest an obvious grouping of the models based on their ocean model lineage, their vertical coordinate representations, or surface salinity restoring strengths. Thus, the solution differences among the models are attributed primarily to use of different subgrid scale parameterizations and parameter choices as well as to differences in vertical and horizontal grid resolutions in the ocean models. Use of a wide variety of sea-ice models with diverse snow and sea-ice albedo treatments also contributes to these differences. Based on the diagnostics considered, the majority of the models appear suitable for use in studies involving the North Atlantic, but some models require dedicated development effort.
    Description: U.S. National Science Foundation (NSF) NSF U.S. Department of Energy NOAA Climate Program Office under Climate Variability Predictability Program NA09OAR4310163 Department of Climate Change and Energy Efficiency Bureau of Meteorology CSIRO National Computational Infrastructure facility at the Australian National University Research Council of Norway through the EarthClim 207711/E10 NOTUR/NorStore projects Centre for Climate Dynamics at the Bjerknes Centre for Climate Research Italian Ministry of Education, University, and Research Italian Ministry of Environment, Land, and Sea under the GEMINA project BNP-Paribas foundation via the PRECLIDE project under the CNRS 30023488 WGOMD
    Description: Published
    Description: 76-107
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: open
    Keywords: Global ocean–sea-ice modelling ; Ocean model comparisons ; Atmospheric forcing ; Experimental design ; Atlantic meridional overturning circulation ; North Atlantic simulations ; 03. Hydrosphere::03.03. Physical::03.03.03. Interannual-to-decadal ocean variability
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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