The new 3.6 version of the Louvain-la-Neuve sea ice model (LIM) is presented, as integrated in the most recent stable release of Nucleus for European Modelling of the Ocean (NEMO) (3.6). The release ...will be used for the next Climate Model Inter-comparison Project (CMIP6). Developments focussed around three axes: improvements of robustness, versatility and sophistication of the code, which involved numerous changes. Robustness was improved by enforcing exact conservation through the inspection of the different processes driving the air–ice–ocean exchanges of heat, mass and salt. Versatility was enhanced by implementing lateral boundary conditions for sea ice and more flexible ice thickness categories. The latter includes a more practical computation of category boundaries, parameterizations to use LIM3.6 with a single ice category and a flux redistributor for coupling with atmospheric models that cannot handle multiple sub-grid fluxes. Sophistication was upgraded by including the effect of ice and snow weight on the sea surface. We illustrate some of the new capabilities of the code in two standard simulations. One is an ORCA2-LIM3 global simulation at a nominal 2° resolution, forced by reference atmospheric climatologies. The other one is a regional simulation at 2 km resolution around the Svalbard Archipelago in the Arctic Ocean, with open boundaries and tides. We show that the LIM3.6 forms a solid and flexible base for future scientific studies and model developments.
We present the global general circulation model IPSL-CM5 developed to study the long-term response of the climate system to natural and anthropogenic forcings as part of the 5th Phase of the Coupled ...Model Intercomparison Project (CMIP5). This model includes an interactive carbon cycle, a representation of tropospheric and stratospheric chemistry, and a comprehensive representation of aerosols. As it represents the principal dynamical, physical, and bio-geochemical processes relevant to the climate system, it may be referred to as an Earth System Model. However, the IPSL-CM5 model may be used in a multitude of configurations associated with different boundary conditions and with a range of complexities in terms of processes and interactions. This paper presents an overview of the different model components and explains how they were coupled and used to simulate historical climate changes over the past 150 years and different scenarios of future climate change. A single version of the IPSL-CM5 model (IPSL-CM5A-LR) was used to provide climate projections associated with different socio-economic scenarios, including the different Representative Concentration Pathways considered by CMIP5 and several scenarios from the Special Report on Emission Scenarios considered by CMIP3. Results suggest that the magnitude of global warming projections primarily depends on the socio-economic scenario considered, that there is potential for an aggressive mitigation policy to limit global warming to about two degrees, and that the behavior of some components of the climate system such as the Arctic sea ice and the Atlantic Meridional Overturning Circulation may change drastically by the end of the twenty-first century in the case of a no climate policy scenario. Although the magnitude of regional temperature and precipitation changes depends fairly linearly on the magnitude of the projected global warming (and thus on the scenario considered), the geographical pattern of these changes is strikingly similar for the different scenarios. The representation of atmospheric physical processes in the model is shown to strongly influence the simulated climate variability and both the magnitude and pattern of the projected climate changes.
The ocean skin is composed of thin interfacial microlayers of temperature and mass of less than 1 mm where heat and chemical exchanges are controlled by molecular diffusion. It is characterized by a ...cooling of ∼−0.2 K and an increase in salinity of ∼0.1 g/kg (absolute salinity) relative to the water below. A surface observation‐based air‐sea CO2 flux estimate considering the variation of the CO2 concentration in these microlayers has been shown to lead to an increase in the global ocean sink of the anthropogenic CO2 by +0.4 PgC yr−1 (15% of the global sink). This study analyzes this effect in more details using a 15‐year (2000–2014) simulation from an Earth System Model (ESM) that incorporates a physical representation of the ocean surface layers (diurnal warm layer and rain lenses) and microlayers. Results show that considering the microlayers increases the simulated global ocean carbon sink by +0.26 to +0.37 PgC yr−1 depending on assumptions on the chemical equilibrium. This is indeed about 15% of the global sink (2.04 PgC yr−1) simulated by the ESM. However, enabling the ocean skin adjustment to feedback on ocean carbon concentrations reduces this increase to only +0.13 (±0.09) PgC y−1. Coupled models underestimate the ocean carbon sink by ∼5% if the ocean skin effect is not included.
Plain Language Summary
The ocean skin is a thin layer of less than a millimeter that is in contact with the atmosphere, where the heat and chemical exchanges are controlled by molecular diffusion. It typically corresponds to a temperature at the ocean interface that is cooler by −0.2 K than the water at a depth of a millimeter. It also corresponds to a salinity that is slightly higher at the interface. Taking into account these temperature and salinity changes in this thin layer can change calculations of the global ocean carbon sink substantially. We use a global Earth System Model including a representation of the ocean skin to study this impact. We found an increase of 15% in the simulated global ocean carbon sink. This is consistent with past studies. Enabling the flux to feedback on the ocean carbon concentration significantly reduces its impact. We conclude by discussing the uncertainties in the global ocean carbon sink associated with the formulation of the carbon flux and the representation of the ocean skin.
Key Points
Considering the ocean skin increases the global ocean CO2 sink by +0.26 to +0.37 PgC yr−1 (∼15% for 2000–2014) in an Earth System Model
Enabling the ocean skin adjustment to feedback on ocean carbon concentrations dampens this increase to +0.13 PgC y−1 (∼5% for 2000–2014)
This global adjustment depends on the CO2 flux formulation and ultimately on the model capacity to transfer CO2 into the ocean interior
ABSTRACT
In late 2009, the meteorological component of the Institute for Environmental Protection and Research (ISPRA)'s Hydro‐Meteo‐Marine Forecasting System (Sistema Idro‐Meteo‐Mare – SIMM), namely ...the hydrostatic Quadrics BOlogna Limited Area Model (QBOLAM), was replaced by an up‐to‐date version of the same model. This new version, which is simply referred to as BOLAM, deploys advanced parameterization schemes for cumulus convection, radiation, soil, and exchange of turbulent fluxes and uses the explicit advection of five hydrometeors. As a part of the SIMM verification programme, it was judged objectively how these changes affected the quality of quantitative precipitation forecasts (QPFs). This was done by intercomparing the current operational BOLAM against QBOLAM. Observational analyses, from April to September 2001, deployed earlier to evaluate the QBOLAM performance, were considered for this intercomparison. An ad hoc reforecast campaign was performed to generate the database of the corresponding retrospective QPFs for BOLAM. A multimethod verification approach was used to assess the spatial scales resolved by the intercompared model versions and the skill at forecasting both frequent, high‐base rate and rare, low‐base rate precipitation events. The effect on performance measures of differences in bias between the intercompared versions was also evaluated. The results indicate an improved performance of BOLAM compared with the older version not only when considering the native 0.1° model grid, where the intercomparison may be affected by differences in the resolved scales, but also when using a coarser 0.5° grid, where the two remapped QPF series show similar spatial scales. Fewer false alarms are produced by BOLAM during the verification time period.
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