Transient climate change scenario simulation of the Mediterranean Sea for the 21st century using a high-resolution ocean circulation model

International audienceA scenario of the Mediterranean Sea is performed for the 21st century based on an ocean modelling approach. A climate change IPCC-A2 scenario run with an atmosphere regional climate model is used to force a Mediterranean Sea high resolution ocean model over the 1960-2099 period. For comparison, a control simulation as long as the scenario has also been carried out under present climate fluxes. This control run shows air-sea fluxes in agreement with observations, stable temperature and salinity characteristics and a realistic thermohaline circulation simulating the different intermediate and deep water masses described in the literature. During the scenario, warming and saltening are simulated for the surface (+3.1°C and +0.48 psu for the Mediterranean Sea at the end of the 21st century) and for the deeper layers (+1.5°C and +0.23 psu on average). These simulated trends are in agreement with observed trends for the Mediterranean Sea over the last decades. In addition, the Mediterranean thermohaline circulation (MTHC) is strongly weakened at the end of the 21st century. This behaviour is mainly due to the decrease in surface density and so the decrease in winter deep water formation. At the end of the 21st century, the MTHC weakening can be evaluated as -40% for the intermediate waters and -80% for the deep circulation with respect to present-climate conditions. The characteristics of the Mediterranean Outflow Waters flowing into the Atlantic Ocean are also strongly influenced during the scenario

Impact of the ocean-atmosphere coupling on high-resolution future projections for the Mediterranean sea and surrounding climate from the Med-CORDEX ensemble

Med-CORDEX is an international initiative that aims at developing fully coupled high resolution Regional Climate System Models (RCSMs) for the Mediterranean basin. After 11 years of work an ensemble of more than 25 multi-model and multi–scenario climatic simulations is now available (Darmaraki et al., 2019; Soto-Navarro et al., 2020). In this study, we analyze the impact of the high-resolution representation of the Mediterranean Sea and of the interaction between ocean and atmosphere, explicitly resolved in the Med-CORDEX simulations, in the projected evolution of the most relevant climatic variables for the Mediterranean basin and the adjacent regions during the 21st century. The final goal is to quantify up to what extent including the explicit and high-resolution representation of the ocean-atmosphere coupling is relevant for regional climate projections. The preliminary results show that, in general, higher resolution coupled simulations project a lower increase in the Sea Surface Temperature (SST) than lower resolution runs. This translates in a smaller input of heat and humidity to the atmosphere that, in turn, affect the cloud cover and precipitation over the basin and the adjacent continental areas. These changes are the result of a better representation of the Mediterranean Sea functioning in the Med-CORDEX RCSMs. In particular, they resolve better the mesoscale processes of the basin, which are partly responsible of the heat transport from the surface to deeper layers, and the ocean-atmosphere feedback that regulates the heat exchange

Atmospheric contribution to Mediterranean and nearby Atlantic sea level variability under different climate change scenarios

The contribution of atmospheric pressure and wind to the XXI century sea level variability in Southern Europe is explored under different climate change scenarios. The barotropic version of the HAMSOM model is forced with the output of the atmospheric ARPEGE model run under scenarios B1, A1B and A2. Additionally, a control simulation forced by observed SST, GHGs and aerosols concentrations for the period 1950-2000 and a hindcast forced by a dynamical downscalling of ERA40 for the period 1958-2001 are also run using the same models. The hindcast results have been validated against tide gauge observations showing good agreement with correlations around 0.8 and root mean square error of 3.2. cm. A careful comparison between the control simulation and the hindcast shows a reasonably good agreement between both runs in statistical terms, which points towards the reliability of the modelling system when it is forced only by GHG and aerosols concentrations. The results for the XXI century indicate a sea level decrease that would be especially strong in winter, with trends of up to - 0.8 ± 0.1. mm/year in the central Mediterranean under the A2 scenario. Trends in summer are small but positive (~. 0.05 ± 0.04. mm/yr), then leading to an increase in the amplitude of the seasonal cycle. The interannual variability also shows some changes, the most important being a widespread standard deviation increase of up to 40%. An increase in the frequency of positive phases of the NAO explains part of the winter negative trends. Also, an increase in the NAO variability would be responsible for the projected increase of the interannual variability of the atmospheric component of sea level. Conversely, the intra-annual variability (1-12. months excluding the seasonal cycle) does not show significant changes. © 2011 Elsevier B.V.This work has been carried out in the framework of the projects VANIMEDAT-2 (CTM2009-10163-C02-01, funded by the Spanish Marine Science and Technology Program and the E-Plan of the Spanish Government) and ESCENARIOS (funded by the Agencia Estatal de METeorología). Additional funding from the Platja de Palma Consortium is also acknowledged. G. Jordà acknowledges a “JAE-DOC” contract funded by the Spanish Research Council (CSIC).Peer Reviewe

The MED-CORDEX ensemble future climate projections for the Mediterranean Sea: impacts of the high resolution and ocean-atmosphere coupling

Med-CORDEX is an international initiative that aims at developing fully coupled high resolution Regional Climate System Models (RCSMs) for the Mediterranean basin. After 11 years of work an ensemble of more than 25 multi-model and multi–scenario climatic simulations is now available. In this study, we analyze the impact of the high-resolution representation of the Mediterranean Sea and of the interaction between ocean and atmosphere, explicitly resolved in the Med-CORDEX simulations, in the projected evolution of the most relevant climatic variables for the Mediterranean basin and the adjacent regions during the 21st century. The final goal is to quantify up to what extent including the explicit and high-resolution representation of the ocean-atmosphere coupling is relevant for regional climate projections. The preliminary results show that, in general, higher resolution coupled simulations project a lower increase in the Sea Surface Temperature (SST) than lower resolution runs. This translates in a smaller input of heat and humidity to the atmosphere that, in turn, affect the cloud cover and precipitation over the basin and the adjacent continental areas. These changes are the result of a better representation of the Mediterranean Sea functioning in the Med-CORDEX RCSMs. In particular, they resolve better the mesoscale processes of the basin, which are partly responsible of the heat transport from the surface to deeper layers, and the ocean-atmosphere feedback that regulates the heat exchange.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Ocean color response to wind forcing in the Alboran Sea: A new forecasting method

This work proposes a new method to reconstruct and forecast surface Chlorophyll (Chl) from remotely sensed (SeaWiFS) data in the Alboran Sea, based on the correlation between zonal wind velocities and satellite Chl concentrations. First, the spatial and temporal variability of Chl and zonal wind have been characterized using standard statistics. Second, the annual cycle and trends are removed from the original time series and the residuals submitted to an EOF computation scheme. Then, the correlations between the amplitudes of the first temporal modes of Chl-wind couple have been quantified. Using the most highly correlated pair (Chl-zonal wind, with r. =. 0.63), a simple linear relationship is proposed to reconstruct and forecast the Chl field. This forecasting method is more efficient than persistence for forecast horizons longer than 100. days, with a mean correlation between original and predicted field of 0.73 as compared to 0.5 for persistence for all the year round. In partic\ular, this new method gives a 0.95 mean correlation for periods from 100 to 290. days (while persistence gives 0.5). However, for a constant 8-days prediction horizon the persistence performs marginally better than the proposed method (0.79 vs. 0.68), giving some insight into the temporal scales of the features studied. These results may have significant implications for both short-term operational applications and seasonal forecasts. © 2012 Elsevier B.V.We acknowledge the support of SESAME Integrated Project (Contract number 036949).Peer Reviewe

Med-CORDEX initiative for Mediterranean climate studies

The Med-CORDEX initiative is a unique framework in which the research community makes use of regional earth system models to increase the reliability of past and future regional climate information. The Mediterranean is expected to be one of the most prominent and vulnerable climate change “hot spots” of the 21st century, and the physical mechanisms underlying this finding are still not clear. Furthermore complex interactions and feedbacks involving ocean-atmosphere-land-biogeochemical processes play a prominent role in modulating the climate and environment of the Mediterranean region on a range of spatial and temporal scales. Therefore it is critical to provide robust climate change information for use in Vulnerability/Impact/Adaptation assessment studies considering the Mediterranean as a fully coupled environmental system. The Med-CORDEX initiative aims at coordinating the Mediterranean climate modeling community towards the development of fully coupled regional climate simulations, improving all relevant components of the system, from atmosphere and ocean dynamics to land surface, hydrology and biogeochemical processes. The primary goals of Med-CORDEX are to improve understanding of past climate variability and trends, and to provide more accurate and reliable future projections, assessing in a quantitative and robust way the added value of using high resolution and coupled regional climate models. The coordination activities and the scientific outcomes of Med-CORDEX can produce an important framework to foster the development of regional earth system models in several key regions worldwide.Peer ReviewedPostprint (published version

Mistral and Tramontane wind systems in climate simulations from 1950 to 2100

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ALADIN-Climate at the Hungarian Meteorological Service: from the beginnings to the present day’s results

This study is focusing on the past and, in particular, the present of the ALADIN-Climate model used at the Hungarian Meteorological Service. The currently applied model version is 5.2 (HMS-ALADIN52). In the recent experiments, the CNRM-CM5 global model outputs were downscaled in two steps to 10 km horizontal resolution over Central and Southeast Europe using RCP4.5 and RCP8.5 scenarios. Temperature and precipitation projections are analyzed for 2021-2050 and 2071–2100 with respect to the reference period of 1971–2000 with focus on Hungary. The results are evaluated in comparison to 26 simulations selected from the 12 km horizontal resolution Euro-CORDEX projection ensemble (including two additional versions of ALADIN-Climate: CNRM-ALADIN53 and CNRM-ALADIN63) to get more information about the projection uncertainties over Hungary and to assess the representativeness of HMS-ALADIN52. The HMS-ALADIN52 simulations project a clear warming trend in Central and Southeast Europe, which is more remarkable in case of greater radiative forcing change (RCP8.5). From the 2040s, the Euro-CORDEX simulations start to diverge using different scenarios. The total range of the annual change over Hungary is 1.3–3.3 °C with RCP4.5 and 3.2–5.7 °C with RCP8.5 by the end of the 21st century. HMS-ALADIN52 results are approximately near to the median: 2.9 °C with RCP4.5 and 4 °C with RCP8.5. CNRM-ALADIN53 shows generally similar results to HMS-ALADIN52, but simulations with CNRM-ALADIN63 indicate higher changes compared to both. In terms of seasonal mean precipitation change, the HMS-ALADIN52 simulations assume an increase between 9% and 33% (less in spring, more in autumn) over Hungary in both periods and with both scenarios. Most of the selected Euro-CORDEX simulations show a precipitation increase, apart from summer, when growth and reduction can be equally expected in 2021–2050, and the drying tendency continues towards the end of the century. Increase projected by HMS-ALADIN52 is mostly confirmed by CNRM-ALADIN53, while CNRM-ALADIN63 predicts precipitation decrease in summer. Precipitation results do not show a significantly striking difference between the scenarios, likely due to the fact that internal variability and model uncertainty are more relevant sources of uncertainty in precipitation projections over our region

On the seasonality of eddies in the Western Mediterranean Sea: answers with altimetry and modeling.

Trabajo presentado en la EGU General Assemby 2013, celebrada del 7 al 12 de abril de 2013 en Viena (Austria)Eighteen years of weekly SLA merged maps in the Western Mediterranean are analyzed using the new method proposed by Chelton et al. (2011) to identify and track mesoscale eddies. The method has been adapted to take into account the specificity of the Mediterranean basin. Results are similar to the global ocean results with a radius smaller due to a smaller Rossby radius. The areas of intense rotational speed and amplitude of eddies are similar to the areas of intense eddy kinetic energy calculated from altimetry sea level anomalies. Eddies propagation speed shows a wide range of values without a clear preferred direction. Nevertheless, eddies seems to propagate following the main currents. Temporal analysis of the number of eddies per day is made focusing on the annual and semiannual variability. This annual and semi-annual cycle is analyzed using a regional model of the Mediterranean Sea and studying the interaction with atmospheric forcingsPeer reviewe

Regional climate model emulator based on deep learning: concept and first evaluation of a novel hybrid downscaling approach

Providing reliable information on climate change at local scale remains a challenge of first importance for impact studies and policymakers. Here, we propose a novel hybrid downscaling method combining the strengths of both empirical statistical downscaling methods and Regional Climate Models (RCMs). The aim of this tool is to enlarge the size of high-resolution RCM simulation ensembles at low cost. We build a statistical RCM-emulator by estimating the downscaling function included in the RCM. This framework allows us to learn the relationship between large-scale predictors and a local surface variable of interest over the RCM domain in present and future climate. Furthermore, the emulator relies on a neural network architecture, which grants computational efficiency. The RCM-emulator developed in this study is trained to produce daily maps of the near-surface temperature at the RCM resolution (12km). The emulator demonstrates an excellent ability to reproduce the complex spatial structure and daily variability simulated by the RCM and in particular the way the RCM refines locally the low-resolution climate patterns. Training in future climate appears to be a key feature of our emulator. Moreover, there is a huge computational benefit in running the emulator rather than the RCM, since training the emulator takes about 2 hours on GPU, and the prediction is nearly instantaneous. However, further work is needed to improve the way the RCM-emulator reproduces some of the temperature extremes, the intensity of climate change, and to extend the proposed methodology to different regions, GCMs, RCMs, and variables of interest