Vincenzo Artale

The CIRCE Simulations: Regional Climate Change Projections with Realistic Representation of the Mediterranean Sea

In this article, the authors describe an innovative multimodel system developed within the Climate Change and Impact Research: The Mediterranean Environment (CIRCE) European Union (EU) Sixth Framework Programme (FP6) project and used to produce simulations of the Mediterranean Sea regional climate. The models include high-resolution Mediterranean Sea components, which allow assessment of the role of the basin and in particular of the air–sea feedbacks in the climate of the region. The models have been integrated from 1951 to 2050, using observed radiative forcings during the first half of the simulation period and the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario during the second half. The projections show a substantial warming (about 1.5°–2°C) and a significant decrease of precipitation (about 5%) in the region for the scenario period. However, locally the changes might be even larger. In the same period, the projected surface net heat loss de...

Future Climate Projections

In this chapter we show results from an innovative multi-model system used to produce climate simulations with a realistic representation of the Mediterranean Sea. The models (hereafter simply referred to as the “CIRCE models”) are a set of five coupled climate models composed by a high-resolution Mediterranean Sea coupled with a relatively high-resolution atmospheric component and a global ocean, which allow, for the first time, to explore and assess the role of the Mediterranean Sea and its complex, small-scale dynamics in the climate of the region. In particular, they make it possible to investigate the influence that local air-sea feedbacks might exert on the mechanisms responsible for climate variability and change in the European continent, Middle East and Northern Africa. In many regards, they represent a new and innovative approach to the problem of regionalization of climate projections in the Mediterranean region.

The SST Multidecadal Variability in the Atlantic–Mediterranean Region and Its Relation to AMO

AbstractTwo sea surface temperature (SST) time series, the Extended Reconstructed SST version 3 (ERSST.v3) and the Hadley Centre Sea Ice and Sea Surface Temperature dataset (HadISST), are used to investigate SST multidecadal variability in the Mediterranean Sea and to explore possible connections with other regions of the global ocean. The consistency between these two time series and the original International Comprehensive Ocean–Atmosphere Dataset version 2.5 (ICOADS 2.5) over the Mediterranean Sea is investigated, evaluating differences from monthly to multidecadal scales. From annual to longer time scales, the two time series consistently describe the same trends and multidecadal oscillations and agree with Mediterranean ICOADS SSTs. At monthly time scales the two time series are less consistent with each other because of the evident annual cycle that characterizes their difference.The subsequent analysis of the Mediterranean annual SST time series, based on lagged-correlation analysis, multitaper met...

Lagrangian Velocity Spectra at 700 m in the Western North Atlantic

Abstract Pending an appropriate scaling of each trajectory by its Lagrangian integral timescale TL, there exists a generic shape of the Lagrangian frequency spectrum for the trajectories of the 700-m dataset in western North Atlantic, which are stationary on the timescale of 200 days. The generic spectral shape contains a plateau at the lowest frequencies extending up to ν0∼(30TL)−1, a power-law behavior with an intermediate spectral slope α = 0.25 between ν0 and ν1∼(3∼4TL)−1, and a steeper slope n ≥ 3 at larger frequencies. Such a steep slope at large frequencies implies that most of Lagrangian dispersion can be ascribed to low and intermediate frequency motions. The variance of the Lagrangian acceleration computed from such a spectrum is finite, indicating continuous particle accelerations and supporting a truly Lagrangian behavior of the 700-m floats. The existence of an intermediate power-law behavior in the spectrum can be linked with the trapping of some trajectories by persistent energetic structur...

Role of surface fluxes in ocean general circulation models using satellite sea surface temperature: Validation of and sensitivity to the forcing frequency of the Mediterranean thermohaline circulation

[1] In this article we study the effect of high-frequency surface momentum and heat fluxes in the numerical simulation of some key ocean processes ofthe Mediterranean thermohaline circulation. The lack of synoptic and reliable heat and freshwater flux data sets is bypassed using the relaxation approach both for the salinity and temperature surface fields. We propose a parameterization of the heat fluxes in which the temperature-restoring coefficient depends on wind intensity and regime and in which the use of simuoultaneous satellite daily sea surface temperature (SST) estimates as a restoring field is required. The consistency of the proposed parameterization and of its numerical implementation with the previous oceanic boundary layer studies has been verified trough the analysis of the Saunders’ proportionality constant. This parameterization coupling simultaneous surface heat fluxes and wind trough the skin-bulk temperature difference, recovers the high variability of the air-sea exchanges of the extreme events in the Mediterranean Sea. The effect of highfrequency surface momentum and heat fluxes is studied comparing results from two differentexperimentsforcedwithmonthlyanddailysurfacewindandsatelliteSSTdatasets. Thesecomparisonsshowtherelevanceofhigh-frequencyforcingintherepresentationofthe dynamical processes relative to the intermediate water mass transformation and horizontal advection as well as in the deep water formation in the northwestern Mediterranean Sea. INDEX TERMS: 4504 Oceanography: Physical: Air/sea interactions (0312); 4255 Oceanography: General: Numerical modeling; 4243 Oceanography: General: Marginal and semienclosed seas; KEYWORDS: air/ interaction, numerical modeling, Mediterranean, satellite, circulation

Robust assessment of the expansion and retreat of Mediterranean climate in the 21st century

The warm-temperate regions of the globe characterized by dry summers and wet winters (Mediterranean climate; MED) are especially vulnerable to climate change. The potential impact on water resources, ecosystems and human livelihood requires a detailed picture of the future changes in this unique climate zone. Here we apply a probabilistic approach to quantitatively address how and why the geographic distribution of MED will change based on the latest-available climate projections for the 21st century. Our analysis provides, for the first time, a robust assessment of significant northward and eastward future expansions of MED over both the Euro-Mediterranean and western North America. Concurrently, we show a significant 21st century replacement of the equatorward MED margins by the arid climate type. Moreover, future winters will become wetter and summers drier in both the old and newly established MED zones. Should these projections be realized, living conditions in some of the most densely populated regions in the world will be seriously jeopardized.

Seasonal Variability of the Tyrrhenian Sea Surface Geostrophic Circulation as Assessed by Altimeter Data

AbstractNew insights into the structure and variability of the Tyrrhenian Seas surface circulation are obtained through the analysis of a very long series of altimetric observations (1993–2010). In late winter and part of spring, a consistent mean flow is individuated in the eastern Tyrrhenian Sea, formed by a stream of Atlantic water that meanders around four anticyclonic structures located along the Italian coast, which have smaller cyclonic companions offshore. The signatures of these vortices are also found in images of chlorophyll and sea surface temperature, as well as in modeling results, both from a high-resolution operational model of the Tyrrhenian Seas circulation and from a dedicated numerical simulation. Analysis of the energy exchange between eddies and mean flow, together with numerical evidence, suggests that this winter–spring circulation pattern may result from basin-scale instability of the Atlantic stream. In summer, the dynamic is dominated by a well-known dipole located to the east...

Chapter 5 The Atlantic and Mediterranean Sea as connected systems

Publisher Summary This chapter discusses that the North Atlantic plus the Mediterranean Sea is viewed as a unique system whose internal dynamics, regulated by the exchanges at the Strait of Gibraltar, is still rather unknown. It discusses numerical modeling results as a complement to the data analysis. Three issues are discusses in the chapter related to the dynamics of such a system. It focuses on the variability of water mass transformation processes inside the Mediterranean Sea with special attention to the time necessary for water masses formed within the Mediterranean Sea to spread into the North Atlantic. The chapter also discusses the physics of the interface between the two sub-systems, which is the exchange at the Strait of Gibraltar. Using results from a hierarchy of numerical ocean model, the chapter reviews the spreading of Mediterranean Outflow Water (MOW) in the North Atlantic and its possible relation to the variability of the meridional overturning circulation of the global ocean.

Thermohaline circulation sensitivity to intermediate-level anomalies

A two-dimensional Boussinesq ocean model has been used to investigate the effect ofintermediate-level thermal and saline anomalies on the known multiple equilibria structure ofthe thermohaline circulation. These anomalies are taken as a crude representation of theMediterranean outflow in the Atlantic Ocean. The associated perturbation drives the systemtowards an overturning which resembles the present average Atlantic thermohaline circulation.The sensitivity to the depth at which the anomaly is placed is also investigated. We found thatnear-surface anomalies are more efficient in affecting the structure of the equilibria.

North Atlantic MOC variability and the Mediterranean Outflow: a box-model study

A simple box-model is used to investigate the effect of intermediate level heat/freshwater fluxes on the variability of the oceanic meridional overturning circulation. The model includes a simple representation of the spreading of the Mediterranean OutflowWater in the North Atlantic.We identify an internal advective feedback affecting the amplitude of the thermohaline oscillations. When a salinity gradient is maintained in the ocean interior the oscillations are amplified. Instead, if the intermediate level fluxes are spread in the ocean deep layers, the model variability is reduced. We suggest that this mechanism may be relevant for climate variability on interdecadal timescales.