Elina Tragou

A mixed-layer study of the formation of Levantine intermediate water

A mixed-layer model is used to investigate the formation of Levantine Intermediate Water (LIW) over the Eastern Mediterranean. The one-dimensional model is initialized with climatological hydrography and integrated over the Levantine basin with forcing by climatological surface fluxes. Realistic and repeated seasonal mixed-layer cycles are obtained if the annual surface heat input and water loss are offset by a parameterized horizontal advection. The model integrations show that LIW is formed during winter in the mixed layer of the Northwestern Levantine. The preferred formation region for LIW is found through idealized experiments to be controlled by the preconditioning of the hydrography, especially that of the cold, cyclonic Rhodes gyre, rather than by the pattern of the climatological fluxes. The annual-mean formation rate of LIW is estimated to be 1.0 Sv using the climatological surface fluxes. The magnitude of the annual surface fluxes alters the formation rate and modifies the formation region. An additional annual heat flux reduces the formation rate of LIW, whereas an extra cooling enhances it, as well as forming waters denser than LIW in the center of the Rhodes gyre.

The Heat and Freshwater Budgets of the Red Sea

Abstract The heat and freshwater transports through the Strait of Bab el Mandab, connecting the Red Sea with the open ocean, are reviewed and used to test air–sea fluxes from a revised version of the Comprehensive Ocean–Atmosphere Data Set (UWM/COADS). Using historical data for the volume fluxes and water properties, the annual-mean net heat transport through the strait is found to require an average surface heat loss of 8 ± 2 W m−2, while the requirement for conservation of salt in the basin implies a net evaporation rate of 1.60 ± 0.35 m yr−1, lower than previously considered. The air–sea heat fluxes from UWM/COADS overestimate the total heat flux by nearly 100 W m−2; the discrepancy is attributed to systematic errors in the bulk formulas used to calculate the heat flux components. In particular, insolation appears to be overestimated by 36 W m−2, largely due to the neglect of aerosols. The effect of these is determined from ground stations and satellite data on the optical thickness index. The net long...

Climate change effects on the marine characteristics of the Aegean and Ionian Seas

This paper addresses the effects of estimated climate change on the sea-surface dynamics of the Aegean and Ionian Seas (AIS). The main aim is the identification of climate change impacts on the severity and frequency of extreme storm surges and waves in areas of the AIS prone to flooding. An attempt is made to define design levels for future research on coastal protection in Greece. Extreme value analysis is implemented through a nonstationary generalized extreme value distribution function, incorporating time harmonics in its parameters, by means of statistically defined criteria. A 50-year time span analysis is adopted and changes of means and extremes are determined. A Regional Climate Model (RegCM3) is implemented with dynamical downscaling, forced by ECHAM5 fields under 20C3M historical data for the twentieth century and the SRES-A1B scenario for the twenty-first century. Storm surge and wave models (GreCSSM and SWAN, respectively) are used for marine climate simulations. Comparisons of model results with reanalysis and field data of atmospheric and hydrodynamic characteristics, respectively, are in good agreement. Our findings indicate that the dynamically downscaled RegCM3 simulation adequately reproduces the present general circulation patterns over the Mediterranean and Greece. Future changes in sea level pressure and mean wind fields are estimated to be small, yet significant for marine extremes. In general, we estimate a projected intensification of severe wave and storm surge events during the first half of the twenty-first century and a subsequent storminess attenuation leading to the resettlement of milder extreme marine events with increased prediction uncertainty in the second half of the twenty-first century.

Spiral eddies in the Aegean Sea derived by satellite radar data

Ocean mesoscale spiral eddies is a phenomenon that came apparent in the last 50 years but until today there are many questions yet to be answered about their formation, distribution and correlation to the dynamical processes on the sea surface. Main objective of the present paper is to provide an extensive analysis on the occurrence and statistics of smallmesoscale eddies over the Aegean Sea using synthetic aperture radar (SAR) images. The study area is characterized from unique hydro-dynamical and topographical conditions that give another aspect on the phenomenon. Present study based on 169 medium resolution (WSM) ENVISAT ASAR images acquired in 2011. As a result of the analysis 192 eddies formations were detected. The majority of those eddies were visualized due to the presence of surfactant films (black eddies) on sea surface and majority of them were cyclonically rotating. The diameter of the observed formations of eddies was within 1 to 16 km. The detected eddies were classified by categories depending on their shape and their generation mechanism. Seasonal and spatial distribution is presented, in order to understand their variability compared with the upper surface circulation. The value of the baroclinic Rossby radius of deformation was used for the discrimination of wind driven or geostrophic balanced spiral eddies. Though most of the observed formations seem to be wind driven, an important correlation with the upper circulation of the Aegean Sea is shown.