Rosalia Santoleri

Seasonal variability of the mixed layer depth in the Mediterranean Sea as derived from in situ profiles

A new 0.5° resolution Mediterranean climatology of the mixed layer depth based on individual profiles of temperature and salinity has been constructed. The criterion selected is a threshold value of temperature from a near-surface value at 10 m depth, mainly derived by a method applied on the global (de Boyer Montegut et al., 2004 dBM04). With respect to dBM04, the main differences reside in the absence of spatial interpolation of the final fields and in the improved spatial resolution. These changes to the method are necessary to reproduce the Mediterranean mixed layers behavior. In the derived climatological maps, the most relevant features of the basin surface circulation are reproduced, as well as the areas prone of the deep water formation are clearly identified. Finally, the role of density in the definition of the mixed layers differing behaviors between the oriental and the occidental regions of the basin is presented.

Longwave radiation budget in the Mediterranean Sea

Direct measurements of infrared budget and meteorological parameters at sea were carried out in the western Mediterranean Sea during different seasons in the years 1989–1992. The spatial and time distribution of this data set allows us to perform an exhaustive test on the most widely used infrared budget bulk formulas. An underestimation of about 30 W/m2 is systematically observed, confirming previous results obtained by a limited data set. This discrepancy is independent of the time of the year and location of measurements, indicating an inability of the bulk formulas to reproduce the infrared Mediterranean budget. The completeness of the data set enables us to determine a new relation between infrared budget and meteorological parameters. Alternative expressions, to be used accordingly with the available data sets, are presented here.

Validation of empirical SeaWiFS algorithms for chlorophyll-a retrieval in the Mediterranean Sea A case study for oligotrophic seas

The major aim of this paper is the validation of SeaWiFS-derived chlorophyll-a concentration in the Mediterranean Sea. A data set containing in situ chlorophyll-a profiles and optical measurements of in-water and above-water radiances was used to evaluate the performances of several ocean color algorithms in the Mediterranean Sea. The analysis revealed a systematic overestimation of chlorophyll-a concentration by National Aeronautics and Space Administration (NASA) global algorithms (OC2v4 and OC4v4). The error appears to be correlated with chlorophyll-a concentration, by exhibiting marked differences at low values (C<0.15 mg/m 3 ). In particular at low concentration, the bias observed for OC2v4 is about twice that observed for OC4v4. The same analysis made using the Gitelson et al. [J. Mar. Syst. 9 (1996) 283.] Coastal Zone Color Scanner (CZCS) regional algorithm (GIT) revealed that this model underestimates the pigments concentration but it does not exhibit a correlation between the error and the measures. On the other hand, when the NASA standard algorithms are applied to remotely sensed data, the behavior appears reversed: the OC2v4 algorithm exhibits better estimates than OC4v4, which is probably more affected by atmospheric correction problems. When applied to satellite data, the GIT algorithm performs better than the NASA global algorithms, although the estimates are very poor in the high chlorophyll-a range. Two new Mediterranean algorithms are then proposed by fitting our Mediterranean bio-optical data set with linear and OC2-like functional forms. The new algorithms perform well when applied either to the bio-optical measurements or to satellite data. The different behavior of the same algorithm when applied to biooptical measurements or to remotely sensed data demonstrates that the atmospheric correction is still the main source of error in ocean color data. Due to the relatively small number of available in situ data, the algorithms that we generated have to be considered very preliminary. Discussion was carried out on the reasons of the global algorithm misfit, providing possible explanations and some preliminary result. The influence of coccolithophores and of the yellow substance on the optical response of the Mediterranean waters is investigated, showing that they can at least partially explain the systematic misfit. All the above shows that a region like the Mediterranean Sea requires an independent treatment of the atmospheric and of the in-water bio-optical term to obtain reliable estimates of phytoplankton activity. D 2002 Elsevier

Hindcast of oil-spill pollution during the Lebanon crisis in the Eastern Mediterranean, July–August 2006

MOON (Mediterranean Operational Oceanography Network http://www.moon-oceanforecasting.eu) provides near-real-time information on oil-spill detection (ocean color and SAR) and predictions [ocean forecasts (MFS and CYCOFOS) and oil-spill predictions (MEDSLIK)]. We employ this system to study the Lebanese oil-pollution crisis in summer 2006 and thus to assist regional and local decision makers in Europe, regionally and locally. The MEDSLIK oil-spill predictions obtained using CYCOFOS high-resolution ocean fields are compared with those obtained using lower-resolution MFS hydrodynamics, and both are validated against satellite observations. The predicted beached oil distributions along the Lebanese and Syrian coasts are compared with in situ observations. The oil-spill predictions are able to simulate the northward movement of the oil spill, with the CYCOFOS predictions being in better agreement with satellite observations. Among the free MEDSLIK parameters tested in the sensitivity experiments, the drift factor appears to be the most relevant to improve the quality of the results.

The sea surface temperature field in the Eastern Mediterranean from advanced very high resolution radiometer (AVHRR) data: Part II. Interannual variability

A ten-year dataset of Advanced Very High Resolution Radiometer-Sea Surface Temperature (AVHRR-SST) with 18-km space resolution and weekly frequency is used to study the seasonal variability of the Eastern Mediterranean Sea surface field. Three main objectives are addressed in this study. The first is to define the time and space scales of the surface temperature distributions. The second objective is to relate the SST features to the upper thermocline circulation and the third is to compare these features with the observational evidence of the Physical Oceanography of the Eastern Mediterranean (POEM) Programme. The time analysis reveals the presence of a strong seasonal signal characterized by two main seasonal extremes, winter and summer. The transition between the overall zonal distribution of the isotherms (winter) and the mostly meridional pattern of the fronts (summer) occurs very rapidly in May and October. The space analysis shows that the dominant scale is the sub-basin scale and the sub-basin gyres are very well resolved allowing the identification of permanent and semipermanent structures. The results for the two further objectives can be summarized together. The seasonal and monthly SST distributions are strongly correlated with the dynamical structure of the basin upper thermocline circulation. A direct comparison of the September 1987 SST pattern with the corresponding surface temperature map of the POEM-87 survey proves this correlation quantitatively. Furthermore, comparison of the SST monthly climatologies with the POEM circulation scheme shows that all the major currents and the sub-basin gyres are also found consistently in our patterns, with the only exception of the anticyclonic Mersa-Matruh Gyre.

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...

Analysis of the seasonal and interannual variability of the sea surface temperature field in the Adriatic Sea from AVHRR data (1984–1992)

Seasonal and interannual variability of the sea surface temperature field in the Adriatic Sea is analyzed from the low-resolution advanced very high resolution radiometer data. The spatial resolution of 18 km allowed analysis of only basin and subbasin scale features. Average monthly and seasonal sea surface temperature fields for the entire studied period (1984–1992) are discussed. The analysis shows the absence of any permanent sea surface thermal features in the Adriatic Sea. The south Adriatic sea surface temperature minimum presumably associated to the cyclonic gyre, previously considered as one of the permanent features, appears to be recurrent, being prominent only in late autumn and early winter, i.e., in the preconditioning and a deepwater formation phases. The major Ionian water inflow is documented in autumn while the thermal signature of the western surface outflow of Adriatic water appears most prominent in winter. The variability of the basin-wide thermal pattern in the Adriatic reveals four distinct seasons, which is different from both the eastern and western Mediterranean, where only two major patterns are recognized. A prominent interannual signal occurs in a northward extension of the warm water plume along the eastern coast, which in some years reaches the northernmost corner of the Adriatic, while in other situations it remains trapped in the south Adriatic cyclonic gyre. The surface thermal signature of the south Adriatic gyre also varies on an interannual timescale, and it was weak or completely absent during the period 1984–1986 while it was rather prominent in the period 1987–1992. A constant trend of sea surface temperature decrease in the center of the south Adriatic gyre and in the northernmost corner of the Adriatic was evidenced over the studied period.

Sea level variability and surface eddy statistics in the Mediterranean Sea from TOPEX/POSEIDON data

Two years of TOPEX/POSEIDON altimeter data have successfully been used to study the mesoscale field in the Mediterranean and to investigate the seasonal and year-to-year variability of the sea level and eddy statistics in this basin. The mesoscale field described by TOPEX/POSEIDON revealed a strong, but subbasin dependent, seasonal signal. Year-to-year variations are also evident in terms of both intensity and position of the main mesoscale features. Crossover analysis indicated the existence of a meridional transport of eddy momentum away from the Algerian current due to the northward migration of mesoscale eddies. A comparison between mesoscale features detected by the altimeter and contemporaneous features observed using advanced very high resolution radiometer (AVHRR) sea surface temperature has been made for the following Mediterranean subbasins: the Algerian basin, the Levantine basin, and the Tyrrhenian Sea. The results definitively prove the direct relation between sea level anomalies and the Mediterranean eddy field.

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

Open Waters Optical Remote Sensing of the Mediterranean Sea

Recent technological and scientific advances related to the Mediterranean Sea surface chlorophyll retrieval from space are discussed in this chapter. In particular, a complete review on the definition and vali- dation of specific regional ocean colour bio-optical algorithms for this area is presented. The need for specific algorithms in the Mediterranean is ex- plained mainly by the observed failure of standard procedures. Latest results, mostly focusing on biological response to deep water formation