S. Brenner

General Circulation of the Eastern Mediterranean

Abstract A novel description of the phenomenology of the Eastern Mediterranean is presented based upon a comprehensive pooled hydrographic data base collected during 1985–1987 and analyzed by cooperating scientists from several institutions and nations (the POEM project). Related dynamical process and modeling studies are also overviewed. The circulation and its variabilities consist of three predominant and interacting scales: basin scale, subbasin scale, and mesoscale. Highly resolved and unbiased maps of the basin wide circulation in the thermocline layer are presented which provide a new depiction of the main thermocline general circulation, composed of subbasin scale gyres interconnected by intense jets and meandering currents. Semipermanent features exist but important subbasin scale variabilities also occur on many time scales. Mesoscale variabilities modulate the subbasin scale and small mesoscale eddies populate the open sea, especially the south-eastern Levantine basin. Clear evidence indicates Levantine Intermediate Water (LIW) to be present over most of the Levantine Basin, implying that formation of LIW is not localized but rather is ubiquitous. The Ionian and Levantine basins are confirmed to form one deep thermohaline cell with deep water of Adriatic origin and to have a turnover time of one and a quarter centuries. Prognostic, inverse, box and data assimilative modeling results are presented based on both climatological and POEM data. The subbasin scale elements of the general circulation are stable and robust to the dynamical adjustment process. These findings bear importantly on a broad range of problems in ocean science and marine technology that depend upon knowledge of the general circulation and water mass structure, including biogeochemical fluxes, regional climate, coastal interactions, pollution and environmental management. Of global ocean scientific significance are the fundamental processes of water mass formations, transformations and dispersion which occur in the basin.

A synthesis of the Levantine Basin circulation and hydrography, 1985-1990

Abstract The Levantine Basin circulation derived from recent data consists of a series of sub-basin-scale to mesoscale eddies interconnected by jets. The basin-scale circulation is masked by eddy variability that modulates and modifies it on seasonal and interannual time scales. Long-term qualitative changes in the circulation are reflected in the bifurcation pattterns of ther mid-basin jets, relative strengths of eddies and the hydrographic properties at the core of these eddies. Confinement within the Basin geometry strongly influences the co-evolution of the circulation features. Surface measurements, satellite images and the mass field indicate an entire range of scales of dynamical features in the region. The complexity of the circulation is consistent with the basin-wide and mesoscale heterogeneity of the hydrographic properties. The interannual variability of LIW (Levantine Intermediate Water) formation in the region appears correlated with the changes in the circulation. Wintertime convective overturning of water masses reach intermediate depths and constitute a dominant mechanism of LIW formation, especially in anticyclonic eddies and along the coasts of the northern Levantine Basin.

Global Climate Models Violate Scaling of the Observed Atmospheric Variability

We test the scaling performance of seven leading global climate models by using detrended fluctuation analysis. We analyze temperature records of six representative sites around the globe simulated by the models, for two different scenarios: (i) with greenhouse gas forcing only and (ii) with greenhouse gas plus aerosol forcing. We find that the simulated records for both scenarios fail to reproduce the universal scaling behavior of the observed records and display wide performance differences. The deviations from the scaling behavior are more pronounced in the first scenario, where also the trends are clearly overestimated.

A review of the Levantine Basin circulation and its variability during 1985–1988

Abstract The variability of the Levantine Basin circulation and hydrography is reviewed based on a collection of recent data sets. The major emphasis is placed on the complexity of the associated dynamics. The region is shown to be populated with synoptic and mesoscale dynamic features. In addition to the complexity arising due to the heterogeneity of water masses and the variability of the atmospheric and thermohaline forcing, the confines of the relatively small basin causes the sub-basin-scale gyres to be in close contact with each other, resulting in interacting, basin-wide turbulent features. The bifurcation of the mid-Levantine jet near Cyprus is variable on interannual time-scales, the amount of bifurcation of the fluxes being dependent on the evolution of the circulation in the multi-connected domain and the relative intensities of the sub-basin-scale gyres. During the 3-year observation programme, qualitative changes are identified in the general circulation. The flow encircling Cyprus is partially blocked in the first phase of the experiments. Later, the two basins on the north and east sides of Cyprus are flushed with new water masses carried in the cores of incident eddies, and a new pattern of basin-wide circulation is established, with a major part of the mid-basin jet flowing coherently along the mainland coasts and cyclonically around Cyprus. As a consequence, the general circulation of the Levantine Basin appears considerably different and more complex than the traditional descriptions of it.

Long-range correlations and trends in global climate models: Comparison with real data

We study trends and temporal correlations in the monthly mean temperature data of Prague and Melbourne derived from four state-of-the-art general circulation models that are currently used in studies of anthropogenic effects on the atmosphere: GFDL-R15-a, CSIRO-Mk2, ECHAM4/OPYC3 and HADCM3. In all models, the atmosphere is coupled to the ocean dynamics. We apply fluctuation analysis, and detrended fluctuation analysis which can systematically overcome nonstationarities in the data, to evaluate the models according to their ability to reproduce the proper fluctuations and trends in the past and compare the results with the future prediction.

Experiment in eastern Mediterranean probes origin of deep water masses

During the last decade the oceanography community has focused much attention on the Mediterranean Sea. One reason for the growing interest is that the Mediterraneans impact on the Northern Atlantic Ocean is more significant than previously realized. The warm, salty Mediterranean water tongue exits the Gibraltar Straits and spreads throughout the North Atlantic at all depths between 1000 and 2500 m. The second reason for the surge in interest is the well-recognized role of the Mediterranean Sea as a laboratory for studying ocean processes that are important in global climate dynamics [Malanotte-Rizzoli and Robinson, 1991; Malanotte-Rizzoli and Robinson, 1994].

Climate network structure evolves with North Atlantic Oscillation phases

We construct a network from climate records of temperature and geopotential-height in two pressure levels at different geographical sites in the North Atlantic. A link between two sites represents the cross-correlations between the records of each site. We find that within the different phases of the North Atlantic Oscillation (NAO) the correlation values of the links in the climate network are significantly different. By setting an optimized threshold on the correlation values, we find that the number of strong links in the network increases during times of positive NAO indices, and decreases during times of negative NAO indices. We find a pronounced sensitivity of the network structure to the NAO oscillations which is significantly higher compared to the observed response of spatial average of the climate records. Our results suggest a new measure that tracks the NAO pattern. Copyright c EPLA, 2012 Introduction. - A network approach has recently been applied in order to follow climate dynamics (1,2). The nodes of the climate network are geographical sites. The dynamics recorded in each site is composed of its intrinsic dynamics and the coupling with the dynamics of other sites. The cross-correlations due to the coupling between the dynamics in two different sites are represented in our network by a link between the sites (see (3) for a lab experiment that demonstrates the relation between the coupling and the correlation). The maximum value of the correlation might appear with a time delay between the two data records. The climate network approach has recently led to the discovery of several novel insights related to El-Nino dynamics (4-12).

Lack of scaling in global climate models

Detrended fluctuation analysis is used to test the performance of global climate models. We study the temperature data simulated by seven leading models for the greenhouse gas forcing only (GGFO) scenario and test their ability to reproduce the universal scaling (persistence) law found in the real records for four sites on the globe: (i) New York, (ii) Brookings, (iii) Tashkent and (iv) Saint Petersburg. We find that the models perform quite differently for the four sites and the data simulated by the models lack the universal persistence found in the observed data. We also compare the scaling behaviour of this scenario with that of the control run where the CO2 concentration is kept constant. Surprisingly, from the scaling point of view, the simple control run performs better than the more sophisticated GGFO scenario. This comparison indicates that the variation of the greenhouse gases affects not only trends but also fluctuations.