398 research outputs found
Superstatistical analysis of sea surface currents in the Gulf of Trieste, measured by high-frequency radar, and its relation to wind regimes using the maximum-entropy principle
No full textTwo years (2021–2022) of high-frequency-radar (HFR) sea surface current data in the Gulf of Trieste (northern Adriatic Sea) are analysed. Two different timescales are extracted using a superstatistical formalism: a relaxation time and a larger timescale over which the system is Gaussian. We propose obtaining an ocean current probability density function (PDF) combining (i) a Gaussian PDF for the fast fluctuations and (ii) a convolution of exponential PDFs for the slowly evolving variance of the Gaussian function rather than for the thermodynamic beta=1/sigma^2 in a system with a few degrees of freedom, as the latter has divergent moments. The Gaussian PDF reflects the entropy maximization for real-valued variables with a given variance. On the other hand, if a positive variable, as a variance, has a specified mean, the maximum-entropy solution is an exponential PDF. In our case the system has 2 degrees of freedom, and therefore the PDF of the variance is the convolution of two exponentials.
In the Gulf of Trieste there are three distinct main wind forcing regimes: bora, sirocco, and low wind, leading to a succession of different sea current dynamics on different timescales. The universality class PDF successfully fits the observed data over the 2 observation years and also for each wind regime separately with a different variance of the variance PDF, which is the only free parameter in all the fits
Estimation of friction parameters in gravity currents by data assimilation in a model hierarchy
No full textThis paper is the last in a series of three investigating the friction laws and their parametrisation in idealised gravity currents in a rotating frame. Results on the dynamics of a gravity current (Wirth, 2009) and on the estimation of friction laws by data assimilation (Wirth and Verron, 2008) are combined to estimate the friction parameters and discriminate between friction laws in non-hydrostatic numerical simulations of gravity current dynamics, using data assimilation and a reduced gravity shallow water model. <br><br> I demonstrate, that friction parameters and laws in gravity currents can be estimated using data assimilation. The results clearly show that friction follows a linear Rayleigh law for small Reynolds numbers and the estimated value agrees well with the analytical value obtained for non-accelerating Ekman layers. A significant and sudden departure towards a quadratic drag law at an Ekman layer based Reynolds number of around 800 is shown, in agreement with classical laboratory experiments. The drag coefficient obtained compares well to friction values over smooth surfaces. I show that data assimilation can be used to determine friction parameters and discriminate between friction laws and that it is a powerful tool in systematically connecting models within a model hierarchy
Tipping of the double-diffusive regime in the southern Adriatic Pit in 2017 in connection with record high-salinity values
No full text<jats:p>Abstract. In double-diffusive mixing, whenever salinity and temperature decrease with depth, the water column is either unstable or predisposed to a state called salt fingering (SF), which exhibits increased vertical mixing. Analysis of a high-frequency time series of thermohaline data measured at the EMSO-E2M3A regional facility in the southern Adriatic Pit (SAP) from 2014 to 2019 reveals that in the south Adriatic, SF is the dominant regime. The same time series shows the presence of a very saline core of the Levantine Intermediate Water that penetrated with unprecedented strength during the winter of 2016/17 at around 550 dbar and even higher-salinity water above. The effect of strong heat loss at the surface during that winter allowed deep convection to transport this high-salinity water from the intermediate to the deep layers within the pit. This resulted in an increased predisposition to SF throughout the water column. In the subsurface layer (350 to 550 dbar) the increase is from 27 % to 72 % of observations. We observe an alteration of vertical stratification throughout the water column during the winter of 2016/17 from a stratified water column to an almost homogeneous water column down to 700 dbar, with no return in the following years.
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A minimal model for intermittency of passive scalars
No full textInternational audienceA shell-model version of Kraichnan's (1994) passive scalar problem is introduced which is inspired by the model of Jensen, Paladin and Vulpiani (1992). The here introduced shell-model is even simpler than the one studied previously (Wirth and Biferale 1996). As in the original problem of Kraichnan, the prescribed random velocity field is Gaussian, delta-correlated in time and has a power-law spectrum
Intermittent supply of North Adriatic Dense Water to the deep South Adriatic Pit through gravity currents: an observational study
No full textSevere winters in the northern Adriatic potentially generate gravity currents flowing along the eastern flank of the Adriatic, filling and ventilating the deepest layer of the southern Adriatic Pit with high-density water. The pulses of gravity current observed by data at the moorings in the Canyon of Bari (BB site) and the shelf-slope observation site (FF) are followed by strong fluctuations in the thermohaline properties in the pit observed at the E2M3A site in 2012, 2017, 2018 and 2022. While temperature was the main driver of gravity flow in 2012, salinity played an equal or greater role in the following extreme gravity current events. Thermohaline data from these three moorings show an arrival from mid-February to June and the relaxation phase of the high frequency oscillations (few tens of hours) lasts about two months. During this phase, the gravity current water displaces and mixes with the surrounding water masses. The gravity currents lead to a restratification of the water column, while local convection processes in winter time erode the stratification.
The effects of gravity currents in the southern Adriatic have a profound impact on the Eastern Mediterranean circulation, influencing its thermohaline properties and facilitating the ventilation of deep waters. The Adriatic dense water formation adds to and competes with the convection in the Gulf of Lion, forming the dense waters in the Mediterranean which outflow through the Strait of Gibraltar into the northern Atlantic.
The European Multidisciplinary Seafloor and water column Observatory (EMSO) South Adriatic Regional Facility (E2M3A in the pit, BB and FF at the edge of the pit) has been providing hourly data on temperature, salinity, oxygen and currents along the water column for about 15 years. This makes it possible to study these high-frequency small-scale processes and their interaction with the surroundings over an extended period of time and to assess their role in a changing climate
Near Real-Time Disturbance Detection in Terrestrial Ecosystems Using Satellite Image Time Series: Drought Detection in Somalia
No full textNear real-time monitoring of ecosystem disturbances is critical for addressing impacts on carbon dynamics, biodiversity, and socio-ecological processes. Satellite remote sensing enables cost-effective and accurate monitoring at frequent time steps over large areas. Yet, generic methods to detect disturbances within newly captured satellite images are lacking. We propose a generic time series based disturbance detection approach by modelling stable historical behaviour to enable detection of abnormal changes within newly acquired data. Time series of vegetation greenness provide a measure for terrestrial vegetation productivity over the last decades covering the whole world and contain essential information related land cover dynamics and disturbances. Here, we assess and demonstrate the method by (1) simulating time series of vegetation greenness data from satellite data with different amount of noise, seasonality and disturbances representing a wide range of terrestrial ecosystems, (2) applying it to real satellite greenness image time series between February 2000 and July 2011 covering Somalia to detect drought related vegetation disturbances. First, simulation results illustrate that disturbances are successfully detected in near real-time while being robust for seasonality and noise. Second, major drought related disturbance corresponding with most drought stressed regions in Somalia are detected from mid 2010 onwards and confirm proof-of-concept of the method. The method can be integrated within current operational early warning systems and has the potential to detect a wide variety of disturbances (e.g. deforestation, flood damage, etc.). It can analyse in-situ or satellite data time series of biophysical indicators from local to global scale since it is fast, does not depend on thresholds or definitions and does not require time series gap filling.early warning, real-time monitoring, global change, disturbance, time series, remote sensing, vegetation and climate dynamics
About the relationship between science and policy. Why a difference exists between the (educational) sience and the trade union of education and science
No full textDer Beitrag ist eine Antwort auf einen vorherigen Artikel von Dieter Wunder, dem ehemaligen Vorsitzenden der Gewerkschaft Erziehung und Wissenschaft (GEW). "In Heft 2/06 hatte Dieter Wunder die Deutung zurückgewiesen, die Achim Leschinsky in der Zeitschrift für Pädagogik für \u27das Scheitern des Deutschen Bildungsrates\u27 formuliert hatte. In seiner Replik erläutert Leschinsky seine Position, dass zwischen Wissenschaft und Politik eine Differenz besteht, die nicht ignoriert werden darf." (DIPF/Orig./So)In number 2/06 of this journal Dieter Wunder rejected the interpretation which Achim Leschinsky (in Zeitschrift für Pädagogik) had formulated concerning the "failure" of the German educational council. In his reply the author explains his position that between science and policy a difference exists which must not be ignored. (DIPF/Orig.
Globalization and deregulation : Does flexicurity protect atypically employed?
No full textHitherto, discussion of flexicurity has focused on normal employment (permanent full-time), with atypical work receiving only cursory attention. Nevertheless, the most affected are just atypically employed (= other than normally employed). To monitor effects of flexicurity policies in Europe, flexicurity indices are constructed from: (a) scores of the strictness of employment protection legislation provided by the OECD, (b) qualitative juridical data on social security benefits (unemployment insurance, public pensions, etc.), and (c) data on the dynamics of employment types (permanent, temporary, full-time, part-time, self-employed, etc.). The empirical investigation shows that, contrary to political promises and theoretical opinions, the deregulation of European labour markets absolutely predominates. Its moderate compensation by advantages in social security occurred only twice: in Denmark and Netherlands at the end of the 1990s. The flexibilization reduces the average employment status, i.e. employees are more often employed not permanently but temporarily, not full-time but part-time, and more frequently they involuntary turn to self-employment. On the other hand, the eligibility to social benefits depends on the employment status. Thereby these trends disqualify employees from social benefits. The apparent compensation of the labour market deregulation by social advantages is therefore insufficient. --flexicurity,labour market flexibility,atypical employment,social security,composite indicators
Flexicurity: Reconciling Social Security with Flexibility - Empirical Findings for Europe
No full textIt is empirically shown that the more flexible employment, the more it is precarious. For this purpose, two families of indices, of flexible work and of precarious work, are defined basing on the Fourth European Survey of Working Conditions 2005 by the European Foundation for the Improvement of Living and Working Conditions. Two methodologies of constructing composite indicators are applied, of the Hans Böckler Foundation, and of the OECD. Both methodologies give very similar results. After the indices have been constructed, the dependence between flexibility and precariousness of work is established by regression analysis with statistical certainty. Besides, it is revealed that the institutional regulation of employment does not necessarily imply the adequate factual effect. For instance, Turkey and Greece with a strict employment protection legislation have a high labour market flexibility due to a large fraction of employees who work with no contract. Among other things, it is shown that the employment flexibility has the strongest negative effect on the employability. It implies serious arguments against the recent reconsideration of the function of social security attempted by the European Commission within the flexicurity discourse. The suggested shift from income security towards a high employability cannot be consistently implemented. Our study provides empirical evidence that a high employability can be hardly attained under flexible employment. --Flexicurity,labour flexibility,precarious work,composite indicators,European Commission,European Employment Strategy
Das faschistische Erbe im Herzen Roms - Das Beispiel Piazza Augusto Imperatore
No full textIm Rahmen eines Vortrags wurde ein begrenzter Bereich ausgewählt, an dessen Entstehung alle fünf Disziplinen, die "la Grande Roma di Mussolini" gestalteten, gleichermaßen Anteil haben. Der Städtebau - wie er bis zum 2. Weltkrieg praktiziert wurde -, die Architektur, die bildenden Künste, die Denkmalpflege und vor allem die Archäologie in einer bis dahin unbekannten Vorreiterrolle. ..
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