Hydrological currents in the Ligurian Sea

Summary Hydrological observations in the Ligurian Sea, north-western part of the Mediterranean Sea, are discussed. They show a steady cyclonic circulation. At theboundary of this circulation meanders and small eddies are rather frequent, in particular North of the Corsica Island. Their presence is in agreement with satellite data. In this paper also a number of simple baroclinic instability models are also considered, in an attempt to explain these current fluctuations.

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Riassunto L'analisi della circolazione generale del Mar Ligure, sulla base dei dati idrologici dell'Istituto Idrografico della Marina, ha rivelato la presenza, in ogni stagione, di una circolazione ciclonica stazionaria ai bordi della quale sono visibili ondulazioni delle linee di corrente e alcuni piccoli vortici. In accordo con le osservazioni da satellite queste piccole circolazioni vorticose si addensano in particolar modo a Nord della Corsica. In questo articolo la formazione dei meandri e dei piccoli vortici presenti nel Mar Ligure è analizzata sulla base di semplici modelli d'instabilità baroclina.

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Резюме Обсуждаются гидрологические наблюдения в Лигурийском море, северо-западной части Средиземного моря. Наблюдения обнаруживают стационарную цилиндрическую циркуляцию. На границе этой циркуляции имеют место извилины и небольшие вихри, особенно на севере Корсики. Их наличие подтверждается данными со спутников. В этой статье рассматривается рад простых моделей неустойчивостей с целью объяснить эти флуктуации течений.

     

On the currents in the strait of Messina

Summary In order to check the tidal currents in the Messina Strait, recent measurements made by Istituto Idrografico della Marina, Genova, are discussed. The classical measurement of Vercelli (1922–23) are confirmed.

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Riassunto Si studiano, con dati recenti raccolti dall'Istituto Idrografico della Marina, Genova, le correnti mareali nello Stretto di Messina. I dati classici di Vercelli sono confermati.

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Резуме Чтобы проверитщ наличие приливных потоков в Мессинском проливе, проводится исследование недавних измерений, выполненных Гидрографическим Институом Морч в Генуе. ПодтверЗдаются классические данные Верчелли (1922–1923).

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The work is supported by a grant from CNR, Progetto Finalizzato Oceanografia.     

Eulerian spectrum of finite-time Lyapunov exponents in compound channels

Fluid flows reveal a wealth of structures, such as vortices and barriers to transport. Usually, either an Eulerian or a Lagrangian frame of reference is employed in order to detect such features of the flow. However, the two frameworks detect structures that have different properties. Indeed, common Eulerian diagnostics (Hua-Klein and Okubo-Weiss criterion) employed in order to detect vortices do not always agree with Lagrangian diagnostics such as finite-time Lyapunov exponents. Besides, the former are Galilean-invariant whereas the latter is objective. However, both the Lagrangian and the Eulerian approaches to coherent structure detection must show some links under any inertial-frame. Compound channels flows have been accurately studied in the past, both from a Lagrangian and an Eulerian point of view. The features detected do not superimpose: Eulerian vortices do not coincide with barriers to transport. The missing link between the two approaches is here recovered thanks to a spectral analysis.

     

Particle-wall collision in shear thinning fluids

The present study deals with the measurements of the impact w_i and rebound w_r velocities of steel particles in different fluids colliding with a rigid wall. The results are presented in terms of the coefficient of restitution e=w_r/w_i as a function of the Stokes number (ratio between the particle inertia and the viscous forces). We focus the attention on possible differences between rebounds that occur in Newtonian fluids and in non-Newtonian, shear thinning fluids. The measurements of wet coefficients of restitution in Newtonian fluid are in good agreement with the experimental data found by Gondret et al. (2002). In the range of Stokes number investigated, an increase of the coefficient of restitution with the shear thinning fluid is clearly observed with respect to the Newtonian data. Particular attention has been dedicated to techniques of image processing to perform an optimal estimation of the particle centroid in highly noisy images.     

Climatological data and superficial thermal balance in the wright dry valley (South Victoria Land-Antarctica)

Summary The microclimate of the Wright Valley, one of the so-called dry valleys of southern Victoria Land, was investigated in the course of an Italian expedition (November 1976–January 1977) financed by Italy's National Research Council and furnished with logistical support by New Zealand's Scott Base (Carlo Stocchino, meteorologist, leader; Enrico Rossi, meteorologist, Italian Navy; Ivo Di Menno, technician; Walter Bonatti, climber). In the course of the expedition, the vertical temperature and the wind profiles of the surface layer of the atmosphere were measured at a single ground site in the Wright Valley. These measurements, combined with data on the principal meteorological parameters, made it possible to calculate the surface heat balance.

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Riassunto Nel periodo novembre 1976-gennaio 1977 è stata effettuata con il supporto finanziario del Consiglio Nazionale delle Ricerche una spedizione scientifica nella regione delle Valli Secche dell'Antartide (Carlo Stocchino, meteorologo, capo-spedizione; Enrico Rossi, meteorologo, Marina Militare; Ivo di menno, tecnico; Walter Bonatti, scalatore). Nel corso della campagna, oltre alle consuete esplorazioni, sono state effetuate misure micrometeorologische nella valle di Wright per caratterizzare il microclima locale. I dati ottenuti sono stati utilizzati per la stima del bilancio di calore superficiale.

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Резюме В период с ноября 1976 по январь 1977 была осуществлена игальянская научная экспедиция, при поддержке Итальянского Национального Совета Исследований, в область Сухих Долин в Антарктиде. Во время экспедиции, помимо обычных иссиедований, были проведены микрометеорологические измерения в Долине Райта для получения характеристик локального микроклимата. Полученные данные используются для оценки поверхностного теплового баланса.