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    La valeur de la méthode otolithométrique pour la détermination de l'age du Merlu (<i>Merlucius merlucius</i> - Pisces, Gadidae) en Méditerranée

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    The otolithometric method rests on 2 (1) the agreement between the number of annual rings and the age of the fish and (2) the length of the fish being proportional to that of the otolith. The length of the fish may be grouped into 5 classes, ranging from 16, 18, 20, 25 to 27 cm though some degree of overlapping is observed. Using 300 otoliths and grouping the individuals according to the number of annual rings their otoliths bear it was possible to determine the frequency of individuals of varying lengths within a particular class. Although the results obtained by the author helped him to verify the 2nd parameter, numerous shortcomings were seen in this method. No consistent unity of measurement, which could be used for comparison, has been adopted by other workers; aberrant results were obtained by considering all the rings as being equivalent; the difficulty in interpreting an annual ring and the uncertainty of these deposits being regular and annual. It is strongly recommended that the otolithometric method be used only after its validity has been determined and a standard for reference in interpreting annual rings has been established

    Momentum and scalar transport within a vegetation canopy following atmospheric stability and seasonal canopy changes: the CHATS experiment

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    Momentum and scalar (heat and water vapor) transfer between a walnut canopy and the overlying atmosphere are investigated for two seasonal periods (before and after leaf-out), and for five thermal stability regimes (free and forced convection, near-neutral condition, transition to stable, and stable). Quadrant and octant analyses of momentum and scalar fluxes followed by space-time autocorrelations of observations from the Canopy Horizontal Array Turbulence Study's (CHATS) thirty meter tower help characterize the motions exchanging momentum, heat, and moisture between the canopy layers and aloft. &lt;br&gt;&lt;br&gt; During sufficiently windy conditions, i.e. in forced convection, near-neutral and transition to stable regimes, momentum and scalars are generally transported by sweep and ejection motions associated with the well-known canopy-top "shear-driven" coherent eddy structures. During extreme stability conditions (both unstable and stable), the role of these "shear-driven" structures in transporting scalars decreases, inducing notable dissimilarity between momentum and scalar transport. &lt;br&gt;&lt;br&gt; In unstable conditions, "shear-driven" coherent structures are progressively replaced by "buo-yantly-driven" structures, known as thermal plumes; which appear very efficient at transporting scalars, especially upward thermal plumes above the canopy. Within the canopy, downward thermal plumes become more efficient at transporting scalars than upward thermal plumes if scalar sources are located in the upper canopy. We explain these features by suggesting that: (i) downward plumes within the canopy correspond to large downward plumes coming from above, and (ii) upward plumes within the canopy are local small plumes induced by canopy heat sources where passive scalars are first injected if there sources are at the same location as heat sources. Above the canopy, these small upward thermal plumes aggregate to form larger scale upward thermal plumes. Furthermore, scalar quantities carried by downward plumes are not modified when penetrating the canopy and crossing upper scalar sources. Consequently, scalars appear to be preferentially injected into upward thermal plumes as opposed to in downward thermal plumes. &lt;br&gt;&lt;br&gt; In stable conditions, intermittent downward and upward motions probably related to elevated shear layers are responsible for canopy-top heat and water vapor transport through the initiation of turbulent instabilities, but this transport remains small. During the foliated period, lower-canopy heat and water vapor transport occurs through thermal plumes associated with a subcanopy unstable layer
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