[1] A prognostic high-resolution model is established to provide an integrated view of the evolution of the spring bloom during the Programme Océan Multidisciplinaire Méso Echelle (POMME) experiments carried out at sea from February to May 2001 (16-22°W and 38°-45°N). Data collected during the first survey were used for model initialization, and data from three other cruises were used for model validation. The model successfully predicts the time evolution of the main reservoirs and fluxes, except for a storm event during postbloom conditions, for which the biological impact is underestimated. The bloom is long in duration (2 months), has low intensity (1 mg Chl m À3 ), and is characterized by a small f-ratio (0.45) and a small e-ratio (0.05). Furthermore, the model reveals much stronger space and time variability than sampled in the data. This large variability results both from the synoptic atmospheric variability and from the stirring induced by oceanic mesoscale eddies. In particular, the bloom starts in specific submesoscale features that correspond to filaments of minimum mixed layer depth. On short timescales (2-3 days), space and time variability have the same order of magnitude. On the seasonal timescale, time variability is larger than space variability. Considering the transient state of the system, this modeling exercise is also used to quantify the nonsynopticity of the observations, which occur mostly during bloom conditions, a crucial point for the data interpretation.

A modeling study of physical processes occurring in an area of the northeast Atlantic (21.33°–15.33°W, 38.00°–45.00°N) that was extensively sampled during the Programme Océan Multidisciplinaire Méso Echelle (POMME) (October 2000–September 2001) is carried out. The model is a mesoscale version of the ocean general circulation model OPA developed at the Laboratoire d'Océanographie Dynamique et de Climatologie in Paris. It is used in a three‐dimensional limited area domain with a high‐resolution grid (approximately 5 km horizontal spacing, 69 vertical levels) and realistic boundary conditions (initial state, air‐sea fluxes, open boundary fluxes, and bottom topography). The objectives of the study are to properly simulate the upper ocean dynamics, particularly mesoscale activity and mixed layer evolution, during a key period (restratification) of the POMME experiment (POMME 1 and POMME 2, from February to May 2001) and to compare model results with oceanographic observations collected during the experiment in order to establish confidence in the model. Some results provided by the high‐resolution simulation, in particular features related to mixed layer depth and vertical velocities, are also presented. There is no pronounced north‐south mixed layer depth gradient, but strong filament‐shaped structures associated with stirring at the periphery of eddies are present. Mixed layer restratification is simulated. It is associated with submesoscale mixed layer depth structures and intense vertical velocity filaments in the upper ocean correlated with the relative vorticity gradient field.

In this article we present some laboratory experiments on stratified flows over isolated obstacles which were aimed at the simulation of atmospheric rotors as induced by the interaction of mountain waves and the boundary layer. For this purpose we modified the classical tank experiments on mountain waves performed with constant density gradients by introducing an elevated density inversion above the obstacle height. This kind of inversion seems to favour very much the development of mountain-induced rotors as was shown in recent numerical simulations. In fact our experimental set-up was guided by the simulations of Vosper, which provided systematically the upstream conditions under which mountain rotors are expected. We were able to confirm the results from these numerical simulations over a wide range of parameters. Detailed analyses of flow structures for some selected cases, as obtained by particle image velocimeter analysis, are presented.

?? 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Urbanized valleys are particularly vulnerable to particulate air pollution during the winter, when ground-based stable layers or cold-air pools persist over the valley floor. We examine whether the temporal variability of PM10 concentration in the section of the Arve River Valley between Cluses and Servoz in the French Alps can be explained by the temporal variability of the valley heat deficit, a bulk measure of atmospheric stability within the valley. We do this on the basis of temperature profile and ground-based PM10 concentration data collected during wintertime with a temporal resolution of one hour or finer, as part of the Passy-2015 field campaign conducted around Passy in this section of valley. The valley heat deficit was highly correlated with PM10 concentration on a daily time scale. The hourly variability of PM10 concentrations was more complex and cannot be explained solely by the hourly variability of the valley heat deficit. The interplay of the diurnal cycles of emissions and local dynamics is demonstrated and a drainage mechanism for observed nocturnal dilution of near-surface PM10 concentrations is proposed