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[en] This study has assembled a climatology of Southwest Pacific explosively developing cyclones, based on the European Centre for Medium-Range Weather Forecasts' ERA-Interim reanalysis data, over the 21-year period from 1989 to 2009. The recently developed 'combined explosive' expression, a refinement of the 'relative explosive' criterion, was used to identify cyclones deemed explosive with respect to both the drop in central pressure and the climatological pressure gradient. Over the period of analysis, 47 explosive cyclones were identified within the Southwest Pacific, equating to an average of 2.2 explosive events per year. Seasonally, explosive cyclones are most frequent during the winter months, while least frequent during the summer. Two case explosive systems are briefly considered, with their corresponding measures of intensity and scale placed into climatological perspective.
[en] The entrainment hypothesis consists of a concise turbulence model, which has been widely used to model geophysical flows including plumes, gravity currents, and breaking internal waves. This paper employs the entrainment hypothesis to obtain a model for the wake of a single wind turbine, without having to linearize the governing equations, or needing to assume a wake radius that grows linearly (or in any other prescribed manner) with distance downstream. Assuming a top-hat velocity deficit and a zero pressure gradient, the analysis presented here re-discovers a result first due to Morton (B.R. Morton. J. Fluid Mech. 10:101–112, 1961), which however appears to have been completely overlooked until now. The predictions from this entrainment wake model are compared with published laboratory data and field observations, finding good agreement. Since the entrainment model does not require assuming a specific relationship between wake diameter and distance downstream, it may also enable simple extensions to account for complex terrain and for effects of yaw. (paper)
[en] On the average overland atmospheric diffusion rates are shown to be three times more rapid than those with overwater trajectories when the water is colder than the air temperatures over the land. The transport distance required to complete the transition from overwater to overland diffusion is shown to be a function of plume height, wind speed, and vertical temperature profile. Diffusion models are suggested to account for the diffusion rates within this transition zone. Coastline atmospheric trajectories are discussed in terms of local effects which result in the daily reversals between land and sea breezes and of large-scale pressure gradient effects which generally result in straight-line trajectories. (author)
[en] Highlights: • Turbulent boundary layer structure depends substantially not only on the local effects of pressure gradient, but also on the upstream history of the flow. • The flow history effect led to the change of the location and maximum value of the streamwise Reynolds stresses. • For the same pressure gradient conditions the increased momentum near the wall for incipient detachment point is observed with the increase of Reynolds number. • The increased momentum is triggered by the rise in convection velocity resulted from stronger large- and small-scale interaction. - Abstract: The present paper deals with the experimental analysis of a strong decelerated turbulent boundary layer developed on a flat plate. The aim of the study was to examine the effects of pressure gradient on a non-equilibrium boundary layer while indicating local areas of equilibrium flow. The effect of the Reynolds number on a turbulent boundary layer developed with matching the external pressure gradient conditions was also analysed. The emphasis was on the analysis of mean flow statistics i.e. mean velocity profiles, streamwise Reynolds stress and the effect of large- and small-scale interactions by analysing the skewness factor and energy isocontours maps. The comparative analysis of the external data indicated that the structure of the turbulent boundary layer depends not only on local effects of pressure gradient but also on the upstream history of the flow. For the same condition of pressure gradient, the increased momentum is observed near the wall with the increase of the Reynolds number at the Incipient Detachment, where increased turbulence production is also observed, leading to the failure of the outer scaling methods. Surprisingly, the effect of the Reynolds number decays at the intermittent transitory detachment where similar profiles were observed. The upper inflection point in the mean profile corresponded well with the outer maximum of the Reynolds stress and zero crossing of skewness factor. Position of this point occurs at different locations, depending on the flow history effects. The last observation demonstrates that the inflection points results from large- and small-scale interactions, which led to the increased convection velocity of small scales near the wall.
[en] The relaxation of the constraint of periodicity imposed by the external confining magnetic field coils in a nominally 4-field period Helias advanced stellarator configuration produces weak periodicity-breaking deformations of the plasma. The corrugations are driven by the interaction of the pressure gradient with the magnetic field line curvature and correspond to saturated ideal magnetohydrodynamic interchanges with a mode structure dominated by nonresonant Fourier components. The conditions of quasi-isodynamicity of the Helias reactor system investigated are not significantly altered by the periodicity-breaking distortions. (letter)
[en] May-Thurner syndrome is known as compression of the left common iliac vein by the right common iliac artery. We describe a case of an atypical compression of the inferior vena cava by the right common iliac artery secondary to a high aortic bifurcation. Despite an extensive collateral network, there was a significant venous gradient between the iliac veins and the inferior vena cava above the compression. After stenting the venous pressure gradient disappeared. Follow-up 4 months later revealed a good clinical response with a patent stent.