Scaling dependence on the fluid viscosity ratio in the selective withdrawal transition

In the selective withdrawal experiment fluid is withdrawn through a tube with its tip suspended a distance S above a two-fluid interface. At sufficiently low withdrawal rates, Q, the interface forms a steady state hump and only the upper fluid is withdrawn. When Q is increased (or S decreased), the interface undergoes a transition so that the lower fluid is entrained with the upper one, forming a thin steady-state spout. Near this transition the hump curvature becomes very large and displays power-law scaling behavior. This scaling allows for steady-state hump profiles at different flow rates and tube heights to be scaled onto a single similarity profile. I show that the scaling behavior is independent of the viscosity ratio.Comment: 33 Pages, 61 figures, 1 tabl

On the highly unsteady dynamics of multiple thermal buoyant jets in cross flows

Thermal plumes of small scale generated by spatially separated heat sources can form, like atoms in a chemical compound, complex structures of different kind and with distinct behaviors. The situation becomes even more complex if plumes can interact with imposed vertical shear (a horizontal wind). In this analysis a ‘minimal framework’ based on the application of a filtering process to the governing balance equations for mass, momentum and energy (falling under the general heading of ‘Large Eddy Simulation’ approach), is used together with Direct Numerical Simulation to inquiry about the relative importance of buoyancy and vertical shear effects in determining the patterning scenario when highly unsteady dynamics are established (turbulent flow). Emerging patterns range from the flow dominated by a static rising jet produced by the aggregation of plumes, which are pushed by horizontal leftwards and rightwards winds towards the center of the physical domain, to convective systems with disconnected thermal pillars of smaller scale, which travel in the same direction of the prevailing wind. The classical sheltering effect, which for flows that are steady ‘in mean’ simply consists of an increased deflection of the leading buoyant jet with respect to the trailing ones, is taken over by a variety of new phenomena, including (but not limited to) fast plume removal-rebirth mechanisms (with local increase in the velocity frequency and shrinkage in the related amplitude), ‘bubble’ formation-rupture and local departure of the frequency spectrum from the Kolmogorov similarity law

Evolving and sustaining ocean best practices and standards for the next decade

The oceans play a key role in global issues such as climate change, food security, and human health. Given their vast dimensions and internal complexity, efficient monitoring and predicting of the planet's ocean must be a collaborative effort of both regional and global scale. A first and foremost requirement for such collaborative ocean observing is the need to follow well-defined and reproducible methods across activities: from strategies for structuring observing systems, sensor deployment and usage, and the generation of data and information products, to ethical and governance aspects when executing ocean observing. To meet the urgent, planet-wide challenges we face, methods across all aspects of ocean observing should be broadly adopted by the ocean community and, where appropriate, should evolve into "Ocean Best Practices." While many groups have created best practices, they are scattered across the Web or buried in local repositories and many have yet to be digitized. To reduce this fragmentation, we introduce a new open access, permanent, digital repository of best practices documentation (oceanbestpractices.org) that is part of the Ocean Best Practices System (OBPS). The new OBPS provides an opportunity space for the centralized and coordinated improvement of ocean observing methods. The OBPS repository employs user-friendly software to significantly improve discovery and access to methods. The software includes advanced semantic technologies for search capabilities to enhance repository operations. In addition to the repository, the OBPS also includes a peer reviewed journal research topic, a forum for community discussion and a training activity for use of best practices. Together, these components serve to realize a core objective of the OBPS, which is to enable the ocean community to create superior methods for every activity in ocean observing from research to operations to applications that are agreed upon and broadly adopted across communities. Using selected ocean observing examples, we show how the OBPS supports this objective. This paper lays out a future vision of ocean best practices and how OBPS will contribute to improving ocean observing in the decade to come