4 results found
McAdam R, van Sebille E, 2018, Surface connectivity and inter-ocean exchanges from drifter-based transition matrices, Journal of Geophysical Research: Oceans, Vol: 123, Pages: 514-532, ISSN: 2169-9275
Global surface transport in the ocean can be represented by using the observed trajectories of drifters to calculate probability distribution functions. The oceanographic applications of the Markov Chain approach to modelling include tracking of floating debris and water masses, globally and on yearly-to-centennial timescales. Here, we analyse the error inherent with mapping trajectories onto a grid and the consequences for ocean transport modelling and detection of accumulation structures. A sensitivity analysis of Markov Chain parameters is performed in an idealised Stommel gyre and western boundary current as well as with observed ocean drifters, complementing previous studies on widespread floating debris accumulation. Focusing on two key areas of inter-ocean exchange - the Agulhas System and the North Atlantic intergyre transport barrier - we assess the capacity of the Markov Chain methodology to detect surface connectivity and dynamic transport barriers. Finally, we extend the methodology's functionality to separate the geostrophic and non-geostrophic contributions to inter-ocean exchange in these key regions.
van Sebille E, Griffies SM, Abernathey R, et al., 2017, Lagrangian ocean analysis: fundamentals and practices, Ocean Modelling, Vol: 121, Pages: 49-75, ISSN: 1463-5003
Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.
McAdam R, 2017, Plastic in the ocean: How much is out there?, Significance, Vol: 14, Pages: 24-27, ISSN: 1740-9705
Plastic waste is found in ocean waters, on beaches and in the marine food chain. Counting it all would be impossible, but the approximate scale of the problem can be estimated. Ronan McAdam highlights the many roles of statistics in describing and tackling this global issue
Collins GS, Lynch E, McAdam R, et al., 2017, A numerical assessment of simple airblast models of impact airbursts, Meteoritics & Planetary Science, Vol: 52, Pages: 1542-1560, ISSN: 1086-9379
Asteroids and comets 10–100 m in size that collide with Earth disrupt dramatically in the atmosphere with an explosive transfer of energy, caused by extreme air drag. Such airbursts produce a strong blastwave that radiates from the meteoroid's trajectory and can cause damage on the surface. An established technique for predicting airburst blastwave damage is to treat the airburst as a static source of energy and to extrapolate empirical results of nuclear explosion tests using an energy-based scaling approach. Here we compare this approach to two more complex models using the iSALE shock physics code. We consider a moving-source airburst model where the meteoroid's energy is partitioned as two-thirds internal energy and one-third kinetic energy at the burst altitude, and a model in which energy is deposited into the atmosphere along the meteoroid's trajectory based on the pancake model of meteoroid disruption. To justify use of the pancake model, we show that it provides a good fit to the inferred energy release of the 2013 Chelyabinsk fireball. Predicted overpressures from all three models are broadly consistent at radial distances from ground zero that exceed three times the burst height. At smaller radial distances, the moving-source model predicts overpressures two times greater than the static-source model, whereas the cylindrical line-source model based on the pancake model predicts overpressures two times lower than the static-source model. Given other uncertainties associated with airblast damage predictions, the static-source approach provides an adequate approximation of the azimuthally averaged airblast for probabilistic hazard assessment.
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