Lagrangian ocean analysis: fundamentals and practices

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

Spatiotemporal scales of larval dispersal and connectivity among oil and gas structures in the North Sea

The ecological role of offshore man-made infrastructure is of growing international interest. By 2030, globally more than 7500 oil and gas platforms could be removed, many of which now host mature hard substrate ecosystems formed by sessile benthic species including sponges, corals and mussels. We investigated the spatiotemporal scales of generalised species dispersal and connectivity among oil and gas structures in the North Sea using strategically designed 3D advective passive particle tracking experiments forced by high resolution (1.8 km, hourly) velocity fields including tide-, density- and wind-driven currents. Trajectories from 2 seasonal releases during mixed winter (February) and stratified summer (July) conditions of 2010 were analysed for a variety of pelagic larval durations (PLDs) spanning 2 to 28 d. Particles dispersed on average 32 km away from their origins after just 5 d, 67 km after 15 d, and 109 km after 28 d, with considerable spatial variability and limited seasonal variations. Short (2 d) PLDs generated highly connected networks over smaller spatial scales, while longer PLDs (28 d) generated less fragmented networks covering a much larger area but with fewer connections. Tidally driven dispersal was isolated using a new method based on the harmonic analysis of the velocity fields: the resulting maximum linear dispersal distances varied from ~4 km in the northern North Sea to ~8 km in the southern North Sea. The present study provides baseline spatiotemporal scales of dispersal and connectivity patterns and optimized relocatable methods to assess connectivity in tidally active shelf seas.</jats:p

Mayorga-AdameCharacterizingCirculationKenyanSupportingInfo.pdf

The Kenyan-Tanzanian coastal region in the western Indian Ocean faces several environmental challenges including coral reef conservation, fisheries management, coastal erosion, and nearshore pollution. The region lacks hydrodynamic records and oceanographic studies at adequate spatial and temporal scales to provide information relevant to the local environmental issues. We have developed a 4 km horizontal resolution ocean circulation model of the region: the Kenyan-Tanzanian Coastal Model (KTCM) that provides coastal circulation and hydrography with higher resolution than previous models and observational studies of this region. Comparisons to temperature profiles, satellite-derived sea surface temperature and sea surface height anomaly fields, indicate that the model reproduces the main features of the regional circulation, while greatly increasing the details of the nearshore circulation. We describe the seasonal ocean circulation and hydrography of the Kenyan-Tanzanian coastal region based on a climatology of 8 years (2000–2007) of the KTCM simulations. The regional monsoon seasonality produces two distinct coastal circulation regimes: (1) during December–March, there are relatively sluggish shelf flows and (2) during April–November, there are strong northward transports. Simulations from the model will be useful for examining dispersal of pollutants and spatial connectivity of coral reef species.Keywords: monsoon seasonality, western Indian Ocean, coastal ocean circulation model, Kenya Tanzania coastal circulationKeywords: monsoon seasonality, western Indian Ocean, coastal ocean circulation model, Kenya Tanzania coastal circulatio

Mayorga-AdameCharacterizingCirculationKenyan.pdf

The Kenyan-Tanzanian coastal region in the western Indian Ocean faces several environmental challenges including coral reef conservation, fisheries management, coastal erosion, and nearshore pollution. The region lacks hydrodynamic records and oceanographic studies at adequate spatial and temporal scales to provide information relevant to the local environmental issues. We have developed a 4 km horizontal resolution ocean circulation model of the region: the Kenyan-Tanzanian Coastal Model (KTCM) that provides coastal circulation and hydrography with higher resolution than previous models and observational studies of this region. Comparisons to temperature profiles, satellite-derived sea surface temperature and sea surface height anomaly fields, indicate that the model reproduces the main features of the regional circulation, while greatly increasing the details of the nearshore circulation. We describe the seasonal ocean circulation and hydrography of the Kenyan-Tanzanian coastal region based on a climatology of 8 years (2000–2007) of the KTCM simulations. The regional monsoon seasonality produces two distinct coastal circulation regimes: (1) during December–March, there are relatively sluggish shelf flows and (2) during April–November, there are strong northward transports. Simulations from the model will be useful for examining dispersal of pollutants and spatial connectivity of coral reef species.Keywords: coastal ocean circulation model, monsoon seasonality, Kenya Tanzania coastal circulation, western Indian Ocea

Characterizing the circulation off the Kenyan-Tanzanian coast using an ocean model

The Kenyan-Tanzanian coastal region in the western Indian Ocean faces several environmental challenges including coral reef conservation, fisheries management, coastal erosion, and nearshore pollution. The region lacks hydrodynamic records and oceanographic studies at adequate spatial and temporal scales to provide information relevant to the local environmental issues. We have developed a 4 km horizontal resolution ocean circulation model of the region: the Kenyan-Tanzanian Coastal Model (KTCM) that provides coastal circulation and hydrography with higher resolution than previous models and observational studies of this region. Comparisons to temperature profiles, satellite-derived sea surface temperature and sea surface height anomaly fields, indicate that the model reproduces the main features of the regional circulation, while greatly increasing the details of the nearshore circulation. We describe the seasonal ocean circulation and hydrography of the Kenyan-Tanzanian coastal region based on a climatology of 8 years (2000–2007) of the KTCM simulations. The regional monsoon seasonality produces two distinct coastal circulation regimes: (1) during December–March, there are relatively sluggish shelf flows and (2) during April–November, there are strong northward transports. Simulations from the model will be useful for examining dispersal of pollutants and spatial connectivity of coral reef species.Keywords: coastal ocean circulation model, monsoon seasonality, Kenya Tanzania coastal circulation, western Indian Ocea

Lagrangian ocean analysis:Fundamentals and practices

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.</p