Depth-Dependent Correction for Wind-Driven Drift Current in Particle Tracking Applications

Mirjam van der Mheen,Charitha Pattiaratchi,Simone Cosoli,Moritz Wandres

doi:10.3389/fmars.2020.00305

Mirjam van der Mheen, Charitha Pattiaratchi + Show 2 more

Open Access

https://doi.org/10.3389/fmars.2020.00305

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Abstract

Predicting the trajectories of buoyant objects drifting at the ocean surface is important for a variety of different applications. To minimise errors in predicted trajectories, the dominant transport mechanisms have to be considered. In addition to the background surface currents (i.e. geostrophic, tidal, baroclinic currents), the wind-driven drift current can have a significant influence on the dynamics of buoyant objects. The drift current consists of two components: Stokes drift and a wind-induced shear current. The drift current has a strong vertical profile that can have a large influence on the transport of buoyant objects. However, few practical methods exist that consider the vertical profile of the drift current when predicting particle pathways on the ocean surface. The aim of this paper is to introduce a depth-dependent drift current correction factor (``drift factor''). We test the usefulness of this drift factor by simulating the transport of two types of ocean surface drifters, released simultaneously within the coverage of a high-frequency ocean radar (HFR) system. Our results show velocity differences between the two types of drifters and the HFR measured ocean surface currents. We suggest that these differences are the result of the drift current vertical profile. Our particle tracking simulations provide an illustrative example, indicating the importance of accounting for a drift factor that takes the variation of the drift current with depth into account.

Highlights

It is important to predict the trajectories of buoyant objects at the ocean surface for a wide variety of applications, such as: search and rescue purposes (e.g., Breivik and Allen, 2008); oil spill mitigation (e.g., Abascal et al, 2009b; le Hénaff et al, 2012); tracking of marine plastic debris (e.g., Lebreton et al, 2012); and determining larval (e.g., Siegel et al, 2003) or seed dispersal (e.g., Erftemeijer et al, 2008)
We introduce a depth-dependent drift current correction factor (“drift factor,” section 2) that is straightforward to apply to Particle Tracking Simulations (PTSs)
Our results show that the two types of drifters behave differently, which we suggest is related to the vertical decay of the wind-driven drift current

Summary

Introduction

It is important to predict the trajectories of buoyant objects at the ocean surface for a wide variety of applications, such as: search and rescue purposes (e.g., Breivik and Allen, 2008); oil spill mitigation (e.g., Abascal et al, 2009b; le Hénaff et al, 2012); tracking of marine plastic debris (e.g., Lebreton et al, 2012); and determining larval (e.g., Siegel et al, 2003) or seed dispersal (e.g., Erftemeijer et al, 2008). Trajectories of buoyant objects are commonly simulated using Lagrangian particle tracking models (PTMs). Many uncertainties are involved in particle tracking simulations (PTSs) (e.g., van Sebille et al, 2018), for example: unresolved processes in the forcing fields used to advect particles; inaccuracy in numerical solvers of PTMs; and uncertainty about the dynamics of objects at the ocean surface. Uncertainty about relevant transport mechanisms (e.g., currents, wind, waves) can lead to large errors (e.g., le Hénaff et al, 2012; van der Mheen et al, 2019). In addition to “background surface currents” (section 2) used to force PTMs, wind has a large impact on the transport of buoyant objects, both directly and indirectly.

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