Particle tracking in the vicinity of Helgoland, North Sea: a model comparison

Abstract

Station Helgoland Roads in the south-eastern North Sea (German Bight) hosts one of the richest longterm time series of marine observations. Hydrodynamic transport simulations can help understand variability in the local data brought about by intermittent changes of water masses. The objective of our study is to estimate to which extent the outcome of such transport simulations depends on the choice of a specific hydrodynamic model. Our basic experiment consists of 3,377 Lagrangian simulations in time-reversed mode initialized every 7 h within the period Feb 2002-Oct 2004. Fifty-day backward simulations were performed based on hourly current fields from four different hydrodynamic models that are all well established but differ with regard to spatial resolution, dimensionality (2D or 3D), the origin of atmospheric forcing data, treatment of boundary conditions, presence or absence of baroclinic terms, and the numerical scheme. The particle-tracking algorithm is 2D; fields from 3D models were averaged vertically. Drift simulations were evaluated quantitatively in terms of the fraction of released particles that crossed each cell of a network of receptor regions centred at the island of Helgoland. We found substantial systematic differences between drift simulations based on each of the four hydrodynamic models. Sensitivity studies with regard to spatial resolution and the effects of baroclinic processes suggest that differences in model output cannot unambiguously be assigned to certain model properties or restrictions. Therefore, multi-model simulations are needed for a proper identification of uncertainties in long-term Lagrangian drift simulations.

Surface drifters in the German Bight: model validation considering windage and Stokes drift

“…For drifter simulations, we used the Lagrangian transport module PELETS-2D (Program for the Evaluation of Lagrangian Ensemble Transport Simulations; Callies et al, 2011) developed at Helmholtz-Zentrum Geesthacht (HZG). The PELETS algorithm was designed for particle tracking on two-dimensional unstructured triangular grids.…”

Tracer Transport and Exchange Processes in the Baltic Sea 2000-2009

“…Engqvist et al [16] investigated transport within a central region of the Baltic Sea, with tracers originating from a hypothetical geological waste repository site (Forsmark), using a hydrodynamic model referred to as AS3D that was presented by Engqvist and Andrejev [17] and Andrejev et al [18]. Tracking of passive particles has been used for characterising transport in surface water under a variety of conditions [19][20][21][22][23]. Frequently, particle tracking is used for identifying pathways and quantifying travel times of tracers released into a surface water body.…”

Seafloor monitoring west of Helgoland (German Bight, North Sea) using the acoustic ground discrimination system RoxAnn

“…The lower eastern half of the study area comprises the western branch of the halotectonic depression known as the Helgoland Hole (Schmidt-Thomé 1982). Water depths range between 17 and 54 m. The hydrography forms part of the anticlockwise circulation of the North Sea, influenced by semidiurnal tides that are strongly flood dominated in the northern part of the study area (Callies et al 2011;Stanev et al 2015). Surface sediments outside the bedrock outcrops include sandy muds and muddy sands (Figge 1981).…”