Arctic sea-ice diffusion from observed and simulated Lagrangian trajectories

Abstract

Abstract. We characterize sea-ice drift by applying a Lagrangian diffusion analysis to buoy trajectories from the International Arctic Buoy Programme (IABP) dataset and from two different models: the standalone Lagrangian sea-ice model neXtSIM and the Eulerian coupled ice-ocean model used for the TOPAZ reanalysis. By applying the diffusion analysis to the IABP buoy trajectories over the period 1979-2011, we confirm that sea-ice diffusion follows two distinct regimes (ballistic and Brownian) and we provide accurate values for the diffusivity and integral timescale that could be used in Eulerian or Lagrangian passive tracers models to simulate the transport and diffusion of particles moving with the ice. We discuss how these values are linked to the evolution of the fluctuating displacements variance and how this information could be used to define the size of the search area around the position predicted by the mean drift. By comparing observed and simulated sea-ice trajectories for three consecutive winter seasons (2007)(2008)(2009)(2010)(2011), we show how the characteristics of the simulated motion may differ from or agree well with observations. This comparison illustrates the usefulness of first applying a diffusion analysis to evaluate the output of modeling systems that include a sea-ice model before using these in, e.g., oil spill trajectory models or, more generally, to simulate the transport of passive tracers in sea ice.

Validation of Oil Spill Transport and Fate Modeling in Arctic Ice

“…Nevertheless, overall, our findings based on the modeled trajectories herein (Tables 3-5; Supplementary Tables S1-S4 1 ), as measured by the ratio of modeled to observed path lengths (indicative of relative speed) and skill scores, are consistent with Rampal et al's (2016b) findings related to relative performance. A comprehensive test series involving statistical comparisons of the modeled trajectories to approximately four hundred 5, 10, 15, and 30 day intervals of IABP drifter trajectories demonstrated that the new neXtSIM model predictions agree more closely with the observations than the operational status quo models represented by TOPAZ4 using the older (standard) EVP rheology.…”

“…A comprehensive test series involving statistical comparisons of the modeled trajectories to ∼400 intervals of 5, 10, 15, and 30 days from IABP drifter trajectories demonstrated that the new neXtSIM model predictions agree more closely with the observations than the operational status quo models represented by TOPAZ4 using the older (standard) EVP rheology, in agreement with findings by Rampal et al (2016b). However, all of the models performed well in operational mode where the modeled locations are updated regularly (every 5 days) with locations of field-deployed drifters.…”

“…Accuracy of ice-ocean model and oil spill trajectory forecasts Rampal et al (2016b) compared modeled trajectories using their updated ice model products with IABP drifter paths, examining speeds and diffusivities, finding that the EBbased neXtSIM model more closely agreed with the IABP observations than TOPAZ-EVP. They found that in general, trajectories were longer when modeled using the TOPAZ data than observed in the IABP data.…”

“…The EB-based neXtSIM model better preserves dynamic features like cracks, ridges, and leads in pack ice than traditional Eulerian models (Rampal et al 2016a). NERSC focused their validation (Rampal et al 2016b) on examination of transport (as compared to drifters and interpretations of satellite imagery), statistical analysis of ice coverage, and on the degree of dispersion (comparing model predictions to drifters). In comparing model predictions to drifter paths in the Beaufort Sea, NERSC noted that the predicted westward ice movements were too fast using TOPAZ coupled with the standard EVP rheology but more similar to observations using the neXtSIM model.…”

Method to characterize directional changes in Arctic sea ice drift and associated deformation due to synoptic atmospheric variations using Lagrangian dispersion statistics

“…Single-particle dispersion also provides a signature of Lévy dynamics (Schlesinger et al, 1993) or processes associated with intermittent "flight" (anomalous or ballistic transport) and "trapping" events, such as are observed in directional changes in the ice cover explored in the present investigation. Previous studies have illustrated the use of Lagrangian dispersion statistics to quantify dynamical regimes in the ice cover (Rampal et al, 2009a,b;Lukovich et al, 2011Lukovich et al, , 2015Rampal et al, 2016). In this study, we build upon previous analyses by identifying inflection points in total absolute dis- persion results to identify transitions in distinct dynamical regimes.…”