Relationships between Arctic sea ice drift and strength modelled by NEMO-LIM3.6

Abstract

Abstract. Sea ice cover and thickness have substantially decreased in the Arctic Ocean since the beginning of the satellite era. As a result, sea ice strength has been reduced, allowing more deformation and fracturing and leading to increased sea ice drift speed. We use the version 3.6 of the global ocean-sea ice NEMO-LIM model (Nucleus for European Modelling of the Ocean coupled to the Louvain-laNeuve sea Ice Model), satellite, buoy and submarine observations, as well as reanalysis data over the period from 1979 to 2013 to study these relationships. Overall, the model agrees well with observations in terms of sea ice extent, concentration and thickness. The seasonal cycle of sea ice drift speed is reasonably well reproduced by the model. NEMO-LIM3.6 is able to capture the relationships between the seasonal cycles of sea ice drift speed, concentration and thickness, with higher drift speed for both lower concentration and lower thickness, in agreement with observations. Model experiments are carried out to test the sensitivity of Arctic sea ice drift speed, thickness and concentration to changes in sea ice strength parameter P * . These show that higher values of P * generally lead to lower sea ice deformation and lower sea ice thickness, and that no single value of P * is the best option for reproducing the observed drift speed and thickness. The methodology proposed in this analysis provides a benchmark for a further model intercomparison related to the relationships between sea ice drift speed and strength, which is especially relevant in the context of the upcoming Coupled Model Intercomparison Project 6 (CMIP6).

Reassessing Sea Ice Drift and Its Relationship to Long‐Term Arctic Sea Ice Loss in Coupled Climate Models

“…Computing drift speed from monthly mean components (i.e., ), produces drift speeds that are about a factor of two lower than in Figure (not shown). Docquier et al () have shown a similar effect of temporal sampling on the computation of sea ice drift speed in one particular model. In some models, temporal sampling also affects the apparent timing of the seasonal peak of sea ice drift speed.…”

“…This sea ice thinning leads to a reduction in sea ice strength, which reduces the sea ice internal stress, allowing for more sea ice deformation, more fracturing, and faster drift. Evidence for such a physical mechanism has been shown in models (Docquier et al, ) and observations (Rampal et al, ; Spreen et al, ). In GFDL‐CM3, the trend of sea ice thickness is approximately −0.3 m dec −1 in the Western Arctic, and the drift speed trend is approximately 0.7 km d −1 dec −1 in this region.…”

“…This is quantitatively comparable to expectations based on the historical relationship between sea ice drift speed and thickness in the seasonal cycles of models and observations. (E.g., note the slopes of the red and black dashed lines in Figure b of Docquier et al, . )…”

“…Higher ice‐ocean drag, C dw , opposes this effect and reduces drift speed. One might also expect a higher sea ice strength parameter, , to inhibit sea ice deformation and thereby reduce drift speed (Docquier et al, ; Rampal et al, ). We will discuss in more detail below the possible influence of these model parameters on simulated climatological drift speed.…”

“…Two models (BCC‐CSM1.1(m) and CanESM2) produce near‐surface wind maxima that appear to lead the maxima of sea ice drift speed. Olason and Notz () and Docquier et al () have performed observational analysis examining the relationships between the seasonal cycles of drift speed, sea ice concentration, and sea ice thickness. We have performed computations (not shown) demonstrating that most models qualitatively reproduce the observed relationships shown in Olason and Notz () and Docquier et al ().…”