TOPAZ5: A high-resolution ocean and sea-ice model for the Arctic and North Atlantic

Abstract. Accurate simulation of coupled ocean-sea ice dynamics is important for understanding Arctic climate variability. This paper evaluates TOPAZ5, a novel high-resolution (6–10 km) hindcast configuration of the HYCOM-CICE model optimized for the Arctic and North Atlantic, over the period 2009–2019. TOPAZ5 is validated against satellite altimetry, in situ observations, and reanalysis products, assessing sea surface temperature (SST), sea surface salinity (SSS), sea level anomaly (SLA), eddy kinetic energy (EKE), mixed layer depth (MLD), volume transports, and sea ice properties. TOPAZ5 captures the large-scale spatial patterns of SST and SSS with strong agreement relative to the OSTIA dataset and WOA climatology; however, persistent warm and saline surface biases remain, particularly during summer and over Arctic shelf regions. SLA trends are generally consistent with satellite altimetry and reanalyses, though positive anomalies in the Norwegian and Barents Seas are underestimated. Compared to observations, the model reproduces similar spatial patterns of EKE but underestimates their amplitude, especially in the Lofoten Basin and Labrador Sea. MLD variability shows reasonable agreement with observed seasonal stratification, though the model tends to produce overly deep winter mixing in the Labrador Sea. Sea ice seasonality is well represented, but the model overestimates the central Arctic thickness and underrepresents spatial and temporal variability in marginal ice zones. While volume transports through the Bering Strait are realistically simulated, the flows through the Fram Strait and Barents Sea Opening are underestimated. Overall, TOPAZ5 demonstrates sufficient skill in simulating large-scale hydrography and sea ice dynamics to support operational forecasting applications in the North Atlantic and Arctic.