Medium-range predictability of early summer sea ice thickness distribution in the East Siberian Sea based on the TOPAZ4 ice–ocean data assimilation system

摘要

Accelerated retreat ofArctic Ocean summertime sea ice has focused attention on the potential use ofthe Northern Sea Route (NSR), for which sea ice thickness (SIT) informationis crucial for safe maritime navigation. This study evaluated themedium-range (lead time below 10 days) forecast of SIT distribution in theEast Siberian Sea (ESS) in early summer (June–July) based on the TOPAZ4ice–ocean data assimilation system. A comparison of the operational modelSIT data with reliable SIT estimates (hindcast, satellite and in situ data)showed that the TOPAZ4 reanalysis qualitatively reproduces the tongue-likedistribution of SIT in ESS in early summer and the seasonal variations.Pattern correlation analysis of the SIT forecast data over 3 years(2014–2016) reveals that the early summer SIT distribution is accuratelypredicted for a lead time of up to 3 days, but that the prediction accuracydrops abruptly after the fourth day, which is related to a dynamical processcontrolled by synoptic-scale atmospheric fluctuations. For longer lead times( >  4 days), the thermodynamic melting process takes over, whichcontributes to most of the remaining predictionaccuracy. In July 2014, during which an ice-blocking incident occurred,relatively thick SIT ( ∼  150 cm) was simulated over the ESS, which isconsistent with the reduction in vessel speed. These results suggest thatTOPAZ4 sea ice information has great potential for practical applications insummertime maritime navigation via the NSR.