Observed Climatology and Formation Mechanisms of Sea Fog Along the Trans‐Arctic Shipping Routes.

As Arctic sea ice rapidly melts, trans‐Arctic shipping routes are emerging with significant economic value and potentially reshaping global shipping patterns. The safety of ships navigating along these routes will be severely threatened by low visibility caused by Arctic sea fog. Here, we utilize ship and coastal site observations spanning 1979–2023 to investigate the climatological features and mechanisms of Arctic sea fog from June to September. We find that the Northern Sea Route (NSR, along the Russian coast) experiences a mean fog frequency of 20.0%, significantly higher than the 11.5% fog frequency observed along the Northwest Passage (NWP, along the Canadian coast). Fog frequency shows null correlation with sea ice but a strong negative correlation (−0.80) with surface air temperature. The lower mean surface air temperature in the NSR region enhances relative humidity and atmospheric stability, which are conducive to fog formation and maintenance. We further reveal that fog formation mechanisms differ between the NSR and NWP. Along the NSR, fog is usually advection fog, associated with upper boundary layer warming and moistening; in contrast, along the NWP, fog is typically radiation fog linked to near‐surface cooling. Our study highlights the distinct fog frequency and dominant mechanisms along the different trans‐Arctic shipping routes, thereby establishing observed reference for the model validation of simulating Arctic sea fog. Plain Language Summary: The rapid retreat of Arctic sea ice, driven by climate change, has led to a gradual increase in the area of open water in the Arctic. Arctic shipping routes will soon be navigable in summer, allowing for a nearly one‐third reduction in distance from the Far East to western Europe, compared with traditional routes via the Suez Canal. In recent years, it has gradually been realized that the frequent occurrence of sea fog in the Arctic summer poses a threat to the safety and speed of Arctic shipping routes. Nevertheless, due to the sparsity of Arctic observations, the understanding of Arctic sea fog remains relatively preliminary. This paper uses multisource observation data to comprehensively investigate the climatological characteristics and formation mechanisms of Arctic sea fog, particularly highlighting their differences along the shipping routes. This work deepens our understanding of Arctic sea fog and provides a scientific observation guidance for enhancing the safety of Arctic navigation. Key Points: Fog frequency along the Northern Sea Route (NSR) is twice of that along the Northwest Passage, dominated by air temperature rather than sea iceFogs along the NSR are associated with warming and moistening at upper boundary layer, which are mostly advection fogFogs along the Northwest Passage are linked to near‐surface cooling, which are mostly radiation fog [ABSTRACT FROM AUTHOR]