Comment on tc-2023-69

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Winter warm air intrusions entering the Arctic ocean can strongly modify the microwave emission of the snow/ice system due to temperature induced snow metamorphism and ice crust formations e.g., after melt-refreeze events. Common microwave radiometer satellite sea ice concentration retrievals are based on empirical models using the snow/ice emissivity and thus can be influenced by strong warm air intrusions. Here, we carry out a long-term study analyzing 41 years of sea ice concentration observations from different algorithms to investigate the impact of warming events on the retrieved ice concentration. Our results show that three out of four analyzed sea ice concentration retrievals underestimate the sea ice concentration during warm air intrusions which increase the 2 m air temperature above -5 &deg;C. This can lead to sea ice area underestimations in the order of 10⁴ to 10⁵ km². If the 2 m temperature during the warm air intrusions cross -2 &deg;C, all retrieval methods are impacted. Our analysis shows that the strength of these strong warm air intrusions increased in recent years, especially in April. Within the scope of future climate change, it is expected that such warm air intrusions will occur even more frequent and also earlier in the season and thus the influence of these warm air intrusions on sea ice climatologies will become more important in future.