Increasing frequency and duration of Arctic winter warming events

Near-surface air temperatures close to 0°C were observed in situ over sea ice in the central Arcticduring the last three winterseasons. Here we use in situ winter(December–March) temperature observations, such as those from Soviet North Pole drifting stations and ocean buoys, to determine how common Arctic winterwarming events are. Observations of winterwarming events exist over most of the ArcticBasin. Temperatures exceeding -5°C were observed during >30% of wintersfrom 1954 to 2010 by North Pole drifting stations or ocean buoys. Using the ERA-Interim record (1979–2016), we show that the North Pole (NP) region typically experiences 10 warming events (T2m > 10°C) per winter, compared with only five in the Pacific Central Arctic(PCA). There is a positive trend in the overall duration of winterwarming events for both the NP region (4.25 days/decade) and PCA (1.16 days/decade), due to an increased number of events of longer duration.