ARTofMELT spring 2023 expedition: Investigating the Arctic sea ice melt onset in the context of climatology and atmospheric circulation

Processes controlling the timing of the Arctic sea ice melt onset still remain unclear, but possible factors include variations in atmospheric circulation patterns and anomalies in clouds, moisture and surface energy budget, all of which are linked to narrow bands of warm and moist-air advection. These filaments, accounting for the majority of the poleward moisture transport, are called Atmospheric Rivers (ARs). Although spring is an important transition period for the sea ice evolution, there are hardly any in-situ observations in the Arctic Ocean for that period. To narrow down the knowledge gaps, the ARTofMELT expedition took place on the Swedish research Icebreaker Oden in the Fram Strait in May-June 2023 with two main objectives: to study processes leading up to the melt onset of Arctic sea ice and to investigate the role of ARs in affecting this timing. This study is motivated by the ARTofMELT expedition, during which the observed surface temperature exceeded the melting point on the 10^th of June 2023 – much later than expected. Questions raised were “was this an anomalously late melt onset?” and “if yes, why?”. To address these questions, we put the year 2023 into a climatological (1981-2020) perspective by linking satellite-derived melt-onset (MO) dates with large-scale circulation features. Due to lack of MO-dates along the track in June 2023, the location of Oden during ARTofMELT is represented by a “Fram Strait sector”. Years are categorized into early and late MO-years based on the relative number of significant MO-anomalies within the sector.

The melt onset timing in the sector within the climatological period has a significant negative trend of -5 days in 10 years. In spring 2023, the average melt onset occurs on 8 June, corresponding to a MO-anomaly of almost 2 weeks relative to a transient climatology. As nearly 60 % of all grid-points obtain significant positive MO-anomalies and only a negligible fraction has significant negative MO-anomalies, we conclude that the melt onset in the sector region during ARTofMELT in spring 2023 was anomalously late.

The period before the MO in the sector was characterized by significant negative SLP anomalies over the whole Arctic Ocean and positive anomalies in SLP and atmospheric blocking over Eurasia. These circulation anomalies were associated with a strong cyclonic activity along the sea ice edge, directing warm and moist air, and most of the ARs, east of Svalbard into the BKS region – leading to an early MO there. The central Arctic Ocean was anomalously dry. The circulation patterns weakened and rather normal conditions prevailed during the MO period in the Fram Strait, where the MO was finally triggered by a transient AR on 10 June 2023.

Analysis between six most extreme early and late MO-years reveal that specific circulation patterns favoring moist and warm air transport towards and the occurrence of ARs within the Fram Strait sector are of more importance in determining the timing of MO for extreme early MO-years, whereas extreme late MO-years seem to be due to an absence of such large-scale features.