Extreme Surface Energy Budget Anomalies in the High Arctic in Winter

In recent decades, the Arctic has warmed faster than the global mean, especially during winter. This has been attributed to various causes, with recent studies highlighting the importance of enhanced downward infrared radiation associated with anomalous inflow of warm, moist air from lower latitudes. Here, we study wintertime surface energy bud-get (SEB) anomalies over Arctic sea ice on synoptic time scales, using ERA5 (1979-2020). We introduce a new algorithm to identify areas with extreme, positive daily mean SEB anomalies and connect them to form spatiotemporal life cycle events. Most of these events are associated with large-scale inflow from the Atlantic and Paciflc Oceans, driven by pole-ward deflection of the storm track and blocks over northern Eurasia and Alaska. Events originate near the ice edge, where they have roughly equal contributions of net longwave radiation and turbulent fluxes to the positive SEB anomaly. As the events move farther into the Arctic, SEB anomalies decrease due to weakening sensible and latent heat-flux anomalies, while the surface temperature anomaly increases toward the peak of the events along with the downward longwave radia-tion anomaly. Due to these temporal and spatial differences, the largest SEB anomalies are not always related to strongest surface warming. Thus, studying temperature anomalies alone might not be sufflcient to determine sea ice changes. This study highlights the importance of turbulent fluxes in driving SEB anomalies and downward longwave radiation in deter-mining local surface warming. Therefore, both processes need to be accurately represented in climate models.SIGNIFICANCE STATEMENT: Mechanisms behind wintertime rapid Arctic warming and sea ice growth changes are not well understood. While much is known about the impact of radiative fluxes on both sea ice variability and sur-face warming, the relative importance of radiative and turbulent fluxes remains unclear. The purpose of this study is to clarify what controls surface energy budget (SEB) anomalies over sea ice. Along the life cycle of synoptic-scale events, positive SEB anomalies are shown to decrease and surface temperature anomalies increase after their onset. Addition-ally, variations in SEB anomalies are primarily controlled by turbulent fluxes, while downward longwave radiative fluxes are mainly responsible for surface temperature variations. These results highlight the need for accurate represen-tations of these fluxes for predicting future Arctic climate.