Contrasting Impacts and Mechanisms of Clustered versus Isolated Summer Atmospheric Rivers on Arctic Sea Ice Melt

Abstract. The rapid decline of Arctic sea ice during summer is increasingly driven by extreme atmospheric moisture transport events, primarily manifested as Atmospheric Rivers (ARs). While the link between individual ARs and localized sea ice loss is well-established, the differential impacts of their temporal distribution – specifically clustered versus isolated occurrences – remain poorly understood. This study investigates the distinct physical mechanisms through which clustered AR sequences and isolated AR events modulate the Arctic surface energy budget and subsequent sea ice retreat.Using high-resolution ERA5 reanalysis data and satellite-derived sea ice concentrations, we identify a paradigm shift in sea ice response depending on AR frequency. Clustered ARs, characterized by successive moisture pulses, induce a "persistent warming effect." This sequence prevents the typical nocturnal radiative cooling and maintains the ice surface skin temperature at the melting point (273.15 K) for extended periods. In contrast, isolated ARs, despite potentially higher peak intensities, often result in transient melting followed by partial thermodynamic recovery. Our analysis reveals that clustered ARs trigger a more potent ice-albedo feedback; the sustained downward longwave radiation (DLR) and latent heat fluxes during clustered events lead to a stepwise reduction in surface albedo that persists long after the moisture pulses subside.Quantitatively, clustered events are associated with a significantly higher number of cumulative melt days and a more profound reduction in net energy gain compared to isolated counterparts of similar total moisture transport volume. These findings suggest that the temporal clustering of ARs is a critical factor in determining the severity of summer sea ice minima, providing a new perspective on the atmospheric driving of the rapidly changing Arctic cryosphere.