Dynamic and Thermodynamic Impacts of Atmospheric Rivers on Sea Ice Thickness in the Arctic since 2000

Abstract The Arctic has witnessed significant sea ice melt and rising temperatures as major indicators of climate system alterations. As a severe weather event conveying heat and moisture from lower latitudes to the higher, atmospheric rivers (ARs) can lead to significant sea ice loss and Arctic warming. Sea ice thickness is applied in this study to quantitatively explore the thermodynamic and dynamic impacts of ARs in winters from 2000 to 2020. ARs from the North Atlantic (AAR) and North Pacific (PAR) account for 44% of AR events and 40% of AR-driven sea ice loss. The AR-induced melting process occurs in three successive stages. In stage I, warm, moist air driven by dipole circulation anomalies ahead of AR causes sea ice melting, with thermal effects accounting for 53% for AAR and 58% for PAR. Stage II starts when the AR enters the Arctic and ends as its moisture transport weakens. Early sea ice loss is driven by wind dynamics, while poleward progression elevates warm, moist air, forming clouds that intensify melting thermodynamically. This stage sees the most significant sea ice melt, dominated by dynamic effects for AAR (59%) and thermodynamic effects for PAR (55%).In stage III, as AR moisture dissipates, sea ice melt continues for about a week, primarily driven by thermodynamic effects. Accompanied by the above three stages, the anticyclonic circulation anomaly on the right side of where AR is headed can also enhance downdrafts and melt perennial ice. By contrast, Pacific-channel ARs have a higher impact on the central Arctic than their Atlantic counterparts, suggesting extensive responses to climate variability. Significance Statement The aim of this study was to clarify the thermodynamic and dynamic effects of atmospheric rivers (ARs) on the melting of Arctic sea ice. We discovered that 44% of AR events, channeled through North Atlantic and Pacific routes, are responsible for 40% of sea ice melting. Notably, the melting process caused by ARs generally comprises three successive stages: Thermal melting is predominant in the first stage, the second stage begins when the main body of the AR enters the Arctic and leads to the most dramatic sea ice melt, which is mainly caused by dynamic effect in Atlantic sector and thermal dynamic effect in Pacific sector. In the last stage, the weakened sea ice decreases mainly caused by the thermodynamic effect with the dispersion of the AR moisture. A dipole-type circulation anomaly was found to exacerbate dynamic melting and sustain thermal melting in both the edge zone of the ice cap and the central Arctic. These findings emphasize the impact of ARs on the climate sensitivity of the Arctic region.