Role of atmospheric rivers in regulating moisture changes in the Arctic and their relationship with sea ice

Details

Supervisors

Fichefet, Thierry

Faculty

Faculté des sciences

Degree label

Master [120] en sciences physiques, à finalité approfondie

Abstract

enThis master’s thesis examines the influence of atmospheric rivers (ARs) on Arctic mois- ture and subsequently their influence on early-winter (November-February) sea ice vari- ability. ARs are thin, elongated structures that transport moisture and heat into the Arctic via the North Atlantic and Pacific. These events influence sea ice through ther- modynamic pathways, primarily by increasing specific humidity, downwelling longwave radiation and surface temperature through cloud formation, and dynamic mechanisms such as wind-driven ice redistribution and the formation of leads. The interactions are quantified using ERA5 reanalysis data and satellite-based sea ice concentration (SIC) observations from 1979-2023. Pearson correlations and Maximum Covariance Analysis (MCA) are applied. The results show a significant increase of AR frequency over the Barents-Kara (BK) Sea which shows a significant anti-correlation with regional sea ice extent (r = −0.47). The first mode of MCA accounts for 58.2% of the squared covariance and represents a strong coupling of increased AR activity over the Eurasian Arctic with local ice concentration reductions. Moreover, the physical variables analysis also confirms that the radiative forcing at the surface is enhanced by the AR intrusions and thus inhibits the seasonal sea ice recovery. This process is demonstrated through a case study of an event in November 2023, which shows how a series of intense ARs can cause a brief pause in autumnal sea ice growth. Overall, results suggest a significant contribution of ARs in the Arctic and a critical role of ARs to determine the long-term decline of winter sea ice.