Polar Climate Variability, Moisture Transport, and Atmospheric Rivers

Polar regions are experiencing some of the fastest and most extreme climate changes on Earth. While most studies and discussions around climate change are about the long term warming trend, this thesis examines how climate variability and extreme events, particularly those linked to atmospheric moisture transport, influence the polar atmosphere and surface. The thesis highlights the role of narrow bands of concentrated moisture transport, called atmospheric rivers (ARs), in driving polar precipitation and surface melt.

The research combines global and regional climate models, observational data, and reanalysis products to analyze present and future polar climate variability. The new findings show that sea ice plays a crucial role in regulating the intensity of ARs as well as the local polar climate. For example, low sea ice concentrations lead to more evaporation, which increases atmospheric moisture in the lower troposphere and favours more ARs that can reach polar ice sheets or ice shelves.

Relative to the present-day climate, extreme AR events are projected to occur more frequently and with greater intensity in the future, mainly driven by the enhanced moisture-holding capacity at higher temperatures. However, the impact of ARs on sea ice and the complex local terrain of ice shelves and ice sheets remains relatively understudied and uncertain. This thesis investigates these surface impacts, and for the first time describes the vertical structure of Antarctic ARs. Modeling cloud and radiation processes remains challenging during AR events, and even high-resolution climate models with improved topography often underestimate surface melt.