Föhn-Induced Melting over Larsen C Modulated by Atmospheric River Shape, Direction and Landfall Location

Abstract In recent decades, the Antarctic Peninsula (AP) has experienced record-high temperatures from the combined impacts of atmospheric rivers (ARs) and föhn warming. However, while ARs often amplify föhn over the AP, not all events cause surface warming over the entire Larsen C Ice Shelf (LCIS). This study uses high-resolution Polar WRF simulations to explore the relationship between ARs and föhn over the AP during austral summers, identifying four distinct AR shapes that cause föhn-induced surface warming over the LCIS: fully zonal, zonal-like, concave, and convex. Convex ARs linked to blocking highs produce the strongest föhn warming across the LCIS, particularly in its southern sections. While fully zonal ARs embedded within coupled low-high pressure systems induce comparable föhn warming, their enhanced moisture and cloud cover suppress the typical increases in downward shortwave radiation associated with föhn-driven cloud clearance. Conversely, zonal-like ARs under coupled low-high pressure systems and concave ARs under single low-pressure systems primarily make landfall over the northern AP, thereby have greater impact over the northern LCIS. With AR frequency and intensity likely to increase under climate change, their complex interplay with föhn over the AP may become a key factor in the future stability of coastal ice shelves.