Journal Article

Strong Summer Atmospheric Rivers Trigger Greenland Ice Sheet Melt through Spatially Varying Surface Energy Balance and Cloud Regimes

Van Tricht, Kristof, Fettweis, Xavier, Pettersen, Claire, Fausto, Robert S., van As, Dirk, Mattingly, Kyle S., Mote, Thomas L., Lhermitte, Stef

2020

Overview

Mass loss from the Greenland Ice Sheet (GrIS) has accelerated over the past two decades, coincident with rapid Arctic warming and increasing moisture transport over Greenland by atmospheric rivers (ARs). Summer ARs affecting western Greenland trigger GrIS melt events, but the physical mechanisms through which ARs induce melt are not well understood. This study elucidates the coupled surface–atmosphere processes by which ARs force GrIS melt through analysis of the surface energy balance (SEB), cloud properties, and local- to synoptic-scale atmospheric conditions during strong summer AR events affecting western Greenland. ARs are identified in MERRA-2 reanalysis (1980–2017) and classified by integrated water vapor transport (IVT) intensity. SEB, cloud, and atmospheric data from regional climate model, observational, reanalysis, and satellitebased datasets are used to analyze melt-inducing physical processes during strong, >90th percentile “AR90+” events. Near AR “landfall,” AR90+ days feature increased cloud cover that reduces net shortwave radiation and increases net longwave radiation. As these oppositely signed radiative anomalies partly cancel during AR901 events, increased melt energy in the ablation zone is primarily provided by turbulent heat fluxes, particularly sensible heat flux. These turbulent heat fluxes are driven by enhanced barrier winds generated by a stronger synoptic pressure gradient combined with an enhanced local temperature contrast between cool over-ice air and the anomalously warm surrounding atmosphere. During AR90+ events in northwestGreenland, anomalousmelt is forced remotely through a clear-sky foehn regime produced by downslope flow in eastern Greenland.

• Publisher: American Meteorological Society
• Subject: Ablation / Aerodynamics / Air temperature / Anomalies / Atmosphere / Atmospheric conditions / Atmospheric data / Barrier winds / Climate models / Cloud cover / Cloud properties / Clouds / Computational fluid dynamics / Earth sciences & physical geography / Energy balance / Enthalpy / Foehn / Glaciation / Greenland ice sheet / Heat / Heat flux / Heat transfer / Ice sheets / Long wave radiation / Physical, chemical, mathematical & earth Sciences / Physique, chimie, mathématiques & sciences de la terre / Pressure gradients / Radiation / Regional climate models / Regional climates / Satellite observation / Sciences de la terre & géographie physique / Sensible heat / Sensible heat flux / Sensible heat transfer / Short wave radiation / Summer / Surface energy / Surface energy balance / Surface properties / Transport / Water vapor / Water vapor transport / Water vapour / Winds