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

• Published in: Journal of Climate
• Main Authors: Mattingly, K., Mote, T., Fettweis, Xavier, van As, D., Van Tricht, K., Lhermitte, S., Pettersen, C., Fausto, R.
• Other Authors: Sphères - SPHERES
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Meteorological Society 2020
• Subjects: Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; Greenland; Ice Sheet
• Online Access: https://orbi.uliege.be/handle/2268/248320; https://orbi.uliege.be/bitstream/2268/248320/1/jcli-d-19-0835.1.pdf; https://doi.org/10.1175/JCLI-D-19-0835.1

peer reviewed 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 affect- ing western Greenland trigger GrIS melt events, but the physical mechanisms through which ARs induce melt are not well understood. This study elu- cidates 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 reanal- ysis (1980–2017) and classified by integrated water vapor transport (IVT) intensity. SEB, cloud, and atmospheric data from regional climate model, observational, reanalysis, and satellite-based 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 re- duces net shortwave radiation and increases net longwave radiation. As these oppositely-signed radiative anomalies partly cancel during AR90+ events, in- creased 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 northwest Greenland, anomalous melt is forced remotely through a clear-sky foehn regime produced by down-slope flow in eastern Greenland.