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Greenland ice sheet melt is a large contributor to rising global sea level and melt is dependent on surface air temperature. Arctic temperatures are strongly coupled to clouds but spatial connections between clouds and temperature have yet to be established across Greenland. By mapping spaceborne lidar measurements and surface observations, it is shown that radiatively opaque clouds generally coincide with anomalously warm near‐surface temperatures at Greenland sites. These results indicate that both temperatures over 0^°C as well as positive daily temperature anomalies relate to spatially extensive opaque cloud cover. While prior studies indicate that clouds enhance extreme melt events, this research shows that opaque cloud cover and surface warming are closely related across the Greenland ice sheet, particularly in the ablation region. These findings establish broadly the spatial relationships between opaque clouds and temperatures and demonstrate the importance of direct observations across Greenland.

 

Ice crystals commonly adopt a horizontal orientation under certain aerodynamic and electrodynamic conditions that occur in the atmosphere. While the radiative impact of horizontally oriented ice crystals (HOIC) has been theoretically studied with respect to their impact on shortwave cloud albedo, the longwave impact remains unexplored. This work analyzes the occurrence of HOIC at Summit, Greenland, from July 2015 to June 2017. Using polarization lidar and ancillary atmospheric sensors, ice crystal orientations are identified and used to interpret cloud radiative impact on the surface radiation budget. We find HOIC occur in at least 25.6% of all ice‐only column observations. We find that the shortwave impact of HOIC is to increase cloud radiative effect by approximately 22% for a given solar zenith angle. We also find that the longwave impact of HOIC compared to randomly oriented ice crystals are statistically different at the p < 0.01 significance level, increasing the surface radiative effect by approximately 8% for clouds with infrared optical depths < ~1. We suggest that the observed difference between the surface radiative effect for clouds containing randomly oriented ice crystals and HOIC may be due to enhanced scattering, but this hypothesis needs to be further explored with more detailed observations and modeling.

 

Abstract. Snowfall is the major source of mass for the Greenland ice sheet (GrIS) but the spatial and temporalvariability of snowfall and the connections between snowfall and mass balance have so far been inadequatelyquantified. By characterizing local atmospheric circulation and utilizing CloudSat spaceborne radarobservations of snowfall, we provide a detailed spatial analysis of snowfall variability and its relationshipto Greenland mass balance, presenting first-of-their-kind maps of daily spatial variability in snowfallfrom observations across Greenland. For identified regional atmospheric circulation patterns, we show that thespatial distribution and net mass input of snowfall vary significantly with the position and strength ofsurface cyclones. Cyclones west of Greenland driving southerly flow contribute significantly more snowfall thanany other circulation regime, with each daily occurrence of the most extreme southerly circulation patterncontributing an average of 1.66 Gt of snow to the Greenland ice sheet. While cyclones east of Greenland,patterns with the least snowfall, contribute as little as 0.58 Gt each day. Above 2 km on the ice sheet wheresnowfall is inconsistent, extreme southerly patterns are the most significant mass contributors, with up to1.20 Gt of snowfall above this elevation. This analysis demonstrates that snowfall over the interior ofGreenland varies by up to a factor of 5 depending on regional circulation conditions. Using independentobservations of mass changes made by the Gravity Recovery and Climate Experiment (GRACE), we verify that thelargest mass increases are tied to the southerly regime with cyclones west of Greenland. For occurrences of thestrongest southerly pattern, GRACE indicates a net mass increase of 1.29 Gt in the ice sheet accumulation zone(above 2 km elevation) compared to the 1.20 Gt of snowfall observed by CloudSat. This overall agreementsuggests that the analytical approach presented here can be used to directly quantify snowfall masscontributions and their most significant drivers spatially across the GrIS. While previous research hasimplicated this same southerly regime in ablation processes during summer, this paper shows that ablation massloss in this circulation regime is nearly an order of magnitude larger than the mass gain from associatedsnowfall. For daily occurrences of the southerly circulation regime, a mass loss of approximately 11 Gt isobserved across the ice sheet despite snowfall mass input exceeding 1 Gt. By analyzing the spatialvariability of snowfall and mass changes, this research provides new insight into connections between regionalatmospheric circulation and GrIS mass balance.