5:15 PM - 6:30 PM
[ACG39-P13] Summer snow/ice surface melt based on the surface energy balance analysis at SIGMA-B site on Qaanaaq Ice Cap, northwestern Greenland
Keywords:Greenland ice sheet, surface energy balance, snow/ice melt
The Greenland Ice Sheet (GrIS) and its peripheral ice caps have been losing their masses rapidly for the past two decades. Especially, the acceleration of a mass loss in some ice caps is more distinguished than that of GrIS (Noël et al., 2017). To understand its current condition and the existing mechanism of the Greenland Ice Caps, it is crucial to analyze surface energy balance based on observed meteorological data. This study investigates summer surface energy balance at the SIGMA-B site located in northwestern Greenland to clarify characteristics of surface melt estimated by surface energy balance and the controlling factors of each energy component.
The meteorological observation has been conducted with an automatic weather station (AWS) at the SIGMA-B site (77° 31’ N, 69° 04’ W, 944 m a.s.l.) on Qaanaaq Ice Cap located in northwestern Greenland. The observation site is located near the equilibrium line of Qaanaaq Ice Cap (Aoki et al. 2014). The meteorological variables observed at SIGMA-B are air temperature, relative humidity, wind direction, wind speed, air pressure, incoming and reflected shortwave radiation, downward and upward longwave radiation, and snow height. All these meteorological variables are recorded hourly. The surface energy balance analysis was conducted using the dataset between August 2012 and August 2020. The longwave-equivalent cloudiness (Nε) (Conway et al., 2015) was calculated in order to clarify the cloud effect on the surface energy balance.
Higher accumulated amounts of estimated JJA (June, July, and August) surface melt during the study period were 1250 mm w.e. (2019), 1179 mm w.e. (2015), and 1032 mm w.e. (2020). For these years, 52.0% (2019), 76.7% (2015), and 69.7% (2020) of JJA accumulated surface melt occurred in July. In 2019, the highest August surface melt of 394 mm w.e. (31.5% of the JJA surface melt) during the study period was estimated.
The remarkably decreased albedo was observed in the periods described above (July 2015, August 2019, and July 2020). In addition, Nεs in July 2015 and July 2020 were lower than those estimated in other years. Therefore, it can be considered that decreased surface albedo and the less occurrence of a cloud cover induced a large amount of surface melt in those periods.
The meteorological observation has been conducted with an automatic weather station (AWS) at the SIGMA-B site (77° 31’ N, 69° 04’ W, 944 m a.s.l.) on Qaanaaq Ice Cap located in northwestern Greenland. The observation site is located near the equilibrium line of Qaanaaq Ice Cap (Aoki et al. 2014). The meteorological variables observed at SIGMA-B are air temperature, relative humidity, wind direction, wind speed, air pressure, incoming and reflected shortwave radiation, downward and upward longwave radiation, and snow height. All these meteorological variables are recorded hourly. The surface energy balance analysis was conducted using the dataset between August 2012 and August 2020. The longwave-equivalent cloudiness (Nε) (Conway et al., 2015) was calculated in order to clarify the cloud effect on the surface energy balance.
Higher accumulated amounts of estimated JJA (June, July, and August) surface melt during the study period were 1250 mm w.e. (2019), 1179 mm w.e. (2015), and 1032 mm w.e. (2020). For these years, 52.0% (2019), 76.7% (2015), and 69.7% (2020) of JJA accumulated surface melt occurred in July. In 2019, the highest August surface melt of 394 mm w.e. (31.5% of the JJA surface melt) during the study period was estimated.
The remarkably decreased albedo was observed in the periods described above (July 2015, August 2019, and July 2020). In addition, Nεs in July 2015 and July 2020 were lower than those estimated in other years. Therefore, it can be considered that decreased surface albedo and the less occurrence of a cloud cover induced a large amount of surface melt in those periods.