Surface energy exchange at the equilibrium line on the Greenland ice sheet during onset of melt

Abstract

The energy balance was measured at the ETH/CU research camp, located at the equilibrium-line altitude of the Greenland ice sheet (69°34′N, 49°17′W), in spring 1993. Prior to the onset of melt the latent energy flux is the only energy sink, with an average value of 1.18 MJ m ⁻²d ⁻¹. This turbulent transfer of moisture is responsible for an average daily snow sublimation of 5 × 10 ⁻⁴ m. The sensible heat flux (0.91 MJ m ⁻²d ⁻¹) is the major energy source, and the net radiation only a minor contributor with a positive balance of 0.12 MJ m ⁻²d ⁻¹. The residual of the turbulent fluxes and the net radiation is about 0.14 MJ m ⁻²d ⁻¹, which agrees surprisingly well with the in situ ground-heat flux measurements of 0.15 MJ m ⁻²d ⁻¹ made at the same location. Assuming a 3°C temperature increase in a global-change scenario, and using the information gained from the energy-balance measurements, a simple calculation showed that 5.4 × 10 ⁻² m w.e. of snow would be lost by sublimation for an area of approximately 400 000 km ². The increased sublimation is due to an increase in the net radiation balance caused by an albedo reduction. This would lead to a total annual mass reduction of 22 km ³ w.e. of snow for the entire Greenland ice sheet, which is 4.2% of today’s annual accumulation.