Sublimation on the Greenland Ice Sheet from automated weather station observations

Greenland Climate Network (GC-Net) surface meteorological observations are used to estimate net surface water vapor flux at ice sheet sites. Results from aerodynamic profile methods are compared with eddy correlation and evaporation pan measurements. Two profile method types are applied to hourly data sets spanning 1995.4 to 2000.4. One method type is shown to accurately gauge sublimation using two humidity and wind speed measurement levels. The other "bulk" method type is shown to underestimate condensation, as it assumes surface saturation. General climate models employ bulk methods and, consequently, underestimate deposition. Loss of water vapor by the surface predominates in summer at lower elevations, where bulk methods agree better with two-level methods. Annual net water vapor flux from the two-level method is as great as -87 ±27 mm at 960 m elevation and -74 ±23 mm at equilibrium line altitude in western Greenland. At an undulation trough site, net deposition is observed (+40 mm ±12). At the adjacent crest site 6 km away and at 50 m higher elevation, net sublimation predominates. At high-elevation sites, the annual water vapor flux is positive, up to +32 ±9 mm at the North Greenland Ice core Project (NGRIP) and +6 ±2 mm at Summit. Sublimation is mapped using trend surface fits to calculated sublimation in terms of elevation and latitude. The resulting ice sheet total sublimation is -0.62 ± 0.25 × 10¹⁴ kg yr^-1 for the two-level profile method and -1.2 ± 0.65 × 10¹⁴ kg yr^-1 for the one-level method, indicating 12% or 23% precipitation loss, respectively. Monthly, seasonal, and annual sublimation grids and the mapping functions are available on the internet at http://cires.colorado.edu/steffen.