Changes in Greenland firn densification from extended IMAU-FDM runs (1939-2023)

Firn densification turns snow into glacial ice. At the surface of ice sheets, ice caps, and glaciers, firn modulates the interaction between atmosphere and ice, and is in turn affected by temperature, precipitation, wind, deposition, and ice dynamics. As climatic factors vary, the rate of firn densification changes even as the mass stays constant. These densification rates are used to correct satellite altimetry measurements of mass balance across the Greenland and Antarctic Ice Sheets. The IMAU Firn Densification Model (IMAU-FDM) is a 1D, semi-empirical model that simulates the evolution of snow grain size, firn density, firn air content, temperature, and liquid water content commonly used for continent-wide altimetry corrections. We will present the results of the FDM from an extended timeseries (1939-2023) and updated forcing (ERA5-forced RACMO2p3.2), along with a toolkit for post-processing and using the output. We show the impact of longer-term forcing changes the overall firn air content and densification rates, and the effects of a longer, earlier spinup period.