Comparing measured and modeled firn compaction rates in Greenland

Abstract:

Quantifying the mass balance of the Greenland and Antarctic ice sheets using satellite and/or airborne altimetry requires a firn-densification model to correct for firn-air content and transient firn-thickness changes. We have developed the Community Firn Model (CFM) that allows users to run firn-densification physics from a suite of published models. Here, we use the CFM to compare model-predicted firn depth-density profiles and compaction rates with observed profiles and compaction rates collected from a network of in situ strain gauges at eight different sites in Greenland. Additionally, we use regional-climate-model output to force the CFM and compare the depth-density profiles and compaction rates predicted by the different models. Many of the models were developed using a steady-state assumption and were tuned for the dry-snow zone. Our results demonstrate the challenges of using these models to simulate firn density in Greenland’s expanding wet firn and percolation zones, and they help quantify the uncertainty in firn-density model predictions. Next-generation firn models are incorporating more physics (e.g. meltwater percolation and grain growth), and field measurements are essential to inform continuing development of these new models.