Talk by Max Stevens from University of Washington

Comparing firn model predictions using the Community Firn Model and the role of field measurements in developing next-generation firn models

Firn densification models are needed (1) to determine the gas-age ice-age offset for ice-core data analysis and (2) to correct altimetry-derived estimates of ice-sheet mass balance 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. The model package also includes a firn-air model which allows users to simulate the effects of transient firn changes on gas transport. Here, we use the CFM to inter-compare firn-model predictions using data from ice-cores and regional climate models. Additionally, we have begun to gather data from a network of in situ strain gauges at eight different sites in Greenland and compare measured compaction rates to model predictions. Many of the firn-densification 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.