More Realistic Intermediate Depth Dry Firn Densification in the Energy Exascale Earth System Model (E3SM). (5th March 2022)

• Record Type: Journal Article
• Authors: Schneider, Adam M.; Zender, Charles S.; Price, Stephen F.
• Is Part Of: Journal of advances in modeling earth systems. Volume 14:Number 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-05
• Subjects: firn densification -- Earth system model -- snow metamorphism -- ice sheets -- surface mass balance -- firn air content; Geological modeling -- Periodicals; Climatology -- Periodicals; Geochemical modeling -- Periodicals; 551.5011
• DOI: 10.1029/2021MS002542
• Languages: English
• ISSNs: 1942-2466

Abstract

Abstract: Earth system models account for seasonal snow cover, but many do not accommodate the deeper snowpack on ice sheets (aka firn) that slowly transforms to ice under accumulating snowfall. To accommodate and resolve firn depths of up to 60 m in the Energy Exascale Earth System Model's land surface model (ELM), we add 11 layers to its snowpack and evaluate three dry snow compaction equations in multi‐century simulations. After comparing results from ELM simulations (forced with atmospheric reanalysis) with empirical data, we find that implementing into ELM a two‐stage firn densification model produces more accurate dry firn densities at intermediate depths of 20–60 m. Compared to modeling firn using the equations in the (12 layer) Community Land Model (version 5), switching to the two‐stage firn densification model (with 16 layers) significantly decreases root‐mean‐square errors in upper 60 m dry firn densities by an average of 41 kg m −3 (31%). Simulations with three different firn density parameterizations show that the two‐stage firn densification model should be used for applications that prioritize accurate upper 60 m firn air content (FAC) in regions where the mean annual surface temperature is greater than roughly −31°C. Because snow metamorphism, firn density, and FAC are major components in modeling ice sheet surface albedo, melt water retention, and climatic mass balance, these developments advance broader efforts to simulate the response of land ice to atmospheric forcing in Earth system models. Plain Language Summary: Massive ice sheets cover Earth's largest island (Greenland) and the Antarctic continent. A large fraction of their surfaces consists of multi‐year snow, known as firn, which goes through the process of densification after falling from the atmosphere. Until now this fundamental process in glaciology has yet to be accounted for in the U.S. Department of Energy's Earth System Model (E3SM). Here, we enhance E3SM's snowpack model to accommodate greater firn depths on ice sheets. Our results demonstrate a new capability in an Earth system model, that is, calculating firn density as deep as 60 m below the surface. Our developments in E3SM combine both seasonal snow and firn processes to advance broader efforts toward simulating ice sheet evolution and sea level rise in Earth system models. Key Points: We intercompare three snow density parameterizations and their effects on firn simulated in Energy Exascale Earth System Model's land model (ELM) Incorporating a two‐stage firn densification model into ELM improves densities at depths of 20–60 m Applied to Greenland and Antarctica, improving 20–60 m depth dry firn density decreases firn air content by more than 20%