[ESS Candidate Seminar] Aschwanden on "Using observations to validate ice sheet models"

Start Date/Time: Thursday, April 11, 2013, 11:30 AM
Ending Date/Time: Thursday, April 11, 2013, 12:30 PM
Location: ATG 154 (near Seismo Lab in the basement)

Andy Aschwanden, Univ. of Alaska Fairbanks, is the first of three candidates for the ESS Research Assistant Prof position.

Title: Using observations to validate ice sheet models


In 2007 the Intergovernmental Panel for Climate Change excluded sea-level rise predictions from numerical ice sheet models due to their inability to simulate recent changes in ice sheet margins and ice streams. This triggered a concerted effort to both improve existing models and to develop a new generation of models.

In this talk I will discuss improvements to the model physics of the open-source Parallel Ice Sheet Model. However, the skill of a predictive ice sheet model depends not only on the implemented model physic but also on the quality of data available for testing. Testing, i.e. validation is a critical component of model development, yet notoriously challenging in ice sheet modeling. One approach to validation is hindcasting, i.e. forcing a model with known or closely-estimated inputs for past events and comparing model results to time-dependent observations. In other words I ask the question: "How successful is the state-of-the art Parallel Ice Sheet Model (PISM) in reproducing observed changes over the last two decades?'' I show that PISM reproduces some observations while struggling with others. This exercise highlights the importance of observation-based validation to reduce the uncertainty in projections of sea level rise.

Speaker Bio: Following his PhD at Institute for Atmospheric and Climate Science at ETH in Zurich, Andy Aschwanden is now a postdoc at University of Alaska Fairbanks, where he is a prime force behind PISM, the open-source Parallel Ice Sheet Model. In addition to continuing to develop the model, Andy insists on testing the model against data. Recently he has worked on prediction of sea-level rise due to ice melt for the upcoming IPCC AR5.