Moving beyond the Total Sea Ice Extent in Gauging Model Biases

TitleMoving beyond the Total Sea Ice Extent in Gauging Model Biases
Publication TypeJournal Article
Year of Publication2017
AuthorsIvanova, Detelina, Gleckler Peter J., Taylor Karl E., Durack Paul J., and Marvel Kate
JournalJournal of Climate
Volumeearly release online
Pages23
Date Published12/2016
Abstract / Summary

This study describes several approaches to improve how model biases in total sea ice distribution are quantified, and applies them to historically forced simulations contributed to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The quantity of hemispheric total sea ice area, or some measure of its Equator-ward extent, is often used to evaluate model performance. A new approach is introduced that investigates additional details about the structure of model errors, with an aim to reduce the potential impact of compensating errors when gauging differences between simulated and observed sea ice. Using multiple observational data sets, several new methods are applied to evaluate the climatological spatial distribution and the annual cycle of sea ice cover in 41 CMIP5 models. It is shown that in some models, error compensation can be substantial, for example resulting from too much sea ice in one region and too little in another. Error compensation tends to be larger in models that agree more closely with the observed total sea ice area, which may result from model tuning. The results herein suggest that consideration of only the total hemispheric sea ice area or extent can be misleading when quantitatively comparing how well models agree with observations. Further work is needed to fully develop robust methods to holistically evaluate the ability of models to capture the finescale structure of sea ice characteristics; however, the ‘‘sector scale’’ metric used here helps reduce the impact of compensating errors in hemispheric integrals.

Journal: Journal of Climate
Year of Publication: 2017
Volume: early release online
Pages: 23
Date Published: 12/2016

This study describes several approaches to improve how model biases in total sea ice distribution are quantified, and applies them to historically forced simulations contributed to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The quantity of hemispheric total sea ice area, or some measure of its Equator-ward extent, is often used to evaluate model performance. A new approach is introduced that investigates additional details about the structure of model errors, with an aim to reduce the potential impact of compensating errors when gauging differences between simulated and observed sea ice. Using multiple observational data sets, several new methods are applied to evaluate the climatological spatial distribution and the annual cycle of sea ice cover in 41 CMIP5 models. It is shown that in some models, error compensation can be substantial, for example resulting from too much sea ice in one region and too little in another. Error compensation tends to be larger in models that agree more closely with the observed total sea ice area, which may result from model tuning. The results herein suggest that consideration of only the total hemispheric sea ice area or extent can be misleading when quantitatively comparing how well models agree with observations. Further work is needed to fully develop robust methods to holistically evaluate the ability of models to capture the finescale structure of sea ice characteristics; however, the ‘‘sector scale’’ metric used here helps reduce the impact of compensating errors in hemispheric integrals.

Citation:
Ivanova, D, PJ Gleckler, KE Taylor, PJ Durack, and K Marvel.  2017.  "Moving beyond the Total Sea Ice Extent in Gauging Model Biases."  Journal of Climate early release online: 23.