Abigail Ahlert (Abigail.Ahlert[@]colorado.edu) and Julienne Stroeve (stroeve[@]nsidc.org).
The scientific questions that will be studied:
-How best to define ice advance and retreat in model and observational studies for the Arctic? For the Antarctic?
-What sea ice concentration threshold should be used for ice retreat/advance calculations?
-How well do models capture the timing of ice advance and ice retreat in the Arctic? In the Antarctic?
-How do ice advance and retreat impact ocean heat content, ice extent and volume?
-Can we use the timing of ice advance and retreat to improve predictability of ice extent?
-What is the role of internal variability in ice advance and retreat?
The processes that will be investigated:
-Mechanisms through which ice advance and retreat impact ice extent and volume (ice-albedo feedback; ocean heat content; ocean heat transport; wave-ice interaction)
-Processes driving ice retreat (melt onset, atmospheric and oceanic circulation)
-Internal variability
-Comparison methods between model projections and satellite observations
The type of analyses that will be conducted:
-Analysis of daily CMIP6 sea ice concentrations, thickness, volume, ocean heat content
-Analysis of large ensembles
-Analysis of daily satellite sea ice concentrations, ice thickness, ocean heat content (SSTs, buoy)
-Development of a passive microwave satellite emulator to provide more direct comparisons between model projections and satellite-derived sea ice concentration data products
References to earlier works
Kay, J. E. et al. The community earth system model (CESM) large ensemble project : A community resource for studying climate change in the presence of internal climate variability. (2015). Bulletin of the American Meteorological Society. 96, 1333–1349. doi:10.1175/BAMS-D-13-00255.1
Markus, T. et al. Recent changes in Arctic sea ice melt onset, freezeup, and melt season length. (2009). Journal of Geophysical Research: Oceans. 114, 1-14. doi:10.1029/2009JC005436
Serreze, M.C., A.D. Crawford, J.C. Stroeve, A.P. Barrett and R.A. Woodgate (2016), Variability, trends and predictability of seasonal sea ice retreat and advance in the Chukchi Sea, J. Geophys. Res.-Oceans.,
Stammerjohn, S., R. Massom, D. Rind, and D. Martinson. Regions of rapid sea ice change: An inter-hemispheric seasonal comparison. (2012). Geophysical Research Letters. 39, L06501,doi:10.1029/2012GL080874.
Stroeve, J., A. Crawford and S. Stammerjohn (2016), Using timing of ice retreat to predict timing of fall freeze-up in the Arctic, Geophys. Res. Lett., doi:10.1002/2016GL069314.
Stroeve et al. Changes in Arctic melt season and implications for sea ice loss. (2014). Geophysical Research Letter. 41, 1216–1225.

• Different melt and freeze onset definitions based on model variables showed that no single definition fully captures satellite observations of melt season characteristics.
Paper: Smith, A. and Jahn, A. (2019), Definition differences and internal variability affect the simulated Arctic sea ice melt season, The Cryosphere, 13, 1–20, https://doi.org/10.5194/tc-13-1-2019.

• Using statistical models to relate the timing of sea ice retreat to timing of ice advance in the Arctic.
Paper: Stroeve, J. C., Crawford, A. D., and Stammerjohn, S. ( 2016), Using timing of ice retreat to predict timing of fall freeze‐up in the Arctic, Geophys. Res. Lett., 43, 6332– 6340, doi:10.1002/2016GL069314.)

• Analysis of CMIP6 melt season characteristics is under way (Smith et al., in preparation)