Joint Seminar: Arctic sea ice melt season length in the CESM Large Ensemble

Melt season length—the difference between the sea ice melt onset date and the sea ice freeze onset date—plays an important role in the radiation balance of the Arctic and the predictability of the sea ice cover. There are multiple possible definitions for sea ice melt and freeze onset in the CESM Large Ensemble, and none of them exactly correspond to the remote sensing definition. We first show how the mismatch between model and remote sensing definitions of melt and freeze onset limits the utility of melt season remote sensing data for bias detection in models. Then, by using the CESM Large Ensemble, we account for the role of internal variability, allowing us to assess the comparability of different melt and freeze onset definitions.  

In the CESM Large Ensemble, we find that the increase in melt season length is not as large as that derived from remote sensing data, even when we account for internal variability and different definitions. At the same time, we find that the CESM ensemble members with September sea ice most sensitive to global warming over the period 1979-2014 also have the largest melt season trend, driven primarily by the trend towards later freeze onsets. Our analysis explores the hypothesis that an underestimation of the melt season length trend is one factor contributing to the generally underestimated sea ice sensitivity in the CESM.




13:30 h


Bundesstr. 53, room 101/102
Seminar Room 101/102, 1st floor, Bundesstr. 53, 20146 Hamburg, Hamburg


Abigail Ahlert, University of Colorado Boulder


Dirk Notz

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