Abstract
The fluctuation statistics of the observed sea-ice extent during the satellite era are compared with model output from CMIP5 models using a multifractal time series method. The two robust features of the observations are that on annual to biannual time scales the ice extent exhibits white noise structure, and there is a decadal scale trend associated with the decay of the ice cover. It is shown that (i) there is a large inter-model variability in the time scales extracted from the models, (ii) none of the models exhibits the decadal time scales found in the satellite observations, (iii) five of the 21 models examined exhibit the observed white noise structure, and (iv) the multi-model ensemble mean exhibits neither the observed white noise structure nor the observed decadal trend. It is proposed that the observed fluctuation statistics produced by this method serve as an appropriate test bed for modelling studies.This article is part of the theme issue ‘Modelling of sea-ice phenomena’.
Highlights
Polar amplification and the ice–albedo feedback focus scientific study on the fluctuations in the areal coverage of high latitude ice
We studied the Arctic equivalent sea-ice extent (EIE), where the EIE is defined as the total surface area, including land, north of the zonal-mean ice edge latitude and is proportional to the sine of the ice edge latitude [11]. (By studying the EIE one minimizes coastal effects.) We find that the EIE is a multifractal in time [10]
The nature and number of figures are such that the majority of the results are presented in appendix A, and here we summarize the key features, which are (i) large inter-model variability in the crossover time scales extracted from the models, (ii) none of the models exhibit the decadal time scales found in the satellite observations, and (iii) only five (CNRM-CM5, Meteorological Research Institute (MRI)-CGCM3, MRI-ESM1, FGOALS-g2, MIROC version 5 (MIROC5)) of the 21 models exhibit the white noise structure observed in the satellite record on annual to biannual time scales
Summary
Polar amplification and the ice–albedo feedback focus scientific study on the fluctuations in the areal coverage of high latitude ice. By area, on average the Southern Hemisphere ice cover is dominated by the Antarctic ice sheet, whereas in the Northern Hemisphere, the.
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