Improvements in September Arctic sea ice predictions via assimilation of
summer CryoSat-2 sea ice thickness observations
Abstract
Because of a spring predictability barrier, the seasonal forecast skill
of Arctic summer sea ice is limited by the availability of melt-season
sea ice thickness (SIT) observations. The first year-round SIT
observations, retrieved from CryoSat-2 from 2011–2020, are assimilated
into the GFDL ocean–sea ice model. The model’s SIT anomaly field is
brought into significantly better agreement with the observations,
particularly in the Central Arctic. Although the short observational
period makes forecast assessment challenging, we find that the addition
of May–August SIT assimilation improves September local sea ice
concentration (SIC) and extent forecasts similarly to the early addition
of SIC assimilation. Although most regional forecasts are improved by
SIT assimilation, the Chukchi Sea forecasts are degraded. This
degradation is likely due to the introduction of negative correlations
between September SIC and earlier SIT introduced by SIT assimilation,
contrary to the increased correlations found in other regions.