The Variability of CryoSat-2 derived Sea Ice Thickness introduced by modelled vs. empirical snow thickness, sea ice density and water density

Abstract. To derive sea ice thickness (SIT) from CryoSat-2 freeboard (FB) estimates, assumptions about snow thickness, snow density, sea ice density and water density need to be made. These parameters are close to impossible to observe alongside FB, so many existing products use climatologies, or empirical values. A resent study proposed to use model parameters for snow thickness, sea ice density and water density instead. In this study, we are evaluating this values against in situ observations and the commonly used climatologies and empirical values. We show that the snow thickness and water density is in better agreement with observations, and that the sea ice density is overall too light. Analyzing the difference in SIT resulting from the model parameter vs. the empirical values, we find that the snow thickness leads to the largest differences with up to 30 cm, closely followed by the sea ice density with 20 cm. For the water density we find an up to 7.5 cm difference, which is small in comparison to the snow thickness and sea ice density, but not negligible, as most studies currently argue. We find that the origin of the assumption that water density is negligible in the FB to SIT conversion originates from a study investing the seasonal Arctic sea ice density variability, not taking into account the spacial variability. For CryoSat-2 based SIT products we recommend to either use a water density climatology, or an uncertainty value of 2.5 kgm^-3 instead of the commonly used value of 0 to 0.5 kgm^-3.