Siberian snow forcing in a dynamically bias-corrected model

Abstract

We investigate the effect of systematic model biases on teleconnections influencing the Northern Hemisphere wintertime circulation. We perform a two-step nudging and bias-correcting scheme for the dynamic variables of the ECHAM6 atmospheric model to reduce errors in the model climatology relative to ERA-Interim. One result is a significant increase in the strength of the Northern Hemisphere wintertime stratospheric polar vortex, reducing errors in the December-February mean zonal stratospheric winds by up to 75%. The bias-corrections are applied to the full atmosphere or stratosphere only.We compare the response of the bias-corrected and control runs to an increase in Siberian snow cover in October - a surface forcing that, in our experiments, weakens the stratospheric polar vortex from October to December. We find that despite large differences in the vortex strength the magnitude of the stratospheric weakening is similar amongst the different climatologies, with some differences in the timing and length of the response. Differences are more pronounced in the stratosphere-troposphere coupling, and subsequent surface response. The snow forcing with the stratosphere-only bias-corrections results in a stratospheric response that is comparable to control, yet with an enhanced surface response that extends into early January. The full atmosphere bias-correction’s snow response also has a comparable stratospheric response but a somewhat suppressed surface response. Despite these differences, our results show an overall small sensitivity of the Eurasian snow teleconnection to the background climatology.