Abstract
Arctic warming was more pronounced than warming in midlatitudes in the last decades making this region a hotspot of climate change. Associated with this, a rapid decline of sea-ice extent and a decrease of its thickness has been observed. Sea-ice retreat allows for an increased transport of heat and momentum from the ocean up to the tropo- and stratosphere by enhanced upward propagation of planetary-scale atmospheric waves. In the upper atmosphere, these waves deposit the momentum transported, disturbing the stratospheric polar vortex, which can lead to a breakdown of this circulation with the potential to also significantly impact the troposphere in mid- to late-winter and early spring. Therefore, an accurate representation of stratospheric processes in climate models is necessary to improve the understanding of the impact of retreating sea ice on the atmospheric circulation. By modeling the atmospheric response to a prescribed decline in Arctic sea ice, we show that including interactive stratospheric ozone chemistry in atmospheric model calculations leads to an improvement in tropo-stratospheric interactions compared to simulations without interactive chemistry. This suggests that stratospheric ozone chemistry is important for the understanding of sea ice related impacts on atmospheric dynamics.
Highlights
In recent decades, Arctic winter temperature has risen at more than double the rate of lower latitudes[1,2,3] accompanied with a strong reduction of Arctic sea-ice extent[4] and decreased sea-ice thickness[5]
During low-ice conditions (LICE) conditions ERA-Interim reanalysis data shows enhanced upward wave propagation from the troposphere into the stratosphere that causes a disturbance of the stratospheric polar vortex, which leads to downward propagating signals in the dynamical atmospheric variables
This process influences tropospheric circulation patterns like the North Atlantic Oscillation (NAO), impacting the daily weather patterns of the midlatitudes. This mechanism can not be fully reproduced by the atmospheric general circulation model (AGCM) ECHAM6, which does not respond with a negative phase shift of the NAO during LICE conditions
Summary
Arctic winter temperature has risen at more than double the rate of lower latitudes[1,2,3] accompanied with a strong reduction of Arctic sea-ice extent[4] and decreased sea-ice thickness[5]. Advection of warm air leads to a reduction of Arctic sea ice and an increased transport of heat and momentum into the atmosphere in fall and winter followed by an increase in wave propagation from the tropo- into the stratosphere and weakening of the stratospheric polar vortex[7,8], which affects the tropospheric circulation in the midlatitudes in subsequent months[9,10,11] To understand this tropo- stratospheric interaction, an improvement of climate models physical mechanisms is essential[12,13]. To investigate the interactions between ozone, sea ice and the atmospheric circulation we couple ECHAM6 with the fast but accurate interactive ozone chemistry scheme SWIFT21 and repeat the model experiments with HICE and LICE conditions Each of these four perpetual model simulations is integrated over 120 years, excluding the first 20 years as a spin-up period from the analysis. Compared to classic chemistry climate models this method can be applied to obtain very large sample sizes while being computationally feasible
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