Implications of all season Arctic sea-ice anomalies on the stratosphere
In this study the impact of a substantially reduced Arctic sea-ice\ncover on the lower and middle stratosphere is investigated. For this\npurpose two simulations with fixed boundary conditions (the so-called\ntime-slice mode) were performed with a Chemistry-Climate Model. A\nreference time-slice with boundary conditions representing the year\n2000 is compared to a second sensitivity simulation in which the\nboundary conditions are identical apart from the polar sea-ice cover,\nwhich is set to represent the years 2089–2099. \n\n\nThree features of Arctic air temperature response have been identified\nwhich are discussed in detail. Firstly, tropospheric mean polar temperatures\nincrease up to 7 K during winter. This warming is primarily driven\nby changes in outgoing long-wave radiation. The tropospheric response\n(e.g. geopotential height anomaly) is in reasonable agreement with\nsimilar studies dealing with Arctic sea-ice decrease and the consequences\non the troposphere. Secondly, temperatures decrease significantly\nin the summer stratosphere caused by a decline in outgoing short-wave\nradiation, accompanied by a slight increase of ozone mixing ratios.\nThirdly, there are short periods of statistical significant temperature\nanomalies in the winter stratosphere probably driven by modified\nplanetary wave activity, but generally there is no clear stratospheric\nresponse. The Arctic Oscillation (AO)-index, which is related to\nthe troposphere–stratosphere coupling favours a more neutral state\nduring winter. The only clear stratospheric response can be shown\nduring November. Significant changes in Arctic temperature, meridional\neddy heat fluxes and the Arctic Oscillation (AO)-index are detected.\n\n\n\nIn this study the overall stratospheric response to the prescribed\nsea-ice anomaly is small compared to the tropospheric changes.