[A-CG33] Extratropical oceans and atmosphere

[ACG33-P12] A hemispheric extreme warm winter in 2019-20 enhanced by the highest sea surface temperature around mid-latitude

Yoshihiro Tachibana², *Yuta Ando¹, Kazuaki Nishii² (1.Faculty of Science, Niigata University, 2.Graduate school of Bioresources, Mie University)

Keywords:Air-sea interaction, Warm winter, Zonal-mean

In 2020 winter, most mid latitudes in the Northern Hemisphere was the historically warmest. The warmth was spreading zonally around all the mid latitudes throughout the season. Zonal-mean sea surface temperature in the mid latitudes was also unprecedently warm. It was substantially different from the recent localized extreme weathers, which were smaller both in temporal and spatial scales than 2020. The global warming might have turned into reality. Here we show that synchronized chain interaction between the warm seas and the warm atmosphere amplified the anomalousness of the warm winter using data analyses and simple numerical experiments. The chain is as follows; the warm seas built up in the previous autumn made overlying air warm, then the warmed air penetrated inland by westerlies, the warm air over the land further flew to the ocean, which again warms the seas. The zonal oceanic warming in mid-latitudes might shift the climate dynamics to a new state. This air-sea chain was responsible for unprecedently positive phase of Arctic Oscillation, which is a good measure of the zonal mean extreme warmth.