[A-CG36] Extratropical oceans and atmosphere

[ACG36-16] Unprecedented Marine Heatwave Significantly Exacerbated the Record-breaking 2023 East Asian Summer Heatwave

*Satoru Okajima¹, Yu Kosaka², Takafumi Miyasaka², Rui Ito³ (1.Institute of Life and Environmental Sciences, University of Tsukuba, 2.RCAST, The University of Tokyo, 3.Japan Agency for Marine-Earth Science and Technology)

Keywords:Atmospheric heatwave, Marine heatwave, East Asia, compound extreme event, midlatitude air-sea interacions, regional atmospheric model

The 2023 East Asian summer experienced a record-breaking compound hot-humid extreme and an unprecedented concurrent marine heatwave (MHW) in surrounding oceans. Understanding and quantifying the impacts of such MHWs on land heatwaves can enhance seasonal prediction skills for these extremes. Here we evaluate the impact of the 2023 MHW on the record-breaking atmospheric heatwave in East Asia during the summer. Through a set of regional atmospheric model experiments, we demonstrate that the MHW significantly exacerbated the 2023 East Asian summer atmospheric heatwave, particularly as a compound hot-humid extreme. The extremely warm ocean amplified both surface air temperature and humidity anomalies, on top of the contributions of background atmospheric circulation anomalies. The MHW influence on air temperature manifests through radiative effects of cloud and water vapor changes. Our results also indicate that the MHW mitigated the strengthening of the western North Pacific subtropical high induced by large-scale background atmospheric conditions. By examining the effects of both temperature and humidity anomalies through wet-bulb globe temperature, we find that the MHW explains ~20-50% of the aggravation and prolonged duration of season-mean hot-humid conditions in East Asia, with notable impacts in Japan. Additionally, the recent trend of sea surface warming is shown to amplify the MHW’s impact on the heatwave substantially. Our findings underscore the key role of ocean variability and air-sea interactions in surrounding oceans on atmospheric heatwaves that occur in the summer climate in East Asia, highlighting a unique process in the humid and low cloud-abundant maritime East Asia region.