An AGCM assessment of oceanic impacts on a heat wave over Japan in July 2018

Hisashi Nakamura, The University of Tokyo, Research Center for Advanced Science and Technology, Tokyo, Japan, Kazuaki Nishii, Mie University, Graduate School of Bioresources, Tsu, Japan and Bunmei Taguchi, University of Toyama, Faculty of Sustainable Design, Toyama, Japan
Through a set of ensemble experiments with an atmospheric general circulation model (AGCM), potential influence of sea-surface temperature (SST) anomalies is assessed on large-scale atmospheric circulation anomalies that induced a heat wave in mid- and late July 2018 over entire Japan, which was due to a prominent anticyclonic anomaly situated to the northwest of Japan. Our AGCM experiments with global SST anomalies can well reproduce this warm, anticyclonic anomaly. The additional experiments have confirmed that SST anomalies in both the tropics and midlatitude North Pacific provide the potential predictability in forcing the leading mode of the atmospheric variability over the western North Pacific, i.e., the Pacific-Japan (PJ) pattern, that brought the heat wave. Both the tropical and extratropical SST anomalies are also found to force poleward shift of the subtropical jet axis over the western Pacific and anomalous tropospheric warming in the midlatitude Northern Hemisphere both of which persisted in June and July.