GISS Lunch Seminar
Speaker: Itsuki Miura (Hokkaido Univ)
Title: Subtropical Atmospheric Response to Extratropical SST Warming in the Western North Pacific Using Large Ensemble AGCM Experiments

Abstract:
While tropics-to-extratropics teleconnections are well-established as stationary Rossby wave responses to convective heating in the tropics, the equatorward teleconnections originating from the extratropics are not well understood. This uncertainty primarily arises from strong atmospheric internal variability, which often obscures the atmospheric response to extratropical sea surface temperature (SST) anomalies. Nevertheless, the Kuroshio Extension (KE) is a key extratropical region where substantial heat and moisture are released into the atmosphere, facilitating extratropical air-sea interactions. Notably, recent marine heatwave events have led to anomalously high SSTs in the KE region, substantially exceeding the global warming trend. These extreme SST events highlight the importance of understanding the role of extratropical SST in equatorward teleconnections, as they have the potential to modulate tropical air-sea coupling. In this talk, I will discuss the large-scale atmospheric response to idealized positive SST forcing in the KE region using large-ensemble AGCM experiments. Despite substantial atmospheric internal variability inherent in the extratropics, the imposed SST forcing consistently induces a lower-tropospheric circulation response over and downstream of the KE, accompanied by westerly wind anomalies extending into the subtropical central North Pacific. These subtropical westerly wind anomalies weaken the prevailing trade winds and reduce surface heat loss, potentially facilitating the development and maintenance of underlying SST warming. Our results suggest that the extratropical SST anomalies in the KE region may contribute to equatorward atmospheric teleconnections via the subtropical westerly wind response, with impacts on air–sea interactions in the subtropical North Pacific.