Abstract
The Pacific Meridional Mode (PMM) is a climate phenomenon in the eastern Pacific, characterized by strong wind-sea surface temperature (SST) interactions. During its positive phase, an atypical north-south SST gradient develops in the northeastern subtropical Pacific, leading to significant global teleconnections, which refers to the mutual influence or correlation between atmospheric or oceanic changes in two distant regions of the Earth. This study examines the relationship between historical summer temperature data for Taiwan (June-August) and PMM indices over a 59-year period (1960-2018), revealing a significant correlation between the two. Regressed large-scale circulations indicate the eastward propagation of a wave train across the Northern Pacific into East Asia, inducing anticyclonic circulations near southeastern China and Taiwan, accompanied by subsidence, which refers to the vertical downward movement of air masses in the atmosphere, typically associated with high-pressure systems and dry weather conditions, that stabilizes the atmosphere. This stabilization reduces the influence of seasonal southwesterly winds while increasing shortwave radiation at the surface, thereby raising surface temperatures in Taiwan.
Our findings are further supported by LBM experiments featuring PMM-like heating forcing and by large-scale responses to PMM-related SST patterns simulated in CMIP6 historical runs. While these results suggest that the PMM could be a valuable tool for predicting Taiwan's summer climate on decadal timescales, we also observe model uncertainties in simulating the teleconnection patterns of PMM-related SSTs in East Asia, including Taiwan's summer temperature response. These findings underscore the need for further investigation into the complex interplay between PMM circulation responses, seasonal monsoons, and other components of climate systems simulated in climate models.
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