Enhancement of Pacific meridional mode in recent years and investigation into its mechanisms
HOU Yingjie
ZHENG Xiaotong
XU Peidong
Abstract：This study uses the monthly sea surface temperature(SST)data from the ERSSTv5 dataset,along with the 10-m wind,sea-level pressure(SLP),latent heat flux,2-m air temperature and 2-m dew point data from the ERA5 reanalysis from 1955 to 2024.The Pacific meridional mode(PMM)is defined via the maximum covariance analysis.Using a combination of statistical methods including the decomposition of wind-evaporation-SST(WES)feedback and regression analysis,we investigate the long-term trends of PMM and explore the potential mechanisms driving its variations from the perspectives of atmospheric variability and subtropical feedback.The results reveal a significant enhancement of PMM since 1990,with a strengthening trend also evident during spring.The enhancement of PMM is attributed to the synergistic effects of mid-to-high-latitude atmospheric variability and subtropical feedback.On the one hand,the North Pacific Oscillation(NPO)exhibits a strengthened driving effect on PMM,where the winter SLP anomalies enhance the sensitivity of subtropical North Pacific SST to atmospheric forcing by modulating latent heat flux and surface wind fields.Notably,the NPO-related spring SST anomalies in the subtropical North Pacific show a high correlation with spring PMM intensity over the study period.On the other hand,the WES feedback intensity in the subtropical North Pacific has significantly strengthened since 1990,further amplifying the PMM-associated SST anomalies.This strengthening primarily stems from the combined effects of sustained background SST warming and reduced relative humidity in the subtropical North Pacific.
Keywords：Pacific meridional mode(PMM)atmospheric forcingwind-evaporation-SST(WES)feedback
Publication Date：2025-10-30
Online Publishing Date：2026-05-22(First online date of this platform, not the publication date of the document)
Pages：12( 1-12 )