3:00 PM - 3:15 PM
[ACG43-06] Predictability of East Asian Winter Monsoon and Its Dependence on Tropical and Extratropical SST Variability
Keywords:East Asian winter monsoon, seasonal forecasting, predictability, ENSO, atmosphere-ocean interactions
Despite recent advancements in climate and weather prediction systems, seasonal prediction of winter climate variability in East Asia remains challenging due to an incomplete understanding of its underlying mechanisms. This study examines seasonal predictability and prediction skill for the interannual variability of winter-mean 850-hPa air temperature in East Asia using monthly JMA/MRI-CPS3 (CPS3) hindcast data, which is an operational seasonal prediction system of the Japan Meteorological Agency. We performed an EOF analysis of the winter-mean 850-hPa air temperature variations over East Asia and found that the two leading principal modes dominate the variability.
The first EOF mode (EOF1) is characterized by widespread cold anomalies over the Eurasian continent. In contrast, the second EOF mode (EOF2) features a north-south dipole pattern with cold (warm) anomalies south (north) of Japan. EOF2 exhibited enhanced equatorward cold advection along the continental coast, which corresponds to strong East Asian winter monsoon (EAWM) years. The predictability and prediction skill are significantly higher for EOF2 than for EOF1.
To explore the predictive factors of EOF2, we conducted sensitivity experiments using the linear baroclinic model (LBM) and atmospheric general circulation model (AGCM) in Meteorological Research Institute Earth System Model version 2.0 (MRI-ESM2.0). Sensitivity experiments for heat source using the LBM indicate that the tripolar structure of tropical convection anomalies associated with La Niña, particularly the enhanced convection in Maritime Continent sector, plays an important role in the variations of EOF2. Sensitivity experiments for sea surface temperature (SST) using the AGCM confirm that formation of the tripolar structure is driven not only by local SST anomalies but also by trans-basin connections between the tropical Indian Ocean and the Pacific. In addition, local cold SST anomalies near Japan contribute to the cold 850-hPa air temperature anomalies south of Japan. The results of this study suggest that tropical and mid-latitude atmosphere-ocean interactions are closely related to EAWM variability.
The first EOF mode (EOF1) is characterized by widespread cold anomalies over the Eurasian continent. In contrast, the second EOF mode (EOF2) features a north-south dipole pattern with cold (warm) anomalies south (north) of Japan. EOF2 exhibited enhanced equatorward cold advection along the continental coast, which corresponds to strong East Asian winter monsoon (EAWM) years. The predictability and prediction skill are significantly higher for EOF2 than for EOF1.
To explore the predictive factors of EOF2, we conducted sensitivity experiments using the linear baroclinic model (LBM) and atmospheric general circulation model (AGCM) in Meteorological Research Institute Earth System Model version 2.0 (MRI-ESM2.0). Sensitivity experiments for heat source using the LBM indicate that the tripolar structure of tropical convection anomalies associated with La Niña, particularly the enhanced convection in Maritime Continent sector, plays an important role in the variations of EOF2. Sensitivity experiments for sea surface temperature (SST) using the AGCM confirm that formation of the tripolar structure is driven not only by local SST anomalies but also by trans-basin connections between the tropical Indian Ocean and the Pacific. In addition, local cold SST anomalies near Japan contribute to the cold 850-hPa air temperature anomalies south of Japan. The results of this study suggest that tropical and mid-latitude atmosphere-ocean interactions are closely related to EAWM variability.