[A-CG38] Climate Variability and Predictability on Subseasonal to Centennial Timescales

[ACG38-P03] Impact of the Australian Summer Monsoon on the Predictability of Tropical Intraseasonal Variability in JMA/MRI-CPS3

*Shion Sekizawa¹, Shoji Hirahara¹, Yukimasa Adachi¹, Hiroaki Naoe¹, Hisashi Nakamura², Yu Kosaka² (1.Meteorological Research Institute, Japan Meteorological Agency, 2.Research Center for Advanced Science and Technology, University of Tokyo)

Keywords:Subseasonal to seasonal predictability, Monsoon, Intraseasonal variability in the tropics, Teleconnection

Intraseasonal variability (ISV) of convective activity in the tropics, such as the Madden-Julian Oscillation (MJO), is often influenced by lower-frequency variability in its background. The interannual variability of the Australian summer monsoon (AUSM) is one such lower-frequency variability that modulates ISV activity. In years with a weak (strong) AUSM during January and February, the amplitude of the tropical ISV is significantly enhanced (suppressed), associated with a distinct (ambiguous) eastward propagation of the MJO from the Maritime Continent into the western Pacific. This modulation of ISV activity appears about one month behind the AUSM anomaly. Therefore, the interannual variability of the AUSM can affect the predictability of the tropical ISV in late winter and early spring.
Based on 30-year hindcast experiments with the operational seasonal prediction system of the Japan Meteorological Agency, JMA/MRI-CPS3, this study investigates the reproducibility of the ISV modulation due to the AUSM variability in the seasonal prediction system and assesses its impact on the ISV predictability. Due to their nature as atmospheric internal variability, both AUSM anomalies and ISV are difficult to predict with long lead times. Nevertheless, for the simulations initialized at the end of January, we confirm that the tropical ISVs of convective activity and large-scale atmospheric circulation are stronger and their prediction skill is higher in February and May in weak AUSM years than in strong AUSM years. Since teleconnections from the tropical ISV is a source of intraseasonal to seasonal predictability in the extratropics, this study also assesses the impact of the ISV modulation by the AUSM variability on the predictability of the extratropical climate.