Over the 21 st century, the ISMR-ENSO relationship has strengthened and almost recovered to its pre-1980 level. 2. On interannual and decadal timescales, the tropical Indian Ocean warming (cooling) indicates a stronger (weaker) ISMR-ENSO relationship. 3. The Indian Ocean basin-wide SST anomaly in summer is related to different types of temporal evolution of ENSO.

Investigating Pacific Meridional Modes (PMM) without the influence of tropical Pacific variability is technically difficult if based on observations or fully coupled model simulations due to their overlapping spatial structures. To confront this issue, the present study investigates both North (NPMM) and South PMM (SPMM) in terms of their associated atmospheric forcing and response processes based on a mechanically decoupled climate model simulation. In this experiment, the climatological wind stress is prescribed over the tropical Pacific, which effectively removes dynamically coupled tropical Pacific variability (e.g., the El Niño-Southern Oscillation). Interannual NPMM in this experiment is forced not only by the North Pacific Oscillation, but also by a North Pacific tripole (NPT) pattern of atmospheric internal variability, which primarily forces decadal NPMM variability. Interannual and decadal variability of the SPMM is partly forced by the South Pacific Oscillation. In turn, both interannual and decadal NPMM variability can excite atmospheric teleconnections over the Northern Hemisphere extratropics by influencing the meridional displacement of the climatological intertropical convergence zone throughout the whole year. Similarly, both interannual and decadal SPMM variability can also excite atmospheric teleconnections over the Southern Hemisphere extratropics by extending/shrinking the climatological South Pacific convergence zone in all seasons. Our results highlight a new poleward pathway by which both the NPMM and SPMM feed back to the extratropical climate, in addition to the equatorward influence on tropical Pacific variability.

The Pacific Meridional Mode (PMM) impacts tropical Pacific sea surface temperature variations, which in turn affect the PMM through the excited atmospheric teleconnections. Previous studies linked this loop to the tropical Pacific‐excited North Pacific Oscillation (NPO; the second empirical mode of North Pacific sea level pressure variability), while a recent study proposed the linkage to the excited Aleutian low (AL) variability (the first empirical mode). Unraveling their relative importance for the loop is thus crucial for better understanding subtropical‐tropical interactions. Here, using tropical Pacific pacemaker experiments we show that tropical Pacific‐forced AL variability is tied to the loop, while the tropical Pacific‐forced NPO does not effectively induce PMM variability, hence not being in the loop. Our study emphasizes the role of tropical Pacific‐forced AL variability in the PMM‐tropical Pacific interaction, which should be paid more attention in future studies.

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