Pacific meridional modes without equatorial pacific influence

Abstract

Investigating Pacific meridional modes (PMMs) without the influence of tropical Pacific variability is technically difficult if based on observations or fully coupledmodel simulations due to their overlapping spatial structures.To confront this issue, the present study investigates both the North PMM(NPMM) and South PMM (SPMM) in terms of their associated atmospheric forcing and response processes based on a mechanically decoupled climatemodel simulation. In this experiment, the climatologicalwind stress is prescribed over the tropical Pacific, which effectively removes dynamically coupled tropical Pacific variability (e.g., El Niño-Southern Oscillation). InterannualNPMMin this experiment is forced not only by theNorth PacificOscillation but also by aNorth Pacific tripole (NPT) pattern of atmospheric internal variability,which primarily forces decadalNPMMvariability. 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 or shrinking the climatological South Pacific convergence zone in all seasons.Our results highlight a new poleward pathway by which both theNPMMand SPMMfeed back to the extratropical climate, in addition to the equatorward influence on tropical Pacific variability.