Zhang, Y. S. Yu, D. J. Amaya, Y. Kosaka, S. M. Larson, X.
Wang, J.-C. Yang, M. F. Stuecker, S.-P. Xie, A. J. Miller and X.
Lin, 2021:
Pacific Meridional Modes without Equatorial Pacific influence.
Journal of Climate, 34 5285-5301.
Abstract.
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.
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