Pacific Meridional Modes without Equatorial Pacific Influence

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  • 1 Frontiers Science Center for Deep Ocean Multispheres and Earth System and Physical Oceanography Laboratory, Ocean University of China, Qingdao, China
  • 2 Qingdao National Laboratory for Marine Science and Technology, Qingdao, China
  • 3 Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
  • 4 Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
  • 5 Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, Colorado, USA
  • 6 Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan
  • 7 Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, USA
  • 8 Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disaster/KLME/ILCEC, Nanjing University of Information Science and Technology, Nanjing, China
  • 9 Department of Oceanography and International Pacific Research Center, School of Ocean and Earth Science and Technology, University of Hawaiʻi at Mānoa, Honolulu, Hawaiʻi, USA
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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.

Corresponding author: Shiyun Yu: yushiyun1177@stu.ouc.edu.cn

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.

Corresponding author: Shiyun Yu: yushiyun1177@stu.ouc.edu.cn
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