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Inter-basin versus intra-basin sea surface temperature forcing of the Western North Pacific subtropical high’s westward extensions
  • Jhordanne Jones,
  • Daniel Chavas,
  • Zachary Freitag Johnson
Jhordanne Jones
Purdue University

Corresponding Author:[email protected]

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Daniel Chavas
Purdue University
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Zachary Freitag Johnson
Central Michigan University
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Zonal extensions of the Western Pacific subtropical high (WPSH) strongly modulate extreme rainfall activity and tropical cyclone (TC) landfall over the Western North Pacific (WNP) region. On seasonal timescales, these zonal extensions are forced primarily by inter-basin zonal sea surface temperature (SST) gradients. However, despite the presence of large-scale zonal SST gradients, the WPSH’s response to SSTs varies from year to year. In this study, we force the atmosphere-only NCAR Community Earth System Model version 2 simulations with two real-world SST patterns, both featuring the large-scale zonal SST gradient characteristic of decaying El Niño/developing La Niña summers. For each of these patterns, we perform four experimental sets that test the relative contributions of the tropical Indian Ocean, Pacific, and Atlantic basin SSTs to simulated westward extensions over the WNP during June-August. Our results indicate that the subtle differences between the two SST anomaly patterns belie two different mechanisms forcing the WPSH’s westward extensions. In one SST pattern, the extratropical North Pacific SST forcing suppresses the tropical Pacific zonal SST gradient forcing, resulting in tropical Atlantic and Indian Ocean SST warming being the main drivers of the Walker Circulation. With an adjacent SST pattern, subsidence over the WNP is driven predominantly by intra-basin Pacific SST forcing. The results of this study have implications for understanding and predicting the impact of the WPSH’s zonal variability on tropical cyclones and extreme rainfall over the WNP.
22 Nov 2023Submitted to ESS Open Archive
22 Nov 2023Published in ESS Open Archive