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Small, RJ, Xie SP, Wang YQ, Esbensen SK, Vickers D.  2005.  Numerical simulation of boundary layer structure and cross-equatorial flow in the Eastern Pacific. Journal of the Atmospheric Sciences. 62:1812-1830. Abstract
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Small, RJ, Xie SP, Wang YQ.  2003.  Numerical simulation of atmospheric response to Pacific tropical instability waves. Journal of Climate. 16:3723-3741. Abstract
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Amaya, DJ, Kosaka Y, Zhou W, Zhang Y, Xie S-P, Miller AJ.  2019.  The North Pacific pacemaker effect on historical ENSO and its mechanisms. Journal of Climate.   10.1175/jcli-d-19-0040.1   Abstract

Studies have indicated that North Pacific sea surface temperature (SST) variability can significantly modulate the El Niño-Southern Oscillation (ENSO), but there has been little effort to put extratropical-tropical interactions into the context of historical events. To quantify the role of the North Pacific in pacing the timing and magnitude of observed ENSO, we use a fully-coupled climate model to produce an ensemble of North Pacific Ocean-Global Atmosphere (nPOGA) SST pacemaker simulations. In nPOGA, SST anomalies are restored back to observations in the North Pacific (>15°N), but are free to evolve throughout the rest of the globe. We find that the North Pacific SST has significantly influenced observed ENSO variability, accounting for approximately 15% of the total variance in boreal fall and winter. The connection between the North and tropical Pacific arises from two physical pathways: 1. A Wind-Evaporation-SST (WES) propagating mechanism, and 2. A Gill-like atmospheric response associated with anomalous deep convection in boreal summer and fall, which we refer to as the Summer Deep Convection (SDC) response. The SDC response accounts for 25% of the observed zonal wind variability around the equatorial dateline. On an event-by-event basis, nPOGA most closely reproduces the 2014-2015 and the 2015-2016 El Niños. In particular, we show that the 2015 Pacific Meridional Mode event increased wind forcing along the equator by 20%, potentially contributing to the extreme nature of the 2015-2016 El Niño. Our results illustrate the significant role of extratropical noise in pacing the initiation and magnitude of ENSO events and may improve the predictability of ENSO on seasonal timescales.

Kwon, EY, Deutsch C, Xie SP, Schmidtko S, Cho YK.  2016.  The North Pacific Oxygen uptake rates over the past half century. Journal of Climate. 29:61-76.   10.1175/jcli-d-14-00157.1   AbstractWebsite

The transport of dissolved oxygen (O-2) from the surface ocean into the interior is a critical process sustaining aerobic life in mesopelagic ecosystems, but its rates and sensitivity to climate variations are poorly understood. Using a circulation model constrained to historical variability by assimilation of observations, the study shows that the North Pacific thermocline effectively takes up O-2 primarily by expanding the area through which O-2-rich mixed layer water is detrained into the thermocline. The outcrop area during the critical winter season varies in concert with the Pacific decadal oscillation (PDO). When the central North Pacific Ocean is in a cold phase, the winter outcrop window for the central mode water class (CMW; a neutral density range of = 25.6-26.6) expands southward, allowing more O-2-rich surface water to enter the ocean's interior. An increase in volume flux of water to the CMW density class is partly compensated by a reduced supply to the shallower densities of subtropical mode water ( = 24.0-25.5). The thermocline has become better oxygenated since the 1980s partly because of strong O-2 uptake. Positive O-2 anomalies appear first near the outcrop and subsequently downstream in the subtropical gyre. In contrast to the O-2 variations within the ventilated thermocline, observed O-2 in intermediate water (density range of = 26.7-27.2) shows a declining trend over the past half century, a trend not explained by the open ocean water mass formation rate.

Okumura, YM, Deser C, Hu A, Timmermann A, Xie SP.  2009.  North Pacific Climate Response to Freshwater Forcing in the Subarctic North Atlantic: Oceanic and Atmospheric Pathways. Journal of Climate. 22:1424-1445.   10.1175/2008jcli2511.1   Abstract
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Xie, S-P, Kubokawa A, Kobashi F, Mitsudera H.  2012.  New developments in mode-water research: an introduction. Journal of Oceanography. 68:1-3.   10.1007/s10872-011-0090-8   Abstract
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