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Xu, H, Xie SP, Wang Y, Zhuang W, Wang D.  2008.  Orographic effects on South China Sea summer climate. Meteorology and Atmospheric Physics. 100:275-289.   10.1007/s00703-008-0309-4   Abstract
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Xu, LX, Xie SP, McClean JL, Liu QY, Sasaki H.  2014.  Mesoscale eddy effects on the subduction of North Pacific mode waters. Journal of Geophysical Research-Oceans. 119:4867-4886.   10.1002/2014jc009861   AbstractWebsite

Mesoscale eddy effects on the subduction of North Pacific mode waters are investigated by comparing observations and ocean general circulation models where eddies are either parameterized or resolved. The eddy-resolving models produce results closer to observations than the noneddy-resolving model. There are large discrepancies in subduction patterns between eddy-resolving and noneddy-resolving models. In the noneddy-resolving model, subduction on a given isopycnal is limited to the cross point between the mixed layer depth (MLD) front and the outcrop line whereas in eddy-resolving models and observations, subduction takes place in a broader, zonally elongated band within the deep mixed layer region. Mesoscale eddies significantly enhance the total subduction rate, helping create remarkable peaks in the volume histogram that correspond to North Pacific subtropical mode water (STMW) and central mode water (CMW). Eddy-enhanced subduction preferentially occurs south of the winter mean outcrop. With an anticyclonic eddy to the west and a cyclonic eddy to the east, the outcrop line meanders south, and the thermocline/MLD shoals eastward. As eddies propagate westward, the MLD shoals, shielding the water of low potential vorticity from the atmosphere. The southward eddy flow then carries the subducted water mass into the thermocline. The eddy subduction processes revealed here have important implications for designing field observations and improving models.

Xu, H, Xu M, Xie S-P, Wang Y.  2011.  Deep Atmospheric Response to the Spring Kuroshio over the East China Sea. Journal of Climate. 24:4959-4972.   10.1175/jcli-d-10-05034.1   Abstract
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Xu, LX, Xie SP, Liu QY, Liu C, Li PL, Lin XP.  2017.  Evolution of the North Pacific subtropical mode water in anticyclonic eddies. Journal of Geophysical Research-Oceans. 122:10118-10130.   10.1002/2017jc013450   AbstractWebsite

Anticyclonic eddies (AEs) trap and transport the North Pacific subtropical mode water (STMW), but the evolution of the STMW trapped in AEs has not been fully studied due to the lack of eddy-tracking subsurface observations. Here we analyze profiles from special-designed Argo floats that follow two STMW-trapping AEs for more than a year. The enhanced daily sampling by these Argo floats swirling around the eddies enables an unprecedented investigation into the structure and evolution of the trapped STMW. In the AEs, the upper (lower) thermocline domes up ( concaves downward), and this lens-shaped double thermocline encompasses the thick STMW within the eddy core. The lighter STMW (25.0 similar to 25.2 sigma(theta)) trapped in AEs dissipates quickly after the formation in winter because of the deepening seasonal thermocline, but the denser STMW (25.2 similar to 25.4 sigma(theta)) remains largely unchanged except when the AE passes across the Izu Ridge. The enhanced diapycnal mixing over the ridge weakens the denser STMW appreciably. While many AEs decay upon hitting the ridge, some pass through a bathymetric gap between the Hachijojima and Bonin Islands, forming a cross- ridge pathway for STMW transport. By contrast, the North Pacific Intermediate Water (NPIW) underneath is deeper than the eddy trapping depth (600 m), and hence left behind east of the Izu Ridge. In Argo climatology, the shallow STMW (< 400 m) intrudes through the gap westward because of the eddy transport, while the NPIW (800 m) is blocked by the Izu Ridge.

Xu, HM, Wang YQ, Xie SP.  2004.  Effects of the Andes on eastern Pacific climate: A regional atmospheric model study. Journal of Climate. 17:589-602. Abstract
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Xu, Y, Xie SP.  2015.  Ocean mediation of tropospheric response to reflecting and absorbing aerosols. Atmospheric Chemistry and Physics. 15:5827-5833.   10.5194/acp-15-5827-2015   AbstractWebsite

Radiative forcing by reflecting (e.g., sulfate, SO4) and absorbing (e.g., black carbon, BC) aerosols is distinct: the former cools the planet by reducing solar radiation at the top of the atmosphere and the surface, without largely affecting the atmospheric column, while the latter heats the atmosphere directly. Despite the fundamental difference in forcing, here we show that the structure of the tropospheric response is remarkably similar between the two types of aerosols, featuring a deep vertical structure of temperature change (of opposite sign) at the Northern Hemisphere (NH) mid-latitudes. The deep temperature structure is anchored by the slow response of the ocean, as a large meridional sea surface temperature (SST) gradient drives an anomalous interhemispheric Hadley circulation in the tropics and induces atmospheric eddy adjustments at the NH mid-latitudes. The tropospheric warming in response to projected future decline in reflecting aerosols poses additional threats to the stability of mountain glaciers in the NH. Additionally, robust tropospheric response is unique to aerosol forcing and absent in the CO2 response, which can be exploited for climate change attribution.

Xu, HM, Xie SP, Wang YQ, Small RJ.  2005.  Effects of Central American mountains on the eastern Pacific winter ITCZ and moisture transport. Journal of Climate. 18:3856-3873. Abstract
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Xu, LX, Xie SP, Liu QY.  2013.  Fast and slow responses of the North Pacific mode water and Subtropical Countercurrent to global warming. Journal of Ocean University of China. 12:216-221.   10.1007/s11802-013-2189-6   AbstractWebsite

Six coupled general circulation models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are employed for examining the full evolution of the North Pacific mode water and Subtropical Countercurrent (STCC) under global warming over 400 years following the Representative Concentration Pathways (RCP) 4.5. The mode water and STCC first show a sharp weakening trend when the radiative forcing increases, but then reverse to a slow strengthening trend of smaller magnitude after the radiative forcing is stablized. As the radiative forcing increases during the 21st century, the ocean warming is surface-intensified and decreases with depth, strengthening the upper ocean's stratification and becoming unfavorable for the mode water formation. Moving southward in the subtropical gyre, the shrinking mode water decelerates the STCC to the south. After the radiative forcing is stabilized in the 2070s, the subsequent warming is greater at the subsurface than at the sea surface, destabilizing the upper ocean and becoming favorable for the mode water formation. As a result, the mode water and STCC recover gradually after the radiative forcing is stabilized.

Xu, L, Xie S-P, Liu Q, Kobashi F.  2012.  Response of the North Pacific subtropical countercurrent and its variability to global warming. Journal of Oceanography. 68:127-137.   10.1007/s10872-011-0031-6   Abstract
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Xu, LX, Xie SP, Jing Z, Wu LX, Liu QY, Li PL, Du Y.  2017.  Observing subsurface changes of two anticyclonic eddies passing over the Izu-Ogasawara Ridge. Geophysical Research Letters. 44:1857-1865.   10.1002/2016gl072163   AbstractWebsite

Eddy-bathymetry interactions are common in the ocean, but the full evolution of the interaction is difficult to observe below the surface. Using 17 Iridium Argo floats, we continually track two anticyclonic eddies (AEs) in the North Pacific that migrate westward and encounter the Izu-Ogasawara Ridge. Based on over 5000 Argo profiles following the two AEs, this study presents the first detailed descriptions of changes in eddy vertical structure and diapycnal mixing as the two AEs pass the Ridge. There, we find that isopycnals dome up and the eddy diameter increases, while the diapycnal mixing is enhanced-to the order of 10(-4) m(2) s(-1) or larger, in comparison with an ambient of 10(-5) m(2) s(-1). The enhanced mixing around the AE center in the upper -1000m appears where the underlying bathymetry is shallower than -4000m and is mainly sustained by tidally generated internal waves.

Xu, HM, Xie SP, Wang YQ.  2005.  Subseasonal variability of the southeast Pacific stratus cloud deck. Journal of Climate. 18:131-142. Abstract
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Xu, H, Tokinaga H, Xie S-P.  2010.  Atmospheric Effects of the Kuroshio Large Meander during 2004-05. Journal of Climate. 23:4704-4715.   10.1175/2010jcli3267.1   Abstract
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Xie, SP.  1995.  INTERACTION BETWEEN THE ANNUAL AND INTERANNUAL VARIATIONS IN THE EQUATORIAL PACIFIC. Journal of Physical Oceanography. 25:1930-1941. 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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Xie, SP, Noguchi H, Matsumura S.  1999.  A hemispheric-scale quasi-decadal oscillation and its signature in Northern Japan. Journal of the Meteorological Society of Japan. 77:573-582. Abstract
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Xie, SP, Zhou ZQ.  2017.  Seasonal modulations of El Nino-related atmospheric variability: Indo-Western Pacific Ocean feedback. Journal of Climate. 30:3461-3472.   10.1175/jcli-d-16-0713.1   AbstractWebsite

The spatial structure of atmospheric anomalies associated with El Nino-Southern Oscillation varies with season because of the seasonal variations in sea surface temperature (SST) anomaly pattern and in the climatological basic state. The latter effect is demonstrated using an atmospheric model forced with a time-invariant pattern of El Nino warming over the equatorial Pacific. The seasonal modulation is most pronounced over the north Indian Ocean to northwest Pacific where the monsoonal winds vary from northeasterly in winter to southwesterly in summer. Specifically, the constant El Nino run captures the abrupt transition from a summer cyclonic to winter anticyclonic anomalous circulation over the northwest Pacific, in support of the combination mode idea that emphasizes nonlinear interactions of equatorial Pacific SST forcing and the climatological seasonal cycle. In post-El Nino summers when equatorial Pacific warming has dissipated, SST anomalies over the Indo-northwest Pacific Oceans dominate and anchor the coherent persisting anomalous anticyclonic circulation. A conceptual model is presented that incorporates the combination mode in the existing framework of regional Indo-western Pacific Ocean coupling.

Xie, SP.  2004.  Satellite observations of cool ocean-atmosphere interaction. Bulletin of the American Meteorological Society. 85:195-+.   10.1175/bams-85-2-195   Abstract
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Xie, SP, Kubokawa A.  1990.  ON THE WAVE-CISK IN THE PRESENCE OF A FRICTIONAL BOUNDARY-LAYER. Journal of the Meteorological Society of Japan. 68:651-657. Abstract
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Xie, SP.  1997.  Stability of equatorially symmetric and asymmetric climates under annual solar forcing. Quarterly Journal of the Royal Meteorological Society. 123:1359-1375. Abstract
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Xie, SP.  2000.  Japanese team measures tropical instability effects. Physics Today. 53:11-11. Abstract
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Xie, SP, Kosaka Y, Okumura YM.  2016.  Distinct energy budgets for anthropogenic and natural changes during global warming hiatus. Nature Geoscience. 9:29-+.   10.1038/ngeo2581   AbstractWebsite

The Earth's energy budget for the past four decades can now be closed(1), and it supports anthropogenic greenhouse forcing as the cause for climate warming. However, closure depends on invoking an unrealistically large increase in aerosol cooling(2) during the so-called global warming hiatus since the late 1990s (refs 3,4) that was due partly to tropical Pacific Ocean cooling(5-7). The difficulty with this closure lies in the assumption that the same climate feedback applies to both anthropogenic warming and natural cooling. Here we analyse climate model simulations with and without anthropogenic increases in greenhouse gas concentrations, and show that top-of-the-atmosphere radiation and global mean surface temperature are much less tightly coupled for natural decadal variability than for the greenhouse-gas-induced response, implying distinct climate feedback between anthropogenic warming and natural variability. In addition, we identify a phase difference between top-of-the-atmosphere radiation and global mean surface temperature such that ocean heat uptake tends to slow down during the surface warming hiatus. This result deviates from existing energy theory but we find that it is broadly consistent with observations. Our study highlights the importance of developing metrics that distinguish anthropogenic change from natural variations to attribute climate variability and to estimate climate sensitivity from observations.

Xie, SP, Xu HM, Kessler WS, Nonaka M.  2005.  Air-sea interaction over the eastern Pacific warm pool: Gap winds, thermocline dome, and atmospheric convection. Journal of Climate. 18:5-20. Abstract
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Xie, S-P, Du Y, Huang G, Zheng X-T, Tokinaga H, Hu K, Liu Q.  2010.  Decadal Shift in El Nino Influences on Indo-Western Pacific and East Asian Climate in the 1970s. Journal of Climate. 23:3352-3368.   10.1175/2010jcli3429.1   Abstract
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