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Annamalai, H, Xie SP, McCreary JP, Murtugudde R.  2005.  Impact of Indian Ocean sea surface temperature on developing El Nino. Journal of Climate. 18:302-319. Abstract
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Seo, H, Xie SP.  2013.  Impact of ocean warm layer thickness on the intensity of hurricane Katrina in a regional coupled model. Meteorology and Atmospheric Physics. 122:19-32.   10.1007/s00703-013-0275-3   AbstractWebsite

The effect of pre-storm subsurface thermal structure on the intensity of hurricane Katrina (2005) is examined using a regional coupled model. The Estimating Circulation and Climate of Ocean (ECCO) ocean state estimate is used to initialize the ocean component of the coupled model, and the source of deficiencies in the simulation of Katrina intensity is investigated in relation to the initial depth of 26 A degrees C isotherm (D26). The model underestimates the intensity of Katrina partly due to shallow D26 in ECCO. Sensitivity tests with various ECCO initial fields indicate that the correct relationship between intensity and D26 cannot be derived because D26 variability is underestimated in ECCO. A series of idealized experiments is carried out by modifying initial ECCO D26 to match the observed range. A more reasonable relationship between Katrina's intensity and pre-storm D26 emerges: the intensity is much more sensitive to D26 than to sea surface temperature (SST). Ocean mixed layer process plays a critical role in modulating inner-core SSTs when D26 is deep, reducing mixed layer cooling and lowering the center pressure of the Katrina. Our result lends strong support to the notion that accurate initialization of pre-storm subsurface thermal structure in prediction models is critical for a skillful forecast of intensity of Katrina and likely other intense storms.

Yang, JL, Liu QY, Xie SP, Liu ZY, Wu LX.  2007.  Impact of the Indian Ocean SST basin mode on the Asian summer monsoon. Geophysical Research Letters. 34   10.1029/2006gl028571   Abstract
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Ueda, H, Ohba M, Xie SP.  2009.  Important Factors for the Development of the Asian-Northwest Pacific Summer Monsoon. Journal of Climate. 22:649-669.   10.1175/2008jcli2341.1   Abstract
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Johnson, NC, Xie SP, Kosaka Y, Li XC.  2018.  Increasing occurrence of cold and warm extremes during the recent global warming slowdown. Nature Communications. 9   10.1038/s41467-018-04040-y   AbstractWebsite

The recent levelling of global mean temperatures after the late 1990s, the so-called global warming hiatus or slowdown, ignited a surge of scientific interest into natural global mean surface temperature variability, observed temperature biases, and climate communication, but many questions remain about how these findings relate to variations in more societally relevant temperature extremes. Here we show that both summertime warm and wintertime cold extreme occurrences increased over land during the so-called hiatus period, and that these increases occurred for distinct reasons. The increase in cold extremes is associated with an atmospheric circulation pattern resembling the warm Arctic-cold continents pattern, whereas the increase in warm extremes is tied to a pattern of sea surface temperatures resembling the Atlantic Multidecadal Oscillation. These findings indicate that large-scale factors responsible for the most societally relevant temperature variations over continents are distinct from those of global mean surface temperature.

Xie, SP, Hu KM, Hafner J, Tokinaga H, Du Y, Huang G, Sampe T.  2009.  Indian Ocean Capacitor Effect on Indo-Western Pacific Climate during the Summer following El Nino. Journal of Climate. 22:730-747.   10.1175/2008jcli2544.1   Abstract
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Schott, FA, Xie SP, McCreary JP.  2009.  INDIAN OCEAN CIRCULATION AND CLIMATE VARIABILITY. Reviews of Geophysics. 47   10.1029/2007rg000245   Abstract
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Zheng, XT, Xie SP, Du Y, Liu L, Huang G, Liu QY.  2013.  Indian Ocean dipole response to global warming in the CMIP5 multimodel ensemble. Journal of Climate. 26:6067-6080.   10.1175/jcli-d-12-00638.1   AbstractWebsite

The response of the Indian Ocean dipole (IOD) mode to global warming is investigated based on simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). In response to increased greenhouse gases, an IOD-like warming pattern appears in the equatorial Indian Ocean, with reduced (enhanced) warming in the east (west), an easterly wind trend, and thermocline shoaling in the east. Despite a shoaling thermocline and strengthened thermocline feedback in the eastern equatorial Indian Ocean, the interannual variance of the IOD mode remains largely unchanged in sea surface temperature (SST) as atmospheric feedback and zonal wind variance weaken under global warming. The negative skewness in eastern Indian Ocean SST is reduced as a result of the shoaling thermocline. The change in interannual IOD variance exhibits some variability among models, and this intermodel variability is correlated with the change in thermocline feedback. The results herein illustrate that mean state changes modulate interannual modes, and suggest that recent changes in the IOD mode are likely due to natural variations.

Zhou, ZQ, Xie SP, Zheng XT, Liu QY.  2013.  Indian Ocean Dipole response to global warming: A multi-member study with CCSM4. Journal of Ocean University of China. 12:209-215.   10.1007/s11802-013-2200-2   AbstractWebsite

Based on a coupled ocean-atmosphere model, the response of the Indian Ocean Dipole (IOD) mode to global warming is investigated with a six member ensemble of simulations for the period 1850-2100. The model can simulate the IOD features realistically, including the east-west dipole pattern and the phase locking in boreal autumn. The ensemble analysis suppresses internal variability and isolates the radiative forced response. In response to increasing greenhouse gases, a weakening of the Walker circulation leads to the easterly wind anomalies in the equatorial Indian Ocean and the shoaling thermocline in the eastern equatorial Indian Ocean (EEIO), and sea surface temperature and precipitation changes show an IOD-like pattern in the equatorial Indian Ocean. Although the thermocline feedback intensifies with shoaling, the interannual variability of the IOD mode surprisingly weakens under global warming. The zonal wind feedback of IOD is found to weaken as well, due to decreased precipitation in the EEIO. Therefore, the atmospheric feedback decreases much more than the oceanic feedback increases, causing the decreased IOD variance in this model.

Zheng, X-T, Xie S-P, Vecchi GA, Liu Q, Hafner J.  2010.  Indian Ocean Dipole Response to Global Warming: Analysis of Ocean-Atmospheric Feedbacks in a Coupled Model. Journal of Climate. 23:1240-1253.   10.1175/2009jcli3326.1   Abstract
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Liu, L, Xie SP, Zheng XT, Li T, Du Y, Huang G, Yu WD.  2014.  Indian Ocean variability in the CMIP5 multi-model ensemble: the zonal dipole mode. Climate Dynamics. 43:1715-1730.   10.1007/s00382-013-2000-9   AbstractWebsite

The performance of 21 Coupled Model Intercomparison Project Phase 5 (CMIP5) models in the simulation of the Indian Ocean Dipole (IOD) mode is evaluated. Compared to CMIP3, CMIP5 models exhibit a similar spread in IOD intensity. A detailed diagnosis was carried out to understand whether CMIP5 models have shown improvement in their representation of the important dynamical and thermodynamical feedbacks in the tropical Indian Ocean. These include the Bjerknes dynamic air-sea feedback, which includes the equatorial zonal wind response to sea surface temperature (SST) anomaly, the thermocline response to equatorial zonal wind forcing, the ocean subsurface temperature response to the thermocline variations, and the thermodynamic air-sea coupling that includes the wind-evaporation-SST and cloud-radiation-SST feedback. Compared to CMIP3, the CMIP5 ensemble produces a more realistic positive wind-evaporation-SST feedback during the IOD developing phase, while the simulation of Bjerknes dynamic feedback is more unrealistic especially with regard to the wind response to SST forcing and the thermocline response to surface wind forcing. The overall CMIP5 performance in the IOD simulation does not show remarkable improvements compared to CMIP3. It is further noted that the El Nio-Southern Oscillation (ENSO) and IOD amplitudes are closely related, if a model generates a strong ENSO, it is likely that this model also simulates a strong IOD.

Du, Y, Xie SP, Yang YL, Zheng XT, Liu L, Huang G.  2013.  Indian Ocean Variability in the CMIP5 Multimodel Ensemble: The Basin Mode. Journal of Climate. 26:7240-7266.   10.1175/jcli-d-12-00678.1   AbstractWebsite

This study evaluates the simulation of the Indian Ocean Basin (IOB) mode and relevant physical processes in models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Historical runs from 20 CMIP5 models are available for the analysis. They reproduce the IOB mode and its close relationship to El Nino-Southern Oscillation (ENSO). Half of the models capture key IOB processes: a downwelling oceanic Rossby wave in the southern tropical Indian Ocean (TIO) precedes the IOB development in boreal fall and triggers an antisymmetric wind anomaly pattern across the equator in the following spring. The anomalous wind pattern induces a second warming in the north Indian Ocean (NIO) through summer and sustains anticyclonic wind anomalies in the northwest Pacific by radiating a warm tropospheric Kelvin wave. The second warming in the NIO is indicative of ocean-atmosphere interaction in the interior TIO. More than half of the models display a double peak in NIO warming, as observed following El Nino, while the rest show only one winter peak. The intermodel diversity in the characteristics of the IOB mode seems related to the thermocline adjustment in the south TIO to ENSO-induced wind variations. Almost all the models show multidecadal variations in IOB variance, possibly modulated by ENSO.

Wang, CY, Xie SP, Kosaka Y.  2018.  Indo-Western Pacific Climate Variability: ENSO Forcing and Internal Dynamics in a Tropical Pacific Pacemaker Simulation. Journal of Climate. 31:10123-10139.   10.1175/jcli-d-18-0203.1   AbstractWebsite

El Nino-Southern Oscillation (ENSO) peaks in boreal winter but its impact on Indo-western Pacific climate persists for another two seasons. Key ocean-atmosphere interaction processes for the ENSO effect are investigated using the Pacific Ocean-Global Atmosphere (POGA) experiment with a coupled general circulation model, where tropical Pacific sea surface temperature (SST) anomalies are restored to follow observations while the atmosphere and oceans are fully coupled elsewhere. The POGA shows skills in simulating the ENSO-forced warming of the tropical Indian Ocean and an anomalous anticyclonic circulation pattern over the northwestern tropical Pacific in the post-El Nino spring and summer. The 10-member POGA ensemble allows decomposing Indo-western Pacific variability into the ENSO forced and ENSO-unrelated (internal) components. Internal variability is comparable to the ENSO forcing in magnitude and independent of ENSO amplitude and phase. Random internal variability causes apparent decadal modulations of ENSO correlations over the Indo-western Pacific, which are high during epochs of high ENSO variance. This is broadly consistent with instrumental observations over the past 130 years as documented in recent studies. Internal variability features a sea level pressure pattern that extends into the north Indian Ocean and is associated with coherent SST anomalies from the Arabian Sea to the western Pacific, suggestive of ocean-atmosphere coupling.

Xie, SP, Kosaka Y, Du Y, Hu KM, Chowdary J, Huang G.  2016.  Indo-western Pacific ocean capacitor and coherent climate anomalies in post-ENSO summer: A review. Advances in Atmospheric Sciences. 33:411-432.   10.1007/s00376-015-5192-6   AbstractWebsite

ENSO induces coherent climate anomalies over the Indo-western Pacific, but these anomalies outlast SST anomalies of the equatorial Pacific by a season, with major effects on the Asian summer monsoon. This review provides historical accounts of major milestones and synthesizes recent advances in the endeavor to understand summer variability over the Indo-Northwest Pacific region. Specifically, a large-scale anomalous anticyclone (AAC) is a recurrent pattern in post-El NiEeno summers, spanning the tropical Northwest Pacific and North Indian oceans. Regarding the ocean memory that anchors the summer AAC, competing hypotheses emphasize either SST cooling in the easterly trade wind regime of the Northwest Pacific or SST warming in the westerly monsoon regime of the North Indian Ocean. Our synthesis reveals a coupled ocean-atmosphere mode that builds on both mechanisms in a two-stage evolution. In spring, when the northeast trades prevail, the AAC and Northwest Pacific cooling are coupled via wind-evaporation-SST feedback. The Northwest Pacific cooling persists to trigger a summer feedback that arises from the interaction of the AAC and North Indian Ocean warming, enabled by the westerly monsoon wind regime. This Indo-western Pacific ocean capacitor (IPOC) effect explains why El Nino stages its last act over the monsoonal Indo-Northwest Pacific and casts the Indian Ocean warming and AAC in leading roles. The IPOC displays interdecadal modulations by the ENSO variance cycle, significantly correlated with ENSO at the turn of the 20th century and after the 1970s, but not in between. Outstanding issues, including future climate projections, are also discussed.

Timmermann, A, Okumura Y, An SI, Clement A, Dong B, Guilyardi E, Hu A, Jungclaus JH, Renold M, Stocker TF, Stouffer RJ, Sutton R, Xie SP, Yin J.  2007.  The influence of a weakening of the Atlantic meridional overturning circulation on ENSO. Journal of Climate. 20:4899-4919.   10.1175/jcli4283.1   Abstract
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Nonaka, M, McCreary JP, Xie SP.  2006.  Influence of midlatitude winds on the stratification of the equatorial thermocline. Journal of Physical Oceanography. 36:222-237. Abstract
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Fuckar, NS, Xie SP, Farneti R, Maroon EA, Frierson DMW.  2013.  Influence of the extratropical ocean circulation on the intertropical convergence zone in an idealized coupled general circulation model. Journal of Climate. 26:4612-4629.   10.1175/jcli-d-12-00294.1   AbstractWebsite

The authors present coupled model simulations in which the ocean's meridional overturning circulation (MOC) sets the zonal mean location of the intertropical convergence zone (ITCZ) in the hemisphere with deep-water production. They use a coarse-resolution single-basin sector coupled general circulation model (CGCM) with simplified atmospheric physics and two idealized land-sea distributions.In an equatorially symmetric closed-basin setting, unforced climate asymmetry develops because of the advective circulation-salinity feedback that amplifies the asymmetry of the deep-MOC cell and the upper-ocean meridional salinity transport. It confines the deep-water production and the dominant extratropical ocean heat release to a randomly selected hemisphere. The resultant ocean heat transport (OHT) toward the hemisphere with the deep-water source is partially compensated by the atmospheric heat transport (AHT) across the equator via an asymmetric Hadley circulation, setting the ITCZ in the hemisphere warmed by the ocean.When a circumpolar channel is open at subpolar latitudes, the circumpolar current disrupts the poleward transport of the upper-ocean saline water and suppresses deep-water formation poleward of the channel. The MOC adjusts by lowering the main pycnocline and shifting the deep-water production into the opposite hemisphere from the channel, and the ITCZ location follows the deep-water source again because of the Hadley circulation adjustment to cross-equatorial OHT. The climate response is sensitive to the sill depth of the channel but becomes saturated when the sill is deeper than the main pycnocline depth in subtropics. In simulations with a circumpolar channel, the ITCZ is in the Northern Hemisphere (NH) because of the Southern Hemisphere (SH) circumpolar flow that forces northward OHT.

Minobe, S, Kuwano-Yoshida A, Komori N, Xie SP, Small RJ.  2008.  Influence of the Gulf Stream on the troposphere. Nature. 452:206-U51.   10.1038/nature06690   Abstract
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Xie, SP, Okumura Y, Miyama T, Timmermann A.  2008.  Influences of Atlantic climate change on the tropical Pacific via the Central American Isthmus. Journal of Climate. 21:3914-3928.   10.1175/2008jcli2231.1   Abstract
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Zheng, XT, Hui C, Xie SP, Cai WJ, Long SM.  2019.  Intensification of El Nino Rainfall Variability Over the Tropical Pacific in the Slow Oceanic Response to Global Warming. Geophysical Research Letters. 46:2253-2260.   10.1029/2018gl081414   AbstractWebsite

Changes in rainfall variability of El Nino-Southern Oscillation (ENSO) are investigated under scenarios where the greenhouse gases increase and then stabilize. During the period of increasing greenhouse forcing, the ocean mixed layer warms rapidly. After the forcing stabilizes, the deeper ocean continues to warm the surface (the slow response). We show that ENSO rainfall variability over the tropical Pacific intensifies in both periods but the rate of increase per degree global mean surface temperature (GMST) warming is larger for the slow response because of greater relative warming in the base state as the mean upwelling changes from a damping to a driver of the surface warming. Our results have important implications for climate extremes under GMST stabilization that the Paris Agreement calls for. To stabilize GMST, the fast surface cooling offsets the slow warming from the prior greenhouse gas increase, while ENSO rainfall variability would continue to increase. Plain Language Summary The Paris Agreement calls for limiting global mean surface temperature increase to well below 2 degrees at the end of the 21st century. This requires the greenhouse gas (GHG) concentration to peak and subsequently decline in the next few decades. After the GHG concentration peak, the heat accumulated in the ocean surface layer continues to penetrate to the deeper ocean. This deeper ocean warming leads to a slow response of surface warming, further influencing the climate system. This study examines scenarios where GHGs increase and then stabilize to isolate the fast and slow responses of El Nino-Southern Oscillation (ENSO) rainfall variability. We find intensification of ENSO rainfall variability both during the increase and after stabilization of GHG concentrations due to a persistent El Nino-like mean warming pattern in the tropical Pacific. Furthermore, for unit global mean surface temperature increase, the changes in the mean state temperature and ENSO rainfall variability in the eastern equatorial Pacific is larger during the slow response. These results imply that there is a need for GHG emission reduction in the near future to avoid more extreme tropical rainfall during El Nino.

Mei, W, Xie SP.  2016.  Intensification of landfalling typhoons over the northwest Pacific since the late 1970s. Nature Geoscience. 9:753-+.   10.1038/ngeo2792   AbstractWebsite

Intensity changes in landfalling typhoons are of great concern to East and Southeast Asian countries(1). Regional changes in typhoon intensity, however, are poorly known owing to inconsistencies among different data sets(2-8). Here, we apply cluster analysis to bias-corrected data and show that, over the past 37 years, typhoons that strike East and Southeast Asia have intensified by 12-15%, with the proportion of storms of categories 4 and 5 having doubled or even tripled. In contrast, typhoons that stay over the open ocean have experienced only modest changes. These regional changes are consistent between operational data sets. To identify the physical mechanisms, we decompose intensity changes into contributions from intensification rate and intensification duration. We find that the increased intensity of landfalling typhoons is due to strengthened intensification rates, which in turn are tied to locally enhanced ocean surface warming on the rim of East and Southeast Asia. The projected ocean surface warming pattern under increasing greenhouse gas forcing suggests that typhoons striking eastern mainland China, Taiwan, Korea and Japan will intensify further. Given disproportionate damages by intense typhoons(1), this represents a heightened threat to people and properties in the region.

Tanimoto, Y, Xie SP.  2002.  Inter-hemispheric decadal variations in SST, surface wind, heat flux and cloud cover over the Atlantic Ocean. Journal of the Meteorological Society of Japan. 80:1199-1219. 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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Okumura, Y, Xie SP.  2004.  Interaction of the Atlantic equatorial cold tongue and the African monsoon. Journal of Climate. 17:3589-3602. Abstract
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