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Small, JR, Xie S-P, Maloney ED, de Szoeke SP, Miyama T.  2011.  Intraseasonal variability in the far-east pacific: investigation of the role of air-sea coupling in a regional coupled model. Climate Dynamics. 36:867-890.   10.1007/s00382-010-0786-2   Abstract
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Zhuang, W, Xie S-P, Wang D, Taguchi B, Aiki H, Sasaki H.  2010.  Intraseasonal variability in sea surface height over the South China Sea. Journal of Geophysical Research-Oceans. 115   10.1029/2009jc005647   Abstract
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Amaya, DJ, Siler N, Xie SP, Miller AJ.  2018.  The interplay of internal and forced modes of Hadley Cell expansion: lessons from the global warming hiatus. Climate Dynamics. 51:305-319.   10.1007/s00382-017-3921-5   AbstractWebsite

The poleward branches of the Hadley Cells and the edge of the tropics show a robust poleward shift during the satellite era, leading to concerns over the possible encroachment of the globe's subtropical dry zones into currently temperate climates. The extent to which this trend is caused by anthropogenic forcing versus internal variability remains the subject of considerable debate. In this study, we use a Joint EOF method to identify two distinct modes of tropical width variability: (1) an anthropogenically-forced mode, which we identify using a 20-member simulation of the historical climate, and (2) an internal mode, which we identify using a 1000-year pre-industrial control simulation. The forced mode is found to be closely related to the top of the atmosphere radiative imbalance and exhibits a long-term trend since 1860, while the internal mode is essentially indistinguishable from the El Nio Southern Oscillation. Together these two modes explain an average of 70% of the interannual variability seen in model "edge indices" over the historical period. Since 1980, the superposition of forced and internal modes has resulted in a period of accelerated Hadley Cell expansion and decelerated global warming (i.e., the "hiatus"). A comparison of the change in these modes since 1980 indicates that by 2013 the signal has emerged above the noise of internal variability in the Southern Hemisphere, but not in the Northern Hemisphere, with the latter also exhibiting strong zonal asymmetry, particularly in the North Atlantic. Our results highlight the important interplay of internal and forced modes of tropical width change and improve our understanding of the interannual variability and long-term trend seen in observations.

Long, SM, Xie SP.  2015.  Intermodel variations in projected precipitation change over the North Atlantic: Sea surface temperature effect. Geophysical Research Letters. 42:4158-4165.   10.1002/2015gl063852   AbstractWebsite

Intermodel variations in future precipitation projection in the North Atlantic are studied using 23 state-of-art models from Phase 5 of the Coupled Model Intercomparison Project. Model uncertainty in annual mean rainfall change is locally enhanced along the Gulf Stream. The moisture budget analysis reveals that much of the model uncertainty in rainfall change can be traced back to the discrepancies in surface evaporation change and transient eddy effect among models. Results of the intermodel Singular Value Decomposition (SVD) analysis show that intermodel variations in local sea surface temperature (SST) pattern exert a strong control over the spread of rainfall projection among models through the modulation of evaporation change. The first three SVD modes explain more than 60% of the intermodel variance of rainfall projection and show distinct SST patterns with mode water-induced banded structures, reduced subpolar warming due to ocean dynamical cooling, and the Gulf Stream shift, respectively.

Zheng, XT, Xie SP, Lv LH, Zhou ZQ.  2016.  Intermodel uncertainty in ENSO amplitude change tied to Pacific Ocean warming pattern. Journal of Climate. 29:7265-7279.   10.1175/jcli-d-16-0039.1   AbstractWebsite

How El Nino-Southern Oscillation (ENSO) will change under global warming affects changes in extreme events around the world. The change of ENSO amplitude is investigated based on the historical simulations and representative concentration pathway (RCP) 8.5 experiments in phase 5 of the Coupled Model Intercomparison Project (CMIP5). The projected change in ENSO amplitude is highly uncertain with large intermodel uncertainty. By using the relative sea surface temperature (SST) as a measure of convective instability, this study finds that the spatial pattern of tropical Pacific surface warming is the major source of intermodel uncertainty in ENSO amplitude change. In models with an enhanced mean warming in the eastern equatorial Pacific, the barrier to deep convection is reduced, and the intensified rainfall anomalies of ENSO amplify the wind response and hence SST variability. In models with a reduced eastern Pacific warming, conversely, ENSO amplitude decreases. Corroborating the mean SST pattern effect, intermodel uncertainty in changes of ENSO-induced rainfall variability decreases substantially in atmospheric simulations forced by a common ocean warming pattern. Thus, reducing the uncertainty in the Pacific surface warming pattern helps improve the reliability of ENSO projections. To the extent that correcting model biases favors an El Nino-like mean warming pattern, this study suggests an increase in ENSO-related SST variance likely under global warming.

Zhou, WY, Xie SP.  2017.  Intermodel spread around the Kuroshio-Oyashio Extension region in coupled GCMs caused by meridional variation of the westerly jet from atmospheric GCMs. Journal of Climate. 30:4589-4599.   10.1175/jcli-d-16-0831.1   AbstractWebsite

The Kuroshio-Oyashio Extension (KOE) is a region of energetic oceanic mesoscale eddies and vigorous air-sea interaction that can influence climate variability over the northwest Pacific and East Asia. General circulation models (GCMs) exhibit considerable differences in their simulated climatology around the KOE region. Specifically, there are substantial intermodel spreads in both sea surface temperature (SST) and the upper-level westerly jet. In this study, the cause for such large spreads is studied by analyzing 21 pairs of coupled and atmospheric GCMs from phase 5 of the Coupled Model Intercomparison Project (CMIP5). It is found that the intermodel spread of the climatological westerly jet among coupled GCMs is largely inherited from their atmospheric models rather than being due to their SST difference as previously thought. An anomalous equatorward shift in the simulated westerly jet can give rise to a cold SST bias around the KOE region as follows. The equatorward jet shift induces cyclonic surface wind anomalies over the North Pacific, which not only enhance the turbulent heat fluxes out of the ocean south of the KOE but also drive an anomalous cyclonic ocean circulation that brings colder (warmer) water into the north (south) of the KOE. The KOE region is consequently cooled due to both the atmospheric and oceanic effects. Such processes are demonstrated through idealized perturbation experiments using an ocean model. The results herein point to reducing atmospheric model errors in the westerly jet as the way forward to improve the coupled simulations around the KOE region.

Ma, J, Xie SP, Xu HM.  2017.  Intermember variability of the summer northwest Pacific subtropical anticyclone in the ensemble forecast. Journal of Climate. 30:3927-3941.   10.1175/jcli-d-16-0638.1   AbstractWebsite

The accurate prediction of the East Asian summer monsoon (EASM) remains a major challenge for the climate research community. The northwest Pacific (NWP) subtropical anticyclone (NWPSA) is the dominant feature of the EASM low-level circulation variability. This study identifies two coupled modes between intermember anomalies of the NWPSA and sea surface temperature (SST). The first mode features SST anomalies over the tropical Pacific. This tropical Pacific mode has little impact on East Asian climate. The second mode features a strong coupling between SST in the north Indian Ocean (NIO)-NWP and NWPSA, with large impacts on East Asia. This resembles the Indo-western Pacific Ocean capacitor (IPOC) mode of interannual variability. Major differences exist in temporal evolution of the intermember SST spread between the equatorial Pacific and NIO. In the equatorial Pacific, the intermember SST spread grows gradually with lead time, while the spread of SST and low-level zonal wind grow rapidly from May to June in the NIO. The rapid growth over the NIO is due to positive feedback arising from the coupling between intermember anomalies of SST and winds. In post-El Nino summer, the intermember spread in equatorial Pacific SST forecast represents the variations in the timing of the El Nino phase transition. The late decay of El Nino relates to SST cooling and an anomalous cyclonic circulation over the South China Sea (SCS) but with little impact on East Asian climate. Thus, a better representation of the IPOC mode of regional ocean-atmosphere interaction over the NIO-NWP holds the key to improving the reliability of seasonal forecast of East Asian climate.

Okajima, H, Xie SP, Numaguti A.  2003.  Interhemispheric coherence of tropical climate variability: Effect of the climatological ITCZ. Journal of the Meteorological Society of Japan. 81:1371-1386. Abstract
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Chowdary, JS, Xie S-P, Tokinaga H, Okumura YM, Kubota H, Johnson N, Zheng X-T.  2012.  Interdecadal Variations in ENSO Teleconnection to the Indo-Western Pacific for 1870-2007. Journal of Climate. 25:1722-1744.   10.1175/jcli-d-11-00070.1   Abstract
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Hu, KM, Huang G, Zheng XT, Xie SP, Qu X, Du Y, Liu L.  2014.  Interdecadal variations in ENSO influences on Northwest Pacific-East Asian early summertime climate simulated in CMIP5 models. Journal of Climate. 27:5982-5998.   10.1175/jcli-d-13-00268.1   AbstractWebsite

The present study investigates interdecadal modulations of the El Nino-Southern Oscillation (ENSO) influence on the climate of the northwest Pacific (NWP) and East Asia (EA) in early boreal summer following a winter ENSO event, based on 19 simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). In the historical run, 8 out of 19 models capture a realistic relationship between ENSO and NWP early summer climate-an anomalous anticyclone develops over the NWP following a winter El Nino event- and the interdecadal modulations of this correlation. During periods when the association between ENSO and NWP early summer climate is strong, ENSO variance and ENSO-induced anomalies of summer sea surface temperature (SST) and tropospheric temperature over the tropical Indian Ocean (TIO) all strengthen relative to periods when the association is weak. In future projections with representative concentration pathways 4.5 and 8.5, the response of TIO SST, tropospheric temperature, and NWP anomalous anticyclone to ENSO all strengthen regardless of ENSO amplitude change. In a warmer climate, low-level specific humidity response to interannual SST variability strengthens following the Clausius-Clapeyron equation. The resultant intensification of tropospheric temperature response to interannual TIO warming is suggested as the mechanism for the strengthened ENSO effect on NWP-EA summer climate.

Xie, SP, Kunitani T, Kubokawa A, Nonaka M, Hosoda S.  2000.  Interdecadal thermocline variability in the North Pacific for 1958-97: A GCM simulation. Journal of Physical Oceanography. 30:2798-2813. Abstract
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Hosoda, S, Xie SP, Takeuchi K, Nonaka M.  2004.  Interdecadal temperature variations in the North Pacific Central Mode Water simulated by an OGCM. Journal of Oceanography. 60:865-877. Abstract
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Li, J, Xie S-P, Cook ER, Huang G, D'Arrigo R, Liu F, Ma J, Zheng X-T.  2011.  Interdecadal modulation of El Nino amplitude during the past millennium. Nature Climate Change. 1:114-118.   10.1038/nclimate1086   Abstract
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Yang, L, Du Y, Xie SP, Wang DX.  2012.  An interdecadal change of tropical cyclone activity in the South China Sea in the early 1990s. Chinese Journal of Oceanology and Limnology. 30:953-959.   10.1007/s00343-012-1258-9   Abstract

Tropical cyclone (TC) genesis in the South China Sea (SCS) during 1979-2008 underwent a decadal variation around 1993. A total of 55 TCs formed in the SCS from May to September during 1994-2008, about twice that during 1979-1993 (27). During the TC peak season (July-September, JAS), there were 43 TCs from 1994-2008, but only 17 during 1979-1993. For July in particular, 13 TCs formed from 1994-2008, but there were none during 1979-1993. The change in TC number is associated with changes of key environmental conditions in atmosphere and ocean. Compared to 1979-1993, the subtropical high was significantly weaker and was displaced more eastward during 1994-2008. In the former period, a stronger subtropical high induced downward flow, inhibiting TC formation. In the latter period, vertical wind shear and outgoing longwave radiation all weakened. Mid-level (850-500 hPa) humidity, and relative vorticity were higher. Sea surface temperature and upper layer heat content were also higher in the area. All these factors favor TC genesis during the latter period. The decadal change of TC genesis led to more landfalling TCs in Southern China during the period 1994-2008, which contributed to an abrupt increase in regional rainfall.

Cheng, XH, Xie SP, Du Y, Wang J, Chen X, Wang J.  2016.  Interannual-to-decadal variability and trends of sea level in the South China Sea. Climate Dynamics. 46:3113-3126.   10.1007/s00382-015-2756-1   AbstractWebsite

Interannual-to-decadal variability and trends of sea level in the South China Sea (SCS) are studied using altimetric data during 1993-2012 and reconstructed sea level data from 1950-2009. The interannual variability shows a strong seasonality. Surface wind anomalies associated with El Nio-Southern Oscillation explain the sea-level anomaly pattern in the interior SCS, while Rossby waves radiated from the eastern boundary dominate the sea-level variability in the eastern SCS. Decadal variability of sea level in the SCS follows that in the western tropical Pacific, with large variance found west of Luzon Island. Local atmospheric forcing makes a negative contribution to decadal variability in the central SCS, and Rossby waves radiated from the eastern boundary appear to be important. During 1993-2012, decadal sea level averaged in the SCS is significantly correlated with the Pacific Decadal Oscillation (PDO) (r = -0.96). The decadal variability associated with the PDO accounts for most part of sea-level trends in the SCS in the last two decades.

Weller, E, Feng M, Hendon H, Ma J, Xie SP, Caputi N.  2012.  Interannual Variations of Wind Regimes off the Subtropical Western Australia Coast during Austral Winter and Spring. Journal of Climate. 25:5587-5599.   10.1175/jcli-d-11-00324.1   Abstract

Off the Western Australia coast, interannual variations of wind regime during the austral winter and spring are significantly correlated with the Indian Ocean dipole (IOD) and the southern annular mode (SAM) variability. Atmospheric general circulation model experiments forced by an idealized IOD sea surface temperature anomaly field suggest that the IOD-generated deep atmospheric convection anomalies trigger a Rossby wave train in the upper troposphere that propagates into the southern extratropics and induces positive geopotential height anomalies over southern Australia, independent of the SAM. The positive geopotential height anomalies extended from the upper troposphere to the surface, south of the Australian continent, resulting in easterly wind anomalies off the Western Australia coast and a reduction of the high-frequency synoptic storm events that deliver the majority of southwest Australia rainfall during austral winter and spring. In the marine environment, the wind anomalies and reduction of storm events may hamper the western rock lobster recruitment process.

Sasaki, H, Xie S-P, Taguchi B, Nonaka M, Hosoda S, Masumoto Y.  2012.  Interannual variations of the Hawaiian Lee Countercurrent induced by potential vorticity variability in the subsurface. Journal of Oceanography. 68:93-111.   10.1007/s10872-011-0074-8   Abstract
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Zhou, ZQ, Zhang RH, Xie SP.  2019.  Interannual variability of summer surface air temperature over central India: Implications for monsoon onset. Journal of Climate. 32:1693-1706.   10.1175/jcli-d-18-0675.1   AbstractWebsite

Year-to-year variability of surface air temperature (SAT) over central India is most pronounced in June. Climatologically over central India, SAT peaks in May, and the transition from the hot premonsoon to the cooler monsoon period takes place around 9 June, associated with the northeastward propagation of intraseasonal convective anomalies from the western equatorial Indian Ocean. Positive (negative) SAT anomalies during June correspond to a delayed (early) Indian summer monsoon onset and tend to occur during post-El Nino summers. On the interannual time scale, positive SAT anomalies of June over central India are associated with positive SST anomalies over both the equatorial eastern-central Pacific and Indian Oceans, representing El Nino effects in developing and decay years, respectively. Although El Nino peaks in winter, the correlations between winter El Nino and Indian SAT peak in the subsequent June, representing a post-El Nino summer capacitor effect associated with positive SST anomalies over the north Indian Ocean. These results have important implications for the prediction of Indian summer climate including both SAT and summer monsoon onset over central India.

Cheng, X, Xie S-P, Tokinaga H, Du Y.  2011.  Interannual Variability of High-Wind Occurrence over the North Atlantic. Journal of Climate. 24:6515-6527.   10.1175/2011jcli4147.1   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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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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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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