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Kosaka, Y, Xie S-P.  2013.  Recent global-warming hiatus tied to equatorial Pacific surface cooling. Nature. advance online publication: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.   10.1038/nature12534   AbstractWebsite

Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century1, 2, challenging the prevailing view that anthropogenic forcing causes climate warming. Various mechanisms have been proposed for this hiatus in global warming3, 4, 5, 6, but their relative importance has not been quantified, hampering observational estimates of climate sensitivity. Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model. Although the surface temperature prescription is limited to only 8.2% of the global surface, our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970–2012 (which includes the current hiatus and a period of accelerated global warming). Moreover, our simulation captures major seasonal and regional characteristics of the hiatus, including the intensified Walker circulation, the winter cooling in northwestern North America and the prolonged drought in the southern USA. Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-Niña-like decadal cooling. Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase.

Xie, SP, Miyama T, Wang YQ, Xu HM, de Szoeke SP, Small RJO, Richards KJ, Mochizuki T, Awaji T.  2007.  A regional ocean-atmosphere model for eastern Pacific climate: Toward reducing tropical biases. Journal of Climate. 20:1504-1522.   10.1175/jcli4080.1   Abstract
Tokinaga, H, Xie S-P, Timmermann A, McGregor S, Ogata T, Kubota H, Okumura YM.  2012.  Regional Patterns of Tropical Indo-Pacific Climate Change: Evidence of the Walker Circulation Weakening. Journal of Climate. 25:1689-1710.   10.1175/jcli-d-11-00263.1   Abstract
Oshima, K, Tanimoto Y, Xie SP.  2012.  Regional Patterns of Wintertime SLP Change over the North Pacific and Their Uncertainty in CMIP3 Multi-Model Projections. Journal of the Meteorological Society of Japan. 90A:385-396.   10.2151/jmsj.2012-A23   Abstract

Regional patterns of wintertime sea level pressure (SLP) trends over the North Pacific and their uncertainty were investigated based on the phase 3 of the Coupled Model Intercomparison Project (CMIP3) multi-model projections under the Special Report on Emissions Scenarios (SRES) A1B emission scenario for the 21st century (2000-2099). While the 24-model ensemble mean of the 100-yr SLP trend over the North Pacific shows a northward shift of the Aleutian low (AL), regional patterns of the SLP change vary among the models. Projected changes deepen the AL in several models but it shifts northward in some others. The different response of the AL results in a large inter-model spread over the North Pacific, which is largest of the Northern Hemisphere and comparable in magnitude to the ensemble mean in the same region. This large spread means a high degree of uncertainty in the 100-yr SLP trend over the North Pacific.|For the total uncertainty in the SLP trends over the North Pacific, we examined the relative importance of the internal climate variability and model uncertainty due to different treatments of physical processes and computational scheme. To evaluate each of contributions, a single-realization ensemble using a subset of 10 CMIP3 models is compared to a multi-realization ensemble for the same models in the A1B projections. Additionally the control simulations under preindustrial conditions are examined to evaluate the background internal variability in each of the CMIP3 models. Our analysis shows that both the model uncertainty and internal climate variability contribute to the total uncertainty in the 100-yr SLP trends during the 21st century, while the internal climate variability largely explains the total uncertainty in the 50-yr SLP trends during the first half of the 21st century.|The changes in surface heat flux and North Pacific subtropical gyre in association with the different response of the AL affect regional patterns of the sea surface temperature trends among models.

Brown, PT, Li W, Xie S-P.  2015.  Regions of significant influence on unforced global mean surface air temperature variability in climate models. Journal of Geophysical Research: Atmospheres.   10.1002/2014JD022576   Abstract

We document the geographic regions where local variability is most associated with unforced global mean surface air temperature (GMT) variability in Coupled Model Intercomparison Project Phase 5 coupled global climate models (GCMs) at both the subdecadal and interdecadal timescales. For this purpose, Regions of Significant Influence on GMT are defined as locations that have a statistically significant correlation between local surface air temperature (SAT) and GMT (with a regression slope greater than 1), and where local SAT variation leads GMT variation in time. In both GCMs and observations, subdecadal timescale GMT variability is most associated with SAT variation over the eastern equatorial Pacific. At the interdecadal timescale, GMT variability is also linked with SAT variation over the Pacific in many GCMs, but the particular spatial patterns are GCM dependent, and several GCMs indicate a primary association between GMT and SAT over the Southern Ocean. We find that it is difficult to validate GCM behavior at the interdecadal timescale because the pattern derived from observations is highly depended on the method used to remove the forced variability from the record. The magnitude of observed GMT variability is near the ensemble median at the subdecadal timescale but well above the median at the interdecadal timescale. GCMs with a stronger subdecadal relationship between GMT and SAT over the Pacific tend to have more variable subdecadal GMT while GCMs with a stronger interdecadal relationship between GMT and SAT over parts of the Southern Ocean tend to have more variable GMT.

Merrifield, A, Lehner F, Xie SP, Deser C.  2017.  Removing Circulation Effects to Assess Central US Land-Atmosphere Interactions in the CESM Large Ensemble. Geophysical Research Letters. 44:9938-9946.   10.1002/2017gl074831   AbstractWebsite

Interannual variability of summer surface air temperature (SAT) in the central United States (U.S.) is influenced by atmospheric circulation and land surface feedbacks. Here a method of dynamical adjustment is used to remove the effects of circulation on summer SAT variability over North America in the Community Earth System Model Large Ensemble. The residual SAT variability is shown to reflect thermodynamic feedbacks associated with land surface conditions. In particular, the central U.S. is a hot spot of land-atmosphere interaction, with residual SAT accounting for more than half of the total SAT variability. Within the hot spot, residual SAT anomalies show higher month-to-month persistence through the warm season and a redder spectrum than dynamically induced SAT anomalies. Residual SAT variability in this region is also shown to be related to preseason soil moisture conditions, surface flux variability, and local atmospheric pressure anomalies.

Wang, LY, Liu QY, Xu LX, Xie SP.  2013.  Response of mode water and Subtropical Countercurrent to greenhouse gas and aerosol forcing in the North Pacific. Journal of Ocean University of China. 12:222-229.   10.1007/s11802-013-2193-x   AbstractWebsite

The response of the North Pacific Subtropical Mode Water and Subtropical Countercurrent (STCC) to changes in greenhouse gas (GHG) and aerosol is investigated based on the 20th-century historical and single-forcing simulations with the Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3). The aerosol effect causes sea surface temperature (SST) to decrease in the mid-latitude North Pacific, especially in the Kuroshio Extension region, during the past five decades (1950-2005), and this cooling effect exceeds the warming effect by the GHG increase. The STCC response to the GHG and aerosol forcing are opposite. In the GHG (aerosol) forcing run, the STCC decelerates (accelerates) due to the decreased (increased) mode waters in the North Pacific, resulting from a weaker (stronger) front in the mixed layer depth and decreased (increased) subduction in the mode water formation region. The aerosol effect on the SST, mode waters and STCC more than offsets the GHG effect. The response of SST in a zonal band around 40A degrees N and the STCC to the combined forcing in the historical simulation is similar to the response to the aerosol forcing.

Zheng, X-T, Xie S-P, Liu Q.  2011.  Response of the Indian Ocean Basin Mode and Its Capacitor Effect to Global Warming. Journal of Climate. 24:6146-6164.   10.1175/2011jcli4169.1   Abstract
Taguchi, B, Xie SP, Mitsudera H, Kubokawa A.  2005.  Response of the Kuroshio Extension to Rossby waves associated with the 1970s climate regime shift in a high-resolution ocean model. Journal of Climate. 18:2979-2995. Abstract
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
Li, G, Xie SP, Du Y.  2016.  A robust but spurious pattern of climate change in model projections over the tropical Indian Ocean. Journal of Climate. 29:5589-5608.   10.1175/jcli-d-15-0565.1   AbstractWebsite

Climate models consistently project reduced surface warming over the eastern equatorial Indian Ocean (IO) under increased greenhouse gas (GHG) forcing. This IO dipole (IOD)-like warming pattern, regarded as robust based on consistency among models by the new Intergovernmental Panel on Climate Change (IPCC) report, results in a large increase in the frequency of extreme positive IOD (pIOD) events, elevating the risk of climate and weather disasters in the future over IO rim countries. These projections, however, do not consider large model biases in both the mean state and interannual IOD variance. In particular, a "present-future relationship" is identified between the historical simulations and representative concentration pathway (RCP) 8.5 experiments from phase 5 of the Coupled Model Intercomparison Project (CMIP5) multimodel ensemble: models with an excessive IOD amplitude bias tend to project a strong IOD-like warming pattern in themean and a large increase in extreme pIOD occurrences under increased GHG forcing. This relationship links the present simulation errors to future climate projections, and is also consistent with our understanding of Bjerknes ocean-atmosphere feedback. This study calibrates regional climate projections by using this present-future relationship and observed IOD amplitude. The results show that the projected IOD-like pattern of mean changes and frequency increase of extreme pIOD events are largely artifacts of model errors and unlikely to emerge in the future. These results illustrate that a robust projection may still be biased and it is important to consider the model bias effect.

Kamae, Y, Ogura T, Watanabe M, Xie SP, Ueda H.  2016.  Robust cloud feedback over tropical land in a warming climate. Journal of Geophysical Research-Atmospheres. 121:2593-2609.   10.1002/2015jd024525   AbstractWebsite

Cloud-related radiative perturbations over land in a warming climate are of importance for human health, ecosystem, agriculture, and industry via solar radiation availability and local warming amplification. However, robustness and physical mechanisms responsible for the land cloud feedback were not examined sufficiently because of the limited contribution to uncertainty in global climate sensitivity. Here we show that cloud feedback in general circulation models over tropical land is robust, positive, and is relevant to atmospheric circulation change and thermodynamic constraint associated with water vapor availability. In a warming climate, spatial variations in tropospheric warming associated with climatological circulation pattern result in a general weakening of tropical circulation and a dynamic reduction of land cloud during summer monsoon season. Limited increase in availability of water vapor also reduces the land cloud. The reduction of land cloud depends on global-scale oceanic warming and is not sensitive to regional warming patterns. The robust positive feedback can contribute to the warming amplification and drying over tropical land in the future.

Wang, GH, Xie SP, Huang RX, Chen CL.  2015.  Robust warming pattern of global subtropical oceans and its mechanism. Journal of Climate. 28:8574-8584.   10.1175/jcli-d-14-00809.1   AbstractWebsite

The subsurface ocean response to anthropogenic climate forcing remains poorly characterized. From the Coupled Model Intercomparison Project (CMIP), a robust response of the lower thermocline is identified, where the warming is considerably weaker in the subtropics than in the tropics and high latitudes. The lower thermocline change is inversely proportional to the thermocline depth in the present climatology. Ocean general circulation model (OGCM) experiments show that sea surface warming is the dominant forcing for the subtropical gyre change in contrast to natural variability for which wind dominates, and the ocean response is insensitive to the spatial pattern of surface warming. An analysis based on a ventilated thermocline model shows that the pattern of the lower thermocline change can be interpreted in terms of the dynamic response to the strengthened stratification and downward heat mixing. Consequently, the subtropical gyres become intensified at the surface but weakened in the lower thermcline, consistent with results from CMIP experiments.

Du, Y, Xie SP, Huang G, Hu KM.  2009.  Role of Air-Sea Interaction in the Long Persistence of El Nino-Induced North Indian Ocean Warming. Journal of Climate. 22:2023-2038.   10.1175/2008jcli2590.1   Abstract
Xie, SP, Xu HM, Saji NH, Wang YQ, Liu WT.  2006.  Role of narrow mountains in large-scale organization of Asian monsoon convection. Journal of Climate. 19:3420-3429. Abstract