North Pacific Sea Surface Temperature Research Articles

Data-driven prediction strategies for low-frequency patterns of North Pacific climate variability

The North Pacific exhibits patterns of low-frequency variability on the intra-annual to decadal time scales, which manifest themselves in both model data and the observational record, and prediction of such low-frequency modes of variability is of great interest to the community. While parametric models, such as stationary and non-stationary autoregressive models, possibly including external factors, may perform well in a data-fitting setting, they may perform poorly in a prediction setting. Ensemble analog forecasting, which relies on the historical record to provide estimates of the future based on past trajectories of those states similar to the initial state of interest, provides a promising, nonparametric approach to forecasting that makes no assumptions on the underlying dynamics or its statistics. We apply such forecasting to low-frequency modes of variability for the North Pacific sea surface temperature and sea ice concentration fields extracted through Nonlinear Laplacian Spectral Analysis. We find such methods may outperform parametric methods and simple persistence with increased predictive skill.

Coupled intraseasonal variations in the East Asian winter monsoon and the South China Sea–western North Pacific SST in boreal winter

The sea surface temperature (SST) in the South China Sea (SCS) displays prominent intraseasonal variations during boreal winter with a spectrum peak in the 10–30-day time period. These intraseasonal SST variations are closely associated with intraseasonal variations of the East Asian winter monsoon (EAWM). A weak EAWM is preceded by cooler SST and followed by warmer SST in the SCS and subtropical western North Pacific. A coherent southward propagation is seen in the SCS in SST, surface wind, and latent heat flux anomalies. This southward propagation is attributed to the wind-evaporation-SST effect under climatological northerly winds in winter, which differs from summer when climatological winds are westerly. The SST-induced wind speed anomalies are larger to the north side of SST anomalies. This induces larger surface evaporation anomalies to the north side, leading to a southward displacement of large SST anomalies. In turn, wind and evaporation anomalies move southward. There appears to be a positive feedback between circulation and precipitation that leads to amplification of meridional wind anomalies when the SST anomalies are weak. Surface latent heat flux is a dominant factor for the SST change in the SCS and the Yellow Sea. Shortwave radiation has a complementary contribution to the SST change in the SCS, but has a negative effect in the Yellow Sea. The wind-induced Ekman advection appears important for the SST warming in the Yellow Sea.

Different responses of Sea Surface Temperature in the North Pacific to greenhouse gas and aerosol forcing

The responses of Sea Surface Temperature (SST) to greenhouse gas (GHG) and anthropogenic aerosol in the North Pacific are compared based on the historical single and all-forcing simulations with Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3). During 1860–2005, the effect of GHG forcing on the North Pacific SST is opposite to that of the aerosol forcing. Specifically, the aerosol cooling effect exceeds the GHG warming effect in the Kuroshio Extension (KE) region during 1950–2004 in the CM3 single forcing. The mid-latitude response of ocean circulation to the GHG (aerosol) forcing is to enhance (weaken) the Subtropical Gyre. Then the SST warming (cooling) lies on the zonal band of 40°N because of the increased (reduced) KE warm advection effect in the GHG (aerosol) forcing simulations, and the cooling effect to SST will surpass the warming effect in the KE region in the historical all-forcing simulations. Besides, the positive feedback between cold SST and cloud can also strengthen the aerosol cooling effect in the KE region during boreal summer, when the mixed layer depth is shallow. In the GHG (aerosol) forcing simulations, corresponding to warming (cooling) SST in the KE region, the weakened (enhanced) Aleutian Low appears in the Northeast Pacific. Consequently, the SST responses to all-forcing in the historical simulations are similar to the responses to aerosol forcing in sign and spatial pattern, hence the aerosol effect is quite important to the SST cooling in the mid-latitude North Pacific during the past 55 years.

Multi-model ensemble analysis of Pacific and Atlantic SST variability in unperturbed climate simulations

We assess internally-generated climate variability expressed by a multi-model ensemble of unperturbed climate simulations. We focus on basin-scale annual-average sea surface temperatures (SSTs) from twenty multicentennial pre-industrial control simulations contributing to the fifth phase of the Coupled Model Intercomparison Project. Ensemble spatial patterns of regional modes of variability and ensemble (cross-)wavelet-based phase-frequency diagrams of corresponding paired indices summarize the ensemble characteristics of inter-basin and regional-to-global SST interactions on a broad range of timescales. Results reveal that tropical and North Pacific SSTs are a source of simulated interannual global SST variability. The North Atlantic-average SST fluctuates in rough co-phase with the global-average SST on multidecadal timescales, which makes it difficult to discern the Atlantic Multidecadal Variability (AMV) signal from the global signal. The two leading modes of tropical and North Pacific SST variability converge towards co-phase in the multi-model ensemble, indicating that the Pacific Decadal Oscillation (PDO) results from a combination of tropical and extra-tropical processes. No robust inter- or multi-decadal inter-basin SST interaction arises from our ensemble analysis between the Pacific and Atlantic oceans, though specific phase-locked fluctuations occur between Pacific and Atlantic modes of SST variability in individual simulations and/or periods within individual simulations. The multidecadal modulation of PDO by the AMV identified in observations appears to be a recurrent but not typical feature of ensemble-simulated internal variability. Understanding the mechanism(s) and circumstances favoring such inter-basin SST phasing and related uncertainties in their simulated representation could help constraining uncertainty in decadal climate predictions.

Atmospheric response to the North Pacific enabled by daily sea surface temperature variability

AbstractOcean‐atmosphere interactions play a key role in climate variability on a wide range of timescales from seasonal to decadal and longer. The extratropical oceans are thought to exert noticeable feedbacks on the atmosphere especially on decadal and longer timescales, yet the large‐scale atmospheric response to anomalous extratropical sea surface temperature (SST) is still under debate. Here we show, by means of dedicated high‐resolution atmospheric model experiments, that sufficient daily variability in the extratropical background SST needs to be resolved to force a statistically significant large‐scale atmospheric response to decadal North Pacific SST anomalies associated with the Pacific Decadal Oscillation, which is consistent with observations. The large‐scale response is mediated by atmospheric eddies. This implies that daily extratropical SST fluctuations must be simulated by the ocean components and resolved by the atmospheric components of global climate models to enable realistic simulation of decadal North Pacific sector climate variability.

Changes in the relationship in the SST variability between the tropical Pacific and the North Pacific across the 1998/1999 regime shift

AbstractThis study shows that sea surface temperature (SST) variability in the central to eastern tropical Pacific has a strong negative correlation with that of the central to eastern North Pacific in the boreal winter after the 1998/1999 regime shift. This phenomenon is in contrast to before the 1998/1999 regime shift. The anomalous Aleutian low pressure associated with the tropical SST forcing became stronger, and its center shifted to the south and to the west after 1998/1999. Such a modulation caused the change in the North Pacific SST response. This also resulted in a close relationship between the tropical Pacific and North Pacific SST variability. The modulation of the Aleutian low pressure is primarily due to the westward shift in the location of the tropical convective heating around the dateline, which occurred during 1998/1999. The results of simple atmospheric model experiments support this hypothesis that the shift in the tropical convective heating to the west is responsible for the modulation of the Aleutian low pressure and the associated change in the relationship of the SST variability between the tropical Pacific and North Pacific. These results imply that the seasonal predictability of the North Pacific SST has increased since 1998/1999 due to its increased correlation with the tropical Pacific SST variability.

Slowing down of North Pacific climate variability and its implications for abrupt ecosystem change

Marine ecosystems are sensitive to stochastic environmental variability, with higher-amplitude, lower-frequency--i.e., "redder"--variability posing a greater threat of triggering large ecosystem changes. Here we show that fluctuations in the Pacific Decadal Oscillation (PDO) index have slowed down markedly over the observational record (1900-present), as indicated by a robust increase in autocorrelation. This "reddening" of the spectrum of climate variability is also found in regionally averaged North Pacific sea surface temperatures (SSTs), and can be at least partly explained by observed deepening of the ocean mixed layer. The progressive reddening of North Pacific climate variability has important implications for marine ecosystems. Ecosystem variables that respond linearly to climate forcing will have become prone to much larger variations over the observational record, whereas ecosystem variables that respond nonlinearly to climate forcing will have become prone to more frequent "regime shifts." Thus, slowing down of North Pacific climate variability can help explain the large magnitude and potentially the quick succession of well-known abrupt changes in North Pacific ecosystems in 1977 and 1989. When looking ahead, despite model limitations in simulating mixed layer depth (MLD) in the North Pacific, global warming is robustly expected to decrease MLD. This could potentially reverse the observed trend of slowing down of North Pacific climate variability and its effects on marine ecosystems.

Role of the North Pacific sea surface temperature in the East Asian winter monsoon decadal variability

In this study, a possible mechanism for the decadal variability in the East Asian winter monsoon (EAWM) is proposed. Specifically, the North Pacific sea surface temperature (SST) may play an important role. An analysis of the observations shows that the North Pacific SST has a remarkable decadal pattern whose phase shifted around the mid-1980s. This North Pacific SST decadal pattern can weaken the East Asian trough and enhance the North Pacific Oscillation through changing air–sea interactions over the North Pacific. The weak East Asian trough enhances the zonal circulation and weakens the meridional circulation over East Asia, consequently leading to a weaker southward cold surge and East Asia warming around the mid-1980s. The numerical experiment further confirms the pronounced physical processes. In addition, over the longer period of 1871–2012, the indices of the EAWM and North Pacific SST decadal pattern are also highly consistent on the decadal timescale, which further confirms the impact of the North Pacific SST decadal pattern on the EAWM decadal variability.

Impacts of Indian and Atlantic oceans on ENSO in a comprehensive modeling framework

The impact of the Indian and Atlantic oceans variability on El Niño–Southern-Oscillation (ENSO) phenomenon is investigated through sensitivity experiments with the SINTEX-F2 coupled model. For each experiment, we suppressed the sea surface temperature (SST) variability in either the Indian or Atlantic oceans by applying a strong nudging of the SST toward a SST climatology computed either from a control experiment or observations. In the sensitivity experiments where the nudging is done toward a control SST climatology, the Pacific mean state and seasonal cycle are not changed. Conversely, nudging toward an observed SST climatology in the Indian or Atlantic domain significantly improves the mean state and seasonal cycle, not only in the nudged domain, but also in the whole tropics. These experiments also demonstrate that decoupling the Indian or Atlantic variability modifies the phase-locking of ENSO to the annual cycle, influences significantly the timing and processes of ENSO onset and termination stages, and, finally, shifts to lower frequencies the main ENSO periodicities. Overall, these results suggest that both the Indian and Atlantic SSTs have a significant damping effect on ENSO variability and promote a shorter ENSO cycle. The reduction of ENSO amplitude is particularly significant when the Indian Ocean is decoupled, but the shift of ENSO to lower frequencies is more pronounced in the Atlantic decoupled experiments. These changes of ENSO statistical properties are related to stronger Bjerknes and thermocline feedbacks in the nudged experiments. During the mature phase of El Niño events, warm SST anomalies are found over the Indian and Atlantic oceans in observations or the control run. Consistent with previous studies, the nudged experiments demonstrate that these warm SSTs induce easterly surface wind anomalies over the far western equatorial Pacific, which fasten the transition from El Niño to La Niña and promote a shorter ENSO cycle in the control run. These results may be explained by modulations of the Walker circulation induced directly or indirectly by the Indian and Atlantic SSTs. Another interesting result is that decoupling the Atlantic or Indian oceans change the timing of ENSO onset and the relative role of other ENSO atmospheric precursors such as the extra-tropical Pacific Meridional Modes or the Western North Pacific SSTs.

Stationary Wave Activity Associated with the East Asian Winter Monsoon Pathway

The pathway of the East Asian winter mon- soon (EAWM) that usually leads to the out-of-phase pat- tern of surface air temperature between northern and southern East Asia is an important feature in the variabil- ity of the EAWM besides its strength. Using the European Centre for Medium-Range Weather Forecasts 40-year (ERA40) reanalysis dataset, this study investigates the pathway-related stationary wave activity to explore the mechanism of the interannual variations in the EAWM pathway. It reveals that when the southern pathway of the EAWM is strong, the phase of the climatological station- ary wave tends to be shifted westward significantly in both the horizontal and vertical directions by an anoma- lous wavenumber 2 pattern at mid-latitudes, whereas the changes are relatively small in the subtropics. The hori- zontal changes in the stationary wave phase facilitate a north-south-oriented East Asian trough in the middle tro- posphere that eventually produces the strong southern pathway of the EAWM. The vertical changes in the sta- tionary wave, in contrast, feature a westward-tilted phase line with height over the North Pacific, indicating en- hanced upward propagation of waves into the strato- sphere. This result suggests that the phase of stationary waves at mid-latitudes dominate the interannual variations in the EAWM pathway. Moreover, it supports our previ- ous interpretation of the possible role of the North Pacific sea surface temperature (SST) in the EAWM pathway variability. It also implies that the excitation of anomalous mid-latitude stationary waves may be the key in the re- sponse of the EAWM pathway to the North Pacific SST.  Keywords: East Asian winter monsoon, pathway, sta- tionary wave, phase Citation: Wang, L., 2014: Stationary wave activity asso- ciated with the East Asian winter monsoon pathway, At- mos. Oceanic Sci. Lett., 7, 7-10, doi:10.3878/j.issn.1674- 2834.13.0043.

Effect of recent sea surface temperature trends on the Arctic stratospheric vortex

AbstractComprehensive chemistry‐climate model experiments and observational data are used to show that up to half of the satellite era early springtime cooling trend in the Arctic lower stratosphere was caused by changing sea surface temperatures (SSTs). An ensemble of experiments forced only by changing SSTs is compared to an ensemble of experiments in which both the observed SSTs and chemically and radiatively active trace species are changing. By comparing the two ensembles, it is shown that warming of Indian Ocean, North Pacific, and North Atlantic SSTs and cooling of the tropical Pacific have strongly contributed to recent polar stratospheric cooling in late winter and early spring. When concentrations of ozone‐depleting substances and greenhouse gases are fixed, polar ozone concentrations show a small but robust decline due to changing SSTs. Ozone loss is larger in the presence of changing concentrations of ozone‐depleting substances and greenhouse gases. The stratospheric changes can be understood by examining the tropospheric height and heat flux anomalies generated by the anomalous SSTs. Finally, recent SST changes have contributed to a decrease in the frequency of late winter stratospheric sudden warmings.

Decadal and interannual variability of the Indian Ocean SST

The variability of the Indian Ocean on interannual and decadal timescales is investigated in observations, coupled model simulation and model experiment. The Indian Ocean Dipole (IOD) mode was specifically analyzed using a data-adaptive method. This study reveals one decadal mode and two interannual modes in the sea surface temperature (SST) of the IOD. The decadal mode in the IOD is associated with the Pacific Decadal Oscillation (PDO) of the North Pacific SST. The two interannual modes are related to the biennial and canonical components of El Nino-Southern Oscillation (ENSO), consistent with previous studies. This study hypothesizes that the relation between the Indian Ocean and the North Pacific on decadal scale may be through the northerly winds from the western North Pacific. The long simulation of Community Climate System Model version 4 also indicates the presence of IOD modes associated with the decadal PDO and canonical ENSO modes. However, the model fails to simulate the biennial ENSO mode in the Indian Ocean. The relation between the Indian Ocean and North Pacific Ocean is further supported by the regionally de-coupled model experiment.

Influence of aerosols in multidecadal SST variability simulations over the North Pacific

AbstractThe influence of aerosol emissions on North Pacific sea surface temperature (SST) variability during the twentieth century is investigated using a comparison between historical simulations with and without anthropogenic aerosol changes. The historical simulations using the Hadley Global Environment Model version 2 show that there is a common externally forced component in relation to the twentieth century North Pacific SST variability. This matches a number of important temporal and spatial characteristics of the observed multidecadal SST variability from the 1920s to 1990s, which is not found in experiments without aerosol changes. This paper explores both direct and indirect aerosol influences, and finds that in this model the aerosol‐cloud interactions dominate the total aerosol forcing of the surface energy budget. These aerosol‐cloud processes were not commonly included in most models in the previous (Coupled Model Intercomparison Project phase 3) generation, which may explain why the potential role of aerosols in Pacific variability has not been previously discussed. However, unlike recently reported aerosol drivers of Atlantic SST variability, the aerosol surface radiative forcing pattern does not map directly onto the historical spatial surface radiative and SST changes but is instead modulated by circulation changes to the Aleutian Low. These circulation changes share common features with previously reported studies of natural drivers of Pacific variability, suggesting that both forced and internally generated SST variability may be modulated via the same circulation response.

On the Relationship between the North Pacific Climate Variability and the Central Pacific El Niño

Abstract This study examined connections between the North Pacific climate variability and occurrence of the central Pacific (CP) El Niño for the period from 1950 to 2012. A composite analysis indicated that the relationship between the North Pacific sea surface temperature (SST), along with its overlying atmospheric circulation, and the CP El Niño during the developing and mature phases was changed when the occurrence frequency of the CP El Niño significantly increased after 1990. Empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses of variability in the tropical Pacific and its relationship to the North Pacific show that the North Pacific anomalous SST and the atmospheric variability are more closely associated with the occurrence of the CP El Niño after 1990 than before 1990. There were noticeable differences in terms of the atmospheric variability conditions over the North Pacific, such as the North Pacific Oscillation (NPO)-like atmospheric variability during the spring and its associated SST anomalies during the following winter before 1990 and after 1990. In addition, combined EOF analysis also indicated that the NPO-like atmospheric circulation becomes more effective at playing a role in initiating El Niño after 1990. Consequently, such a change might have been associated with the frequent occurrence of the CP El Niño after 1990.

Dynamics-Adapted Cone Kernels

We present a family of kernels for analysis of data generated by dynamical systems. These so-called cone kernels feature a dependence on the dynamical vector field operating in the phase space manifold, estimated empirically through finite differences of time-ordered data samples. In particular, cone kernels assign strong affinity to pairs of samples whose relative displacement vector lies within a narrow cone aligned with the dynamical vector field. The outcome of this explicit dependence on the dynamics is that, in a suitable asymptotic limit, Laplace--Beltrami operators for data analysis constructed from cone kernels generate diffusions along the integral curves of the dynamical vector field. This property is independent of the observation modality, and endows these operators with invariance under a weakly restrictive class of transformations of the data (including conformal transformations), while it also enhances their capability to extract intrinsic dynamical timescales via eigenfunctions. Here, we study these features by establishing the Riemannian metric tensor induced by cone kernels in the limit of large data. We find that the corresponding Dirichlet energy is governed by the directional derivative of functions along the dynamical vector field, giving rise to a measure of roughness of functions that favors slowly varying observables. We demonstrate the utility of cone kernels in nonlinear flows on the 2-torus and North Pacific sea surface temperature data generated by a comprehensive climate model.

中国冬季极端低温事件与海温和海冰的关系

本文利用站点资料和再分析资料分析中国冬季南、北方区域极端低温事件与海温和海冰的关系。研究发现，中国南、北方区域极端低温频数下降趋势与全球变暖有关，极端低温频数的线性趋势与印度洋和北大西洋海温异常呈负相关，还与前期边缘海海冰特别是格陵兰–巴伦支海海冰异常呈正相关。对于北方区域，在年代际变化尺度上，极端低温事件偏多时，冬季北太平洋海温表现为北负南正的异常分布，格陵兰–巴伦支海海冰呈正异常。在年际变化尺度上，冬季北太平洋中部与北美西岸海域海温出现西负东正的异常分布，北美东岸海温表现为负异常，楚科奇海和新瓦尔巴群岛以北海区海冰呈负异常。对南方区域，在年代际变化尺度上，极端低温事件偏多与PDO冷位相有关，并与格陵兰海和白令海海冰异常呈正相关，其他海区海冰异常呈负相关。在年际变化尺度上，前期阿拉斯加湾和白令海海区异常偏冷，对应着冬季南方区域极端低温事件偏多，另外还与冬季太平洋扇区海冰异常存在显著负相关关系。 Based on the dataset of daily minimum temperature in China during 1961-2010 and reanalysis data, the relationship between winter extreme minimum temperature (EMT) frequency and sea surface temperature (SST) and sea ice is analyzed. Research shows that, the decline of EMT fre-quency both in the north and south of China is associated with global warming. The linear trend has a negative correlation with the SST anomalies in the North Atlantic and India Ocean, and can be preceded by melting of the marginal sea ice, especially in the Greenland-Barents Sea ice during the preceding summer and autumn. For the north of China, its inter-decadal (ID) component may be affected by North Pacific SST anomalies which has a north-negative and south-positive distribution, and has a positive correlation with Greenland-Barents sea ice. While inter-annual (IA) component has a significant negative correlation with the SST anomalies along the east coast of North American and the anomalous SST between the subtropical North Pacific Ocean and the Gulf of Alaska represents a distribution of the dipole oscillation. And it is also affected by the sea ice melting in Chukchi Sea and Sea area in the north of Svalbard. On the other hand, for the south of China, its ID component is remarkable influenced by Pacific Decadal Oscillation (PDO). It also has a negative correlation with the marginal sea ice except the Greenland Sea and the Bering Sea. Beyond the IA time scale, the SST anomalies over the Bering Sea and the Gulf of Alaska prelude the anomalous winter EMT in the south of China. In addition, it also has a significant negative correlation with Pacific sector sea ice.

Influence of Pacific-Indian Ocean SSTA on Interannual Variation of Summer Precipitation in Shaanxi

Based on the Shaanxi summer precipitation data from 1961 to 2008,NOAA monthly sea surface temperature( SST),NCEP / NCAR monthly global reanalysis data,the relationship between early to the same period in different seasons of the Pacific,Indian Ocean and Shaanxi summer precipitation was analyzed using regression method,SVD method and the cross wavelet analysis method in order to provide clues and foundation for Shaanxi climate prediction. The results showthat: The correlation between Shaanxi summer precipitation with central eastern equatorial Pacific and the western Indian Ocean SST in early autumn and winter is positive,and with North Pacific SST is negative. The distribution of SST correlation coefficient is El Nino SST distribution. To the summer over the same year,the significant positive correlation zone move westward to the eastern Indian Ocean and the eastern coastal of China. The significant regions of influence of Pacific-Indian Ocean SSTA on Shaanxi summer precipitation over Preperiod and the same period locate in Guanzhong and the southeast of Shaanxi. The winter Nino3 SST and Shaanxi summer precipitation has the same phase resonance cycle in the 4 ~ 5 years scale and Nino3 SST ahead of the Shaanxi summer precipitation change is about 4 ~ 6 months. The correlations between East Asia,the South China Sea,Southeast Asia summer monsoon index and Shaanxi summer precipitation and Nino3 SST is all negative. When early Nino3 SST is abnormally high,the East Asian summer monsoon weakened,the Western Pacific subtropical high is stronger and more west,it always appears anomalies southwest wind water vapor transport in southern of Shaanxi,and appears anomalies north wind in northern of Shaanxi Province; the confluence of the warm and cold wind flowin Shaanxi cause more summer precipitation in Shaanxi Province,otherwise summer precipitation in Shaanxi less.

Season-dependent predictability and error growth dynamics of Pacific Decadal Oscillation-related sea surface temperature anomalies

By performing perfect model predictability experiments in a coupled general circulation model from the point of view of initial error growth, it is demonstrated that there may exist a “summer prediction barrier” (SPB) in the predictions of Pacific Decadal Oscillation-related sea surface temperature anomalies (PDO-related SSTA), which refers to the phenomenon that initial errors exhibit a significant season-dependent evolution, with the largest error growth occurring in the August–September–October (ASO) season. Due to the effect of the SPB, the prediction error of PDO-related SSTA events starts to grow rapidly during the ASO season and yields a positive (negative) prediction error for the warm (cold) events, essentially inducing a delay of the events. The SPB may be one of the main factors limiting the predictability of North Pacific sea surface temperature. The physical and dynamical mechanisms of the SPB are explored from two aspects: thermodynamics and dynamics. In terms of thermodynamics, we demonstrate that the fastest error growth of PDO-related SST cold (warm) events during the ASO season is mainly due to the largest anomalous release (absorption) of the latent heat flux in this season; while for dynamics, the effect of the vertical gradient of climatological mean sea temperature on the anomalous upwelling (downwelling) dominates the contribution of the dynamical temperature advections to the error growth of the PDO-related SST cold (warm) events during the ASO season. The anomalous release (absorption) of the latent heat flux and anomalous upwelling (downwelling) of the ocean currents are both related to the anomalous northwesterly or cyclonic (southeasterly or anticyclonic) wind over the PDO-related SSTA region, which indicates that the error growth associated with the SPB of PDO-related SST cold (warm) events is mainly driven by anomalous wind stress. The error growth associated with the SPB for PDO-related SSTA may also explain why the SSTA in the Kuroshio–Oyashio Extension is much less predictable than in other regions of the North Pacific, as shown by some state-of-the-art climate models.

Pollen-based temperature reconstructions from Jeju island, South Korea and its implication for coastal climate of East Asia during the late Pleistocene and early Holocene

We derived statistically robust, Weighted Averaging Partial Least Squares (WAPLS) transfer functions using modern surface pollen samples from Mt. Halla in Jeju Island, Korea. Pollen-based temperature reconstructions were performed by applying the best transfer function to lake sediments from Hanon maar paleolake in the southern part of Jeju Island. These quantitatively reconstructed temperatures were thereafter adjusted for the lack of warm analogue with the aid of Japanese and Russian transfer functions. Our temperature reconstructions demonstrated that annual mean temperatures during the Last Glacial Maximum (LGM) were ~8.5°C, i.e., about 8°C lower than the present, and that the Younger Dryas (YD) cooling amplitude was ~1.5°C between Bølling–Allerød (BA) (~11.3°C) and YD (~9.8°C). Spectral and wavelet analyses on detrended paleotemperatures identified significant periodicities at 1340years, primarily after 13,000calyr BP. The influence of Antarctic deglacial climate on the western North Pacific probably decreased with increasing northern latitude, as expected. Our results and Borneo oxygen isotope data showed very high correlation, indicating that Jeju Island was substantially influenced by the deglacial variabilities of the western Pacific warm pool via the Kuroshio Current. The climate of the study area seemed to have been mainly controlled by variation in the Atlantic Meridional Overturning Circulation (AMOC) before the beginning of the last deglaciation and subsequently by variation in the Western Tropical Pacific (WTP) Sea Surface Temperature (SST). We present significant information on the correlation of the late Pleistocene climate change with the Greenland oxygen isotope data and western North Pacific SST records. This correlation bridges the gap between terrestrial records, which mostly show AMOC variability, and oceanic records, which show WTP variability. These study results will increase our understanding of regional-scale climate change during the late Pleistocene and Early Holocene.

Pacific Decadal Oscillation and its relation to the extratropical atmospheric variation in CMIP5

It is investigated how the simulated Pacific Decadal Oscillation (PDO) differs among various coupled general circulation models (CGCMs), and how it is related to the simulated atmospheric variation in the North Pacific. The dataset of the historical runs of the 26 CGCMs reported to the Coupled Model Intercomparison Project Phase 5 are used. It is shown that the differences in the PDO pattern among 26 CGCMs are closely related to diverse displacements of the simulated Aleutian Low (AL), that is, the PDO pattern is highly dependent on longitudinal and latitudinal position of the anomalous AL associated with the PDO (PDO-related AL; ALPDO). In addition, it is demonstrated that in the models that have the southward shift of the ALPDO, the North Pacific sea surface temperature anomalies (SSTAs) associated with the PDO tend to modulate the atmospheric circulation strongly, implying strong two-way feedback between ocean and atmosphere. Therefore, this gives relatively strong persistency of the PDO. It is also found that the PDO in these models is highly correlated with the variation of the Kuroshio Extension current, implying that ocean dynamical processes play an important role in developing SSTAs.