Search

Osteoarthritis (OA) is the most prevalent joint disease and is one of the major causes of disability in the world. There has been an increase in the incidence of OA, which is associated with an aging population, sedentary lifestyle, and reduced physical activity. Due to the complex OA pathogenesis, there are limited diagnostic tools. OA is a degenerative joint disorder with a recognized inflammatory component, usually described as abnormal expression of inflammatory factors. For instance, interleukin 6 (IL‐6) has been shown to be upregulated in serum and synovial fluid among patients with OA. Most of the inflammatory factors have been associated with the expression of long noncoding RNAs (lncRNAs). However, the role of the novel lncRNA Fer-1-like protein 4 (FER1L4) in OA is yet to be determined. Here, we interrogated the expression profile of FER1L4 in patients with OA to define its potential application as a diagnostic marker. We collected synovial fluid and blood samples from both OA cases and normal controls. Using qRT-PCR, we evaluated the expression of FER1L4 in plasma and synovial fluid. On the other hand, the expression of IL-6 in plasma and synovial fluid was assessed using ELISA. Besides, the effect of age, gender or disease stage in the expression of the FER1L4 in plasma was also estimated. Moreover, the receiver operating characteristic (ROC) curves were used to determine the impact of FER1L4 in OA cases compared with the normal controls. In addition, we analyzed the correlation between FER1L4 and IL-6 through Pearson correlation analysis. Also, IL-6 expression in overexpressed FER1L4 samples was detected in chondrocytes through western blot analysis, while FER1L4 expression following endogenous IL-6 exposure was detected by qRT-PCR. Our data showed that whereas lncRNA FER1L4 is downregulated in OA patients, IL‐6 is upregulated. The plasma FER1L4 levels among the OA cases were suppressed with disease progression and old age, and the down-regulation could efficiently discriminate OA patients from normal subjects. In addition, upregulation of FER1L4 inhibited IL‐6 expression in human chondrocyte cells, and treatment with different concentrations of exogenous IL‐6 did not affect the expression of FER1L4. Taken together, our data demonstrates that FER1L4 could efficiently identify OA cases from normal subjects, and can also modulate the expression of IL‐6 in human chondrocytes.

The dynamic origin of the interannual variability of West China autumn rainfall (WCAR), a special weather/climate phenomenon over western-central China in September and October, was investigated via observational diagnosis and numerical simulations. Here we found that the interannual variability of WCAR is closely related to the local horizontal trough, which is passively induced by two lower-level anticyclonic (high pressure) anomalies over East Asia. The anticyclonic anomaly over the south is a Gill-type response to the central and eastern Pacific diabatic cooling, while that over the north is part of the mid- to high-latitude barotropic Rossby wave train, which could be induced by either the thermal forcing of the central and eastern Pacific Ocean sea surface temperature (SST) cooling or that of the subtropical northern Atlantic Ocean SST warming. The quasi-barotropic high pressure anomaly over East Asia acts as an “invisible mountain” that steers the low-level anomalous southwesterly into a southeasterly and hinders the water vapor going farther to the north, leading to enhanced WCAR. However, the real mountain ranges in the region (the Qinglin and Ba Mountains) have no essential impact on the formation and interannual variability of WCAR.

The regional transport of air pollutants, controlled by emission sources and meteorological factors, results in a complex source–receptor relationship of air pollution change. Wuhan, a metropolis in the Yangtze River middle basin (YRMB) of central China, experienced heavy air pollution characterized by hourly PM2.5 concentrations reaching 471.1 µg m−3 in January 2016. To investigate the regional transport of PM2.5 over central eastern China (CEC) and the meteorological impact on wintertime air pollution in the YRMB area, observed meteorological and other relevant environmental data from January 2016 were analyzed. Our analysis presented noteworthy cases of heavy PM2.5 pollution in the YRMB area with unique “non-stagnant” meteorological conditions of strong northerly winds, no temperature inversion, and additional unstable structures in the atmospheric boundary layer. This unique set of conditions differed from the stagnant meteorological conditions characterized by near-surface weak winds, air temperature inversion, and stable structure in the boundary layer that are typically observed in heavy air pollution over most regions in China. The regional transport of PM2.5 over CEC aggravated PM2.5 levels, thus creating heavy air pollution in the YRMB area. This demonstrates a source–receptor relationship between the originating air pollution regions in CEC and the receiving YRMB region. Furthermore, a backward trajectory simulation using a Flexible Particle dispersion (FLEXPART) Weather Research and Forecasting (WRF) model to integrate the air pollutant emission inventory over China was used to explore the patterns of regional transport of PM2.5 governed by the strong northerly winds in the cold air activity of the East Asian winter monsoon season. It was estimated that the regional transport of PM2.5 from non-local air pollutant emissions contributes more than 65 % of the PM2.5 concentrations to the heavy air pollution in the YRMB region during the study period, revealing the importance of the regional transport of air pollutants over China as a causative factor of heavy air pollution over the YRMB area.

This study explored the effect of sea surface temperature (SST) on the interannual variations in wintertime haze days (WHDs) in the Pearl River Delta (PRD) region (WHDPRD) of China. Analyses unravel that SST anomalies in the adjoining area of the northern Indian and Pacific sector (the NIP region) can drive the interannual variations in the frequency of wintertime haze over the PRD region, which is deemed a salient oceanic driver. The SST anomalies have a stable and significant anticorrelation with the interannual component of the WHDPRD. This anticorrelation is highest in the concurrent winter and thus exerts a strong influence on the variability of localized WHDs. Further observational and simulation results suggest that the cold SST anomalies in the NIP region can induce a large-scale east–west dipole pattern by triggering diabatic cooling to the northwest. This dipole resembles the pattern tied to a higher WHDPRD, with an anticyclonic anomaly centered over the Indo-China Peninsula and a cyclonic anomaly centered over the western North Pacific. Under such circumstances, the PRD region is dominated by consistent northerly wind anomalies, facilitating the formation of two crucial processes responsible for a higher WHDPRD: the northward transportation of aerosols and a decrease in local wet deposition.

Analogous to the circumstances in wintertime, the increasing severity of autumnal haze pollution over the Beijing–Tianjin–Hebei (BTH) region may also lead to impairment of the socioeconomic development and human health in this region. Despite man-made aerosol emissions, the interannual variability of autumnal (September–October–November) haze days (AHDs) in the BTH region (AHDBTH) is apparently tied to the global and regional meteorological anomalies. The present study suggests that an above-normal AHDBTH is closely associated with the simultaneous sea surface temperature (SST) warming in two regions (over the North Atlantic subtropical sector, R1, and over the western North Pacific sector, R2). When the autumnal SST warming in both R1 and R2 is significant, the likelihood of a higher AHDBTH is greatly enhanced. Observational and simulation evidence demonstrated how remote SST anomalies over R1 and R2 influence variation of AHDBTH via two different pathways. Firstly, SST warming in R1 can induce a downstream midlatitudinal Rossby wave train, leading to a barotropic high-pressure and subsidence anomaly over the BTH region. Secondly, SST warming in R2 can also result in air subsidence over the BTH region through an anomalous local meridional cell. Through these two distinct pathways, localized meteorological circumstances conducive to a higher AHDBTH (i.e., repressed planetary boundary layer, weak southerly airflow, and warm and moist conditions) can be established.

In contrast with the considerable number of studies on the variability of winter haze pollution over eastern China, there have been few studies of autumnal haze in this region. The interannual variability of autumnal (September–November) haze days in the Beijing–Tianjin–Hebei region (AHDBTH) is significantly correlated with the Scandinavia–central Siberia–Western Pacific (SCSWP) teleconnection pattern, a quasi-barotropic atmospheric circulation anomaly. The SCSWP teleconnection pattern may therefore be a useful indicator for forecasting AHDBTH. The positive phase of the SCSWP teleconnection pattern enhances the anomalous anticyclonic circulation centered over the Western Pacific via the southeastward propagating Rossby wave train emanating from Scandinavia. The positive SCSWP teleconnection pattern, together with the northward shift of the East Asian jet stream induced by low-level atmospheric baroclinicity, could provide the favorable local meteorological circumstances (i.e., suppressed cold air activity, higher surface temperatures and low-level atmospheric inversion, and lower planetary boundary layer height and decreased surface wind speed) required to explain the recent increased incidence of AHDBTH.

The seismic action will cause the radiation wave movement of the water body around bridge structure in deep water, which will exert hydrodynamic pressure on the underwater structure and affect the dynamic response of the bridge. In this paper, a continuous girder bridge across sea is taken as an example to study the effect of hydrodynamic pressure on seismic response for deep-water bridges with different seismic isolation systems. The seismic response analysis method of deep-water bridges under hydrodynamic pressure is firstly established, and the dynamic response analyses of the bridge with friction pendulum system and cable-sliding friction bearing system are carried out, respectively. The results show that the hydrodynamic pressure increases the seismic response of deep-water bridges. Under friction pendulum system, the influence of hydrodynamic pressure on the longitudinal internal force of each pier and pile is greater than that on the transverse internal force, and the influence on the internal force of the pile top is greater than that of the pier bottom. The influence of hydrodynamic pressure on seismic response under cable-sliding friction bearing system is obviously less than that under friction pendulum, which shows the superiority of cable-sliding friction bearing in seismic design of deep-water bridges.

Regional transport of air pollutants controlled by both emission sources and meteorological factors results in a complex source-receptor relationship of air pollution change. Wuhan, a metropolis in the Yangtze River Middle Basin (YRMB) of central China experienced heavy air pollution characterized by excessive PM2.5 concentrations reaching 471.1 μg m−3 in January 2016. In order to investigate the regional transport of PM2.5 over China and the meteorological impact on wintertime air pollution in the YRMB area, observational meteorological and other relevant environmental data from January 2016 were analyzed. Our analysis presented the noteworthy cases of heavy PM2.5 pollution in the YRMB area with the unique “non-stagnant” meteorological conditions of strong northerly winds, no temperature inversion and additional unstable structures in the atmospheric boundary layer. This unique set of conditions differed from the stagnant meteorological conditions characterized by near-surface weak winds, air temperature inversion, and stable structure in the boundary layer observed in heavy air pollution over most regions in China. The regional transport of PM2.5 over central-eastern China aggravated PM2.5 levels present in the YRMB area, thus demonstrating the source-receptor relationship between the originating air pollution regions in central-eastern China and the receiving YRMB regions. Furthermore, a backward trajectory simulation using FLEXPART-WRF to integrate the air pollutant emission inventory over China was used to explore the patterns of regional transport of PM2.5 governed by the strong northerly winds in the cold air activity of the East Asian winter monsoon over central-eastern China, which contributes markedly to the heavy PM2.5 pollution in the YRMB area. It was estimated that the regional transport of PM2.5 of non-local air pollutant emissions could contribute more than 65 % of the PM2.5 concentrations to the heavy air pollution in the YRMB region during the study period, revealing the importance of the regional transport of air pollutants over central-eastern China in the formation of heavy air pollution over the YRMB region.

The wintertime haze day (HD) in the Yangtze River Delta (YRD) region of China shows a significant upward trend during the past decades due to the rapid industrialization and urbanization. Besides the enhanced anthropogenic emission, climate change also plays the important role in the long term HD variations. In this study, the significant decadal variation of wintertime HD during the period 1960-2012 in YRD is examined by the empirical orthogonal function (EOF) analysis, featured as less HD occurrence before 1980 and more occurrence after 2000. The numerical simulations by the global transport and chemical model (Model for Ozone and Related chemical Tracers, MOZART) with the same emission inventory suggest 8.4% enhancement of wintertime PM2.5 (particulate matter with the equivalent diameter of air dynamics less than or equal to 2.5μm) mass concentration in YRD during 2001-2009 compared with that during 1971-1979 attributed to meteorological changes, indicating the significant effect of climate anomaly on the decadal variations of wintertime HD. Through the composite analysis on the atmospheric dynamical and thermal conditions based on the reanalysis data, the faster warming in the lower and middle troposphere over the continent in the recent decade is suggested to be important for the out-of-phase decadal HD variation in YRD. The thermal anomaly not only reverses the zonal thermal difference of land-sea to stimulate the anomalous southerlies over YRD leading to reduced prevailing north wind in winter, but also develops the deep inversion below the mid-troposphere to enhance the atmospheric stability. As a result, more frequent and persistent air stagnations in recent decade are expected for the reduction of atmospheric horizontal dispersion and vertical diffusion capacity leading to more occurrence of wintertime HD in YRD.

The impact of surface sensible heating over the Tibetan Plateau (SHTP) on the western Pacific subtropical high (WPSH) with and without air–sea interaction was investigated in this study. Data analysis indicated that SHTP acts as a relatively independent factor in modulating the WPSH anomaly compared with ENSO events. Stronger spring SHTP is usually followed by an enhanced and westward extension of the WPSH in summer, and vice versa. Numerical experiments using both an AGCM and a CGCM confirmed that SHTP influences the large-scale circulation anomaly over the Pacific, which features a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to different background circulation in spring and summer, such a response facilitates a subdued WPSH in spring but an enhanced WPSH in summer. Moreover, the CGCM results showed that the equatorial low-level westerly at the south edge of the cyclonic anomaly brings about a warm SST anomaly (SSTA) in the equatorial central Pacific via surface warm advection. Subsequently, an atmospheric Rossby wave is stimulated to the northwest of the warm SSTA, which in turn enhances the atmospheric dipole anomalies over the western Pacific. Therefore, the air–sea feedbacks involved tend to reinforce the effect of SHTP on the WPSH anomaly, and the role of SHTP on general circulation needs to be considered in a land–air–sea interaction framework.

Analogous to the circumstances in wintertime, the increasing severity of autumnal haze pollution over the Beijing–Tianjin–Hebei (BTH) region may also lead to impairment of the socioeconomic development and human health in this region. Despite manmade aerosol emissions, the interannual variability of autumnal (September–October–November) haze days (AHD) in the BTH region (AHDBTH) is apparently tied to the global and regional meteorological anomalies. The present study suggests that an above-normal AHDBTH is closely associated with the simultaneous sea surface temperature (SST) warming in two regions [over the North Atlantic subtropical sector (R1) and over the western North Pacific sector (R2)]. When the autumnal SST warming in R1 and R2 are both remarkably significant, the joint impacts can greatly enhance the likelihood of a higher AHDBTH. Observational and simulation evidence suggests that SST anomalies can affect the variation in AHDBTH via two different pathways. Firstly, SST warming in R1 can induce a downstream mid-latitudinal Rossby wave train, leading to a barotropic high-pressure and subsidence anomaly over the BTH region. Secondly, SST warming in R2 can also result in air subsidence over the BTH region through an anomalous local meridional cell. Through these two distinct pathways, localized meteorological circumstances conducive to a higher AHDBTH (i.e., repressed planetary boundary layer, weak southerly airflow, and warm and moist conditions) can be established.

The East Asian subtropical summer monsoon (EASSM) is one component of the East Asian summer monsoon system, and its evolution determines the weather and climate over East China. In the present paper, we firstly demonstrate the formation and advancement of the EASSM rainbelt and its associated circulation and precipitation patterns through reviewing recent studies and our own analysis based on JRA-55 (Japanese 55-yr Reanalysis) data and CMAP (CPC Merged Analysis of Precipitation), GPCP (Global Precipitation Climatology Project), and TRMM (Tropical Rainfall Measuring Mission) precipitation data. The results show that the rainy season of the EASSM starts over the region to the south of the Yangtze River in early April, with the establishment of strong southerly wind in situ. The EASSM rainfall, which is composed of dominant convective and minor stratiform precipitation, is always accompanied by a frontal system and separated from the tropical summer monsoon system. It moves northward following the onset of the South China Sea summer monsoon. Moreover, the role of the land–sea thermal contrast in the formation and maintenance of the EASSM is illustrated, including in particular the effect of the seasonal transition of the zonal land–sea thermal contrast and the influences from the Tibetan Plateau and midlatitudes. In addition, we reveal a possible reason for the subtropical climate difference between East Asia and East America. Finally, the multi-scale variability of the EASSM and its influential factors are summarized to uncover possible reasons for the intraseasonal, interannual, and interdecadal variability of the EASSM and their importance in climate prediction.

Air quality change is generally driven by two factors: pollutant emissions and meteorology, which are difficult to distinguish via observations. To identify the contribution of meteorological factor to air quality change, an aerosol simulation from 1995 to 2004 with the global air quality model GEM-AQ/EC was designed without year-to-year changes in the anthropogenic aerosol (including sulfate and organic and black carbon) emissions over the 10-year span. To assess the impact of interannual variations of East Asian monsoon (EAM) on air quality change in China, this modeling study focused on the region of central-eastern China (CEC), a typical East Asian monsoon (EAM) region with high anthropogenic aerosol emissions. The simulation analysis showed that the interannual variability in surface aerosols over CEC was driven by fluctuation in meteorological factors associated with EAM changes. Large amplitudes of interannual variability in surface aerosol concentrations reaching 20–30% relative to the 10-year averages were found over southern CEC in summer and over northern CEC in winter. The weakened near-surface winds of EAMs in both summer and winter were significantly correlated with aerosol increases over most areas of CEC. The summer and winter monsoon changes enhance the surface aerosol concentrations with increasing trend rates exceeding 30% and 40% over the southern and northern CEC region, respectively, during the 10 years. The composite analyses of aerosol concentrations in weak and strong monsoon years revealed that positive anomalies in surface aerosol concentrations during weak summer monsoon years were centered over the vast CEC region from the North China Plain to the Sichuan Basin, and the anomaly pattern with “northern higher” and “southern lower” surface aerosol levels was distributed over CEC in weak winter monsoon years. Aerosol washout by summer monsoon rainfall exerted an impact on CEC aerosol distribution in summer; aerosol dry depositions in connection with atmospheric boundary layer conditions resulted in wintertime aerosol variations over CEC. Climate change with regard to EAMs could modulate the interannual variations in aerosols and air quality over CEC by changing near-surface winds, precipitation and atmospheric boundary layer.

Spring (March–May) rainfall after a dry period in winter has a substantial impact on agriculture and water management in populous southern China. The occurrence of low-frequency spring rainfall anomalies has been linked with the tropical Madden–Julian Oscillation (MJO) through its modulation of large-scale circulation and moisture supply over southern China. Using the spatial and temporal information of the MJO as a predictor, an empirical model for extended-range forecasting of spring rainfall in southern China was constructed. We first obtained the coupled patterns between the preceding MJO evolutions (real-time multivariate MJO index) and the succeeding rainfall variability in southern China based on singular value decomposition analysis. Then, a prediction was carried out by projecting the predictor onto the spatiotemporal coupled patterns. Useful skill, in terms of the temporal correlation coefficient (TCC) between the predicted and observed rainfall over southern China, persisted up to a forecast lead-time of six pentads. The forecast amplitude bias in terms of root-mean-square error was around 1.0 standard deviation. Also, the forecast skill was highly dependent on the strength of the MJO signal. During active MJO periods, the TCC skill was around twofold larger than that during weak MJO periods. The current statistical model shows encouraging ability, but additional work is required to improve its forecasting skill.

Vehicle emissions are a major source of urban air pollution. In recent decade, the Chinese government has introduced a range of policies to reduce vehicle emissions. In order to understand the chemical characteristics of PM2.5 from on-road vehicle emissions in the Pearl River Delta (PRD) region and to evaluate the effectiveness of control policies on vehicle emissions, the emission factors of PM2.5 mass, elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), water-soluble inorganic ions (WSII), metal elements, organic compounds and stable carbon isotopic composition were measured in the Zhujiang tunnel of Guangzhou, in the PRD region of China in 2013. Emission factors of PM2.5 mass, OC, EC and WSOC were 92.4, 16.7, 16.4 and 1.31 mg vehicle−1 km−1 respectively. Emission factors of WSII were 0.016 (F-) ~ 4.17 (Cl−) mg vehicle−1 km−1, contributing about 9.8% to the PM2.5 emissions. The sum of 27 measured metal elements accounted for 15.2% of PM2.5 emissions. Fe was the most abundant metal element, with an emission factor of 3.91 mg vehicle−1 km−1. Emission factors of organic compounds including n-alkanes, polycyclic aromatic hydrocarbons, hopanes and steranes were 91.9, 5.02, 32.0 and 7.59 μg vehicle−1 km−1, respectively. Stable carbon isotopic composition δ13C value was −25.0‰ on average. An isotopic fractionation of 3.2‰ was found during fuel combustion. Compared to a previous study in Zhujiang tunnel in 2004, emission factors of PM2.5mass, EC, OC, WSII except Cl- and organic compounds decreased by 16.0 ~ 93.4%, which could be attributed to emission control policy from 2004 to 2013. However, emission factors of most of the metal elements increased significantly, which could be partially attributed to the changes in motor oil additives and vehicle conditions. There are no mandatory national standards to limit metal content from vehicle emissions, which should be a concern of the government. A snapshot of the 2013 characteristic emissions of PM2.5 and its constituents from the on-road vehicular fleet in the PRD region retrieved from our study would be helpful for the assessment of past and future implementations of vehicle emission control policy.

The relationship between the South China Sea summer monsoon (SCSSM) onset and the subsequent subtropical East Asian monsoon rainfall from May to September (SEAMR) is investigated. The SCSSM onset is found to have a significant positive correlation with the SEAMR stretching from the lower reaches of the Yangtze River valley (LYR) to the southern Japan; e.g. the early onset of the SCSSM tends to be succeeded by less SEAMR, whereas the late onset is likely to be followed by more SEAMR. The positive relationship between the SCSSM onset and the SEAMR is directly controlled by the persistent western North Pacific anti-cyclonic/cyclonic (WNPAC/WNPC) circulation anomaly from boreal spring to summer. The persistence of the large-scale circulation anomalies are accompanied by the decaying phase of El Nino (La Nina) with the pronounced sea-surface temperature anomalies (SSTA) over the tropical Indian Ocean (IO), the western North Pacific and the topical central and eastern Pacific Ocean (PO), respectively. Further numerical experiments indicate that the topical IO SSTA governs the positive relationship between the SCSSM onset and the subsequent SEAMR. On one hand, the wavelength of the Kevin-wave response to tropical IO SSTA forcing is three times that of the Rossby-wave response to the western North Pacific SSTA forcing. The Kevin-wave response directly influences the low level circulation anomalies field throughout the South China Sea region, determining the onset date of the SCSSM. On the other hand, the horizontal wind shear that induced by the persistent Kevin-wave response would also maintain the WNPAC/WNPC and further control the SEAMR from May to September. Thus, it is the topical IO SSTA forcing that consolidates the positive relationship between the SCSSM onset and the SEAMR.

Using the daily outgoing longwave radiation (OLR), the pentad Climate Prediction Center Merged Analysis of Precipitation (CMAP), and the 6-h Climate Forecast System Reanalysis (CFSR) dataset from 1979 to 2010, a composite analysis along with space–time wave filtering is performed to examine the linkage between the Madden–Julian oscillation (MJO) and the onset of the East Asian subtropical summer monsoon (EASSM) (over 20°–30°N, 110°–120°E). The onset of the EASSM is shown to be best characterized by the reversal of the mean meridional wind shear related to the rapid reestablishment of the South Asian high (SAH) over the southern Indochinese Peninsula in the upper troposphere. The mean date of EASMM onset is near the end of April, which is about a month earlier than the typical onset of the East Asian summer monsoon. Further analysis indicates that the onset of the EASSM and the reestablishment of SAH are often associated with the arrival of the wet phase of the tropical MJO over the central and eastern Indian Ocean.

An extended singularity value decomposition based statistical model, namely the spatial–temporal projection model (STPM), was constructed for the extended-range (10–30-day) forecast of tropical outgoing longwave radiation anomalies (OLRA). The special feature of this empirical model is using the spatial and temporal information of predictor–predictand coupled patterns to predict the temporally varying predictand field at all-time leads (i.e., 10–35 days) at once. A 10-year hindcast result shows that, different from previous statistical models, the skill scores of the STPM dropped slowly with forecast lead times. Useful skills can be detected at 30–35 day leads over most tropical regions. The highest temporal correlation coefficient of 0.4–0.5 appears over the Maritime Continent (Indian and western North Pacific monsoon regions) in boreal winter (summer), exceeding a 99 % confidence level. The STPM is also capable in predicting the spatial evolutions of convective anomalies, including the zonal and meridional propagation of OLRA. The forecast of the Real-time Multivariate MJO indices shows that the STPM attains a higher skill than previous statistical models. The STPM also shows comparable skills with the state-of-the-art dynamic models during the Dynamics of the Madden–Julian Oscillation campaign period, especially at 15-day and longer leads.

The sea surface temperature (SST) or sea level pressure (SLP) has usually been used to measure the strength of El Nino–Southern Oscillation (ENSO) events. In this study, two new indices, based on the upper-ocean heat content (HC), are proposed to quantify the two “flavours” of El Nino (i.e., the Cold Tongue El Nino (CTE) and Warm Pool El Nino (WPE)). Compared with traditional SST or SLP indices, the new HC-based indices can distinguish CTE and WPE events much better and also represent the two leading modes of the interannual variability of the atmosphere–ocean coupled system in the tropical Indo-Pacific region. The two leading modes are obtained by performing multivariate Empirical Orthogonal Function analysis on two oceanic variables (SST and HC) over the tropical Pacific (30°S–30°N, 120°E–80°W) and six atmospheric variables (outgoing longwave radiation, SLP, streamfunction, and velocity potential at 850 hPa and 200 hPa) over the tropical Indo-Pacific region (30°S–30°N, 60°E–80°W) for the period ...

The present work identifies two types of La Nina based on the spatial distribution of sea surface temperature (SST) anomaly. In contrast to the eastern Pacific (EP) La Nina event, a new type of La Nina (central Pacific, or CP La Nina) is featured by the SST cooling center over the CP. These two types of La Nina exhibit a fundamental difference in SST anomaly evolution: the EP La Nina shows a westward propagation feature while the CP La Nina exhibits a standing feature over the CP. The two types of La Nina can give rise to a significantly different teleconnection around the globe. As a response to the EP La Nina, the North Atlantic (NA)–Western European (WE) region experiences the atmospheric anomaly resembling a negative North Atlantic Oscillation (NAO) pattern accompanied by a weakening Atlantic jet. It leads to a cooler and drier than normal winter over Western Europe. However, the CP La Nina has a roughly opposing impact on the NA–WE climate. A positive NAO-like climate anomaly is observed with a strengthening Atlantic jet, and there appears a warmer and wetter than normal winter over Western Europe. Modeling experiments indicate that the above contrasting atmospheric anomalies are mainly attributed to the different SST cooling patterns for the two types of La Nina. Mixing up their signals would lead to difficulty in seasonal prediction of regional climate. Since the La Nina-related SST anomaly is clearly observed during the developing autumn, the associated winter climate anomalies over Western Europe could be predicted a season in advance.

A multivariate empirical orthogonal function (MV-EOF) analysis for 1979–2010 shows that low-level circulation and rainfall over East Asia experienced a significant decadal shift around the mid-1990s. During boreal spring (March–May), the first principal component (PC) of the MV-EOF exhibits a marked decadal change around the mid-1990s, while during boreal summer (June–August) the second PC shows a pronounced decadal shift around the same time. It is further noted that the decadal rainfall change over southern China experienced an out-of-phase relationship between boreal spring and summer; that is, from the pre-1994 to the post-1994 period, the rainfall tends to decrease in boreal spring but increase in boreal summer. A mechanism is put forward to explain the out-of-phase decadal rainfall change over southern China between boreal spring and summer. In boreal spring, the composite differences of SST between the latter and former decadal periods indicate a La Niña–like pattern with warming in the western Pacific and cooling in the eastern Pacific. This pattern leads the enhanced convection over the Maritime Continent, which may further induce anomalous subsidence and thus negative rainfall anomalies over southern China through the local Hadley circulation. In boreal summer, dominant decadal SST warming appears in the entire tropical Indian Ocean while the negative SST anomalies in eastern Pacific are much weaker. The warm SST anomaly over the Indian Ocean leads to suppressed convection over the Maritime Continent, which, through the local Hadley cell, favors the strengthening the East Asian monsoon trough and leads to a positive rainfall anomaly over southern China.

During year-to-year El Niño events in recent decades, major sea surface warming has occurred frequently in the central Pacific. This is distinct from the eastern Pacific warming pattern during canonical El Niño events. Accordingly, the central-Pacific El Niño exerts distinct impacts on ecosystems, climate and hurricanes worldwide. The increased frequency of the new type of El Niño presents a challenge not only for the understanding of El Niño dynamics and its change but also for the prediction of El Niño and its global impacts at present and future climate. Previous studies have proposed different indices to represent the two types of El Niño for better understanding, prediction and impact assessment. Here, we find that all popularly used indices for the central-Pacific El Niño show a dominant spectral peak at a decadal period with comparatively weak variance at interannual timescales. Our results suggest that decadal anomalies have an important contribution to the occurrence of the central-Pacific El Niño over past decades. Removing the decadal component leads to a significant reduction in the frequency of the central-Pacific El Niño in observations and in Coupled Model Intercomparison Project Phase 5 simulations of preindustrial, historical and future climate.