ENSO Cycle Research Articles

LINEAR REGRESSION ANALYSIS OF THE INFLUENCE OF WESTERN NORTH PACIFIC TROPICAL CYCLONES ON THEIR LARGE‐SCALE ENVIRONMENT

AbstractInfluences of the western North Pacific (WNP) tropical cyclones (TCs) on their large‐scale environment are investigated by lag regressing several physical variables, including 850 hPa relative vorticity, surface zonal wind, total column water vapor, outgoing longwave radiation (OLR), precipitation and sea surface temperature (SST), on an index of TC activity accumulated cyclone energy (ACE) on a monthly time scale. Differences between these variables on the monthly and weekly time scales are discussed. The results show that: (1) The zonal wind regressed against ACE on the monthly time scale is more significant than that on the weekly time scale for both its intensity and scope. The high‐intensity and long‐lifetime TCs near the equatorial region have a positive effect on triggering or strengthening surface westerly anomalies in the equatorial region. The long‐lived and intense equatorial surface westerly anomalies can cause westerly wind bursts, which is believed to be a major factor during the occurrence and development of ENSO events. (2) More variables such as OLR, precipitation and SST exhibit a feature corresponding to El Niño on a monthly time scale compared to that on a weekly time scale, which suggests that TC activities on a monthly time scale are more closely associated with the ENSO cycle. (3) One to two months after the genesis of TCs, the column water vapor decreases while OLR increases at the TC genesis region. This could reduce the potential for TC genesis. Although the SST decrease caused by TCs only occurs at a small spatial scale, it can be spread to a large scale via oceanic and atmospheric propagation exhibiting feedback effect. In addition, the feedback does not occur instantaneously but with a certain lag, which explains why the signal of TC influences on large‐scale environment is more pronounced on the monthly time scale.

Zonal Transport from the Western Boundary and Its Role in Warm Water Volume Changes during ENSO

AbstractObservations from TRITON buoys in the warm/fresh pool and a global ocean general circulation model are used to study the interannual variability of the equatorial western Pacific and the relationship between the zonal warm water transport, meridional convergence, and the warm water volume (WWV). The simulated temperature, salinity, and zonal warm water transport are validated with the mooring observations for the period 2000–14. The model results are then used to examine the WWV balance in ENSO cycles in an extended period from 1980 to 2014. It is shown that the zonal transport is highly correlated with meridional convergence and leads by about 4–5 months, and their phase offset determines the WWV changes. This result differs from the recharge paradigm in which the meridional convergence is supposed to be mainly responsible for the WWV changes. There is also no apparent change in relationship between zonal and meridional transports since 2000, unlike that between WWV and SST. The study suggests that the zonal warm water transport from the western boundary could have major implications for ENSO dynamics.

Enhanced mesoscale climate projections in TAR and AR5 IPCC scenarios: a case study in a Mediterranean climate (Araucanía Region, south central Chile).

Climate change scenarios are computed on a large scale, not accounting for local variations presented in historical data and related to human scale. Based on historical records, we validate a baseline (1962–1990) and correct the bias of A2 and B2 regional projections for the end of twenty-first century (2070–2100) issued from a high resolution dynamical downscaled (using PRECIS mesoscale model, hereinafter DGF-PRECIS) of Hadley GCM from the IPCC 3rd Assessment Report (TAR). This is performed for the Araucanía Region (Chile; 37°–40°S and 71°–74°W) using two different bias correction methodologies. Next, we study high-resolution precipitations to find monthly patterns such as seasonal variations, rainfall months, and the geographical effect on these two scenarios. Finally, we compare the TAR projections with those from the recent Assessment Report 5 (AR5) to find regional precipitation patterns and update the Chilean `projection. To show the effects of climate change projections, we compute the rainfall climatology for the Araucanía Region, including the impact of ENSO cycles (El Niño and La Niña events). The corrected climate projection from the high-resolution dynamical downscaled model of the TAR database (DGF-PRECIS) show annual precipitation decreases: B2 (−19.19 %, −287 ± 42 mm) and A2 (−43.38 %, −655 ± 27.4 mm per year. Furthermore, both projections increase the probability of lower rainfall months (lower than 100 mm per month) to 64.2 and 72.5 % for B2 and A2, respectively.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-3157-6) contains supplementary material, which is available to authorized users.

Drivers of coupled model ENSO error dynamics and the spring predictability barrier

Despite recent improvements in ENSO simulations, ENSO predictions ultimately remain limited by error growth and model inadequacies. Determining the accompanying dynamical processes that drive the growth of certain types of errors may help the community better recognize which error sources provide an intrinsic limit to predictability. This study applies a dynamical analysis to previously developed CCSM4 error ensemble experiments that have been used to model noise-driven error growth. Analysis reveals that ENSO-independent error growth is instigated via a coupled instability mechanism. Daily error fields indicate that persistent stochastic zonal wind stress perturbations $$(\tau_{x}^{\prime } )$$ near the equatorial dateline activate the coupled instability, first driving local SST and anomalous zonal current changes that then induce upwelling anomalies and a clear thermocline response. In particular, March presents a window of opportunity for stochastic $$\tau_{x}^{\prime }$$ to impose a lasting influence on the evolution of eastern Pacific SST through December, suggesting that stochastic $$\tau_{x}^{\prime }$$ is an important contributor to the spring predictability barrier. Stochastic winds occurring in other months only temporarily affect eastern Pacific SST for 2–3 months. Comparison of a control simulation with an ENSO cycle and the ENSO-independent error ensemble experiments reveals that once the instability is initiated, the subsequent error growth is modulated via an ENSO-like mechanism, namely the seasonal strength of the Bjerknes feedback. Furthermore, unlike ENSO events that exhibit growth through the fall, the growth of ENSO-independent SST errors terminates once the seasonal strength of the Bjerknes feedback weakens in fall. Results imply that the heat content supplied by the subsurface precursor preceding the onset of an ENSO event is paramount to maintaining the growth of the instability (or event) through fall.

The strong El Niño of 2015/16 and its dominant impacts on global and China's climate

The oceanic and atmospheric conditions and the related climate impacts of the 2015/16 ENSO cycle were analyzed, based on the latest global climate observational data, especially that of China. The results show that this strong El Nino event fully established in spring 2015 and has been rapidly developing into one of the three strongest El Nino episodes in recorded history. Meanwhile, it is also expected to be the longest event recorded, attributable to the stable maintenance of the abnormally warm conditions in the equatorial Pacific Ocean since spring 2014. Owing to the impacts of this strong event, along with climate warming background, the global surface temperature and the surface air temperature over Chinese mainland reached record highs in 2015. Disastrous weather in various places worldwide have occurred in association with this severe El Nino episode, and summer precipitation has reduced significantly in North China, especially over the bend of the Yellow River, central Inner Mongolia, and the coastal areas surrounding Bohai Bay. Serious drought has occurred in some of the above areas. The El Nino episode reached its peak strength during November-December 2015, when a lower-troposphere anomalous anticyclonic circulation prevailed over the Philippines, bringing about abnormal southerlies and substantially increased precipitation in southeastern China. At the same time, a negative phase of the Eurasia-Pacific teleconnection pattern dominated over the mid-high latitudes, which suppressed northerly winds in North China. These two factors together resulted in high concentrations of fine particulate matter (PM2.5) and frequent haze weather in this region. Currently, this strong El Nino is weakening very rapidly, but its impact on climate will continue in the coming months in some regions, especially in China.

Orthogonal PDO and ENSO Indices

Abstract A framework for interpreting the Pacific decadal oscillation (PDO) and ENSO indices is presented. The two leading principal components (PCs) of sea surface temperature [SST; strictly speaking, the departure from globally averaged SST (SST*)] over the entire Pacific basin comprise a two-dimensional phase space. A linear combination of these pan-Pacific PCs corresponding to a +45° rotation (designated by P) is nearly identical to the PDO, the leading PC of Pacific SST* poleward of 20°N. Both P and the PDO index exhibit apparent “regime shifts” on the interdecadal time scale. The orthogonal axis (rotated by −45° and designated by T′) is highly correlated with conventional ENSO indices, but its spatial regression pattern is more equatorially focused. SST variability along these two rotated axes exhibits sharply contrasting power spectra, the former (i.e., P) suggestive of “red noise” on time scales longer than a decade and the latter (i.e., T′) exhibiting a prominent spectral peak around 3–5 years. Hence, orthogonal indices representative of the ENSO cycle and ENSO-like decadal variability can be generated without resorting to filtering in the time domain. The methodology used here is the same as that used by Takahashi et al. to quantify the diversity of equatorial SST patterns in ENSO; they rotated the two leading EOFs of tropical Pacific SST, whereas the two leading EOFs of pan-Pacific SST* are rotated here.

Alluvial plain dynamics in the southern Amazonian foreland basin

Abstract. Alluvial plains are formed with sediments that rivers deposit on the adjacent flood-basin, mainly through crevasse splays and avulsions. These result from a combination of processes, some of which push the river towards the crevasse threshold, while others act as triggers. Based on the floodplain sedimentation patterns of large rivers in the southern Amazonian foreland basin, it has been suggested that alluvial plain sediment accumulation is primarily the result of river crevasse splays and sheet sands triggered by above-normal precipitation events due to La Niña. However, more than 90 % of the Amazonian river network is made of small rivers and it is unknown whether small river floodplain sedimentation is influenced by the ENSO cycle as well. Using Landsat images from 1984 to 2014, here I analyse the behaviour of all 12 tributaries of the Río Mamoré with a catchment in the Andes. I show that these are very active rivers and that the frequency of crevasses is not linked to ENSO activity. The data suggest that most of the sediments eroded from the Andes by the tributaries of the Mamoré are deposited in the alluvial plains, before reaching the parent river. The mid-to-late Holocene paleo-channels of these rivers are located tens of kilometres further away from the Andes than the modern crevasses. I conclude that the frequency of crevasses is controlled by intrabasinal processes that act on a yearly to decadal timescale, while the average location of the crevasses is controlled by climatic or neo-tectonic events that act on a millennial scale. Finally, I discuss the implications of river dynamics on rural livelihoods and biodiversity in the Llanos de Moxos, a seasonally flooded savannah covering most of the southern Amazonian foreland basin and the world's largest RAMSAR site.

ENSO-Like Variability: 1900–2013*

Abstract ENSO-like variability is examined using a set of univariate indices based on unfiltered monthly global sea surface temperature (SST), sea level pressure (SLP), outgoing longwave radiation (OLR), sea level, and the three-dimensional ocean temperature (OT) fields. These indices, many of which correspond to the leading principal components (PCs) of the respective global fields, are highly correlated with each other. In combination with their spatial regression patterns, they provide a comprehensive description of ENSO-like variability in the atmosphere and ocean across time scales ranging from months to decades, from 1950 onward. The SLP and SST indices are highly correlated with one another back to the late nineteenth century. The interdecadal-scale shifts in the prevailing polarity of ENSO that occurred in the 1940s, the 1970s, and around the year 2000 are clearly evident in low-pass-filtered time series of these indices. On the basis of empirical mode decomposition, ENSO-like variability is partitioned into an interannual “ENSO cycle,” to which equatorial ocean wave dynamics imparts a distinctive equatorial signature, and a red noise background continuum, most prominent on the interdecadal time scale, which resembles the ENSO-like variability in some models in which the atmosphere is coupled to a slab ocean. The background continuum bears the imprint of the Pacific–North American (PNA) pattern, the leading mode of the Northern Hemisphere wintertime variability of the atmospheric circulation over the Pacific sector. The superposition of the ENSO cycle and the background continuum imparts a distinctive frequency dependence to the patterns of ENSO-like climate variability.

Role of subsurface entrainment temperature (Te) in the onset of El Niño events, as represented in an intermediate coupled model

An improved intermediate coupled model (ICM) is described for use in ENSO-related modeling in the tropical Pacific, with ten baroclinic modes included in the vertical and horizonatally varying stratification taken into account. One crucial component of the model is the way in which the subsurface entrainment temperature in the surface mixed layer (Te) is explicitly used to determine the sea surface temperature (SST) variability. An optimized procedure is developed to depict Te using inverse modeling from an SST anomaly equation and its empirical relationship with the sea surface pressure variability. The coupled system realistically produces interannual variability associated with ENSO cycles, with a dominant 4-year oscillation. The onset and development of El Nino events from this ICM are examined in view of the well-known delayed oscillator paradigm; an example is given for the evolution of La Nina conditions in model year 2 to El Nino conditions in year 4. Right after a La Nina event (e.g., in year 2), there is a clear signature of reflections at the western boundary in early year 2, with related equatorial signals propagating eastward along the equator into the eastern basin in middle year 2. However, these reflected signals on the equator do not directly lead to an onset of an El Nino event at that time. Instead, approximately 1-year delay, a major El Nino event is seen to develop in the following year (late year 3), at a time when there is no reflected signal explicitly from the western boundary, indicating that the origin of the El Nino event cannot be directly ascribed to the reflection processes. Instead, Kelvin waves in the ocean that actually triggers the El Nino event in early year 3 are generated by interior wind anomalies near the date line that are associated with the first appearance of warm SST anomalies off the equator. Persisted Te anomalies off the equator in the western tropical Pacific initiate the warm SST anomaly near the date line along the North Equatorial Countercurrent region, which induces wind anomalies and an ocean–atmosphere coupling, leading to the El Nino event in year 4. The relevance of these ICM-based results to other onset mechanisms of El Nino and observations is also discussed.

CAMBIO CLIMÁTICO Y VARIABILIDAD CLIMÁTICA PARA EL PERIODO 1981-2010 EN LAS CUENCAS DE LOS RÍOS ZULIA Y PAMPLONITA, NORTE DE SANTANDER – COLOMBIA

This work is based on a brief theoretical foundation that supports a methodological structure aimed at the calculations of climate change, the study of climate variability in the territory of the basins of the Zulia and Pamplonita rivers in Norte de Santander and the initial identification of potential measures of adaptation to climate change and climate variability..In its development, the climate change trends and the most likely alterations of the climate variability phenomena associated with the ENSO cycle for the period 1981-2010 in the basins of the object of study were identified and spatialized. The results obtained show that the average temperature has changed between 0.1 and 0.4°C per decade in the basins, precipitation has increased from 0 to 250 mm/decade and the ENSO cycles generate alterations in the climate variability of the basins on a differentiated manner on a seasonal and year-on-year level, especially in the Dec-Jan-Feb, Jun-Jul-Aug and Sep-Oct-Nov quarters.

A study on the physical processes of the formation of the ENSO cycle

The physical processes involved in the formation of the ENSO cycle, as well as the possible roles of the Hadley circulation (HC), Walker circulation (WC), and the propagating waves of the Southern Oscillation/Northern Oscillation (SO/NO) in its formation, were studied using composite and regression methods. The analysis showed that the convection and heat release triggered by ENSO in the central-eastern equatorial Pacific are the primary drivers for the 3–5 year cycle of the HC, WC and the meridional/zonal circulation. The HC plays a key role in the influence of ENSO on the circulation outside the tropics through angular momentum transportation. Meanwhile, the feedback effects of the anomalous circulation in the mid-high latitudes on ENSO are accomplished by the propagating waves of SO/NO associated with the evolutions of HC and WC. These propagating waves are the main agents of the connections among the meridional/zonal circulation outside the tropics, the Asian/Australian monsoon, the anomalous easterly/westerly winds over the tropical Pacific, and ENSO events. It was found that the 3–5 year cycle of the meridional/zonal circulation forced by ENSO is quite different from the several-week variation of the circulation index triggered by the inner dynamic processes of the atmosphere. The former occurs at the global scale with a definite flow pattern, while the latter occurs only in a wide area without a definite flow pattern. Finally, a physical model for the formation of the ENSO cycle composed of two fundamental processes at the basin and global scale, respectively, is proposed.

Structure and effect of ocean biology-induced heating (OBH) in the tropical Pacific, diagnosed from a hybrid coupled model simulation

Recent modeling studies have demonstrated that ocean biology plays a significant role in modulating the climate over the tropical Pacific through its effect on the vertical distribution of sunlight in the upper ocean, which can be simply represented by penetration depth (Hp). Previously, remotely sensed ocean color data have been used to derive an empirical model to depict interannual Hp variability (H′p) in the region. The derived H′p model is then incorporated into a hybrid coupled model (HCM) of the tropical Pacific to parameterize ocean biology-induced heating (OBH) effects. In this paper, outputs from the HCM simulations are diagnosed to reveal the structure and variability of OBH terms that are directly influenced by Hp and the depth (Hm) of the mixed layer (ML), including the penetrative solar radiation flux out of the ML (Qpen), the fraction absorbed within the ML (Qabs), and the related time rate of change of the ML temperature (Rsr). Coherent relationships are found among interannual variations in Hp, Hm, Qpen, Qabs and Rsr, with geographical dependence. It is found that Hp tends to have largest interannual variations over the western-central equatorial Pacific where its effects on Qpen are out of phase with those of Hm during ENSO cycles. It is further demonstrated that Qpen is a field whose interannual variability is significantly enhanced by H′p in the western-central equatorial region; the resultant differential heating in the vertical between the ML and subsurface layers acts to modulate the thermal stratification, the stability, vertical mixing and entrainment in the upper ocean. These induced ocean processes further affect sea surface temperatures in the equatorial Pacific.

The importance of eddy permitting model resolution for simulation of the heat budget of tropical instability waves

The heat budget of the eastern tropical Pacific Ocean is analysed in the global NEMO model at 1° and 0.25° resolution. The meridional component of heating of the equatorial cold tongue by tropical instability waves (TIWs) is 37% larger in the higher resolution model and in better agreement with observational estimates. During La Niña and neutral conditions the difference is more pronounced and meridional heat transports by TIWs in the 0.25° model are 74% larger than in the low resolution model. During El Niño the difference between the models is much smaller. There is less difference between the resolutions in simulation of the zonal component of the heating by TIWs. The results suggest that TIWs in the higher resolution model help to warm the equatorial cold tongue during La Niña events reducing the equatorial cold tongue bias and improving the simulation of the asymmetry of the ENSO cycle. Further, it is suggested that the currently available observational estimates of TIW heat budget contributions may be an underestimate as they cover a period dominated by El Niño or neutral conditions and do not include a La Niña event.

The role of the ENSO cycle in the modulation of moisture transport from major oceanic moisture sources

The influence that the evolution of the ENSO cycle has on the moisture transport from the major oceanic moisture sources is investigated using a sophisticated Lagrangian approach informed by ERA-interim data, together with composites of ENSO phases. When maintaining the sources of moisture defined for the climatological period 1980–2012, the variations in the moisture sinks associated with each of these evaporative sources throughout the ENSO cycle reproduce the known patterns of variations of the large-scale atmospheric and precipitation systems over this cycle. Such variations include those observed in rainfall over the equatorial Pacific, in the major Summer monsoon systems, and in subtropical rainfall. When the areas of the sources were redefined according to the phase of ENSO, most of them remained stationary over the period of interest, nevertheless four of them showed notable differences in terms of their extents, namely the South Pacific and the Coral Sea (Pacific Ocean); the Mexican Caribbean (Atlantic), and the Arabian Sea (Indian).

Multivariate ocean-climate indicators (MOCI) for the central California Current: Environmental change, 1990–2010

Temporal environmental variability may confound interpretations of management actions, such as reduced fisheries mortality when Marine Protected Areas are implemented. To aid in the evaluation of recent ecosystem protection decisions in central-northern California, we designed and implemented multivariate ocean-climate indicators (MOCI) of environmental variability. To assess the validity of the MOCI, we evaluated interannual and longer-term variability in relation to previously recognized environmental variability in the region, and correlated MOCI to a suite of biological indicators including proxies for lower- (phytoplankton, copepods, krill), and upper-level (seabirds) taxa. To develop the MOCI, we selected, compiled, and synthesized 14 well-known atmospheric and oceanographic indicators of large-scale and regional processes (transport and upwelling), as well as local atmospheric and oceanic response variables such as wind stress, sea surface temperature, and salinity. We derived seasonally-stratified MOCI using principal component analysis. Over the 21-year study period (1990–2010), the ENSO cycle weakened while extra-tropical influences increased with a strengthening of the North Pacific Gyre Oscillation (NPGO) and cooling of the Pacific Decadal Oscillation (PDO). Correspondingly, the Northern Oscillation Index (NOI) strengthened, leading to enhanced upwelling-favorable wind stress and cooling of air and ocean surface temperatures. The seasonal MOCI related well to subarctic copepod biomass and seabird productivity, but poorly to chlorophyll-a concentration and krill abundance. Our results support a hypothesis of enhanced sub-arctic influence (transport from the north) and upwelling intensification in north-central California over the past two decades. Such environmental conditions may favor population growth for species with sub-arctic zoogeographic affinities within the central-northern California Current coastal ecosystem.

Epipelagic and mesopelagic fishes in the southern California Current System: Ecological interactions and oceanographic influences on their abundance

We use zooplankton and ichthyoplankton data from the ~60-year CalCOFI time series to examine relationships of mesopelagic (i.e. midwater) fishes in the California Current System with midwater predators, potential competitors (epipelagic planktivorous fishes) and zooplankton prey, within the context of local and basin-scale oceanography. Equilibrium-based near-steady state models and the “wasp-waist” paradigm for eastern boundary currents predict tightly-coupled trophic interactions, with negative correlations between the abundance of planktivorous competitors and between dominant planktivores and their prey. Testing these hypotheses with the CalCOFI time series, we found them to be generally invalid. Potential competitors within the mesopelagic community (planktivorous vertical migrators (VMs) and non-migrators (NMs)) were highly positively correlated, as were these groups with the mesopelagic piscivores (e.g. dragonfishes) that prey on them. In addition, the abundance of VMs was mostly positively correlated with that of epipelagic planktivores, such as anchovy, mackerels and hake. The VMs and epipelagic planktivores were negatively correlated with key potential planktonic prey groups, indicating a lack of bottom-up forcing. However, neither do these negative correlations appear to signify top-down forcing, since they seem to be mediated through correlations with key environmental drivers, such as the Pacific Decadal Oscillation (PDO), sea surface temperature, and the relative strength of the California Current. We suggest that the web of correlations linking key meso- and epipelagic planktivores, their predators and prey is mediated through common links with basin-scale oceanographic drivers, such as the PDO and ENSO cycles. Thus, the abundance of mesopelagic fishes in the California Current is closely tied to variation in the oxygen minimum zone, whose dynamics have been linked to the PDO. The PDO and other drivers are also linked to the transport of the California Current System, which influences the abundance of many dominant taxa off southern California that have broad biogeographic distributions linked to water masses that extend to the north (Transition Zone/sub-Arctic faunas) or the south (tropical/subtropical faunas).

ENSO indices and analyses

New ENSO indices were developed and the spatial variability and temporal evolution of ENSO were analyzed based on the new indices and modeling experiments, as well as multiple data resources. The new indices, after being defined, were validated with their good diagnostic characteristics and correlation with wind and SST. In the analysis after the definition and validation of the new indices, ENSO feedbacks from wind, heat fluxes, and precipitation were spatially and temporally examined in order to understand ENSO variability and evolution with some emphasized points such as the interaction among the feedbacks, the role of westerly wind bursts and the transformation between zonal and meridional circulations in an ENSO cycle, and the typical pattern of modern ENSO.

Precipitation periodicities in Kurdistan – Iraqi region

Periodicities in the annual precipitation of Sulaimani, Erbil and Duhok cities of Kurdistan, Iraq have been studied visualising the data for 70 years. The three precipitation series, North Atlantic oscillation (NAO) index series and Southern oscillation index series were subjected to spectral analysis by Blackman-Tukey method to investigate the possible periodicities exist that in the rainfall series and their relations to NAO, ENSO and solar cycle. It was found that the cycles of 2, 2.7, 3.6, 4 and 10 years are related to NAO cycles, 5.4 year cycle is related to ENSO cycle and 11.1 year cycle is related to the solar cycle at Sulaimani site. The common rainfall cycles among the three sites were 2.8, 4.8 and 10 years.

STAGES,CYCLICITY AND TRENDS OF AIR TEMPERATURE IN THE SUBTROPICAL ZONE OF SOUTH CHINA DURING 1901-2011

Understanding the regional air temperature changing process will significantly improve the knowledge of global temperature pattern and its future trend.In this paper,we analyzed the air temperature variations over the period of 1901—2011in the South China subtropical zone based on the instrumental data from eight weather stations,and reached the conclusions as follows.(1)The annual temperature had experienced an overall rising tendency at an average rate of 1.26 ℃/100aduring the period 1901—2011,which was equivalent to the global mean rate.(2)Due to the urban heat island effect,some stations in the study area showed significantly higher warming rates than the global value and the mean values within China,while other stations such as Hengchun,Penghu and Macau had little effect of urbanization and showed a warming rate of 0.97 ℃/100a.(3)Two significant warming periods,i.e.,the period from the mid-1910sto the mid-1950sand the period since the mid-1980s,were identified in the last 110years,suggesting multidecadal climatic variations.(4)Wavelet analysis further indicated that some interannual oscillations such as 3~6years ENSO cycles were superimposed on the decadal-scale variations.(5)Trend analysis suggests that the current warming period since 1998will continue until the mid-2020s,and the temperature in 2100will be(1.2±0.5)℃above the mean value of the period of 1961—1990.

Statistical features of tropical cyclones affecting China and its key economic zones

Recent trends and variability in tropical cyclone (TC) frequency and intensity are examined for TCs that affected China, with particular focus on those TCs that affected China’s key economic zones (e.g., the Yangtze River Delta, the Pearl River Delta, and the Beijing-Tianjin area). The results show that the frequency of TCs affecting China weakly declined during the 1980s and 2000s, followed by a slight increase. The time series of TC frequency shows insignificant variations at periods of 2–6 yr during the past 60 years; these variations are significantly correlated with ENSO activity. The frequency of TCs affecting the Pearl River Delta area is strongly correlated with the ENSO cycle while the frequency of TCs affecting the Yangtze River Delta is not. The TC frequency varies differently for TCs of different intensities. Tropical storms (TSs) affecting China were small in total number, but have clearly increased in frequency. The frequencies of severe tropical storm (STS), typhoon (TY), severe typhoon (STY), and super typhoon (super TY) affecting China declined significantly during the 1970s and 1980s, but the numbers of STY and super TY have increased over the 2000s. The typical intensity of TCs affecting China declined over the 60-yr timeframe, but increased over the most recent 10 years (2000–2010). This increase in the intensity of TCs has particularly impacted the Yangtze River Delta area, which has experienced increased numbers of STYs and super TYs. These tendencies are observed in changes of the maximum intensity of TCs affecting both China in general and the Yangtze River Delta in particular during both the full 60-yr analysis period and the latest 10-yr period; however, these tendencies are not observed in changes of the average intensity of TCs. By contrast, both the extreme intensity and the average intensity of TCs affecting the Pearl River Delta have decreased throughout the analysis period, including the most recent decade.