The impact of combined ENSO and PDO on the PNA climate: a 1,000-year climate modeling study

This study analyzes the atmospheric response to the combined Pacific interannual ENSO and decadal–interdecadal PDO variability, with a focus on the Pacific-North American (PNA) sector, using a 1,000-year long integration of the Canadian Center for Climate Modelling and Analysis (CCCma) coupled climate model. Both the tropospheric circulation and the North American temperature suggest an enhanced PNA-like climate response and impacts on North America when ENSO and PDO variability are in phase. The anomalies of the centers of action for the PNA-like pattern are significantly different from zero and the anomaly pattern is field significant. In association with the stationary wave anomalies, large stationary wave activity fluxes appear in the mid-high latitudes originating from the North Pacific and flowing downstream toward North America. There are significant Rossby wave source anomalies in the extratropical North Pacific and in the subtropical North Pacific. In addition, the axis of the Pacific storm track shifts southward with the positive PNA. Atmospheric heating anomalies associated with ENSO variability are confined primarily to the tropics. There is an anomalous heating center over the northeast Pacific, together with anomalies with the same polarity in the tropical Pacific, for the PDO variability. The in-phase combination of ENSO and PDO would in turn provide anomalous atmospheric energy transports towards North America from both the Tropical Pacific and the North Pacific, which tends to favor the occurrence of stationary wave anomalies and would lead to a PNA-like wave anomaly structure. The modeling results also confirm our analysis based on the observational record in the twentieth century.     

A Statistical Comparison of the Westerly Wind Bursts between the Positive and Negative Phases of the PDO

To understand the diversity of the El Niño-Southern Oscillation (ENSO) under the background of Pacific decadal oscillation (PDO) during recent decades, characteristics of westerly wind bursts (WWBs) during positive and negative phases of the PDO were analyzed. It is shown that, during the ENSO developing period, the El Niño evolution may be affected by stronger or more frequent WWBs in the positive PDO phase than in the negative PDO phase. The sustained effects of atmospheric dynamics on the equatorial ocean can be indicated by the accumulated WWB strength, which contains most WWB characteristics, including the accumulated days, occurrence frequency, strength, and spatial range of WWBs. The synoptic/climate systems that are directly related to WWBs show a wider spatial distribution in the positive PDO phase than in the negative PDO phase.     

Cycles and shifts: 1,300 years of multi-decadal temperature variability in the Gulf of Alaska

The Gulf of Alaska (GOA) is highly sensitive to shifts in North Pacific climate variability. Here we present an extended tree-ring record of January–September GOA coastal surface air temperatures using tree-ring width data from coniferous trees growing in the mountain ranges along the GOA. The reconstruction (1514–1999), based on living trees, explains 44% of the temperature variance, although, as the number of chronologies decreases back in time, this value decreases to, and remains around ∼30% before 1840. Verification of the calibrated models is, however, robust. Utilizing sub-fossil wood, we extend the GOA reconstruction back to the early eighth century. The GOA reconstruction correlates significantly (95% CL) with both the Pacific Decadal Oscillation Index (0.53) and North Pacific Index (−0.42) and therefore likely yields important information on past climate variability in the North Pacific region. Intervention analysis on the GOA reconstruction identifies the known twentieth century climate shifts around the 1940s and 1970s, although the mid-1920s shift is only weakly expressed. In the context of the full 1,300 years record, the well studied 1976 shift is not unique. Multi-taper method spectral analysis shows that the spectral properties of the living and sub-fossil data are similar, with both records showing significant (95% CL) spectral peaks at ∼9–11, 13–14 and 18–19 years. Singular spectrum analysis identifies (in order of importance) significant oscillatory modes at 18.7, 50.4, 38.0, 91.8, 24.4, 15.3 and 14.1 years. The amplitude of these modes varies through time. It has been suggested (Minobe in Geophys Res Lett 26:855–858, 1999) that the regime shifts during the twentieth century can be explained by the interaction between pentadecadal (50.4 years) and bidecadal (18.7 years) oscillatory modes. Removal of these two modes of variance from our GOA time series does indeed remove the twentieth century shifts, but many are still identified prior to the twentieth century. Our analysis suggests that climate variability of the GOA is very complex, and that much more work is required to understand the underlying oscillatory behavior that is observed in instrumental and proxy records from the North Pacific region.

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Combined effect of El Niño-Southern Oscillation and Pacific Decadal Oscillation on the East Asian winter monsoon

Using long-term observational data and numerical model experiments, the combined effect of the El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on the variability of the East Asian winter monsoon is examined. In the observations, it is found that when the ENSO and PDO are in-phase combinations (i.e., El Niño/positive PDO phase and La Niña/negative PDO phase), a negative relationship between ENSO and East Asian winter monsoon is significantly intensified. In other words, when El Niño (La Niña) occurs with positive (negative) PDO phase, anomalous warm (cold) temperatures are dominant over the East Asian winter continent. On the other hand, there are no significant temperature anomalies when the ENSO and PDO are out-of-phase combinations (i.e., El Niño/negative PDO phase and La Niña/positive PDO phase). Further analyses indicate that the anticyclone over the western North Pacific including the East Asian marginal seas plays an essential role in modulating the intensity of the East Asian winter monsoon under the changes of ENSO–PDO phase relationship. Long-lasting high pressure and warm sea surface temperature anomalies during the late fall/winter and following spring over the western North Pacific, which appear as the El Niño occurs with positive PDO phase, can lead to a weakened East Asian winter monsoon by transporting warm and wet conditions into the East Asian continent through the southerly wind anomalies along the western flank of the anomalous high pressure, and vice versa as the La Niña occurs with negative PDO phase. In contrast, the anomalous high pressure over the western North Pacific does not show a prominent change under the out-of-phase combinations of ENSO and PDO. Numerical model experiments confirm the observational results, accompanying dominant warm temperature anomalies over East Asia via strong anticyclonic circulation anomalies near the Philippine Sea as the El Niño occurs with positive PDO phase, whereas such warming is weakened as the El Niño occurs with negative PDO phase. This result supports the argument that the changes in the East Asian winter monsoon intensity with ENSO are largely affected by the strength of the anticyclone over the western North Pacific, which significantly changes according to the ENSO–PDO phase relationship.     

Interdecadal change in the Eurasia–Pacific anti-phase relation of atmospheric mass and its possible link with PDO

Based on the known climatic shift that occurred in 1976, we divide the present study period into two epochs: epoch-I, for 1958–1976; and epoch-II, for 1977–2002. Using ERA-40 and the 20th century reanalysis data, we investigate the interdecadal change in the Eurasia–Pacific anti-phase relation (EPAR) pattern of atmospheric mass (AM) during boreal winter before and after 1976. It is found that anomalous AM over lands is highly and negatively correlated with anomalous AM over oceans in the Northern Hemisphere during the winter season. This correlation does not change much from epoch-I to epoch-II. However, the correlation pattern of surface air pressure anomalies with variations of anomalous AM over lands changes remarkably from epoch-I to epoch-II; the EPAR pattern emerges evidently in the later period, whereas it is not significant in epoch-I. The occurrence of the EPAR pattern in epoch-II may be attributable to the Pacific Decadal Oscillation (PDO). The PDO may modulate the EPAR pattern in two ways. Firstly, the interdecadal component of the PDO as a background may modulate the intensities of the Aleutian low, East Asian trough, and westerly flow, acting as a waveguide during the warm phase (epoch-II) of the PDO. Secondly, the interannual variations of sea surface temperature anomalies in the North Pacific, in association with the PDO, may affect the interannual variations of AM, which facilitates the existence of the EPAR pattern in epoch-II only. With the teleconnection pattern having changed before and after 1976, winter climate anomalies, including rainfall and temperature, are found to be different in many regions in the Northern Hemisphere between epoch-I and epoch-II. All the results of the present work are meaningful for a better understanding of climate anomalies during boreal winter.     

A history of ENSO events since A.D. 1525: implications for future climate change

Reconstructions of past climate are important for providing a historical context for evaluating the nature of 20th century climate change. Here, a number of percentile-based palaeoclimate reconstructions were used to isolate signals of both phases of El Niño–Southern Oscillation (ENSO). A total of 92 (82) El Niño (La Niña) events were reconstructed since A.D. 1525. Significantly, we introduce the most comprehensive La Niña event record compiled to date. This annual record of ENSO events can now be used for independent verification of climate model simulations, reconstructions of ENSO indices and as a chronological control for archaeologists/social scientists interested in human responses to past climate events. Although extreme ENSO events are seen throughout the 478-year ENSO reconstruction, approximately 43% of extreme and 28% of all protracted ENSO events (i.e. both El Niño and La Niña phase) occur in the 20th century. The post-1940 period alone accounts for 30% of extreme ENSO years observed since A.D. 1525. These results suggest that ENSO may operate differently under natural (pre-industrial) and anthropogenic background states. As evidence of stresses on water supply, agriculture and natural ecosystems caused by climate change strengthens, studies into how ENSO will operate under global warming should be a global research priority.     

Quantitative assessment of the climate components driving the pacific decadal oscillation in climate models

The Pacific decadal oscillation (PDO) is defined as the first empirical orthogonal function (EOF) mode of the North Pacific sea surface temperature anomalies. In this study, we reconstructed the PDO using the first-order autoregressive model from various climate indices representing the El Niño-Southern oscillation (ENSO), Aleutian Low (AL), sea surface height (SSH), and thermocline depth over the Kuroshio–Oyashio extension (KOE) region. The climate indices were obtained from observation and twentieth-century simulations of the eight coupled general circulation models (CGCMs) participating in the Climate Model Intercomparison Project Phase III (CMIP3). In this manner, we quantitatively assessed the major climate components generating the PDO using observation and models. Based on observations, the PDO pattern in the central to eastern North Pacific was accurately reconstructed by the AL and ENSO indices, and that in the western North Pacific was best reconstructed by the SSH and thermocline indices. In the CMIP3 CGCMs, the relative contribution of each component to the generation of the PDO varied greatly from model to model, and observations, although the PDO patterns from most of the models were similar to the pattern observed. In the models, the PDO pattern in the eastern and western North Pacific were well reconstructed using the AL and SSH indices, respectively. However, the PDO pattern reconstructed by the ENSO index was quite different from the observed pattern, which was possibly due to the model's common deficiency in simulating the amplitude and location of the ENSO. Furthermore, the differences in the contribution of the KOE thermocline index between the observed pattern and most of the models indicated that the PDO pattern associated with ocean wave dynamics is not properly simulated by most models. Therefore, the virtually well simulated PDO pattern by models is a result of physically inconsistent processes.     

太平洋年代际振荡与中国气候变率的联系

利用 195 1～ 1998年的太平洋年代际振荡 (PDO)指数、全球海洋和大气分析资料及中国降水和气温站点观测资料 ,分析了太平洋年代际振荡在海洋中的特征及其与东亚大气环流和中国气候变率的联系。结果表明 ,PDO与东亚大气环流及中国气候年代际变化关系密切。对应于PDO暖位相期 (即中纬度北太平洋异常冷、热带中东太平洋异常暖 ) ,冬季 ,阿留申低压增强 ,蒙古高压也增强 (但东西伯利亚高压减弱 ) ,中国东北、华北、江淮以及长江流域大部分地区降水偏少 ,东北、华北和西北地区气温异常显著偏高 ,而西南和华南地区气温偏低 ;夏季 ,海平面气压在北太平洋的负异常较弱 ,而在东亚大陆的正异常较强 ,东亚夏季风偏弱 ,西太平洋副热带高压偏南 ,热带太平洋信风减弱 ,赤道西风增强 ,此时华北地区降水异常偏少而长江中下游、华南南部、东北和西北地区降水异常偏多 ,东北、华北及华南地区气温异常偏高 ,而西北、西南和长江中下游地区气温异常偏低。对应于PDO冷位相期 ,上述形势相反。结果还表明 ,处于不同阶段的ENSO事件对中国夏季气候异常的影响明显受到PDO的调制。在PDO冷位相期 ,当ENSO事件处于发展阶段 ,华南地区夏季降水偏少 ,东北地区夏季多低温 ,在其衰减阶段 ,华北地区和长江流域降水偏多 ,淮河地区降水偏少 ;     

Tree-ring estimates of Pacific decadal climate variability

 Decadal-scale oscillatory modes of atmosphere-ocean variability have recently been identified in instrumental studies of the Pacific sector. The regime shift around 1976 is one example of such a fluctuation, which has been shown to have significantly impacted climate and the environment along the coastline of the western N and S Americas. The length of meteorological data for the Pacific and western Americas critically limits analyses of such decadal-scale climate variability. Here we present reconstructions of the annual Pacific Decadal Oscillation (PDO) index based on western North American tree-ring records which account for up to 53% of the instrumental variance and extend as far back as AD 1700. The PDO reconstructions indicate that decadal-scale climatic shifts have occurred prior to the period of instrumental record. Evaluation of temperature and precipitation-sensitive tree-ring series from the northeast Pacific as well as these reconstructions reveals evidence for a shift towards less pronounced interdecadal variability after about the middle 1800s. Our analyses also suggest that sites from both the northeast Pacific coast as well as the subtropical Americas need to be included in proxy data sets used to reconstruct the PDO. Received: 15 September 2000 / Accepted: 30 March 2001     

The Flexible Global Ocean-Atmosphere-Land system model, Spectral Version 2: FGOALS-s2

The Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 (FGOALS-s2) was used to simulate realistic climates and to study anthropogenic influences on climate change. Specifically, the FGOALS-s2 was integrated with Coupled Model Intercomparison Project Phase 5 (CMIP5) to conduct coordinated experiments that will provide valuable scientific information to climate research communities. The performances of FGOALS-s2 were assessed in simulating major climate phenomena, and documented both the strengths and weaknesses of the model. The results indicate that FGOALS-s2 successfully overcomes climate drift, and realistically models global and regional climate characteristics, including SST, precipitation, and atmospheric circulation. In particular, the model accurately captures annual and semi-annual SST cycles in the equatorial Pacific Ocean, and the main characteristic features of the Asian summer monsoon, which include a low-level southwestern jet and five monsoon rainfall centers. The simulated climate variability was further examined in terms of teleconnections, leading modes of global SST (namely, ENSO), Pacific Decadal Oscillations (PDO), and changes in 19th–20th century climate. The analysis demonstrates that FGOALS-s2 realistically simulates extra-tropical teleconnection patterns of large-scale climate, and irregular ENSO periods. The model gives fairly reasonable reconstructions of spatial patterns of PDO and global monsoon changes in the 20th century. However, because the indirect effects of aerosols are not included in the model, the simulated global temperature change during the period 1850–2005 is greater than the observed warming, by 0.6°C. Some other shortcomings of the model are also noted.     

A global analysis of austral summer ocean wave variability during SAM–ENSO phase combinations

Anticipating and mitigating wave-related hazards rely heavily on understanding wave variability drivers. Here, we describe wave conditions related to concurrent Southern Annular Mode (SAM) and El Niño–Southern Oscillation (ENSO) phases during the austral summer. To identify such conditions, significant wave height (Hs) and peak wave period (Tp) daily anomalies were composited during different SAM–ENSO phase combinations over the last four decades (1979–2018). Surface wind anomalies were also composited to assist in the interpretation of wave conditions. The composites show significant wave variability across all ocean basins and in several semi-enclosed seas throughout the different SAM–ENSO phase combinations. The Southern, Indian, and Pacific Oceans generally experience the strongest Tp anomalies during combinations of SAM phases with El Niño, and the weakest Tp anomalies during combinations of SAM phases with La Niña. The anomalously large waves observed in the south-western Pacific, Tasman Sea, and the Southern Ocean, previously ascribed to ENSO conditions, seem to be instead associated with the SAM variability. SAM-related atmospheric conditions are found to be able to modulate the intensity of ENSO-related winds over the South China Sea, which, in turn, alter the magnitude of waves in that region. These and other wave anomaly structures described here, especially those contrasting the behaviour expected for a given ENSO phase, such as the one found along the California coast, stress the importance of understanding relationships between wave parameters and climate patterns interactions.     

Interdecadal variability of the relationship between the East Asian winter monsoon and ENSO

Summary The authors examine relationships between the East Asian winter monsoon and the ENSO, particularly on the interdecadal timescales. Based on the analyses of SLP data from 1899 to 1997, the East-Asian winter monsoon index (WMI) is defined as the zonal difference of SLP between ∼120° E and ∼160° E. It is found that 18 out of 28 strong winter monsoon years are either before the development of an El Ni?o or during the decaying La Ni?a event, 12 out of 28 weak winter monsoon are before the development of a La Ni?a or during the decaying El Ni?o event. There is a significant positive correlation coefficient value of about 0.49 between the normalized 11-yr running mean of WMI and ENSO index, however, the WMI-ENSO relationship is not consistently highly correlated. The temporal evolution of correlation between WMI and ENSO indices in both 11-yr and 21-yr moving window shows that the WMI-ENSO relationship clearly undergo low-frequency oscillation. Obviously, both observational and IPSL air-sea coupled modeling WMI index has a near-decadal peak with PDO timescales and internal peaks with ENSO timescales by applying the Multitaper method. Moreover, the cross wavelet and wavelet coherence analysis of WMI/ENSO indicate that there is a larger significant sections with an in phase behavior between WMI and ENSO at period of 20–30 yrs, suggesting that the interdecadal variation of the WMI-ENSO relationship might exist.     

太平洋年代际振荡冷、暖背景下ENSO循环的特征

利用英国气象局哈德莱中心的月平均海温距平资料、美国Scripps海洋研究所联合环境分析中心(JEDAC)的海表和次表层海温观测资料以及NCEP/NCAR再分析资料,研究了太平洋年代际振荡(PDO)不同背景下ENSO循环的特征.结果表明,PDO为ENSO循环提供了一个年代际气候背景,在PDO的暖位相时期,El Nino事件发生的频率较高,强度较强;反之,在PDO的冷位相时期,La Nina事件发生的频率较高,强度较强.而且在不同的太平洋年代际振荡背景下,ENSO循环表现出不同的特征.在PDO冷位相时期,发生El Nino(La Nina)事件时,正(负)的SOTA从西太平洋沿温跃层向东传播,正(负)的SSTA从赤道东太平洋向西扩展到中太平洋,ENSO事件先在赤道东太平洋爆发.在PDO的暖位相时期,发生El Nino(La Nina)事件时,正(负)的SOTA首先出现在赤道中太平洋,然后沿温跃层向东传播,正(负)的SSTA从赤道中太平洋向东扩展到东太平洋,ENSO事件首先在中太平洋爆发.这为ENSO预测提供了新的线索.     

Impacts of shortwave radiation forcing on ENSO: a study with a coupled tropical ocean-atmosphere model

 We describe a coupled tropical ocean-atmosphere model that represents a new class of models that fill the gap between anomaly coupled models and fully coupled general circulation models. Both the atmosphere and ocean are described by two and half layer primitive equation models, which emphasize the physical processes in the oceanic mixed layer and atmospheric boundary layer. Ocean and atmosphere are coupled through both momentum and heat flux exchanges without explicit flux correction. The coupled model, driven by solar radiation, reproduces a realistic annual cycle and El Nino-Southern Oscillation (ENSO). In the presence of annual mean shortwave radiation forcing, the model exhibits an intrinsic mode of ENSO. The oscillation period depends on the mean forcing that determines the coupled mean state. A perpetual April (October) mean forcing prolongs (shortens) the oscillation period through weakening (enhancing) the mean upwelling and mean vertical temperature gradients. The annual cycle of the solar forcing is shown to have fundamental impacts on the behavior of ENSO cycles through establishing a coupled annual cycle that interacts with the ENSO mode. Due to the annual cycle solar forcing, the single spectral peak of the intrinsic ENSO mode becomes a double peak with a quasi-biennial and a low-frequency (4–5 years) component; the evolution of ENSO becomes phase-locked to the annual cycle; and the amplitude and frequency of ENSO become variable on an interdecadal time scale due to interactions of the mean state and the two ENSO components. The western Pacific monsoon (the annual shortwave radiation forcing in the western Pacific) is primarily responsible for the generation of the two ENSO components. The annual march of the eastern Pacific ITCZ tends to lock ENSO phases to the annual cycle. The model's deficiencies, limitations, and future work are also discussed. Received: 15 June 1999 / Accepted: 11 December 1999     

Interannual variations and future change of wintertime extratropical cyclone activity over North America in CCSM3

Climatology and interannual variations of wintertime extratropical cyclone frequency in CCSM3 twentieth century simulation are compared with the NCEP/NCAR reanalysis during 1950–1999. CCSM3 can simulate the storm tracks reasonably well, although the model produces slightly less cyclones at the beginning of the Pacific and Atlantic storm tracks and weaker poleward deflection over the Pacific. As in the reanalysis, frequency of cyclones stronger than 980 hPa shows significant correlation with the Pacific/North America (PNA) teleconnection pattern over the Pacific region and with the North Atlantic Oscillation (NAO) in the Atlantic sector. Composite maps are constructed for opposite phases of El Nino-Southern Oscillation (ENSO) and the NAO and all anomalous patterns coincide with observed. One CCSM3 twenty-first century A1B scenario realization indicates there is significant increase in the extratropical cyclone frequency on the US west coast and decrease in Alaska. Meanwhile, cyclone frequency increases from the Great Lakes region to Quebec and decreases over the US east coast, suggesting a possible northward shift of the Atlantic storm tracks under the warmer climate. The cyclone frequency anomalies are closely linked to changes in seasonal mean states of the upper-troposphere zonal wind and baroclinicity in the lower troposphere. Due to lack of 6-hourly outputs, we cannot apply the cyclone-tracking algorithm to the other eight CCSM3 realizations. Based on the linkage between the mean state change and the cyclone frequency anomalies, it is likely a common feature among the other ensemble members that cyclone activity is reduced on the East Coast and in Alaska as a result of global warming.     

不同太平洋年代际振荡和ENSO位相下大气水分收支变化对北半球冬季太平洋蒸发量的影响

本文利用OAFlux资料研究了1958~2015年北半球冬季太平洋蒸发量在不同厄尔尼诺—南方涛动（ENSO）和太平洋年代际振荡（PDO）位相下的分布特征,并从水汽收支的角度分析了蒸发量异常的成因,结果表明:ENSO主要影响热带东太平洋、副热带西北太平洋和中纬度北太平洋中部的蒸发量。El Ni?o（La Ni?a）时水汽在北太平洋中部异常辐散（辐合）,有利于当地大气水汽含量减小（增大）,造成蒸发量增大（减小）;副热带西北太平洋异常的水汽辐合（辐散）有利于蒸发量减小（增大）;除此以外,蒸发量在热带东太平洋蒸发量增大（减小）则主要是降水量增大（减小）导致。与此同时,ENSO对上述海区蒸发量的影响还受到PDO的调控,当PDO处于暖（冷）位相时,El Ni?o（La Ni?a）造成蒸发量异常程度在中纬度北太平洋中部显著增大,这主要是由降水量增大（减小）引起的大气水汽含量减小（增大）所致,此时对应着风暴轴异常增大（减小）;当PDO处于冷（暖）位相时,El Ni?o（La Ni?a）造成的蒸发量异常程度在副热带西北太平洋和热带东太平洋显著增大,而这与湿度变化引起的水汽平流异常程度增大紧密相关。     

华北春季沙尘暴频次与环流年际变率的相关分析

分析了近40年来华北春季沙尘暴频次与前秋、前冬和当年春季大尺度大气环流因子的关系,重点是检查年际尺度上的相关。结果表明,年际尺度上与沙尘暴频次有密切关系的环流因子包括:春季太平洋/北美遥相关型(PNA)、春季北太平洋指数(NP)、冬季亚洲区极涡面积。前者为正相关,后二者为负相关。这与用包含低频变率的原始序列进行分析的结果有很大的不同。原始序列分析的结果表明,与华北沙尘暴频次有关的环流因子主要是春季太平洋准10年振荡(PDO,为负相关),春季北半球极涡面积和亚洲区极涡面积(正相关)、前冬西大西洋型(WA,为正相关),以及前秋亚洲区极涡面积(正相关)。说明在不同时间尺度上,大气环流因子有不同的作用。此外,除了PNA、NP和亚洲区极涡面积外,年际尺度上ENSO及WA也可能对沙尘暴频次存在适度的影响。年际尺度上春季12个环流因子对春季沙尘暴频次的方差贡献率为65.3%。     

冬季北太平洋多尺度水汽输送和大气河的变化特征及其与PDO和ENSO的联系

利用1950-2015年NCEP/NCAR大气再分析资料和NOAA海表面温度资料,通过回归分析和合成分析的方法研究了冬季北太平洋不同尺度水汽输送和大气河(Atmospheric River,AR)的变化特征及其与PDO、ENSO的联系.结果表明,在PDO正位相时期,时间平均的水汽输送将大量水汽从太平洋北部和中部地区输送...     

Spatiotemporal mapping of ENSO and PDO surface meteorological signals in British Columbia,Yukon, and southeast Alaska

Abstract

We assessed the impacts of some key Pacific ocean‐atmosphere circulation patterns on annual cycles of temperature and precipitation across British Columbia, Yukon, and southeast Alaska. The El Niño‐Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and ENSO conditional on PDO states were considered in composite analyses of 71 long, high‐quality datasets from surface meteorological stations. Month‐by‐month, station‐by‐station Monte Carlo bootstrap tests were employed to assess statistical significance. The results trace precipitation and temperature responses as a function of location, season, and climate mode. In summary, temperature responses were relatively uniform, with higher (lower) temperatures during the warm (cool) phases of these circulation patterns. Nevertheless, strength and seasonal persistence varied considerably with location and climate mode. Impacts were generally most consistent in winter and spring but could extend through most of the year. Overall spatiotemporal patterns in precipitation response were decoupled from those in temperature and were far more heterogeneous. Complexities in precipitation signals included north‐south inverse teleconnectivity along the Pacific coast, with a zero‐response hinge point in the approximate vicinity of northern Vancouver Island; seasonally opposite anomalies in several interior regions, which might conceivably reflect contrasting effects of Pacific climate modes on wintertime frontal storms versus summertime convective storms; and a consistent lack of substantial response in northwestern British Columbia and possibly southwestern Yukon, conjectured to reflect complications associated with the Icefield Ranges. The product is intended primarily as a basic‐level set of climate response maps for hydrologists, biologists, foresters, and others who require empirical assessments of relatively local‐scale, year‐round ENSO and PDO effects across this broad region.     

北太平洋海温Victoria模态与ENSO年际关系的非对称特征

利用美国NOAA海表温度资料,重点分析了北太平洋海温异常EOF第二模态Victoria模态(VM)与ENSO年际关系的非对称特征.研究发现,VM和ENSO在年代际尺度上相关性较弱,而在年际尺度上有很好的相关关系,两者同期为负相关,VM超前1 a为正相关.然而,正负VM事件与ENSO冷暖位相在年际尺度上的联系存在着一定的...