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The Pacific–North American (PNA) teleconnection pattern is shown to be remarkably influenced by the South China Sea (SCS), through causal inference with information flow, a real physical notion which has just been rigorously derived from first principles. The information flow rate, which measures the strength of causality from the Pacific sea surface temperature anomaly (SSTA) to the PNA index, shows a distinct causal pattern within the SCS. This pattern is rather robust; it exists with different datasets, and lasts through time. To validate, sensitivity experiments have been designed with purported SCS warming and cooling. By comparing the forced PNA evolutions to the standard case, PNA-like responses have been revealed. Specifically, relatively strong positive (negative) SCS SSTA would trigger a positive (negative) propagating PNA-like response. The responding wave train carries energy toward Pacific and North America, and hence affects the PNA growth. Also located is the wave origin using the Rossby wave source diagnosis. This study suggests that the SCS effect should be taken into account in interpreting and predicting PNA.

This study has investigated the relationship between temperature extremes and a subseasonal hemispheric teleconnection pattern over the Northern Hemisphere during boreal summer. By applying self-organizing map (SOM) analysis to 200-hPa geopotential fields from the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) for the period 1979–2012, a teleconnection pattern is identified that increased dramatically in its occurrence after the late 1990s. This pattern is characterized by a zonal wavenumber-5 pattern with anomalous high pressure cores over eastern Europe, northeastern Asia, the eastern North Pacific, the eastern United States, and Greenland. These high pressure centers coincide with regions of increasingly frequent temperature extremes in recent decades. To investigate the temporal evolution of the identified SOM pattern, time-lagged composites were performed relative to the days in which the 200-hPa geopotential field most closely resembled the SOM pattern. From day −10 to day 0, a wave train propagated from the central tropical Pacific to the Canadian Arctic Archipelago and Greenland. This poleward wave propagation was followed by the establishment of quasi-stationary high pressure centers over Greenland, Europe, and Asia. This study suggests that more frequent occurrence of the hemispheric teleconnection is linked to more severe and longer extreme weather events over the Northern Hemisphere since the late 1990s.

The co-occurrence of wintertime temperature anomalies over eastern Asia and eastern North America is examined. The winter days during 1948–2014 are assigned to nine regimes by applying the Self-Organizing Map clustering method to the area-averaged land surface temperature anomalies over these two regions. About half of the winter days are associated with concurrent temperature anomalies. The occurrence of the concurrent/non-concurrent regimes is closely related to the large-scale circulation conditions. The Eurasian teleconnection pattern and the Pacific-North American teleconnection pattern are two dominant large-scale circulation modes associated with the co-occurrence of the temperature anomalies, through their impacts on the intensities of the corresponding troughs. The precursor analysis reveals that the lead time of the early signals for the concurrent cold anomalies is about four days longer than that for the concurrent warm anomalies. In addition, the average lead time of the precursor signals for the wintertime temperature anomalies over eastern Asia is longer than that is over eastern North America.

It is shown here that the teleconnections of El Nino-Southern Oscillation (ENSO) are contributed by two anomalous precipitation forcings in the equatorial central Pacific (CP; 160°E–120°W, 5°S–5°N) and western North Pacific (WNP; 110°E–150°E, 0°N–20°N). The positive CP precipitation anomalies induce a prevailing cyclonic flow over the North Pacific (120°E–110°W, 20°N–70°N), whereas the negative WNP precipitation forcing tends to induce anticyclonic anomalies over the Kuroshio extension region and North Pacific. It is demonstrated that the equatorial CP and WNP precipitation anomalies play relative roles in generating atmospheric teleconnections over the North Pacific, which can be determined by the competing responses to the CP and WNP precipitation anomalies. The reconstructed teleconnection patterns based on only the two tropical forcings capture the majority of the subseasonal evolution of the ENSO teleconnection. In addition, we find that the diversity of inter-ENSO events in the atmospheric teleconnection can be better-explained by considering the relative roles of the CP and WNP precipitation anomalies.

The Asian–Bering–North American (ABNA) teleconnection index is constructed from the normalized 500-hPa geopotential field by excluding the Pacific–North American pattern contribution. The ABNA pattern features a zonally elongated wavetrain originating from North Asia and flowing downstream across Bering Sea and Strait towards North America. The large-scale teleconnection is a year-round phenomenon that displays strong seasonality with the peak variability in winter. North American surface temperature and temperature extremes, including warm days and nights as well as cold days and nights, are significantly controlled by this teleconnection. The ABNA pattern has an equivalent barotropic structure in the troposphere and is supported by synoptic-scale eddy forcing in the upper troposphere. Its associated sea surface temperature anomalies exhibit a horseshoe-shaped structure in the North Pacific, most prominent in winter, which is driven by atmospheric circulation anomalies. The snow cover anomalies over the West Siberian plain and Central Siberian Plateau in autumn and spring and over southern Siberia in winter may act as a forcing influence on the ABNA pattern. The snow forcing influence in winter and spring can be traced back to the preceding season, which provides a predictability source for this teleconnection and for North American temperature variability. The ABNA associated energy budget is dominated by surface longwave radiation anomalies year-round, with the temperature anomalies supported by anomalous downward longwave radiation and damped by upward longwave radiation at the surface.

Kinematic mechanisms of the Pacific–North America (PNA)-like teleconnection pattern induced by the Madden–Julian oscillation (MJO) is examined using an atmospheric general circulation model (GCM) and a barotropic Rossby wave theory. Observation shows that a negative PNA-like teleconnection pattern emerges in response to MJO phase-2 forcing with enhanced (suppressed) convection located over the Indian (western Pacific) Ocean. The GCM simulations show that both forcing anomalies contribute to creating the PNA-like pattern. Indian Ocean forcing induces two major Rossby wave source (RWS) regions: a negative region around southern Asia and a positive region over the western North Pacific (WNP). The negative RWS to the north of the enhanced convection in the Indian Ocean arises from southerly MJO-induced divergent wind crossing the Asian jet. Unexpectedly, another significant RWS region develops over the WNP owing to refracted northerly divergent wind. A ray-tracing method demonstrates three different ways of wave propagation emanating from the RWS to the PNA region: 1) direct arclike propagation from the negative RWS to the PNA region occurs in the longest waves, 2) shorter waves are displaced first downstream by the jet waveguide effect and then emanate at the jet exit to the PNA region, and 3) waves with zonal wavenumbers 1 and 2 exhibit canonical wave propagation from the positive RWS at the jet exit to the PNA region. On the other hand, the positive RWS induced by western Pacific forcing shows similar characteristics to feature 3 described above, with some relaxation such that much shorter waves also contribute to the formation of the southern cells.

The mechanisms that drive the Pacific–North American (PNA) teleconnection pattern with and without its canonical tropical convection pattern are investigated with daily ERA-Interim and NOAA OLR data (the former pattern is referred to as the convective PNA, and the latter pattern is referred to as the nonconvective PNA). Both the convective and nonconvective positive PNA are found to be preceded by wave activity fluxes associated with a Eurasian wave train. These wave activity fluxes enter the central subtropical Pacific, a location that is favorable for barotropic wave amplification, just prior to the rapid growth of the PNA. The wave activity fluxes are stronger for the positive nonconvective PNA, suggesting that barotropic amplification plays a greater role in its development. The negative convective PNA is also preceded by a Eurasian wave train, whereas the negative nonconvective PNA grows from the North Pacific contribution to a circumglobal teleconnection pattern. Driving by high-frequency eddy vorticity fluxes is largest for the negative convective PNA, indicating that a positive feedback may be playing a more dominant role in its development. The lifetimes of convective PNA events are found to be longer than those of nonconvective PNA events, with the former (latter) persisting for about three (two) weeks. Furthermore, the frequency of the positive (negative) convective PNA is about 40% (60%) greater than that of the positive (negative) nonconvective PNA.

Previous studies have identified an Asian-Pacific Oscillation (APO) teleconnection pattern, which exhibits an out-of-phase relationship in the summer tropospheric temperature with warming over the Eurasia and cooling over the Northern Pacific and the Northern America, and vice versa. But the interannual variation of this teleconnection remains obscure. This study points out that interannual variation of the APO teleconnection is associated with the second empirical orthogonal function (EOF) mode of the northern-hemisphere upper tropospheric temperature during boreal summer, which accounts for 14% of the variance. A heat budget analysis is conducted for the Eurasian region and the North Pacific region respectively to reveal the cause of the zonal dipole mode temperature structure. For the Eurasia region, the warming is contributed by the adiabatic heating process due to downward vertical motion anomalies. For the Northern Pacific region, the temperature variation is mainly contributed by zonal advection associated with interannual zonal wind perturbation acting on the climatological temperature gradient. Composite analysis and numerical experiments with an atmospheric general circulation model (AGCM) shows the interannual zonal wind perturbation is related to the sea surface temperature anomalies over the equatorial eastern Pacific.

The Tianshan Mountains are known as the “water tower” in the arid region of Central Asia. Change in precipitation amount and pattern can have a profound impact on regional civilization and life supporting ecosystems. For this study, a systematic analysis of long-term precipitation data for the eastern Tianshan Mountains was conducted to investigate the influence of climate teleconnections on annual and intra-annual precipitation using data collected between 1951 and 2014 from 39 meteorological stations. Annual precipitation has increased during the past six decades at an average rate of 6.7 mm/10 years largely due to the increase in precipitation during the intra-annual wet period (May–October). The annual precipitation and its rate of increase were higher in the northwestern region. Annual precipitation was found to be most strongly correlated with index of Indian Summer Monsoon (ISM), and partially correlated with indices of Pacific Decadal Oscillation (PDO), Pacific North American Teleconnection Pattern (PNA), Arctic Oscillation (AO), El Nino–Southern Oscillation (ENSO), and North Atlantic Oscillation (NAO). ISM was positively correlated with the precipitation in almost the entire region during the intra-annual wet period, while it showed positive correlations in the northern slope and the alpine region, and negative correlations in the southern slope during the intra-annual dry period (November to April). PDO had much weaker influence both in spatial scale and strength and primarily affected low elevations on the southern slopes of the middle and western regions. The impacts of PNA and AO on precipitation were weak and localized. ENSO and NAO indices were almost not correlated with annual precipitation observation in the eastern Tianshan Mountains.

The western Pacific (WP) pattern, characterized by north–south dipolar anomalies in pressure over the Far East and western North Pacific, is known as one of the dominant teleconnection patterns in the wintertime Northern Hemisphere. Composite analysis reveals that monthly height anomalies exhibit baroclinic structure with their phase lines tilting southwestward with height in the lower troposphere. The anomalies can thus yield not only a poleward heat flux across the climatological thermal gradient across the strong Pacific jet but also a westward heat flux across the climatological thermal gradient between the North Pacific and the cooler Asian continent. The resultant baroclinic conversion of available potential energy (APE) from the climatological-mean flow contributes most efficiently to the APE maintenance of the monthly WP pattern, acting against strong thermal damping effects by anomalous heat exchanges with the underlying ocean and anomalous precipitation in the subtropics and by the effect of anomalous eddy heat flux under modulated storm-track activity. Kinetic energy (KE) of the pattern is maintained through barotropic feedback forcing associated with modulated activity of transient eddies and the conversion from the climatological-mean westerlies, both of which act against frictional damping. The net feedback forcing by transient eddies is therefore not particularly efficient. The present study suggests that the WP pattern has a characteristic of a dynamical mode that can maintain itself through efficient energy conversion from the climatological-mean fields even without external forcing, including remote influence from the tropics.

A new atmospheric teleconnection pattern on the interdecadal time scale, interdecadal circumglobal teleconnection pattern (ID-CGT pattern), is identified. The ID-CGT pattern dominates the interdecadal variability of the Northern Hemisphere (NH) extratropical circulation during boreal summer. The ID-CGT pattern has a great climate effect and can cause an alternatively positive and negative pattern of the NH mid-latitude land surface temperature anomalies. Compared with its counterpart on the interannual time scale (IA-CGT pattern), the ID-CGT pattern shows following three distinctive features. Firstly, although both ID-CGT and IA-CGT patterns show zonal wavenumber-5 structures, the former nodes shift westward relative to the latter by about 1/4 wavelength. Secondly, all the five nodes of the ID-CGT pattern possess barotropic structures, unlike the IA-CGT, which has a baroclinic node. Thirdly, the ID-CGT pattern is associated with the Atlantic multi-decadal oscillation, whereas the IA-CGT pattern is with the Indian summer monsoon precipitation anomalies.

A teleconnection between the North Atlantic Ocean and the Eurasian continent is suggested by statistical and dynamical analysis of the northern summer 500-hPa geopotential height field. This teleconnection, termed the Atlantic–Eurasian (AEA) teleconnection, has five centers of action, in the subtropical North Atlantic Ocean, northeastern North Atlantic Ocean, Eastern Europe, the Kara Sea, and north China. The AEA index (AEAI) shows that the AEA undergoes a high degree of variability from year to year, and the AEAI has an increasing trend over the last 30 years. Our results suggest that this phenomenon is a large-scale Rossby wave train that originates in the subtropical North Atlantic Ocean. We support this conclusion by the methods of stationary wave ray tracing in non-uniform horizontal basic flow, wave activity flux calculations, and numerical models. The AEA and midlatitude circumglobal teleconnection pattern manifest distinct features at the hemispheric scale, despite the anomalies associated with them bear some similarities in the northeastern North Atlantic and Eastern Europe. Regional climate variations are strongly linked to this AEA along its path through northern Eurasia.

This study demonstrates the relationship between the Pacific–North American (PNA) teleconnection pattern and the Great Plains low-level jet (GPLLJ). The negative phase of the PNA, which is associated with lower heights over the Great Plains and ridging in the southeastern United States, enhances the GPLLJ by increasing the pressure gradient within the GPLLJ on 6-hourly to monthly time scales. Strong GPLLJ events predominantly occur when the PNA is negative. Warm-season strong GPLLJ events with a very negative PNA (

Using monthly data from the European Centre for Medium-Range Weather Forecasts 40 year Re-Analysis, this study investigated the interannual relationship between the Asian-Pacific Oscillation (APO) and the North Atlantic Oscillation (NAO) for the period of May to August. The NAO is represented by the leading Empirical Orthogonal Function of sea level pressure anomalies over the Atlantic sector. The difference of upper tropospheric eddy air temperature (T′) between Asia and the North Pacific is used to measure the APO. Results clearly show that the APO and the NAO correlated very well on the interannual time scale, with the positive (negative) phase of the APO corresponding to the strong (weak) NAO. Such a relationship is well supported by the atmospheric dynamic process. When the APO is in the positive phase (characterized by the positive T′ anomaly over Asia and the negative T′ anomaly over the North Pacific in the upper troposphere), the upper tropospheric geopotential height increases over Asia and decreases over the North Pacific. Accordingly, anticyclonic circulation and cyclonic circulation anomalies are introduced, respectively, over Asia and south of the North Pacific, and a zonal teleconnection wave train is excited from Asia to the North Atlantic. As a consequence, an anomalous anticyclonic circulation prevails in the low level of the North Atlantic and an anomalous cyclonic circulation appears to its north, which corresponds to the atmospheric pattern of strong NAO. Further study proposes that the quasi-stationary wave pattern emanating from the western North Pacific region may serve as a bridge for this linkage.

Almost all of CMIP5 climate models show cold SST biases in the extratropical North Atlantic (ENA) and tropical North Atlantic (TNA) as well as in the North Pacific which are commonly linked with the weak simulated Atlantic meridional overturning circulation (AMOC). A weak AMOC and its associated reduced northward oceanic heat transport are associated with a cooling of the ENA Ocean, whereas the TNA cooling is attributable to both weak AMOC and surface heat flux. The cold biases in the ENA and TNA have remote impacts on the SST bias in the North Pacific. Here we use coupled ocean-atmosphere model experiments to show the mechanisms and pathways by which the ENA and TNA affect the North Pacific. The model simulations demonstrate that the cooling SST bias in the North Pacific is largely due to the remote effect of the cooling SST bias in the ENA, while the remote impact of the TNA cooling SST bias is of secondary importance. The ENA cooling bias triggers the circumglobal teleconnection via the Northern Hemisphere annular mode, producing a strengthening of the Aleutian low, an enhancement of the southward Ekman and Oyashio cold advection, and thus a cooling SST in the North Pacific. In contrast, the TNA cooling produces a surface high extending to the eastern tropical North Pacific, inducing the northeasterly wind anomalies north, northerly cross-equatorial wind anomalies, and northwesterly wind anomalies south of the equator. This C-shape wind anomaly pattern generates an SST warming in the tropical southeastern Pacific, which eventually leads to an SST warming in the tropical central and western Pacific by the wind-evaporation-SST feedback. The tropical Pacific warming in turn leads to an SST cooling in the North Pacific by the Pacific North American teleconnection pattern.

Though tropical SST anomalies associated with El Nino change slowly during the mature phase of El Nino, the resultant extratropical teleconnection patterns are quite different with time. In this study, the intra-winter changes in the teleconnection pattern associated with El Nino are investigated using the NCEP reanalysis and observational data and the high-resolution seasonal prediction data. The observational analyses show that there are distinctively changes in the teleconnection pattern over the North Pacific within the winter. In the early winter (November-December) of El Nino years, there is a distinctive anomalous Kuroshio anticyclone, which is closely related to the East Asian climate. In January, in contrast, the Kuroshio anticyclone suddenly disappears and a strong cyclonic flow, which is part of the Pacific-North American (PNA) teleconnection pattern, develops. It is suggested that the intra-winter changes are controlled by the relative roles of the equatorial central Pacific (CP) and western north Pacific (WNP) precipitation anomalies on the extratropical teleconnection over the North Pacific. On the other hand, the prediction data failed to capture the observed intra-winter changes in the teleconnection pattern, though the predictive skills for tropical SST and precipitation are high. It is revealed that this model’s discrepancy in the extratropical teleconnection is partly originated from the failure in predicting the relative magnitude of CP and WNP precipitation anomalies. Further analyses on the ensemble spread of the prediction data support the relative roles of CP and WNP precipitation anomalies in affecting the extratropical circulation over the North Pacific.

Teleconnection in atmospheric science refers to a significant correlation between climate anomalies in widely separated regions (typically thousands of kilometres), and it is often considered to be responsible for extreme weather conditions occurring simultaneously over large distances. In this paper, we study the influence of El Nino-Southern Oscillation teleconnection on meteorological droughts represented by the Palmer severity drought index across North America from 1870 to 1990. We develop a flexible statistical framework based on spatial random effects to model the covariance (teleconnection) between winter (October–March) sea surface temperature in the tropical Pacific and summer (June–August) droughts in North America. Our model allows us to analyse the dynamic pattern of teleconnection over space and time, and results indicate that the influence of El Nino-Southern Oscillation teleconnections on droughts varies spatially and temporally across North America. We further provide the time-varying teleconnection estimates with their uncertainties for 12 subregions in North America. Copyright ©2015 John Wiley & Sons, Ltd.

The Pacific–North American (PNA) pattern and the North Atlantic Oscillation (NAO) are known to contain a tropical sea surface temperature (SST)-forced component. This study examines the sensitivity of the wintertime NAO and PNA to patterns of tropical SST anomalies using a linear statistical–dynamic method. The NAO index is sensitive to SST anomalies over the tropical Indian Ocean, the central Pacific Ocean, and the Caribbean Sea, and the PNA index is sensitive to SST anomalies over the tropical Pacific and Indian Oceans. The NAO and PNA patterns can be reproduced well by combining the linear operator with the consistent SST anomaly over the Indian Ocean and the Niño-4 regions, respectively, suggesting that these are the most efficient ocean basins that force the teleconnection patterns. During the period of 1950–2000, the NAO time series reconstructed by using SST anomalies over the Indian Ocean + Niño-4 region + Caribbean Sea or the Indian Ocean + Niño-4 region is significantly correlated with the observation. Using a cross-spectral analysis, the NAO index is coherent with the SST forcing over the Indian Ocean at a significant 3-yr period and a less significant 10-yr period, with the Indian Ocean SST leading by about a quarter phase. Unsurprisingly, the PNA index is most coherent with the Niño-4 SST at 4–5-yr periods. When compared with the observation, the NAO variability from the linear reconstruction is better reproduced than that of the coupled model, which is better than the Atmospheric Model Intercomparison Project (AMIP) run, while the PNA variability from the AMIP simulations is better than that of the reconstruction, which is better than the coupled model run.

El Niño–Southern Oscillation (ENSO) induces climate anomalies around the globe. Atmospheric general circulation model simulations are used to investigate how ENSO-induced teleconnection patterns during boreal winter might change in response to global warming in the Pacific–North American sector. As models disagree on changes in the amplitude and spatial pattern of ENSO in response to global warming, for simplicity the same sea surface temperature (SST) pattern of ENSO is prescribed before and after the climate warming. In a warmer climate, precipitation anomalies intensify and move eastward over the equatorial Pacific during El Niño because the enhanced mean SST warming reduces the barrier to deep convection in the eastern basin. Associated with the eastward shift of tropical convective anomalies, the ENSO-forced Pacific–North American (PNA) teleconnection pattern moves eastward and intensifies under the climate warming. By contrast, the PNA mode of atmospheric internal variability remains largely unchanged in pattern, suggesting the importance of tropical convection in shifting atmospheric teleconnections. As the ENSO-induced PNA pattern shifts eastward, rainfall anomalies are expected to intensify on the west coast of North America, and the El Niño–induced surface warming to expand eastward and occupy all of northern North America. The spatial pattern of the mean SST warming affects changes in ENSO teleconnections. The teleconnection changes are larger with patterned mean warming than in an idealized case where the spatially uniform warming is prescribed in the mean state. The results herein suggest that the eastward-shifted PNA pattern is a robust change to be expected in the future, independent of the uncertainty in changes of ENSO itself.

Previous studies have demonstrated that the NAO, the leading mode of atmospheric low-frequency variability over the North Atlantic, could be linked to northeast Pacific climate variability via the downstream propagation of synoptic waves. In those studies, the NAO and the northeast Pacific climate variability are considered as two separate modes that explain the variance over the North Atlantic sector and the east Pacific–North American sector, respectively. A newly identified low-frequency atmospheric regime—the Western Hemisphere (WH) circulation pattern—provides a unique example of a mode of variability that accounts for variance over the whole North Atlantic–North American–North Pacific sector. The role of synoptic waves in the formation and maintenance of the WH pattern is investigated using the ECMWF reanalysis datasets. Persistent WH events are characterized by the propagation of quasi-stationary Rossby waves across the North Pacific–North American–North Atlantic regions and by associated storm-track anomalies. The eddy-induced low-frequency height anomalies maintain the anomalous low-frequency ridge over the Gulf of Alaska, which induces more equatorward propagation of synoptic waves on its downstream side. The eddy forcing favors the strengthening of the midlatitude jet and the deepening of the mid-to-high-latitude trough over the North Atlantic, whereas the deepening of the trough over eastern North America mostly arises from the quasi-stationary waves propagating from the North Pacific. A case study for the 2013/14 winter is examined to illustrate the downstream development of synoptic waves. The roles of synoptic waves in the formation and maintenance of the WH pattern and in linking the northeast Pacific ridge anomaly with the NAO are discussed.

In the extratropics of the Northern Hemisphere, there exist many kinds of atmospheric teleconnection patterns. According to their spatial structure, these teleconnection patterns are generally divided into two groups. One group comprises north-south dipole patterns, such as the North Atlantic Oscillation and the North Pacific Oscillation, which have two anomalous centers of opposite signs in the north-south direction. The other group includes the wave train-like patterns, which have several anomalous centers of opposite signs distributed mainly in the zonal direction, such as the Pacific/North American and Eurasian Patterns. These teleconnection patterns greatly impact weather and climate not only in the regions where the teleconnection patterns are active, but also in the regions thousands of kilometers away. Studying and understanding the formation mechanisms of these teleconnection patterns form the basis for the short-term climate prediction. This paper reviews advances in the study of the dynamics of these teleconnection patterns, with particular attention paid to the teleconnection patterns that significantly influence the weather and climate of East Asia.

The Pacific–North American (PNA) teleconnection pattern has a strong influence on North America’s winter climate, but much less is known about how the PNA pattern controls precipitation isotopes (e.g., δ18O) across the United States. In this study, an isotopically equipped atmospheric general circulation model (isoGSM) is used to investigate how divergent phases of the PNA affect precipitation δ18O values across the United States. A simulation using observational climate and isotope data over the United States is evaluated first. The simulation explains 84% of the spatial variability of winter precipitation δ18O, with an overestimation in the northern Rocky Mountains and the Great Lakes. Temporally, the simulation explains 29%–81% of the interannual variability of winter precipitation δ18O, with typically a higher explained variance in the east than the west. The modeled winter precipitation δ18O exhibits a clear northwest–southeast (NW–SE) dipolelike pattern in response to shifts in the PNA pattern, with the center of positive polarity in the northwestern United States and the Canadian prairies and the center of negative polarity over the Ohio River valley. This dipolelike spatial pattern is a result of the difference in atmospheric circulation and moisture sources associated with the PNA pattern. These results highlight the importance of the PNA-associated circulation dynamics in governing precipitation isotope patterns across the United States. This understanding improves our ability to interpret paleoclimate records of water isotope/hydrologic change across the United States with a much greater appreciation of regional traits. The robust antiphase oscillation in precipitation isotopes in response to shifting the PNA pattern provides a promising opportunity to reconstruct the past variability in the PNA pattern that may be recorded in ice cores, tree rings, lake sediments, and speleothems.

Tropical convection from the Madden–Julian oscillation (MJO) excites and amplifies extratropical Rossby waves around the globe. This forcing is reflected in teleconnection patterns like the Pacific–North American (PNA) pattern, and it can ultimately result in temperature anomalies over North America. Previous studies have not explored whether the extratropical response might vary from one MJO event to another. This study proposes a new index, the multivariate PNA (MVP), to identify variations in the extratropical waveguide over the North Pacific and North America that might affect the response to the MJO. The MVP is the first combined EOF of 20–100-day OLR, 850-hPa streamfunction, and 200-hPa streamfunction over the North Pacific and North America. The North American temperature patterns that follow each phase of the MJO change with the sign of the MVP. For example, real-time multivariate MJO (RMM) phase 5 usually leads to warm anomalies over eastern North America. This relationship was only found when the MVP was negative, and it was not associated with El Niño or La Niña. RMM phase 8, on the other hand, usually leads to cold anomalies. Those anomalies only occur if the MVP is positive, which happens somewhat more frequently during La Niña years. Composite analyses based on combinations of the MJO and the MVP show that variability in the Pacific jet and its associated wave breaking play a key role in determining whether and how the MJO affects North American temperatures.

Understanding long-term, ocean wave climate variability is important to assess climate change impacts on coastal and ocean physics and engineering. Teleconnection patterns can represent wave climate variability in the context of climate change. The objective of this study is to identify how large-scale spatial distributions of wave heights vary on a monthly basis and how they are influenced by various teleconnection patterns using reanalysis datasets. The wave height climate responses to teleconnection patterns in the eastern part of the North Pacific and North Atlantic are more sensible than in the corresponding western parts. The dominant spatial patterns of monthly averaged wave height variability in winter were obtained by empirical orthogonal function analysis. The three dominant patterns in the North Pacific and North Atlantic are similar. It is remarkable that one of the three dominant patterns, a band-shaped pattern, exhibits a strong relation to the teleconnection pattern in each ocean. The band-shaped pattern for the North Pacific was investigated in detail and found to be related to the west Pacific (WP) pattern. Where and how each teleconnection pattern influences wave climate becomes apparent especially during winter.

[1] The anomalously snowy winter season of 2010/2011 in the Sierra Nevada is analyzed in terms of snow water equivalent (SWE) anomalies and the role of atmospheric rivers (ARs)—narrow channels of enhanced meridional water vapor transport between the tropics and extratropics. Mean April 1 SWE was 0.44 m (56%) above normal averaged over 100 snow sensors. AR occurrence was anomalously high during the period, with 20 AR dates during the season and 14 in the month of December 2010, compared to the mean occurrence of nine dates per season. Fifteen out of the 20 AR dates were associated with the negative phases of the Arctic Oscillation (AO) and the Pacific-North American (PNA) teleconnection pattern. Analysis of all winter ARs in California during water years 1998–2011 indicates more ARs occur during the negative phase of AO and PNA, with the increase between positive and negative phases being ∼90% for AO, and ∼50% for PNA. The circulation pattern associated with concurrent negative phases of AO and PNA, characterized by cyclonic anomalies centered northwest of California, provides a favorable dynamical condition for ARs. The analysis suggests that the massive Sierra Nevada snowpack during the 2010/2011 winter season is primarily related to anomalously high frequency of ARs favored by the joint phasing of −AO and −PNA, and that a secondary contribution is from increased snow accumulation during these ARs favored by colder air temperatures associated with −AO, −PNA, and La Nina.

In this study, a statistical model is developed to predict the frequency of tropical cyclones (TCs) that influence Taiwan in boreal summer. Predictors are derived from large-scale environments from February to May in six regions, including four atmospheric circulation predictors over the western sea and eastern sea of Australia, the subtropical western North Pacific (SWNP), and the eastern sea of North America, and two sea surface temperature predictors in the Southeast Indian Ocean and the North Atlantic. The statistical model is verified based on statistical cross-validation tests and by contrasting the differences in the large-scale environments between high and low TC frequency years hindcasted by the model. The results show the relationships of two atmospheric circulation predictors and one SST predictor around Australia with Antarctic Oscillation (AAO) pattern, as well as the relationships of those in the SWNP and around eastern sea of North America with Pacific/North American teleconnection (PNA) pattern. When the anomalous anticyclone around Australia (positive AAO pattern) and the one over the region from eastern sea of North America and the Aleutian Islands to the SWNP (negative PNA pattern) are both strengthened from February, the trade wind in the equatorial Pacific is intensified and consequently plays an important role in steering TCs towards Taiwan during boreal summer.

Changes in global sea surface temperature (SST) since the end of last century display a pattern of widespread warming intercepted by cooling in the eastern equatorial Pacific and western coasts of the American continent. Studies have suggested that the cooling in the eastern equatorial Pacific may be partly induced by warming in the North Atlantic. However, it remains unknown how stable this inter-tropical teleconnection will be under global warming. Here we show that the inter-tropical teleconnection from the tropical Atlantic to Pacific weakens substantially as the CO2 concentration increases. This reduced impact is related to the El Niño-like warming of the tropical Pacific mean state, which leads to limited seasonal migration of the Pacific inter-tropical convergence zone (ITCZ) and weakened ocean heat transport. A fast decay of the tropical Atlantic SST anomalies in a warmer climate also contributes to the weakened teleconnection. Our study suggests that as greenhouse warming continues, the trend in the tropical Pacific as well as the development of ENSO will be less frequently interrupted by the Atlantic because of this attenuation. The weakened teleconnection is also supported by CMIP5 models, although only a few of these models can capture this inter-tropical teleconnection.

The boreal summer intraseasonal oscillation (BSISO) has strong convective activity centers in Indian (I), Western North Pacific (WNP), and North American (NA) summer monsoon (SM) regions. The present study attempts to reveal BSISO teleconnection patterns associ- ated with these dominant intraseasonal variability centers. During the active phase of ISM, a zonally elongated band of enhanced convection extends from India via the Bay of Bengal and Philippine Sea to tropical central Pacific with suppressed convection over the eastern Pacific near Mexico. The corresponding extratropical circulation anomalies occur along the waveguides generated by the North African-Asian jet and North Atlantic-North Euro- pean jet. When the tropical convection strengthens over the WNPSM sector, a distinct great circle-like Rossby wave train emanates from the WNP to the western coast of United States (US) with an eastward shift of enhanced meridional circulation. In the active phase of NASM, large anticyclonic anomalies anchor over the western coast of US and eastern Canada and the global teleconnection pattern is similar to that during a break phase of the ISM. Exami- nation of the evolution of the BSISO teleconnection reveals quasi-stationary patterns with preferred centers of tele- connection located at Europe, Russia, central Asia, East Asia, western US, and eastern US and Canada, respec- tively. Most centers are embedded in the waveguide along the westerly jet stream, but the centers at Europe and Russia occur to the north of the jet-induced waveguide. Eastward propagation of the ISO teleconnection is evident over the Pacific-North America sector. The rainfall anom- alies over the elongated band near the monsoon domain over the Indo-western Pacific sector have an opposite ten- dency with that over the central and southern China, Mexico and southern US, providing a source of intrasea- sonal predictability to extratropical regions. The BSISO teleconnection along and to the north of the subtropical jet provides a good indication of the surface sir temperature anomalies in the NH extratropics.

Observational data show that the dominant mode of the boreal winter rainfall anomalies in the tropical Indo-Western Pacific (IWP) is a west-east dipolar pattern, which is called the Indo-Western Pacific Dipole (IWPD) mode and is related to El Nino-Southern Oscillation. It is found that corresponded to the IWPD mode is a new atmospheric teleconnection pattern—a wave train pattern emitted from the IWP toward Asia and the northwest Pacific in winter. During the positive (negative) phase of the IWPD, the teleconnection pattern features the negative (positive) anomalies of 200-hPa geopotential height (H200) centered at 30°N, 110°E and the positive (negative) anomalies of H200 centered at 45°N, 140°E. The teleconnection pattern represents the dominant mode of the boreal winter H200 anomaly over Asia. A series of simple atmospheric model experiments are performed to confirm that this winter teleconnection pattern is induced by the heating anomalies associated with the IWPD, and the heating anomalies over the equatorial central Pacific are not important to this teleconnection pattern from the IWP toward Asia and the northeast Pacific. The IWPD is strengthened after the climate regime shift of the 1970s, which leads to a stronger teleconnection pattern.

The spatiotemporal evolution of various meteorological phenomena associated with El Niño–Southern Oscillation (ENSO) in the North Pacific–North American–North Atlantic sector is examined using both NCEP–NCAR reanalyses and output from a 2000-yr integration of a global coupled climate model. Particular attention is devoted to the implications of downstream eddy developments on the relationship between ENSO and the atmospheric circulation over the North Atlantic.The El Niño–related persistent events are characterized by a strengthened Pacific subtropical jet stream and an equatorward-shifted storm track over the North Pacific. The wave packets that populate the storm tracks travel eastward through downstream development. The barotropic forcing of the embedded synoptic-scale eddies is conducive to the formation of a flow that resembles the negative phase of the North Atlantic Oscillation (NAO). The more frequent and higher persistence of those episodes during El Niño winters contribute to the prevalence of negative NAO conditions.The above processes are further delineated by conducting a case study for the 2009/10 winter season, in which both El Niño and negative NAO conditions prevailed. It is illustrated that the frequent and intense surface cyclone development over North America and the western Atlantic throughout that winter are associated with upper-level troughs propagating across North America, which in turn are linked to downstream evolution of wave packets originating from the Pacific storm track.

Long time-scale teleconnection patterns, with common features in both the northern Atlantic and Pacific regions, are identified. The teleconnection patterns arise in an investigation of the internally generated variability in a multimodel ensemble of coupled climate model control simulations. The large amount of data involved offers statistical robustness and the benefits of combining results across models. Maxima of decadal potential predictability identify regions where long time-scale variability is an appreciable fraction of the total variability and serve as index regions for the teleconnection analysis. Annual, 5-yr, and decadal mean temperatures over these Atlantic and Pacific index regions are correlated with corresponding temperatures and precipitation rates over the globe. The resulting teleconnection patterns are reasonably similar despite the different long time-scale variability mechanisms thought to exist in the two ocean basins. Although lacking statistical robustness, some aspects of the temperature teleconnection patterns are obtained based on the Hadley Centre Sea Ice and Sea Surface Temperature (HadISST) dataset. The similarity of the teleconnection patterns in the two northern ocean regions suggests that common variability mechanisms may be involved.

The connection between Tropical Pacific and North Pacific variability is investigated in a state-of-the-art coupled ocean-atmosphere model, comparing two 20th century simulations at T30 and T106 atmospheric horizontal resolutions. Despite a better simulation of the frequency and the spatial distribution of the Tropical Pacific anomalies associated with the El Nino Southern Oscillation (ENSO) in the high-resolution experiment, the response in the North Pacific is scarcely different from the low-resolution experiment where the ENSO variability is weaker and at higher than observed frequency. In the North Pacific, the response of surface atmospheric fields to the variability in the Tropical Pacific appears to be affected by local coupling processes significantly different in the two experiments. The coupling between sea level pressure (SLP) and sea surface temperature (SST) in the North Pacific as well as the influence of the Tropical Pacific SST has been measured here by means of the coupled manifold technique. In the low-resolution case the SLP variances linked to the fraction of North Pacific SST not influenced by the Tropical Pacific are weak suggesting that the remote influence is strong, consistently with the observations. On the contrary, in the high-resolution experiment the fractions and the patterns of the SLP variances due to the Tropical Pacific SST and those linked to the North Pacific SST are comparable. In the latter case, model systematic errors in the northwestern Pacific influences the local coupling processes thus triggering the remote response. We conclude that an increased atmospheric horizontal resolution does not reduce the coupled model systematic errors in the representation of the teleconnection between the North and the Tropical Pacific and that the validation of coupled models has to consider both remote and local processes. Copyright (c) 2011 Royal Meteorological Society

In this study, we use various diagnostic techniques to investigate the synoptic evolution of the Pacific–North American teleconnection pattern (PNA). National Center for Environment Prediction/National Center for Atmospheric Research reanalysis data are used. These data cover the years 1948–2008 for the months of November–March. It is found that the positive PNA is initiated by enhanced convection over the western tropical Pacific and weakened convection over the tropical Indian Ocean. The excitation of the negative PNA exhibits opposite features. For both phases, the response to tropical convection excites a small-amplitude PNA about 8–12 days prior to the pattern attaining its maximum amplitude. This is followed by slow, steady growth for about 5 days, after which driving by synoptic scale waves, via their eddy vorticity flux, together with stationary eddy advection lead to much more rapid growth and the establishment of the full PNA. For the positive PNA, the synoptic scale waves propagate eastward into the midlatitude northeastern Pacific, where they are observed to undergo cyclonic wave breaking. For the negative PNA, the synoptic scale waves first amplify over the midlatitude northeastern Pacific and then propagate equatorward into the Subtropics where they undergo anticyclonic wave breaking. Once established, for both phases, the PNA appears to be maintained through a positive feedback that involves a succession of wave breakings. These results suggest that preconditioning may play an important role in the formation of the PNA. For the positive PNA, in its early development, the strengthening and eastward extension of the subtropical jet result in an increase in the cyclonic shear and a decrease in the meridional potential vorticity gradient, features that are known to favour cyclonic wave breaking. For the negative PNA, opposite changes were observed for the background flow, which favour equatorward wave propagation and anticyclonic wave breaking. The role of optimal growth is also discussed. Our results also suggest that the PNA is potentially predictable 1–2 weeks in advance. Copyright © 2011 Royal Meteorological Society

The extratropical teleconnections associated with Madden–Julian Oscillation (MJO) are shown to have an action center in the North Pacific where the pressure anomalies have opposite polarities between the Phase 3 (convective Indian Ocean) and Phase 7 (convective western Pacific) of the MJO. The teleconnection in the same phase of MJO may induce opposite anomalies over East Asia and North America between El Nino and La Nina years. During MJO Phase 3, a gigantic North Pacific anticyclonic anomaly occurs during La Nina, making coastal northeast Asia warmer/wetter than normal, but the west US colder/drier; whereas during El Nino the anticyclonic anomaly is confined to the central North Pacific, hence the northwest US experiences warmer than normal weather under influence of a downstream cyclonic anomaly. During Phase 7, an extratropical cyclonic anomaly forms over the northwest Pacific during La Nina due to convective enhancement over the Philippine Sea, causing bitter winter monsoon over Japan; whereas during El Nino, the corresponding cyclonic anomaly shifts to the northeast Pacific due to enhanced convection over the equatorial central Pacific, which causes warm and wet conditions along the west coast of US and Canada. Further, the presence of ENSO-induced seasonal anomalies can significantly modify MJO teleconnection, but the aforementioned MJO teleconnection can still be well identified. During Phase 3, the MJO teleconnection pattern over North Pacific will be counterbalanced (enhanced) by El Nino (La Nina)-induced seasonal mean anomalies. During Phase 7, on the other hand, the MJO teleconnection anomalies in the northeastern Pacific will be enhanced during El Nino but reduced during La Nina; thereby the impacts of MJO teleconnection on the North America is expected to be stronger during El Nino than during La Nina.

Through observational analyses, an inter-hemispheric teleconnection is identified between the subtropical region of the South China Sea to the western Pacific near the Philippines (WP) and the region to the east of Australia (AE). The teleconnection is significantly correlated with sea surface temperature anomalies (SSTAs) in key sea areas (including the Indian Ocean, the South China Sea, and the area to the east of Australia). Based on the IAP T42L9 model, numerical experiments are performed to explore a possible mechanism for the formation of the teleconnection. The results show that the positive SST anomalies in the key sea areas may jointly contribute to the occurrence and maintenance of the positive geopotential height anomalies over both the WP and AE and be a critical factor in the teleconnection formation. The large-scale SST anomaly in the Indian Ocean, involving the tropics and subtropics of both hemispheres, may lead to concurrent atmospheric responses over both the WP and AE, while the effect of the local SST anomaly to the east of Australia seems to reinforce and maintain the positive height anomaly over the AE.

The influence of teleconnections on the Intra-Americas Sea (IAS; Gulf of Mexico and Caribbean Sea) has been mostly analyzed from the perspective of El Niño–Southern Oscillation (ENSO) on the Caribbean Sea (the latter being an extension of the tropical North Atlantic). This emphasis has overlooked both 1) the influence of other teleconnections on the IAS and 2) which teleconnections affect the Gulf of Mexico climate variability. In this study the different fingerprints that major teleconnection patterns have on the IAS during boreal spring are analyzed. Indices of teleconnection patterns are regressed and correlated to observations of oceanic temperature and atmospheric data from reanalyses and observational datasets. It is found that the Pacific teleconnection patterns that influence the IAS SSTs do so by affecting the Gulf of Mexico in an opposite manner to the Caribbean Sea. These analyzed Pacific climate patterns are the Pacific–North American (PNA) teleconnection, the Pacific decadal oscillation (PDO), and ENSO. The North Atlantic Oscillation (NAO) is related to a lesser degree with the north–south SST anomaly dipole than are Pacific teleconnection patterns. It is also found that the IAS influence from the midlatitude Pacific mostly affects the Gulf of Mexico, whereas the influence from the tropical Pacific mostly affects the Caribbean Sea. Therefore, the combination of a warm ENSO event and a positive PNA event induces a strong IAS SST anomaly dipole between the Gulf of Mexico and the Caribbean Sea during spring. By calculating an index that represents the IAS SST anomaly dipole, it is found that the dipole forms mostly in response to changes in the air–sea heat fluxes. In the Gulf of Mexico the dominant mechanisms are the air–sea differences in humidity and temperature. The changes in shortwave radiation also contribute to the dipole of net air–sea heat flux. The changes in shortwave radiation arise, in part, by the cloudiness triggered by the air–sea differences in humidity, and also by the changes in the convection cell that connects the Amazon basin to the IAS. Weaker Amazon convection (e.g., in the event of a warm ENSO event) reduces the subsidence over the IAS, and henceforth the IAS cloudiness increases (and the shortwave radiation decreases). This study contributes to a greater understanding of how the IAS is influenced by different Pacific and Atlantic teleconnections.

Substantial change was found in the El Nino/Southern Oscillation (ENSO) teleconnection during the boreal winter after the regime shift of the late 1970s. The ENSO teleconnection pattern of the earlier period is characterized by a wave-train-like structure over the Pacific/North American sector that also propagates into the stratosphere. In contrast, the recent ENSO-related extratropical circulation anomalies are characterized by changes in the tropospheric subtropical jet. The interaction of zonal winds with large-scale topography creates meridional dipole-type height anomalies downstream of the Rockies and the Tibetan Plateau, which may characterize the recent ENSO teleconnection pattern.

The wintertime Pacific–North American (PNA) teleconnection pattern has previously been shown to influence springtime snow conditions over portions of North America. This paper develops a more complete physical understanding of this linkage across the continent, using a recently released long-term, continental-scale gridded North American snow depth dataset and the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis data. An empirical orthogonal function–based filtering process is used to identify and isolate the interannual snow depth variations associated with PNA. Then linear and partial correlations are employed to investigate the physical mechanisms that link winter PNA with spring snow depth. In the positive phase of PNA, the enhanced PNA pressure centers lead to warmer temperatures over northwestern North America and less precipitation at midlatitudes. The temperature and precipitation pathways act independently and in distinct geographical regions, and together they serve to reduce winter snow depth across much of North America. Winter anomalies in the snow depth field then tend to persist into spring. Dynamic mechanisms responsible for the PNA-influenced North American precipitation and temperature anomalies, involving moisture transport and cold air intrusions, are confirmed in this study and also extended to continental snow depth anomalies.

The ability of coupled atmosphere–ocean general circulation models (AOGCMs) to simulate variability in regional and global atmospheric dynamics is an important aspect of model evaluation. This is particularly true for recurring large-scale patterns known to be correlated with surface climate anomalies. Here, the authors evaluate the ability of all Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) historical Twentieth-Century Climate in Coupled Models (20C3M) AOGCM simulations for which the required output fields are available to simulate three patterns of large-scale atmospheric internal variability in the North Atlantic region: the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), and the Atlantic multidecadal oscillation (AMO); and three in the North Pacific region: the El Niño–Southern Oscillation (ENSO), the Pacific decadal oscillation (PDO), and the Pacific–North American Oscillation (PNA). These patterns are evaluated in two ways: first, in terms of their characteristic temporal variability and second, in terms of their magnitude and spatial locations. It is found that historical total-forcing simulations from many of the AOGCMs produce seasonal spatial patterns that clearly resemble the teleconnection patterns resulting from identical calculation methods applied to reanalysis and/or observed fields such as the 40-yr ECMWF Re-Analysis, NCEP–NCAR, or Kaplan sea surface temperatures (SSTs), with the exception of the lowest-frequency pattern, AMO, which is only reproduced by a few models. AOGCM simulations also show some significant biases in both spatial and temporal characteristics of the six patterns. Many models tend to either under- or overestimate the strength of the spatial patterns and exhibit rotation about the polar region or east–west displacement. Based on spectral analysis of the time series of each index, models also appear to vary in their ability to simulate the temporal variability of the teleconnection patterns, with some models producing oscillations that are too fast and others that are too slow relative to those observed. A few models produce a signal that is too periodic, most likely because of a failure to adequately simulate the natural chaotic behavior of the atmosphere. These results have implications for the selection and use of specific AOGCMs to simulate climate over the Northern Hemisphere, with some models being clearly more successful at (i.e., displaying less bias in) simulating large-scale, low-frequency patterns of temporal and spatial variability over the North Atlantic and Pacific regions relative to others.

The meridional teleconnection patterns over the western North Pacific and East Asia (WNP–EA) during summer have a predominant role in affecting East Asian climate on the interannual time scale. A well-known seesaw pattern of tropical–subtropical precipitation is associated with the meridional teleconnection, and the subtropical precipitation anomaly has been previously viewed as a result of anomalous circulations associated with the teleconnection. In this study, however, the authors suggest that subtropical precipitation anomalies, in turn, can significantly affect large-scale circulations and may be crucial for maintenance of the meridional teleconnection. Diagnosis by using observational and reanalysis data indicates that the meridional teleconnection patterns are clearer in summers when the subtropical rainfall anomalies are greater. The simulated results by a linear baroclinic model indicate that a subtropical heat source, which is equivalent to the diagnosed positive subtropical precipitation anomaly, induces zonally elongated zonal wind anomalies that resemble the diagnosed ones in both the upper and lower troposphere over the extratropical WNP–EA. The simulated results also indicate that the horizontal and vertical structures of circulation responses are insensitive to the locations and shapes of imposed subtropical heat anomalies, which implies the important role of basic flow in circulation responses. This study suggests that, for confidential dynamical seasonal forecasting in East Asia, general circulation models should be required to capture the features of interannual subtropical rainfall variability and basic-state flows in WNP–EA.

In this study, using the ECMWF reanalysis data, the possible linkage between the Pacific-North American teleconnection pattern (PNA) and the North Atlantic Oscillation (NAO) during boreal winter (December- February) is investigated. The PNA and the NAO pattern are obtained by performing Rotated Empirical Orthogonal Function (REOF) analysis on an anomalous daily mean 300-hPa geopotential height field. The composite daily NAO indices show that the NAO indices are prone to be negative (positive) when the contemporary PNA indices are extremely positive (negative). The correlation coefficients between the daily PNA and NAO indices also confirm that, indeed, there is a significant anti-correlation between the PNA and NAO indices. The correlation peaks at a lag of 0 days (meaning contemporary correlation), and its value is 0.202. Analyses of a newly defined Rossby wave breaking index and diagnostics of the stream function tendency equation indicate that the anti-correlation between PNA and NAO may be caused by the anomalous Rossby wave breaking events associated with the PNA pattern.

Analysis of the monthly NCEP–NCAR reanalysis data and station data reveals a teleconnection pattern (NAULEA) that links climate changes over the North Atlantic and Eurasia. The NAULEA pattern has five action centers. It extends from the North Atlantic to northwestern Europe, and then stretches eastward to the Urals, with its eastern end over North China. Certain climate changes over East Asia, such as the cooling changes in both the upper troposphere and surface in the last few decades of the twentieth century, can be attributed to the NAULEA pattern anomalies and traced upstream to the North Atlantic. The NAULEA pattern is suggested to be another NAO-related teleconnection pattern. Compared with the pattern with the Asian jet waveguide path, which leads to temperature anomalies over northeastern Asia, the NAULEA pattern with a high-latitude path exerts stronger influences on the climate of southwestern China.

The North Pacific Oscillation (NPO) in sea level pressure and its upper-air geopotential height signature, the west Pacific (WP) teleconnection pattern, constitute a prominent mode of winter midlatitude variability, the NPO/WP. Its mature-phase expression is identified from principal component analysis of monthly sea level pressure variability as the second leading mode just behind the Pacific–North American variability pattern. NPO/WP variability, primarily on subseasonal time scales, is characterized by a large-scale meridional dipole in SLP and geopotential height over the Pacific and is linked to meridional movements of the Asian–Pacific jet and Pacific storm track modulation. The hemispheric height anomalies at upper levels resemble the climatological stationary wave pattern attributed to transient eddy forcing. The NPO/WP divergent circulation is thermal wind restoring, pointing to independent forcing of jet fluctuations. Intercomparison of sea level pressure, geopotential height, and zonal wind anomaly structure reveals that NPO/WP is a basin analog of the NAO, which is not surprising given strong links to storm track variability in both cases. The NPO/WP variability is influential: its impact on Alaskan, Pacific Northwest, Canadian, and U.S. winter surface air temperatures is substantial—more than that of PNA or ENSO. It is likewise more influential on the Pacific Northwest, western Mexico, and south-central Great Plains winter precipitation. Finally, and perhaps, most importantly, NPO/WP is strongly linked to marginal ice zone variability of the Arctic seas with an influence that surpasses that of other Pacific modes. Although NPO/WP variability and impacts have not been as extensively analyzed as its Pacific cousins (PNA, ENSO), it is shown to be more consequential for Arctic sea ice and North American winter hydroclimate.

Identification of teleconnection patterns at a local scale is challenging, largely due to the coexistence of non-stationary and non-linear signals embedded within the ocean-atmosphere system. This study develops a method to overcome the problem of non-stationarity and nonlinearity and investigates how the non-leading teleconnection signals as well as the known teleconnection patterns can affect precipitation over three pristine sites in the United States. It is presented here that the oceanic indices which affect precipitation of specific site do not have commonality in different seasons. Results also found cases in which precipitation is significantly affected by the oceanic regions of two oceans within the same season. We attribute these cases to the combined physical oceanic-atmospheric processes caused by the coupled effects of oceanic regions. Interestingly, in some seasons, different regions in the South Pacific and Atlantic Oceans show more salient effects on precipitation compared to the known teleconnection patterns. Results highlight the importance of considering the seasonality scale and non-leading teleconnection signals in climate prediction.

We evaluate the ability of two coupled atmospheric–oceanic GCMs—the Hadley Center's third generation coupled climate model (HadCM3) and the Canadian Center for Climate Modeling and Analysis second-generation coupled model (CGCM2)—to simulate the North Atlantic Oscillation (NAO), the Pacific North American teleconnection pattern (PNA), and map patterns in the Midwest region of the United States, relative to NCEP/NCAR reanalysis (NNR) data. The observed (NNR-derived) and GCM-derived probability distributions and temporal behavior of the daily teleconnection indices exhibit agreement over the 1990–2001 reference period, and both GCMs successfully reproduce the range of 500-hPa map patterns over the study region. During the reference period, observed and modeled map patterns are similar in terms of frequency, coherence, persistence, and progression, although the most common map pattern occurs too often in HadCM3 relative to NNR and CGCM2-derived map patterns generally exhibit closer agreement with those derived from NNR data. Despite the relatively high degree of correspondence between the observed and simulated teleconnection indices and map patterns in the study area, differences between the GCM and NNR-derived map-pattern frequencies in the reference period are greater than either (1) recent historical changes in map-pattern frequencies or (2) changes in the map-pattern frequencies as derived from twenty-first century GCM simulations, indicating that changes in these phenomena over recent and approaching decades are of insufficient magnitude relative to model uncertainty to be definitively identified. Copyright © 2005 Royal Meteorological Society.

The Circum-Pacific Teleconnection Pattern (CPTP) is revealed in the meridional wind in the high troposphere via an emprirical orthogonal function (EOF) and correlation analysis on NCEP/NCAR re-analysis data. The CPTP is found to be composed of the North Pacific-North American teleconnection pattern (PNA), the South Pacific-South American teleconnection pattern (PSA), and the teleconnection patterns over the tropical western Pacific and the tropical eastern Pacific (or, Central America, or, tropical Atlantic). There is substantial interannual variability of the CPTP and a typical CPTP can be detected in some years. It is speculated that the zonal wind anomalies over the equatorial region in the western and eastern sides of the Pacific may play a role in linking the two hemispheres. The anomalous convection activities in the Tropics are plausible triggering factors for the zonal wind anomalies that are responsible for the composition of the CPTP.

In this study we show a teleconnection pattern relating Outgoing Longwave Radiation (OLR) anomalies over the western Pacific Ocean and sea surface temperature anomalies (SSTA) over the western Indian Ocean over two seasons (Sept-Oct-Nov and Dec-Jan-Feb) at zero lag from observations and atmospheric general circulation model (AGCM) integrations. This teleconnection pattern suggests that a positive SSTA in Sept-Oct-Nov (SON) and Dec-Jan-Feb (DJF) seasons over the western Indian Ocean increases the contemporaneous positive OLR anomalies over the western Pacific Ocean. This teleconnection pattern is also simulated by the Center for Ocean-Land- Atmosphere studies (COLA) AGCM forced with observed SST’s. From the experimental COLA AGCM runs (wherein the Pacific Ocean SST variability is suppressed except for the climatological annual cycle) it is diagnosed that the interannual variability of OLR over the western Pacific Ocean persists because of this teleconnection. In relation to this teleconnection pattern it is shown that there is a significant linear response of the SON and DJF equatorial zonal wind anomaly over the Pacific Ocean to contemporaneous SSTA over the western Indian Ocean which is comparable to that of the eastern and western Pacific Oceans. The experimental AGCM runs clearly show that this response of the equatorial zonal wind anomaly to the western Indian Ocean forcing shifts westward towards the Indian Ocean in the absence of Pacific SST variability. Published

Four teleconnection patterns that are possibly associated with the anomalous summer climate in Japan and the surrounding regions, were extracted by applying empirical orthogonal function and regression analyses to stream function anomalies. The two teleconnection patterns prevailing over northern Eurasia, especially in early summer, called the Europe-Japan (EJ) 1 and EJ2, are linked with the variability of the Okhotsk high. The third teleconnection pattern, called the West Asia-Japan (WJ), is a stationary wave-train pattern along the upper-level subtropical jet from West Asia to the central North Pacific, which is possibly excited by the anomalous convective heating of the Indian summer monsoon. The final teleconnection pattern is identified with the Pacific-Japan (PJ), found by Nitta. Teleconnection indices that account for the variability of those patterns are also defined on a monthly basis. The PJ and WJ patterns, which are more influential teleconnection patterns than the others, are closely related to the summer temperature anomalies, especially in northern and western Japan, respectively. EJ1 and EJ2 were amplified in several extreme summers, and they played a vital role in the cool summer of 2003, along with PJ. A combination of two or three teleconnection patterns was also responsible for the occurrence of the recent extreme summers. Monitoring the major teleconnection patterns is very useful for understanding and forecasting the anomalous summer climate in East Asia.

Teleconnection patterns have been extensively investigated, mostly with linear analysis tools. The lesser-known asymmetric characteristics between positive and negative phases of prominent teleconnections are explored here. Substantial disparity between opposite phases can be found. The Pacific–North American (PNA) pattern exhibits a large difference in structure and statistical significance in its downstream action center, showing either a large impact over the U.S. southern third region or over the western North Atlantic Ocean. The North Atlantic–based patterns display significant impacts over the North Atlantic for large positive anomalies and even larger impacts over the European sector for large negative anomalies. The monthly variance is distributed nearly evenly over the entire North Atlantic basin. A teleconnection pattern based on different regions of the basin has been known to assume different structure and time variations. The extent of statistical significance is investigated for thr...

Decadal variability in the North Pacific is studied in a series of coupled global ocean–atmosphere simulations using coupled modeling surgery—a set of modeling approaches that can be used to identify the origins and causes of a specific variability mode in the coupled climate system. Both modeling and observational studies suggest two distinctive internal modes in the North Pacific: the North Pacific mode (NPM) and the eastern North Pacific mode (ENPM). The ENPM originates from atmospheric stochastic forcing through spatial resonance. Both local ocean–atmosphere coupling and remote tropical teleconnective forcing can enhance the ENPM, but none of them is a necessary precondition. The influence of the tropical forcing in the midlatitudes is dominated by atmospheric teleconnection, while the oceanic teleconnection is negligible. The upper-ocean heat budget reveals that SST anomalies in the central North Pacific and the eastern North Pacific are generated by anomalous Ekman advection and surface hea...