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The asymmetric impacts of El Niño and La Niña on the Pacific–North American teleconnection pattern in boreal winter have important implications for the surface air temperature and precipitation anomalies in North America. Previous studies have shown that the varying tropical convective heating contributes to the zonal shift of the teleconnection pattern during different El Niño/Southern Oscillation phases. In this study, using reanalysis, atmospheric general circulation model (AGCM) simulations, and a linear baroclinic model, we further present that the discrepancy of the subtropical jet stream (STJ) during El Niño and La Niña also contributes to the asymmetry. The atmospheric anomalies readily extract kinetic energy and effectively develop at the exit of the STJ. During El Niño (La Niña) years, as the central-eastern tropical Pacific warms up (cools down), the meridional temperature gradient in central subtropical Pacific increases (decreases), leading to the eastward (westward) shift of the STJ. The movement of the STJ leads to the shift of the location where disturbance develops most efficiently, ultimately contributing to the asymmetry of the teleconnection pattern.

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 interdecadal change in the relationship between the El Nino–Southern Oscillation (ENSO) and atmospheric circulation over the North Pacific is investigated using both observational data and an a...

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.

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.

The North Atlantic Oscillation (NAO) response to the northeast Pacific climate variability is examined using the ERA-40 dataset. The main objective is to validate a mechanism involving downstream wave propagation processes proposed in a recent idealized companion study: a low-frequency planetary-scale ridge (trough) anomaly located in the eastern Pacific–North American sector induces more equatorward (poleward) propagation of synoptic-scale wave packets on its downstream side, which favors the occurrence of anticyclonic (cyclonic) wave breakings in the Atlantic sector and the positive (negative) NAO phase. The mechanism first provides an interpretation of the canonical impact of the El Niño–Southern Oscillation on the NAO in late winter. The wintertime relationship between the Pacific–North American oscillation (PNA) and the NAO is also investigated. For out-of-phase fluctuations between the PNA and NAO indices (i.e., the most recurrent situation in late winter), the eastern Pacific PNA ridge (trough) anomaly modifies the direction of downstream wave propagation, triggering more anticyclonic (cyclonic) wave breakings over the North Atlantic. For in-phase fluctuations, the effect of the eastern Pacific PNA anomalies is cancelled out by the North American PNA anomalies. The latter anomalies being deeper and more centered in the latitudinal band of downstream wave propagation, they are able to reverse the direction of wave propagation just before waves enter the Atlantic domain. The contrasting relationship between the PNA and NAO is similar to what occurs for the two leading hemispheric EOFs of geopotential height: the northern annular mode (NAM) and the cold ocean–warm land (COWL) pattern. The proposed mechanism provides a physical meaning for the NAM and COWL patterns.

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.

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.

The frequency of tropical cyclones (TCs) in Taiwan during June to October (JJASO) is found to have a strong negative correlation with the Pacific/North American (PNA) pattern in the preceding April. In the negative PNA phase, the anomalous cyclonic and the anomalous anticyclonic circulations are intensified at low latitudes and midlatitudes from East Asia to the North Atlantic, respectively, from April to JJASO. Particularly in East Asia, the anomalous southeasterly that converges between the anomalous anticyclone to the east of Japan and the anomalous cyclone to the east of Taiwan plays a decisive role in moving TCs not only to Taiwan, but also to the midlatitude coastal regions of East Asia as a result of the steering flow. In addition, a southwestward extension of a western North Pacific (WNP) high during the positive PNA phase also contributed to a frequent movement of TCs to southern China without traveling north toward the midlatitude regions of East Asia. Due to the difference in the typical tracks of the TC in the WNP according to the PNA phase, the intensity of the TC in the negative PNA phase is stronger than that in the positive PNA phase.

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.

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.

The anomalous circulation patterns during an unusually prolonged stormy-weather period in Hawaii from 19 February to 2 April 2006 are analyzed and are compared with those of two previously known prolonged heavy-rainfall periods (March 1951 and February 1979). The circulation patterns for these three periods are characterized by 1) a negative Pacific–North American (PNA) pattern in the midlatitudes with a blocking high southwest of the Aleutian Islands, 2) retraction and splitting of the zonal jet into a polar jet north of 50°N and a persistent subtropical jet to the south over the central Pacific Ocean, 3) an anomalous low west of the Hawaiian Islands embedded in the subtropical jet, and 4) a weaker-than-normal Hadley circulation in the mid-Pacific. The moisture advected from low latitudes by the southerly wind component east of the persistent anomalous low, combined with upward motion, provides the large-scale setting for the unusually prolonged unsettled weather across the Hawaiian Islands. For all three cases, the prolonged stormy weather started after the onset of large-scale blocking and a negative PNA pattern over the North Pacific and the occurrence of a persistent anomalous low embedded in the subtropical jet west of the Hawaiian Islands. Furthermore, the persistent low was located at the optimal position to bring moisture from the central equatorial Pacific to Hawaii. The stormy weather ceased after the midlatitude blocking pattern weakened and the anomalous low in the subtropics decayed and/or shifted westward. There are no apparent common precursors in the 2-week period prior to the prolonged stormy weather among these three cases, however.

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

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.

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.

The inter-basin teleconnection between the North Atlantic and the North Pacific ocean–atmosphere interaction is studied using a coupled ocean–atmosphere general circulation model. In the model, an idealized oceanic temperature anomaly is initiated over the Kuroshio and the Gulf Stream extension region to track the coupled evolution of ocean and atmosphere interaction, respectively. The experiments explicitly demonstrate that both the North Pacific and the North Atlantic ocean–atmosphere interactions are intimately coupled through an inter-basin atmospheric teleconnection. This fast inter-basin communication can transmit oceanic variability between the North Atlantic and the North Pacific through local ocean-to-atmosphere feedbacks. The leading mode of the extratropical atmospheric internal variability plays a dominant role in shaping the hemispheric-scale response forced by oceanic variability over the North Atlantic and Pacific. Modeling results also suggest that a century (two centuries) long observations are necessary for the detection of Pacific response to Atlantic forcings (Atlantic response to Pacific forcing).

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.

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

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...

The relationship between the Pacific–North American (PNA) teleconnection pattern and Ohio River Valley (ORV) winter precipitation and hydrology is described. The PNA is significantly linked to moisture variability in an area extending from southeastern Missouri, northeastward over states adjacent to the Ohio River through Ohio. Maximum correlation between the PNA index and station precipitation peaks in southern Indiana at r = −0.71, making the circulation/climate teleconnection one of the strongest in the Northern Hemisphere. The North Pacific index (NPI), a Pacific basin sea level pressure index that is highly correlated to the PNA, confirms a strong circulation–ORV precipitation relationship extending back to 1899. In contrast, measures such as the Tahiti–Darwin Southern Oscillation index (SOI) and Nino-3.4 (5°S–5°N, 120°–170°W) sea temperatures are not significantly correlated to ORV winter precipitation. Wettest (driest) winters occur with zonal (meridional) flow with the PNA negative (posit...

Sea surface temperatures (SSTs) exhibit an interannual seesaw between the eastern and western tropical Pacific in concert with the El Nino–Southern Oscillation (ENSO) cycle. Evidence accumulated from previous studies suggests that a teleconnection link may exist between enhanced rainfall/convection in the western Pacific and precipitation/severe weather over North America. The aforementioned link could possibly be established by a teleconnection wave pattern induced by the anomalously warm/cold SST anomalies in the western tropical Pacific. To demonstrate this possibility, a Fourier scale separation was introduced to divide the ENSO anomalous circulation into two wave regimes: long wave (waves 1–3) and short wave (waves 4–15). The classic Pacific–North American teleconnection pattern is formed by the long-wave regime. In contrast, emerging in the short-wave regime is a well organized wave train that propagates from the western subtropical Pacific along the North Pacific rim into North America. In...

One-point correlation analysis on upper-level meridional wind identified the existence of ateleconnection pattern in July, which emerges from North Africa to East Asia along the westerlyjet in the middle latitudes. We examined the spatial and temporal structures of this teleconnectionpattern, and found the unique characteristics rather different from the patterns in otherelements such as geopotential height, streamfunction and vorticity. We also investigated therelationship between this teleconnection and precipitation, and suggested that the teleconnectionis a possible linkage of the EASM to the Indian monsoon, and even to subtropical heatinganomalies over Atlantic.DOI: 10.1034/j.1600-0870.2002.00248.x

From analyses based on Singular Value Decomposition of rainfall and 500 hPa geopotential height anomalies, we have identified two atmospheric teleconnection pattern linking interannual variability of summertime precipitation over East Asia and the continental United States. The first pattern is associated with enhanced rainfall over the Yangtze River region to above-normal rainfall over the US northern Great Plains and the Midwest, and reduced rainfall over the Atlantic coast. It features zonally elongated 500 hPa height anomalies over the subtropical and extratropical western North Pacific coupled to a regional circulation pattern over North American that regulates moisture transport from the Gulf of Mexico to the Northern Great Plains. The second pattern shows enhanced rainfall anomalies over the Huaihe River, northeastern and southern China and deficient rainfall over the central US. It connects the East Asian and North American continents via a pan-Pacific wavetrain signal, possibly stemming from Rossby wave dispersion from fluctuations of large-scale heat sources, and sinks in the Indo-Pacific region. Examination of associated sea surface temperature variability in the North Pacific suggests that the first pattern may be influenced by El Nino in the preceding spring, but becomes increasing decoupled from tropical SST during the summer and fall. However, the second pattern has no significant relationship with El Nino. Analysis of extreme rainfall statistics between regions in East Asia and North America suggests that occurrence of the aforementioned teleconnection patterns is associated with increased probability for extreme rainfall events over the Yangtze River Valley, coupled to increased probability of anomalies of the same sign over the US Midwest, and of the opposite sign over the US Mid-Atlantic coast. Our results suggest that the summertime teleconnection patterns should be further explored for additional sources of potential predictability of summertime floods or droughts over regions of East Asia and North America.

This study examines inconsistencies in the Pacific/North American (PNA) index relative to atmospheric circulation over North America. Two types of atmospheric circulation were found to be associated with high PNA values. The first type is the true PNA pattern characterized by an amplified ridge-trough system. It appears to be related to the leading mode of sea surface temperature variability in the North Pacific. The second type is observed during El Nino events. It is characterized by a flattening of the polar jet stream and southward shift of the subtropical jet stream. The recognition of these two types of the PNA index improves our understanding of the relative role of to El Nino/Southern Oscillation events and sea surface temperatures in the North Pacific in affecting winter atmospheric circulation over North America.

The Asian–Pacific Oscillation (APO) is a relatively new teleconnection index and a number of peer-reviewed studies have confirmed its’ existence. This study reexamines the concept of the APO teleconnection as currently published in the literature. Most results have found that this pattern could be defined as its own teleconnection pattern within the Pacific Ocean Basin. This work demonstrates that the APO is inevitably associated with an additional action centre located over the North Atlantic Ocean, and the index can be extended. Previous studies have used a variety of methods to represent the APO, and a method is proposed here to standardise the formulation. It is argued that the extended index proposed here provides a more robust result. The APO typically is identified using the eddy temperature rather than geopotential height as the source material for its construction, as geopotential could not adequately represent this teleconnection pattern. This leads to a discussion regarding the basic criterion for defining teleconnective activity within the extratropical regions. We also identify other problems in the current understanding of APO theory that need to be addressed. Keywords: teleconnection, EOF, eddy temperature, Pacific Ocean Basin, Northern Hemisphere, Atlantic Ocean Basin (Published: 4 October 2016) Citation: Tellus A 2016, 68, 31779, http://dx.doi.org/10.3402/tellusa.v68.31779

A new and significant correlation is found between the amplitude of mean-winter atmospheric anomalies over the North Atlantic Ocean and those over the North Pacific Ocean and western North America three winters later. It is as strong as the previously known and much discussed correlation between the ocean temperature in the eastern tropical Pacific (El Nino region) and the North Pacific winter atmospheric anomalies. No physical explanation is given at this time for this correlation. A statistical prediction model for mean-winter conditions is constructed based on the above new and previously known correlations. The prediction model is tested on 36 winters of the past. The model predictions are shown to be of remarkable quality over the North Pacific and western North America.

Evidence gleaned from the instrumental record of climate data identifies a robust, recurring pattern of ocean–atmosphere climate variability centered over the midlatitude North Pacific basin. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal timescales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals correspond to dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures, as well as streamflow in major west coast river systems, from Alaska to California.

Considerable evidence has emerged of a sub- stantial decade-long change in the north Pacific atmo- sphere and ocean lasting from about 1976 to 1988. Ob- served significant changes in the atmospheric circula- tion throughout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Conse- quently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coast of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurred in the surface wind stress, and, by inference, in the Sverdrup trans- port in the north Pacific Ocean. Changes in the month- ly mean flow were accompanied by a southward shift in the storm tracks and associated synoptic eddy activi- ty and in the surface ocean sensible and latent heat fluxes. In addition to the changes in the physical envi- ronment, the deeper Aleutian low increased the nu- trient supply as seen through increases in total chloro- phyll in the water column, phytoplankton and zoo- plankton. These changes, along with the altered ocean currents and temperatures, changed the migration pat- terns and increased the stock of many fish species. A north Pacific (NP) index is defined to measure the de- cadal variations, and the temporal variability of the in- dex is explored on daily, annual, interannual and de- cadal time scales. The dominant atmosphere-ocean re- lation in the north Pacific is one where atmospheric changes lead SSTs by one to two months. However, strong ties are revealed with events in the tropical Pa- cific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Changes in the storm tracks in the north Pacific help to reinforce and maintain the anomalous circulation in the upper tro

The PNA teleconnection index, a measure of the strength and phase of the Pacific/North American teleconnection pattern, is used to examine changes in the midtropospheric flow over North America on decadal, interannual, and intra-annual time scales. The index corroborates previous findings that a major change in the midtropospheric circulation took place over North America during the late 1950s. The time series of index values also demonstrates the existence of a previously unknown quasi periodicity in the configuration of midtropospheric heights over the North American sector. A seasonal specification analysis is conducted to identify climate system components that are closely linked to the PNA teleconnection. The selection of predictor variables is based on recent modeling and observational work suggesting their probable involvement with midiatitude flow variations. These include sea surface temperatures for locations in the tropical Pacific and North Pacific, along with Asian land surface tempe...

The relationships between 300/1000 mbar thickness anomalies over the North Pacific Ocean and thickness anomalies over the adjacent North American continent are investigated on the basis of monthly anomalies for the 34-month period January 1986 to October 1988. It is found that in 21 out of the 34 months a pattern exists that links negative anomalies over the North Pacific Ocean to positive anomalies over the North American continent. Using teleconnection analysis, it can be shown, that in spring a strong relationship exists between positive anomalies over the western half of the North American continent in mid-latitudes and negative thickness anomalies over the North Pacific Ocean in mid-latitudes as well as between positive anomalies over the North Pacific Ocean in tropical and subtropical latitudes. Statistically, the strongest relationships emerged between the thickness gradient departures 20°–30°N over the east-central Pacific Ocean and positive anomalies over North America. The abnormal warmth over the North American continent in the springs of 1986, 1987, and 1988 may be explained in terms of an intensified circulation across the Pacific Ocean, which resulted in large positive thickness anomalies downstream over the North American continent. The intensification of those anomalies in the spring of 1988 is discussed as a contributing factor to the initiation of the 1988 North American drought.

[1] An observational analysis is presented that reveals an August teleconnection involving both the Northern Hemisphere (NH) and the Southern Hemisphere (SH). The teleconnection includes three primary anomalies in the monthly average surface pressure field: (1) a high southern latitude component including Wilkes Land, Antarctica, the nearby Southern Ocean, and the Ross Sea, (2) a SH midlatitude component near Australia and New Zealand, and (3) a NH subtropical component over the extreme western Pacific Ocean. Surface pressure for the SH high-latitude anomaly is negatively correlated to the other two primary anomalies. The SH midlatitude and NH subtropical component are positively correlated. Furthermore, the teleconnection is correlated to surface pressure near the Aleutian Islands. The teleconnection anomalies result from tropical convection on intraseasonal timescales. Monsoon rainfall over East Asia during August is correlated to the teleconnection. Furthermore, August precipitation at several other locations in the NH and SH is modulated by the teleconnection. Two different sets of numerical experiments with the National Center for Atmospheric Research (NCAR) Community Climate Model version 2 (CCM2) show a similar-appearing teleconnection during late boreal summer. The modeled teleconnection, however, is forced from high southern latitudes.

We have investigated the well-known tendency for winter temperatures to be low over northern Europe when they are high over Greenland and the Canadian Arctic, and conversely. Well-defined pressure anomalies over most of the Northern Hemisphere are associated with this regional seesaw in temperature, and these pressure anomalies are so distributed that the pressure in the region of the Icelandic low is negatively correlated with the pressure over the North Pacific Ocean and over the area south of 50°N in the North Atlantic Ocean, Mediterranean and Middle East, but positively correlated with the pressure over the Rocky Mountains. The composite patterns of pressure anomalies in the seesaw are almost identical to the fist eigenvector in the monthly mean pressure, but the standard deviations of pressure anomalies in seesaw mouths are as large as the standard deviations of monthly means in general. Since 1840 the seesaw, as defined by temperatures in Scandinavia and Greenland, occurred in more than 40%...

The “high index” response of the northeast Pacific westerlies to big positive anomalies of equatorial sea temperature, observed in the winter of 1957–58, has been found to repeat during the major equatorial sea temperature maxima in the winters of 1963–64 and 1965–66. The 1963 positive temperature anomaly started early enough to exert the analogous effect on the atmosphere of the south Indian Ocean during its winter season. The maxima of the sea temperature in the eastern and central equatorial Pacific occur as a result of anomalous weakening of the trade winds of the Southern Hemisphere with inherent weakening of the equatorial upwelling. These anomalies are shown to be closely tied to the “Southern Oscillation” of Sir Gilbert Walker.