Major Teleconnection Patterns Research Articles

Qualifying Contributions of Teleconnection Patterns to Extremely Hot Summers in Japan

Extremely hot days in Japan are known to persist for a week or more, and they are measured by the temperature anomaly at 850 hPa averaged over Japan derived from the JRA-55 reanalysis data, denoted as T850JP. Severe high-temperature anomalies are often accompanied by multiple teleconnection patterns that affect the weather in Japan, but their relative contribution to individual heat wave events has not yet been quantified. In this study, we examined the effects of three major teleconnection patterns, namely, the Pacific-Japan (PJ), circumglobal teleconnection (CGT), and Siberian patterns, on T850JP in July and August from 1958–2019 using daily low-pass-filtered anomalies with 8 days cutoff timescale derived from the reanalysis.

Possible influence of the warm pool ITCZ on compound climate extremes during the boreal summer

In a globally changing climate, there is a growing concern for understanding and predicting compound climate extremes. However, the relationship of compound climate extremes with each other has been mostly analyzed in isolation and/or on regional scales. Little attention has been paid to their simultaneous occurrence and compound impacts worldwide. Here we demonstrate that the compound climate extremes in the Northern Hemisphere during the boreal summer are interconnected from the tropics to the Arctic. This connection originates from the interannual variations of the Indo-Pacific warm pool’s intertropical convergence zone (ITCZ). We demonstrate that the warm pool ITCZ (WPI) convection possibly influences three major teleconnection patterns (i.e. zonal, meridional, and circumglobal) where compound climate extremes occur along the wave train excited by the WPI convection. Most notably, the WPI can sufficiently explain climate variabilities in the North Atlantic region, which influences the occurrence of compound climate extremes in many parts of Europe and North America. Our findings advance the understanding of the interannual global/regional variability of climate extremes and are potentially valuable for predicting seasonal high-impact climate extremes.

체계 변위 전후 기간 동안 남한 12월 기온 변동에 대한 원격상관 패턴의 영향 변화

This study analyzed how the impacts of major teleconnection patterns on December mean temperature in Korea have been changed during the period before and after the regime shift of 1986 for the last 61 years from 1958 to 2018. During the period before the regime shift, the teleconnection patterns originating from the North Atlantic mainly affected the temperature variability in Korea, but its influence almost disappeared after the regime shift. On the other hand, the Arctic Oscillation (AO) and warm Arctic and cold Eurasia (WACE) patterns played a more important role in the temperature variability in Korea after the regime shift. Regression analysis showed that the AO could explain about 12% of the total temperature variability before the regime shift, but about 22% after the regime shift. WACE pattern also explained about 4% before the regime shift, but after the regime shift, the importance increased by about 4.5 times to 18%. On the other hand, East Atlantic pattern (EA) and North Atlantic Oscillation (NAO), which are east-west teleconnection patterns, explained 27% and 11%, respectively, before the regime shift, but had little influence within 3% after the regime shift. This means that the influence of east-west teleconnection patterns disappeared after the regime shift, and teleconnection patterns by the Arctic Circle became more important.

Evaluation of Historical CMIP5 GCM Simulation Results Based on Detected Atmospheric Teleconnections

Atmospheric teleconnections are characteristic to the climate system and exert major impacts on the global and regional climate. Accurate representation of teleconnections by general circulation models (GCMs) is indispensable given their fundamental role in the large scale circulation patterns. In this study a statistical method is introduced to evaluate historical GCM outputs of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) with respect to teleconnection patterns. The introduced method is based on the calculation of correlations between gridded time series of the 500 hPa geopotential height fields in the Northern Hemisphere. GCMs are quantified by a simple diversity index. Additionally, potential action centers of the teleconnection patterns are identified on which the local polynomial regression model is fitted. Diversity fields and regression curves obtained from the GCMs are compared against the NCEP/NCAR Reanalysis 1 and the ERA-20C reanalysis datasets. The introduced method is objective, reproducible, and reduces the number of arbitrary decisions during the analysis. We conclude that major teleconnection patterns are positioned in the GCMs and in the reanalysis datasets similarly, however, spatial differences in their intensities can be severe in some cases that could hamper the applicability of the GCM results for some regions. Based on the evaluation method, best-performing GCMs can be clearly distinguished. Evaluation of the GCMs based on the introduced method might help the modeling community to choose GCMs that are the most applicable for impact studies and for regional downscaling exercises.

Application of Wavelet Coherence Method to Investigate Karst Spring Discharge Response to Climate Teleconnection Patterns

AbstractThe impact of climate teleconnections on the regional hydrometeorology has been well studied, but very little effort has been made to relate climate teleconnections with groundwater flow variation. In this study, we used a wavelet coherence method to analyze monthly climate indices, precipitation, and spring discharge data, and investigated the relation between major teleconnection patterns (the Arctic Oscillation, North Atlantic Oscillation, Pacific Decadal Oscillation, El Niño‐Southern Oscillation, and Indian Ocean Dipole) and karst hydrological process in Niangziguan Springs Basin, China. The results indicate precipitation and spring discharges correlate well with climate indices at intra‐ and inter‐annual time scales. Further, the climate indices are mainly correlated with precipitation at shorter periodicities, but correlated with spring discharge at longer scales. The difference reflects the modulation of karst aquifers on precipitation‐spring discharge during the processes of precipitation infiltration into the ground, and subsequent transformation into spring discharge. When teleconnection signals are transmitted into spring discharge via precipitation infiltration and groundwater propagation, some high‐frequency climatic signals are likely to be filtered, attenuated, and delayed, thus only low‐frequency climatic signals are preserved in spring discharge.

Changing correlation structures of the Northern Hemisphere atmospheric circulation from 1000 to 2100 AD

Abstract. Atmospheric circulation modes are important concepts in understanding the variability of atmospheric dynamics. Assuming their spatial patterns to be fixed, such modes are often described by simple indices from rather short observational data sets. The increasing length of reanalysis products allows these concepts and assumptions to be scrutinised. Here we investigate the stability of spatial patterns of Northern Hemisphere teleconnections by using the Twentieth Century Reanalysis as well as several control and transient millennium-scale simulations with coupled models. The observed and simulated centre of action of the two major teleconnection patterns, the North Atlantic Oscillation (NAO) and to some extent the Pacific North American (PNA), are not stable in time. The currently observed dipole pattern of the NAO, its centre of action over Iceland and the Azores, split into a north–south dipole pattern in the western Atlantic with a wave train pattern in the eastern part, connecting the British Isles with West Greenland and the eastern Mediterranean during the period 1940–1969 AD. The PNA centres of action over Canada are shifted southwards and over Florida into the Gulf of Mexico during the period 1915–1944 AD. The analysis further shows that shifts in the centres of action of either teleconnection pattern are not related to changes in the external forcing applied in transient simulations of the last millennium. Such shifts in their centres of action are accompanied by changes in the relation of local precipitation and temperature with the overlying atmospheric mode. These findings further undermine the assumption of stationarity between local climate/proxy variability and large-scale dynamics inherent when using proxy-based reconstructions of atmospheric modes, and call for a more robust understanding of atmospheric variability on decadal timescales.

Hydro-climatic forecasting using sea surface temperatures: methodology and application for the southeast US

Sea surface temperatures (SSTs) are often used for the development of hydro-climatic variable forecasts based on teleconnection methods. Such methods rely on projections or linear combinations of teleconnection indices [e.g. El Nino-Southern Oscillation (ENSO)] and other predictor fields. This study introduces a new hydro-climatic forecasting method identifying SST “dipole” predictors motivated by major teleconnection patterns. An SST dipole is defined as a function of average SST anomalies over two oceanic areas of specific sizes and geographic locations. An optimization algorithm is developed to search for the most significant SST dipole predictors of an external hydro-climatic series based on the Gerrity Skill Score. The significant dipoles are cross-validated and used to generate multiple forecast values. The new method is applied to the forecasting of seasonal precipitation over the southeast US. Hindcasting results show that significant dipoles related to ENSO as well as other prominent patterns at different lead times can indeed be identified. The dipole method also compares favorably with existing statistical forecasting schemes with respect to multiple skill measures. Furthermore, an operational forecasting framework able to produce ensemble forecast traces and uncertainty intervals that can support regional water resources planning and management is also developed.

Dominant impact of South Asian low heat on summer monsoon rainfall over Central India

Although previous literature have considered Southern Oscillation Index (SOI), Indian Dipole, and SST as the major teleconnection patterns to explain the variability of summer monsoon rainfall over India. South Asia low pressure and Indian Ocean high are the centers of action that dominates atmospheric circulations in Indian continent. This paper examines the possible impact of South Asian low pressure distribution on the variability of summer monsoon rainfall of India using centers of action approach. Our analysis demonstrates that the explanation of summer monsoon rainfall variability over Central India is improved significantly if the SOI is replaced by South Asian low heat. This contribution also explains the physical mechanisms to establish the relationships between the South Asian low heat and regional climate by examining composite maps of large-scale circulation fields using NCEP/NCAR Reanalysis data.

Trends and extremes of drought indices throughout the 20th century in the Mediterranean

Abstract. Average monthly precipitation, the original Palmer Drought Severity Index (PDSI) and a recent adaptation to Europe, the Self Calibrated PDSI (scPDSI) have been used here to analyse the spatial and temporal evolution of drought conditions in the Mediterranean during the 20th century. Monthly, seasonal and annual trends were computed for the period 1901–2000 and also for the first and second halves of this period. The statistical significance of trends was obtained with a modified version of the Mann-Kendall test that accounts for serial auto-correlation. The results show a clear trend towards drier conditions during the 20th century in most western and central Mediterranean regions, with the exceptions of northwestern Iberia and most of Turkey that reveal an increase of moisture availability. A Generalized Extreme Values (GEV) analysis was applied to the maximum and minimum regional values of scPDSI, with results pointing towards a significant decline of absolute extreme values in central areas (Italy and Balkans) and a less clear picture emerging in western (Iberia) and eastern (Turkey) realms. The inter-annual variability of the scPDSI index series is shown to be more realistic than the corresponding PDSI version, fitting better the drought episodes sequence and magnitude described in the literature for each sub-region. We assess the decadal and inter-annual variability of the scPDSI for each sub-domain and evaluate the role played by the major teleconnection patterns, and by several sea surface temperature (SST) anomalies. The main driver of scPDSI in western and central Mediterranean areas is the winter North Atlantic Oscillation (NAO) pattern that is also relevant during the following spring and summer seasons with anti-correlation values below −0.60. The second most important mode corresponds to the Scandinavian Pattern that is significantly associated to the scPDSI between winter and summer over central Mediterranean (correlation values around 0.50). Finally, the teleconnection and SST analysis has allowed us to calibrate a stepwise regression model, enabling the forecasting of summer drought conditions six months in advance. The final model obtained is capable of reproducing the observed scPDSI time series fairly well, with a correlation coefficient of 0.79 (0.77 after cross-validation) and a significant gain over climatology (SSc=59%), while the corresponding result against persistence is more modest (SSp6=11%).

Winter 2009–2010: A case study of an extreme Arctic Oscillation event

Winter 2009–2010 made headlines for extreme cold and snow in most of the major population centers of the industrialized countries of the Northern Hemisphere (NH). The major teleconnection patterns of the Northern Hemisphere, El Niño/Southern Oscillation (ENSO) and the Arctic Oscillation (AO) were of moderate to strong amplitude, making both potentially key players during the winter of 2009–2010. The dominant NH winter circulation pattern can be shown to have originated with a two‐way stratosphere‐troposphere interaction forced by Eurasian land surface and lower tropospheric atmospheric conditions during autumn. This cycle occurred twice in relatively quick succession contributing to the record low values of the AO observed. Using a skillful winter temperature forecast, it is shown that the AO explained a greater variance of the observed temperature pattern across the extratropical landmasses of the NH than did ENSO.

Trends in long-term gaseous mercury observations in the Arctic and effects of temperature and other atmospheric conditions

Abstract. Gaseous elemental mercury (GEM) measurements at Alert, Canada, from 1995 to 2007 were analyzed for statistical time trends and for correlations with meteorological and climate data. A significant decreasing trend in annual GEM concentration is reported at Alert, with an estimated slope of −0.0086 ng m−3 yr−1 (−0.6% yr−1) over this 13-year period. It is shown that there has been a shift in the month of minimum mean GEM concentration from May to April due to a change in the timing of springtime atmospheric mercury depletion events (AMDEs). These AMDEs are found to decrease with increasing local temperature within each month, both at Alert and at Amderma, Russia. These results support the temperature dependence suggested by previous experimental results and theoretical kinetic calculations on both bromine generation and mercury oxidation and highlight the potential for changes in Arctic mercury chemistry with climate. A correlation between total monthly AMDEs at Alert and the Polar/Eurasian Teleconnection Index was observed only in March, perhaps due to higher GEM inputs in early spring in those years with a weak polar vortex. A correlation of AMDEs at Alert with wind direction supports the origin of mercury depletion events over the Arctic Ocean, in agreement with a previous trajectory study of ozone depletion events. Interannual variability in total monthly depletion event frequency at Alert does not appear to correlate significantly with total or first-year northern hemispheric sea ice area or with other major teleconnection patterns. Nor do AMDEs at either Alert or Amderma correlate with local wind speed, as might be expected if depletion events are sustained by stable, low-turbulence atmospheric conditions. The data presented here – both the change in timing of depletion events and their relationship with temperature – can be used as additional constraints to improve the ability of models to predict the cycling and deposition of mercury in the Arctic.

The Intra-Americas Springtime Sea Surface Temperature Anomaly Dipole as Fingerprint of Remote Influences

Abstract 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.

Analysis on the Dynamics of a Wave-like Teleconnection Pattern along the Summertime Asian Jet Based on a Reanalysis Dataset and Climate Model Simulations

The Silk Road pattern, a wave-like anomaly pattern observed along the summertime Asian jet, is one of the major teleconnection patterns that can influence the East Asian summertime climate. Our analysis based on a reanalysis (JRA-25) dataset confirms the conventional notion that the pattern has a characteristic of a free stationary Rossby wave train, with its horizontal wavenumber close to the stationary Rossby wavenumber determined by the mean intensity of the jet. However, our analysis reveals its more essential characteristic as a dynamical mode whose extraction of available potential energy from the baroclinic Asian jet is highly efficient for its self-maintenance. Our analysis also reveals high sensitivity of its barotropic energy conversion to subtle zonal asymmetries of the Asian jet, which can be regarded as a critical factor to anchor the strongest vorticity anomaly around the western jet core and thereby determine the preferred longitudinal phase alignment of the wave train as observed. In fact, singular value decomposition of a global baroclinic model linearized about the observed mean state for boreal summer leads to identification of a perturbation similar to the Silk Road pattern with respect to its structure and energetics. It is thus indicated that the configuration of the mean flow determines the dominant phase, as well as the meridional location and the wavenumber, of the Silk Road pattern.The aforementioned dynamical characteristics of the Silk Road pattern are found useful for assessing and interpreting the reproducibility of the pattern in the present-day climate simulated in climate models that participated in the phase 3 of the Coupled Model Intercomparison Project (CMIP3). The pattern tends to be identified as the dominant mode of upper-tropospheric meridional wind variability as observed in such models that can reproduce the mean Asian jet realistically, including its zonal structure, which confirms the dynamics of the Silk Road pattern revealed in our observational analysis. On the basis of our analysis, a metric is proposed for assessing the models' reproducibility of the pattern.

Combined Effects of Teleconnection Patterns on Anomalous Summer Weather in Japan

Using ERA-40 and NCEP/NCAR reanalysis data, the characteristics of major teleconnection patterns were examined, particularly the West Asia-Japan (WJ) and Pacific-Japan (PJ) patterns, with a high-frequency (HF) component (from half a week to two or three weeks), and a low-frequency (LF) component (greater than about one month), and discussed the combined effects of the teleconnection patterns on the anomalous summer weather in Japan and the surrounding regions.Both patterns of the HF-WJ and LF-WJ, which propagate eastward along the upper-level Asian jet, induce an anomalous barotropic anticyclone centered on the Japan Sea. The HF-WJ pattern has no close link with the Asian summer monsoon activity, but, in contrast, the LF-WJ pattern is significantly correlated with anomalous monsoonal heating over the summer monsoon region. The HF-PJ and LF-PJ patterns, which can be identified with stationary waves stimulated by intense convection around the Philippine Sea, generate a nearly barotropic anticyclone anomaly to the east of Japan. A combination of the HF-WJ and HF-PJ patterns establishes a zonally elongated anticyclonic anomaly over northern Japan, resulting in anomalous high surface temperatures in northern Japan. Such a coupling was found to lead to a larger temperature increase in that region than a single teleconnection pattern alone.A typical case of the LF-WJ and LF-PJ combination also indicates a zonally elongated anticyclonic anomaly over northern Japan, which is similar to the combined pattern of HF-WJ and HF-PJ. The dynamic impact of LF-WJ on the surface temperature field around Japan differs significantly from that of LF-PJ. The dominance of the LF-WJ causes enhanced subsidence over Japan, which can bring about adiabatic heating and increased incoming solar radiation. On the other hand, PJ-induced anomalous anticyclone in the lower troposphere facilitates northward warm advection to the east of northern Japan, where the north-south temperature gradient is large. As for the extreme hot summer of 2004, no combined patterns of the LF-WJ and LF-PJ were found during the summer. Alternatively, a tripole structure appeared in the lower geopotential height field in mid-June. Such a tripole pattern may be established by a combination of the LF-PJ and a barotropic Rossby wave train propagating southeastward from high latitudes.

What Do Networks Have to Do with Climate?

The study of networks has recently exploded into a major research tool in many areas of science. The discovery of “small world” and scale-free networks has led to many new insights about the collective behavior of a large number of interacting agents and complex systems. Here we introduce the basic ideas behind networks, as well as some initial applications of networks to the climate system. Our results suggest that the climate system exhibits aspects of small-world networks as well as scale-free networks, with supernodes corresponding to major teleconnection patterns. This result suggests that the organization of teleconnections may play a role in the stability of the climate system. In addition, preliminary work suggests that temporal changes in the network's architecture may be used to identify signatures of global change. These and other applications suggest that networks provide a new tool for investigating and reconstructing climate dynamics from both models and observations.

NOTES AND CORRESPONDENCE; Extraction of Major Teleconnection Patterns Possibly Associated with the Anomalous Summer Climate in Japan

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.

A review of Northern Hemisphere winter-time teleconnection patterns

This chapter reviews the major teleconnection patterns that occur in the boreal winter season. The history of teleconnection research is first reviewed emphasising the pioneering work of Sir Gilbert Walker. This is followed by a review of contemporary research that focuses on eleven teleconnnection patterns classified into two groups: Euro-Atlantic and Pacific/North American patterns. Structure, impacts on weather and climate and temporal variability of each pattern are discussed by critically comparing major teleconnection studies. The lack of agreement on structure and occasionally the very existence of certain teleconnection patterns is also highlighted. These disagreements can be attributed to the absence of a universally accepted definition of teleconnections and the use of different statistical methods and data sets.

冬期低気圧経路、遠隔伝播パターン、および降水量の年々変動

Three major teleconnection patterns prevailing at 500hPa height, e. g., North Atlantic Oscillation (NAO), Pacific-North American (PNA) and Western Pacific (WP) patterns, are investigated in the northern Winter season associated with cyclone tracks and precipitation patterns. Cyclone position and tracks, objectively analyzed using NCAR Sea Level Pressure Grids (1964-1990) and ECMWF 1000hPa height grids (1980-1990), are composited in reference to the extreme appearance of positive or negative teleconnection patterns around the Atlantic and Pacific. The correlations between the teleconnections and the inter-annual variability of precipitation are also investigated.Significant changes of major cyclone routes are commonly and clearly found in the two data sets as follows. In case of ± NAO patterns, major zonal cyclone tracks fluctuate meridionally, and cyclones tend to move eastward in the middle parts of North Atlantic, or they direct northeastward along the northwestern Atlantic to reach the Norwegian Sea. Significant variations of precipitation associated with these changes of cyclone tracks are found in southwestern and northwestern parts of the west coast of Europe. In the case of dominant ± PNA patterns, cyclones tend to direct eastward within 40°-50°N over the North Pacific and turn north to migrate to the Gulf of Alaska to Bristol Bay, or they move northeastward along the northwestern edge of Pacific to migrate to the Bering Sea or strike on the east coast of Canada. The former pattern corresponds to a strengthening of the eastern part of the Aleutian low, and the latter pattern provides the positive correlation with precipitation on the east coast of Japan and a part of the west coast of Canada. Dominant ± WP patterns are responsible for the meridional fluctuations of apparent zonal distribution of cyclone tracks with its strike of a SSW-NNE direction over the Northern Pacific. The northward shift of this distribution provides the increase of the precipitation amount in the southwestern islands and central Pacific regions of Japan.