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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.

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 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

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 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.