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Richard Kleeman

spectrum of ENSO variability (e.g., Kleeman 2008b ) and another that is proposed as a mechanism for midlatitude decadal variability (see Saravanan and McWilliams 1998 ). In both these cases one can show that the basic behavior of the stochastic model is explicable using a two-dimensional OU process (see Kleeman 2002 , 2008a ). Qualitatively such a system is a white noise–forced damped oscillation with the period of oscillation determined by a natural physical time scale. In the ENSO case this is

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Dehai Luo, Yao Yao, and Aiguo Dai

winter, including those of NAO + , NAO − , and regime transition events in winter, exhibits clear interdecadal variability from a dominant negative-phase epoch (1950–77) to a dominant positive-phase epoch (1978–2011) ( Hurrell 1995 ; ). The decadal relationship between the winter-mean NAO index and the Euro-Atlantic blocking frequency from the 1960s to the 1990s has been investigated by many

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L. L. Hood and B. E. Soukharev

records (<4 decades) and the absence of a detailed physical model connecting solar variability with the tropical lower stratosphere have inhibited general acceptance of a solar origin. For the sake of brevity, in the remainder of this paper, we will refer to the decadal variation of the tropical lower stratosphere as the “quasi-decadal oscillation” (QDO). However it is emphasized that the lengths of available data records are still insufficient to determine whether the term oscillation is appropriate

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Faming Wang

can have a large impact on the SST–dipole oscillation ( Xie 1999 ; Lee and Wang 2008 ), and the atmospheric heating, surface heat flux, and SST usually do not collocate ( An 2000 ). How all those processes interact with the thermodynamical coupled modes identified here will be explored in a future study. Finally, we point out that in the current study only the basin-scale thermodynamically coupled modes are discussed, which are known to affect interannual to decadal climate variability

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Edwin K. Schneider and Meizhu Fan

the wind stress noise then enhances the sharpness of the peak from the response to the heat flux weather noise. Weng and Neelin (1998) analyzed a related simplified model of a decadal time scale tripole-like mode of North Atlantic SST variability, including processes similar to those in CM01 . Neelin and Weng (1999) and Weng and Neelin (1999) generalized the model and included multiplicative as well as additive noise. The rectangular basin ocean model includes a surface mixed layer SST

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John Marshall, David Ferreira, J-M. Campin, and Daniel Enderton

set up annular modes in the zonal jets of the ocean. The ultimate source of the variability of the coupled system is the “shake” due to the interaction between atmospheric synoptic systems with the atmospheric zonal jet. However, we find that coupling between the annular modes in the two fluids leads to a distinct decadal signal in both fluids. A simple stochastic model of the observed variability is developed and captures the essence of the coupled mechanism. In section 4 we conclude

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James S. Risbey, Terence J. O’Kane, Didier P. Monselesan, Christian Franzke, and Illia Horenko

southern annular mode (SAM) regime. The residence times in these states exhibited a trend away from the blocking state and toward the zonal state in the recent period. O’Kane et al. (2013a) used FEM-BV-VARX to analyze thermocline temperatures in a Southern Ocean domain of the Geophysical Fluid Dynamics Laboratory (GFDL) ocean GCM (OGCM). The OGCM exhibited metastable states featuring a decadal mode of variability in the South Pacific Ocean, with additional structure in the Southern Ocean storm track

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Nandini Ramesh and Mark A. Cane

measured using indices such as the Pacific decadal oscillation (PDO; Mantua and Hare 2002 ), which is based on temperature anomalies in the North Pacific, or the interdecadal Pacific oscillation (IPO), which additionally incorporates the influence and variability of the southern midlatitudes ( Henley et al. 2015 ). The behavior captured by these indices is composed of contributions from a number of phenomena including the variability of the Aleutian low, air–sea heat flux anomalies in the midlatitudes

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Meizhu Fan and Edwin K. Schneider

1. Introduction There are two dominant modes of low-frequency SST variability in the North Atlantic observed in the twentieth century, the decadal time scale tripole mode and the multidecadal time scale monopole mode. This study concentrates on attempting to understand the interplay of mechanisms that is responsible for the tripole mode. Deser and Blackmon (1993) and Kushnir (1994) found an SST anomaly (SSTA) dipole spatial pattern in the North Atlantic with biennial and decadal time scales

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Qiong Zhang, Karin Holmgren, and Hanna Sundqvist

rainfall variability. For instance, decadal variability has long been known to be a feature of the southern African climate system data ( Neukom et al. 2014 ; Reason and Rouault 2002 ; Tyson 1986 ). The presence of the approximately 18-yr climate oscillation has been identified in instrumental and tree-ring series ( Tyson et al. 2002a ; Visagie 1985 ), as well as in a recent precipitation reconstruction from the last 200 years ( Neukom et al. 2014 ). A 16–20-yr band has also been observed in ocean

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