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  • Global Drought Information System - Drought Characterization, Occurrence, Driving Mechanisms, and Predictability Worldwide (GDIS Worldwide) x
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Lixia Zhang and Tianjun Zhou

. The Silk Road teleconnection is a teleconnection along the westerly jet stream in the upper troposphere over the Asian continent. Following Kosaka et al. (2012) , the Silk Road pattern is identified by performing an EOF on 200-hPa meridional wind velocity over (30°–50°N, 30°–130°E) in summer. Both of the first two leading modes can be seen as a Silk Road pattern. Considering the robust correlation with the East Asian summer rainfall, only the first leading mode (EOF1) and the corresponding

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Mathew Barlow, Benjamin Zaitchik, Shlomit Paz, Emily Black, Jason Evans, and Andrew Hoell

the westerlies and associated synoptic activity to a warm season regime under the influence of the Indian monsoon. The strong westerly jet and associated synoptic activity during the cold season are seen in Figs. 8a and 8e , respectively, and the extension of the northwestern-most branch of the monsoon into northern Pakistan and southeastern Afghanistan is seen in the July–September panels of Fig. 7 . Cold season synoptic precipitation is important over much of the region and has been studied by

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Bradfield Lyon

between the Ethiopian and Kenyan highlands leading to the formation of the Turkana low-level jet, which channels southeasterly flow from over the Indian Ocean inland ( Kinuthia and Asnani 1982 ; Kinuthia 1992 ; Viste and Sorteberg 2013 ). Given such complexities, it is not surprising that the annual cycle of precipitation also shows considerable spatial heterogeneity ( Figs. 2b–d ). Across much of the region the annual cycle is generally bimodal, with greatest amounts occurring during the long rains

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Wenju Cai, Ariaan Purich, Tim Cowan, Peter van Rensch, and Evan Weller

also influenced by a weakening of the subtropical storm track due to the decreasing baroclinic instability of the subtropical jet and increasing instability in the polar latitudes ( Frederiksen et al. 2011b ) and a poleward shift of the ocean–atmosphere circulation ( Cai and Cowan 2013a ). The well-documented poleward expansion of the subtropical dry zone ( Fu et al. 2006 ; Hu and Fu 2007 ; Seidel et al. 2008 ; Johanson and Fu 2009 ; Lucas et al. 2012 ), particularly during April–May, is shown

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Siegfried D. Schubert, Hailan Wang, Randal D. Koster, Max J. Suarez, and Pavel Ya. Groisman

of blocking that focus on the Atlantic and impacts on Eurasia go back to Obukhov et al. (1984) and a number of earlier studies reviewed therein. That study in particular reviewed various potential mechanisms of blocking, including those linked to orography and the instability of the polar jet, and it emphasized atmospheric blocking as a precondition for drought in summer, with both the downward movement of air within the associated anticyclone (acting to heat and dry the air) and the blocking

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Belen Rodríguez-Fonseca, Elsa Mohino, Carlos R. Mechoso, Cyril Caminade, Michela Biasutti, Marco Gaetani, J. Garcia-Serrano, Edward K. Vizy, Kerry Cook, Yongkang Xue, Irene Polo, Teresa Losada, Leonard Druyan, Bernard Fontaine, Juergen Bader, Francisco J. Doblas-Reyes, Lisa Goddard, Serge Janicot, Alberto Arribas, William Lau, Andrew Colman, M. Vellinga, David P. Rowell, Fred Kucharski, and Aurore Voldoire

:// ). The Sahel drought during the 1970s and 1980s was the most significant climate event at the continental scale during the twentieth century, and is arguably among the largest climatic changes worldwide ( Trenberth et al. 2007 ). The event was associated with changes in the intensity, spatial distribution, and temporal evolution of the WAM and associated circulation features, such as the trade winds, African easterly jet (AEJ), and tropical easterly jet (TEJ) ( Le Barbe et al. 2002 ; Sultan and

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Siegfried D. Schubert, Ronald E. Stewart, Hailan Wang, Mathew Barlow, Ernesto H. Berbery, Wenju Cai, Martin P. Hoerling, Krishna K. Kanikicharla, Randal D. Koster, Bradfield Lyon, Annarita Mariotti, Carlos R. Mechoso, Omar V. Müller, Belen Rodriguez-Fonseca, Richard Seager, Sonia I. Seneviratne, Lixia Zhang, and Tianjun Zhou

Atlantic SST, a result consistent with Kushnir et al. (2010) and Wang et al. (2008) , who showed that a larger Atlantic warm pool leads to a suppressed Great Plains low-level jet and associated reduced central U.S. precipitation. On the other hand, summertime precipitation is positively (although weakly) correlated with SST along the west coast of North America extending into the central tropical Pacific, with a structure reminiscent of the PDO. The link to the Indian Ocean also has substantial

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