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1. Introduction
The so-called Silk Road pattern (SRP) is a teleconnection pattern trapped along the Asian upper-tropospheric westerly jet in summer. It spans across the Eurasian continent roughly along 40°N, where the Asian jet is located during summer, emanating from North Africa and propagating to East Asia (Lu et al. 2002; Enomoto et al. 2003; Kosaka et al. 2012). The SRP tends to be geographically fixed (Lu et al. 2002; Sato and Takahashi 2003; Ding and Wang 2005; Kosaka et al. 2009) and has a wavelength of about 60° in the zonal direction (e.g., Kosaka et al. 2009). Some previous studies have viewed the SRP as a part of the circumglobal teleconnection pattern, which appears to propagate zonally through the whole hemisphere (Ding and Wang 2005; Yasui and Watanabe 2010; Chen and Huang 2012; Kosaka et al. 2012; Lin 2014).
Various studies have indicated that the SRP significantly affects climate over a broad area, including but not limited to the latitudes of the Asian jet. Corresponding to the SRP, there are precipitation anomalies over the Indian subcontinent, Europe, northern China, and Japan (Lu et al. 2002; Huang et al. 2011; Chen and Huang 2012; Lin 2014; Saeed et al. 2014). In addition, the SRP also influences surface air temperature, especially in Japan (Enomoto 2004; Wakabayashi and Kawamura 2004; Ding and Wang 2005; Sato and Takahashi 2006; Ding et al. 2011). These effects of the SRP on the climate, in turn, motivate investigation about the physical mechanisms of the SRP.
Many important features of the SRP can be well explained by the dynamics of stationary Rossby waves and the interaction between the stationary waves and basic flow. Based on the Rossby wave ray theory, Hoskins and Ambrizzi (1993) suggested that the strong westerly jet acts as the waveguide and confines the waves within it. Also according to the wave ray theory, the wavenumber of the waves trapped in the westerly jet is determined by the basic flow, or more exactly, the shape of the westerly jet. On the other hand, the interaction between stationary waves and basic flow can explain the phase-locking feature and maintenance mechanism of the SRP. The SRP can be maintained through its efficient extraction of kinetic energy from the basic flow through...