A Research On The Interannual Variability Of The Silk Road Pattern

In this paper, the interannual variability of the Silk Road pattern has been studied. Therelationship between the Silk Road pattern and the Asian jet, Atlantic-Euro blockingsand SSTA over North Atlantic Ocean is inspected. Our analysis reveals that there areconsistency and independency between the three action centers of the wave-likepattern. Thus, asymmetric characteristics are found between the phase and theintensity variations of the Silk Road pattern. The main conclusions of this paper arederived as follows:（1）The intraseasonal variations of the Silk Road pattern are investigated in thisstudy. The wave train estabilishes in July with Asian jet enhancing northward, andpeaks in August. While in June, the Rossby wave pattern is inapparent. Onclimatology-mean time scale, the Silk Road pattern is the leading stationaryteleconnection pattern over Asian jet wave guide. Actually, the spatial phases of theSilk Road pattern tend to lock to preferred longitudes. Statistics analysis indicatesthat the preferred longitudes of the pattern are70-75oE,90-95oE, and115-120oE.On the other hand, the meridional variation of the three action centers has beeninspected. Compared with the other two action centers, the middle one has thelargest interannual variations.（2）Most of the Historical runs from Coupled Model Intercomarison Projectsphase5(CMIP5) models capture the key features of the Silk Road pattern: Thequasi-stationary Rossby wave with preferred longitudinal phase locking is primarilyconfined within the waveguide which is associated with the Asian jet. Additionally,our results illustrate the limitations of the models in reproducing the interannualvariations of the Silk Road pattern.（3）Remarkable interannual variations consist in the three action centers.Correlation analysis indicates that the meridional perturbations of the east center arein phase with the west one, but out-of-phase with the middle one. When the east and the west center move northword, the middle center moves southword, which featuresa wave-like pattern over the Euraisan continent. On interannual time scale, the middlecenter shifts zonally in accordance with the east one. While in the case of the westaction center, the location of it is almost immovable, suggesting the consistency andindependency of the three action centers. The meridional and longitudinal variationsof the action centers are also related to the intensity variations of the pattern. Namely,in the presence of all the action centers shifting together westward and southward thewave train enhances.（4）The asymmetric responses of atmospheric circulation over Euraian todifferent phases are the main mechanisms of asymmetric impacts of East Asia. Duringpositive phase years, the wave train which is excited in the jet exit region of the NorthAtlantic and propagates toward East Asia exhibits zonal teleconnection pattern. TheSilk Road pattern in its negative phase features a northwest-southeast mode withScandinavian blocking events.（5）A close inspection reveals that the jet over east and west action centers areregarded as the critical factor to anchor the longitudinal phases over the preferredregions, while the variations of jet over the middle center modulates the intensity ofthe Silk Road pattern. Additionally, Euro-blocking is highly efficient for thequasi-stationary Rossby wave pattern to be negative phase. It is thus indicated thatAtlantic-blocking events lead to the wave train reinforcing. The spatial pattern of sealevel pressure anomaly matches well with the tripole pattern of the North AtlanticSST anomaly. The sea level pressure anomalies modulate the Silk Road pattern byinducing divergent flow at the upper troposphere, and the advection of vorticity by thedivergent component of the flow act as effective Rossby wave sources over NortheastAtlantic and Europe. The impacts of the upstream disturbance of the Silk Road patternare critical for its interannual variability.