Baroclinic Instability of the Silk Road Pattern Induced by Thermal Damping

Abstract

Abstract In this paper, the internal dynamics of the Silk Road pattern has been studied. Since observation indicates that the Silk Road pattern could be considered as stationary external Rossby waves, the quasigeostrophic three-layer model has been used to study the dynamics of external Rossby waves. The three-layer model well captures the essential dynamical features of stationary external Rossby waves in accordance with the observations. Theoretical analysis indicates that the quasi-stationary external modes could be destabilized by the weak thermal damping. For destabilization to occur, the vertical structures of the external modes must have a warm ridge and a cold trough from the lower to middle layers. The effect of thermal damping could be considered as modifying the eddy streamfunction in such way that the eddy streamfunction has a vertical phase tilt, so the eddy could feed on the basic zonal flow by extracting the potential energy. The implications for this baroclinic instability on the self-maintenance of the Silk Road pattern are discussed. The observations imply that this dissipative destabilization mechanism could explain the self-maintenance of the Silk Road pattern.