Upper‐troposphere saddle‐like response to springtime surface sensible heating over the Tibetan Plateau combined effect from baroclinic and barotropic process

The surface sensible heating over the Tibetan Plateau (TP) is a significant, elevated heating source in spring (March-April-May, MAM). It exerts considerable thermal effects on both regional and global climate. During MAM, the surface sensible heating over the TP triggers a giant saddle-like circulation anomaly in the upper troposphere at 200 hPa. Although this structure was observed a long time ago and it contributes to the stationary wave, its formation mechanism remains unclear. Using the Linear Baroclinic Model, we reveal the evolution of this structure in detail. In the initial state, a typical baroclinic anticyclone with a vertical phase tilt forms around the heating source. When the wave propagates downstream due to strong relative vorticity advection and favorable lower level circulation, an anticyclone with a barotropic structure forms downstream. Our analysis indicates that both the barotropic process and baroclinic process contribute to the formation of the saddle-like structure, and the latter is associated with the spring unique background circulation and vertical heating structure over the TP.