THE EVOLUTION OF OPTIMAL SENSITIVITY PER-TURBATION AND THE PERSISTENT ANOMALOUS CIRCULATION AT URAL IN SUMMER

In this work,the process of the set up of anomalous circulation patterns through unstable development of initial disturbances was investigated by numerical experiments.We chose as basic flow the mean circulation of two typical anomalo us East A sian summer monsoon years of 1991 and 1985,and as initial disturbances the optimal sensitivity perturbations obtained from adjoint sensitivity anal yses.The development of these disturbances in different circulation background has been analyzed.The result shows that,the instability of the 1991 basic flow in Eurasia region is stronger,and the initial perturbation possesses the structure of preferred growing perturbation.Therefore the disturbances are excited near U ralarea through energy dispersion,then grow very rapidly and develop the blocking circulation.Whereas the disturbances in 1985 developed into a positive vorticity anomaly and is not favorable for the set up of blocking high.This lead to the almost opposite anom alous circulation patterns in Uralarea in 1991 and 1985.A series of experiments indicate that the development of anomalous circulation is due to the growth of disturbances by extracting energy from basic flow through barotropic instability as well as energy dispersion.This depends not only on the instability of the basic flow it self but also the structure of the initial disturbance and its position with respect to the basic flow.The basic flow selects the initial disturbance with specific structure.When there is a disturbance at certain favorable position,it can excite the whole wave train and develop into a strong anomalous pattern.No matter how the phase distribution of the initial wave train changes within certain range,the disturbances tends to develop in the same unst able area of the basic flow.