DIAGNOSE ANALYSE ATMOSPHERIC BLOCKING HIGH BY FREE MODE

Aimed at stud of atmospheric free mode and blocking high,firstly,the relationships between blockings and China summer rainfall are clarified,and the 500 hPa height in the summer of 1998 are det ailed analysed.Then,using 21-wave rhomboidal truncation spectral model procedure,it is searched for steady solutions to the inviscid,unforced barotrpic vorticity equation,which are called free solutions or free modes.These free solutions are extremely similar to the planetary scale structure of observed flows.Thirdly,the characteristics of atmospheric free modes are particularly discussed.Finaly,by virtue of at mospheric free modes,we diagnose observed at mospheric circulation and put stress on analyzing the anomalous circulation during the summer of 1998,and the Normal-mode instability analysis is performed to examine observed stability of free modes and blocking.The results show the following:(1)The mid-high latitudes blocking has a close relationship with China summer rainfall,and the atmosphere underwent three times blocking anomaly in the summer of 1998.(2) Each observed flow is corresponding to a free mode,and the scatter field between observed free mode streamf unction and the corresponding absolute vorticity (also called plots) reflects their subsection-linear even nonlinear relationship.The plots for observed stream flow lay out the linear relationship in different slope between streamfunction and the corresponding absolute vorticity,but the scatters are relatively emanative.(3) Observed atmospheric free modes show most characteristics of at mospheric circulation in large scale,while neglect the mesoscale and microscale vortex.