Blocking High And The Actual Atmospheric Free Mode

In this paper, firstly, atmospheric free mode and blocking are summarized and defined. Free mode is classified and northern hemispheric blocking is divided into several regions.In the second place, the climate characteristics of Okhotsk blocking, Baikal blocking and Ural blocking are particularly analyzed. These blockings have a important relationship with atmospheric circulation and China summer rainfall. It is shown that the three key blockings obviously take on annual and staggered variation , and the establish and maintenance of the blocking in the east of Asia will lead to divarication of west wind circulation, so that their southern frontal zone move southward and subtropical high move southward a little, so there is plentiful rainfall in the middle and lower reaches of Changjiang River in summer.Thirdly, using 15-wave rhomboidal truncation spectral model procedure, we numerically search for steady solutions to the inviscid, unforced barotrpic vorticity equation. The free solutions are extremely similar to the planetary scale structure of observed flows. The distribution, characteristic and stability of the free mode are particularly discussed. We can conclude that each observed flow is respondent to a free mode ,and the free states are abundant but not dense. The scatter field between observed free mode streamfunction and the corresponding absolute vorticity shows that their relationship is subsection-linear even nonlinear. Normal-mode instability analysis is performed to examine observed stability of free modes. The result suggest that all the observed free modes are locally unstable and durative, and the e-folding times of the four fastest growing modes are one week at least.Finally, using observed atmospheric free modes, we diagnose atmospheric circulation and think free modes give prominence to important characteristic of atmospheric circulation , such as cross equatorial flow, zonal flow, blocking, subtropical high and boundary effects at polar regions. The zonal flow and middle latitude blocking are analyzed by free modes, the result show through free modes we can identify zonal flow and blocking anomaly and examine the stability of blocking.