Propagation features of wave-packet signal of interdecadal change of the East Asian summer monsoon

Based on NCEP/NCAR reanalysis materials, the key areas with impact on change of strength of East Asian summer monsoon are determined and the wave-packet features of East Asian summer monsoon are diagnosed in wave-packet propagation diagnosis method and through calculation of wave-packet values in strong and weak monsoon periods. (1) During 1948 and 2005, East Asian summer monsoon became weaker in middle and late 1960s and kept in relatively weak phase in post period. (2) In period of strong East Asian summer monsoon, the wave-packet value is large in middle and high latitude areas of Arica, South Asia and East Asia. Large wave-packet value centers are formed in North Africa and middle and high latitude areas of East Asia. With increase of height, the wave-packet becomes smaller and interdecadal change is weaker. (3) In strong summer monsoon period, key middle and high latitude areas of East Asia and North Africa witness large wave-packet values and the wave-packet values are propagated from middle and high latitude areas of southern hemisphere to north and to middle and high latitude areas of northern hemisphere in late 1950s and early and middle 1960s while there was no obvious propagation features in key areas of North Africa. In weak summer monsoon period, wave packets of key middle and high latitude areas of East Asia are propagated from middle and high latitude areas of northern hemisphere to south and to middle and high latitude areas of southern hemisphere while wave packets of key areas of North Africa are propagated to high latitude areas of northern hemisphere and to middle latitude areas of southern hemisphere from North Africa and to middle and high latitude areas of southern hemisphere from low and middle latitude areas of southern hemisphere. Wave packets in middle and high latitude areas of East Asia are also propagated to the east.