Research Of Wave-packet Propagation Features Of Interdecadal Changes Of The East Asian Summer Monsoon And Its Effect

The change and effect of East Asian monsoon is one of the main features of China's climate, especially East Asian summer monsoon, which has the most effect on distribution of rainfall in summer in China. Abnormal interdecadal change of the East Asian summer monsoon not only affects interannual and interdecadal change of China's climate but also affects China's rainfall on century time scale. Thus, it is full of meaning to research rules and effects of interdecadal changes of the East Asian summer monsoon. Based on NCEP/NCAR reanalysis materials, this paper analyzes and discusses interdecadal change features, abnormal circulation, perturbation wave energy distribution and propagation features of East Asian summer monsoon as well as its change system from the point of wave energy propagation by wave-packet propagation diagnosis (WPD) and relevant statistics data.(1) According to multi-scale perturbation wave-packet climate, the global perturbation wave-packet is basically distributed in zonal belt shape. In the transition from winter to summer, high value areas of wave packet in equator area move northwards to 10°N. Strong large wave-packet value centers appear in west wind perturbation areas in torrid and middle-latitude zones while major areas under control of subtropical high pressure suffer small wave-packet value centers.(2) East Asian summer monsoon during 1950 and 2008 showed obvious interdecadal change features and it can be divided into three interdecadal change periods, namely relatively strong summer monsoon period from 1950 to 1965, relatively weak summer monsoon period from 1975 to 2008 and interdecadal transition period from relatively strong to relatively weak summer monsoon from 1966 to 1974. According to the comprehensive analysis, in relatively strong (weak) summer monsoon period, the major circulation features of high, middle and low aerosphere of northern hemisphere are as follows:north of Asia and North Africa continent are negative (positive) anomaly centers, north of the Pacific Ocean is weak negative (positive) anomaly, and during strong (weak) summer monsoon period low pressure system is relatively strong (weak) in Asia and North Africa and sub-tropical high pressure system is relatively strong (weak). Meanwhile, in strong summer monsoon period, low aerosphere (aerosphere at sea level is 850hPa) in middle latitude areas of Asia including East Asian monsoon area and North Africa area are the strongest perturbation energy centers in the world, followed by Arabian Sea, Indian Subcontinent, Bay of Bengal and Asian Indo-China Peninsula and north of Australia, north of Indian Ocean, Equatorial Pacific region.(3) East Asian summer monsoon has positive correlation relationship with large-scale perturbation energy. Perturbation wave-packet affects key areas of change of East Asian summer monsoon. The sea level and 850hPa low atmosphere include middle latitude areas of East Asia (30～50°N,80～120°E), North Africa (0～20°N,0～40°E) and North Australia areas (15°S～15°N,90～120°E).500hPa middle atmosphere includes middle latitude areas of East Asia (30～50°N,80～120°E) and North Australia areas (15°S～15°N,90～120°E). Average wave-packet of each key area suffers transition of strong and weak phase before that of East Asian summer monsoon. Low aerosphere (aerosphere at sea level is 850hPa) in middle latitude areas of East Asia and North Africa areas suffer change of wave-packet before major areas of East Asian summer monsoon, and so do the middle atmosphere (500hPa) tropical North Australia areas and middle latitude areas of East Asia. Besides, average wave-packet of key areas has interdecadal rectilinear oscillation change.(4) According to meridional and zonal propagation features of perturbation energy, in strong summer monsoon period, perturbation energy in middle and low aerosphere (aerosphere at sea level is 500hPa and 850hPa) in East Asian monsoon area mainly comes from high latitude (40o～60°N) and south of Suvara Dvipa in low latitude areas of southern hemisphere, without obvious zonal propagation effects. In weak summer monsoon period, perturbation energy in middle and low aerosphere (20°～40°N) is propagated to lower latitude areas and is weakened and during that period low aerosphere (aerosphere at sea level is 850hPa) in middle latitude (30°N) areas of East Asia is affected by propagation of perturbation energy from West Pacific from east to west, low latitude (0°～20°N) areas are affected by propagation of perturbation energy from North Africa, and middle aerosphere shows no obvious zonal propagation features.(5) Wave-packet propagation of interdecadal changes of the East Asian summer monsoon is obviously related with Asia-Pacific flow pattern, sea temperature, North China, Southwest of China and rainfall in the Yangtze River drainage area.