Research Of Intrseasonal Evolution Of East Asian Pacific Teleconnection And Maintaining Mechanism

In this paper, use the NCEP reanalysis data, precipitation and SST data, the East Asian Pacific (EAP) pattern intraseasonal evolution characteristics has been investigated by applying lead lag regression, phase composite analysis. Through the diagnosis of vorticity, thermal equation budget and barotropic, baroclinic energy conversion and the heat forcing and initial perturbation test conducted by Linear Baroclinic Mode (LBM) we discusses the EAP intraseasonal development and maintain mechanism, main conclusions have been summarized as follows:(1) EAP merdional wave train is the main mode of East Asian summer monsoon intraseasonal variability, with a oscillation period of5～12pentads or25-60days. Take positive EAP event for example, the disturbance firstly appeared in the central of North Pacific, in the upper troposphere the Rossby energy propagate southward, enhance convection and stimulate equatorial Rossby waves in Western North Pacific, the low-and mid-latitude anomaly shift westward consistently. During the peak stage, three polar wave train appear along the coast of the East Asia, the meiyu-baiu front is abated, the formation of cyclone anomaly near Okhotsk is relate to its upstream eastward Rossby energy dispersion. During EAP attenuation period, energy propagate northeastward form high-latitude anomaly and low-latitude circulation anomaly continue moving northwest and weakening, but in Yangtze valley basin precipitation anomaly is able to maintain.(2) The dynamics diagnosis shows that, in the central North Pacific, disturbance get energy through baortropic energy conversion process and develop; In the development of cyclone anomalous vorticity in WNP in lower level, the divergence term of vortex source corresponding convection strengthen the vorticity anomaly, the merdional wind advection and beta effect term shift positive vorticity anomaly north-westward, due to friction convergence, the boundary moisture convergent to the northwest of convection, lead convection coupling with circulation and propagating north-westward consistently; During the EAP peak stage, the merdional wind advection adjust EAP type vertical structure. The following reasons may responsible for EAP pattern developing and maintaining in the East Asian coast: firstly, there may exist a positive feedback between anomaly convection and circulation, makes the convection anomaly strengthening rapidly, the eastserly vertical shear above WNP is also in favor of the unstable development of equatorial Rossby as well as the excitation of extratropical barotropic mode; Secondly, there are westerly vertical shear and special northerly vertical shear baroclinic instability exist in East Asian basic flow, during the peak stage, the EAP pattern tile westward in mid-latitude and northward in both latitude in vertical direction, making EAP pattern get energy form basic state though baroclinic process.(3) The stationary forcing test conducted by LBM model show that, the easterly vertical shear play an important role in stimulating extratropical barotropic mode, the tropical convection heating and the extratropical heating work together to produce the EAP pattern, the northerly vertical shear in the basic flow in East Asian makes the EAP tilt northward. The initial value experiment show that the westward-propagating ISO in WNP establish the merdional EAP wave train in East Asian coast. The zonal temperature gradient and northerly vertical shear in East Asian summer monsoon circulation are the key factors to its formation, the EAP wave train can adapt to basic flow actively, gain energy from basic state from baroclinic process. There is a likelihood that the EAP pattern is the most unstable mode in the northerly vertical shear baroclinic basic flow.