Development of Synoptic-Scale Disturbances over the Tropical Western North Pacific Associated with the Boreal Summer Intraseasonal Oscillation and the Interannual Pacific–Japan Pattern

The development mechanism of synoptic-scale disturbances over the tropical western North Pacific (WNP) associated with boreal summer intraseasonal oscillation (BSISO) under different phases interannual Pacific-Japan (PJ) pattern is investigated. Intraseasonal convection enhanced widely WNP for BSISO 5-7 in positive PJ years, when seasonal-mean convective activity enhanced. By contrast, developed confined South China Sea negative years. Similar features are also found horizontal distributions eddy kinetic energy (K′) representing and cyclone occurrences. differences location between years likely lead to teleconnection midlatitude East Asia. non-PJ show mixed A K′ budget analysis reveals that conversion from available potential (PeKe) synoptic primarily contributes generation during convectively active BSISO. barotropic mean K′, KmKe, second largest contributor increase lower troposphere, especially early stage disturbances. Large produced by PeKe KmKe tropics advected subtropics flow late mature stages development. There two factors can determine locations where develop KmKe. One sea surface warming suppressed preceding phases. other convergence or shear winds fluctuations monsoon westerlies WNP.