A quasi-oscillatory semidecadal cycle in Northern Hemisphere seasonal networks

Abstract

Abstract The relationships among tropical and extratropical climate modes in different seasons and the accumulative influences are not fully understood. After removing time-varying climatological averages, this study identified a semidecadal cycle in two tropical climate modes, namely the Indian Ocean Dipole (IOD) and El Niño–Southern Oscillation (ENSO). A regression of the nonseasonal convective activity of the Indo-Pacific warm pool on seasonal sea surface temperature gradients associated with the autumntime IOD and subsequent wintertime ENSO, indicated that the spring Arctic Oscillation (AO) and Asian-Pacific summer monsoons have a strong relationship before and 1 year after convection peaks. The seasonal Network on Decadal Echo (NODE) was noted to exhibit quasi-oscillatory characteristics, particularly during negative Atlantic Multidecadal Oscillation (AMO) phases. A semidecadal NODE is associated with a strong North Pacific center of action within the AO during a negative AMO phase. By contrast, during a positive AMO phase, the AO’s influence on the NODE cycle weakens or disappears. During NODE cycles, a stronger monsoon Hadley cell following a negative spring AO is associated with a weaker oceanic trough in the western North Pacific (WNP) and suppressed tropical convection, favoring a negative IOD in autumn and a La Niña winter. Conversely, a positive AO leads to a deeper WNP trough and a weaker monsoon Hadley cell in summer, resulting in a positive IOD and an El Niño winter. The AO–monsoon Hadley cell–IOD and AO–WNP trough–ENSO relationships identified in this study provide process insights into mechanisms governing seasonal networks. Furthermore, multidecadal state-dependent oscillatory NODE cycles shed light on potential for hemispheric accumulation.