Contrasting northward and southward propagations of intraseasonal precipitation under the southern China summer rainfall pattern

Abstract

Propagations of intraseasonal precipitation are essential for subseasonal prediction of East Asian summer rainbelt. In this study, under the background of the southern China summer rainfall pattern (SCSRP), the intraseasonal northward and southward propagation types are first identified and then their propagation characteristics and influencing factors on the 20–90-day intraseasonal timescale are deeply examined. Results show that the northward propagation type, being primary during the SCSRP in its most cases, features robust northward propagation of anomalous signals in the low-level southwesterly wind, outgoing longwave radiation, and 500-hPa geopotential height (Z500) towards the Yangtze River basin. For the southward propagation type, anomalous signals of Z500 with low-level northeasterly wind mainly exhibit a clear southward propagation from the northwest continental area, towards the precipitation anomaly center in southern China. We further reveal that the northward propagation type of intraseasonal precipitation is dynamically related to the first mode of boreal summer intraseasonal oscillation (BSISO) that exhibits significant precipitation anomalies over the southern China in its Phases 5 and 8, and to the intraseasonal oscillation in the East Asia-Western North Pacific (EAWNP ISO) that shows significant precipitation anomalies in its Phases 3 and 5. In contrast, the southward propagation type is primarily influenced by the wave trains of anomalous circulation over mid-to-high latitudes.