Mechanisms of persistent heavy rainfall related to 10–30‑day oscillation during pre- and post-monsoon-onset periods in the first rainy season over South China

• Published in: Climate dynamics Vol. 62; no. 7; pp. 6519 - 6537
• Main Authors: Li, Chunhui, Wang, Jing, Gu, Dejun, Lin, Ailan, Zheng, Bin, Peng, Dongdong, He, Jinhai
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2024; Springer; Springer Nature B.V
• Subjects: Advection; Atmospheric effects; Boundary layers; China; Climate cycles; Climatology; Convective systems; Distribution; Earth and Environmental Science; Earth Sciences; Environmental aspects; Geophysics/Geodesy; Heavy rainfall; Intraseasonal oscillation; Laboratories; Lower troposphere; Measurement; Moisture; Moisture budget; Moisture gradient; Mongolia; monsoon season; Monsoons; Oceanography; Philippines; Planetary boundary layer; Precipitation; Propagation; Rain; Rain and rainfall; Rainfall; Rainy season; Sea surface temperature; Sea surface temperature anomalies; South China Sea; Summer monsoon; Surface temperature; surface water temperature; Teleconnections; Temperature anomalies; Troposphere; Wet season; Wind; China; South China Sea; Mongolia; 10–30-day; Persistent heavy rainfall; Pre- and post-monsoon-onset periods; Atmospheric circulations
• ISSN: 0930-7575; 1432-0894
• DOI: 10.1007/s00382-024-07222-1

   This study investigates the physical mechanisms for the persistent heavy rainfall (PHR) events over South China (SC) associated with the 10–30-day intraseasonal oscillation (ISO) before the South China Sea Summer Monsoon (SCSSM) onset (SCSSM-I) and after the SCSSM onset (SCSSM-II) in the first rainy season (April–June). About 25.0% and 65.3% of the total PHR events over SC occur during SCSSM-I and SCSSM-II, respectively. A PHR process usually experiences a suppressed phase, a developing phase, an active phase, a decaying phase, and an ending phase. At the active phase of PHR events during SCSSM-I (SCSSM-II), a northwest–southeast (southeast-northwest)-oriented wavetrain emanated from northwestern Mongolia (the Philippines) migrates southeastward (northwestward) at the lower troposphere; and meanwhile, a circumglobal teleconnection with the positive (negative) phase propagates eastward along the westerly jet, forming a shallower (deeper) convective system over SC. Specifically during SCSSM-II, a positive Pacific–Japan-like teleconnection also makes a contribution to the PHR events over SC. Further planetary boundary layer (PBL) integrated moisture budget diagnosis suggests that the vertical moisture advection dominates the lower-tropospheric moistening for the PHR events at the developing and active phases, in which the leading term is the advection of the background mean moisture by the ISO ascending flow associated with PBL moisture convergence. The magnitude of the horizontal moisture advection is five times smaller than the vertical moisture advection, which is mainly contributed by the advection across the background mean moisture gradient by the ISO flow. We also present further discussions regarding the factors dominating the low-frequency ascending motions over SC and the role of low-frequency sea surface temperature anomalies before and after the SCSSM onset, which may deepen the understanding of the effects of atmospheric internal dynamical processes and the external forcing factors on the formation, strengthening, and demise of the SC PHR events.