Abstract
It is urgent to improve the prediction accuracy of precipitation in the preflood season (PFS) over South China (SC) under the background of global warming, and thus the research of water vapor conditions is the key. For the period of 1960–2012, using the daily precipitation data from 60 meteorology stations in SC and National Centers for Environmental Prediction (NCEP) reanalysis data, the synergistic effect of PDO (the Pacific Decadal Oscillation) &IOD (the Indian Ocean Dipole Mode) on water vapor transport process to frontal/monsoon precipitation is revealed, based on the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT_4.9). For the frontal precipitation, the positive PDO phase (PDO+) compared with the negative PDO phase (PDO−), there is more water vapor over the West Pacific (WP), the northern South China Sea (SCS), and the Bay of Bengal (BOB). Water vapor for frontal precipitation mainly comes from WP and SCS. When PDO and IOD are in phase resonance, the water vapor transport tracks from the SCS, WP are shorter and westward, so more water vapor is transported to SC, the precipitation efficiency of water vapor to PFS precipitation is higher too. For the summer monsoon precipitation, the tropical Indian Ocean (IO)-BOB is rich in water vapor, especially for PDO−& IOD+. The main water vapor transport tracks are the cross-equatorial flows in the IO, BOB and SCS. The precipitation efficiency of water vapor from the IO-BOB is higher for the positive IOD phase (IOD+) than that for the negative IOD phase (IOD−); however, the precipitation efficiency of water vapor from SCS is higher for the IOD− than that for IOD+. Compared with frontal precipitation, the strong westerly anomaly in the northern IO increases the water vapor transport from the north IO, BOB to SC during monsoon precipitation. For the PDO+&IOD+, the stronger Indian Low and cyclonic anomaly in the WP increases the water vapor transported from the IO-BOB to SC, improving the precipitation efficiency of water vapor. Understanding the synergistic effect of the PDO and IOD on water vapor transport will help to improve the accuracy of precipitation prediction, and reduce the negative impact of drought and flood disasters.
Highlights
The frontal precipitation, when the Pacific Decadal Oscillation (PDO) and Indian Ocean Dipole Mode (IOD) are in phase resonance, most
Events are shorter and westward, so more water vapor is transported to South China (SC), the precipitation over SC are the Mediterranean-Eurasian interior, Indian Ocean (IO), Bay of Bengal (BOB), South China Sea (SCS), West Pacific (WP), and East China
HYSPLIT 4.9 is used to simulate the trajectories of air parcels formed during preflood season (PFS) precipitation events, cluster analysis is conducted on the trajectories to identify the main water vapor channels
Summary
Previous studies have shown [16,17] that the water vapor transport in the PFS has obvious interdecadal variation characteristics. The summer precipitation in SC is affected by the tropical IO SST, spring snow cover over the Tibetan Plateau [37], summer intraseasonal oscillation in the Northern Hemisphere [38], and summer convective activity in the SCS [39], a synergistic effect of external forcing factors The results of these studies have contributed to a deeper understanding of the complexity of precipitation variability, and showed that the SST anomaly of the IO and WP has an important impact on the water vapor transport for the PFS. Our findings will provide a theoretical basis for an in-depth understanding of the factors governing the PFS precipitation, provide additional information for analyzing drought and flood disasters
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