Study On Spatiotemporal Correlation Of Extreme Rainfall In Southwest China Based On Complex Network Theory

The extreme rainfall in Southwest China is affected by multiple climate system interactions and has complex internal interactions,with typical spatiotemporal correlation characteristics and nonlinear dynamic behavior of complex systems.In recent years,theoretical and applied research on complex networks based on the climate system is in the ascendant.Using the complex network method can transform the complex climate dynamics system into the form of a climate network,and the complex interaction and nonlinear behavior in the original system can be described through the topology parameters and dynamics of the network.Applying the complex network theory in systems science to the study of extreme rainfall in Southwest China can capture the large-scale climate elements that affect extreme rainfall in this region,and effectively describe the internal interaction of the system,which helps open up new directions for studying the complexity and predictability of extreme rainfall in this region.The extreme rainfall in Southwest China is less predictable than in other regions in China.The fundamental reason is that it is difficult to correctly describe the correlation of extreme rainfall between Southwest China and other regions.This thesis reveals the spatiotemporal synchronization characteristics of extreme rainfall between the Southwest China and Asia-Pacific regions through the synchronization network and reveals the spatiotemporal and dynamic characteristics of extreme rainfall between the Southwest China and Asia-Pacific regions.It is found that the probability of significant synchronization of extreme rainfall events between Southwest China and the Asia Pacific as a function of distance changes from a power-law decay behavior to a teleconnection one at around 2000 km.Specifically,Southwest China-the middle and lower reaches of the Yangtze River-Japan band(SYJ)is a typical teleconnection pattern of extreme rainfall in the Asia Pacific region.This SYJ teleconnection pattern is associated with the water vapor flux convergence along the main water vapor transport route from the low latitude ocean.In addition,the teleconnection characteristics of SYJ rain belt is characterized through the definition of SYJ telecorrelation index.The inter-annual variation of the SYJ teleconnections index can reflect the evolution of synchronization rainfall features from Southwest China to Japan.It is also found that the SYJ index is strongly correlated with sea surface temperature anomalies over the northern Indian Ocean and the western Pacific.The warm sea surface temperature over the northern Indian Ocean and the western Pacific can motivate the transfer of water vapor from Southwest China to Japan,yielding the synchronization of extreme rainfall along with the SYJ band.The significant synchronization of extreme rainfall events in Southwest China has the characteristics of short-range correlation,and the extreme rainfall in this region has the characteristics of north-south movement in space.Therefore,we further reveal the asymmetric features of the synchronization of extreme rainfall events in Southwest China by a complex network approach.The significant synchronization pattern of extreme rainfall events in Southwest China,which is closely associated with the convergence of warm-wet air and cold-dry air and the corresponding occurrence of extreme rainfall in Southwest China.The network divergence indicates a dominated direction of the net influence of extreme rainfall from the Sichuan Basin to the Yunnan-Guizhou plateau,implying the extreme rainfall synchronization moving from north to south in Southwest China is more frequent than the opposite direction.The development of the low vortex and the north wind system usually shows a movement from north to south,resulting in the evolution of extreme rainfall events more tend to present a southward movement.The low-reinforced latitude cyclonic circulation leads to the strengthened transportation of water vapor from the tropical area to the north and converges with the anticyclonic circulation in the mid-latitudes to form the movement of heavy rainfall events from the Yunnan-Guizhou plateau to the Sichuan Basin.Therefore,the synchronization direction of extreme rainfall events in Southwest China has obvious asymmetry spatial feature due to the more frequent and stronger circulation system moving from north to south than the opposite.The ocean plays a very important role in regulating atmospheric circulation and climate change.Southwest China is located near the Indian Ocean and the Pacific Ocean,and sea surface temperature anomalies have an important impact on the climate in this region.This thesis uses the delayed correlation network to study the teleconnection characteristics between the global sea surface temperature anomalies and the rainfall anomalies in Southwest China in different seasons and reveals the teleconnection between global sea surface temperature and rainfall anomalies in Southwest China in different seasons.Our results show that the out-degree patterns in the Pacific,Atlantic and the Indian Ocean significantly influence the rainfall anomalies in Southwest China.In particular,we find that such patterns dominated by extreme rainfall change with the seasons.Further research found that the teleconnections between the global sea surface temperature anomalies and rainfall anomalies can be described by the indegree patterns,which are dominated by several vital nodes within Southwest China.Based on the characteristics of these nodes,we found that the node patterns in Southwest China are mainly affected by the sea surface temperature in some key areas such as the equatorial Indian Ocean,the equatorial central and eastern Pacific,the equatorial Atlantic and the northwestern Pacific and have a specific time delay.