The Temporal And Spatial Characteristics Of The Low-frequency Rainfall Regimes Over Southern China In Summer

Using the daily precipitation dataset covering southern China and the NCEP/NCAR daily reanalysis for the period1961-2011, the Intra-seasonal and inter-decadal variations, circulation patterns and precursor signals of the low-frequency rainfall regimes over Southern China in summer are investigated through multiple statistical methods. Main conclusions are summarized as follows:(1) The low-frequency oscillation of rain in southern China is conducted by Morlet wavelet analysis and power spectral analysis. Result show rainfalls in different regions have differences in oscillation intensity, amplitude and periods.(2) Five rainfall regimes (RRs) generated from the10-day low-pass filtered data are identified by applying empirical orthogonal function and cluster analysis method, namely, Yangtze River regime, South of Yangtze River regime, South China regime, Southeast China regime, and rainless regime. Analyses show that RRs match well with the large-scale circulation and significant difference exists in characteristics of water vapor transport.(3) The new RRs can describe intra-seasonal dynamic characteristics of large-scale rainfall anomalies, which is the most significant difference between the new RRs and the conventional season average rainfall patterns. Moreover, significant inter-decadal variation is observed in statistical characters in last five decades:peak values of the regimes appear in succession from1980s to1990s; in the21th century, the statistic of rainless regime shows a significant increasing trend, while most low-frequency regimes are less seen.It indicates that the southern China is entering a period of the decrease of intra-seasonal precipitation.(4) The precursor signals of the RRs are investigated. Different phases of circulation anomalies from lower to upper levels are composited at10-20days and30-60days time scale by performing Butterworth filter. Result shows that:significant differences of signals sources from lower to upper levels are revealed. The Yangtze River regime rainfalls are outcomes anomalous signals at both low latitude and mid-high latitude. The Southeast China regime rainfalls is dominated by northwest ward anomalous signals at low latitude. The South China regime rainfalls in earlier period are related with anomalous signals at mid-high latitude; while have relationship with signals at low latitude in later period.