Characteristics and the inter-decadal variation 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 data for the period 1961-2011, the intra-seasonal and inter-decadal variations of the low-frequency rainfall regimes over southern China in summer are investigated. Five rainfall regimes (RRs) generated from the 10 day low-pass filtered data are identified by applying the empirical orthogonal function and cluster analysis method. The results show that RRs match well with the large-scale circulation and significant difference exists in characteristics of water vapor transport. It is more important that 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, a significant inter-decadal variation is observed in statistical characters in the last five decades: peak values of the regimes appear in succession from 1980s to 1990s； in the 21 century, the statistics of the rainless regime shows a significant increasing trend, while most low-frequency regimes are less seen .It indicates that southern China is entering a period of the decrease of intra-seasonal precipitation.