| Based on ERA-Interim、NCEP/NCAR gridded reanalysis datasets and CMAP、 GPCP data, a study is conducted with focus on the characteristics of the seasonal variations of the East Asian Subtropical Summer Monsoon rainfall and monitoring、 predicting its30-60days intra-seasonal variability. The main results are as follows:1. Deeply understanding the characteristics of the seasonal variations of the East Asian Subtropical Summer Monsoon rainfallBased on’wind’and’rainfall’which are the two characteristics of monsoon, we find the seasonal variation of precipitation and low level wind is very different:The seasonal difference of the precipitation over East Asia is significant, presenting the monsoon rainfall characteristic called’wet summer and dry winter’. In low tropo-sphere, the prevailing wind direction in East Asia in summer is opposite to that in winter. However, the situation in East North America is opposite. Furthermore, as the essential force of monsoon, the land sea thermal contrast in East Asia is different from that in East North America. There is prominent inversion of meridional and zonal temperature gradient in East Asia. On the other hand, the inversion does exist in zonal temperature gradient in East North America, but does not in meridional temperature gradient. Besides, that the large scale circulation is different in the two areas is also contributed to the difference between the Tibet Plateau and Rocky Mountains. Therefore, the difference of the seasonal evolution of meridional and zonal temperature gradient and the force of Tibet Plateau and Rocky Mountains may be the main cause of the subtropical monsoon climate in East Asia and the non-monsoon climate in North America. The numerical experiment will be needed to confirm this conclusion.2. A new real-Time monitoring indices about the prominent meridional propagation of the30-60days intra-seasonal variability in boreal summer in the East Asian Subtropical Summer Monsoon region Based on the deeply understanding the characteristics of the seasonal variations of the East Asian Subtropical Summer Monsoon rainfall, a new real-Time monitoring indices are defined to capture the prominent meridional propagation of the30-60days intra-seasonal variability in boreal summer in the East Asian Subtropical Sum-mer Monsoon region. It is based on the first two modes of Multivariate Empirical Orthogonal Function (MV-EOF) analysis of the combined fields of daily anomalies of700hPa relative vorticity and total precipitation. For real-time application, a non-filtering method is employed to extract the30-60-day ISO signal. This non-filtering method is reliable and efficient in extracting the ISO signal. Besides, a detailed study about the composites of the700hPa relative vorticity and total pre-cipitation anomaly for different phases are shown. The results show that the seasonal variation of the East Asian Subtropical Summer Monsoon rainbelt is closely related to the meridional propagation.3. Discuss the predictability of the indicesAn extended singularity value decomposition (E-SVD) based statistical model, namely the spatial-temporal projection model (STPM), was constructed for the ex-tended-range (10-30-day) forecast (ERF) of the new monitoring indices above. The empirical models were built based22-yr (1979-2000) data and a12-yr (2001-2012) independent forecast was then conducted. The assessment of the12-year forecast of monitoring indices indicates that the monitoring indices above can be predicted well by using the STPM which has a usefull skill (with a temporal correlation coefficient exceeding95%significance level) up to lead time of30days. Furthermore, based on the relationship between monitoring indices and actual intra-seasonal rainfall, the future one-five pentads precipitation can be well predicted.Generally, the monitoring and predicting the intra-seasonal variability in the East Asian Subtropical Summer Monsoon region is significant for the Short term climate prediction in China. |
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