Dominant Mode Of Boreal Summer Monsoon Precipitation And Its Linkage To The SSTAs On Interannual Timescale

The study utilized the GPCP and CMAP products, HadSST2 dataset and the ERA-Interim reanalysis dataset, and applied regression, principal component analysis and error evaluation methods to (1) compare the boreal summer monsoon (BSM) precipitation between the GPCP and CMAP products and (2) identify the interannual co-variation of the BSM rainfall and its connection with the tropical SSTAs during 1979-2014. Results suggested that:(1) Major diversities between GPCP and CMAP are found in the rainfall pattern and the magnitude in climatology over the oceanic monsoon areas, especially the western North Pacific (WNP) monsoon region, as well as in the interannual variability of summer rainfall anomalies over the North Africa (NAF) and India monsoon regions. Although inconsistency between the two datasets is evident before the 1990s, the use of their arithmetic mean is demonstrated to be an efficient way to reduce the uncertainty between them.(2) The first dominant mode shows that the interannual variability of the summer monsoon rainfall over the WNP is different from the other four BSM components, presenting the distinct circulation over the monsoon regions in the Northern Hemisphere. When the WNP rainfall decreases, the anomalous descending over the WNP will enhances the ascending over the other monsoon regions by altering their vertical coupling between the upper-and lower-level circulation, except for the NAF with the weak low-level circulation. Thus, the anomalous circulations cooperatively form the dominant mode of BSM rainfall.(3) The polarity of the dominant mode can be ascribed to the El Nifio events in previous winter. Specifically, the El Nino-induced TIO warming in boreal summer can change the phase of this dominant mode through producing the abnormal circulation and the rainfall anomalies over the WNP. Moreover, the dominant mode is more significant with low ENSO events decaying speed.