Pacific SST Modulates Latitude of Boreal Summer Intraseasonal Oscillation-related Rainfall in Eastern China

The boreal summer intraseasonal oscillation (BSISO) is a key source of subseasonal to seasonal predictability and has significant impacts on east Asian precipitation. Previous studies have examined the modulation of precipitation by the BSISO, but the interannual variability of the modulation remains elusive. In this study, the real-time multivariate indices of the BSISO, the Climate Prediction Center global unified gauge-based analysis of daily precipitation, the NCEP/NCAR reanalysis and the ERSSTv5 are combined to investigate how the equatorial Pacific sea surface temperature (SST) modulates the latitudinal position of the BSISO-related precipitation anomalies in east Asia. We define the wet spell as the phases when the BSISO convection is over the Indian Ocean (phase 2-4) and the dry spell as the phases when the BSISO convection is over the northwestern Pacific (phase 5-7), and verify that the wet spell enhances precipitation in east Asia, while the dry spell suppresses it. However, the latitudinal position of the precipitation area varies interannually depending on the equatorial Pacific SST. Specifically, cold SST anomalies over the western equatorial Pacific in April and warm SST anomalies over the central and eastern equatorial Pacific in May tend to strengthen the Western Pacific subtropical high and weaken the 850 hPa westerlies, which in turn hinder the BSISO-related northward moisture transport and the Rossby wave propagation triggered by BSISO convection. As a result, the BSISO-related precipitation anomalies shift southward for both the wet and dry spell. This study identifies the interannual variability of the BSISO modulation on east Asian summer precipitation and has implications for improving its subseasonal to seasonal prediction.