资源环境科技发展态势分析平台

Intraseasonal variability of rainfall over the Indian subcontinent (IS) and the Tibetan Plateau (TP) has been discussed widely but often separately. In this study, we investigate the covariability of rainfall across the IS and the TP on intraseasonal time scales and its impact on interannual variability of regional rainfall. The most dominant mode of rainfall intraseasonal variability across the region features a dipole pattern with significant out-of-phase rainfall anomalies between the southeastern TP and the central and northern IS. This dipole rainfall pattern is associated with intraseasonal oscillations (ISOs) of 10-20 days and 30-60 days, especially the latter. An active spell of rainfall in the central and northern IS (southeastern TP) is associated with the strengthening (northward shift) of water vapor transport of the Indian summer monsoon, resulting in more water vapor entering into the central and northern IS (southeastern TP) and thus more rainfall. The 10-20-day ISO of the dipole rainfall pattern is caused by the 10-20-day atmospheric ISO in both the tropics and the extratropics, whereas the 30-60-day ISO of the dipole rainfall pattern is only associated with atmospheric ISO in the tropics. The dipole rainfall pattern resembles the most dominant mode of interannual variability of July-August mean rainfall. The 30-60-day ISO of the dipole rainfall pattern has an important contribution to the dipole pattern of July-August mean rainfall anomalies on an interannual time scale due to the different frequencies of occurrence of the active and break phases.