资源环境科技发展态势分析平台

It has been widely accepted that the Indian Ocean Dipole (IOD) can influence the global climate and thus improvement of its understanding is beneficial to our society. In this study, we show that the April snow cover extents (SCEs) over Tibetan Plateau and the central Eurasia may play an important role on triggering the occurrence of IOD. The correlation coefficient between the April SCE indices and the subsequent September-November dipole mode indices is -0.51 in the recent 40 years, significant at the 99% confidence level. In years with the larger April SCEs, the thermally driven ascending over the plateau becomes weaker and causes anomalous subsidence over the plateau and its southern contiguous region. This, together with the cooler-than-normal continent, can delay the onset of Bay of Bengal (BOB) summer monsoon. As a result, the northwards migration of the major rainbelt from the eastern tropical Indian Ocean to the eastern BOB in accordance with the monsoon onset will be delayed, leading to increased precipitation in the eastern tropical Indian Ocean. The increased precipitation may lead to generation of the negative IOD through the local air-sea interactions. The observed April SCEs-IOD relation has been examined in historical runs of 19 coupled models participating phase 5 of the Coupled Model Intercomparison Project (CMIP5). Most models except MRI-CGCM3 fail to reproduce the observed April SCEs-IOD relationship. This is probably due to their difficulties in realistically simulating the snow impacts on the BOB summer monsoon and the air-sea coupling during the IOD development.