A dominant mode of interannual variability of Indian summer monsoon rainfall shows west-east dipole pattern with above normal rainfall towards west and central India and subdued rainfall towards the east and northeast India, and is related to the vigorous Azores High. The vigorous Azores High is accompanied by enhanced subsidence resulting in well-built widespread upper-troposphere convergence. This forms the meridional vorticity dipole consisting of anomalous cyclonic and anti-cyclonic circulation at 30°N and 50°N, respectively, and boosts the Rossby wave source. The cascading down Rossby wave train imposes successive negative, positive and negative Geopotential height (GPH) anomalies over north Mediterranean, northwest and northeast of India, respectively. The negative GPH anomaly at the north Mediterranean increases the Asian jet towards the Caspian Sea, strengthening the monsoon circulation through the ‘silk-road’ pattern. While, the dipole GPH anomaly north of India shift the Tibetan High westwards, triggering monsoon activity towards the west.

印度夏季季风降水的年际变化的一种主导模式显示出东西向偶极子模式，其中向印度西部和中部的降雨高于正常，向印度东部和东北部的降水偏低，并且与旺盛的亚速尔群岛高压有关。充满活力的亚速尔群岛高地伴随着沉陷的加剧，导致构造良好的广泛的对流层高层汇合。这形成了分别由30°N和50°N的异常气旋和反气旋环流组成的子午旋涡偶极子，并增强了Rossby波源。向下的Rossby波列级联分别在印度北部地中海，西北和东北施加了连续的负，正和负地势高度（GPH）异常。地中海北部的负GPH异常增加了亚洲人向里海的喷射，从而通过“丝路”模式加强了季风环流。同时，印度北部的偶极子GPH异常将藏高转变为西移，从而引发季风活动向西移动。