Connection between the November snow cover over northeast Asia and the following January precipitation in southern China

摘要

In this paper, the connection between the November northeast Asian snow cover and the following winter precipitation over southern China is studied for the period of 1979-2014. The results indicate that, when there is more November snow cover over northeast Asia, the precipitation in southern China is depressed during the following January, and vice versa. Mechanism analysis suggests that the troposphere-stratosphere interaction may play an important role in the delayed connection between the two. The more November snow cover over northeast Asia could enhance the vertical propagation of the wave activity, and it could also weaken the westerly winds over northern Asia in the troposphere by decreasing the meridional temperature gradient over the region. The persistent weakening of the tropospheric westerly winds is in favour of the upward propagation of the wave activity into the stratosphere in November and December, and the associated convergence anomalies of the E-P flux in the stratosphere induce the weakened stratospheric polar vortex. Thereafter, the abnormal polar vortex propagates downward to the lower troposphere and produces a low pressure anomaly to the east of Lake Baikal during January. Such a low pressure anomaly tends to strengthen the southward invasion of the cold air to southern China, which is unfavourable for the precipitation there. This leading signal of the November snow cover over northeast Asia provides a potential source for the prediction of the January precipitation over southern China.