MAINTENANCE AND SEASONAL TRANSITIONS OF THE STATIONARY WAVES DURING EAST ASIAN MONSOON

Abstract

The dominant stationary wave features during the East Asian monsoon season, from April to October, are examined in this study using the NCEP/NCAR reanalysis and the linear and nonlinear stationary wave models. The study focuses on the stationary wave maintenance and seasonal transition and their relations to the monsoon diabatic heating. Monsoon rainfall indices over China, the stationary wave and diabatic heating indices over the monsoon region are constructed for easy comparisons. Four stationary wave features, i.e., the Tibetan anticyclone, the East Asian trough, the subtropical high, and the monsoon trough, are examined in detail. All four stationary wave centers go through distinct seasonal cycle during this seven-month period, with the Tibetan anticyclone, the subtropical high and the monsoon trough intensifying from April to July, and weakening from August to October, while the East Asian trough weakens from April to August and re-establishes itself from August to October. The linear and nonlinear stationary wave models indicate that the effect of the heating is the most dominant in contributing to the stationary wave seasonal cycle. Further decomposition of the heating shows that the monsoon heating is the one that causes the seasonal variation of the stationary wave centers except the East Asian trough.