Convective cloud systems over the Tibetan Plateau and their impact on meso-scale disturbances in the Meiyu/Baiu frontal zone - A case study in 1998

The relationship between convective activity over the Tibetan Plateau (TP) and meso-scale cloud systems in the Baiu/Meiyu frontal zone, are examined for the 1998 summer monsoon season by using GEWEX Asian Monsoon Experiment (GAME) reanalysis data and Geostationary Meteorological Satellite (GMS)-IR Tbb data. Diurnal cycle of the plateau-scale heat low associated with convective clouds is dominated, forming a plateau-scale convergence line. Moisture transport from south of TP is essential for developing convective clouds, and the convergence line. Occasionally, the convergence line extends to the eastern edge of the TP, which triggers a meso-scale cyclonic vortex over the head of the Yangtze River basin through the plateau edge cyclogenesis (PEC). This vortex induces a strong low level jet with moisture inflow to the east of it, which facilitates further development of the vortex to a meso-alpha scale cloud system embedded in the Baiu/Meiyu front (BMF) over China. The occurrence of PEC is likely to be modulated by an interaction between mid-latitude westerly waves, with a quasi-biweekly time scale, passing over the TP, and a shorter-period oscillation of the monsoon trough over the Indian sub-continent, with around a 4-7 day period.