Convective Cloud Systems over the Tibetan Plateau and Their Impact on Meso-Scale Disturbances in the Meiyu/Baiu Frontal Zone

Abstract

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-a 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.

Comparison of the diurnal variations of warm-season precipitation for East Asia vs. North America downstream of the Tibetan Plateau vs. the Rocky Mountains

“…High-resolution convection-permitting simulations also show similar eastward propagation of precipitation over the US (Trier et al, 2006). Over the "three-step" terrain in East Asia, the summer precipitation on the TP maximizes in the afternoon to early evening, and nocturnal rainfall occurs over the Sichuan Basin (SCB) areas and precipitation phase delays over the low-lying plains (Tao, 1980;Ninomiya, 2000;Asai et al, 1998;Wang et al, 2004Wang et al, , 2005Yasunari and Miwa, 2006;Bao et al, 2011;Zipser, 2009, 2011;Sun et al, 2010;Yu et al, 2007Yu et al, , 2009). Wang et al (2004Wang et al ( , 2005 used hourly infrared (IR) brightness temperatures observed by the Geostationary Meteorological Satellite (GMS) to compile a climatology of warmseason cloud/precipitation episodes over East Asia; they found that the propagating events moved eastward at phase speed of ∼ 10-25 ms −1 and compared the similarity of cloud/precipitation events to the rain streaks in CAR02.…”

A new transport mechanism of biomass burning from Indochina as identified by modeling studies

“…The Tibetan Plateau represents a huge obstacle which can block basic atmospheric flows and split the prevailing westerlies into the northern and southern branches (Yeh, 1950;Staff Member, 1957). The interaction between the westerly flow and the Tibetan Plateau causes the production of shallow vortices in the lee of the Plateau (Staff Member, 1958;Wu et al, 1985;Wang and Orlanski, 1987;Wang et al, 1993;Chang et al, 2000;Yasunari and Miwa, 2006). These vortices are obviously related to the leeside trough, and their relationship with the trough will be discussed later in a separate report.…”

Large-Scale Dynamics of the Meiyu-Baiu Rainband: Environmental Forcing by the Westerly Jet*

“…In the meiyu-baiu rainband, synoptic-scale and various types of mesoscale disturbances are indeed frequently observed to propagate eastward (Ninomiya and Shibagaki 2007). Some of those mesoscale disturbances originate from so-called southwest vortices on the eastern flank of the Tibetan Plateau, which develop from the interaction of the southerly flow, orography, and convection (Tao and Ding 1981;Ding and Chan 2005;Yasunari and Miwa 2006). Sometimes the vertical coupling with mid-/upper-tropospheric disturbances can lead to strong (sub-) synoptic lows (Chang et al 1998).…”