Characteristics of Summer Convective Systems Initiated over the Tibetan Plateau. Part I: Origin, Track, Development, and Precipitation

Abstract

Summer convective systems (CSs) initiated over the Tibetan Plateau identified by the International Satellite Cloud Climatology Project (ISCCP) deep convection database and associated Tropical Rainfall Measuring Mission (TRMM) precipitation for 1998-2001 have been analyzed for their basic characteristics in terms of initiation, distribution, trajectory, development, life cycle, convective intensity, and precipitation. Summer convective systems have a dominant center over the Hengduan Mountain and a secondary center over the Yaluzangbu River Valley. Precipitation associated with these CSs contributes more than 60% of total precipitation over the central-eastern area of the Tibetan Plateau and 30%-40% over the adjacent region to its southeast. The average CS life cycle is about 36 h; 85% of CSs disappear within 60 h of their initiation. About 50% of CSs do not move out of the Tibetan region, with the remainder split into eastwardand southward-moving components. These CSs moving out the Tibetan Plateau are generally larger, have longer life spans, and produce more rainfall than those staying inside the region. Convective system occurrences and associated rainfall present robust diurnal variations. The midafternoon maximum of CS initiation and associated rainfall over the plateau is mainly induced by solar heating linked to the unique Tibetan geography. The delayed afternoon-late night peak of rainfall from CSs propagating out of this region is a combined outcome of multiple mechanisms working together. Results suggest that interactions of summer Tibetan CSs with the orientation of the unique Tibetan geography and the surrounding atmospheric circulations are important for the development, intensification, propagation, and life span of these CSs.

Generation processes of mesoscale convective systems following midlatitude troughs around the Sichuan Basin

“…According to the surface weather map produced by the Japan Meteorological Agency, the Meiyu front corresponded to the frontal zone in the cloud images for period 1. During period 2, a cloud zone located along the coastal line over southern China (Figure 5 Li et al [2008] pointed out that MCS occurrence and associated rainfall present robust diurnal variation around the eastern TP and agreed with those characteristics. In addition, the occurrence of MCS on the eastern plateau did not always continue until the MCS developed over the low-elevation areas.…”

“…MCSs were generated in the south of 35°N, except just over the Great Himalayan ranges, and their distribution almost overlapped with the maximum areas of CI distribution. Li et al [2008] emphasized the large number of summer convective systems initiating on the southern TP. However, Figure 3 shows that MCS generation in the south and southeast of the TP was also dominant even in a limited period.…”

“…On the other hand, some studies have stressed that convections or convergence zones caused by the diurnal heating on the TP could also be a trigger for the MCSs in the leeward of the TP [Wang, 1987;Yasunari and Miwa, 2006]. Li et al [2008] statistically revealed that one third of the total precipitation in the region adjacent to the southeast of the TP was affected by the summer convective system developed on the TP. Many previous studies have relied on weather maps, reanalysis data, or numerical models with coarse gridding to diagnose the development of mesoscale precipitation systems.…”

Formation of mesoscale convective systems over the eastern Tibetan Plateau affected by plateau‐scale heating contrasts

“…Recently, case studies by Chen [2003a, 2003b] attributed the MCS formation to either baroclinic instability caused by the approach of a synoptic trough or the convective available potential energy (CAPE) due to the strong land-surface thermal forcing, according to radiosonde sounding data the three-dimensional numerical simulation. However, the major distributions of the low vortex do not correspond to the maximum areas of the occurrence frequency of MCSs, such as those of Li et al [2008], and also differ from the distributions of precipitation identified by modern satellite images. One of the reasons for the discrepancies between the appearance of the low vortex and mesoscale disturbances with precipitation may be differences in the spatial resolution of data, for example, many previous studies were based on the objective analysis data or model outputs with coarse resolution.…”

“…Precipitation radar (PR) images of Tropical Rainfall Measuring Mission (TRMM) also indicated that precipitation systems with more than 10 4 km 2 occurred over the eastern TP in the afternoon and through the night [Hirose and Nakamura, 2005]. According to the statistical analysis of multiple satellite IR images by Li et al [2008], precipitation with convective systems (CSs), which was defined as lower than 245 K of cloud top temperature and larger than 90 km of minimum radius, accounted for more than 60% of the total precipitation over the eastern TP and the CSs sometimes migrated to eastern China, South Asia, and the Bay of Bengal. Yasunari and Miwa [2006] showed cases of the eastward movement of the vortex with cloud convective systems, which was formed by large-scale convergence over the TP, triggered flooding in the middle and lower reaches of the Yangtze River.…”