Transition of the Rainfall Characteristics Related to the Moistening of the Land Surface over the Central Tibetan Plateau during the Summer of 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-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.

Section: Introductionmentioning

confidence: 64%

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

Yasunari

Miwa

2006

“…They forced the model using latent and sensible heat fluxes over the paddy field observed in GAMEHuaihe Basin Experiment (HUBEX), and found that meso-scale cloud systems embedded in the Meiyu (Baiu) front developed through moisture supply to ABL and change of moist static stability of the lower troposphere. The change of land-atmosphere interaction and its impact on cloud/precipitation systems through the seasonal change of soil moisture (surface wetness) condition was also observed over the Tibetan Plateau during the GAME-Tibet (Yamada and Uyeda 2006). Yamada (2007) simulated the feature over the plateau, showing that dry elevated surface on the Tibetan Plateau is favorable for more convective rain whereas wetter surface condition is favorable for stratiform cloud but with more rainfall amount as shown in Fig.…”

Section: Role Of Vegetationmentioning

confidence: 75%

Role of Land-Atmosphere Interaction on Asian Monsoon Climate

Yasunari

2007

This paper has discussed the land-atmosphere interaction associated with the Asian monsoon climate and its variability. The snow cover and soil moisture are internal factors of the climate system particularly in the seasonal to interannual time scales, but are suggested to play some important roles in changing large-scale surface energy and water balance, which in turn affect the monsoon circulation and precipitation. From the modeling as well as observational studies it has been suggested that the snow cover is most likely to influence atmosphere essentially through the albedo effect particularly in lower latitudes and on the Tibetan Plateau. The GCM experiments have strongly suggested that soil moisture anomalies efficiently affect the atmosphere under dry or semi-arid condition. Vegetation has also been noted as an important variable for the formation of moist monsoon flow over the continent, in addition to the dynamical and thermo-dynamical effect of the Tibetan Plateau.Through the GCM and RCM experiments the anthropogenically-induced change of land cover/use including the deforestation has proved to be a great impact on regional precipitation and water cycle of the monsoon region by changing characteristics of vegetation control in energy and water cycle, which in turn affect atmospheric boundary layer (ABL) and cloud/precipitation processes in regional-scale. The discussion has also been made on how the land surface changes could induce change of precipitation through feedback processes of moisture convergence and in-situ evapo-transpiration processes. The critical role of moisture amount near surface and in the ABL is emphasized, to induce positive feedback to change of precipitation over land in the monsoon region.

“…Yamada and Uyeda (2006) focused on the differences in synoptic conditions, such as the prevailing cumulus convection with a dominant Tibetan High (Upper High; UH type) and the passage of a synoptic disturbance (TROUGH; TR type), and they detected that a cumulus structure of the UH type changes with the moistening of the land-surface. Mid-latitude oscillation effects on this intraseasonal variability of precipitation activity over the TP.…”

Section: Introductionmentioning

confidence: 99%

Transportation of Water Vapor into the Tibetan Plateau in the Case of a Passing Synoptic-Scale Trough

Sugimoto

Ueno

Sha

2008

The passing of a synoptic trough is expected to contribute strongly to water vapor (WV) transport processes from the Indian Ocean to the Tibetan Plateau (TP) during the monsoon season. However, the pathway of the WV into the plateau associated with passing a trough and its contribution to the WV budget over the TP are not clear. In this study, the processes of WV transport in the case of a passing trough in 1998 were analyzed using GAME reanalysis data and the numerical model, focusing especially on the WV transportation pattern in the Indian Monsoon region and the diurnal variation of WV intrusion from south of the Himalayas to the TP.WV advection into the TP was larger in the case of a passing synoptic trough than in the case of a prevailing Tibetan High. Sub-continental scale circulation for the two synoptic types corresponded with active/break phase of the Indian monsoon. In case of prevailing Tibetan High, a cyclonic circulation with a low-pressure area over India, associated with active Indian monsoon phase, prevented the WV intrusion into the TP in the middle troposphere. However, in the case of the trough that corresponded with break phase of Indian Monsoon, WV was transported directly from Arabian Sea to the southern foot of the Himalayas with a northward shift of the low-level monsoon westerly and it intruded into the southeastern TP.Numerical experiments showed that the WV transport process was composed of multiple steps in the case of the passing trough. WV was transported by the monsoon westerly to the southern foot of the Himalayas at 1500 m above sea level (a.s.l.). The moist air mass reached south of the TP with at about 5500 m a.s.l. during the noon to evening because of the development of a mixing layer and the enhancement of an upslope wind in southern slope of the Himalayas. A moist southwesterly flow was converged latitudinally in the southeastern TP because of the dry northwesterly flow prevailing in the rear of the passing trough over the TP. This convergence area expanded northward from mid-afternoon into the night and disappeared early next morning.