Browsing by Author "Ma, Yaoming"

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The Kobresia pygmaea ecosystem of the Tibetan highlands - Origin, functioning and degradation of the world's largest pastoral alpine ecosystem: Kobresia pastures of Tibet.
(2018-01) Miehe, Georg; Schleuss, Per-Marten; Seeber, Elke; Babel, Wolfgang; Biermann, Tobias; Braendle, Martin; Chen, Fahu; Coners, Heinz; Foken, Thomas; Gerken, Tobias; Graf, Hans-F.; Guggenberger, Georg; Hafner, Silke; Holzapfel, Maika; Ingrisch, Johannes; Kuzyakov, Yakov; Lai, Zhongping; Lehnert, Lukas; Leuschner, Christoph; Li, Xiaogang; Liu, Jianquan; Liu, Shibin; Ma, Yaoming; Miehe, Sabine; Mosbrugger, Volker; Noltie, Henry J.; Schmidt, Joachim; Spielvogel, Sandra; Unteregelsbacher, Sebastian; Wang, Yun; Willinghöfer, Sandra; Xu, Xingliang; Yang, Yongping; Zhang, Shuren; Opgenoorth, Lars; Wesche, Karsten
With 450,000 km^2 Kobresia (syn. Carex) pygmaea dominated pastures in the eastern Tibetan highlands are the world's largest pastoral alpine ecosystem forming a durable turf cover at 3000–6000 m a.s.l. Kobresia's resilience and competitiveness is based on dwarf habit, predominantly below-ground allocation of photo assimilates, mixture of seed production and clonal growth, and high genetic diversity. Kobresia growth is co-limited by livestock-mediated nutrient withdrawal and, in the drier parts of the plateau, low rainfall during the short and cold growing season. Overstocking has caused pasture degradation and soil deterioration over most parts of the Tibetan highlands and is the basis for this man-made ecosystem. Natural autocyclic processes of turf destruction and soil erosion are initiated through polygonal turf cover cracking, and accelerated by soil-dwelling endemic small mammals in the absence of predators. The major consequences of vegetation cover deterioration include the release of large amounts of C, earlier diurnal formation of clouds, and decreased surface temperatures. These effects decrease the recovery potential of Kobresia pastures and make them more vulnerable to anthropogenic pressure and climate change. Traditional migratory rangeland management was sustainable over millennia, and possibly still offers the best strategy to conserve and possibly increase C stocks in the Kobresia turf.
Mechanism of Daytime Strong Winds on the Northern Slopes of Himalayas, near Mount Everest: Observation and Simulation
(2018-02) Sun, Fanglin; Ma, Yaoming; Hu, Zeyong; Li, Maoshan; Tartari, Gianni; Salerno, Franco; Gerken, Tobias; Bonasoni, Paolo; Cristofanelli, Paolo; Vuillermoz, Elisa
The seasonal variability of strong afternoon winds in a northern Himalayan valley and their relationship with the synoptic circulation were examined using in situ meteorological data from March 2006 to February 2007 and numerical simulations. Meteorological observations were focused on the lower Rongbuk valley, on the north side of the Himalayas (4270m MSL), where a wind profile radar was available. In the monsoon season (21 May-4 October), the strong afternoon wind was southeasterly, whereas it was southwesterly in the nonmonsoon season. Numerical simulations were performed using the Weather Research and Forecasting Model to investigate the mechanism causing these afternoon strong winds. The study found that during the nonmonsoon season the strong winds are produced by downward momentum transport from the westerly winds aloft, whereas those during the monsoon season are driven by the inflow into the Arun Valley east of Mount Everest. The air in the Arun Valley was found to be colder than that of the surroundings during the daytime, and there was a horizontal pressure gradient from the Arun Valley to Qomolangma Station (QOMS), China Academy of Sciences, at the 5200-m level. This explains the formation of the strong afternoon southeasterly wind over QOMS in the monsoon season. In the nonmonsoon season, the colder air from Arun Valley is confined below the ridge by westerly winds associated with the subtropical jet.
Observation of strong winds on the northern slopes of Mount Everest in monsoon season
(2017-11) Sun, Fanglin; Ma, Yaoming; Hu, Zeyong; Li, Maoshan; Gerken, Tobias; Zhang, Lang; Han, Cunbo; Sun, Genhou
An analysis of the local atmospheric circulation in a northern Himalayan valley in the region of Mount Everest is presented. Data were collected using an automatic weather station over a one-year period in 2014. A ground-based wind profiler radar (WPR) and an in situ GPS radiosonde (RS) were also employed. This study focuses on the characteristics of afternoon strong wind events in the downstream of Rongbuk Valley. We found that: (1) The occurrence of the southwesterly wind during non-monsoon was in good consistency with high values of westerly wind at high levels over this region and confirmed to be driven by the strong westerly jet aloft. (2) The strong afternoon wind in monsoon season has a persistent southeasterly direction, which differs from the prevailing direction of the strong wind in non-monsoon. This flow was found to be independent of the wind aloft and was strongly seasonal, developing at Qomolangma Station (QOMS) when the subtropical jet stream had moved northward and was most stable and strongest in the early monsoon season but before the rainy season. (3) The southeasterly wind in monsoon is colder than local air, suggesting that it is driven by a strong thermal gradient from the Arun Valley to QOMS. Our results contribute to improving our knowledge of local circulation patterns in the Himalayas, and also to gaining a detailed understanding of the mountain chain\'s role in both the monsoon system and regional transport of atmospheric pollutants.