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Technische Universität Berlin (2020)

Atmospheric moisture transport and dynamic precipitation controls on the Tibetan Plateau

Curio, Julia

Titre : Atmospheric moisture transport and dynamic precipitation controls on the Tibetan Plateau

Atmosphärischer Wassertransport und dynamische Kontrollfaktoren des Niederschlags auf dem Tibetischen Plateau

Auteur : Curio, Julia

Université de soutenance : Technische Universität Berlin

Grade : Doktor der Naturwissenschaften - Dr. rer. nat. - 2020

Résumé partiel
The Tibetan Plateau (TP) is the origin of many large Asian rivers, which provide water resources for large regions in south and east Asia. Therefore, the water cycle on the TP and adjacent high mountain ranges, in particular the precipitation distribution and variability play an important role for the water availability for billions of people in the downstream regions of the TP. The respective influence of the Indian and East Asian summer monsoon on TP precipitation and regional water resources, together with the detection of moisture transport pathways and source regions are the subject of recent research.

The aim of this thesis is to gain a better understanding of the spatial and temporal precipitation variability on the TP. In order to do so we examine the moisture transport to and on the TP, analyse the underlying processes leading to enhancement or suppression of precipitation, and examine how those processes are affected by the mid-latitude westerlies and the monsoon system. A newly developed high-resolution dataset, the High Asia Refined analysis (HAR), is used to examine atmospheric water transport (AWT) and dynamical factors that influence precipitation variability in the TP region. The HAR is the result of dynamically downscaling an operational analysis. Due to the higher spatial and temporal resolution of the HAR, it better represents the complex topography of the TP and surrounding high mountain ranges than coarse-resolution data sets like reanalyses, thereby reducing precipitation biases.

Analysing the AWT, we focus on spatiotemporal patterns, vertical distribution and transport through the TP boundaries. The results show that the mid-latitude westerlies have a higher share in summertime AWT over the TP than assumed so far. High mountain valleys in the Himalayas facilitate AWT from the south, whereas the high mountain regions inhibit AWT to a large extent and limit the influence of the Indian summer monsoon. Our results show that 36.86.3% of the atmospheric moisture needed for precipitation comes from outside the TP, while the remaining 63.2% is provided by local moisture recycling.

We use monthly correlations of selected dynamic variables with the precipitation to analyse what controls precipitation variability on the TP and in the surrounding high mountain regions. The selected variables, called dynamic precipitation controls, are the wind speed at 300 hPa wind and the wind speed 2 km above ground, the vertical wind speed at 300 hPa, the vertically integrated atmospheric water transport, and the height of the planetary boundary layer. We focus on the seasonality and the spatial variability of the relationship between dynamic controls and precipitation.

Mots clés  : Tibetan Plateau ; atmospheric moisture transport ; precipitation variability ; water cycle ; monsoon ; mid-latitude westerlies ; Tibetisches Hochland ; atmosphärischer Wassertransport ; Niederschlagsvariabilität ; Wasserkreislauf ; Monsun ; Westwinde der mittleren Breiten


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