The Relationship Between Precipitation Isotope And Large Scale Atmospheric Circulation In Yamdruk-Tso Basin Over The Southern Tibetan Plateau

The Tibetan Plateau has long been known as the roof of the world and the third pole of the earth.It is at the junction of the westerly wind and the Indian monsoon,plays an important role in local and global climate through thermal and dynamic effects.It is very sensitive to climate change.The impact of climate change on the water cycle is a hot issue in the current academic community.Hydrogen and oxygen stable isotopes,as natural indicators,are widely used in hydrological cycle research.Natural isotope information,including ice cores,stalagmites,tree rings,and lake sediments,is an important tool for the study of modern climate,paleoclimatic and hydrological cycles,which are often used to reconstruct the paleotemperature.The study of stable isotopes and key influencing factors of modern precipitation is the foundation for reconstructing past climate and environmental changes.More and more studies have shown that,in addition to the local climatic conditions,the fluctuation of the large-scale atmospheric circulation is a more significant factor in controlling the change of the isotope component in precipitation.Especially in middle and low latitudes,large-scale atmospheric circulation fluctuations are one of the main controlling factors affecting the interannual component of isotope in precipitation.It is one of the new directions of global isotope research on precipitation that how the change of atmospheric circulation affects the isotope in precipitation in the Asian monsoon region.Precipitation stable isotopes are influenced by the sources of water vapor,the precipitation process during the transport of water vapor,and the local meteorological conditions during precipitation.There are still deficiencies to understand which factor mainly controls the isotope changes of precipitation in the water cycle process,especially in the monsoon region.In order to verify the impact of local climate and large-scale atmospheric circulation on stable isotopes of precipitation over the southern Tibetan Plateau in the Indian monsoon region,we have combined the observed precipitation stable isotope,with the clould cover data in both the local scale and large scale from the European Centre for Medium-Range Weather Forecasts,based on the continuous observation precipitation isotopes from the Yamdruk-tso basin in the southern Tibet Plateau collected from 2004 to 2016.We analyzed the correlation between precipitation isotopes in this basin and meteorological elements of large-scale atmospheric circulation.For the first time,we conducted a pioneering study on the"precipitation effect"of stable isotopes in the southern Tibet Plateau and its relation to cloud volume in convective activities.This study used large-scale cloud cover,different characteristics of local clouds and the components of stable isotopes of precipitation to analyze how large-scale atmospheric circulation affects the components of isotopes in precipitation in the monsoon region of the southern Tibetan Plateau by affecting convection and water vapor transport processes.We still compared and analyzed the effects of local and large-scale atmospheric circulation on precipitation isotopes.The main results obtained by the thesis are as follows:?1?We clarified the characteristics of isotope variations of precipitation in the Yamdruk-tso basin in the southern Tibet Plateau:The variation range of?¹⁸O during the observation period was-29.16‰to 5.15‰,with an average of-15.078‰.The change of?²H and?¹⁸O in precipitation was synchronous.Precipitation is concentrated in summer,and the variation of precipitation isotopic value is great within a month;We also established the local meteoric water line of the basin:?²H=8.31?¹⁸O+10.04?R²=0.97,p<0.01?,it is close to the global meteoric water line.?2?We found a significant correlation between cloud cover obtained by ECMWF and isotopes of precipitation in the Yamdruk-tso basin over the southern Tibet Plateau,through analyse the correlation between precipitation isotopes and a lot of large-scale meteorological factors.And the region with significant correlation was in the central India to northern regions.We analyzed the relationship between?¹⁸O in precipitation and large-scale atmospheric circulation patterns and their impact mechanisms depend on it.?3?We revealed the main influencing factors which control isotopes of precipitation in the Yamdruk-tso basin.The seasonal variation of precipitation isotopes in the Yamdruk-tso basin of the southern Tibetan Plateau?“precipitation effect”?is mainly related to the occurrence of strong convection rather than the local climatic conditions.The back trajectories simulated with HYSPLIT model showed that:during the monsoon period?May-September?,approximately 91%of the humid water vapor was transported to the Yamzho Yugao basin with the Indian monsoon,forming a major year-round precipitation.The weak“temperature effect”and weak“amount effect”,as well as low correlation coefficients between?¹⁸O in precipitation with local wind speed,sunshine duration,OLR suggest that the local meteorological elements are not the main influencing factors of isotope components changes of precipitation in Yamdruk-tso basin in the monsoon region.The?¹⁸O in precipitation in Yamdruk-tso basin is more closely related to large-scale convective activities.The conclusions of this paper have improved the understanding of the controlling factors for isotopes of precipitation in the monsoon region,and have also provided more scientific evidence for studying the significance of the palaeoclimatic records of isotope information obtained in the Indian monsoon region.