2:15 PM - 2:30 PM
[ACG44-03] An analysis of the atmospheric circulation around the Tibetan Plateau revealed by the stable isotope in precipitation—A case study of GEWEX-GAME/Tibet in 1998
Keywords:stable isotope in precipitation, the Tibetan Plateau, atomospheric circulation
Data of temporally and spatially stable isotopes in precipitation were obtained over the Tibetan Plateau and Nepal during a field campaign of the Global Energy and Water Experiment Asian Monsoon Experiment/Tibet in 1998. The data reveal a relationship between stable isotopes in precipitation over the Tibetan Plateau and active/break variations of the Indian monsoon.
During a break phase, low δ18O values and low d-excess values were observed at all observational sites. Transportation in this phase was an upslope process in which an air parcel gains altitude near the Himalayas. This trend can be explained by air parcels crossing over the Himalayas.
During an active phase, a characteristic trend of stable isotopes in precipitation over Tibetan Plateau was observed. Low δ18O and low d-excess values were observed around the south of the Tibetan Plateau (hereinafter called region 1) while high δ18O and high d-excess values were observed around the north of the Tibetan Plateau (hereinafter called region 2). The phase of region 1 coincided with the break phase, and transport might be an upslope process. However, the phase of region 2 was different because of the inland effect. To interpret the high δ18O values, we used the forward trajectory from convective cloud over central India, and examined the top height of convective cloud around region 2 over the Tibetan Plateau using measurements made by the precipitation radar onboard the Tropical Rainfall Measuring Mission satellite. Results showed that air parcels at an altitude exceeding 8,000 m in convective cloud around central India were transported to the Tibetan Plateau, and high δ18O values between 8,000 and 10,000 m in convective cloud around central India might be associated with precipitation around region 2 over the Tibetan Plateau.
To interpret the characteristics of stable isotopes in precipitation around the Tibetan Plateau, it is important to consider the active/break phase and trajectory of air parcels of the Indian monsoon. Clarifying the vertical distribution of stable isotopes in precipitation in convective cloud can improve our knowledge of the paleoclimate and help determine an isotope model in future work.