Large-scale atmospheric circulation control on stable water isotopes in precipitation over the northwestern and southeastern Tibetan Plateau
Xiaoxin Yang1,2, Sunil Acharya1,3, and Tandong Yao1,21Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, No. 16 Lincui Rd., Chaoyang District, Beijing 100101, China 2CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China 3University of Chinese Academy of Sciences, China
Received: 30 Sep 2016 – Accepted for review: 02 Nov 2016 – Discussion started: 14 Nov 2016
Abstract. The mid-latitude westerlies and South Asian Summer Monsoon (SASM) are two major atmospheric circulation systems influencing the Tibetan Plateau (TP). We report a seven-year (2007/2008–2013/2014) dataset of δ18O in precipitation (δ18Op) collected at three stations. Taxkorgan (TX) and Bulunkou (BLK) are located on the northwestern TP where westerly winds dominate while Lulang (LL) is situated on the southeastern TP where the SASM dominates. δ18O in precipitation (δ18Op) in northwestern TP varies with surface temperature (T) throughout the study period, and is depleted in 18O in precipitation during June to September when the monsoonal circulation enters the TP. Integration with model outputs suggests that large-scale atmospheric circulation plays a major role in isotopic seasonality in both regions. A teleconnection between precipitation on the northwestern TP and the El Niño-Southern Oscillation (ENSO) warm phase is suggested by changes in the relationship between δ18O and δD (e.g., reduced slope and weighted d-excess) in precipitation samples. These observations are indicative of a weakening of the mid-latitude westerly jet allowing local processes in the continental interior to become more dominant, thereby increasing the contribution of secondary evaporation from falling raindrops and kinetic fractionation. Under the conditions of a high Northern Annular Mode (NAM) the westerly jet is intensified over the southeastern TP which enhances local evaporation and continental recycling as revealed by a lower δD-δ18O slope and intercept, but higher d-excess average in contemporaneously collected precipitation samples. The significant correlation between T and δ18Op in the northwestern TP during various composite periods highlights a variation from 0.39 ‰ / ℃ (ENSO warm) to 0.77 ‰ / ℃ (high NAM), attributable to decreased (increased) water vapor availability over the northwestern TP during the ENSO warm (strong positive NAM) phase. ENSO cold and strong negative NAM phases show analogous effects on atmospheric circulation over both regions.
Yang, X., Acharya, S., and Yao, T.: Large-scale atmospheric circulation control on stable water isotopes in precipitation over the northwestern and southeastern Tibetan Plateau, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-876, in review, 2016.