Indian monsoon precipitation isotopes linked with high level cloud cover on local and regional scales.

Precipitation isotopes preserve information about the histories from evaporation in the sourceregions, moisture transport, and to precipitation events, and hence was used in revealing thedynamics of regional hydrological cycle and paleoclimate rebuilding. In the monsoon region,quite a few studies emphasized the strong inverse impact of convective activity onprecipitation isotope ratio, envoke the debate about the interpretation of these ice core recordsas temperature proxies on the Tibetan Plateaus. Recent study also showed statistically theinverse influence of the proportions of stratiform to convective precipitation on water isotopein tropical and mid-latitude regions, highlighting the important role of precipitation type onisotope hydrological cycle. The influence mechanism on seasonal and interannual scaleremain highly uncertain and poorly understood, which is crucial for the utilization ofisotopes in paleoclimate studies. To further address the influence of precipitationpattern, in particular the large regional cloud cover, on water isotopes, here we use adecade of precipitation isotopes from southern Tibetan Plateau (TP) to explore thethe close relationship with both the large scale cloud cover and local climate. Wecalculated the correlation between local precipitation δ18O with different levelcloud data archived in ECMWF. Sensitive zone is identified in the northern Indiasubcontinent to the seasonal precipitation isotope in southern TP, and high negativecorrelation with total cloud cover (TCC) and high cloud cover, indicates high-levelconvection in the upper stream of moisture transport is among some of the importantfactors in controlling the seasonal precipitation isotope in southern TP. However, thecorrelation with local cloud cover in the sampling basin is less significant. Themechanism underlying with the finding is that strong convection activity in themoisture source region and on the route significantly depletes heavy isotopes in thevapor, and subsequently, produces much decreased precipitation δ18O values inthe study region. On the interannual scale, there are robust negative precipitationδ18O-TCC correlations, large positive correlations between TCC and SouthernOscillation Index over the Arabian Sea, where is different from the most significantcorrelative region of the seasonal variation. It indicates that the processes influencethe seasonal variations of the precipitation isotopes is different from those whichare important for the interannualy means. The interannual to decadal interannualprecipitation δ18O record monsoon intensity and upstream rainout resulting from ENSO.The specific study site is located in the Yamdruk-tso basin at an elevation over4400m, and thus the results from this elevation are of more significance for the higherelevation ice core records in that region. Moreover, these findings throw light on theinterpretation of paleoisotope records obtained from the India Summer Monsoonregion. KeywordsPrecipitation isotopes; Cloud cover; Convective activity; Local and regionalcontrol; Yamdruk-tso basin; Southern Tibetan Plateau [ABSTRACT FROM AUTHOR]