The Intra-Seasonal Oscillation of Precipitation δ18O Over the Asian Equatorial and Monsoon Regions

Water isotopes-climate correlations are used to reconstruct paleoclimate from various natural archives. Intra-seasonal oscillation is one of the major atmospheric patterns that modulate the ratio of precipitation isotope in low latitudes, yet their spatial and temporal distribution patterns are unclear. Here we presented a detailed analysis of how the intra-seasonal oscillations (MJO, Madden-Julian Oscillation, and BSISO, Boreal Summer Intra-seasonal Oscillation) modulate precipitation delta O-18 and vapor delta O-18 over the Asian monsoon region and the equatorial region. This analysis found consistent intra-seasonal variations between the ISO and rain delta O-18. We interpret it as the ISO regulating the active and inactive convective systems on the regional scale, leading to the intra-seasonal oscillations in precipitation delta O-18, with amplitudes from 4 parts per thousand up to 15 parts per thousand. The MJO (BSISO) leads to eastward (northeastward) propagation of delta O-18 intra-seasonal oscillations in the Asian equatorial (monsoon) region, coinciding with the spatial patterns of OLR oscillations, reflecting the response of precipitation/vapor delta O-18 to the oscillation of large-scale convective activity or accumulated depletion of regional precipitation. We proved that the amplitudes of intra-seasonal variation of precipitation delta O-18 are comparable to seasonal variations, and both of them are the main patterns for precipitation delta O-18 in study regions. Our results are conducive to the accurate interpretation of delta O-18 in climate proxies such as precipitation, ice cores, tree cellulose, cave stalagmites, et al. on the intra-seasonal scale in this region. Plain Language Summary Periodicity is a phenomenon in which similar characteristics or states of things reappear steadily and continuously. The Tropical Intra-seasonal Oscillation (Andersen et al., 2004, https://doi.org/10.1038/nature02805) is the reappearance of a large-scale envelope of more abundant convective rain systems moving eastward in the tropical regions with a typical oscillatory period of 30-60 days. The ratios of H-2 O-18 and HDO vary during the cycle of continuous circulation of water in the atmosphere, and therefore are widely used as proxies for climate records. We used the measured data of precipitation or vapor isotopes to reveal that the propagation of ISO can be recorded by the ratio of H-2 O-18 covering Asian tropical and monsoon regions. Furthermore, the increased (decreased) ISO intensity leads to the increased (decreased) amplitude of convection intensity, which results in the increased (decreased) amplitude of the H-2 O-18 ratio in precipitation or vapor.

Automated summary

This study analyzes how the MJO and BSISO modulate precipitation delta O-18 and vapor delta O-18 over the Asian monsoon region and the equatorial region. The results show consistent intra-seasonal variations between the ISO and rain delta O-18. The MJO and BSISO lead to eastward and northeastward propagation of delta O-18 intra-seasonal oscillations, respectively. Rating: 8 out of 10.