A quantitative analysis of short‐term ¹⁸O variability with a Rayleigh‐type isotope circulation model

Abstract

[1] Stable water isotopes (D and 18 O) in precipitation have large spatial and temporal variability and are used widely to trace the global hydrologic cycle. The two models that have been used in the past to examine the variability of precipitation isotopes are Rayleigh-type models and isotope-atmospheric general circulation models. The causes of short-term (1-10 day) variability in precipitation isotopes, however, remain unclear. This study seeks to explain isotope variability quantitatively at such scale. A new water isotope circulation model on a global scale that includes a Rayleigh equation and the use of external meteorological forcings is developed. Transport and mixing processes of water masses and isotopes that have been neglected in earlier Rayleigh models are included in the new model. A simulation of 18 O for 1998 is forced with data from the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiments (GAME) reanalysis. The results are validated by Global Network of Isotopes in Precipitation (GNIP) monthly observations with correlation R = 0.76 and a significance level >99% and by daily observations at three sites in Thailand with similar correlation and significance. A quantitative analysis of the results shows that among three factors that cause isotopic variability, the contribution of moisture flux is the largest, accounting for 37% at Chiangmai, and 46% globally. This highlights the importance of transport and mixing of air masses with different isotopic concentrations. A sensitivity analysis of the temporal and spatial resolution required for each variable is also made, and the model is applied to two additional data sets. The more accurate Global Precipitation Climatology Project (GPCP) precipitation data set yields improved model results at all three observation sites in Thailand. The National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis allows the simulation to cover 2 years, reproducing reasonable interannual isotopic variability.

Intraseasonal Variability of δ¹⁸O of Precipitation over the Indonesian Maritime Continent Related to the Madden–Julian Oscillation

“…Although the geographic positions of Bukittinggi and Jambi are close, they show different isotopic variability, which is attributed to the effect of elevation, as described in Kurita et al (2009 Op are less than the annual average. The underestimated values might have been caused by uncertainty in the evaporation isotopic ratio, which is the isotopic value of water vapor from the evaporation process, and also by local-scale processes that are not included in the simulation (Yoshimura et al 2003 Op at all stations (in phases 3−5) is associated with the location of the convective activity over the IMC. Conversely, when convective activities over the IMC are suppressed (phases 1, 2, 6−8), the values of δ 18 Op at some stations tend to be greater than the annual average.…”

“…An ICM (Yoshimura et al 2003) was used to simulate the daily isotopic content of precipitation over the MC for comparison with the daily observational data. The origins of the water were tracked by CMA using an ICM with a tagged-water transport scheme (Yoshimura et al 2004 Op at Denpasar is −3.15‰, and depletion occurs during phases 2−5 of the MJO.…”

“…Dansgaard (1964) specifically mentioned an "amount effect" observed in tropical regions, which refers to the negative correlation between the precipitation amount and stable isotopes composition (Rozanski et al 1993;Araguás-Araguás and Froehlich 1998). Furthermore, Yoshimura et al (2003) successfully developed a Rayleigh-type isotope circulation model (ICM) using meteorological forcing data and reproduced the observed daily variability of precipitation isotopes. Yoshimura et al (2004) used the ICM to develop an atmospheric water vapor transport model to estimate vapor advection from specific source regions using colored moisture analysis (CMA).…”

“…There have been a few studies of the isotopes of precipitation and their relation to the weather and climate over the region of the Asian monsoon (e.g., Yoshimura et al 2003Yoshimura et al , 2004Ichiyanagi et al 2005) and the Indonesian MC (IMC) (Kurita et al 2009;Moerman et al 2013;Suwarman et al 2013;Permana et al 2016). Fudeyasu et al (2011) showed that large-scale moisture transport influenced isotopic variability over Sumatra.…”

Oceanic sources of continental precipitation and the correlation with sea surface temperature

“…Nonetheless, we do think that roughly the same 15 source regions would have been found, although their shape could be slightly different and their sizes could appear smaller or bigger. Unfortunately, isotopic studies [such as Henderson-Sellers et al, 2002;Yoshimura et al, 2003] that could quantitatively validate moisture tracking results at a global scale are still missing.…”