Interannual variability of isotopic composition in water vapor over western Africa and its relationship to ENSO

Abstract

Abstract. This study was performed to examine the relationship between isotopic composition in near-surface vapor (δ 18 O v ) over western Africa during the monsoon season and El Niño-Southern Oscillation (ENSO) activity using the Isotope-incorporated Global Spectral Model. The model was evaluated using a satellite and in situ observations at daily to interannual timescales. The model provided an accurate simulation of the spatial pattern and seasonal and interannual variations of isotopic composition in column and surface vapor and precipitation over western Africa. Encouraged by this result, we conducted a simulation stretching 34 years to investigate the relationship between atmospheric environment and isotopic signature on an interannual timescale. The simulation indicated that the depletion in the monsoon season does not appear every year at Niamey. The major difference between the composite fields with and without depletion was in the amount of precipitation in the upstream area of Niamey. As the interannual variation of the precipitation amount is influenced by the ENSO, we regressed the monsoon season averaged δ 18 O v from the model and annually averaged NINO3 index and found a statistically significant correlation (R = 0.56, P < 0.01) at Niamey. This relationship suggests that there is a possibility of reconstructing past western African monsoon activity and ENSO using climate proxies.

Simultaneous monitoring of stable oxygen isotope composition in water vapour and precipitation over the central Tibetan Plateau

“…2a and f). Okazaki et al (2015) also found that the main driver of the more depleted δ 18 O v from Niamey was a larger amount of precipitation at the Guinea coast.…”

Importance of the Saharan heat low in controlling the North Atlantic free tropospheric humidity budget deduced from IASI &lt;i&gt;δ&lt;/i&gt;D observations

“…Nevertheless, because of the integrated nature of δD, we show that some information can be derived from the δD signature of air parcels coming from the desert. Former studies have already been dedicated to the interpretation of isotopic variations observed in precipitation and in water vapour in West Africa (Frankenberg et al, 2009;Risi et al, 2010;Okazaki et al, 2015) by combining models with observations, but solely focusing on the role of convection. From in situ measurements at Izana, have shown that different air mass pathways could be detected in H 2 O-δD pair distribution.…”

El Niño Southern Oscillation Signature in Atmospheric Water Isotopes over Maritime Continent during Wet Season

“…The performance of IsoGSM in producing atmospheric isotopic variability data has been evaluated in several previous studies. Simulated IsoGSM data show good agreement with observed isotopic spatiotemporal variability, suggesting that the model can reproduce the dynamics of atmospheric moisture transport satisfactorily (Berkelhammer et al 2012;Ishizaki et al 2012;Nakamura et al 2014;Okazaki et al 2015). In this study, the simulated stable isotope ratios in the precipitation data over the JAMSTEC and GNIP stations were correlated significantly with the observations (significance exceeding 95 %); the root mean square errors (RMSEs) were 1.71-2.98 ‰ for δ 18 O, while the standard deviations (σ) of the observed isotopes were 1.73-3.01 ‰.…”