Articles | Volume 15, issue 6
Research article
20 Mar 2015
Research article |  | 20 Mar 2015

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

A. Okazaki, Y. Satoh, G. Tremoy, F. Vimeux, R. Scheepmaker, and K. Yoshimura

Abstract. This study was performed to examine the relationship between isotopic composition in near-surface vapor (δ18Ov) 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 (1979–2012) 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 δ18Ov 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.

Final-revised paper