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Assessment of moisture budget over West Africa using MERRA-2’s aerological model and satellite data

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Abstract

The study assessed the performance of NASA’s Modern-Era Retrospective Analysis for Research and Applications (MERRA) and MERRA-2 aerological (PE*) model in reproducing the salient features of West Africa water balance including its components from 1980 to 2013. In this study we have shown that recent reanalysis efforts have generated imbalances between regional integrated precipitation (P) and surface evaporation (E), and the effect is more in the newly released MERRA-2. The atmospheric water balance of MERRA and MERRA-2 were inter-compared and thereafter compared with model forecast output of European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-I) and Japanese 55-year Reanalysis (JRA-55). Results indicated that a bias of 12–20 (5–13) mm/month in MERRA-2 (ERA-I) leads to the classification of the Sahel (14°N–20°N) as a moisture source during the West African Summer Monsoon. Comparisons between MERRA/MERRA-2 and prognostic fields from two ERA-I and JRA-55 indicated that the average PE* in MERRA is 18.94 (52.24) mm/month which is less than ERA-I (JRA-55) over Guinea domain and 25.03 (4.53) mm/month greater than ERA-I (JRA-55) over the Sahel. In MERRA-2, average PE* indicated 25.76 (59.06) mm/month which is less than ERA-I (JRA-55) over Guinea and 73.72 (94.22) mm/month less than ERA-I (JRA-55) over the Sahel respectively. These imbalances are due to adjustments in data assimilation methods, satellite calibration and observational data base. The change in convective P parameterization and increased re-evaporation of P in MERRA-2 is suggestive of the cause of positive biases in P and E. The little disagreements between MERRA/MERRA-2 and CRU precipitation highlights one of the major challenges associated with climate research in West Africa and major improvements in observation data and surface fluxes from reanalysis remain vital.

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Acknowledgements

We are grateful to anonymous reviewers and the Editor for their valuable comments and suggestions, which have greatly, helped us to improve the original version of the manuscript. This work was supported by the National Key Research and Development Program of China (no. 2016YFD0300101), the Natural Science Foundation of China (no. 31571565, no. 31671585),CAS Strategic Priority Research Program ( No. XDA19030402), Open Fund of Key Lab. of Urban Land Resources Monitoring and Simulation, Ministry of Land and Resources (no. KF-2016-02-026), “Taishan Scholar” Project of Shandong Province, and Key Basic Research Project of Shandong Natural Science Foundation of China (no. ZR2017ZB0422).

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Correspondence to Jiahua Zhang.

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Igbawua, T., Zhang, J., Yao, F. et al. Assessment of moisture budget over West Africa using MERRA-2’s aerological model and satellite data. Clim Dyn 52, 83–106 (2019). https://doi.org/10.1007/s00382-018-4126-2

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  • DOI: https://doi.org/10.1007/s00382-018-4126-2

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