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PMIP2 Characterizations of the Mid-Holocene African Monsoon

Zheng, W. and Braconnot, P. 2013. Characterization of model spread in PMIP2 Mid-Holocene simulations of the African Monsoon. Journal of Climate 26: 1192-1210.
Writing as background for their work, authors Zheng and Braconnot (2013) say that "despite recent progress in the monitoring and understanding of the WAM [West African Monsoon] within the framework of the African Monsoon Multidisciplinary Analysis (AMMA), there are still large uncertainties in projections of future climate in this region, such that even the sign of future precipitation change is uncertain [italics added]," citing Solomon et al. (2007).

Against this backdrop, the authors "revisit the results of PMIP2 simulations over Africa using two approaches." The first "considers the ensemble of simulations in order to determine how well the PMIP2 models [of today] reproduce some of the basic features of the summer monsoon precipitation," while the objective of the second is "to understand model differences by considering model characteristics for present-day climate and their sensitivities to insolation change." And what did they learn from the simulations?

First of all, the two scientists report that the "meridional temperature gradient is underestimated between 0° and 20°N by the PMIP2 model median, resulting in a smaller gradient of sea level pressure between the Gulf of Guinea and [the] Sahel," which helps to explain "a lower than observed low-level moisture flux and an underestimate of rainfall intensity when compared with observations." Second, they say that "the northward extent of the rain belt and the intensity of precipitation change are underestimated." Third, they indicate that "the models overestimate the solar radiation." Fourth, they acknowledge that the models "underestimate the cloud radiative forcing in deep and moderate convective regimes." And fifth, they state that "some of the models have too strong a coupling between the latent heat and convection in deep convective regimes."

Quite clearly, there is still a lot of work to be done by the climate modeling community before their models can perform acceptably, especially in the case of the West African Monsoon.

Additional Reference
Solomon, S., Qin, D., Manning, M., Marquis, M., Averyt, K., Tignor, M.B., Miller Jr., H.L. and Chen, Z. (Eds.). 2007. Climate Change 2007: The Physical Science Basis. Cambridge University Press, Cambridge, United Kingdom.

Archived 3 July 2013