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Winter Frontal Precipitation Problems of CMIP5 Climate Models

Paper Reviewed
Catto, J.L., Jakob, C. and Nicholls, N. 2015. Can the CMIP5 models represent winter frontal precipitation? Geophysical Research Letters 42: 8596-8604.

Writing as background for their work, Catto et al. (2015) atate that "much of the day-to-day variability of rainfall in the mid-latitudes is controlled by the passage of extratropical cyclones and their related fronts." And they state that "by employing an automated front identification scheme, we have investigated the representation of winter frontal precipitation in 18 of the CMIP5 historical simulations and the contribution of any errors to the total precipitation errors," further noting that "a good representation of fronts and their associated rainfall in climate models is essential to have confidence in future projections of mid-latitude precipitation."

In an attempt to obtain that confidence, therefore, the three Australian researchers applied what they called an "objective front identification method" to data from ERA-Interim and 18 Coupled Model Intercomparison Project, version 5 (CMIP5) models, along with "the fronts linked with daily precipitation estimates to investigate how winter front-related precipitation is represented in the models." And what did this undertaking reveal?

Catto et al. report that (1) the frequency of frontal precipitation "is too high in all the models," that (2) the intensity "is too low," so that (3) "in the models, when a front is present, the intensity of precipitation is amplified over the background value by more than that in the observations," but they find that (4) "despite the compensating errors and the over-amplification of the frontal precipitation over the background value, the proportion of precipitation associated with fronts is too low over much of the mid-latitudes."

And these results, in the words of the authors, "are consistent with previous climate model evaluations of the characteristics of precipitation," citing the studies of Sun et al. (2006), Wilcox and Donner (2007) and Stephens et al. (2010).

Stephens, G.L., L'Ecuyer, T., Forbes, R., Gettlemen, A., Golaz, J.-C., Bodas-Salcedo, A., Suzuki, K., Gabriel, P. and Haynes, J. 2010. Dreary state of precipitation in global models. Journal of Geophysical Research 115: 10.1029/2010JD014532.

Sun, Y., Solomon, S., Dai, A. and Portmann, R.W. 2006. How often does it rain? Journal of Climate 19: 916-934.

Wilcox, E.M. and Donner, L.J. 2007. The frequency of extreme rain events in satellite rain-rate estimates and an atmospheric general circulation model. Journal of Climate 20: 53-69.

Posted 24 March 2016