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Tropical Cyclones in High-Resolution Global Climate Models

Paper Reviewed
Roberts, M.J., Vidale, P.L., Mizielinski, M.S., Demory, M.-E., Schiemann, R., Strachan, J., Hodges, K., Bell, R. and Camp, J. 2015. Tropical cyclones in the UPSCALE ensemble of high-resolution global climate models. Journal of Climate 28: 574-596.

Writing in the Journal of Climate, Roberts et al. (2015) say "there is an increasing need for skillful climate information at regional and local scales, particularly for considering variability and extremes," but they note that the "current phase 5 of the Coupled Model Intercomparison Project (CMIP5)-class models (Taylor et al., 2012) generally fall short of being able to provide information on these small space and time scales," citing the study of Christensen et al. (2014). And, hence, they proceed to report the results of their latest "objective, resolution-independent feature-tracking methodology," which they used to identify and track tropical cyclone (TC)-like features in several of the CMIP5 models that they then compared with real-world observations.

This work revealed, in the words of the nine UK researchers, that (1) "all model storms are weak compared to observations, particularly with regard to 10-m wind speed ... but also applying to wind at other levels," that (2) "the models produce typically too few TCs in the NA [North Atlantic]," as well as (3) "too many in the EP [Eastern Pacific]," that (4) "the models also generate storms in the South Atlantic [SA], where hurricanes are observed to be rare," that (5) "increased model resolution enhances an error in the CP [Central Pacific], where the density becomes too high compared to observations," along with (6) "tracks that are too zonal," together with (7) "fewer storms being generated nearer to the equator in the western Pacific than seen in the observations," that (8) "an additional model bias lies in the Gulf of Mexico/EP region, where the track density is again too high," that (9) "in the Southern Hemisphere, the main error in distribution is found in the SWI [Southwestern Indian Ocean] basin, where the track density is strongly enhanced to the west near Madagascar," that (10) "in the NA [North Atlantic] the season starts too early," that (11) it "does not increase strongly through July-September, as seen in the observations," that (12) "the EP has too many storms in the higher-resolution models," that (13) there are "too many easterly waves propagating into this region" with (14) "a dip in September that is not seen in observations," that (15) there is "poor simulation of the Indian monsoon," that (16) "in general, the Southern Hemisphere has too many storms," and that (17) the mean ACE [accumulated cyclone energy] in the models "is much smaller than observed, typically by 3-10 times."

Not exactly a ringing endorsement for the climate modeling enterprise.

References
Christensen, J.H. et al. 2014. Climate phenomena and their relevance for future regional climate change. Climate Change 2013: The Physical Science Basis. Cambridge University Press, pp. 1217-1308.

Taylor, K.E., Stouffer, R.J. and Meehl, G.A. 2012. An overview of CMIP5 and the experiment design. Bulletin of the American Meteorological Society 93: 485-498.

Posted 19 May 2015