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Modeling Atlantic Tropical Cyclones Associated with Pacific ENSOs

Paper Reviewed
Wang, H., Long, L., Kumar, A., Wang, W., Schemm, J.-K.E., Zhao, M., Vecchi, G.A., Larow, T.E., Lim, Y.-K., Schubert, S.D., Shaevitz, D.A., Camargo, S.J., Henderson, N., Kim, D., Jonas, J.A. and Walsh, K.J.E. 2014. How well do global climate models simulate the variability of Atlantic tropical cyclones associated with ENSO? Journal of Climate 27: 5673-5692.

In this test of five state-of-the-art global climate models with a total of 16 ensemble members, Wang et al.. (2014) explore the veracity of 28-year simulations of Atlantic tropical cyclones (TCs) as forced by Pacific sea surface temperatures observed over the period 1982-2009. And in this regard, they begin by noting that "observational studies show a strong association between ENSO and Atlantic TC activity," but they note that analyses of TC track densities and origins indicate that "each model has different mean biases." And as a result, they say "there is no indication of increasing TC activity over the U.S. southeast coastal region during CP [Central Pacific] El Niño as in observations," which difference between the model simulations and real-world observations they attribute to biases of the models. So what are some of the unfortunate biases they discovered?

In answer to this question, the sixteen authors of the paper that is the subject of this review say that the differences between the model predictions and real-world observations may be due to (1) "the bias of vertical wind shear in response to the shift of tropical heating associated with CP El Niño," as well as (2) "model bias in the mean circulation," plus (3,4) "biases in simulating the ENSO-related variations of the large-scale humidity field and deep-layer steering flow," both of which are said by them to "affect the genesis of TCs and the distribution of TC tracks.:"

Last of all, in the concluding paragraph of their paper, Wang et al.. indicate "there is a possibility that the relationship between Atlantic TC activity and ENSO under the present-day climate found in Kim et al.. (2009) might not be maintained under a warming climate," noting that "changes in atmospheric teleconnections in response to ENSO have been detected in model simulations for the twenty-first century (e.g., Stevenson, 2012)." And they write that if such is truly the case, "this would add additional uncertainty to the future projection of Atlantic TC variability."

And thus we have the sorry state of uncertainty added upon uncertainty, as climate-model development continues its seemingly unending journey.

Kim, H.-M. Webster, P.J. and Curry, J.A. 2009. Impact of shifting patterns of Pacific Ocean warming on North Atlantic tropical cyclones. Science 325: 77-80.

Stevenson, S.L. 2012. Significant changes to ENSO strength and impacts in the twenty-first century: Results from CMIP5. Geophysical Research Letters 39: 10.1029/2012GL052759.

Posted 8 December 2014