Abstract
AbstractThe role of model resolution in simulating geophysical vortices with the characteristics of realistic tropical cyclones (TCs) is well established. The push for increasing resolution continues, with general circulation models (GCMs) starting to use sub-10-km grid spacing. In the same context it has been suggested that the use of stochastic physics (SP) may act as a surrogate for high resolution, providing some of the benefits at a fraction of the cost. Either technique can reduce model uncertainty, and enhance reliability, by providing a more dynamic environment for initial synoptic disturbances to be spawned and to grow into TCs. We present results from a systematic comparison of the role of model resolution and SP in the simulation of TCs, using EC-Earth simulations from project Climate-SPHINX, in large ensemble mode, spanning five different resolutions. All tropical cyclonic systems, including TCs, were tracked explicitly. As in previous studies, the number of simulated TCs increases with the use of higher resolution, but SP further enhances TC frequencies by ~30%, in a strikingly similar way. The use of SP is beneficial for removing systematic climate biases, albeit not consistently so for interannual variability; conversely, the use of SP improves the simulation of the seasonal cycle of TC frequency. An investigation of the mechanisms behind this response indicates that SP generates both higher TC (and TC seed) genesis rates, and more suitable environmental conditions, enabling a more efficient transition of TC seeds into TCs. These results were confirmed by the use of equivalent simulations with the HadGEM3-GC31 GCM.
Highlights
The simulation of tropical cyclones (TCs) in contemporary climate models remains a challenge, with a systematic underestimation of both the number of TCs and their intensity (Shaevitz et al 2014; Walsh et al 2015; Roberts et al 2020)
We extended our genesis potential index (GPI) analysis to its temporal behavior, considering monthly means of GPI terms in each basin, using, wherever possible, the same domain definitions as in Wing et al (2015), albeit altering the seasons to July–November for the Northern Hemisphere, and November–March for the Southern Hemisphere, for two reasons: 1) these new definitions of season provide significantly stronger correlations, when compared to those shown in Wing et al (2015); and 2) a longer, more homogeneous seasonality, closer to operational criteria, makes it possible to retain the same definitions for the analysis of climate change experiments
Statistics of TCs identified in Climate-SPHINX confirm past and current findings that increasing model resolution systematically improves the simulated climatology—numbers and distribution—in both hemispheres
Summary
VIDALE ET AL. PIER LUIGI VIDALE,a KEVIN HODGES,a,b BENOIT VANNIÈRE,a PAOLO DAVINI,c MALCOLM J. ROBERTS,d KRISTIAN STROMMEN,e ANTJE WEISHEIMER,f,g ELINA PLESCA,a AND SUSANNA CORTIc a NCAS-Climate, Department of Meteorology, University of Reading, Reading, United Kingdom b Department of Meteorology, University of Reading, Reading, United Kingdom c Istituto di Scienze dell’Atmosfera e del Clima, Consiglio Nazionale delle Ricerche, Torino, Italy d Met Office Hadley Centre, United Kingdom e Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, United Kingdom f NCAS, Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, United Kingdom g ECMWF, Reading, United Kingdom (Manuscript received 7 July 2020, in final form 25 January 2021)
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