Influence of Model Resolution on Bomb Cyclones Revealed by HighResMIP-PRIMAVERA Simulations

Abstract:

Bomb cyclones are explosively intensifying extratropical cyclones that can cause severe damage to life and property. However, the poor ability of coarse-resolution climate models to simulate bomb cyclones, including underestimation of the frequency of bomb cyclones, remains a problem. In this study, the dependence of bomb cyclone characteristics on horizontal resolution from 135 to 18 km is investigated by analyzing the outputs of HighResMIP historical simulations of six atmospheric general circulation models and four reanalysis datasets. For each model and reanalysis, bomb cyclones are identified from extratropical cyclone tracks by calculating the 24-h deepening rate of sea-level pressure minimum. Robust resolution dependence of bomb cyclone characteristics is identified for both the models and the reanalyses. Finer horizontal resolution significantly increases the frequency of bomb cyclones and reduces their average horizontal size. Our regression analysis indicates that bomb cyclone frequency is roughly doubled from 140 km to 25 km resolution. This overall increase in bomb cyclone number is associated with a large increase in small bomb cyclones and a moderate decrease in large ones. Bomb cyclones in higher-resolution models are also accompanied by a higher maximum wind speed and more extreme wind events, which is probably related to the increased pressure gradients due to the smaller size of the bomb cyclones.The present study demonstrates that the HighResMIP project provides valuable datasets for bomb cyclone studies and imply that high-resolution climate models should be used for evaluating the impacts of bomb cyclones in the future.