Understanding How Tropical Cyclone Intensification Rates Increase with Projected Radiative Forcing in HiFLOR

The High-Resolution Forecast-Oriented Low Ocean Resolution model (HiFLOR) was recently developed at the Geophysical Fluid Dynamics Laboratory (GFDL). HiFLOR contains high-resolution (~25-km mesh) atmosphere and land components coupled to a low-resolution (~100-km mesh) sea ice and ocean component. Murakami et al. (2015) demonstrated HiFLOR can simulate and predict extremely intense (Saffir–Simpson hurricane categories 4 and 5) tropical cyclones (TCs) and their interannual variations, which represents the first time a global, coupled model has been able to achieve this feat.

In this study, three experiments are performed to identify the effects of radiative forcing on TC intensity change. For each of the experiments, SST and atmospheric radiative forcing are relaxed to different targets, allowing us to explore the sensitivity of TCs to these conditions. The prescribed SST climatology for the control experiment is based on the Met Office Hadley Centre Sea Ice and SST dataset (HadISST1.1) over the years 1986-2005. The two climate change experiments, “early” and “late” 21st century simulations, use the same climatological SSTs plus mean SST anomalies and atmospheric radiative forcing from either 2016-2035 or 2081-2100. These anomalies are based on the CMIP5 multi-model response to the Representative Concentration Pathway 4.5 W/m² scenario.

As a climate model that can simulate the strongest TCs, these HiFLOR experiments provide a unique database with thousands of rapid intensification (RI) cases. After comparing the three experiments, more TCs are found to undergo RI in response to increased radiative forcing. The global mean intensification rate and distributions of intensification rate also shift to higher values, with significantly larger localized impacts in individual basins. These results are observed in a climate model with a grid that is still quite coarse, which suggests that there are large-scale parameters that are important to the most extreme wind speed changes. As a result, several synoptic variables are tested for the ability to diagnose RI and investigated as possible pathways for a warming climate to affect TC intensification.