Abstract
Abstract. We use a high-resolution regional climate model to investigate the changes in Atlantic tropical cyclone (TC) activity during the period of the mid-Holocene (MH: 6000 years BP) with a larger amplitude of the seasonal cycle relative to today. This period was characterized by increased boreal summer insolation over the Northern Hemisphere, a vegetated Sahara and reduced airborne dust concentrations. A set of sensitivity experiments was conducted in which solar insolation, vegetation and dust concentrations were changed in turn to disentangle their impacts on TC activity in the Atlantic Ocean. Results show that the greening of the Sahara and reduced dust loadings (MHGS+RD) lead to a larger increase in the number of Atlantic TCs (27 %) relative to the pre-industrial (PI) climate than the orbital forcing alone (MHPMIP; 9 %). The TC seasonality is also highly modified in the MH climate, showing a decrease in TC activity during the beginning of the hurricane season (June to August), with a shift of its maximum towards October and November in the MHGS+RD experiment relative to PI. MH experiments simulate stronger hurricanes compared to PI, similar to future projections. Moreover, they suggest longer-lasting cyclones relative to PI. Our results also show that changes in the African easterly waves are not relevant in altering the frequency and intensity of TCs, but they may shift the location of their genesis. This work highlights the importance of considering vegetation and dust changes over the Sahara region when investigating TC activity under a different climate state.
Highlights
Tropical cyclones (TCs) are one of the most powerful atmospheric phenomena on Earth
We use the CRCM6 regional climate model with a high horizontal resolution (0.11◦) to better investigate the role played by vegetation cover in the Sahara and airborne dust on TC activity in the Atlantic Ocean during a warm climate period, the mid-Holocene
Our results show that the Saharan greening and related reduction in dust concentrations (MHGS+RD experiment) significantly increase the number of TCs in the North Atlantic Ocean by about 27 %, whereas the increase associated with the orbital forcing alone is smaller (9 %; MHPMIP)
Summary
Tropical cyclones (TCs) are one of the most powerful atmospheric phenomena on Earth. With increasing damages and costs due to natural disasters and recent upswing in Atlantic TCs, it becomes more and more important to understand how TC activity may change in the future. Both Korty et al (2012) and Koh and Brierley (2015) have focused on simulations of the Paleoclimate Modelling Intercomparison Project (PMIP), which only account for the change in orbital forcing and the greenhouse gas (GHG) concentrations during the MH, assuming pre-industrial vegetation cover and dust concentrations These studies do not explicitly simulate the changes in TCs but rather investigate how key environmental variables affect TC genesis due to the insolation forcing. Pausata et al (2017) used a statistical thermodynamical downscaling approach (Emanuel, 2006; Emanuel et al, 2008) to generate a large number of synthetic TCs and assess their changes during the MH with an enhanced vegetation cover over the Sahara and reduced airborne dust concentrations Their results suggest a large increase in TC activity worldwide and in particular in the Atlantic Ocean in the MH climate.
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