Atlantic Hurricane response to Sahara greening and reduced dust emissions during the mid-Holocene

Abstract

Abstract. We use a high-resolution regional climate model to investigate the changes in Atlantic tropical cyclone (TC) activity during a warm climate state, the mid-Holocene (MH: 6,000 yrs BP). This period was characterized by increased boreal summer insolation, a vegetated Sahara, and reduced airborne dust concentrations. A set of sensitivity experiments were conducted in which solar insolation, vegetation and dust concentrations were changed in turn to disentangle their impacts on TC activity. 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 climate (PI) 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.

A Westward Shift in Tropical Cyclone Potential Intensity and Genesis Regions in the North Atlantic During the Last Interglacial

“…Although robust evidence for TC activity during the LIG is lacking, our results are supported by other modeling studies which suggest enhanced TC activity over the western MDR during the mid‐Holocene (6 ka) (Korty et al., 2012b; Koh & Brierley, 2015; Pausata et al., 2017; Dandoy et al., 2021), a period sharing a similar pattern of orbital forcing with the LIG. Additionally, the westward shift of TC activity could be more pronounced if the changes in vegetations and dust concentrations (e.g., over the Sahara) during the LIG are considered (Otto‐Bliesner et al., 2017; Dandoy et al., 2021; Pausata et al., 2017). This is attributed to the fact that the greening of the Sahara and reduced dust loadings could further intensify the west African monsoon (arising from enhanced warming and intensified Saharan low) and warms the tropical North Atlantic via vegetation‐albedo feedbacks (Dandoy et al., 2021; Pausata et al., 2016, 2017), which results in reduced wind shear and higher potential intensity over the western MDR, favoring a westward shift of genesis potential.…”

“…The GPI and steering flows provide useful information on changes in TC frequency and track, but the trajectory and intensity of individual storms cannot be predicted here. Although robust evidence for TC activity during the LIG is lacking, our results are supported by other modeling studies which suggest enhanced TC activity over the western MDR during the mid‐Holocene (6 ka) (Korty et al., 2012b; Koh & Brierley, 2015; Pausata et al., 2017; Dandoy et al., 2021), a period sharing a similar pattern of orbital forcing with the LIG. Additionally, the westward shift of TC activity could be more pronounced if the changes in vegetations and dust concentrations (e.g., over the Sahara) during the LIG are considered (Otto‐Bliesner et al., 2017; Dandoy et al., 2021; Pausata et al., 2017).…”

“…Additionally, the westward shift of TC activity could be more pronounced if the changes in vegetations and dust concentrations (e.g., over the Sahara) during the LIG are considered (Otto-Bliesner et al, 2017;Dandoy et al, 2021;Pausata et al, 2017). This is attributed to the fact that the greening of the Sahara and reduced dust loadings could further intensify the west African monsoon (arising from enhanced warming and intensified Saharan low) and warms the tropical North Atlantic via vegetation-albedo feedbacks (Dandoy et al, 2021;Pausata et al, 2016Pausata et al, , 2017, which results in reduced wind shear and higher potential intensity over the western MDR, favoring a westward shift of genesis potential. Using a high-resolution regional climate model with improved spatial coverage in SST records could provide more detailed information on TC activity over the North Atlantic, further helping to resolve the controversy on the inference of LIG superstorms.…”