Influence of African Easterly Wave Suppression on Atlantic Tropical Cyclone Activity in a Convection‐Permitting Model

Abstract

Understanding the physical controls on tropical cyclone (TC) frequency represents a major challenge, as there is no theory to explain why the global annual number of TCs is relatively constant in historical observations and no consensus on future changes in TC frequency (Sobel et al., 2021). Pre-existing low-pressure disturbances, or TC "seeds," may trigger TC genesis, and have been identified as one possible factor in determining TC frequency. The typical Atlantic TC seed is provided by African easterly waves (AEWs), which are synoptic-scale disturbances that grow off of the baroclinic and barotropic instability of the African easterly jet (AEJ) (Burpee, 1972). AEWs generate between 5°N and 30°N over tropical northern Africa (Kiladis et al., 2006) and propagate westward over the tropical Atlantic Ocean.There is a strong connection between AEWs and Atlantic TCs on the synoptic time scale (Dieng et al., 2017;Landsea et al., 1998), with about 60%-80% of major Atlantic hurricanes originating from AEWs (Landsea, 1993;Russell et al., 2017). However, some studies have suggested that the relationship between TC frequency and AEWs may not be as straightforward as previously thought, especially on climate time scales. For instance, results from Hodges (2001) andHopsch et al. (2007) suggest that the relationship between AEWs and Atlantic TC activity could depend on the period considered, with the former finding them to be correlated for one period whereas the latter found them to be uncorrelated for a different period using the same data product. Moreover, Thorncroft and Hodges (2001) showed that only AEWs leaving the West African coast with significant low-level amplitudes, rather than the total number of AEWs, may influence the seasonal Atlantic

The Relationship Between African Easterly Waves and Tropical Cyclones in Historical and Future Climates in the HighResMIP‐PRIMAVERA Simulations

“…AEWs are synoptic‐scale disturbances that propagate along the African easterly jet (AEJ) in two tracks north and south of ∼15°N and grow off of the baroclinic‐barotropic instability of the AEJ (Burpee, 1972; Pytharoulis & Thorncroft, 1999). Recently, the relationship between AEWs and TCs has been called into question, with regional climate model data indicating that suppressed AEW activity did not affect basin‐wide Atlantic TC frequency (Danso et al., 2022; Patricola et al., 2018). The AEW‐TC relationship is further complicated by the potential effects of anthropogenic climate change, where studies have shown that climate change may double the economic damages of TCs by the year 2100 through increased TC intensity, precipitation, and storm surge (Knutson et al., 2020; Mendelsohn et al., 2012; Patricola & Wehner, 2018).…”

“…(2018) and Danso et al. (2022) used a regional climate model to examine the AEW‐TC relationship by comparing ensembles of simulations where AEWs were either prescribed or removed through the lateral boundary conditions. Both studies found that suppressed AEW activity did not affect basin‐wide Atlantic TC frequency (Danso et al., 2022; Patricola et al., 2018).…”

“…Studies have found conflicting results on the response of both AEWs (Bercos‐Hickey & Patricola, 2021; Brannan & Martin, 2019; Kebe et al., 2020) and TCs to climate change (Bhatia et al., 2018; Tory et al., 2013; Wehner et al., 2015, 2018). The relationship between AEWs and TCs is also not completely clear, with some studies finding a connection between the two (Hopsch et al., 2009; Landsea, 1993; Russell et al., 2017), but more recent work calling this relationship into question (Danso et al., 2022; Patricola et al., 2018). In this study, our objective is to better understand the AEW‐TC relationship and how it may be affected by future climate change.…”

“…Similarly, Emanuel (2022) found that climatological TC frequency is controlled primarily by environmental conditions and Hoogewind et al (2020) found that the spatiotemporal distribution of favorable environmental conditions strongly modulates the seasonal cycle of TCs. and Danso et al (2022) used a regional climate model to examine the AEW-TC relationship by comparing ensembles of simulations where AEWs were either prescribed or removed through the lateral boundary conditions. Both studies found that suppressed AEW activity did not affect basin-wide Atlantic TC frequency (Danso et al, 2022;.…”

“…Other studies have found that large-scale environmental conditions are a stronger control than TC seeds on TC genesis (Caron & Jones, 2012;Danso et al, 2022;Emanuel, 2022;Hoogewind et al, 2020;. Caron and Jones (2012) used a regional climate model to examine the effects of lateral boundary conditions and domain size on AEWs and TCs.…”