# Imprint of Mesoscale Eddies on Air-Sea Interaction in the Tropical Atlantic Ocean
## 3 Results
### Eddy-Induced SST Anomalies and Composite Analysis  
#### 3.2.1 Spatial Distribution of Eddy-Induced SST Anomalies  
On average, \(\sim\)60% of AEs and \(\sim\)40% of CEs have a positive SST anomaly, while the remaining \(\sim\)40% of AEs and \(\sim\)60% of CEs have a negative SST anomaly (Table 1). This suggests that AEs and CEs are not systematically warm-core or cold-core eddies, contrary to popular belief. However, the observed fraction of cold-core AEs and warm-core CEs in the TAO is higher than in the global ocean, where cold-core AEs and warm-core CEs account for about one-third of all eddies [32]. The spatial distributions of warm-core and cold-core eddies are comparable (Figure 6a,b). Eddy activities are most pronounced in the eastern and western boundaries, specifically in the eastern boundary upwelling systems (EBUS), along the southeastern coast of America, and north of 15\({}^{\circ}\)N and south of 20\({}^{\circ}\)S (Figure 6a,b). However, there are some regional differences, such as in the northern Hemisphere, south of 20\({}^{\circ}\)S and in SST frontal areas in the Cape Verde Frontal Zone (CVFZ) and in the Angola Benguela Frontal Zone (ABFZ). Indeed, in these regions, cold-core eddies slightly outnumber warm-core eddies with a maximum of 600 eddies per square degree. In the equatorial region, similarly to previous studies [1; 5; 6], the number of both warm-core and cold-core eddies is limited. However, a hot spot of both cold-core and warm-core eddies can be found beneath the ITCZ, between 40\({}^{\circ}\)W and 10\({}^{\circ}\)W longitude (Figure 6b), probably due to the zonal current instabilities, especially the North Equatorial Countercurrent, combined with equatorial upwelling which induces strong SST gradient. In the following, and for consistency, areas with a small number of eddies were discarded and were not taken into account in our analysis.  
Figure 6c,d, displays the distribution of the mean eddy-induced SST anomalies in the TAO during the study period. In general, the distribution indicates low values of averaged eddy-induced SST anomalies of \(\pm\)0.2 \({}^{\circ}\)C in the most areas. However, SST anomalies of \(\pm\)0.4 \({}^{\circ}\)C are found in some regions such as in (i) the EBUS, (ii) the equatorial regions beneath  
Figure 5: Histograms of eddy (**a**) amplitude, (**b**) kinetic energy, (**c**) radius and (**d**) lifespan in the TAO.  
the ITCZ, and (iii) southwest of the TAO off Brazil. There is also a hot spot of SST anomalies near the northern coast of the Gulf of Guinea. Despite these areas not being highly energetic in terms of EKE [1], they have a relatively high number of eddies (Figure 6a,b).  
Despite the large number of warm-core CEs and cold-core AEs, the mean SST anomalies induced by all CEs (AEs respectively) remain dominantly negative (positive), reflecting what has been traditionally admitted. In addition, the observed positive and negative anomalies witin all detected eddies do not cancel each other, highlighting the imprint of mesoscale eddies on SST in the TAO. On average, the ratio of the variance of eddy-induced SST anomalies to the total SST variability indicates that mesoscale eddies contribute to 10-25% oh the total SST variability in the TAO (not shown), with the maximum contribution observed beneath the ITCZ.  
At the basin scale, eddy-induced SST anomalies exhibit no strong seasonal variability (not shown). However, in particular regions, mainly in the coastal and equatorial upwelling areas, a seasonal amplitude of eddy-induced SST anomalies up to 0.5 \({}^{\circ}\)C are observed. The seasonal amplitude is defined as the absolute difference of the maximum and minimum monthly anomalies.