# Imprint of Mesoscale Eddies on Air-Sea Interaction in the Tropical Atlantic Ocean
## 3 Results
### Eddy-Induced SST Anomalies and Composite Analysis
#### 3.2.2 Composite Analysis of Eddy-Induced SST Anomalies  
The composite analysis of eddy-induced SST anomalies was conducted in the Northern and Southern Hemispheres using the method outlined in Section 2. The results show that the maximum SST anomalies in both hemispheres are generally displaced from eddy centers and are closer to the edges (Figure 7). More precisely, in the Northern Hemisphere, maximum anomalies of about \(\pm\)0.3 \({}^{\circ}\)C were found in the northwest quadrant for warm-core AEs and in the southeast quadrant for cold-core AEs (Figure 7a,b). AEs rotate clockwise in the Northern Hemisphere, and the mean large-scale SST gradient is southward-oriented in the rotated frame as shown by Figure 4a. This leads to the horizontal advection of warm SST from the south to the northwest and concurrently, cold SST from the north to the southeast. This mechanism of horizontal advection leads to positive SST anomalies in the northwest side of the eddies and negative SST anomalies in the southeast side. Similar processes have also been found to play a key role in eddy-induced SST, sea surface salinity and chlorophyll anomalies in some regional studies outside of the TAO [44; 45; 46; 47]. In the Southern Hemisphere, maximum positive and negative SST anomalies were observed in opposite  
Figure 6: Distribution of (**a**,**b**) warm-core and cold-core eddies, and (**c**,**d**) eddy-induced SST anomalies over the 2010–2017 period. Solid and dashed curves represent the mean annual and extreme (during boreal winter and summer) location of the ITCZ. White areas stand for areas where not enough eddies were available. quadrants due to the anticlockwise rotation of AE (Figure 7e,f). Similar results were also obtained for CEs, but with opposite rotation direction in both hemispheres (Figure 7c,d,g,h). Figure 8 shows the spatial distribution of axisymmetric and non-axisymmetric components of SST anomalies within AEs, averaged in 15\({}^{\circ}\)\(\times\) 15\({}^{\circ}\) longitude/latitude subregions. Axisymmetric component distribution displays a similar pattern as the spatial distibution of mean SST anomalies (see Figure 6b,d), for both AEs and CEs (Figures 8a,b and 9a,b). Stronger positive and negative composite anomalies are located along the eastern and southwestern boundaries of the TAO basin where coastal upwelling and where eddy activities are more intense. It is likely that these areas are favorable for vertical processes, basically because of uplifting/downlifting of isopycnal levels that occur inside eddies leading to cooling/warming of the ocean surface. In addition, as suggested by [33] in the Mediterranean Sea, vertical mixing modulation by eddies may also contribute in SST cooling and warming within AEs and CEs respectively, especially during spring and summer seasons. Moreover [21] demonstrated that AEs are more productive during winter due to the modulation of vertical mixing. Such a mechanism may lead to the cooling (warming) of SST witin AEs (CEs). The non-axisymmetric components of SST anomalies are almost similar for both warm-core and cold-core AEs (Figure 8b,d). They are relatively weak, with average anomalies of around \(\pm\)0.1 \({}^{\circ}\)C across the basin. However, certain areas, such as the ABFZ (near 10\({}^{\circ}\)E and 15\({}^{\circ}\)S) and the Cabo Frio Frontal Zone (CFFZ) (near 42\({}^{\circ}\)W and 23\({}^{\circ}\)S) display strong anomalies (Figure 8b,d) due to strong large-scale SST gradients as displayed in Figure 1. Likewise south of the equator and east of 25\({}^{\circ}\)W, where the seasonal Atlantic cold tog appears, causing a strong SST gradient, composite of SST anomalies are up to 0.2. Similar observations are valid for composite SST anomalies within CEs, as shown in Figure 9b,d. However, anomalies tend to be slightly higher compared with AEs non-axisymmetric composite, especially in high SST frontal areas.