# Imprint of Mesoscale Eddies on Air-Sea Interaction in the Tropical Atlantic Ocean
## 2 Materials and Methods
### Eddy Induced Anomalies and Composite Analysis  
To obtain mesoscale signals, large-scale structures and low-frequency variations unrelated to eddies were removed from the background features (SST, LHF, SHF, IRF and PR). The high-pass filtering of the background features was performed in both space and time using a 6\({}^{\circ}\)\(\times\) 6\({}^{\circ}\) longitude/latitude and 120 days Hanning filter as described in [44]. Slight variations in the spatial and temporal filtering scales did not affect the results significantly. Eddies detected on ADT maps were then colocalized with high-pass filtered data to determine anomalies in SST, LHF, SHF, IRF and PR that are induced by the eddies, following the method outlined in [10]. As an example for SST, the Figure 2 shows the detected eddies on 25 November 2012, colocalized with the corresponding daily high-pass filtered SST. The SST anomalies within eddy contours were then extracted from each daily SST map. Mesoscale eddies were classified into 2 groups, depending on whether eddy-induced SST anomalies were positive or negative. A warm-core (cold-core) eddy is defined as an eddy that has, on average, a positive (negative) SST anomaly within its central core. The central core of an eddy, as depicted by Figure 3a, is defined as the inner part between the center and 2/3 of its radius. The outer parts were not considered in the classification to eliminate potential biases from the surrounding water masses as in [44]. The Figure 3b,c show the example of the detected eddies on 25 November 2012 that were separated into warm-core and cold-core eddies and their corresponding mean SST anomalies. Both of them are composed of AEs and CEs. After eddies were classified, the corresponding LHE, SHF, IRF and PR anomalies were also determined. From daily eddy-induced anomaly maps the mean eddy-induced anomalies throughout the study period were calculated. For each group of eddies (warm-core or cold-core) we performed composite analysis of the various properties (SST, LHF, SHF, IRF and PR). To study the impact of the eddies regardless of their size, we interpolated the property anomalies onto a high-resolution two-dimensional Cartesian grid for each identified vortex, normalized by the radial distance  
Figure 3: (a) A representative example of an eddy with its central core, where the mean anomalies were computed. (b,c) Mean SST anomalies induced by warm-core and cold-core eddies on 25 November 2012. White areas are areas without eddies. Figure 2: High-pass filtered SST (background color) and detected eddies on 25 November 2012. Cyclonic and anticyclonic eddy edges are represented in thick and thin black contours, respectively. from the center of the vortex to twice its radius. Note that eddies were classified regardless of their trajectories. This is the same as eddy composite analysis. SST can be influenced by eddy surface currents through horizontal advection [44; 45], which can result in dipolar anomalies with opposite signs depending on the large-scale background SST gradient and the eddy's rotation (clockwise or counterclockwise). To highlight these influences, we examined composite anomalies in a rotated frame, aligning the large-scale SST gradients to a same direction (here to a polar angle of \(-90^{\circ}\) such that warmer SST are oriented in a southward direction (\(\partial SST/\partial x=0\) and \(\partial SST/\partial y<0\)) in both the northern and southern hemispheres for all eddies. Figure 4a displays an example of the mean composite of large-scale SST within a set of eddies (case of AEs) after rotation. For this example, eddy effects of warm surface water advection northward and cold surface water southward can be readily observed. This approach eliminated the horizontal blurring of dipolar structures in anomalies caused by spatial variations in the large scale SST gradient and its direction as in [44].