Fig. 4: Direction of eddy-induced heat flux controlled by eddy directional-dependence.

Spatial structures of composited normalized sea surface height anomaly (SSHA) distributions in the normalized eddy-centric coordinate of a meridional, b zonal, c Northeast-Southwest (NESW) and d Northwest-Southeast (NWSE) directed eddies, respectively. The azimuth angle \(\theta\) ranges are \((3\pi /{{{{\mathrm{8,5}}}}}\pi /8)\) for meridional directed eddies; \((0,\pi /8)\) and \((7\pi /8,\pi )\) for zonal directed eddies, \((\pi /{{{{\mathrm{8,3}}}}}\pi /8)\) for NESW directed eddies, and \((5\pi /{{{{\mathrm{8,7}}}}}\pi /8)\) for NWSE directed eddies. Color represents the normalized SSHA and black bold contours represent eddies’ boundary. Red number over each subfigure represents the percentage of eddies with the corresponding direction among all observed eddies. Eddy-induced surface heat flux directions by the e meridional, f zonal, g NESW and h NWSE directed eddies in the Northern Hemisphere. Blue shade is the eddy counting numbers for each direction and red vector represents the averaged direction of the eddy-induced heat flux of all available eddies with the corresponding direction. Panels i–l are the corresponding sea surface temperature and surface velocity anomaly fields of anticyclonic eddies in the Northern Hemisphere, both composited by satellite remote sensing data. Black vectors represent the surface velocity anomaly field, and color shade represents the sea surface temperature anomalies (SSTA). Only the asymmetric part of the temperature anomaly is shown here for demonstration, which is computed by subtract the symmetric SSTA \({{{{{{\boldsymbol{T}}}}}}}_{{{{{{\bf{0}}}}}}}({{{{{\boldsymbol{r}}}}}})\) from the total SSTA after composition. Black contours in each subfigure represent the ideal eddy boundary. Source data are provided as a Source Data file.