Hourly satellite-tracked surface drifter data are utilized to study energy transfer from eddies to Near-Inertial Waves (NIWs). Spatial velocity gradients are computed from two consecutive velocity estimates derived from the same drifter, providing variable spatial resolutions of O (1 km). The eddy-to-NIW energy transfer can be positive or negative, with the positive transfer (forward energy cascade) dominant. The global integrated energy transfer rate (ε ) is 0.025 TW, with the anticyclonic eddy contribution dominant over the cyclonic eddy contribution. Given that the global near-inertial wind work (W ) is 0.2 TW, the eddy-to-NIW energy transfer efficiency (ε/W ) is about 13%, which is one order of magnitude larger than that in low resolution simulations. This result may still underestimate the Eulerian energy transfer by a factor of 2. To our knowledge, this is the first time that this energy transfer is calculated from global drifter observations, providing a baseline for comparison in future studies.

mesoscale eddies, near-inertial waves, surface drifter, energy transfer