Third‐Order Structure Functions of Zonal Winds in the Thermosphere Using CHAMP and GOCE Observations

We use multi‐year observations of cross‐track winds ( u ) from the CHAllenging Minisatellite Payload (CHAMP) and the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) to calculate third‐order structure functions in the thermosphere as a function of horizontal separation ( s ). They are computed using the mean (〈 δu 3 〉) and the median and implemented over non‐polar satellite paths in both hemispheres. On height averages, 〈 δu 3 〉 is shown to scale with s 2 for s ≃ 80–1,000 km, in agreement with equivalent estimates in the lower atmosphere from aircraft observations. Conversely, follows an s 3 power law for almost the whole s range, consistent with the two‐dimensional turbulence scaling law for a direct enstrophy cascade. These scaling laws appear independent of winds in distinct atmospheric regions. Furthermore, the functions are predominantly positive, indicating a preferential cyclonic motion for the wind.