Horizontal velocity structure functions in the upper troposphere and lowerstratosphere 1. Observations

We compute horizontal velocity structure functions using quasiglobal data a ccumulated by specially equipped commercial aircraft on 7630 flights from A ugust 1994 to December 1997. Using the ozone concentration measurements, we classify the results as tropospheric or stratospheric. We further divide t he results into four absolute latitude bands. For separation distance r bet ween 10 and 100 km, the lower stratospheric diagonal third-order structure functions are proportional to negative r. This implies a downscale energy c ascade, and we estimate the mean energy dissipation rate to be (E) approxim ate to 6 x 10(-5) m(2) s(-3). For r between 300 and 1500 km a positive r(3) dependence was visible for the polar stratospheric data. This may be the r esult of a two-dimensional (2D) turbulence downscale enstrophy cascade, and we estimate the average enstrophy flux to be IIomega approximate to 2 x 10 (-15) s(-3) and the energy spectral constant to be K approximate to 2. The negative sign of these third-order functions at mesoscales in both the uppe r troposphere and lower stratosphere provide no support for an inverse ener gy cascade 2D turbulence. At scales above similar to 100 km, the second-ord er structure functions increase with latitude in the troposphere and decrea se with latitude in the stratosphere. The off-diagonal third-order function s in the stratosphere show a remarkably clean negative r(2) dependency from 10 to 1000 km in scale.