Small-scale wind fluctuations in the tropical tropopause layer from aircraft measurements: Occurrence, nature, and impact on vertical mixing

During active events, they are in broad agreement with inertial-range turbulence theory: the motions are close to 3D isotropic and the spectra follow a -5/3 power-law scaling. The diffusivity induced by turbulent bursts is estimated to be on the order of 10(-1) m(2) s(-1) and increases from the top to the bottom of the TTL (from; similar to 2 x 10(-2) to; similar to 3 x 10(-1) m(2) s(-1)). Given the uncertainties involved in the estimate, this is in reasonable agreement (about a factor of 3-4 lower) with the parameterized turbulent diffusivity in ERA-Interim, but it disagrees with other observational estimates from radar and radiosondes.

The magnitude of the consequent vertical transport depends on the altitude and the tracer; for the species considered, it is generally smaller than that induced by the mean tropical upwelling.