The GPS dropsonde has demonstrated considerable utility in measuring wind structure in tropical cyclones. Analysis has tended to concentrate so far on the mean wind structure, although a casual inspection of dropsonde wind profiles suggests that a substantial amount of information on the turbulence is present also. Observed turbulent spectra above the boundary-layer in the inner-core of some intense tropical cyclones will be presented and shown to contain several highly unusual features, including a power-law behaviour with slope -3 at high frequencies, and a marked anisotropy between the storm-relative velocity components, where the power in the radial velocity fluctuations at high frequencies is about 5 times that in the azimuthal.

It will be argued that the above power-law is due to the flow curvature. A reduced second-order turbulence closure model will be presented and used to show that the turbulent anisotropy can likewise be understood as a consequence of the flow curvature.

Turbulence closure in strongly curved flows has received significant attention in the fluid dynamics community, with particular focus on engineering applications. The effects of curvature are known to be large, but these ideas do not appear to have been previously applied to tropical cyclones. The talk will include some discussion on the potential implications for tropical cyclone dynamics, modelling, boundary-layer flow and wind damage mechanisms.