Turbulence in the Cirrus Canopy of Tropical Cyclones

Turbulence in the cirrus canopy of tropical cyclones (TCs) can give an indication about the physical processes that occur in this expansive cloud deck. The low stability and/or large shear that likely coincides with turbulent layers can be produced by radiative forcing, convective forcing, and sublimation of frozen precipitation from the cirrus canopy. As a result, turbulence in the cirrus canopy can give an indication about the impact of various physical processes in tropical cyclones. A direct measure of turbulence is available from the flight-level vertical aircraft acceleration data from the NOAA G-IV aircraft. This 1 Hz data on about a 250 m scale has been collected for years but to our knowledge has not been examined in any detail. We began with a case study on Hurricane Ivan (2004). Turbulence was found to be about 50% larger between 200 and 500 km radii overnight than during the day, suggesting that cloud-top cooling within the cirrus canopy at night is enhancing turbulence, while during the day the cooling is being offset by solar heating. We will evaluate the differences in magnitude of turbulence by radius, height, and time of day, both within and outside of the cirrus canopy, as well as an analysis of the locations of extreme turbulence. These calculations will be extended to all sampled storms from 1998 to 2015.