Observations of turbulence in cirrus clouds

Three daytime flights of the UK Meteorological Office's C-130 aircraft through thick frontal cirrus have been analysed with the aim of determining the length scales at which energy is produced, and which mechanisms are responsible. The data was obtained as part of the EUCREX campaign. It will be shown that the occurrence of turbulence is patchy, weak and rather 2-dimensional with most turbulent kinetic energy being contained in the horizontal wind components. Evidence for the production of turbulence by the breaking of Kelvin-Helmholtz waves is found for all of the flights analysed. In one case there also seems to be turbulence production at a scale of 2 km by convection set up by radiative cloud top cooling.