By LIDAR and CCD camera analysis the geometrical evolution of a vortex phase contrail (descent rate V_d equals 2.7 m/s, vortex separation D equals 47 m, vertical extension (sigma) _z equals 140 m after 77 s) is analyzed. The contrail of a four-engine aircraft is showing a diffuse central wake phenomenon. From coincident in situ measurements all relevant meteorological parameters are characterized. Ambient humidity had been close to ice saturation. From this a non-exhaust formation of ice can be excluded. Also the mechanism of non- entrainment of exhaust into the vortices is excluded of being responsible for the observed early onset of the central wake (870 m behind aircraft). The central wake onset originates from early detrainment starting after a 3/4 roll-up period of the vortex. Baroclinic and shear forces do not contribute to the detrainment (imaginary Brunt-Vaisala-frequency N² equals negative 3 multiplied by 10^-5 s^-2, shear dS/dz equals negative 0.01 s^-1, bulk Richardson number R_i, equals N²/(dS/dz)² equals negative 0.3). Ambient turbulence had been fully developed with an inertial range and locally isotropic turbulence for wavenumbers k-equals 0.004 - 0.1 radian/m. The eddy dissipation rate (epsilon) equals 7.4 plus or minus 0.5 multiplied by 10^-5 m²s^-3 exceeds the values found over the North Atlantic flight corridor at cruising altitude by a factor of 1000. Turbulence was identified as the dominating detrainment mechanism.

Date Published: 26 May 1997
PDF: 12 pages
Proc. SPIE 3104, Lidar Atmospheric Monitoring, (26 May 1997); doi: 10.1117/12.275153

Published in SPIE Proceedings Vol. 3104:
Lidar Atmospheric Monitoring
Jean-Pierre Wolf, Editor(s)