Large eddy simulations of contrail development: Sensitivity to initial and ambient conditions over first twenty minutes

Abstract

[1] A three-dimensional large-eddy simulation with size-resolved ice microphysics was used to model persistent contrails and compute their optical depth and area coverage. Eleven cases were run with various levels of vertical wind shear, aircraft type, relative humidity, ice nuclei effective emission index, and atmospheric stability and were analyzed with respect to their fluid dynamics and ice bulk properties. The effects of these properties on optical depth and contrail width were also compared between cases. Ice properties, optical depths, and contrail widths were consistent with limited observational field studies. For the conditions considered, contrail peak optical depth after twenty minutes simulation time ranged from 0.15 to 0.87, while contrail width ranged from 450 m to over 3 km. Optical depth and contrail width varied most strongly with vertical shear. For a 4-engine aircraft and 130% ambient relative humidity with respect to ice, a moderate shear of 0.005 s−1 reduced the peak optical depth by 79% and increased the width by 450% after twenty minutes compared to a zero shear case. In cases with no vertical shear, optical depth was also sensitive to aircraft type, humidity, and effective emission index, but variations in width with these parameters were small. In these cases, larger aircraft, higher humidity, and higher emission indices resulted in optical depths ranging from 20% to 50% larger than baseline cases. Atmospheric stability variations qualitatively changed the fluid dynamical development of the contrail, but differences in optical depth and contrail width were small.